Charging my LifePo4 with an alternator

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shivadas asked Aug 10, '19

Charging my LifePo4 with an alternator

Hi,

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 Battery BMS Orion DC-DC Converters not smart alternator charge current limit

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Justin Cook answered · Aug 12, 2019 at 05:00 PM

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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shivadas commented · Aug 12, 2019 at 05:04 PM

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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shivadas commented · Aug 12, 2019 at 05:17 PM

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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Justin Cook ♦♦ shivadas commented · Aug 12, 2019 at 06:02 PM

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 Justin Cook ♦♦ commented · Aug 12, 2019 at 07:10 PM

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! https://stroomwinkel.nl/cyrix-li-ct-12-24-120a-combiner.html

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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nebulight shivadas commented · Aug 12, 2019 at 08:39 PM

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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shivadas nebulight commented · Mar 03, 2020 at 12:16 PM

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 Justin Cook ♦♦ commented · Aug 12, 2019 at 07:24 PM

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?

https://youtu.be/vFJSRucsZsw?t=202

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Modifications Space

Node Red Space

Answer 1 · 2019-08-10T18:06:26Z

imutt answered · Aug 10, 2019 at 06:06 PM

Hello,

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 :)
https://www.youtube.com/watch?v=YW_xDerTycQ

edit: this might be what you are looking for
https://www.youtube.com/watch?v=vCOJ3nBFpIM

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Answer 2 · 2019-08-13T06:19:48Z

lucas-mill answered · Aug 13, 2019 at 06:19 AM

Hi,

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

https://www.grepow.com/page/bms-battery.html

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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Answer 3 · 2020-11-19T23:22:51Z

Trina answered · Nov 19, 2020 at 11:22 PM

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 (https://m.youtube.com/watch?v=_PgthByAYz4).

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

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