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Old 01-08-2019, 07:28   #1
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Alternator to LiFePO4 charging

What's the simplest way to safely charge a LiFePO4 bank from a standard Hitatchi or equivalent alternator without having to mess around opening up the alternator to use external regulation.

I'm aware that an 80am Hitatchi unit isn't going to be able to output that for long without overheating or burning itself out.

That is where the Sterling alternator to battery charger I have comes in. It has a temp sensor and reduces alternator output as needed. It's no good for charging LiFePO4 though as it doesn't have manually customisable profiles. It's AGM 1 setting at 14.1 and 13.4 float is probably the closest, but that float is still a bit high no?

I'm guessing the solution is a FLA start battery then some kind of fully programable DC-DC charger.

P.S I'd expect solar to easily take care of charging the batteries for the most part. The alternator would just be a backup or boost on low solar days, so I can live with reduced output due to thermal throttling.
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Old 01-08-2019, 08:20   #2
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Re: Alternator to LiFePO4 charging

The 13.4V float doesn't seem high to me. My LFP batteries are fine at that voltage. Just remember not to store LFP at 100% SOC.
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Old 01-08-2019, 09:25   #3
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Re: Alternator to LiFePO4 charging

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Originally Posted by mikedefieslife View Post
That is where the Sterling alternator to battery charger I have comes in. It has a temp sensor and reduces alternator output as needed. It's no good for charging LiFePO4 though as it doesn't have manually customisable profiles.
You can put a DC-DC BB unit in line if you don't want to live with the "off" voltages.

Or use HVD to disconnect the input when you get where you want.

Shouldn't be Floating at Full anyway, but 13.25 or lower is at least below Full.



> I'm guessing the solution is a FLA start battery then some kind of fully programable DC-DC charger. Not some kind Sterling BB as above, more than one if you need the high current.



> I'd expect solar to easily take care of charging the batteries for the most part. The alternator would just be a backup or boost on low solar days, so I can live with reduced output due to thermal throttling.

Then if you want to avoid buying the BB, just use alt output to get you to say 90%, and when you want to go closer to Full, use your solar for that.

Another idea - Sterling may be able to adjust the A-B unit to a custom voltage, just fixed not adjustable, doesn't hurt to ask.
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Old 01-08-2019, 10:45   #4
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Re: Alternator to LiFePO4 charging

A HVC sounds the easiest so long as there is a starting battery for the alternator current to be dumped to.

Is there a recommended HVC, that is widely available off the shelf? I've seen the Victron battery protect, but I think is something slightly different no?

From what i've seen these HVC devices are just relays. I'm looking for something where I can program the voltage I want it disconnect the inputs at.
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Old 01-08-2019, 14:21   #5
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Re: Alternator to LiFePO4 charging

The two parts are the

contactor (or relay, solenoid) that needs to be robust and reliable at the desired working current it's breaking, and the

voltage-sensor / controller that triggers the open vs close, signal voltages and NO vs NC matching the specs of the contactor.

Some people use the Victron 712-BMV for things like this, overkill but known reliable.

Some DIY use Arduino.
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Old 01-08-2019, 15:37   #6
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Re: Alternator to LiFePO4 charging

OK it all makes sense now. The Victron 712-BMV would be nice to have, but I have a perfectly good Mastervolt battery monitor lite at the moment. I don't believe it can control a relay though it does have an alarm contact 60v/1A, otherwise I'd need another method either off the shelf, or DIY as you've suggested.
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Old 03-08-2019, 09:35   #7
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Re: Alternator to LiFePO4 charging

Isn't a solar charger just a DC to DC converter? Presumably you could have an alternator charging a start battery, then a smart solar controller charging a LFP bank. Victron make them in the 100-250 range, but they are expensive.

I also recently came across this B2B charger. It says it custom programable
https://www.donrowe.com/KISAE-DMT125...-p/dmt1250.htm
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Old 03-08-2019, 10:21   #8
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Re: Alternator to LiFePO4 charging

Some solar controllers include DC-DC converter circuitry.

But no, that is not the whole of their functionality.

Some DC-DC controllers can act as solar controllers, but they are not as efficient in extracting maximum power over the course of a solar day.

Some SC can accept non-panel inputs, others cannot.

In general, it is best to use the tool designed for the job at hand.
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Old 04-08-2019, 00:36   #9
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Re: Alternator to LiFePO4 charging

My Sterling Pro Alt C have a lifepo4 setting (14,6-14,4) that is supposed to be used together with a BMS/HVC system
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Old 04-08-2019, 03:43   #10
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Re: Alternator to LiFePO4 charging

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My Sterling Pro Alt C have a lifepo4 setting (14,6-14,4) that is supposed to be used together with a BMS/HVC system


Mine has those settings too. They are too high. No one wants to float a LFP at 14,4. 13,2 is more like it.

The DC to DC charger i linked to above can do it. Albeit at 50 amps.
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Old 04-08-2019, 08:15   #11
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Re: Alternator to LiFePO4 charging

Yes, no LFP setting I've seen is appropriate.

All you need for a charge source to be "LFP ready" is user-custom adjustability of output setpoints. Or a BB charger in between to give you that from any old source.
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Old 05-08-2019, 00:35   #12
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Re: Alternator to LiFePO4 charging

According to my observations the Sterling does not really float the batteries in Lifepo4 mode. I have two different cases since I use it both for the alternator and for the shore power. When running the Alternator It will dial down the current after 1,5-2hours and then my bank is mostly full, after that I will only give 4-8A and thatís what I use when sailing. When I connect the shore power it charges the batteries to more or less full (3,5ish v) and then shutdown. Maybe there is some algorithm in the Sterling that actually senses both current and voltage
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Old 05-08-2019, 00:56   #13
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Re: Alternator to LiFePO4 charging

Well, you need an alternator output at a voltage which will not charge the batteries after they're full, but will drive loads, presumably 27v or whatever for a 24v system. Just isolating the alternator with the HVC will not do it.

So we need a regulator which will drop to float on command from the BMS, don't we?
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Old 05-08-2019, 03:02   #14
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Re: Alternator to LiFePO4 charging

Does page 3 from this help?

https://cdn.shopify.com/s/files/1/19...14524986592305
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Old 05-08-2019, 07:42   #15
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Re: Alternator to LiFePO4 charging

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Well, that presumes you have connected the alternator to a lead battery, and charge the lithium with a B2B charger. That's not the only way to do it, and not the way I will be doing it, for various reasons.


Nor am I sure that the Sterling B2B charger actually does what is needed. You can force it into float mode with the remote control:


https://cdn.shopify.com/s/files/1/06...08434148284241


See page 10.


But there does not seem to be any inputs available which would allow the BMS to do that automatically.


A little off topic, but you would sure want to be able to force the charger/inverter into float as well. You definitely don't want for the charger/inverters to automatically fill up the lithium bank, if you are at a dock for a long period of time. See MaineSail's articles on that. With some perhaps you can just switch off the charger, but you can't do that with Victron -- the charger is always on if AC power is on.


I would definitely want the charger/inverters to be capable of being "on" -- so that I could use Power Boost, all the more useful with lithium batteries -- but with charging off or forced to a float voltage which won't charge the batteries but drive the DC loads. i'd like to have a switch to do that.
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