Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lee Hart via EV]

Jan Steinman via EV wrote:

The fashionable way to balance is by switching a resistor (or some
equivalent) across the cells if they get high while charging.


Seems like a job for power MOSFETs, no?

Then, you'd have a voltage-variable resistor that could handle the boundary 
conditions you cited.


Except that MOSFETs normally fail shorted. Then you need a fuse or 
something to handle the shorted-MOSFET case. Resistors have the 
advantage that they don't normally have a "shorted" failure mode.


Also, most MOSFETs aren't rated for linear operation. They have a habit 
of being unstable or oscillating.


Lee Hart
--
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- someone to take good care of
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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Jan Steinman via EV]

> From: Lee Hart 
> 
> The fashionable way to balance is by switching a resistor (or some 
> equivalent) across the cells if they get high while charging.

Seems like a job for power MOSFETs, no?

Then, you'd have a voltage-variable resistor that could handle the boundary 
conditions you cited.

 New evolutionary jumps emerge out of the chaos of high-energy systems. -- 
David Holmgren  
 Jan Steinman, EcoReality Co-op 

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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[EVDL Administrator via EV]

As a non-engineer I don't have much to contribute to this discussion.  
However, I might point out that from what I've read you're talking about 
designing a BMS for EVhobbyists, not for production EVs.  IMO, that calls 
for a somewhat less stringent level of fault tolerance.  

Safety is still critical in a hobbyist BMS, but it's worth remembering that 
EV hobbyists are infamous for their strong preference for low cost over 
reliability.  It's a really bad idea for a production EV with a BMS fault to 
stop the car in the middle of a busy rush-hour LA expressway.  For hobbyist 
EVs, though, not catching fire will probably be considered success. :-)

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lee Hart via EV]

Lawrence Winiarski via EV wrote:

Suppose you run a single wire out to 150 different batteries and you
have a good system. Suppose ONE of those 300 different connections
goes bad... Wouldn't it be nice to be able to have an alternate method of
communication... that didn't cost anything extra except a little
software to twiddlethe balancing shunt...that could be used in a
quiescent system to troubleshoot those 300 different
connections?so you at least knew where to start taking stuff
apart?


Lawrence, I understand where you're coming from; I really do. 150 cells 
means 300 connections between them; and that's just for the propulsion 
wiring. They *have* to be reliable, or you don't have a practical car.


Reliability analysis works by figuring out the failure rate of each 
part, and then multiplying it by the number of parts. If a part has a 
failure rate of once every 10 years (gee, that sounds pretty good), then 
300 of them have about 300 failures in 10 years, or 30 every year -- 
almost one a week! Such an EV would be un-drivable.


*Doubling* the number of connections -- for example, by adding a BMS 
that needs two more wires per cell -- makes the problem is TWICE as bad!


The only way to make such a system work is for each connection to be 
*extremely* reliable. You need failure rates 100 times better. That 
won't happen with basement engineering or sweatshop manufacturing.


When Tesla announced they were using thousands of cells, and hundreds of 
thousands of connections in their battery packs, I was skeptical that 
they could ever make that work. But they did! Though it took an 
*enormous* amount of money, engineering, and manufacturing effort to 
pull it off.


With that kind of effort, I'm sure they could also make a 
mains-communication system work. But again, I'm skeptical that any of us 
will ever have the amount of skill, time, and money to perfect it.


I *do* think we could make a wired system reliable enough. I know, 
because there are real-world examples to learn from. But... they don't 
use cheap connectors, ad-hoc engineering, and extreme complexity to do 
it. You have to look at ultra-reliable dirt-simple setups like telephone 
systems and alarm systems to find your examples.


I also think there is promise in wireless or optical technologies. They 
too have working examples with very high reliability. But again, you've 
got to be sure you know what you're doing. Use parts and methods with a 
*proven* reliability record; not whatever is cheap and handy.


Lee

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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lee Hart via EV]

Peter C. Thompson via EV wrote:

In a bus system (USB, CANbus, etc.) any failed
device takes out the entire system.



Actually not correct.  CAN BUS works if a unit fails - UNLESS that unit
is blasting data on the bus.


But, that is one of the failure modes. It could also fail by shorting 
the bus, or doing something else that prevents transfers. If there's a 
micro in every node, the ways it can crash are endless.



Most likely, there will be separate circuits for each, so one
failure doesn't take them all out.



Redundancy is a nice-to-have feature, but overkill for this purpose.


Are you sure? If you build a system with 100+ micros (especially cheap 
ones, made offshore, not conformally coated, with no watchdogs, etc.) 
the odds of failure are pretty high. If each has an MTBF (mean time 
before failure) of 100 years, one is likely to die about once a year. 
Would *you* want a car that quits working every year, because one of 
them fails, buried deep in a sealed-up pack, and the dealer wants to 
replace the entire pack to fix it?



If you have a major failure that takes out the bus, then it is common
sense to stop the system.


Yes. But common sense is pretty uncommon. People routinely defeat 
automatic safety shutdowns so they can keep using it anyway.


How many people do you know that put black tape over the "check engine" 
light so they can just keep driving? In that case, they may wreck their 
engine for lack of oil, loss of coolant, etc. But in this case, 
defeating or ignoring the "check battery" light can cause a fire!



I used the Elithion system for my first iteration of CALB battery pack.
I LOVED the data gathering aspect, but HATED the communication failures
that were all too common.
I then switched to the miniBMS, and it covered all of my needs - EXCEPT
for data gathering.

Both systems covered the safety aspects, just had different approaches
to how communication needed to work.
Elithion - RS232, miniBMS - open a circuit in case of trouble.


These are perfect examples of what I'm talking about. The complex system 
is great when it works, but it's not likely to be reliable. The simple 
system is more likely to work.


But note that people still reported lots of failures even with the 
simpler miniBMS. It is really *really* hard to design cheap things with 
low failure rates!



If we are to create a new system, we could definitely provide the data
monitoring as well as safety monitoring - as long as we are using a
robust communication transport.  For me, that's either CAN BUS or
100BaseT1.  Both are well proven in automotive environments.


They could work. But keep the communication circuits *separate* from the 
safety circuits.


For one thing, you want the safety circuit to be able to say, "reported 
cell voltages are wrong!"


This is a case where redundant circuits are necessary, because mistakes 
can KILL people.


