280ah lifpo4 12v as a starter battery

[JulianG]

Help needed please Why can't you use a lifepo4 as a starter battery mine runs the bow thruster pulling 170amps. My bms is rated at 200a continuous. Is it to do with chemistry ?

 

[bgflyguy]

What is the required startup current?

It very well may be possible to use it as a startup battery, if you don't need more current than the battery is rated for.

 

[A.Justice]

Is it to do with chemistry ?

LiFePO4 can't be charged below freezing. That would mean the battery would require a heater, or to be taken inside when cold. IMHO, that's the reason that most people don't use LiFePO4 for starter batteries.

 

[meetyg]

How would this battery be charged? Via alternator? If so, that could also be problematic: Lifepo4 batteries have a very low internal resistance. Thus means that they will pull some massive amps while charging.
This could damage both the battery and the alternator.
Lithium batteries in general also need a special charging profile: constant current (untill max voltage) and then constant voltage (untill current draw falls below a certain threshold).
Most alternators act more like a constant voltage charger. Some can also output too high of a voltage (15v for example).

There are solutions to limit the alternator (search alternator to battery charger).

 

[wholybee]

You can, as long as certain conditions are met. You need to know the starting current of the engine, and confirm the BMS can handle it. Usually that means a BMS with contactors. The cells themselves need to be able to handle the current. Assuming a 1C max rate, 280 is pretty small, but might work for a smaller engine. You could parallel them for 560Ah.
Lastly, LiFePO4 does not like to be held at full charge, and most starting batteries are always at 100%. OTOH, Lead batteries prefer to be held at full charge. So a lead battery could see as long of a life as LFP in a starting application.
However, I know of some installations where there was no separate starting battery, the house battery served both functions. They were large ~1000Ah, had contactors, and because they were used for house loads were not often at 100%. After many years (>10) they still work great.
Re: the alternator. Not really related to staring applications, as Alternators often charge house batteries also. The best solution is an externally regulated alternator with a regulator that has an LFP charge profile. This allows the alternator to run at max safe current, protected by a temperature sensor on the alternator, and charges the LFP at the correct rate/profile.

 

[Lithium design]

you never said what kind of engine your trying to start....?

 

[mikefitz]

Starting an IC engine will take a high inrush current .

Consider also that most alternators have no protection against load disconnect, ( they go over volts and blow the rectifier pack and perhaps any other electrics in circuit). In addition there is no limit to current, other that the maximum output of the alternator. They tend to be constant voltage.

Graph for a 3 liter diesel engine.


Mike

 

[svsagres]

I wouldn’t do it (and didn’t for my boat), but not for the reasons posted here.

1. The internal resistance on LFP is so low, and when you close the solenoid on your starter you momentarily have a dead short until the motor starts up. I was worried about welding my solenoid or at the very least causing it to wear faster.
2. A group 24 Marine Start battery is so cheap as to be effectively disposable. I think I paid $120 for mine, including the battery case, core charge, and environmental fees.

The lead acid starter I have will basically live forever because it’s kept constantly topped up by the Victron DC:DC, and the only thing it lowers is the (very) basic engine electronics and starter motor.