Re: [Emc-users] Adding feedback to an existing stepper motor.

[Chris Albertson]

THose add-on boards look good for small motors.  I just downloaded the user
manual.

But for a machine tool, even a mini-size one you might want more power.
 Stepper-online has that for about $125 per axis.

About adding an index,  why swap ou the encoder?  just add a magnetic or
optical pickup someplace.

A larger closed loop motor is going on my mill's vertical axis bacuse it
needs to hold a static load.   The closed system uses much less power for
static loads than do open loop systems.

Those add on boards might work on small robot arm I want to build.


On Fri, May 17, 2019 at 1:44 PM Greg Bentzinger via Emc-users <
emc-users@lists.sourceforge.net> wrote:

> {Greg}
>
> There are options to converting existing steppers to closed loop feed back.
>
> The LCNC software/hardware option would be to add an encoder and run the
> stepper in velocity mode. This does not offer the many advantages of the
> direct feedback drivers.
>
> Then for small steppers there is the Mechaduino bolt on option. Buy direct
> from
>
> https://tropical-labs.com/
>
>
> https://hackaday.com/2016/06/01/mechaduino-closed-loop-stepper-servos-for-everyone/
>
> https://github.com/jcchurch13/Mechaduino-Hardware
>
> https://github.com/jcchurch13/Mechaduino-Firmware
>
> The latest firmware release was 26 November 2018 so this is not a dead
> item.
>
> If someone were to build on this open source project and produce a unit
> with a 50VDC / 6A working power capacity it could cover most steppers.
>
> IIRC Gecko drive was once working on this idea and had it working, I think
> maybe it was not released because it was not economical and would not match
> performance of matched motor drive combos, but that is just my speculation.
>
> I would like to get one of the matched motor/driver units and see if the
> encoder could be replaced with a unit which included a index channel.
>
> {/Greg}
>
>
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Re: [Emc-users] Atomic pi

[Alan Condit]

Well I received a fedex tracking number that says they shipped my AtomicPi 
order on the 15th. In 2 days it made it from San Jose, to Troutdale, OR, about 
35-40 miles from home. They say it should arrive home on Tuesday the 21st. So 2 
days to make it most of the way and 4 more days to cover the last 40 miles. :-)

The website now shows $45 for the AtomicPi and $119 for the “Full Developers 
Kit”. We’ll soon see if it is worth the shekels.

Alan

> On May 14, 2019, at 4:55 PM, Alan Condit  wrote:
> 
> Chris and Gene,
> 
> I just went to the dlidirect.com  website and clicked 
> on the “Full Developer Kit” pull down, it showed out of stock when I looked 
> but while I was on the page looking I got a invitation to chat box. I asked 
> whether you could order the developers kit through the website or if you had 
> to buy it through Amazon. The chat person said give me a call and posted 
> their phone number. They said they had a limited number of developer kits in 
> stock but the price was now $119 plus $20 shipping. So, I placed an order and 
> was told that it will ship tomorrow.
> 
> Assuming that I didn’t get scammed, I should have it in a few days.
> 
> Alan
> 
>> From: Chris Albertson > >
>> Subject: Re: [Emc-users] Atomic pi
>> Date: May 13, 2019 at 9:58:57 PM PDT
>> To: "Enhanced Machine Controller (EMC)" > >
>> 
>> 
>> I looked at their web site.  About $108 for the full developer kit but you
>> get two units, the pwr supply, and a camera.   It's a fantastic deal but
>> they are sold out.  They say "restocking now" and to buy them on Amazon.
>> 
>> $108 for two is a great deal.
>> 
>> On Mon, May 13, 2019 at 9:21 PM Gene Heskett > > wrote:
>> 
>>> On Monday 13 May 2019 11:43:56 pm jeremy youngs wrote:
>>> 
 https://dlidirect.com/products/atomic-pi?fbclid=IwAR0k6hdGM6u1RJSVNLPn 
 
 kMxKnkg6CfnWs1szLEF9zhEj2YDZB0Z_PaWxVpQ
 
 Any trying this ?
 
