LiIon battery temperatures, any guidance

[audia2ev]

Hello to everyone,

Just joined the forum, now that I am underway with my conversion (Audi A2).

I'm figuring out battery locations and wonder if anyone has some advice. I have HiPower HP IFPs, 50Ah, arranged in 5 banks of 20 cells and connected in series for a 320V pack (well, it might be reduced to 5 banks of 19 cells but that's another story).

If I locate the battery banks in different places round the vehicle, there is a likelihood that they might get different ambient temperatures. For example, I might have three banks inside the rear of the car, and two banks in the engine bay (kind of outside, even if they would be in closed, polypropylene boxes).

I assume that the charger could handle any potential balancing problem when charging.

But is there a problem if the battery banks which are connected in series have some differential temperature when driving the motor? To be frank, it would probably be minimal - maybe max 5 degrees C? - but just wondered if there was any experience on this. Note that this temperature differential might not always be when it is cold - could also be when it is hot (bonnet in sun, for example... I live in Italy).

Any comments on what temperature management I should do?

Thanks

Simon

[retepsnikrep]

Welcome

That sounds an interesting and impressive project.

What BMS are you going to be using?

What charger/controller are you going to be using?

The batteries will be better if they can all be together with minimal temperature variation. Cold cells are not able to provide as higher current as warm ones. The colder ones will suffer a bit at higher current draw forcing the BMS to work a bit harder to keep them in balance.

I suggest an insulated central location with provison for forced air cooling (Vital in Italian summer I suspect) and some under cell heating for the winter months. You may not need the heating in italy. All controlled by some sort of clever thermostat/pic hardware.

Please photo document you project and post the details here we are very interested.

Peter

[audia2ev]

Welcome

Thanks, Peter

That sounds an interesting and impressive project.

A challenge you mean Thought I'd go in at the deep end.

What BMS are you going to be using?

Not yet established. Probably the next thing I need to scrape on this forum...

What charger/controller are you going to be using?

Charger is HiPower supplied 300V5A with balancing for the five banks of 20 cells. Controller is Azure Dynamics DMOC445.

The batteries will be better if they can all be together with minimal temperature variation. Cold cells are not able to provide as higher current as warm ones. The colder ones will suffer a bit at higher current draw forcing the BMS to work a bit harder to keep them in balance.

Yep, that's what I was thinking, any idea of what differential temperature starts to be important?
For example I suppose that the cells do change temperature when being operated. This means even inside a bank - or inside a pack - the inner ones probably get warmer than the outer ones. What sort of differentials get important?

I suggest an insulated central location with provison for forced air cooling (Vital in Italian summer I suspect) and some under cell heating for the winter months. You may not need the heating in italy. All controlled by some sort of clever thermostat/pic hardware.

Round here (north of Milano) it is 35C in the summer, -5 in the winter (10cm snow outside as I write this). No garage for the car at the moment.

Please photo document you project and post the details here we are very interested.

http://groups.google.com/group/audia2ev/web/home and on YouTube, http://www.youtube.com/user/audia2ev
Still a way to go... just started the dismantling.

Simon

[retepsnikrep]

What sort of differentials get important?

Simon

I would not be happy with more than about 5C between hottest and coldest, I can't back that up with any hard data though.
It's just my gut feeling after using Lithium since 2003. Closer would be better.