Lee
--
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- someone to take good care of
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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Peter C. Thompson via EV]

On 4/29/20 6:46 PM, Lee Hart via EV wrote:

Peri Hartman via EV wrote:

- Is it a safety system, there to prevent damage and fires?
    (battery SAFETY system)

Doesn't matter. It can still be handled by a poll from a master.


For this to work, both the master and all the slaves have to be 
working. No failures. In a bus system (USB, CANbus, etc.) any failed 
device takes out the entire system.
Actually not correct.  CAN BUS works if a unit fails - UNLESS that unit 
is blasting data on the bus.


In any case, if the bus fails, then system must stop.



In regard to your three example flavors, it seems that for a robust BMS
each individual cell monitor must do all three.


Yes. Most likely, there will be separate circuits for each, so one 
failure doesn't take them all out.
Redundancy is a nice-to-have feature, but overkill for this purpose. If 
you have a major failure that takes out the bus, then it is common sense 
to stop the system.



I'm out of my domain here, but can't balancing be handled by checking
cell voltage?


Measuring cell voltage only tells you that there might be a problem. 
It doesn't correct the problem, or even tell you what to do about it.


The fashionable way to balance is by switching a resistor (or some 
equivalent) across the cells if they get high while charging. There 
are issues with this, but it's generally the cheap way to do it. This 
is the "balancing" part of the three. Common failures here are a) the 
load didn't switch on when it should have, b) it didn't turn off when 
it should have, c) the charger didn't cut back, so it overwhelms the 
resistor and the cell overcharges anyway, d) the cells are too far out 
of balance for a small resistor to correct, e) insuring that the 
resistors aren't overheating due to excessive on-time.
Top-balancing works, but only if the cells were close to SoC in the 
first place.


Where measuring cell voltage is useful is doing long-term analysis - and 
this is done by a human (typically), using stored data over months of 
collection. This is how you would determine that a cell is dying - 
before it becomes a problem.



What needs to be done for safety?


The safety circuits need to detect these failures, stop the charger 
(and driving, if regen could occur), and alter the driver that there's 
a problem that must be fixed.


Besides these, it needs to watch for other failure modes. Things like 
excessively high or low cell temperatures, excessively high or low 
voltages, loose terminals (such as by high terminal temperatures), and 
ground faults.


The safety circuits also need to be fail-safe. If something goes wrong 
with them, they *shut down* the vehicle rather than let you keep 
driving it unprotected.


Lee Hart

Completely agree with you, Lee.

I used the Elithion system for my first iteration of CALB battery pack.  
I LOVED the data gathering aspect, but HATED the communication failures 
that were all too common.
I then switched to the miniBMS, and it covered all of my needs - EXCEPT 
for data gathering.


Both systems covered the safety aspects, just had different approaches 
to how communication needed to work.

Elithion - RS232, miniBMS - open a circuit in case of trouble.

If we are to create a new system, we could definitely provide the data 
monitoring as well as safety monitoring - as long as we are using a 
robust communication transport.  For me, that's either CAN BUS or 
100BaseT1.  Both are well proven in automotive environments.


Cheers, Peter

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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lee Hart via EV]

Peri Hartman via EV wrote:

- Is it a safety system, there to prevent damage and fires?
(battery SAFETY system)

Doesn't matter. It can still be handled by a poll from a master.


For this to work, both the master and all the slaves have to be working. 
No failures. In a bus system (USB, CANbus, etc.) any failed device takes 
out the entire system.



In regard to your three example flavors, it seems that for a robust BMS
each individual cell monitor must do all three.


Yes. Most likely, there will be separate circuits for each, so one 
failure doesn't take them all out.



I'm out of my domain here, but can't balancing be handled by checking
cell voltage?


Measuring cell voltage only tells you that there might be a problem. It 
doesn't correct the problem, or even tell you what to do about it.


The fashionable way to balance is by switching a resistor (or some 
equivalent) across the cells if they get high while charging. There are 
issues with this, but it's generally the cheap way to do it. This is the 
"balancing" part of the three. Common failures here are a) the load 
didn't switch on when it should have, b) it didn't turn off when it 
should have, c) the charger didn't cut back, so it overwhelms the 
resistor and the cell overcharges anyway, d) the cells are too far out 
of balance for a small resistor to correct, e) insuring that the 
resistors aren't overheating due to excessive on-time.



What needs to be done for safety?


The safety circuits need to detect these failures, stop the charger (and 
driving, if regen could occur), and alter the driver that there's a 
problem that must be fixed.


Besides these, it needs to watch for other failure modes. Things like 
excessively high or low cell temperatures, excessively high or low 
voltages, loose terminals (such as by high terminal temperatures), and 
ground faults.


The safety circuits also need to be fail-safe. If something goes wrong 
with them, they *shut down* the vehicle rather than let you keep driving 
it unprotected.


Lee Hart

--
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- someone to love
- someone to take good care of
- and misbehave, just a little
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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lawrence Winiarski via EV]

Well, perhaps I'm wrong.   I suppose no one can see the future.   

But riddle me this :-).   Suppose you run a single wire out to 150 different 
batteries andyou have a good system.   Suppose ONE of those 300 different 
connections goes bad...
Wouldn't it be nice to be able to .even if everything was turned off, to 
have an alternatemethod of communicationthat didn't cost anything extra 
except a little software to twiddlethe balancing shunt...that could be used in 
a quiescent system to troubleshoot those 300 different connections?so you 
at least knew where to start taking stuff apart?

Perhaps I'm grasping at straws here, but I even see this stupid idea as useful.

 
 > From: Lee Hart 
> 
> All these problems are solvable if you throw enough engineering and 
> money at them. But it's not goiong to lead to a cheap simple system.
> 
> That's why everyone avoids using the propulsion wiring itself to carry 
> data. It's far cheaper and more reliable to run separate wires for data.

I agree there doesn't seem to be much practical advantage to re-using the 
traction power lines.

As a minimum, you'd need a filter at the controller. Caps are cheap, but a 500A 
choke is going to cost more than the #18 (or smaller) wire you'd have to run if 
you use dedicated wire. A huge ferrite bead might be enough for VHF and up.

That's why the whole "wideband over power line" never got out of the starting 
chute. You'd need a high-frequency bridge over every transformer in the system. 
I can see ten of them out my window — in a rural, low-density area!