>>> Not yet, sure looks interesting though. What does the whole kit, bob and
>>> pdu shown cost?
>>> 
>>> Maybe it could be our next D525MW but with an spi interface to a 7i90HD?
>>> 
>>> Cheers, Gene Heskett
>>> --
>>> "There are four boxes to be used in defense of liberty:
>>> soap, ballot, jury, and ammo. Please use in that order."
>>> -Ed Howdershelt (Author)
>>> Genes Web page >> >


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Re: [Emc-users] Lead acid batteries

[Chris Albertson]

Have you run the numbers?  What do they cost per KWH over 10 years?   The
cost of each battery is meaningless.
The "price to beat" right now is about $500  (the cost to buy and maintain
over 10 years in dollars/KWH)

THose Telco batteries do last a LONG time because the telcos NEVER
discharge them but at 50% discharge they get about 500 cycles which is
REALLY good compared to most LA batteries.   But in this use case --
storing solar power they will see one cycle per day and a 500 cycle
battery will not last two years.So you look at the chart and see that
if you discharge only to 10% or 5% thy can last thousands of cycles.  No
kidding that is the intended use case on the telco industry. But at 10%
discharge limit you need five times more batteries so the initial cost is
to high.

The key to economy with LA is to selects a discharge limits that
maximise KWH per lifetime.

Here is how to design a lead-acid system for the best long term
economyFigure out your total usage of KWH per day.  Look at you
utility bill in a peak usage month.  Perhaps you use air conditioning in
summer so use a summer month.  Divide by the number of days.

IN the US 850 KWH per monnth is average, so figure you use 28 KWH per day.
FOr best economy size the system for two days of usage and this will reduce
the number and depth of charge cycles per years.SO we need a 60 KHW
system for the average house in the US.

Next, choose a discharge limit for your battery.  50% is good.   This means
you can only use 50AH from a 100AH battry.

convert KWH to AH by dividing by 10. (not 12, as that is way to optimistic.
10 accounts for losses)

OK you still with me?  60KHW / 10 = 6,000 AH of usable power.  But our 50%
limit means we need 12,000 AH of lead-acid batteries

Lets assume you use the generic brand "deep cyce"  batteries.  These at
about 100AH and $200 each.   You need to buy 120 batteries at a cost of
$24,000.This is not bad.BUt you still need an inverter/charger that
can handle the entire load of the house.  Likey a peak at over 100 amps.
You need a shed and lots of wire.   Lets say $30K.

The above is absolute mainstream design for 15 years ago.  and results in a
minimum cost to own battery system for a home owner.
$30K is not bad and it compares to buying an actual "Power Wall" of the
same size that would cost $29.6K .  About the same price.

But what has happened is the new battery management systems combined with
new chemistry has knocked down the maintenance price to "zero". The
lead-acid systems costs about what you pay up from to operated for 10 years
as in that time you will have replaced EVERY battery at least once.




On Fri, May 17, 2019 at 1:14 PM Greg Bentzinger via Emc-users <
emc-users@lists.sourceforge.net> wrote:

> {Greg}
>
> If I were going to install a full off grid potential solar power system
> for my ranch I would buy lead acid Telco system batteries.
>
> They are not true deep cycle, but have such high capacity that it isn't an
> issue. They are initially expensive and huge. ( I might buy some 10yr old
> units being decommissioned )
>
>
> On the plus sign they can have up to a 30 year service life and are user
> serviceable with rebuild kits which swap out the battery plates.
>
> Back in the 80's the phone company would look at the budget come 4th
> quarter and if there was a surplus they would rebuild older battery banks
> of 12 year or older.
>
> Now with OSHA and Hazmat regs they hire independent battery maintenance to
> service these batts.
>
> New installs are likely going away from lead acid due to acid vapor and
> hydrogen issues as well as a much reduced foot print per KWh.
>
> But EMP proof? - hard to kill a plain lead acid system.
>
> {/Greg}
>
>
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[Emc-users] Adding feedback to an existing stepper motor.

[Greg Bentzinger via Emc-users]

{Greg}

There are options to converting existing steppers to closed loop feed back.

The LCNC software/hardware option would be to add an encoder and run the 
stepper in velocity mode. This does not offer the many advantages of the direct 
feedback drivers.

