Replacing 12v battery with Lipo?

[Sutitan]

I know this question has been asked a few times, but im trying to do a small feasibility research. Im looking to power a small formula car. Currently I use a 12v lead acid battery and im looking to drop some weight. my battery is around 10ah, but I believe I can use a smaller sized pack. Currently, im looking at a 6.6ah turnigy lipo nanotech battery http://www.hobbyking.com/hobbyking/store/__20585__Turnigy_nano_tech_6600mah_2S2P_65_130C_Hardcase_Lipo_Pack.html

My external load is not very high. I plan to try to measure it sometime in the coming week. im also not sure what the output of the alternator is. My main question is if I could essentially just run two of those packs I listed (in series for the correct voltage), and be fine. Im not trying to send my car up in smokes, and I know lipos are a bit temperamental. Im just wondering if I would need any external BMS to make sure the system is almost self sufficient.

any advice is appreciated! thanks

 

[wesnewell]

This would be what you want I would think. Maybe parallel 2 of them if one isn't enough ah.
http://www.hobbyking.com/hobbyking/store/__14067__ZIPPY_Flightmax_4200mAh_4S2P_30C_LiFePo4_Pack.html
I use the 4s rc lipo packs to start my portable generator, but don't leave the battery connected because most alternators only put out 13.5-14.5V, so it would never keep the 4s lipo charged. However 4s lifepo4 is the perfect voltage to replace a 12v lead battery.

 

[Sutitan]

Maybe I should shift my search into LIFePo4. My main concern was weight. LiPo packs seem to come in a multitude of configurations already prepackaged with individual cell leads. If only they made 10ah A123 pouch cells. I really dont want to deal with welding tabs onto cells.

 

[wesnewell]

What is the battery going to be used for? Starting the car? Engine size? If it's just to run acc, then a single pack like I posted should be plenty. If it's going to be used to turn the starter, then you wouldn't want to draw more than 120A from it. If you need more than that, then get 2 and parallel them for 240A.

 

[dogman dan]

The biggest problem would be if the cars alternator was going to overcharge the battery. Then you'd get a fire. Lifepo4 would get ruined just as easy, but less likely to actually flame. They make lifepo4 car batteries.

 

[wesnewell]

Unless there's a fault in the circuit, charge voltage would never exceed 14.5V, so it would never overcharge the pack.
http://en.wikipedia.org/wiki/Automotive_battery#Charge_and_discharge

 

[marcexec]

What did you end up doing?

Check my signature, I used a 4S Headway P-cell pack for a couple of months in a motorbike and a scooter.
No issues, better start in the winter

 

[agniusm]

I have almost finished mine to replace lead. I tryed to crank Russian old t-40 tractor and the battery worked wanders. I have used A123 cells.
endless-sphere.com/forums/viewtopic.php?f=14&t=38545&start=600
I will yet to try it long term.