I did play with the X-11 home power control protocol some decades ago, and 
built a Heathkit powerline-carrier intercom as a kid. But the grid wideband 
response is tremendously difficult to characterize, which I'd expect the 
traction bus to be, too. 

I've seen TDR graphs of different power line situations at different 
frequencies — it is totally unpredictable what characteristic impedance you can 
count on! The best scheme would probably be diversity spread spectrum, which 
ain't cheap.

 We need an energy policy that encourages consumption. -- George W. Bush 
 
 Jan Steinman, EcoReality Co-op  

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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Jan Steinman via EV]

> From: Lee Hart 
> 
> All these problems are solvable if you throw enough engineering and 
> money at them. But it's not goiong to lead to a cheap simple system.
> 
> That's why everyone avoids using the propulsion wiring itself to carry 
> data. It's far cheaper and more reliable to run separate wires for data.

I agree there doesn't seem to be much practical advantage to re-using the 
traction power lines.

As a minimum, you'd need a filter at the controller. Caps are cheap, but a 500A 
choke is going to cost more than the #18 (or smaller) wire you'd have to run if 
you use dedicated wire. A huge ferrite bead might be enough for VHF and up.

That's why the whole "wideband over power line" never got out of the starting 
chute. You'd need a high-frequency bridge over every transformer in the system. 
I can see ten of them out my window — in a rural, low-density area!

I did play with the X-11 home power control protocol some decades ago, and 
built a Heathkit powerline-carrier intercom as a kid. But the grid wideband 
response is tremendously difficult to characterize, which I'd expect the 
traction bus to be, too. 

I've seen TDR graphs of different power line situations at different 
frequencies — it is totally unpredictable what characteristic impedance you can 
count on! The best scheme would probably be diversity spread spectrum, which 
ain't cheap.

 We need an energy policy that encourages consumption. -- George W. Bush 
 
 Jan Steinman, EcoReality Co-op  

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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lee Hart via EV]

Bill Dube via EV wrote:

The key is that the cell electronics are the simple part. They don't
have to be very sensitive or selective at all. They are just listening
to a a 100 kW radio station that is transmitting FM on its PWM carrier.
It is actually difficult _not_ to listen.


That's true. The problem is that this requires that the charger and 
controller be designed together with the BMS. That works for a big auto 
company. It does not work for small manufacturers or hobby EVs.



The transmission band can be in the high MHz, or low GHz band.


If it's in the low MHz range (AM radio), then switching transient from 
the sharp-edged charger and controller interfere. Try operating an AM 
radio in an EV with its antenna near the propulsion wiring.


If it's in the high MHz range (FM radio), then ringing and reflections 
within the wiring will create ghosts and echoes. These force the data 
rate way down into the range where controller and charger harmonics 
cause trouble. Look at what happens to a TTL signal at the end of a 3 
ft. piece of wire.


If it's in GHz range (cellphone frequencies), EV noise won't bother it. 
But then transmission line effects will create peaks and nulls every few 
inches.


All these problems are solvable if you throw enough engineering and 
money at them. But it's not goiong to lead to a cheap simple system.


That's why everyone avoids using the propulsion wiring itself to carry 
data. It's far cheaper and more reliable to run separate wires for data.


Lee Hart
--
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- something to look forward to
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- someone to take good care of
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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Bill Dube via EV]

The key is that the cell electronics are the simple part. They don't 
have to be very sensitive or selective at all. They are just listening 
to a a 100 kW radio station that is transmitting FM on its PWM carrier. 
It is actually difficult _not_ to listen.


    The more sensitive receiver is the single central "brain" that is 
listening to the messages that the cell electronics are transmitting. 
This central brain is the most difficult part, but there is only one of 
them, so the cost of the system can be low overall.


    Again, you can _briefly_ pause the drive to listen, perhaps for a 
several milliseconds out of every second, and it would be imperceptible 
to the customer. I doubt that the motor would even notice. You might 
even listen between "on" pulses of the ~20 kHz PWM base frequency. The 
transmission band can be in the high MHz, or low GHz band.


    While charging, which is much more critical for safety, you can 
turn the charger off for much longer periods to get much more detailed 
information from the cell, if you like.


    When you are driving, you only need to hear from a cell when it is 
too hot, too cold, or low voltage. You also need some sort of cell roll 
call occasionally, but you can do that at a slow pace.


Bill D.



On 4/29/2020 5:30 PM, Lawrence Winiarski via EV wrote:

Isn't  "Wide Band Noise" what RF guys overcome every day?   The reason you tune 
a radio is to ignore the 50 million otherchannels and the 
sun/jupiter/everyelectronicdevice known to man and concentrate on your own..
I can use my cell phone in my EV just fine.   If noise was really 
insurmountable, then I wouldn't be able to do that.

Seems to me that with enough selectivity over enough time, you can ignore every 
bit of noise known to man.
As I said the Ham guys can pick out signal in signal to noise ratios of -120db. 
 That's 12 orders of magnitude and they can detecta walkie/talkie on the 
other side of the globe.   It's amazing.   Sure it's only a few bits/min, but 
the point is that it IS doable.

It requires a different mindset than just straight digital manipulation.   You 
accept error rates and deal with them using math.



On Tuesday, April 28, 2020, 9:58:47 PM PDT, Offgrid Systems via EV 
 wrote:
  
  Yeah I'm gonna agree with Lee here. I've been thinking about this for

years also, going as far as testing some ac powerline comm chips adapted
to DC power busses. I found it's impossible with all the noise coming
from the drive on an EV.  But Lee, you don't even need a spectrum
analyser, just fire up your EV drive train, looking at any of the phases
with a oscilloscope. It's wide band noise, and the motor control is
modulating to operate the motor, but with sinewave drives, or even the
old PWM drives, there is noise during the entire cycle, and the only way
you get a quiet time is if you actually shut off and short the motor for
a brief period. But if you do that there will be high peak currents that
will not be good for the efficiency of the drive. If reliability is the
key, you will not want to use the DC busses, unless it's a low noise
application, and you can control and build all of the power devices,
like maybe a powerwall with a pure sinewave inverter, and you make the
charger (solar charge controller) and the inverter. But for motor
control, it's a difficult problem to solve.

Tim Economu

On 4/28/2020 6:48 PM, ev-requ...@lists.evdl.org wrote:

It sounds easy; but put a spectrum analyzer on your battery leads to see
what's*really*  there. I think you'd be shocked at the noise level.