Then for small steppers there is the Mechaduino bolt on option. Buy direct from 

https://tropical-labs.com/

https://hackaday.com/2016/06/01/mechaduino-closed-loop-stepper-servos-for-everyone/

https://github.com/jcchurch13/Mechaduino-Hardware

https://github.com/jcchurch13/Mechaduino-Firmware

The latest firmware release was 26 November 2018 so this is not a dead item.

If someone were to build on this open source project and produce a unit with a 
50VDC / 6A working power capacity it could cover most steppers.

IIRC Gecko drive was once working on this idea and had it working, I think 
maybe it was not released because it was not economical and would not match 
performance of matched motor drive combos, but that is just my speculation.

I would like to get one of the matched motor/driver units and see if the 
encoder could be replaced with a unit which included a index channel.

{/Greg}


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[Emc-users] Lead acid batteries

[Greg Bentzinger via Emc-users]

{Greg}

If I were going to install a full off grid potential solar power system for my 
ranch I would buy lead acid Telco system batteries.

They are not true deep cycle, but have such high capacity that it isn't an 
issue. They are initially expensive and huge. ( I might buy some 10yr old units 
being decommissioned )


On the plus sign they can have up to a 30 year service life and are user 
serviceable with rebuild kits which swap out the battery plates.

Back in the 80's the phone company would look at the budget come 4th quarter 
and if there was a surplus they would rebuild older battery banks of 12 year or 
older.

Now with OSHA and Hazmat regs they hire independent battery maintenance to 
service these batts.

New installs are likely going away from lead acid due to acid vapor and 
hydrogen issues as well as a much reduced foot print per KWh.

But EMP proof? - hard to kill a plain lead acid system.

{/Greg}


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Re: [Emc-users] How come....

[Chris Albertson]

On Fri, May 17, 2019 at 3:05 AM Erik Christiansen 
wrote:

> On 16.05.19 23:25, andy pugh wrote:
> > On Thu, 16 May 2019 at 23:07, Chris Albertson  >
> > wrote:
> >
> >
> > > ill never beat Tesla's price.  Even if you build a factory and mass
> > > produce them
> >
> >
> > So, let's turn that on its head. How can I run my cordless tools from
> Tesla
> > cells...
>
> IIRC, the individual cells¹ are around 3.2 or 3.4v, so 4 would make a
> 12v pack, 6 for 18v, etc. Since their form factor probably won't suit an
> existing tool, it's either fabricate a new battery compartment, or run a
> cable to a pack on your belt or the floor. (I was going to do the latter
> with a small spare 12v lead acid battery, but in the end fitted an even
> smaller one into the existing battery compartment. It's adequate for the
> small jobs I use the cordless for.)
>

Almost all power tools use packs of cylindrical batteries.  The batteries
come in
a standardized size.   Cheaper notebook PCs also usethese  cylindrical
batteries.
They are easy to buy but you need a spot welder to make the packs, Soldering
or spring clips do not work

Some high-end equipment does use custom batteries made in a space to fit the
space, Apple does this in their Macs but mostly replacment cells will just
drop in like C size cells, if you have a spot welder.

For Lipo the nominal voltage is 3.7 per cell.  Howerev that can be at 4.2
when fully
charged and 3.0 when completely dead.Never dischange then below 3.5
volts
or you can shorten the life of the cell dramatically.

So a 3-cell battery is a goo replacement for a Lead Acid as the 3-cell pipo
will
range for 12.6 to 10.5   A fully changed 4-cell (at 16.8 volts might damage
equipment
designed for 12V LA.

I've build a lot of stuff that uses LiPo and the best solution, the OLNLY
way to go
is to design-in a monitoring system.  Human operators will destroy any LiPo
battery quickly.   But computers are good at this kind of thing.



> A 13.8v LA charger was easier to make out of a spare plugpack than would
> be a Li-Ion charger. Might have to snoop fleabay.
>
> Erik
>
> ¹ The ones which flew in the air, spewing flame and smoke, in one EV
>   battery pack repurposing I saw on youtube.
>
>
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Re: [Emc-users] About hybrid stepper

[Chris Albertson]

I don't think it is possible to convert a stepper.   You need to replace
both the motor and the driver with a matched set.   In this kind of setup,
all the "magic" lives inside the driver box.  This is where the control
loop is closed and it runs in specialized DSP hardware.   The driver and
motor have to be matched.  You buy them as a set.

