Re: [EVDL] custom battery

[jkenny23 via EV]

Yes, more safety can't hurt (especially the fail-safe, or nearly fail-safe
kind). I would highly recommend going with a well known and reliable BMS
system though, and not try and design your own. There are hundreds available
on the market already (DIY versions and marketed versions). 

Did you settle on a voltage? 48V is my preferred system voltage for high
power, it's a good middle ground between the wire size and system component
issues of going with low voltage (very high current) and having to deal with
potentially dangerous to handle DC voltages on the battery side (you can
still get a shock from 48V, but not too bad). Your pack configuration will
depend on the inverter you pick, but "standard" for 48V would be 14s for
Li-Ion.

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Re: [EVDL] custom battery

[Peri Hartman via EV]

Justin,

Right, I need a high current DC contactor (not necessarily high voltage 
but that may be the way they come).


I was planning to hook the relay to a normally-open thermostat (one that 
will fail in the open state) rather than have it controlled by the 
arduino. If the arduino fails, I want to be sure my contactor will still 
shut off if something overheats.


Do you think I'm doing something unnecessary ?

Peri

-- Original Message --
From: "Justin Kenny" 
To: "Peri Hartman" 
Cc: "Electric Vehicle Discussion List" 
Sent: 19-Apr-20 8:08:10 PM
Subject: Re: Re[2]: [EVDL] custom battery

Well I assumed by disconnect you meant a manual one (e.g. big on/off 
switch), which would still have to take all the power required through 
it. That'd be the service disconnect I linked from EV West. The battery 
management system would control the contactor, which also switches all 
of the required power for your application, and that would handle over 
temp, over voltage, under voltage, etc. fault conditions. None of those 
*should* happen in a well designed system, so it shouldn't need to 
hard-switch hundreds of amps, but it should be designed to be able to 
without welding contacts shut or arcing etc., and that's why you need a 
proper high voltage/high current DC contactor, and not just a big relay 
that technically can handle hundreds of amps.


- Justin

On Sun, Apr 19, 2020 at 7:55 PM Peri Hartman  wrote:

Why shouldn't I use a disconnect. Or am I using the wrong term:
something like a contactor that breaks the power connection if the 
temp
rises too much. I'm figuring I'll need two: one for the load and one 
for

the charger power. The latter should be easy: 120VAC, 15A.

With 6kW or more, if something goes wrong, there'll be a lot of heat 
in

the wrong place.

Peri

-- Original Message --
From: "jkenny23 via EV" 
To: ev@lists.evdl.org
Cc: "jkenny23" 
Sent: 19-Apr-20 6:16:39 PM
Subject: Re: [EVDL] custom battery

>Well you shouldn't need to use the disconnects; but yes, those 
amperage
>levels are used commonly in EVs of course. EV West has pretty good 
prices
>for stuff like this (service disconnect, rated for max current your 
system

>would see):
>https://www.evwest.com/catalog/product_info.php?cPath=2_42_id=267=na4hdbkd5u5i6u7ne1lltda641
>
>And here's an example of the contactor you'd need to control with the 
BMS

>(quite cheap for this model, good deal actually):
>https://www.ebay.com/itm/293546196201
>
>--
>Sent from: 
http://electric-vehicle-discussion-list.413529.n4.nabble.com/

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Re: [EVDL] custom battery

[Justin Kenny via EV]

Well I assumed by disconnect you meant a manual one (e.g. big on/off
switch), which would still have to take all the power required through it.
That'd be the service disconnect I linked from EV West. The battery
management system would control the contactor, which also switches all of
the required power for your application, and that would handle over temp,
over voltage, under voltage, etc. fault conditions. None of those *should*
happen in a well designed system, so it shouldn't need to hard-switch
hundreds of amps, but it should be designed to be able to without welding
contacts shut or arcing etc., and that's why you need a proper high
voltage/high current DC contactor, and not just a big relay that
technically can handle hundreds of amps.

- Justin

On Sun, Apr 19, 2020 at 7:55 PM Peri Hartman  wrote:

> Why shouldn't I use a disconnect. Or am I using the wrong term:
> something like a contactor that breaks the power connection if the temp
> rises too much. I'm figuring I'll need two: one for the load and one for
> the charger power. The latter should be easy: 120VAC, 15A.
>
> With 6kW or more, if something goes wrong, there'll be a lot of heat in
> the wrong place.
>
> Peri
>
> -- Original Message --
> From: "jkenny23 via EV" 
> To: ev@lists.evdl.org
> Cc: "jkenny23" 
> Sent: 19-Apr-20 6:16:39 PM
> Subject: Re: [EVDL] custom battery
>
> >Well you shouldn't need to use the disconnects; but yes, those amperage
> >levels are used commonly in EVs of course. EV West has pretty good prices
> >for stuff like this (service disconnect, rated for max current your system
> >would see):
> >
> https://www.evwest.com/catalog/product_info.php?cPath=2_42_id=267=na4hdbkd5u5i6u7ne1lltda641
> >
> >And here's an example of the contactor you'd need to control with the BMS
> >(quite cheap for this model, good deal actually):
> >https://www.ebay.com/itm/293546196201
> >
> >--
> >Sent from: http://electric-vehicle-discussion-list.413529.n4.nabble.com/
> >___
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>
>
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Re: [EVDL] custom battery

[Peri Hartman via EV]

Why shouldn't I use a disconnect. Or am I using the wrong term: 
something like a contactor that breaks the power connection if the temp 
rises too much. I'm figuring I'll need two: one for the load and one for 
the charger power. The latter should be easy: 120VAC, 15A.


With 6kW or more, if something goes wrong, there'll be a lot of heat in 
the wrong place.


Peri

-- Original Message --
From: "jkenny23 via EV" 
To: ev@lists.evdl.org
Cc: "jkenny23" 
Sent: 19-Apr-20 6:16:39 PM
Subject: Re: [EVDL] custom battery


Well you shouldn't need to use the disconnects; but yes, those amperage
levels are used commonly in EVs of course. EV West has pretty good prices
for stuff like this (service disconnect, rated for max current your system
would see):
https://www.evwest.com/catalog/product_info.php?cPath=2_42_id=267=na4hdbkd5u5i6u7ne1lltda641

And here's an example of the contactor you'd need to control with the BMS
(quite cheap for this model, good deal actually):
https://www.ebay.com/itm/293546196201

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Re: [EVDL] custom battery

[jkenny23 via EV]

Well you shouldn't need to use the disconnects; but yes, those amperage
levels are used commonly in EVs of course. EV West has pretty good prices
for stuff like this (service disconnect, rated for max current your system
would see):
https://www.evwest.com/catalog/product_info.php?cPath=2_42_id=267=na4hdbkd5u5i6u7ne1lltda641

And here's an example of the contactor you'd need to control with the BMS
(quite cheap for this model, good deal actually):
https://www.ebay.com/itm/293546196201

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Re: [EVDL] custom battery

[Lee Hart via EV]

Peri Hartman via EV wrote:

Thanks for responding.