There are a few clever tricks you can employ. During charging, you can
have the charger pause for a regular "moment of silence" in which the
BMS can communicate quickly and in the clear without having to "shout"
over the charger PWM. Perhaps the same thing could occur to a lesser
extent with the inverter.

Same as above. Are you going to design a special charger that must be
used with your BMS?

There are lots of solutions that work*some*  of the time. There are a
few that work*most*  of the time. But it gets damnably difficult to find
schemes that work*all*  of the time.

The problem is that a BMS is a safety system that you want to work*all*
of the time.

Lee Hart



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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lawrence Winiarski via EV]

So by SAFETY system, what do you want to do?   I guess I only see two things
A.   Stop the Car.B.   Stop the Charger.
Suppose you queried 1 time per second.  Suppose you got 3600 good readings then 
ONE bad one (or failed to get one), then started getting good ones again, would 
you really want to
A.  Stop the car
B.  Start and stop the charger?
I would think that you could tolerate some error rate with a little bit of 
software intelligence such as
IF last readings were near limits then execute safety stop
IF last reading was well within tolerance, ignoreIF Failed to get reading for N 
consecutive seconds the execute safety stop
Would this really be so unreasonable or unsafe?



On Tuesday, April 28, 2020, 9:10:40 PM PDT, Lee Hart via EV 
 wrote:  
 
 Peri Hartman via EV wrote:
> The BMS for each cell would normally be quiet and only send something when
> prompted by a central BMS component.

I think it is important to consider just what you want a BMS to do.

- Is it just there to provide feedback on what each cell is doing?
    (battery MONITORING system)
- Is it there to actively balance cells?
    (battery BALANCING system)
- Is it a safety system, there to prevent damage and fires?
    (battery SAFETY system)

These are three very different devices, with completely different design 
requirements.

When you talk about systems with a computer on every cell, and CAN bus 
networking with TCP/IP, you're talking about a Monitoring system. It's 
supposed to provide accurate real-time data on things like cell 
voltages, currents, and temperatures. It probably needs a fancy display 
(blinkinlights), and data logging (pretty charts and graphs).

Such a system is necessarily complicated, with correspondingly high cost 
and low reliability. It will need hundreds, perhaps thousands of parts, 
and so have many failure modes. Given the heavy dependence on software, 
it will be nearly impossible to predict what happens when it fails.

And, it's going to be the exact opposite of a safety system.

Lee Hart
-- 
If happiness is on your mind, here's a daily list to find:
    - something to do
    - something to look forward to
    - someone to love
    - someone to take good care of
    - and misbehave, just a little
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Peri Hartman via EV]

See below.

-- Original Message --
From: "Lee Hart" 
To: "Peri Hartman" ; "Electric Vehicle Discussion 
List" 

Sent: 28-Apr-20 9:10:37 PM
Subject: Re: [EVDL] Communicating over "mains" (Was: Minibms?)


Peri Hartman via EV wrote:

The BMS for each cell would normally be quiet and only send something when
prompted by a central BMS component.


I think it is important to consider just what you want a BMS to do.

- Is it just there to provide feedback on what each cell is doing?
(battery MONITORING system)
- Is it there to actively balance cells?
(battery BALANCING system)
- Is it a safety system, there to prevent damage and fires?
(battery SAFETY system)
Doesn't matter. It can still be handled by a poll from a master. The 
point I was trying to make is to find a way to not have a bunch of data 
collisions and keep the comm part of the system simple. Since the comm 
is fast, it would be easy to round-robin monitor all cells 100s if not 
1000s of times a second.


By "simple" extension of the protocol, one could add instructions back 
to the cells. As long as the master is in control, there won't be 
collisions.


You could have an interrupt based system where cells try to send to the 
master when an emergency condition happens. But I don't think there's 
any need for that. If the master is working, it will poll the cell soon 
enough to respond to the emergency. If the master is not working, it 
won't respond to the interrupt, anyway.


I think the real issue is how to handle a failure of the comm system or 
the master. The cells need to have some sort of built-in timer that 
shuts them down if the master fails to poll them. Or maybe there are 
some other, better ways to do that.


In regard to your three example flavors, it seems that for a robust BMS 
each individual cell monitor must do all three. I'm out of my domain 
here, but can't balancing be handled by checking cell voltage ? That is, 
when charging, slow the charge current (shunt the excess current) as the 
voltage reaches the cut-off (and opposite for discharging). What needs 
to be done for safety ? I presume that's primarily keeping current 
within limits and watching the temperature.


Peri



These are three very different devices, with completely different design 
requirements.

When you talk about systems with a computer on every cell, and CAN bus 
networking with TCP/IP, you're talking about a Monitoring system. It's supposed 
to provide accurate real-time data on things like cell voltages, currents, and 
temperatures. It probably needs a fancy display (blinkinlights), and data 
logging (pretty charts and graphs).

Such a system is necessarily complicated, with correspondingly high cost and 
low reliability. It will need hundreds, perhaps thousands of parts, and so have 
many failure modes. Given the heavy dependence on software, it will be nearly 
impossible to predict what happens when it fails.

And, it's going to be the exact opposite of a safety system.

Lee Hart
-- If happiness is on your mind, here's a daily list to find:
- something to do
- something to look forward to
- someone to love
- someone to take good care of
- and misbehave, just a little
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, http://www.sunrise-ev.com


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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lee Hart via EV]

Peri Hartman via EV wrote:

The BMS for each cell would normally be quiet and only send something when
prompted by a central BMS component.


I think it is important to consider just what you want a BMS to do.

- Is it just there to provide feedback on what each cell is doing?
(battery MONITORING system)
- Is it there to actively balance cells?
(battery BALANCING system)
- Is it a safety system, there to prevent damage and fires?
(battery SAFETY system)

These are three very different devices, with completely different design 
requirements.


When you talk about systems with a computer on every cell, and CAN bus 
networking with TCP/IP, you're talking about a Monitoring system. It's 
supposed to provide accurate real-time data on things like cell 
voltages, currents, and temperatures. It probably needs a fancy display 
(blinkinlights), and data logging (pretty charts and graphs).


Such a system is necessarily complicated, with correspondingly high cost 
and low reliability. It will need hundreds, perhaps thousands of parts, 
and so have many failure modes. Given the heavy dependence on software, 
it will be nearly impossible to predict what happens when it fails.