Yes, they are dramatically quieter and more "sitf" and they use about 1/2
the power and don't get as warm.Cost roughly $100 per axis

You can actually downsize going from open toclosed loop steppers because
with open loop you have to spec the motor oversized so that it has zero
chance of losing steps.  But the closed loop stepper does not ned this over
specification.That said, replace what you have with same size motors
and gain some performance

On Fri, May 17, 2019 at 8:19 AM Davide <77...@tiscali.it> wrote:

> Hi, I would like to convert my Nema23-4NM stepper to Hybrid closed loop,
> and I would be thankful if you could give me some hint, respect some aspect:
>
> is it true that they are going to be way less noisy, also if set at say
> 1000 PPR?
>
> is it true that they are going to be more linear-like about torque/RPM?
>
>
> Can I just buy the driver (like the HSS86) and use my stepper
> (KL23H2100-50-4B) with an encoder on (AMT102)? or hybrid steppers are
> really different from normal steppers?
>
>
> Thank you, Davide.
>
>
>
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Re: [Emc-users] How come....

[Kirk Wallace]

On 5/17/19 7:20 AM, Dave Cole wrote:

OK,
Buy  a new "cheap" Tesla - about $35,800 right now.
Remove the battery pack  ;-)

You guys on the west coast make it sound like you have Tesla's sitting 
on the side of the road with "$500 or best offer" sale signs.


Here is a fairly common surplus Tesla module:


https://www.ebay.com/itm/262333679871


If these have have not been abused after they were removed from the car 
they should last many thousands of deep cycles.  They are 6s but a 7th s 
can be added in order to cycle them deeper on a common 24 volt system.


My system (single, living in an RV) is close to this except I am using 
two Johnson Controls modules rewired as 7s:

https://www.mobile-solarpower.com/tesla-solar-battery-diy.html
https://www.ebay.com/itm/123187038180


This technology is changing so quickly that it is hard to keep current 
and reviews become stale in a month or two.



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[Emc-users] About hybrid stepper

[Davide]

Hi, I would like to convert my Nema23-4NM stepper to Hybrid closed loop, and I 
would be thankful if you could give me some hint, respect some aspect:

is it true that they are going to be way less noisy, also if set at say 1000 
PPR?

is it true that they are going to be more linear-like about torque/RPM?


Can I just buy the driver (like the HSS86) and use my stepper (KL23H2100-50-4B) 
with an encoder on (AMT102)? or hybrid steppers are really different from 
normal steppers?


Thank you, Davide.



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Re: [Emc-users] New PC Hardware for preempt-rt and Mesa Ethernet

[Gene Heskett]

On Friday 17 May 2019 10:19:54 am Peter C. Wallace wrote:

> On Thu, 16 May 2019, bari wrote:
> > Date: Thu, 16 May 2019 15:10:12 -0500
> > From: bari 
> > Reply-To: "Enhanced Machine Controller (EMC)"
> > 
> > To: "Enhanced Machine Controller (EMC)"
> >  Subject: [Emc-users] New PC
> > Hardware for preempt-rt and Mesa Ethernet
> >
> > Anyone care to list which new cpus and motherboards (currently on
> > store shelves) they have found to work well with preempt_rt and Mesa
> > Ethernet cards?
>
> For a 1 KHz servo thread, Most PC hardware can be made to work though
> slower and lower power hardware is worse. Current fanless MBs that
> seem ok are MBs using Intel - J3355, J3455, J4005, J4105, J4205. Not
> sure on low power AMD since my last AMD test CPU was a 1 GHz E1-2100
> which was on the lower edge of usability at 1 KHz. Likely any current
> AMD or Intel CPU with a fan will be fine.
>
> Note that for the Ethernet cards, the latency is not terribly
> important, you just need to reliably communicate on the Ethernet port
> at a 1 KHZ rate (3 K packets per second)
>
> If you need a faster servo thread, then you have to test MBs, I have a
> couple Motherboards that will reliably run a 4 KHz servo thread (12K
> packets per second), none are fanless.
>
> Ive had the best luck with Realtek or Intel Macs, Broadcom and Atheros
> are best avoided.
>
I'd be interested in what you think of the atomic pi, when it ships in 
qty's. My problem is that its bigger than a pi...
> > ___
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>
> Peter Wallace
> Mesa Electronics
>
>
>
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Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 



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Re: [Emc-users] How come....

