A123 20Ah pouch cell - temperaure problems @ 170A??

[vile]

Hi all,

I'd like to know if anyone of you has tested the A123 20Ah prismatic cells with discharge currents at about 170-180A and recuperation currents up to 300A or similar loads (not continuously)?
Could there be any issues with temperatures in such a pack with no space/air between the cells?
Should I build an aluminium case or frame for the cells to act as a heatsink or even thin aluminium or copper sheets between each cells mounted to a bigger heatsink?
Or do you think there are no problems with heat?
I won't discharge the battery with a continuous current; I'm going to build four of these 32S1P packs (-> 128S1P) for a traction battery of a racing vehicle with about 60kW total power.

I'd like to collect some ideas before I buy the cells. I also thought to do a little test with a small 8S1P pack and some 24V 500W halogen bulbs and measure the temperatures (maybe ir camera from my university).
What do you think?

Vile

 

[davec]

i've seen docbass do 100amps
and someone on this forum shorted the cell with jumper cables doing 200a for very short period of time- but i dont recall that they recorded the temps- would be interesting to see the results.

 

[agniusm]

Its a concern. http://endless-sphere.com/forums/viewtopic.php?f=14&t=38545&start=400

 

[megacycle]

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=15093&start=105
This thread was a while back were LFP really put the pouches through the wars.
The IR camera was interesting.
Suggestions are they need electrically insulating from each due to electrical leakage and keep the pack width confined so cells cant puff out.
Thermal management not sure, some guys are placing the packs, electrically insulated first, in aluminium cases.
My tabs connect via a copper bus, smeared with thermal paste and sandwiched between 3mm aluminium spacers and thin insulators.
I tested a cell i had accidentaly blew a tab off, to prove it could still provide full short circuit current, with just 2mm of tab, due to slip stream effect. Yeh melted a 16mm2 shorting strap, these cells rock.
I'm waiting for cash for a controller to run an mars motor at 24S1P@200A so i can blitz them.

I dont know if anyone has hammered them for long, need to look for guys doing the same application.They might be some pointers regarding longivity under heavy cycling somewhere.
A123's data is about on their site too.
The sag would be heavy down to 2.9V, might be best 2P.
I think you might have been on a thread with Jonesy, he's expecting to pull 200kW+ from i think 700V+ 15Ah cells @3P?.

 

[jonescg]

All I can say is for high current discharges, make sure you have plenty of copper with good, solid connections between them.

All cells will get warm at high C rates, the difference is how well they perform once warm. Do they stay warm, or do they continue to get hotter and hotter until something comes out? I'm passing 200 A through my connections and they are able to keep the cells relatively cool until the last part of the discharge curve.

The single biggest issue with high C rates on pouch cells is having a goodly sized lump of copper to sink the heat being generated at the tab. If the tab gets hot, the biggest, closest sink to the tab is the cell. So if there's plenty of copper it will sink the worst of it. Ideally you will have air blowing across the busbars so they can keep wicking heat out.

 

[agniusm]

All I can say is for high current discharges, make sure you have plenty of copper with good, solid connections between them.

All cells will get warm at high C rates, the difference is how well they perform once warm. Do they stay warm, or do they continue to get hotter and hotter until something comes out? I'm passing 200 A through my connections and they are able to keep the cells relatively cool until the last part of the discharge curve.

The single biggest issue with high C rates on pouch cells is having a goodly sized lump of copper to sink the heat being generated at the tab. If the tab gets hot, the biggest, closest sink to the tab is the cell. So if there's plenty of copper it will sink the worst of it. Ideally you will have air blowing across the busbars so they can keep wicking heat out.

Agree on that. In my case it was end terminals that were heating up, but then i changed them to cooper and all went good but cells got hot. I need to get that done again as i got myself one of those laser thermometers.

 

[vile]

Thanks, these posts are very helpful, especially the ir shots.
As i'm going to use this part under the cell tabs http://shop.lipopower.de/LiNANOZ-XPS-Klemmstein-Aluminium-6-x-6-x-65mm and this one for the upper side of the tabs http://shop.lipopower.de/LiNANOZ-1P-Verbinderplatte-Aluminium-10-x-65-x-3-mm it would be the best to build a kind of aircanal above the connectors, on one end some powerful fans and the other end open. Just like a graphic card cooler. Then the hot parts, the connectors should stay only warm or even cool, not hot.
In the next weeks I'll also test the cells with currents up to maybe 220A.
What kind of load could I use to get up to 220A @24V from the LiFePo4 battery? Are the halogen bulbs the best?

 

[agniusm]

Thanks, these posts are very helpful, especially the ir shots.
As i'm going to use this part under the cell tabs http://shop.lipopower.de/LiNANOZ-XPS-Klemmstein-Aluminium-6-x-6-x-65mm and this one for the upper side of the tabs http://shop.lipopower.de/LiNANOZ-1P-Verbinderplatte-Aluminium-10-x-65-x-3-mm it would be the best to build a kind of aircanal above the connectors, on one end some powerful fans and the other end open. Just like a graphic card cooler. Then the hot parts, the connectors should stay only warm or even cool, not hot.
In the next weeks I'll also test the cells with currents up to maybe 220A.
What kind of load could I use to get up to 220A @24V from the LiFePo4 battery? Are the halogen bulbs the best?

Does look bad quality bars. Give me a shout, I could get you sorted with better built ones for half the price.

 

[vile]

Thanks for your offer, but I'll first buy there, check out the dimension and how easy mounting is.
The car is a project at my university, I think it would be the best to build for the whole battery pack the connectors ourselves and maybe increase the size of the upper connector plate for better heat flow.
Maybe we should then use copper.