shivadas avatar image
shivadas asked

Charging my LifePo4 with an alternator


I am designing my setup but the only thing that is not clear to me is how to safely have my batteries charge through my alternator.

The battery will be a LiFePo4 battery, 12V 600Ah.
Inverter/charger Victron Phoenix 12/2500/120
700W of Solar through SmartSolar 100/50

I am still deciding on the BMS. My van is a 2006 Renault Master, so I'm pretty sure it's not one of the newer "smart alternators".

From what I can find online it looks like there might be a way to use either a BMS or a VE.Bus BMS to do this? I would like the alternator to be connected to my starter battery at all times, and connect a system to that that
A) Doesn't destroy my alternator
B) Doesn't drain my starter
C) Shuts off charging when battery is full

Has anyone already made a setup like this?

Thank you!!!

Lithium BatteryBMSOrion DC-DC Converters not smartalternatorcharge current limit
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4 Answers
Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

I would advise using a Victron Cyrix Li-Charge or Li-CT intelligent battery combiner. You could also use a Sterling Battery to Battery Charger, but given your application and the relative simplicity of your system, the Cyrix combiners will be your simplest and most cost-effective solution, as well as having the smallest footprint.

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Thanks @Justin Cook. That indeed looks like a very economical solution

Don't I run the danger of overloading my alternator without a limiter of current, knowing that the battery can take quite the charge current if it would be more heavily depleted?

Is there a separate piece I can limit the charging current through?

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Thanks again @Justin Cook

I find three types it seems:

Victron Cyrix Lithium charge relais (most expensive of the three)
Victron Cyrix-Lithium load relais
Victron Cyrix-ct combiner relais (cheapest)

Which one is advisable? I have a hard time discerning the difference. Is it just the delay time?

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Your alternator can only put out "x" amount of amperage, the battery bank isn't a "load" exactly, so it can't pull more than the alternator is capable of generating... I'd say a charge limiter would be unnecessary for you.

As for which Cyrix to use, I would think the Cyrix Li-CT, as the voltage cutoffs and timers are particularly designed for a lead-acid starting battery and a lithium battery bank.

What kind of lithium are you using? Just curious because you mention the BMS but most lithium systems I'm aware of have their own BMS built-in.

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shivadas avatar image shivadas Justin Cook - Bay Marine Supply USA ♦ ·

Thanks @Justin Cook.

I'm building my own using Greatmax LiFePo4 3.2V 100Ah cells and a BMS they provide (still waiting for their specs before going for their BMS)

So I will be getting this one then!

I'm looking for a BMS that can control a relay that switches off the solar array input from the MPPT when the battery disconnects (or keeps that line open while shutting the rest off).

Probably connecting a BP as well just for safety, unless people tell me it's overkill with the correct BMS.

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DO NOT connect a BP inline with a battery combiner. Current may only flow in one direction with a BP. You will damage the BP if used in this way.

Also if you have a relay connecting your inverter charger, that too can be damaged from the high inrush current if not sized properly. For a BMS, I'd suggest looking into a REC-BMS Active. It's a compact unit for 12v systems and can interface with a Victron Venus device like a color control or Venus GX. They also sell a precharge circuit to protect your contactor/relay and your inverter.

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Hi @Justin Cook, a follow up question: I finally have gathered all the parts (needed to save up a bit more) to put everything together. An advisor of mine said I also need to have a relay to stop the charging from my starter battery when full. But from what I understand it seems the Li-Ct stops when the house battery is full. Is that correct?

The victron description of course mentions the VE.Bus BMS. I use the 123SmartBMS, which has relay outputs for starting & stopping charging. Will this work?

Is it correct to think of the cyrixes as follows:

Li-CT: open charging from starter battery when starter is full

The difference between Li-Ct and Li-Charge is lost to me.

Li-Load: for disengaging loads when battery is low (also here: do I need to disengage the multiplus, or does it figure that out on it's own ==> only connect it to my DC loads)

All these cyrixes rely on receiving a signal from the BMS, correct?

Sorry for all the questions, but I'm trying to figure this out and not finding much expertise in my city! Thank you all!

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shivadas avatar image shivadas Justin Cook - Bay Marine Supply USA ♦ ·

thanks again @Justin Cook. looked it up on youtube and indeed looks like an easy install. They do mention something about an "off switch" for longer drives to avoid overcharge. I guess I could do that automatically through a bms?

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imutt avatar image
imutt answered ·


I watched a youtube series where victron built a demo van, with all sorts of gadgets and functinos you are interested in.
I cannot find the exact link/time right now. Here is the beginning of the interesting series :)

edit: this might be what you are looking for

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lucas-mill avatar image
lucas-mill answered ·


That's I know a company can provide the custom BMS, they can make the BMS for LiFePO4 battery.

As I know, they can make BMS separately for the battery, functions involved "Shuts off charging when battery is full", "Self-Discharging in Fully Charged Storage" and some protection, so it may help you.

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Trina avatar image
Trina answered ·

For people coming here and reading and learning about how to do this kind of an install with any kind of CUSTOM lifepo4 where you are supplying your own BMS and are using a solar charge controller it is very important that you use a

Separate Port BMS

To protect your MPPT if the BMS cuts out and stops the charge (disconnecting the MPPT from the battery and leaving the solar still connected...)! I don't know if Victron has a solution built into the charge controllers now but the usual common port bms (widely available and what most people use and can find) will NOT protect your MPPT from damage in a DIY lithium setup!

The Separate Port BMS will have a 3rd wire coming out of the P side for your solar charge controller to remain connected.

Kinda older stuff but important esp. if using an (often high output) vehicle alternater for additional charging.

Here's a video I found on it -about 23 minutes in (

Just if you are doing a DIY LITHIUM BUILD don't forget this need!

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