# Charging the Lifepo4



## lazer (Feb 25, 2009)

My dad ones this jacht. The jacht have 3 120amp 12v lead acid batteries. And I was thinking to replace those with lifepo4 batteries. My question is: the boat has a diesel engine that is charging those batteries via 12v ordinary car alternators. 
Can I use those to charge the lifepo4 cells? If not why?

I was reading that the maximum charge voltage on those cells was 4.5volts and with 4 cells in series I would think that at least that should be ok.

Thanks
Martin


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## dimitri (May 16, 2008)

what are those batteries used for? this would help us understand required duty cycle, i.e. "starter" - short bursts of high amps, or "trolling" - i.e. hours of pulling relatively low amps? This would help selecting correct Lithium battery, there are few different types out there. Once correct battery is selected, you can check their charging profile and see how you can use those alternators.


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## lazer (Feb 25, 2009)

Well the batteries are used for everything like lighting, fridge, starting the diesel engine, tv, comunication equipment, gps, sonar, radar, computers and stuff, anchor winch and a 15hp (11kw) bow thruster. This is for a 44 foot sailboat. All this power is currently drawn from 3 12v 120amp batteries.

You can stay uncharged for 48houres with only the basic stuff on. like radio equipment, fridge and lighting.
I would realy like this to improve so that we don't have to start the engine for houres every 2 days.

Thanks again
Martin


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## dimitri (May 16, 2008)

Well, in that case I would recommend 12 large prismatic cells like TS LFP200AHA, considering their low Puekert loss, it would give you 2-3 times useable capacity compared to current LA batteries. If you have room and cash to spare, you could go even higher capacity.

As for charging, depends on exact voltage those alternators produce, say for example they put out 14V, that means 3.5V per Lithium cell, well under safe limit, although it will not get to full capacity, it may prolong its life.

You will need some kind of balancing solution, see the "real life LiFePo4 experience thread" below.

Also, you need to find out how much current those alternators produce, so you don't overwhelm the cells at the end of the charge cycle and don't burn the balancers.

I think its definitely doable...


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## lazer (Feb 25, 2009)

The alternators are rated: number one is at 120amp and number to is only 55amp. they alreaady have a charge controller which I fine tuned to 14,4v when i fitted the batteries. As for the bmc. I can build that myself no problem.
I've been reading that.. that's what got me interested


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## madderscience (Jun 28, 2008)

seems like maybe instead of fancy / bigger batteries, a better solution might be a wind generator or solar panels to supplement the batteries, recharging them? 120AH at 36V is only 1/2kwh or so. a 100 watt solar panel (weather permitting) or a small wind turbine will be able to produce that much power in a day easily.

At fairly low amp draws peukert doesn't make any difference. If you are taking 48 hours to draw down the batteries, you are draining them at a 48 hour rate, and they are going to be rated at a 20 hour rate, so in your case you can probably get MORE than their rated capacity.

The lithiums are going to be lighter and probably will last many years if well kept for (the lead probably needs to be changed every 4 or 5 years I am guessing) but in your situation I don't think going lithium is the best solution. I would try to find a way to charge up independently of firing up those engines.

Good Luck.


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