lifepo4 12V car battery build advice

[gsd2000]

Hi

I am after some advice as to which lifepo4 cells to use for my application.

I am planning on building a 12V lifepo4 battery to run my car.

My car is a 2004 Vauxhall Monaro CV8 which has a 5.7 litre V8 engine, the current battery produces around 320CCA and 60Ah.

I was planning on using 8 12Ah 38140s Headway cells in 4S2P setup, but i am unsure.

http://eclipsebikes.com/headway-lifepo4-38140s-12ah-p-1012.html

Ideally i would like to purchase the cells in the UK where i am from to reduce shipping cost and import fees.

thank you

 

[miro13car]

FalconEV sells automotive Lithium batteries, go Google themand see how they do it?
A123 round cells are only ones I can see fit for it, unless you want paraller and paraller, why to complicate?

 

[heathyoung]

Vauxhall? Its a Holden mate! (http://en.wikipedia.org/wiki/Holden_Monaro)

From memory these don't use a reduction starter, so the current demand is a bit high. Any particular reason for Lifepo4? Its a heavy beast, I don't think the weight reduction will be noticed...

 

[gsd2000]

Okay okay its a Holden

I've started doing some drag racing and want to reduce the weight on the nose of the car to help with weight transfer.

In current drag trim the car is 60kg lighter but I'm hoping with a lifepo4 battery I can save another 10-12kg, along with lighter front seats which should save around another 35-40kg.

A smaller lifepo4 also makes it much easier to change headlights lamps, as currently I have to remove the battery to swap them.

 

[ZOMGVTEK]

Do you have, or can you borrow a DC current clamp? It wouldn't be a bad idea to see the current demands of your starter. Preferably on a cold day, after it hasn't been running for a day or so.

Unfortunately this isn't terribly easy to do as reliably and maintenance free as the stock lead battery. You don't really need much capacity, you just need a ton of peak amps, and a BMS capable of ensuring the thing never overcharges.

I'd think LiPo might be better suited here. What about simply using the highest capacity 4S1P Nanotech LiPo pack you can get? The alternator should never charge it past the 16.8V which would make for 4.2V/cell. I'd wonder how well that would work out, for starting a car at a relatively low SoC. You shouldn't even need a BMS, but there would be little capacity left over for when the alternator isn't putting out power. Basically bolt up a 4S LiPo brick at 50% SOC and see how it does?

 

[gsd2000]

My GM manual states 140 Amps peak from the alternator

I was planning lifepo4 because i thought it was safer than Lipo

I did have some small a123's but wasn't sure how well they would cope with the current from the alternator charging them

 

[heathyoung]

I think docbass used some A123 26650's from dewalt packs for a snowmobile starter battery, not the same thing but they can crank out the amps.

 

[gsd2000]

i know that the small a123's should crank it, but how well will they cope with the alternator running charging them up?

Wont the cells get damaged by the constant large current from the alternator charging them up?

 

[ZOMGVTEK]

The alternator should be regulated to something like 14.2-14.6V, and should not force large currents into the battery. The idea is, the battery would be nearly that voltage when it goes into the system, so minimal current will flow.

As long as the battery never really deeply discharges, it should be fine. However, in all honesty, you do not sound like you should be attempting this project right now. If you are worried about LiPo fires, and stating the max current from your alternator, designing a rugged battery system capable of very high discharge rates is a bit extreme.

This is not something people commonly do, since this just isn't best suited for the application. The advantages are minimal. If you remove the alternator, and just run a total loss setup, it's plug and play. If you want it to be gas and go, and stupid reliable, thats something entirely different.

 

[Icewrench]

Initial current draw is 220 to 240 amps to crank over most V8 engines and starters draw 110 amps or so to keep the motor rolling over till it starts. Starters work best if voltage does not sag below 10 volts.