Yep. about 1 min discharge - load can vary a bit. I can use pretty much
any voltage, but the lower the voltage, the higher the current and I'll
need huge cables and disconnects. The higher the voltage, the more cells
and cell monitors I need, plus need for higher voltage components. Cost
goes up.

I could use an inverter, but I still have the disconnect problem. Let's
say I paralleled groups of cells so that I have about 11V. Then I'd have
about 600A. That's huge. Or 22V, 300A, still huge. Can I get a
disconnect for that ?


Well, an ordinary SLI car battery can deliver 300 amps for a minute. 
Cheap and available, and no BMS is needed. That's a negligible depth of 
discharge, so they can do it thousands of times if recharged promptly 
between uses. You can use two of them; so 24v at 300a. There are 
off-the-shelf inverters to boost this to 240vac or 300vdc; whichever you 
prefer.


The main drawback is the weight.

Lee Hart
--
Whether we or our politicians know it or not, Nature is party to all
our deals and decisions, and she has more votes, a longer memory,
and a sterner sense of justice than we do. -- Wendell Berry
--
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Re: [EVDL] custom battery

[Peri Hartman via EV]

Thanks for responding.

Yep. about 1 min discharge - load can vary a bit. I can use pretty much 
any voltage, but the lower the voltage, the higher the current and I'll 
need huge cables and disconnects. The higher the voltage, the more cells 
and cell monitors I need, plus need for higher voltage components. Cost 
goes up.


I could use an inverter, but I still have the disconnect problem. Let's 
say I paralleled groups of cells so that I have about 11V. Then I'd have 
about 600A. That's huge. Or 22V, 300A, still huge. Can I get a 
disconnect for that ?


Peri

-- Original Message --
From: "jkenny23 via EV" 
To: ev@lists.evdl.org
Cc: "jkenny23" 
Sent: 18-Apr-20 6:06:08 PM
Subject: Re: [EVDL] custom battery


You got me stumped. What application do you need only 85WH at 6.6kW for?
That's a discharge period of 46 seconds if I have my math right...

Do you truly need 240VDC for this application also? What about using the
first stage of a 6.6kW 240VAC inverter, which would produce a high voltage,
high power DC rail from a much safer/more manageable battery voltage (e.g.
24 or 48V), though there will be a size and efficiency impact by adding
this. I think it would easily offset the complexity in BMS and charger to
manage a 240VDC battery pack though.

The question of cycle life is interesting.. I could try some experiments
around this now with my high power cycle tester.

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Re: [EVDL] custom battery

[jkenny23 via EV]

You got me stumped. What application do you need only 85WH at 6.6kW for?
That's a discharge period of 46 seconds if I have my math right...

Do you truly need 240VDC for this application also? What about using the
first stage of a 6.6kW 240VAC inverter, which would produce a high voltage,
high power DC rail from a much safer/more manageable battery voltage (e.g.
24 or 48V), though there will be a size and efficiency impact by adding
this. I think it would easily offset the complexity in BMS and charger to
manage a 240VDC battery pack though.

The question of cycle life is interesting.. I could try some experiments
around this now with my high power cycle tester.

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Re: [EVDL] custom battery

[Peri Hartman via EV]

Thanks to everyone who has responded so far. This is definitely a 
challenge !


Summary first, question at bottom.

I've refined my modeling and determined that about 85Wh is sufficient 
and 6.6kW max constant discharge.


If I did my calcs correctly, that means
240VDC total. With
3.7V per cell, requires
65 total cells

They would have
28A max current and need at least
350mAh capacity.

Choosing a higher capacity cell, say
1500mAh brings down the minimum C-rating to
18C, and means using only about
25% of the cells capacity, keeping it nicely in the middle charge state 
area


As an example, I've looked at the LG HB6 (which is a discontinued cell, 
but cheaper :)

3.6V
1500mAh
30A max continuous current.

QUESTIONS:
If I use these cells as I describe above (keeping in the middle 25% 
charge state), will they probably last a long time, meaning 1000s of 
cycles ? Even at near max continuous current ? (Bear in mind the 
discharge time will be short and there will be ample cooling off between 
uses.)


Peri


-- Original Message --
From: "Cor van de Water" 
To: "Peri Hartman" ; "Electric Vehicle Discussion 
List" 

Sent: 13-Apr-20 10:59:58 PM
Subject: Re: [EVDL] custom battery


Peri,
That is 50C discharge, not impossible but also not trivial.
The good old A123 cells could do this.
The cylindrical cells are almost 10Wh and can discharge at metal 
melting speeds.

I have a bunch of them here, in case you are interested.
Cor.

On Mon, Apr 13, 2020, 9:33 PM Peri Hartman via EV  
wrote:

Hi,

I need a battery with about 150Wh and a discharge rate of 8kW for up 
to
a minute or so. I've spent a few hours searching and there doesn't 
seem

to be anything on the market that fits this. There are, of course,
higher capacity batteries that can deliver 8kW, but that's not what 
I'm

after.

This isn't for an EV, so I suppose this is somewhat off topic, 
although

BMSs are a relevant topic to EVs. It's for a home appliance that I'm
prototyping.

I'm pretty sure I can find affordable cells that I can put together to
do this, but then I'm stuck with a custom BMS. I suspect that's the
route I'm going to have to take. So, let's talk about that.

Each cell (or group of parallel cells) needs a monitoring circuit (is
there a name for this?). And theses monitors need to communicate with 
a
BMS. I'm less concerned about designing the BMS as I think I can use 
an
arduino and do it in software. The arduino can control the charger, 
too.
I can revisit this later. But for the monitors, I need to get it 
right.
Since the battery will be in the house, it cannot cause a fire. Ever. 
Of
course, I will have over temperature sensors which shut off the 
charger

and shut off the load.

Here's what I think each monitor's role is, based on what I've read on
EVDL over the years and some common sense :)
- cell over voltage
- cell under voltage
- cell over current
- cell temperature
In all of the above the circuit should shunt the cell.
In addition, the monitor should constantly report the cell voltage,
current, and temp to the BMS.

If there's something reliable I can buy, at a reasonable price, that's
my first choice. Otherwise, I guess it's getting someone to help 
design

and fabricate these.

I would be grateful for your suggestions.

