Charging LiFePO4 with Alternator and Diode

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Marcus asked Jan 7, '22

Charging LiFePO4 with Alternator and Diode

Hello,
I have an existing system with a starter battery (12V AGM 100Ah), a bow thuster battery (12V AGM 280Ah) and a new service battery bank (12V LiFePO4 560Ah with REC Smart BMS). Additionally this will be charged via Victron Multiplus using shore power or a VICTRON MPPT solar charge controller (only for the service battery bank) or it all can be charged by an alternator, which is connected via a diode (VICTRON ARGOFET 200-3) to all three batteries.

The old system was quite simple as usual in yachts, as the alternator just charges as the service battery tells him, how much more can be charged.

Now with LiFePO4 I read this should be charged via DC-DC charger from the starter battery.

Is this really necessary or cannot the ARGOFET still make sure the LiFePO4 batteries are charged by the alternator, especially since the SmartBMS will shut down the loading process, as soon as there is bad voltage/current coming to the system?

DC-DC chargers only deliver up to 30A and charging a 560Ah battery bank from a 100Ah starter battery seems unlogical, especially using a 130Ah alternator.

Is there something to make sure, if I want to charge the LiFePO4 directly from the ARGOFET?

Thanks for the feedback...

-Marcus

Lithium Battery BMS alternator Argo FET Diode

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kevgermany answered · Jan 07, 2022 at 09:19 PM

Alternators are designed for lead acid. Lithium needs a different charge routine. The diode is a switch, not a charger. Charging direct from the alternator may kill alternator, batteries.

You can use multiple Orion dc:dc chargers in parallel to get to the required current

Be aware that lithium can burn out alternators because they accept a higher current. There's a victron YouTube video about it.

Assuming there's a direct alternator to starter battery connection, your lithium is charged by the alternator when the dc:dc chargers are connected direct to the starter battery. You configure them to start charging when the starter battery is being charged. There's effectively no load on the starter battery at any time.

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Marcus commented · Jan 09, 2022 at 03:42 PM

Ok, thanks for the answer.

I hoped to save the additional 200+€ per B2B loader for this.

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Answer 1 · 2022-01-07T21:57:18Z

Wayne answered · Jan 07, 2022 at 09:57 PM

LiFeP04 can overwork and damage alternators. When I changed from a lead bank to 600Ah Relion LiFeP04, I installed two Orion TR Smart 24/12-30's in parallel (2x30amps).

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Marcus commented · Jan 09, 2022 at 03:41 PM

That's 200€ just for one B2B Loader (30A, which I will have to triple, and then pull 90A from the starter battery in the service battery, when it is loading).

I really hoped not to have to put even more money in this, than I already did. :-(

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Answer 2 · 2022-01-08T06:45:48Z

Nev answered · Jan 08, 2022 at 06:45 AM

Marcus

I have a different setup but have charged our 300Ah 4 cell LiFePO4 battery for the last 7 years of full-time travel via our Canter 100A rated alternator at 70-85A until full. No smoke yet. Yes I have seen those YouTube videos where they show smoke with low revving alternators. Mine spins >3000 rpm even at fast idle.

I have only a single battery that both starts the truck often multiple time daily and runs our house behind.

I added a Victron Argodiode battery isolator in series with the alternator. This reduces the end voltage to 14.1V down from the original 14.4V and lowers the current by about 10 amps.

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kevgermany ♦♦ commented · Jan 08, 2022 at 02:06 PM

You're running the alternator nice and fast, well below max output. So not as surprising about the alternator. But it will be at/close to the charge limit of the BMS continuously.

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Answer 3 · 2022-01-08T15:05:57Z

hjohnson answered · Jan 08, 2022 at 03:05 PM

It’s entirely possible to directly charge your LiFePO4s with an alternator (that’s what I’m doing) but you will need to upgrade your alternator and its regulator to make this viable. On my boat, I’m installing a Wakespeed WS500 regulator to drive my alternator. It’s under the control of the REC BMS via the CAN Bus. The Wakespeed also monitors the alternator temperature to make sure it doesn’t burn out. It also has some other nice features for those of us running a big alternator on a small engine.

My starting battery will then be charged using a DC:DC charger. (Orion-tr 12/12-18 in my case.

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bathnm commented · Jan 12, 2022 at 10:24 PM

Great setup, and I have the same. One day due to the CANbus maybe we can even hook the Wakespeed up to the Cerbo and see what is going on.

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Answer 4 · 2022-01-09T17:11:12Z

Marcus answered · Jan 09, 2022 at 05:11 PM

Can I connect the Orion 12V 30A directly to the ARGOFET or do I need to connect them to the starter battery and get the load from there?
I have the diode, why not use it?

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Marcus commented · Jan 12, 2022 at 08:47 PM

No one an idea?

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