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Old 22-05-2024, 08:20   #1
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Lifepo4 house back up starting?

For those with a lifepo4 house, can you use it as a backup for starting your engine?
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Old 22-05-2024, 10:30   #2
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Re: Lifepo4 house back up starting?

It depends on the size of the bank, the BMS maximum current, and the engine. It may work, give it a try.
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Old 22-05-2024, 10:38   #3
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Re: Lifepo4 house back up starting?

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Originally Posted by donradcliffe View Post
It depends on the size of the bank, the BMS maximum current, and the engine. It may work, give it a try.
I'm in the process of shopping the batteries to switch over. I'm trying to determine if I should be saving space for 2 starting batteries or 1. Was interested to hear how people here with lithium house are setup for contingency. I have a trawler (so bigger engine), but I figure if anybody is doing it, it would be monohull sailboaters.
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Old 22-05-2024, 13:58   #4
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Re: Lifepo4 house back up starting?

A few years ago, no, the bms in drop in LifePo4 batteries couldn't handle starting current. That is changing, we are starting to see more and more batteries that can handle high starting current for short periods.
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Old 24-05-2024, 12:12   #5
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Re: Lifepo4 house back up starting?

I could probably do it with a set of jumper cables. I’m mostly worried about welding my starter solenoid and/or popping my 400A class T. (I’m running a DIY LFP with a contactor based BMS).

But that’s unlikely to ever be an issue. My starter battery is a traditional 12v FLA Marine Start, that spends its entire life on the float thanks to my DC-DC charger.
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Old 24-05-2024, 13:08   #6
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Re: Lifepo4 house back up starting?

If you plan for it and build or install batteries that can, then of course you can start you engine with LFP. Many boats to that, no problems at all.

If you go cheap and buy Drop-ins with a BMS with low current handling capability, then no, you can't.
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Old 24-05-2024, 13:43   #7
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Re: Lifepo4 house back up starting?

does the BMS have to be rated for the cranking current, the inrush current, or some other "locked motor" condition?
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Old 25-05-2024, 05:31   #8
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Re: Lifepo4 house back up starting?

It can be done as Donrad stated.

I have an 800 aH (4x200] Victron lithium battery setup with their 500amp lynx BMS. Works like a charm. I only use AGM batts now for my bow thruster.
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