Peri
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Re: [EVDL] custom battery

[Lee Hart via EV]

Peri Hartman via EV wrote:

Ok, I did a little bit of research. Anyone care to double check this ?


Looks correct (at a casual glance).


I'll say right now that 100 caps at $40 is a non starter :)


Yes. It's possible, but not cheap. :-)

The cheapest solution is probably an ICE and generator. Small engines 
and generators can deliver amazing amounts of power if they only have to 
do it for a monute.


I wonder if compressed air or a hydraulic accumulator could store the 
kind of energy needed? Air and hydraulic motors can deliver enormous 
peak power levels.


Also look at it from the opposite direction. What can you do to reduce 
the peak power requirements? Can the energy be used more efficiently, or 
spread out over a longer period to reduce the peak to normal battery levels?


Lee Hart
--
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and a sterner sense of justice than we do. -- Wendell Berry
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Re: [EVDL] custom battery

[David Kerzel via EV]

5,000j is 5000 watt/seconds or 6.7 HP for 1 second
100 amp-hour battery at 360 volts is 36KW-Hr or 129,000,000 watt-seconds or 
joules.
To store 36KWhr at 360 volts, you would need 2,000F of capacitor rated at 
>360volts.  When 50% discharged, the voltage would be 254volts.

David Kerzel

-Original Message-
From: EV  On Behalf Of Jan Steinman via EV
Sent: Wednesday, April 15, 2020 11:03 PM
To: ev@lists.evdl.org
Cc: Jan Steinman 
Subject: Re: [EVDL] custom battery

I think the answer is really quite simple — and very expensive: capacitors!

I have a fence charger that charges/discharges six joules every second or so.

I have studio strobe lights that can charge/discharge nearly 5,000 joules in 
under ten seconds.

Other than the magnitude of energy that is moved about, these applications are 
perfectly safe, and no BMS is necessary.

So-called super capacitors have come down in price dramatically recently, 
although they are still a couple orders of magnitude more expensive than 
batteries. But your application sounds like it needs capacitors, or you may end 
up paying nearly as much in safety, failure prevention, and battery management.

Jan

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Re: [EVDL] custom battery

[Peri Hartman via EV]

Yes, so in practice I probably could only get about 70-80% of the energy 
out, I presume. And then I need to step up the voltage. Complicated.


Peri

-- Original Message --
From: "Jay Summet via EV" 
To: ev@lists.evdl.org
Cc: "Jay Summet" 
Sent: 16-Apr-20 8:12:16 AM
Subject: Re: [EVDL] custom battery


The other issue with Capacitors is that the voltage goes down quickly, and to 
get all the energy out you need to be able to make use of the widely varying 
voltage range.

Jay

On 4/16/20 11:00 AM, Peri Hartman via EV wrote:

Ok, I did a little bit of research. Anyone care to double check this ?

Here's one for $42 at unit quantity. 1200F, max voltage 2.7V
https://www.digikey.com/product-detail/en/tecate-group/TPLH-2R7-1200SL60X74/2085-TPLH-2R7-1200SL60X74-ND/9930298

Energy is
 E = 1/2 CV^2
where E is joules.

Joules to watt hours is
 Wh = 0.000278 J (approx)

So,
Wh = 0.000278 * 1/2 * 1200 * 2.7^2
   = 1.2 Wh

If that's correct, I'd need about 100 of these to have an operating energy 
capacity of around 100Wh. (My original parameter was 150Wh for a battery, but 
that included margin to ensure only charging between about 15% and 80%.)

I'll say right now that 100 caps at $40 is a non starter :)

Peri

-- Original Message --
From: "Peri Hartman" 
To: "Electric Vehicle Discussion List" 
Sent: 16-Apr-20 7:06:38 AM
Subject: Re[2]: [EVDL] custom battery


I'm looking at supercaps. I appreciate that a few people have suggested this, 
though I don't know yet whether it could be done economically.
Peri



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Re: [EVDL] custom battery

[Jay Summet via EV]

The other issue with Capacitors is that the voltage goes down quickly, 
and to get all the energy out you need to be able to make use of the 
widely varying voltage range.


Jay

On 4/16/20 11:00 AM, Peri Hartman via EV wrote:

Ok, I did a little bit of research. Anyone care to double check this ?

Here's one for $42 at unit quantity. 1200F, max voltage 2.7V
https://www.digikey.com/product-detail/en/tecate-group/TPLH-2R7-1200SL60X74/2085-TPLH-2R7-1200SL60X74-ND/9930298 



Energy is
     E = 1/2 CV^2
where E is joules.

Joules to watt hours is
     Wh = 0.000278 J (approx)

So,
Wh = 0.000278 * 1/2 * 1200 * 2.7^2
   = 1.2 Wh

If that's correct, I'd need about 100 of these to have an operating 
energy capacity of around 100Wh. (My original parameter was 150Wh for a 
battery, but that included margin to ensure only charging between about 
15% and 80%.)


I'll say right now that 100 caps at $40 is a non starter :)

Peri

-- Original Message --
From: "Peri Hartman" 
To: "Electric Vehicle Discussion List" 
Sent: 16-Apr-20 7:06:38 AM
Subject: Re[2]: [EVDL] custom battery

I'm looking at supercaps. I appreciate that a few people have 
suggested this, though I don't know yet whether it could be done 
economically.

Peri



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Re: [EVDL] custom battery

[Peri Hartman via EV]

Ok, I did a little bit of research. Anyone care to double check this ?

Here's one for $42 at unit quantity. 1200F, max voltage 2.7V
https://www.digikey.com/product-detail/en/tecate-group/TPLH-2R7-1200SL60X74/2085-TPLH-2R7-1200SL60X74-ND/9930298

Energy is
E = 1/2 CV^2
where E is joules.

Joules to watt hours is
Wh = 0.000278 J (approx)

So,
Wh = 0.000278 * 1/2 * 1200 * 2.7^2
  = 1.2 Wh

If that's correct, I'd need about 100 of these to have an operating 
energy capacity of around 100Wh. (My original parameter was 150Wh for a 
battery, but that included margin to ensure only charging between about 
15% and 80%.)


I'll say right now that 100 caps at $40 is a non starter :)

Peri

-- Original Message --
From: "Peri Hartman" 
To: "Electric Vehicle Discussion List" 
Sent: 16-Apr-20 7:06:38 AM
Subject: Re[2]: [EVDL] custom battery


I'm looking at supercaps. I appreciate that a few people have suggested this, 
though I don't know yet whether it could be done economically.
Peri



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Re: [EVDL] custom battery

[Peri Hartman via EV]

I'm looking at supercaps. I appreciate that a few people have suggested 
this, though I don't know yet whether it could be done economically.