And, it's going to be the exact opposite of a safety system.

Lee Hart
--
If happiness is on your mind, here's a daily list to find:
- something to do
- something to look forward to
- someone to love
- someone to take good care of
- and misbehave, just a little
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Peri Hartman via EV]

Since this is a well defined system, in the sense that the composition 
of components is normally static, it seems reasonable to have a 
centrally controlled communication protocol. The BMS for each cell would 
normally be quiet and only send something when prompted by a central BMS 
component. You can imagine building some additonal layers of safety such 
as the cell automatically shutting down if no poll comes from the 
central BMS for some period of time.


TCP/IP is probably overkill but it's well established and could be used 
to ensure fail-safe communications. If one is to embed a radio in each 
cell with some logic processing, it seems a small extension to add the 
bottom layers of comm.


I suppose I'm regurgitating what's been done with wired systems, but it 
seems straight forward enough.


Peri

-- Original Message --
From: "Bill Dube via EV" 
To: ev@lists.evdl.org
Cc: "Bill Dube" 
Sent: 28-Apr-20 7:46:26 PM
Subject: Re: [EVDL] Communicating over "mains" (Was: Minibms?)


Indeed, you would have to design the entire system, inverter, charger, etc. to 
accommodate this communication scheme. Not an "add-on" type BMS my any means.

All of the "noise" comes from the components, and the designers have control over each 
and every component in that environment. A regularly spaced, "moment of silence" is not 
difficult to coordinate if you talk to every component with the CAN bus. It can be so short that 
the user will not be able to sense that it has happened.

You can also pick your communication band without a care, because you are on a private 
"network". Perhaps have the cell BMS sweep to find a band that works best 
during commissioning.

The input caps might block the cell BMS RF signal from _entering_ the inverter 
(or charger). However, the signal will still be present and detectable as a 
_current_ in the traction wiring, rather than as a voltage on the input 
terminals of the inverter (or charger.)

Bill D.

On 4/29/2020 1:48 PM, Lee Hart via EV wrote:

Bill Dube via EV wrote:

I have thought about doing this for perhaps 20 years. It may well be
possible to communicate via the traction conductors. It is probably
worth the effort to do so because it would allow you to incorporate the
BMS in the cell. Sealing the BMS inside each cell could be very useful,
especially from a warranty/liability angle. The cell manufacturer would
love to have a log of the SOC history of the cell.


It is certainly possible. The problem is whether it is practical.

If you are an automaker, with control over every aspect of the vehicle, the situation may 
be manageable. You can pick a part of the RF spectrum for your BMS communications where 
you know (or create) a "hole" in the noise from the other parts of the vehicle.

You can also route your wiring so as not to create any "dead spots". When you 
don't have a controlled impedance (known capacitance and inductance in the wiring), RF 
systems will have peaks and nulls that can prevent certain locations from communicating, 
where moving it a foot down the wire either way works.

But I think the situation is nearly hopeless in an open-source hobby EV. It 
would boil down to trial and error, where the installer doesn't know what noise 
the pieces are producing, and can't do anything to change them, and can't 
change the RF spectrum that the BMS is trying to use.

That's why providing a separate communication channel is almost universal. It 
might be wired, or optical, or RF (not relying on the traction wiring to carry 
the signal). You have a far better chance of it working.


Communicating _to_ the BMS is simple. You have two VERY large
transmitters, the charger and the inverter. Simply frequency modulate
the pwm of the inverter and/or the charger and put an FM detector in
each BMS on the cell level. You turn the "noise" source into the
communication transmitter. Done.


That works if you designed the charger and inverter and BMS specifically to 
work together to do this.


Communication _from_ the cells is not quite as simple, but doable. Use
the by-pass circuit to talk to the outside world. Put a capacitor in
parallel with the by-pass resistor so that when you switch on the
resistor, you get a spike.


Perhaps; but the batteries themselves still have a huge equivalent capacitance. 
The charger and controller are also likely to have huge low-ESR filter 
capacitors across them, which try to short out any RF signals present.

It sounds easy; but put a spectrum analyzer on your battery leads to see what's 
*really* there. I think you'd be shocked at the noise level.


There are a few clever tricks you can employ. During charging, you can
have the charger pause for a regular "moment of silence" in which the
BMS can communicate quickly and in the clear without having to "shout"
over the charger PWM. Perhaps the same thing could occur to a less

Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Bill Dube via EV]

Indeed, you would have to design the entire system, inverter, charger, 
etc. to accommodate this communication scheme. Not an "add-on" type BMS 
my any means.


All of the "noise" comes from the components, and the designers have 
control over each and every component in that environment. A regularly 
spaced, "moment of silence" is not difficult to coordinate if you talk 
to every component with the CAN bus. It can be so short that the user 
will not be able to sense that it has happened.


You can also pick your communication band without a care, because you 
are on a private "network". Perhaps have the cell BMS sweep to find a 
band that works best during commissioning.


The input caps might block the cell BMS RF signal from _entering_ the 
inverter (or charger). However, the signal will still be present and 
detectable as a _current_ in the traction wiring, rather than as a 
voltage on the input terminals of the inverter (or charger.)


Bill D.

On 4/29/2020 1:48 PM, Lee Hart via EV wrote:

Bill Dube via EV wrote:

I have thought about doing this for perhaps 20 years. It may well be
possible to communicate via the traction conductors. It is probably
worth the effort to do so because it would allow you to incorporate the
BMS in the cell. Sealing the BMS inside each cell could be very useful,
especially from a warranty/liability angle. The cell manufacturer would
love to have a log of the SOC history of the cell.


It is certainly possible. The problem is whether it is practical.

If you are an automaker, with control over every aspect of the 
vehicle, the situation may be manageable. You can pick a part of the 
RF spectrum for your BMS communications where you know (or create) a 
"hole" in the noise from the other parts of the vehicle.


You can also route your wiring so as not to create any "dead spots". 
When you don't have a controlled impedance (known capacitance and 
inductance in the wiring), RF systems will have peaks and nulls that 
can prevent certain locations from communicating, where moving it a 
foot down the wire either way works.


But I think the situation is nearly hopeless in an open-source hobby 
EV. It would boil down to trial and error, where the installer doesn't 
know what noise the pieces are producing, and can't do anything to 
change them, and can't change the RF spectrum that the BMS is trying 
to use.