[Gene Heskett]

On Friday 17 May 2019 10:20:54 am Dave Cole wrote:

> OK,
> Buy  a new "cheap" Tesla - about $35,800 right now.
> Remove the battery pack  ;-)
>
> You guys on the west coast make it sound like you have Tesla's sitting
> on the side of the road with "$500 or best offer" sale signs.
>
> We now have 11 supercharger stations in the state of Indiana.
> If Tesla's burned coal or biowaste we would be all set.   :-/
>
Our local Sheets, in a WV county (Lewis) of about 9k two legged air 
breathers, installed 8 charger stations about 18 months back. I saw 3 of 
them occupied a few days ago. But wasn't close enough to determine where 
the plates they were wearing said they were from.

> What is is a "cheap" Tesla going for in places where they are popular?
>
> Dave
>
> > So, let's turn that on its head. How can I run my cordless tools
> > from Tesla cells...
>
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Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 



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Re: [Emc-users] New PC Hardware for preempt-rt and Mesa Ethernet

[Peter C. Wallace]

On Thu, 16 May 2019, bari wrote:


Date: Thu, 16 May 2019 15:10:12 -0500
From: bari 
Reply-To: "Enhanced Machine Controller (EMC)"

To: "Enhanced Machine Controller (EMC)" 
Subject: [Emc-users] New PC Hardware for preempt-rt and Mesa Ethernet

Anyone care to list which new cpus and motherboards (currently on store
shelves) they have found to work well with preempt_rt and Mesa Ethernet
cards?



For a 1 KHz servo thread, Most PC hardware can be made to work though slower 
and lower power hardware is worse. Current fanless MBs that seem ok are MBs 
using Intel - J3355, J3455, J4005, J4105, J4205. Not sure on low power AMD 
since my last AMD test CPU was a 1 GHz E1-2100 which was on the lower edge of 
usability at 1 KHz. Likely any current AMD or Intel CPU with a fan will be 
fine.


Note that for the Ethernet cards, the latency is not terribly important, you 
just need to reliably communicate on the Ethernet port at a 1 KHZ rate (3 K 
packets per second)


If you need a faster servo thread, then you have to test MBs, I have a couple 
Motherboards that will reliably run a 4 KHz servo thread (12K packets per 
second), none are fanless.


Ive had the best luck with Realtek or Intel Macs, Broadcom and Atheros are 
best avoided.




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Peter Wallace
Mesa Electronics



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Re: [Emc-users] How come....

[Dave Cole]

OK,
Buy  a new "cheap" Tesla - about $35,800 right now.
Remove the battery pack  ;-)

You guys on the west coast make it sound like you have Tesla's sitting 
on the side of the road with "$500 or best offer" sale signs.


We now have 11 supercharger stations in the state of Indiana.
If Tesla's burned coal or biowaste we would be all set.   :-/

What is is a "cheap" Tesla going for in places where they are popular?

Dave



So, let's turn that on its head. How can I run my cordless tools from Tesla
cells...




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Re: [Emc-users] How come....

[Dave Cole]

Chris,
You need to look at the link... they look at the costs over a 10 year 
period.
Including battery bank replacement for the Lead Acid batteries.   Lead 
Acid is still cheaper.
And I think their prices for Lead Acid batteries are inflated.   I would 
also consider using a Lead Acid forklift battery (or multiples).

They are made to be rebuilt.

Sure they are heavy.   And that might be an issue for some, but if you 
have a tractor with a loader, or a forklift, then that is really not an 
issue.


Dave


On 5/16/2019 6:24 PM, Chris Albertson wrote:

Let's see your parts list for a 13.6 KWH system and let's look at the cost
over a 10 year period.  List the charger/inverter  and the frame and
housing.

