Tesla Cobra, Orion 2 Discharge Limits

[mtrehy]

Hi All,

I'm looking for some advice on the current limits that I should put in the Orion BMS for the Cobra I have built. It's Tesla LDU, 12 Tesla 5.3KW Modules (300V), Openinverter logic board.

At the moment if it is accelerated very hard uphill the Orion BMS is logging a P0A07 fault (Discharge Limit due to temperature) and power is cut completely. I haven't altered the temp limits (just pulled from entering the Tesla module profile. The temp limits are currently: -20=0, -15 = 100, -10 = 200, -5 = 300, 0 = 400, then 5 to 40 degrees is 500A, 45 = 250, 50 = 0. The car owner doesn't drive it anything as aggressively as I have and has never exceeded the 500A limit so the problem hasn't manifested before.

I'm wondering whether I can safely increase this 500A limit. I have 600A fuse in the battery box but had thought that I could probably safely exceed that for short periods.

The owner doesn't want or need any more performance as the car is already very quick but if I can safely increase a bit then I'd like to....

Any help greatly appreciated.

Video of the car if anyone is interested:

[jrbe]

Can the owner handle it and would they want the extra power?

I'd suggest setting it up to keep the batteries happy and leave it as is unless the owner wants more.

[mtrehy]

Thanks, I'm not sure how I judge battery happiness? While I think it's unlikely that they would ever drive it that hard, if it was ok to increase those numbers and still be reasonably safe then reducing the chances of it cutting out on them under power seems prudent

Cheers

[johu]

The low temperature discharge limit is pointless, I'd take that out. But that's not really the question

I would not exceed 50°C by much either. If you really reach a temperature that high just by driving maybe the cooling is not adequate? Well not for you anyway but for your customer it is.

Apart from that shortly exceeding 500 A on a Tesla pack seems perfectly fine

[mtrehy]

Cheers johu, the battery temp is not going above 25.

If I was to remove the current limits that at the moment are being restricted by temperature, what mechanism am I using to keep the discharge current within a safe limit?

[P.S.Mangelsdorf]

Cheers johu, the battery temp is not going above 25.

If I was to remove the current limits that at the moment are being restricted by temperature, what mechanism am I using to keep the discharge current within a safe limit?

From a motor/inverter perspective, there are two things: first settings iacmax and idcmax, second, from my experience, the Tesla LDU gate drivers, which remain intact with the OI board, seem to have a built in current limit/desat shut down.

[johu]

Orion BMS is logging a P0A07 fault (Discharge Limit due to temperature)

Cheers johu, the battery temp is not going above 25.

?

[mtrehy]

?

Hi Johu,

Sorry, I'm maybe not being clear. In the Orion BMS in Discharge Limits, there is a dialogue box for temperature derate settings. See pic attached.

I didn't enter these settings, I assume they are pulled in when I told the BMS I was using Tesla Model S 5.3KW modules.

So my question really is, what should the a reasonably safe discharge limit be for my setup and how should they be affected by temp? I think Tesla say that the modules are good for 1500a for short bursts, I've seen 750a in other searches. My setup described has 600a fuse, 12 x 5.3 Tesla modules, LDU.

limits.jpg (24.42 KiB) Viewed 971 times

[jrbe]

I misunderstood your original question. Upping the BMS current limits should be ok as long as it's within the battery specs / limits for the time allowed

Yes you can exceed the fuse current for a short time.

Does it log what temp it throws the code at?
The confusion is if your not exceeding the temp, why is there a code for temp? Or is it really current limit exceed in this temp window?

[mtrehy]

It's not that I'm exceeding a temperature it is that I'm exceeding the current limit at any given temperature on that temperature derating setting.

Hypothetically if I set maximum discharge limit to 750a, I'd then also set the derating to 750a between 5 and 40 degrees?

Does 750 sound reasonable for model s module?

Cheers

[tom91]

Look at pulse limit settings.

https://www.orionbms.com/manuals/utility_o2/

You can have the Open Inverter board listen to current limits over CAN, no idea if will be accurate enough for the Orion.