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teddillard
15 October 2011, 0122
I wanted to talk more about battery cooling, maybe the mods might see fit to move the discussion I started hijacking over to here...

http://www.elmoto.net/showthread.php?1077-Catavolt-Interview-with-Jon-Eggenhuizen/page2

Anyway, Noah, the only reason I was asking about the chemistry was to get at, if I'm running lead, or Thundersky, or Headway, or Turnigy, do I have to worry about one chemistry over another? Or is it more about the actual battery? Like, here's a good one, the A123. They come in pouches as well as cylinders... does one heat up more than another, given the same chemistry but different construction?

I s'pose that's what Travis will ultimately find out. :D

When I was running lead, the batteries heated up regularly, but it didn't damage them significantly, but I'm pretty sure cooling wouldn't have made any difference. The Turnigy lipo, well, I don't want those heating up at all, since it could be catastrophic (but again, I'm pretty sure that's not about cooling, that's about managing the load).

I'm off to start trying to find out what the TTXGP and LSR bikes do about battery cooling. May even look at Chips bike. Ahhhh... nah. :O

"Going Thermal" is now my favorite phrase.

Ken Will
15 October 2011, 0412
One way to estimate how much heat the batteries are producing is to watch Voltage drop.
Heat is a byproduct of efficiency, if the battery is delivering 85% of the power that it is producing than the other 15% is going into heat.


To get rid of the heat you could slather the batteries with thermal paste and make a sandwich with the batteries and a sheet of aluminum, with cooling fins on the ends

teddillard
15 October 2011, 1256
Just got a note from Richard Hatfield (Lightning) saying that, mostly, the races are short enough to avoid any thermal runaway, but that batteries heating up are certainly an issue. They basically do have a sort of passive air cooling, which works pretty well, since they're running the bike at speed most of the time.

podolefsky
15 October 2011, 1453
This is one of those things where I suspect it's going to be hard to compare apples to apples. Even with the A123, which are both the same chemistry, they're different construction. Even different A123 cylindrical cells aren't the same - the ratio of plate/separator volume to electrolyte differs.

Since they have a lower Ri (or IR), lithium will produce less wasted energy as heat than lead for the same pack voltage and load. But for the same kWh pack, lithium will be smaller and have less mass, hence will cool more quickly.

So then the question is, and maybe this is what you're asking, how bad is heat for different chemistries? Lead is pretty robust. LiFePO4 is very safe, but going over 60 deg C for very long will destroy cells. LiPo will catch on fire. But I think there are so many variables that the only way to know how a particular cell will do is to test it under the conditions you'll actually be using it.

Incidentally, this is definitely an issue - Tesla has an air cooled motor, but liquid cooled batteries.

frodus
16 October 2011, 1400
Always good to have a temp sensor of some sort. Ones on ebay are cheap.

teddillard
17 October 2011, 0411
Good to note here that the Manzanita BMS, for one, does have battery temperature monitoring... But this all begs the question, who here has some battery cooling strategy built into their bikes?

I know Ed has been running Headways fully enclosed, I don't think he has any air porting or venting. remotecontact's lipo modules are completely enclosed polycarb, to pull out two that I can call to mind. The Thundersky and CALB packs require banding, certainly eliminating and sort of cooling, I don't think I've ever seen any of those packs that have any airflow to the interior packs.

...this is what's confusing me.

Noah, I believe the batteries on Tesla are also heated. It's more a strategy of "battery climate control", if you will...

Nuts & Volts
17 October 2011, 0518
...this is what's confusing me.

Noah, I believe the batteries on Tesla are also heated. It's more a strategy of "battery climate control", if you will...

Dont be confused. Tesla is pushing their little cells to the limits. With the climate control (pretty much what it is) they are able to pull max power, while keeping cycle life as high as possible.

We dont need to be cooling because we arent pulling 50kW+ out of a battery and we arent trying to package 70-90kWh into a very small volume. Our bikes batteries have a high Surface Area to Volume ratio compared to the Tesla pack and other car packs. This allows our packs to naturally cooling better. We also arent using 100kW which at 98% eff of a battery creates 10X more heat to remove than a 10kW setup most of us have.

Cooling my batteries is the least of my concerns. My needs are heat battery (to 25-30C) and cool motor (to 60-70C) in 40 to 80F weather.

Richard230
17 October 2011, 0800
Hi Power batteries seem to have a cooling system whereby they increase their surface area to dissipate heat when they are overworked. :rolleyes:

DaveAK
17 October 2011, 0835
My strategy is to live in Alaska. :D

podolefsky
17 October 2011, 0944
Cooling my batteries is the least of my concerns. My needs are heat battery (to 25-30C) and cool motor (to 60-70C) in 40 to 80F weather.

Yup - at 3C or more, my motor will overheat long before my batteries.

As to lead vs lithium, I just remembered that the S10 EV (and probably the EV1 as well) had a battery thermal management system for the 26s lead pack. IIRC, those cells are in a sealed box attached to the vehicle's air conditioning system. But that's a 100 kW system pushing a 4000 lb truck.

teddillard
17 October 2011, 1142
OK then... I'm going to conclude this is a non-issue, especially for us home builders. It all came from Travis commenting about Headways providing cooling passages as a byproduct of their cylindrical form, but I really don't see it as being a long-term issue for anything but a race bike. Even a drag bike, I figure, doesn't pull long enough to make batteries go thermal before the motor does so (based on the fact that Ed is using them on his uber 100mph cafe bike and his drag bike, fully enclosed).

So until someone shows me otherwise, I'm going to chalk it up to Travis liking his Headways. :D

frodus
17 October 2011, 1154
at continuous discharges of 5C or greater, you will have heating..... but is it going to go thermal? I say just get a thermal probe and watch it.... real data is the best.