That's why providing a separate communication channel is almost 
universal. It might be wired, or optical, or RF (not relying on the 
traction wiring to carry the signal). You have a far better chance of 
it working.



Communicating _to_ the BMS is simple. You have two VERY large
transmitters, the charger and the inverter. Simply frequency modulate
the pwm of the inverter and/or the charger and put an FM detector in
each BMS on the cell level. You turn the "noise" source into the
communication transmitter. Done.


That works if you designed the charger and inverter and BMS 
specifically to work together to do this.



Communication _from_ the cells is not quite as simple, but doable. Use
the by-pass circuit to talk to the outside world. Put a capacitor in
parallel with the by-pass resistor so that when you switch on the
resistor, you get a spike.


Perhaps; but the batteries themselves still have a huge equivalent 
capacitance. The charger and controller are also likely to have huge 
low-ESR filter capacitors across them, which try to short out any RF 
signals present.


It sounds easy; but put a spectrum analyzer on your battery leads to 
see what's *really* there. I think you'd be shocked at the noise level.



There are a few clever tricks you can employ. During charging, you can
have the charger pause for a regular "moment of silence" in which the
BMS can communicate quickly and in the clear without having to "shout"
over the charger PWM. Perhaps the same thing could occur to a lesser
extent with the inverter.


Same as above. Are you going to design a special charger that must be 
used with your BMS?


There are lots of solutions that work *some* of the time. There are a 
few that work *most* of the time. But it gets damnably difficult to 
find schemes that work *all* of the time.


The problem is that a BMS is a safety system that you want to work 
*all* of the time.


Lee Hart



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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lawrence Winiarski via EV]

Let me play devils advocate.    If it was so hard, then why does my cell 
phone/radio/satellite work?   They pickup microvolts out of the air and work 
pretty well.   I'm communicating my email to a tower 10 miles away.  I'm doing 
itwith 2 watts!   That's pretty amazing.

the bypass resistor can do 0.5-1 amp.  That's a non trivial signal to look for. 
 Now put it at a particular freq and give itenough cycles and look for it with 
an FFT in software and I'd guess it's going to be detectable.   Now addCRC for 
errors and viola.    

And if occasionally 1 out of 10 times you get a bad reading...who cares.  
It's a BMS.   It's not going to explode.Just make some annoying beep.   I can 
live with that.
The advantage is no wires.  No fire hazard.  Decent stats on the battery.
I'd say the wins outweigh the disadvantages.

Don't let the perfect be the enemy of the good.   Things change relatively slow 
in the battery world and a fewbad readings are probably acceptable.   In a 
master/slave system if the BMS doesn't respond to a query, thentreat it as a t  
fault.   Turn off the charger, or let the user know by beeping or blinking or 
something.  

 I think that the proof will be in someone doing it.   Perhaps I'm opotomistic, 
but  I have confidence that it would work.


   On Tuesday, April 28, 2020, 6:48:38 PM PDT, Lee Hart via EV 
 wrote:  
 
 Bill Dube via EV wrote:
> I have thought about doing this for perhaps 20 years. It may well be
> possible to communicate via the traction conductors. It is probably
> worth the effort to do so because it would allow you to incorporate the
> BMS in the cell. Sealing the BMS inside each cell could be very useful,
> especially from a warranty/liability angle. The cell manufacturer would
> love to have a log of the SOC history of the cell.

It is certainly possible. The problem is whether it is practical.

If you are an automaker, with control over every aspect of the vehicle, 
the situation may be manageable. You can pick a part of the RF spectrum 
for your BMS communications where you know (or create) a "hole" in the 
noise from the other parts of the vehicle.

You can also route your wiring so as not to create any "dead spots". 
When you don't have a controlled impedance (known capacitance and 
inductance in the wiring), RF systems will have peaks and nulls that can 
prevent certain locations from communicating, where moving it a foot 
down the wire either way works.

But I think the situation is nearly hopeless in an open-source hobby EV. 
It would boil down to trial and error, where the installer doesn't know 
what noise the pieces are producing, and can't do anything to change 
them, and can't change the RF spectrum that the BMS is trying to use.

That's why providing a separate communication channel is almost 
universal. It might be wired, or optical, or RF (not relying on the 
traction wiring to carry the signal). You have a far better chance of it 
working.

> Communicating _to_ the BMS is simple. You have two VERY large
> transmitters, the charger and the inverter. Simply frequency modulate
> the pwm of the inverter and/or the charger and put an FM detector in
> each BMS on the cell level. You turn the "noise" source into the
> communication transmitter. Done.

That works if you designed the charger and inverter and BMS specifically 
to work together to do this.

> Communication _from_ the cells is not quite as simple, but doable. Use
> the by-pass circuit to talk to the outside world. Put a capacitor in
> parallel with the by-pass resistor so that when you switch on the
> resistor, you get a spike.

Perhaps; but the batteries themselves still have a huge equivalent 
capacitance. The charger and controller are also likely to have huge 
low-ESR filter capacitors across them, which try to short out any RF 
signals present.

It sounds easy; but put a spectrum analyzer on your battery leads to see 
what's *really* there. I think you'd be shocked at the noise level.

> There are a few clever tricks you can employ. During charging, you can
> have the charger pause for a regular "moment of silence" in which the
> BMS can communicate quickly and in the clear without having to "shout"
> over the charger PWM. Perhaps the same thing could occur to a lesser
> extent with the inverter.

Same as above. Are you going to design a special charger that must be 
used with your BMS?

There are lots of solutions that work *some* of the time. There are a 
few that work *most* of the time. But it gets damnably difficult to find 
schemes that work *all* of the time.

The problem is that a BMS is a safety system that you want to work *all* 
of the time.

Lee Hart

-- 
If happiness is on your mind, here's a daily list to find:
    - something to do
    - something to look forward to
    - someone to love
    - someone to take good care of
    - and misbehave, just a little
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
___

Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lee Hart via EV]

Bill Dube via EV wrote:

I have thought about doing this for perhaps 20 years. It may well be
possible to communicate via the traction conductors. It is probably
worth the effort to do so because it would allow you to incorporate the
BMS in the cell. Sealing the BMS inside each cell could be very useful,
especially from a warranty/liability angle. The cell manufacturer would
love to have a log of the SOC history of the cell.


It is certainly possible. The problem is whether it is practical.