Peri

-- Original Message --
From: "Jan Steinman via EV" 
To: ev@lists.evdl.org
Cc: "Jan Steinman" 
Sent: 15-Apr-20 11:03:27 PM
Subject: Re: [EVDL] custom battery


I think the answer is really quite simple — and very expensive: capacitors!

I have a fence charger that charges/discharges six joules every second or so.

I have studio strobe lights that can charge/discharge nearly 5,000 joules in 
under ten seconds.

Other than the magnitude of energy that is moved about, these applications are 
perfectly safe, and no BMS is necessary.

So-called super capacitors have come down in price dramatically recently, 
although they are still a couple orders of magnitude more expensive than 
batteries. But your application sounds like it needs capacitors, or you may end 
up paying nearly as much in safety, failure prevention, and battery management.

Jan

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Re: [EVDL] custom battery

[Jan Steinman via EV]

I think the answer is really quite simple — and very expensive: capacitors!

I have a fence charger that charges/discharges six joules every second or so.

I have studio strobe lights that can charge/discharge nearly 5,000 joules in 
under ten seconds.

Other than the magnitude of energy that is moved about, these applications are 
perfectly safe, and no BMS is necessary.

So-called super capacitors have come down in price dramatically recently, 
although they are still a couple orders of magnitude more expensive than 
batteries. But your application sounds like it needs capacitors, or you may end 
up paying nearly as much in safety, failure prevention, and battery management.

Jan

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Re: [EVDL] custom battery

[paul dove via EV]

 https://www.lipobattery.us/high-c-rating-li-poly-battery-50c-2/
On Wednesday, April 15, 2020, 2:28:44 PM CDT, jkenny23 via EV 
 wrote:  
 
 Let's keep the discussion in the context of the original ask too. A 50C(!!)
battery is a very different beast than a laptop or a cell phone that
discharges over the period of a few hours. Honestly, I think this is a
rather bad idea. Even high performance EVs don't slam batteries that hard.
Here's an example of what very high discharge does to RC batteries (there's
many others on Youtube I'm sure):
https://www.youtube.com/watch?v=-46h7Hshl2c

You'll be getting into serious discussions about thermal management and wire
resistance, resistance of other components in the system, etc. You won't be
able to just switch it with a simple relay/FET arrangement, you'll need a
proper EV level contactor (which itself is rather large, power hungry, and
expensive).

If you need to provide high power, it's /much/ better to just up-size your
battery to give it a gentler discharge.

--
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Re: [EVDL] custom battery

[jkenny23 via EV]

Let's keep the discussion in the context of the original ask too. A 50C(!!)
battery is a very different beast than a laptop or a cell phone that
discharges over the period of a few hours. Honestly, I think this is a
rather bad idea. Even high performance EVs don't slam batteries that hard.
Here's an example of what very high discharge does to RC batteries (there's
many others on Youtube I'm sure):
https://www.youtube.com/watch?v=-46h7Hshl2c

You'll be getting into serious discussions about thermal management and wire
resistance, resistance of other components in the system, etc. You won't be
able to just switch it with a simple relay/FET arrangement, you'll need a
proper EV level contactor (which itself is rather large, power hungry, and
expensive).

If you need to provide high power, it's /much/ better to just up-size your
battery to give it a gentler discharge.

--
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Re: [EVDL] custom battery

[paul dove via EV]

I design electronics for a living. It’s not that hard you just have to do a lot 
of testing. I can design one for you but it would not be free. TI has some 
really good parts for BMS systems and the have videos and app notes. I don’t 
think it would be worthwhile for a one time project but it sounds like he’s 
developing a product in which case engineering may pay off. 

The hoverboard BTW had faulty batteries not a faulty BMS.

Sent from my iPhone

> On Apr 14, 2020, at 8:12 PM, Peri Hartman via EV  wrote:
> 
> Ok, Paul, I challenge you. You get to design my cell monitoring boards and 
> the BMS. Then you get to put it in a closet in your house while it charges 
> and discharges over and over. If you're living in the same house a year 
> later, you win !
> 
> Point being, there are commercial products whose BMS has been designed by 
> competent engineers and they work nearly 100% without catastrophic failure.
> 
> On the other hand, there are shadier companies that have poorly designed 
> systems. Remember the hoverboard fires ? There's nothing wrong with 
> hoverboards, but some company made a popular one and it caught fire on a 
> number of occasions.
> 
> If I were to design the monitor circuit, I'd be in the latter category, 
> though not with the intention of selling a faulty product :)
> 
> Peri
> 
> -- Original Message --
> From: "paul dove via EV" 
> To: "Electric Vehicle Discussion List" 
> Cc: "paul dove" 
> Sent: 14-Apr-20 12:35:14 PM
> Subject: Re: [EVDL] custom battery
> 
>> There are literally hundreds of products out there using these batteries.
>> It is rare to see a fire caused by one. I have computers, phones, tools cars 
>> etc. none have ever blown up or caught on fire.
>> 
>> 
>>On Tuesday, April 14, 2020, 1:36:12 PM CDT, Lee Hart via EV 
>>  wrote:
>> 
>> I agree with Bill. The battery itself can be built with today's
>> technology. It's the BMS that's going to give you trouble.
>> 
>> As Bill said, the pack will be used until it breaks. And *when* it
>> breaks, it could easily start a fire that leads to a disaster. It's
>> really hard to design things that are not only foolproof, but DAMN fool
>> proof.
>> 
>> For years I worked for Robertshaw and Honeywell designing furnace
>> controls. A furnace control has to be DAMN fool proof, or it could (for
>> example) open the gas valve without lighting the burner, fill the house
>> with gas, and THEN light it. So the controls had every safety interlock
>> we could think of to prevent this from ever happening.
>> 
>> Nevertheless... A control failed this way, and blew up a house, causing
>> several fatalities. On examination, it turned out that the installer had
>> mis-wired the 24v power transformer across two GND terminals. The high
>> current burned the PCB trace open between them. Then he corrected his
>> mistake, and wired it correctly. The furnace seemed to work, so he left.
>> But the open trace defeated one of the safety circuits. Later, when
>> something else when wrong with the furnace, it set fire to the house.
>> 
>> Despite having only contributory negligence, Honeywell still had to pay
>> millions of dollars in settlements. And, the AGA (the regulatory body
>> that sets standards for gas furnaces) added requirements that all
>> controls must pass a "miswire" test, where no safety issue is created
>> even if the control is mis-wired.
>> 
>> Can you imagine how hard it is to design something so it is *impossible*
>> to hook it up wrong? But those are the kind of lengths you have to go to
>> when there is any chance of it causing a disaster.
>> 
>> Lee Hart
>> --
>> Whether we or our politicians know it or not, Nature is party to all
>> our deals and decisions, and she has more votes, a longer memory,
>> and a sterner sense of justice than we do. -- Wendell Berry
>> --
>> Lee Hart, 814 8th Ave N, Sartell MN 56377, http://www.sunrise-ev.com
>> ___
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Re: [EVDL] custom battery

[EVDL Administrator via EV]

On 14 Apr 2020 at 19:35, paul dove via EV wrote:

> I have computers, phones, tools cars etc. none have ever blown up or
> caught on fire. 

