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Testing a traction pack before using

Posted: Tue, 15 Oct 2019, 21:41
by soyachips
I've almost finished building my traction pack and wanted to see how others test them before using them. I've seen people using elements in a bucket of water or a series of light bulbs etc but still not sure what's the best thing to do and exactly what to look out for. Also seen people using IR thermometers to check for excessive heat, I think looking for bad cells or bad connections?

Re: Testing a traction pack before using

Posted: Wed, 16 Oct 2019, 13:03
by Richo
I've used both.
Water and electronics don't mix so I prefer the light bulbs.
Everybody's pack is different so each setup is different.

Re: Testing a traction pack before using

Posted: Wed, 16 Oct 2019, 13:27
by jonescg
You can run most resistive AC loads on DC, and universal motors are happy on DC too, they just spin slower. So set up a power board and start plugging AC loads in until you get to your desired currents.

Re: Testing a traction pack before using

Posted: Wed, 16 Oct 2019, 14:06
by antiscab
I use a grid tie inverter for capacity testing

Re: Testing a traction pack before using

Posted: Wed, 16 Oct 2019, 14:10
by jonescg
antiscab wrote:
Wed, 16 Oct 2019, 14:06
I use a grid tie inverter for capacity testing
Assuming your grid tie inverter can handle an unimpeded 144 V DC supply?

Re: Testing a traction pack before using

Posted: Wed, 16 Oct 2019, 14:21
by antiscab
all grid tie inverters can handle an unimpeded supply

I used a vintage PVE2500, but there are more modern inverters that will work down to 100v

Re: Testing a traction pack before using

Posted: Wed, 16 Oct 2019, 14:29
by jonescg
Oh good. Cause I was thinking about doing the same :D

Re: Testing a traction pack before using

Posted: Wed, 16 Oct 2019, 14:39
by antiscab
Goodwe make a single phase inverter that goes down to 80vdc input, and also supports export limiting.

I've been looking for a cheap second hand one to implement an on grid battery

Re: Testing a traction pack before using

Posted: Wed, 16 Oct 2019, 18:53
by soyachips
jonescg wrote:
Wed, 16 Oct 2019, 13:27
You can run most resistive AC loads on DC, and universal motors are happy on DC too, they just spin slower. So set up a power board and start plugging AC loads in until you get to your desired currents.
Ok so simple things like a toaster, kettle etc will run fine on DC?

I picked up a cheap IR thermometer from Bunnings tonight so if the toaster and kettle will work I’ll set that up, put the battery under load and check the temperatures of the busbars and cells don’t heat up too much. Is that what you normally check?

Re: Testing a traction pack before using

Posted: Wed, 16 Oct 2019, 19:20
by jonescg
Yeah the dumber the better - fan heaters, bar heaters, kettles, etc.
I like to keep an eye on individual cell voltages when doing a discharge test - any cells which drop markedly lower than the rest are laggards and will need to be watched carefully. Hot spots are always worth keeping an eye on. If you are using a laser thermometer, point the reading beam at matt black surfaces for best results. Reflective surfaces can give erroneous temperatures. If you can coulomb count you should, to check the battery capacity, otherwise a current clamp, stopwatch, pen and paper. Take a reading every minute or so and plot a discharge curve.

Re: Testing a traction pack before using

Posted: Wed, 16 Oct 2019, 21:23
by antiscab
for things with a thermostat, be aware that switching dc is much harder on the contacts than switching ac. Might be better to use a bar heater that rarely switches, rather than a kettle that switches often

Re: Testing a traction pack before using

Posted: Wed, 16 Oct 2019, 21:48
by coulomb
antiscab wrote:
Wed, 16 Oct 2019, 21:23
be aware that switching dc is much harder on the contacts than switching ac.
Yes! In fact, I would not use any AC switch at all. It's OK for the switch to be there, as long as it's on (or switches on). Never switching off!

For that reason, a pop-up toaster or the like is a no goer. I'd also rule out a kettle. Use a proper DC rated switch for the load, e.g. an EV200 run from a 12 V battery.

Re: Testing a traction pack before using

Posted: Thu, 17 Oct 2019, 11:16
by jonescg
antiscab wrote:
Wed, 16 Oct 2019, 14:39
Goodwe make a single phase inverter that goes down to 80vdc input, and also supports export limiting.