If you are an automaker, with control over every aspect of the vehicle, 
the situation may be manageable. You can pick a part of the RF spectrum 
for your BMS communications where you know (or create) a "hole" in the 
noise from the other parts of the vehicle.


You can also route your wiring so as not to create any "dead spots". 
When you don't have a controlled impedance (known capacitance and 
inductance in the wiring), RF systems will have peaks and nulls that can 
prevent certain locations from communicating, where moving it a foot 
down the wire either way works.


But I think the situation is nearly hopeless in an open-source hobby EV. 
It would boil down to trial and error, where the installer doesn't know 
what noise the pieces are producing, and can't do anything to change 
them, and can't change the RF spectrum that the BMS is trying to use.


That's why providing a separate communication channel is almost 
universal. It might be wired, or optical, or RF (not relying on the 
traction wiring to carry the signal). You have a far better chance of it 
working.



Communicating _to_ the BMS is simple. You have two VERY large
transmitters, the charger and the inverter. Simply frequency modulate
the pwm of the inverter and/or the charger and put an FM detector in
each BMS on the cell level. You turn the "noise" source into the
communication transmitter. Done.


That works if you designed the charger and inverter and BMS specifically 
to work together to do this.



Communication _from_ the cells is not quite as simple, but doable. Use
the by-pass circuit to talk to the outside world. Put a capacitor in
parallel with the by-pass resistor so that when you switch on the
resistor, you get a spike.


Perhaps; but the batteries themselves still have a huge equivalent 
capacitance. The charger and controller are also likely to have huge 
low-ESR filter capacitors across them, which try to short out any RF 
signals present.


It sounds easy; but put a spectrum analyzer on your battery leads to see 
what's *really* there. I think you'd be shocked at the noise level.



There are a few clever tricks you can employ. During charging, you can
have the charger pause for a regular "moment of silence" in which the
BMS can communicate quickly and in the clear without having to "shout"
over the charger PWM. Perhaps the same thing could occur to a lesser
extent with the inverter.


Same as above. Are you going to design a special charger that must be 
used with your BMS?


There are lots of solutions that work *some* of the time. There are a 
few that work *most* of the time. But it gets damnably difficult to find 
schemes that work *all* of the time.


The problem is that a BMS is a safety system that you want to work *all* 
of the time.


Lee Hart

--
If happiness is on your mind, here's a daily list to find:
- something to do
- something to look forward to
- someone to love
- someone to take good care of
- and misbehave, just a little
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lawrence Winiarski via EV]

Simple idea  as a start of discussion assuming an AVR on the BMS and a 
cap/comparator circuit to detect and 
amplify comm signal

Assumes each BMS has an "uniq NODE".

Monitor COM voltages at F1 hz.  Store.  
Analyze stored data for master signal  at F2 hz.   Decode and sync local clock 
to master clock.   

IF we have data to report, wait for TimeSlot for NODE, then send.   use use 
bypass resistor to send square wave at F3 hz  cycles, 


Messages would be sent using something like manchester coding and messages 
could be stretched across multiple time slots.
Messages would use something like CRC to guarantee validity.




   On Tuesday, April 28, 2020, 4:54:11 PM PDT, Lawrence Winiarski via EV 
 wrote:  
 
 Awesome. 

I like the idea of the transmitter in the charger, but it would also be cool to 
make it an add-on with an existing charger.   
 I would think you would want the frequency to be well off the freq of the 
charger switchers.   Any ideas on that?
Have any idea what the small signal impedance vs frequency is for lifepo4 100ah 
batteries?   I would think that batterieshave high impedance at high freq 
regardless of SOC.   Chemistry just doesn't happen that fast.

I think a possibility would be to have a synchronizing pulse sent from the 
"master" and use time slots for each bms slave 
to respond.  I would think that making the BMS as a slave saves energy too.   
It doesn't waste energy talking unless ithas too.



  On Tuesday, April 28, 2020, 4:38:16 PM PDT, Bill Dube via EV 
 wrote:  
 
 I have thought about doing this for perhaps 20 years. It may well be 
possible to communicate via the traction conductors. It is probably 
worth the effort to do so because it would allow you to incorporate the 
BMS in the cell. Sealing the BMS inside each cell could be very useful, 
especially from a warranty/liability angle. The cell manufacturer would 
love to have a log of the SOC history of the cell.

Communicating _to_ the BMS is simple. You have two VERY large 
transmitters, the charger and the inverter. Simply frequency modulate 
the pwm of the inverter and/or the charger and put an FM detector in 
each BMS on the cell level. You turn the "noise" source into the 
communication transmitter. Done.

Communication _from_ the cells is not quite as simple, but doable. Use 
the by-pass circuit to talk to the outside world. Put a capacitor in 
parallel with the by-pass resistor so that when you switch on the 
resistor, you get a spike. Again, you can transmit via FM using "spikes" 
generated by switching the by-pass on and off briefly.

There are a few clever tricks you can employ. During charging, you can 
have the charger pause for a regular "moment of silence" in which the 
BMS can communicate quickly and in the clear without having to "shout" 
over the charger PWM. Perhaps the same thing could occur to a lesser 
extent with the inverter.

Also, cells that are in a high SOC or low SOC have a high impedance, 
which would tend to make the BMS signal "louder". Since this is the most 
critical time for BMS communication, this helps quite a bit. During 
these times they can "scream" to the inverter to stop for a moment so 
they can give details about the problem.

Just a thought

     Bill D.

On 4/29/2020 9:35 AM, Lawrence Winiarski via EV wrote:
>> Because there are no "mains" in a vehicle.???
> Is it really "That" Noisy?   I suspect it is very doable, it's just that no 
> one has done it yet.The trick is probably using signal processing to get rid 
> of the noise and doing extremelylow bit rates, which is fine for a BMS.    
> Ham radio guys can send stuff over the entire earthon 10 watts using 
> techniques like jt65.   I expect they can deal with a little noise.   it's 
> justnot going to be trivial, but it would be doable.
>
> IMHO the main use for the BMS is in charging anyway.
>
>    On Tuesday, April 28, 2020, 2:12:26 PM PDT, Lee Hart 
> wrote:
>  
>  Lawrence Winiarski wrote:
>> Anyone know anything about data over powerlines?  Why can't the BMS
>> communicate over the mains?
> Because there are no "mains" in a vehicle.
>
> That said, it is possible to communicate via the DC power cables already
> connected to each cell. But this is an extremely noisy environment. It
> would require substantial filtering and protection to keep driving
> currents from trashing data transfers. Some chargers are also extremely
> noisy, and could block data transfers while charging.
>
> Lee


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Re: [EVDL] Communicating over "mains" (Was: Minibms?)