Market researchers have a saying: "The plural of anecdote is not data."

In other words, when estimating how likely an unfortunate incident is to 
happen, your experience and mine don't mean a bloody thing.  

David Roden - Akron, Ohio, USA
EVDL Administrator

= = = = = = = = = = = = = = = = = = = = = = = = = = = = =
EVDL Information: http://www.evdl.org/help/
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Note: mail sent to "evpost" and "etpost" addresses will not 
reach me.  To send a private message, please obtain my 
email address from the webpage http://www.evdl.org/help/ .
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Re: [EVDL] custom battery

[Peri Hartman via EV]

Ok, Paul, I challenge you. You get to design my cell monitoring boards 
and the BMS. Then you get to put it in a closet in your house while it 
charges and discharges over and over. If you're living in the same house 
a year later, you win !


Point being, there are commercial products whose BMS has been designed 
by competent engineers and they work nearly 100% without catastrophic 
failure.


On the other hand, there are shadier companies that have poorly designed 
systems. Remember the hoverboard fires ? There's nothing wrong with 
hoverboards, but some company made a popular one and it caught fire on a 
number of occasions.


If I were to design the monitor circuit, I'd be in the latter category, 
though not with the intention of selling a faulty product :)


Peri

-- Original Message --
From: "paul dove via EV" 
To: "Electric Vehicle Discussion List" 
Cc: "paul dove" 
Sent: 14-Apr-20 12:35:14 PM
Subject: Re: [EVDL] custom battery


 There are literally hundreds of products out there using these batteries.
It is rare to see a fire caused by one. I have computers, phones, tools cars 
etc. none have ever blown up or caught on fire.


On Tuesday, April 14, 2020, 1:36:12 PM CDT, Lee Hart via EV 
 wrote:

 I agree with Bill. The battery itself can be built with today's
technology. It's the BMS that's going to give you trouble.

As Bill said, the pack will be used until it breaks. And *when* it
breaks, it could easily start a fire that leads to a disaster. It's
really hard to design things that are not only foolproof, but DAMN fool
proof.

For years I worked for Robertshaw and Honeywell designing furnace
controls. A furnace control has to be DAMN fool proof, or it could (for
example) open the gas valve without lighting the burner, fill the house
with gas, and THEN light it. So the controls had every safety interlock
we could think of to prevent this from ever happening.

Nevertheless... A control failed this way, and blew up a house, causing
several fatalities. On examination, it turned out that the installer had
mis-wired the 24v power transformer across two GND terminals. The high
current burned the PCB trace open between them. Then he corrected his
mistake, and wired it correctly. The furnace seemed to work, so he left.
But the open trace defeated one of the safety circuits. Later, when
something else when wrong with the furnace, it set fire to the house.

Despite having only contributory negligence, Honeywell still had to pay
millions of dollars in settlements. And, the AGA (the regulatory body
that sets standards for gas furnaces) added requirements that all
controls must pass a "miswire" test, where no safety issue is created
even if the control is mis-wired.

Can you imagine how hard it is to design something so it is *impossible*
to hook it up wrong? But those are the kind of lengths you have to go to
when there is any chance of it causing a disaster.

Lee Hart
--
Whether we or our politicians know it or not, Nature is party to all
our deals and decisions, and she has more votes, a longer memory,
and a sterner sense of justice than we do. -- Wendell Berry
--
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Re: [EVDL] custom battery

[paul dove via EV]

 There are literally hundreads of products out there using these batteries.
It is rare to see a fire caused by one. I have computers, phones, tools cars 
etc. none have ever blown up or caught on fire.


On Tuesday, April 14, 2020, 1:36:12 PM CDT, Lee Hart via EV 
 wrote:  
 
 I agree with Bill. The battery itself can be built with today's 
technology. It's the BMS that's going to give you trouble.

As Bill said, the pack will be used until it breaks. And *when* it 
breaks, it could easily start a fire that leads to a disaster. It's 
really hard to design things that are not only foolproof, but DAMN fool 
proof.

For years I worked for Robertshaw and Honeywell designing furnace 
controls. A furnace control has to be DAMN fool proof, or it could (for 
example) open the gas valve without lighting the burner, fill the house 
with gas, and THEN light it. So the controls had every safety interlock 
we could think of to prevent this from ever happening.

Nevertheless... A control failed this way, and blew up a house, causing 
several fatalities. On examination, it turned out that the installer had 
mis-wired the 24v power transformer across two GND terminals. The high 
current burned the PCB trace open between them. Then he corrected his 
mistake, and wired it correctly. The furnace seemed to work, so he left. 
But the open trace defeated one of the safety circuits. Later, when 
something else when wrong with the furnace, it set fire to the house.

Despite having only contributory negligence, Honeywell still had to pay 
millions of dollars in settlements. And, the AGA (the regulatory body 
that sets standards for gas furnaces) added requirements that all 
controls must pass a "miswire" test, where no safety issue is created 
even if the control is mis-wired.

Can you imagine how hard it is to design something so it is *impossible* 
to hook it up wrong? But those are the kind of lengths you have to go to 
when there is any chance of it causing a disaster.

Lee Hart
-- 
Whether we or our politicians know it or not, Nature is party to all
our deals and decisions, and she has more votes, a longer memory,
and a sterner sense of justice than we do. -- Wendell Berry
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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[EVDL] custom battery - DKblock

[Offgrid Systems via EV]

Hi Peri,

I've designed an open source BMS and cell packaging system, if you don't 
want to design your own.


You need to source some pretty amazing lithium ion cells for that 53C 
discharge rate! I think you might end up with a larger battery to get 
that big C rate.


Anyway it's free to use if you want here is the website for all the 
files. https://github.com/offgridsystems


There are some parts up on ebay if you don't want to make/order your 
own. 
https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=dkblock&_sacat=0


Also a website if you want so build information. 
https://dkblock922508958.wordpress.com


You may need to reprogram the Teensy (arduino like) controller (using my 
code) for your application.