I've been looking for a cheap second hand one to implement an on grid battery
If you wanted to play silly buggers, you could get yourself a 2.5 kW grid tie inverter, a 7 kW solar array and a 60 kWh battery. Power the grid tie inverter from the 350 V, 60 kWh battery, and charge the battery with a direct PV-> battery charger. You would effectively be a renewable energy powerhouse 24/7 :D

Re: Testing a traction pack before using

Posted: Thu, 17 Oct 2019, 18:57
by soyachips
Awesome thanks everyone for the replies. Looks like I need to go out an buy a bar heater ... we don’t have one because they’re not energy efficient! :lol:

Re: Testing a traction pack before using

Posted: Fri, 18 Oct 2019, 12:50
by Richo
Don't forget at 90Vdc a 2400W mains heater only is 300-350W.
So you'd need a few...

For $10 you get 10 x Halogen globes 12V 35W from bunnykings.
8 in series will be ~250W.
$20 - 500W
$40 - 1250W
On plus side you'll brighten everyone's day

Re: Testing a traction pack before using

Posted: Fri, 18 Oct 2019, 12:53
by jonescg
Richo wrote:
Fri, 18 Oct 2019, 12:50

On plus side you'll brighten everyone's day
Do remember to point them away from whatever you're doing. The seared retina effect gets rather tiresome before too long.

Re: Testing a traction pack before using

Posted: Fri, 18 Oct 2019, 13:41
by antiscab
Richo wrote:
Fri, 18 Oct 2019, 12:50
Don't forget at 90Vdc a 2400W mains heater only is 300-350W.
So you'd need a few...

For $10 you get 10 x Halogen globes 12V 35W from bunnykings.
8 in series will be ~250W.
$20 - 500W
$40 - 1250W
On plus side you'll brighten everyone's day
On the subject of hot lights as dump loads
Their resistance changes with temperature - in practice this means they draw nearly the same power at 240vac as they do at 140vdc

Re: Testing a traction pack before using

Posted: Sun, 20 Oct 2019, 19:33
by soyachips
OK great ... I might still have some halogens from when we switched them out for LEDs :)

Re: Testing a traction pack before using

Posted: Mon, 21 Oct 2019, 07:59
by coulomb
soyachips wrote:
Sun, 20 Oct 2019, 19:33
OK great ... I might still have some halogens...
Just be aware that connecting bulbs in series generally isn't a good idea, because they tend to drop slightly different voltages as they warm up, and one ends up getting much more voltage and power than the others and blows. It might be OK as long as you don't run the bulbs at full power, say 50% maximum. So if you had a 360 V battery to test and were using 240 V bulbs, you'd want not just 360/240 = 1.5 bulbs (round up to 2), but double that number, 3 or more. Obviously, they should also all have the same power rating, and it's best if they are similar as possible (same brand bought at about the same time, for example).

Edit: maybe it's not as bad as I remembered; here is the original discussion in case you're interested. Over the page is a link to an EVDL discussion with more detail.

[ Edit: added EVDL discussion link. ]

Re: Testing a traction pack before using

Posted: Mon, 21 Oct 2019, 18:47
by Richo
antiscab wrote:
Fri, 18 Oct 2019, 13:41
Their resistance changes with temperature
Mmmm I tested the ones I have here.
They changed +1.6%

So 8 in series run at 90V would go from 246W cold to 242W hot.
I'm in the opinion that this is not significant enough to concern a load test.

Re: Testing a traction pack before using

Posted: Mon, 21 Oct 2019, 19:25
by Richo
coulomb wrote:
Mon, 21 Oct 2019, 07:59
...one ends up getting much more voltage and power than the others and blows
I tested 10 x Halgoen globes 35V 12V.
In the cold state they are within +/-1%
In the hot state they are within +/-1%

Perhaps the tolerance on mains voltage incandescence globes is more relaxed.
In this case I think running 8 in series (96V) from a pack that wont reach 90V fully charged will be ok.

Re: Testing a traction pack before using

Posted: Mon, 21 Oct 2019, 19:35
by Richo
Alternatively you can be confident in your work, assume its all good, and not test it.
Then you only waste time and money if it isn't :|

Re: Testing a traction pack before using

Posted: Mon, 21 Oct 2019, 19:38
by Richo
jonescg wrote:
Wed, 16 Oct 2019, 13:27
universal motors are happy on DC too, they just spin slower.
Except the ones with SCR controllers...