[Lawrence Winiarski via EV]

Awesome. 

I like the idea of the transmitter in the charger, but it would also be cool to 
make it an add-on with an existing charger.   
 I would think you would want the frequency to be well off the freq of the 
charger switchers.   Any ideas on that?
Have any idea what the small signal impedance vs frequency is for lifepo4 100ah 
batteries?   I would think that batterieshave high impedance at high freq 
regardless of SOC.   Chemistry just doesn't happen that fast.

I think a possibility would be to have a synchronizing pulse sent from the 
"master" and use time slots for each bms slave 
to respond.  I would think that making the BMS as a slave saves energy too.   
It doesn't waste energy talking unless ithas too.



   On Tuesday, April 28, 2020, 4:38:16 PM PDT, Bill Dube via EV 
 wrote:  
 
 I have thought about doing this for perhaps 20 years. It may well be 
possible to communicate via the traction conductors. It is probably 
worth the effort to do so because it would allow you to incorporate the 
BMS in the cell. Sealing the BMS inside each cell could be very useful, 
especially from a warranty/liability angle. The cell manufacturer would 
love to have a log of the SOC history of the cell.

Communicating _to_ the BMS is simple. You have two VERY large 
transmitters, the charger and the inverter. Simply frequency modulate 
the pwm of the inverter and/or the charger and put an FM detector in 
each BMS on the cell level. You turn the "noise" source into the 
communication transmitter. Done.

Communication _from_ the cells is not quite as simple, but doable. Use 
the by-pass circuit to talk to the outside world. Put a capacitor in 
parallel with the by-pass resistor so that when you switch on the 
resistor, you get a spike. Again, you can transmit via FM using "spikes" 
generated by switching the by-pass on and off briefly.

There are a few clever tricks you can employ. During charging, you can 
have the charger pause for a regular "moment of silence" in which the 
BMS can communicate quickly and in the clear without having to "shout" 
over the charger PWM. Perhaps the same thing could occur to a lesser 
extent with the inverter.

Also, cells that are in a high SOC or low SOC have a high impedance, 
which would tend to make the BMS signal "louder". Since this is the most 
critical time for BMS communication, this helps quite a bit. During 
these times they can "scream" to the inverter to stop for a moment so 
they can give details about the problem.

Just a thought

     Bill D.

On 4/29/2020 9:35 AM, Lawrence Winiarski via EV wrote:
>> Because there are no "mains" in a vehicle.???
> Is it really "That" Noisy?   I suspect it is very doable, it's just that no 
> one has done it yet.The trick is probably using signal processing to get rid 
> of the noise and doing extremelylow bit rates, which is fine for a BMS.    
> Ham radio guys can send stuff over the entire earthon 10 watts using 
> techniques like jt65.   I expect they can deal with a little noise.   it's 
> justnot going to be trivial, but it would be doable.
>
> IMHO the main use for the BMS is in charging anyway.
>
>    On Tuesday, April 28, 2020, 2:12:26 PM PDT, Lee Hart 
> wrote:
>  
>  Lawrence Winiarski wrote:
>> Anyone know anything about data over powerlines?  Why can't the BMS
>> communicate over the mains?
> Because there are no "mains" in a vehicle.
>
> That said, it is possible to communicate via the DC power cables already
> connected to each cell. But this is an extremely noisy environment. It
> would require substantial filtering and protection to keep driving
> currents from trashing data transfers. Some chargers are also extremely
> noisy, and could block data transfers while charging.
>
> Lee


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[EVDL] Communicating over "mains" (Was: Minibms?)

[Bill Dube via EV]

I have thought about doing this for perhaps 20 years. It may well be 
possible to communicate via the traction conductors. It is probably 
worth the effort to do so because it would allow you to incorporate the 
BMS in the cell. Sealing the BMS inside each cell could be very useful, 
especially from a warranty/liability angle. The cell manufacturer would 
love to have a log of the SOC history of the cell.


Communicating _to_ the BMS is simple. You have two VERY large 
transmitters, the charger and the inverter. Simply frequency modulate 
the pwm of the inverter and/or the charger and put an FM detector in 
each BMS on the cell level. You turn the "noise" source into the 
communication transmitter. Done.


Communication _from_ the cells is not quite as simple, but doable. Use 
the by-pass circuit to talk to the outside world. Put a capacitor in 
parallel with the by-pass resistor so that when you switch on the 
resistor, you get a spike. Again, you can transmit via FM using "spikes" 
generated by switching the by-pass on and off briefly.


There are a few clever tricks you can employ. During charging, you can 
have the charger pause for a regular "moment of silence" in which the 
BMS can communicate quickly and in the clear without having to "shout" 
over the charger PWM. Perhaps the same thing could occur to a lesser 
extent with the inverter.


Also, cells that are in a high SOC or low SOC have a high impedance, 
which would tend to make the BMS signal "louder". Since this is the most 
critical time for BMS communication, this helps quite a bit. During 
these times they can "scream" to the inverter to stop for a moment so 
they can give details about the problem.


Just a thought

    Bill D.

On 4/29/2020 9:35 AM, Lawrence Winiarski via EV wrote:

Because there are no "mains" in a vehicle.???

Is it really "That" Noisy?   I suspect it is very doable, it's just that no one 
has done it yet.The trick is probably using signal processing to get rid of the noise and 
doing extremelylow bit rates, which is fine for a BMS.    Ham radio guys can send stuff 
over the entire earthon 10 watts using techniques like jt65.   I expect they can deal 
with a little noise.   it's justnot going to be trivial, but it would be doable.

IMHO the main use for the BMS is in charging anyway.

On Tuesday, April 28, 2020, 2:12:26 PM PDT, Lee Hart 
 wrote:
  
  Lawrence Winiarski wrote:

Anyone know anything about data over powerlines?  Why can't the BMS
communicate over the mains?

Because there are no "mains" in a vehicle.

That said, it is possible to communicate via the DC power cables already
connected to each cell. But this is an extremely noisy environment. It
would require substantial filtering and protection to keep driving
currents from trashing data transfers. Some chargers are also extremely
noisy, and could block data transfers while charging.

Lee



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