Cheers,

Tim Economu
Offgrid Systems LLC
Whidbey Island


On 4/14/2020 11:36 AM, ev-requ...@lists.evdl.org wrote:

Message: 1
Date: Tue, 14 Apr 2020 04:33:04 +
From: "Peri Hartman"
To: "Electric Vehicle Discussion List"
Subject: [EVDL] custom battery
Message-ID: 
Content-Type: text/plain; charset="utf-8"; Format="flowed"

Hi,

I need a battery with about 150Wh and a discharge rate of 8kW for up to
a minute or so. I've spent a few hours searching and there doesn't seem
to be anything on the market that fits this. There are, of course,
higher capacity batteries that can deliver 8kW, but that's not what I'm
after.

This isn't for an EV, so I suppose this is somewhat off topic, although
BMSs are a relevant topic to EVs. It's for a home appliance that I'm
prototyping.

I'm pretty sure I can find affordable cells that I can put together to
do this, but then I'm stuck with a custom BMS. I suspect that's the
route I'm going to have to take. So, let's talk about that.

Each cell (or group of parallel cells) needs a monitoring circuit (is
there a name for this?). And theses monitors need to communicate with a
BMS. I'm less concerned about designing the BMS as I think I can use an
arduino and do it in software. The arduino can control the charger, too.
I can revisit this later. But for the monitors, I need to get it right.
Since the battery will be in the house, it cannot cause a fire. Ever. Of
course, I will have over temperature sensors which shut off the charger
and shut off the load.

Here's what I think each monitor's role is, based on what I've read on
EVDL over the years and some common sense:)
- cell over voltage
- cell under voltage
- cell over current
- cell temperature
In all of the above the circuit should shunt the cell.
In addition, the monitor should constantly report the cell voltage,
current, and temp to the BMS.

If there's something reliable I can buy, at a reasonable price, that's
my first choice. Otherwise, I guess it's getting someone to help design
and fabricate these.

I would be grateful for your suggestions.

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Re: [EVDL] custom battery

[Jim Walls via EV]

On 04/14/2020 11:35, Lee Hart via EV wrote:
For years I worked for Robertshaw and Honeywell designing furnace 
controls. A furnace control has to be DAMN fool proof, or it could 
(for example) open the gas valve without lighting the burner, fill the 
house with gas, and THEN light it. So the controls had every safety 
interlock we could think of to prevent this from ever happening.


Lee,  I have a Robertshaw furnace control in my house.  So THANK YOU for 
your efforts!  Actually I did have one fail a couple years ago after 25 
years or so in service.  The failure mode was that it would light the 
pilot, but never turn on the main gas flow (and yes it was the 
controller, not the sensor that detects that the pilot is lit). But I 
would much rather have the house cold then on fire!



--
73
-
Jim Walls - K6CCC
j...@k6ccc.org
Ofc:  818-548-4804
http://members.dslextreme.com/users/k6ccc/
AMSAT Member 32537 - WSWSS Member 395

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Re: [EVDL] custom battery

[Lee Hart via EV]

I agree with Bill. The battery itself can be built with today's 
technology. It's the BMS that's going to give you trouble.


As Bill said, the pack will be used until it breaks. And *when* it 
breaks, it could easily start a fire that leads to a disaster. It's 
really hard to design things that are not only foolproof, but DAMN fool 
proof.


For years I worked for Robertshaw and Honeywell designing furnace 
controls. A furnace control has to be DAMN fool proof, or it could (for 
example) open the gas valve without lighting the burner, fill the house 
with gas, and THEN light it. So the controls had every safety interlock 
we could think of to prevent this from ever happening.


Nevertheless... A control failed this way, and blew up a house, causing 
several fatalities. On examination, it turned out that the installer had 
mis-wired the 24v power transformer across two GND terminals. The high 
current burned the PCB trace open between them. Then he corrected his 
mistake, and wired it correctly. The furnace seemed to work, so he left. 
But the open trace defeated one of the safety circuits. Later, when 
something else when wrong with the furnace, it set fire to the house.


Despite having only contributory negligence, Honeywell still had to pay 
millions of dollars in settlements. And, the AGA (the regulatory body 
that sets standards for gas furnaces) added requirements that all 
controls must pass a "miswire" test, where no safety issue is created 
even if the control is mis-wired.


Can you imagine how hard it is to design something so it is *impossible* 
to hook it up wrong? But those are the kind of lengths you have to go to 
when there is any chance of it causing a disaster.


Lee Hart
--
Whether we or our politicians know it or not, Nature is party to all
our deals and decisions, and she has more votes, a longer memory,
and a sterner sense of justice than we do. -- Wendell Berry
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] custom battery

[Peri Hartman via EV]

I think you're right. For example, here's one that's pretty close:

https://www.hobbytown.com/gens-ace-4s-lihv-100c-lipo-battery-pack-15.2v-7500mah-ga-b1102/p779337

Did I do the math right ?

capacity 7.5Ah
rate: 100C
volts: 15.2

That's
capacity 7.5 * 15.2 = 114Wh
rate: 100 * 114 = 11.4kW

Peri

-- Original Message --
From: "Lawrence Winiarski" 
To: "Electric Vehicle Discussion List" ; "Peri 
Hartman" 

Sent: 13-Apr-20 10:22:34 PM
Subject: Re: [EVDL] custom battery

Isn't 60c or 100C common in Radio Control stuff now? Lots of 
solutions there.


On Monday, April 13, 2020, 9:51:43 PM PDT, Peri Hartman via EV 
 wrote:



Nominally 240. But it really can be anything and I can convert it to
what I need.
Peri

-- Original Message --
From: "Alan Arrison via EV" 
To: ev@lists.evdl.org
Cc: "Alan Arrison" 
Sent: 13-Apr-20 9:48:53 PM
Subject: Re: [EVDL] custom battery

>That sounds like almost super-capacitor territory. What voltage is 
needed?

>
>Designing and implementing a BMS is something even EE's have trouble 
with.

>
>However, if the voltage is low enough, it makes it much easier.
>
>Al
>
>On 4/14/2020 12:33 AM, Peri Hartman via EV wrote:
>>Hi,
>>
>>I need a battery with about 150Wh and a discharge rate of 8kW for up 
to a minute or so. I've spent a few hours searching and there doesn't 
seem to be anything on the market that fits this. There are, of course, 
higher capacity batteries that can deliver 8kW, but that's not what I'm 
after.

>>
>>This isn't for an EV, so I suppose this is somewhat off topic, 
although BMSs are a relevant topic to EVs. It's for a home appliance 
that I'm prototyping.