When you do you costing assume the system is used cycled daily.  Design in
enough margin so that tyou system still meets speciications after 10 years
of use.   Itmust still have 13.6 KWHafter 10 years of daily cycling.
  Yes, this can be done with LA.

You can get the initial cost way low but you can't run it for 10 years
without replacing all the batteries 3 or 4 times.   That is the problem is
lead-acid batteries, it is their very limited number of cycles.   You can
work out different designs.   If the goal is only low initial cost then you
will find you need a VERY frequent battery replacement schedule.   You can
greatly reduce the number of times you need to replace each cell over the
10 year period if you double the initial cost.

You can't claim LA is lower cost until you look at the total cost
of ownership, not just the up from cost.   It is possble to get  very low
up from cost or you can also "cheat" assume the system is only used for
backup power a few times a year.  But realistically you need to look at
costs of a system that is actually used over an extended period.


So, you have to make a spreadsheet or punch buttons on a calculator.A
LA cell is good for about 300 cycles to 50% discharge before it looses bout
1/2 it's capacity. SO Youfigure maybe we only go to 40% and extend this
is 400 cyccles and buy 2X as may calls so we still meet specs after 400
cyccles.Then you work out how many batteries you need using them to
only 40%of their rating and stating with 2X over capsity.  You are
"shocked" at the cost so you think about designing a yearly schedule where
you add a few batteries everyyears and remove a few every year, but maybe
you don't add and removethe same number, so long as you kee the same 13.6
KWH spaec.  Work this over a 10 year period.

The up front cost means nothing because you can make that very low but it
will cost you a LOT later. I doubt you can do $6,700 total cost over 10
years.



On Thu, May 16, 2019 at 12:03 PM Dave Cole  wrote:


https://www.wholesalesolar.com/blog/lead-acid-vs-lithium-batteries/

This solar company wrote up this analysis regarding Lead Acid vs Lithium
and generally recommend Lead Acid for off grid residential use.
I went through their analysis and the only problem I had with it is that
their lead acid batteries are over priced.
Which, if their Lithium batteries are priced right, means that Lead Acid
is by far the best way to go.

I think their numbers for a Crown Lead Acid bank was $2800.  I did some
numbers and figured I could create a deep cycle bank of the same
capacity for about $1800.
Making your own power wall or Lithium battery pack is certainly a
possibility, but as mentioned cell balancing circuity is required.

I have a sailboat and participate in several sailboat lists and the
overwhelming way to go for house power on a larger sailboat is to use 6V
golf cart batteries.
The cost per power stored is cheaper than using 12 volt batteries and
golf cart batteries are true deep cycle batteries which are commonly
available.
A lot of 12 volt deep cycle batteries are compromised designs.

Now if these batteries were in a mobile device, like a car, that would
be an entirely different comparison since weight is a big deal in a
mobile device.
But these are for a stationary application.

Regarding the power wall concept.  The idea of having 20+ KWHR of stored
energy in my house is a little daunting.
If a short circuit occurs and the batteries melt down, your house could
be gone.

I'd put the battery bank in an outbuilding.  If something shorts out and
the battery bank melts down, the little building may burn but my house
won't.

Dave



On 5/14/2019 2:11 PM, Kirk Wallace wrote:

On 5/14/19 9:33 AM, Dave Cole wrote:

I've been planning to put up an array on my roof.  But I have plenty
of space so I may do a ground level install.
It would be a lot easier to maintain.

FLA batteries seem to be the general recommendation for a constant
use residential install.

In my opinion, lead-acid batteries of any format are far inferior to
lithium. LA batteries need to be at full charge most of the time or
they will degrade and with good management will only last about 5
years. I ended up running my generator to charge my FLA batteries in
the 

Re: [Emc-users] How come....

[Dave Cole]

DC power contactors are available. They are used in Golf Carts, Fork 
Lifts etc.


But you are right, DC arcs are not easy to extinguish, and that can be a 
problem.


BTW, most electric forklifts are still using Lead Acid batteries and 
many have 5 year warranties on the batteries.

Most fork trucks are used at least 5 days a week.

