Building a pack for Engine Starting

[toddbailey]

Hi All,

I'm done with Lead acid batteries, My Rv sits most of the time and no matter how much I monitor the batteries when ever I want to use it the batteries have failed. Enough is enough. Time for a different chemistry.
I am trying to start a diesel cummins L10 engine, the battery compartment is separate from the engine so no heat issues.

I'm seeing more engine starting batteries on the market, but they are grossly over priced, so My only option is to BIY (build it yourself)

I'm thinking of using 4 LiFePO4 100 amp hr 3.2 volt in a 4s for 12.8 volt total. The starter + and chassis ground lead will be taken directly off the pack, a BMS will connect to the battery to the charging system and other coach power systems, ie lights, radio etc. I don't know the exact starting current needed but the oem battery is rated at a max of 1500 CCA.

Any thoughts so far?

 

[toddbailey]

forgot to mention, i'll be using sinopoly 12volt 100 ah bundle at about $500

 

[Stealth_Chopper]

My Thoughts?
( 'Re-inventing the wheel' @ ~ $1K vs. a couple hundred clams every year. )

 

[toddbailey]

nah, improving the wheel. a replacement 8D easily sets me back $350, plus I have to drive 40 miles to exchange, plus having to deal with all the corrosion and maint. A LiFePO4 battery bank will set me back about 500 and be 100 pounds lighter, and last 4x longer.

 

[spinningmagnets]

Another benefit is that...LiFePO4 can be thought of as a deep cycle battery. When the RV is parked, the battery can be used with the engine/charger off.

Lead-acid dies quickly when actually used as a deep cycle. The lead acid batteries that are labeled as deep cycle simply have thicker plates, since the lead erodes away with each deep cycle.

 

[kdog]

4s lifepo4 is good replacement for the LA battery. Has many benefits, but your issue is more the bms side of the project. A quality 500amp+ bms is going to be pricey or difficult to find, you might even need more amps. First thing I'd do is measure your cranking amps with a clamp metre so you know what you're dealing with. Then, you might find auto style bms's for 4s lifepo available in huge currents (I haven't looked) but if you can't you'll have to go the bms->contactor route.

So I just had a 2min look at 500-1000amp bms's in 4s. Cheap crappy things on aliexpress $240usd
Whole lifepo battery on eBay @1000a ~$400usd probably cheap and crappy as well.
I'd get a smaller bms, and use it to drive a contactor.

 

[jhaz6471]

Take a look at LTO , 40AH 6cell battery puts out 1600CCA at zero degrees F .

I have tested a 30AH version at a local dairy farm for the last 3 years on a 8 liter diesel tractor . It started it at -15 F with no problems

The 30AH puts out 1000 CCA and has a voltage equalizer on it and nothing else (No BMS) , no need to worry about leaving your either.
Zero volts are not a problem either , I have been testing a cell for 2 years , Zero volts at 6 months at at time with no aparent capacity
loss.

The costs are batteries, copper connectors , Volt meter, Shrink wrap and QNBBM 6S Voltage Equalize == @ 550.00$

The cells are rated for 60% output at -50 C ( -58 F)

The only thing you need Not to do, Is use a "dumb charger" . They will over charge your battery -- 15v plus , Bad news for your electrical system.

JimJr