>>
>>I'm pretty sure I can find affordable cells that I can put together 
to do this, but then I'm stuck with a custom BMS. I suspect that's the 
route I'm going to have to take. So, let's talk about that.

>>
>>Each cell (or group of parallel cells) needs a monitoring circuit (is 
there a name for this?). And theses monitors need to communicate with a 
BMS. I'm less concerned about designing the BMS as I think I can use an 
arduino and do it in software. The arduino can control the charger, 
too. I can revisit this later. But for the monitors, I need to get it 
right. Since the battery will be in the house, it cannot cause a fire. 
Ever. Of course, I will have over temperature sensors which shut off 
the charger and shut off the load.

>>
>>Here's what I think each monitor's role is, based on what I've read 
on EVDL over the years and some common sense :)

>>- cell over voltage
>>- cell under voltage
>>- cell over current
>>- cell temperature
>>In all of the above the circuit should shunt the cell.
>>In addition, the monitor should constantly report the cell voltage, 
current, and temp to the BMS.

>>
>>If there's something reliable I can buy, at a reasonable price, 
that's my first choice. Otherwise, I guess it's getting someone to help 
design and fabricate these.

>>
>>I would be grateful for your suggestions.
>>
>>Peri
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Re: [EVDL] custom battery

[Cor van de Water via EV]

Peri,
That is 50C discharge, not impossible but also not trivial.
The good old A123 cells could do this.
The cylindrical cells are almost 10Wh and can discharge at metal melting
speeds.
I have a bunch of them here, in case you are interested.
Cor.

On Mon, Apr 13, 2020, 9:33 PM Peri Hartman via EV  wrote:

> Hi,
>
> I need a battery with about 150Wh and a discharge rate of 8kW for up to
> a minute or so. I've spent a few hours searching and there doesn't seem
> to be anything on the market that fits this. There are, of course,
> higher capacity batteries that can deliver 8kW, but that's not what I'm
> after.
>
> This isn't for an EV, so I suppose this is somewhat off topic, although
> BMSs are a relevant topic to EVs. It's for a home appliance that I'm
> prototyping.
>
> I'm pretty sure I can find affordable cells that I can put together to
> do this, but then I'm stuck with a custom BMS. I suspect that's the
> route I'm going to have to take. So, let's talk about that.
>
> Each cell (or group of parallel cells) needs a monitoring circuit (is
> there a name for this?). And theses monitors need to communicate with a
> BMS. I'm less concerned about designing the BMS as I think I can use an
> arduino and do it in software. The arduino can control the charger, too.
> I can revisit this later. But for the monitors, I need to get it right.
> Since the battery will be in the house, it cannot cause a fire. Ever. Of
> course, I will have over temperature sensors which shut off the charger
> and shut off the load.
>
> Here's what I think each monitor's role is, based on what I've read on
> EVDL over the years and some common sense :)
> - cell over voltage
> - cell under voltage
> - cell over current
> - cell temperature
> In all of the above the circuit should shunt the cell.
> In addition, the monitor should constantly report the cell voltage,
> current, and temp to the BMS.
>
> If there's something reliable I can buy, at a reasonable price, that's
> my first choice. Otherwise, I guess it's getting someone to help design
> and fabricate these.
>
> I would be grateful for your suggestions.
>
> Peri
> -- next part --
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Re: [EVDL] custom battery

[Bill Dube via EV]

On 4/14/2020 4:51 PM, Peri Hartman via EV wrote:
Nominally 240. But it really can be anything and I can convert it to 
what I need.

Peri


 Cells <

You can get about one third of the specific energy (~8000 W/kg) from 
ordinary A123 26650 cordless tool cells.


    You can get over 20,000 W/kg from A123 F1 cells, but the cost will 
take your breath away.


    John Metric sells some very high-performance drag racing cells that 
might work for you.


 BMS <

    At first look, it seems extremely simple to build your own BMS.
    Measure the cell voltage, switch on a by-pass resistor, turn off 
the charger, turn off the controller, blink a few LEDs. Piece of cake, 
right?
    It is, in practice, a _very_ hard thing to build. It has to be 100% 
reliable in _all_ respects, or you will absolutely get a fire. Guaranteed.


   It has to withstand very large, very broad spectrum, magnetic 
fields. The EMI and RFI issues are enormous. Then, you have to deal with 
the high voltages, and figure out how to deal safely (and reliably) with 
those large voltages.


    When it fails, (it will fail at some point,) it must warn that it 
has failed, and fail in a manner that does not cause the pack to become 
unbalanced or cause some safety issue.
    It also has to deal with battery faults like an open cell, a 
reversed cell, over voltage, etc. in a safe and predictable manner that 
warns the user in every instance, and shut down the charger or 
controller in a safe manner.
   Processors, like Arduinos, fail in unpredictable ways when subjected 
to the large magnetic fields, the huge broad spectrum RFI and huge EMI 
that the inverter and the charger subjects the battery to.


   _Huge_ undertaking. You will ruin several packs trying to work out 
the bugs.



Bill D.
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Re: [EVDL] custom battery

[Lawrence Winiarski via EV]

Isn't 60c or 100C common in Radio Control stuff now? Lots of solutions 
there.

On Monday, April 13, 2020, 9:51:43 PM PDT, Peri Hartman via EV 
 wrote:  
 
 Nominally 240. But it really can be anything and I can convert it to 
what I need.
Peri

-- Original Message --
From: "Alan Arrison via EV" 
To: ev@lists.evdl.org
Cc: "Alan Arrison" 
Sent: 13-Apr-20 9:48:53 PM
Subject: Re: [EVDL] custom battery

>That sounds like almost super-capacitor territory. What voltage is needed?
>
>Designing and implementing a BMS is something even EE's have trouble with.
>
>However, if the voltage is low enough, it makes it much easier.
>
>Al
>
>On 4/14/2020 12:33 AM, Peri Hartman via EV wrote:
>>Hi,
>>
>>I need a battery with about 150Wh and a discharge rate of 8kW for up to a 
>>minute or so. I've spent a few hours searching and there doesn't seem to be 
>>anything on the market that fits this. There are, of course, higher capacity 
>>batteries that can deliver 8kW, but that's not what I'm after.
>>
>>This isn't for an EV, so I suppose this is somewhat off topic, although BMSs 
>>are a relevant topic to EVs. It's for a home appliance that I'm prototyping.
>>
>>I'm pretty sure I can find affordable cells that I can put together to do 
>>this, but then I'm stuck with a custom BMS. I suspect that's the route I'm 
>>going to have to take. So, let's talk about that.
>>
>>Each cell (or group of parallel cells) needs a monitoring circuit (is there a 
>>name for this?). And theses monitors need to communicate with a BMS. I'm less 
>>concerned about designing the BMS as I think I can use an arduino and do it 
>>in software. The arduino can control the charger, too. I can revisit this 
>>later. But for the monitors, I need to get it right. Since the battery will 
>>be in the house, it cannot cause a fire. Ever. Of course, I will have over 
>>temperature sensors which shut off the charger and shut off the load.
>>
>>Here's what I think each monitor's role is, based on what I've read on EVDL 
>>over the years and some common sense :)
>>- cell over voltage
>>- cell under voltage
>>- cell over current
>>- cell temperature
>>In all of the above the circuit should shunt the cell.
>>In addition, the monitor should constantly report the cell voltage, current, 
>>and temp to the BMS.
>>
>>If there's something reliable I can buy, at a reasonable price, that's my 
>>first choice. Otherwise, I guess it's getting someone to help design and 
>>fabricate these.
>>
>>I would be grateful for your suggestions.
>>
>>Peri
>>-- next part --
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>>
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Re: [EVDL] custom battery

