LiFePO4 House; AGM Engine - how to charge?

[Delfin]

Originally Posted by Q Xopa

Why wouldnt you connect your Alternator to your LFP house bank and to the FLA start bank via your ACR?
If the BMS discons the LFP it is still connected to the FLA via the ACR to absorb any surges.
If connect your Alternator to the Start then via a B2B to the LFP it will typically limit your LFP charging to 60A.
Most LFP, which arent cheap setups also mostly have bigger than 60A Alternators so dont want the charge current restricted.
60A is only 0.3C rate for a 180AH LFP bank. Most LFP banks are bigger.
Just something to consider.

Although I see that you meant connection of the LFP to LA via a B2B charger and not the ACR, connection via an ACR, or for that matter a simple switch works just fine. Concerns about charging the LA starter bank with settings appropriate to LFP are misplaced IMO.

[anthem00]

You generally put the chargers on the bank that needs the most charge - that is usually the house bank. The start bank usually is drawn down very minimally. So it will be trickle charging almost immediately. So that’s why many house banks are set to charge from the alternator with the starter banks on a separate dc to dc charger or relay after the house banks have hit a decent level (this is much trickier with lifepo4 banks).

Also there is some merit in putting an inline LA battery with an alternator that charges a lithium bank. Lithium prefers to be cut off once it hits its level (no real absorption and float). So you would need to cut the alternator The safest way to cut the alternator is to cut the B+to the regulator - but this can’t be an instantaneous cut. After you cut it - you have to delay the battery cut off by 6 plus seconds to safely protect the diodes from being fried.

[sdj]

Congrats, thats a really good move. Did you figure this arrangement out or was it recomended to you?

Buy the correct mains AGM charger and plug into your inverter. Job done. Buy two of them for each battery and leave one turned off, redundancy done. Do the same for any AGM batteries onboard.

Charger fails? Turn other one on.

Need new charger? Buy one. Simple.

Complicated impossible-to-follow wiring, no way! It's all consumer plug-in mains stuff, just like at home, nothing complicated about it.

[TaylorO]

I installed a 600 ah Battleboarn LiPO4 bank charged by a 1,050 watt solar array, 400 w wind generator, and a 100 amp alternator with a remote programmable controller I programmed for the lithium batteries. installed an Xantrex Echo Charge ($110) from the house bank (with breaker) to the starter battery. I also added a cheap Amazon digital voltage multimeter ($14 - and is backlit) to the starter battery which I can glance at anytime to see what voltage the starter battery is holding. It works great and gives me peace of mind knowing the starter battery voltage at all times. I now can go onto other projects not worrying about power!
Cheers,
Taylor

[ramblinrod]

Originally Posted by Q Xopa

Why wouldnt you connect your Alternator to your LFP house bank and to the FLA start bank via your ACR?
If the BMS discons the LFP it is still connected to the FLA via the ACR to absorb any surges.
If connect your Alternator to the Start then via a B2B to the LFP it will typically limit your LFP charging to 60A.
Most LFP, which arent cheap setups also mostly have bigger than 60A Alternators so dont want the charge current restricted.
60A is only 0.3C rate for a 180AH LFP bank. Most LFP banks are bigger.
Just something to consider.

The resting voltage of the LFP bank may be seem as a charge source by the ACR, keeping the start battery combined.

[Q Xopa]

Originally Posted by ramblinrod

The resting voltage of the LFP bank may be seem as a charge source by the ACR, keeping the start battery combined.

You have had trouble with this?

If this is an issue you could something like a Victron Argo FET Batt combiner. The Alternator/s can charge either Batts but no current can flow the other way so the Batts banks are never actually combined.

[john61ct]

Originally Posted by ramblinrod

The resting voltage of the LFP bank may be seem as a charge source by the ACR, keeping the start battery combined.

Not an issue as long as the VSR/ASR "close setpoint" is above 13.32V, easy to check.

There are adjustable combiners.

And finally, the Starter bat should not be accepting much if any current flow.

[Dockhead]

I don't think you can say one or the other configuration is "best practice". Each has its own pluses and minuses. As far as I can tell:


A. Externally Regulated Alternator > Lithium > B2B charger [or cheap Echocharger] > start battery

Advantages:
1. Full output of alternator available to be dumped into the lithium (but be careful about overheating it)
2. Can use cheap Echocharger instead of B2B


Disadvantages:
1. No alternator protection (requires separate device)
2. Requires external regulation of alternator

B. Alternator > Start Batt > B2B > Lithium
Advantages:
1. Alternator protection built-in
2. Simple fail-safe charging of the start batt
3. No external regulation required for the alternator


Disadvantages:
1. Charge current to lithium limited by B2B
2. B2B is expensive


Right?

I'm not clear how you would use an ACR. You would externally regulate the alternator with a lithium charging profile and with a control connected to the BMS. Then parallel to the start battery -- under what circumstances? These are normally voltage controlled, but how would you set the voltage, if you can even find one with settable voltage?

[sdj]

Originally Posted by john61ct

Not an issue as long as the VSR/ASR "close setpoint" is above 13.32V, easy to check.

There are adjustable combiners.

And finally, the Starter bat should not be accepting much if any current flow.

While this will work initially, there is no opportunity for the AGM battery to ever enter float conditions, and as such it could never reach full charge. Repeated abuse such as this won't be tolerated by the battery, nor should it be tolerated by any system designer.

Charge the start battery with the correct technology multi-stage charger run from your inverter.

[john61ct]

We're talking about a Starter right?

Annual cost less than taking the fam to a meal at McD's?

I mean, fine you do you. . .

[john61ct]

This really is a switch, when **I'm** the one saying no need to fuss so much, batteries are consumables 8-)

[sdj]

Originally Posted by john61ct

This really is a switch, when **I'm** the one saying no need to fuss so much, batteries are consumables 8-)

If you have a nice boat, you don't care about a hundred dollar battery, but do you care if it is going to start??

Two seperated engine-start batteries charged with mains multi stage chargers is always going to start. Always.

[Dockhead]

Originally Posted by sdj

If you have a nice boat, you don't care about a hundred dollar battery, but do you care if it is going to start??

Two separated engine-start batteries charged with mains multi stage chargers is always going to start. Always.

True, and important.


I would never mix house power system with starting systems. Too much to go wrong. My main engine and genset each have their own totally separated start batts, charged by totally dedicated alternators, and even separate AC charger. I will not change that.

[john61ct]

Reliability and redundancy can be achieved in many ways.

Including plugging a mains charger into the inverter running off House, if you want to.

There is no "one right way"

[sdj]

“Everything should be made as simple as possible, but no simpler.” -- Einstein.

Buy the correct one off the shelf and plug it in, simple. Buy a spare one in case the other one fails, simple.

The LiFePo4 charger is responsible for it's job - leave it to do that and don't screw with it or have a better idea. You do not know better than your lithium battery management system,

The electronic 5-stage computer-controlled AGM start battery charger DOES know better than you do about your start battery. Don't skrew with it! If it quits then plug the spare one in.