Dave


On 5/17/2019 6:23 AM, Erik Christiansen wrote:

On 16.05.19 21:18, Nicklas Karlsson wrote:

...
I'd put the battery bank in an outbuilding.  If something shorts out and
the battery bank melts down, the little building may burn but my house
won't.

There certainly is a lot of power from a byttery and it could be a
little bit hard to turn off. You put a fuse at battery cable?

If local regulations do not require a HRC (High Rupture Capacity) fuse
between the battery bank and any connection to it, then it's an
invitation to disaster. A dc arc is much more difficult to extinguish,
because there are no zero crossings, and molten metal can end up flowing
on the floor.

Small HRC fuses are generally in ceramic tubes, and are sand-filled, to
quench the arc when the element fuses. The one I have on the desk beside
me is a 100 A with a 100 kA (100,000 A) arc rupture capacity, but it's
27x44x49 mm, and is overkill. Just 10 times AH rating seems to be normal,
i.e. 2000 A rupture capacity for a 200 AH bank. (The fault current will
be limited by battery internal resistance.)


I also think DC relays have to be a little bit different than AC
relays, used an ordinary AC relay for a few few days connected to a DC
voltage and even though two switches is connected in series it
sometimes make a buzzing sound then turned off.

Most relays and switches are marked with both AC and DC current ratings.
The DC rating is always much lower, due to the difficulty of rupturing a
DC arc. Rather than bother with maintenance/replacement due to contact
deterioration after many switching cycles, I prefer to switch DC loads
with MOSFETs - they're easy to parallel, as the inherently share.

Erik


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Re: [Emc-users] How come....

[Erik Christiansen]

On 16.05.19 21:18, Nicklas Karlsson wrote:
> > ...
> > I'd put the battery bank in an outbuilding.  If something shorts out and 
> > the battery bank melts down, the little building may burn but my house 
> > won't.
> 
> There certainly is a lot of power from a byttery and it could be a
> little bit hard to turn off. You put a fuse at battery cable?

If local regulations do not require a HRC (High Rupture Capacity) fuse
between the battery bank and any connection to it, then it's an
invitation to disaster. A dc arc is much more difficult to extinguish,
because there are no zero crossings, and molten metal can end up flowing
on the floor.

Small HRC fuses are generally in ceramic tubes, and are sand-filled, to
quench the arc when the element fuses. The one I have on the desk beside
me is a 100 A with a 100 kA (100,000 A) arc rupture capacity, but it's
27x44x49 mm, and is overkill. Just 10 times AH rating seems to be normal,
i.e. 2000 A rupture capacity for a 200 AH bank. (The fault current will
be limited by battery internal resistance.)

> I also think DC relays have to be a little bit different than AC
> relays, used an ordinary AC relay for a few few days connected to a DC
> voltage and even though two switches is connected in series it
> sometimes make a buzzing sound then turned off.

Most relays and switches are marked with both AC and DC current ratings.
The DC rating is always much lower, due to the difficulty of rupturing a
DC arc. Rather than bother with maintenance/replacement due to contact
deterioration after many switching cycles, I prefer to switch DC loads
with MOSFETs - they're easy to parallel, as the inherently share.

Erik


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Re: [Emc-users] How come....

[Erik Christiansen]

On 16.05.19 23:25, andy pugh wrote:
> On Thu, 16 May 2019 at 23:07, Chris Albertson 
> wrote:
> 
> 
> > ill never beat Tesla's price.  Even if you build a factory and mass
> > produce them
> 
> 
> So, let's turn that on its head. How can I run my cordless tools from Tesla
> cells...

IIRC, the individual cells¹ are around 3.2 or 3.4v, so 4 would make a
12v pack, 6 for 18v, etc. Since their form factor probably won't suit an
existing tool, it's either fabricate a new battery compartment, or run a
cable to a pack on your belt or the floor. (I was going to do the latter
with a small spare 12v lead acid battery, but in the end fitted an even
smaller one into the existing battery compartment. It's adequate for the
small jobs I use the cordless for.)

A 13.8v LA charger was easier to make out of a spare plugpack than would
be a Li-Ion charger. Might have to snoop fleabay.

Erik

¹ The ones which flew in the air, spewing flame and smoke, in one EV
  battery pack repurposing I saw on youtube. 


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