[Peri Hartman via EV]

Nominally 240. But it really can be anything and I can convert it to 
what I need.

Peri

-- Original Message --
From: "Alan Arrison via EV" 
To: ev@lists.evdl.org
Cc: "Alan Arrison" 
Sent: 13-Apr-20 9:48:53 PM
Subject: Re: [EVDL] custom battery


That sounds like almost super-capacitor territory. What voltage is needed?

Designing and implementing a BMS is something even EE's have trouble with.

However, if the voltage is low enough, it makes it much easier.

Al

On 4/14/2020 12:33 AM, Peri Hartman via EV wrote:

Hi,

I need a battery with about 150Wh and a discharge rate of 8kW for up to a 
minute or so. I've spent a few hours searching and there doesn't seem to be 
anything on the market that fits this. There are, of course, higher capacity 
batteries that can deliver 8kW, but that's not what I'm after.

This isn't for an EV, so I suppose this is somewhat off topic, although BMSs 
are a relevant topic to EVs. It's for a home appliance that I'm prototyping.

I'm pretty sure I can find affordable cells that I can put together to do this, 
but then I'm stuck with a custom BMS. I suspect that's the route I'm going to 
have to take. So, let's talk about that.

Each cell (or group of parallel cells) needs a monitoring circuit (is there a 
name for this?). And theses monitors need to communicate with a BMS. I'm less 
concerned about designing the BMS as I think I can use an arduino and do it in 
software. The arduino can control the charger, too. I can revisit this later. 
But for the monitors, I need to get it right. Since the battery will be in the 
house, it cannot cause a fire. Ever. Of course, I will have over temperature 
sensors which shut off the charger and shut off the load.

Here's what I think each monitor's role is, based on what I've read on EVDL 
over the years and some common sense :)
- cell over voltage
- cell under voltage
- cell over current
- cell temperature
In all of the above the circuit should shunt the cell.
In addition, the monitor should constantly report the cell voltage, current, 
and temp to the BMS.

If there's something reliable I can buy, at a reasonable price, that's my first 
choice. Otherwise, I guess it's getting someone to help design and fabricate 
these.

I would be grateful for your suggestions.

Peri
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Re: [EVDL] custom battery

[Alan Arrison via EV]

That sounds like almost super-capacitor territory. What voltage is needed?

Designing and implementing a BMS is something even EE's have trouble with.

However, if the voltage is low enough, it makes it much easier.

Al

On 4/14/2020 12:33 AM, Peri Hartman via EV wrote:

Hi,

I need a battery with about 150Wh and a discharge rate of 8kW for up 
to a minute or so. I've spent a few hours searching and there doesn't 
seem to be anything on the market that fits this. There are, of 
course, higher capacity batteries that can deliver 8kW, but that's not 
what I'm after.


This isn't for an EV, so I suppose this is somewhat off topic, 
although BMSs are a relevant topic to EVs. It's for a home appliance 
that I'm prototyping.


I'm pretty sure I can find affordable cells that I can put together to 
do this, but then I'm stuck with a custom BMS. I suspect that's the 
route I'm going to have to take. So, let's talk about that.


Each cell (or group of parallel cells) needs a monitoring circuit (is 
there a name for this?). And theses monitors need to communicate with 
a BMS. I'm less concerned about designing the BMS as I think I can use 
an arduino and do it in software. The arduino can control the charger, 
too. I can revisit this later. But for the monitors, I need to get it 
right. Since the battery will be in the house, it cannot cause a fire. 
Ever. Of course, I will have over temperature sensors which shut off 
the charger and shut off the load.


Here's what I think each monitor's role is, based on what I've read on 
EVDL over the years and some common sense :)

- cell over voltage
- cell under voltage
- cell over current
- cell temperature
In all of the above the circuit should shunt the cell.
In addition, the monitor should constantly report the cell voltage, 
current, and temp to the BMS.


If there's something reliable I can buy, at a reasonable price, that's 
my first choice. Otherwise, I guess it's getting someone to help 
design and fabricate these.


I would be grateful for your suggestions.

Peri
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[EVDL] custom battery

[Peri Hartman via EV]

Hi,

I need a battery with about 150Wh and a discharge rate of 8kW for up to 
a minute or so. I've spent a few hours searching and there doesn't seem 
to be anything on the market that fits this. There are, of course, 
higher capacity batteries that can deliver 8kW, but that's not what I'm 
after.


This isn't for an EV, so I suppose this is somewhat off topic, although 
BMSs are a relevant topic to EVs. It's for a home appliance that I'm 
prototyping.


I'm pretty sure I can find affordable cells that I can put together to 
do this, but then I'm stuck with a custom BMS. I suspect that's the 
route I'm going to have to take. So, let's talk about that.


Each cell (or group of parallel cells) needs a monitoring circuit (is 
there a name for this?). And theses monitors need to communicate with a 
BMS. I'm less concerned about designing the BMS as I think I can use an 
arduino and do it in software. The arduino can control the charger, too. 
I can revisit this later. But for the monitors, I need to get it right. 
Since the battery will be in the house, it cannot cause a fire. Ever. Of 
course, I will have over temperature sensors which shut off the charger 
and shut off the load.


Here's what I think each monitor's role is, based on what I've read on 
EVDL over the years and some common sense :)

- cell over voltage
- cell under voltage
- cell over current
- cell temperature
In all of the above the circuit should shunt the cell.
In addition, the monitor should constantly report the cell voltage, 
current, and temp to the BMS.


If there's something reliable I can buy, at a reasonable price, that's 
my first choice. Otherwise, I guess it's getting someone to help design 
and fabricate these.


I would be grateful for your suggestions.

Peri
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