LiFePO4 House; AGM Engine - how to charge?

[john61ct]

Or a $20 lead batt hardwired to the alt, allows full current to the LFP House bank.

[expozen]

Originally Posted by john61ct

Or a $20 lead batt hardwired to the alt, allows full current to the LFP House bank.

I'm really curious how you implement this solution. Are you saying that you essentially have a LA battery wired in parallel to your LFP battery?

[Q Xopa]

Originally Posted by john61ct

^^^^this

But expensive, only worth doing if alternators are a **significant** contributor to you overall energy inputs.

If not, as I stated, leave the alt going to Starter.

Some boats, esp stinkpots, may get by with alternators as the **main** energy input.

All depends on the context, no "one best" solution works for all.

A Starter batt only normally works for a few seconds every engine start. Even with say a pretty standard 55A Alternator it will take maybe 20 mins, lets say an hour tops, to fully recharge your Starter batt.

If use your Alternator to charge your start batt we are just hauling around a battery and alternator, still spinning wearing brushes and belts, doing nothing for a lot of the time.

Lets say we do a 6 hour motor, we charge our start batt for 1 hour, then nothing for the next 5 hours.

Its one way to do it. But I'd rather have it charging up my house batts for all those 6 hours. If your motor is running anyway why would you not want to get max utilisation out of our gear.

[mvweebles]

For the comments about using engine alternator omly for engine start battery, how do you charge the house bank underway? There are three hi amp charging sources: solar (800w = 60a), inverter/charger for shore power or generator (125a), and an engine alternator (could be balmar 150a, but even if stock 70a).

[Q Xopa]

Originally Posted by ramblinrod

Well, it depends.

A load must always be on the operating alternator.

In the case of FLA batteries, one method is to connect all charging sources, including alternator to the house, and charge the start battery with an ACR or echo charger.

Since the BMS can disconnect the LFP batteries, if the alternator were connected to that, that could be a bad thing. So the alternator should be connected to the start battery, with an ACR or B2B charger to the LFP bank, if the charge algorithm is suitable for the LFP.

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.

[expozen]

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?

I believe that would wire the FLA battery and LFP is parallel. And wouldn't that undercharge the FLA and overcharge the LFP?

[Q Xopa]

Originally Posted by expozen

I believe that would wire the FLA battery and LFP is parallel. And wouldn't that undercharge the FLA and overcharge the LFP?

Yes, sorry correct. Meant a B2B, not an ACR.
Set the Alternator output to the LFP and the B2B output to you FLA settings.

[john61ct]

Originally Posted by Q Xopa

Why wouldnt you connect your Alternator to your LFP house bank and to the FLA start bank via your

DCDC

Exactly the best practice recommended from the start.

[john61ct]

Originally Posted by mvweebles

For the comments about using engine alternator omly for engine start battery, how do you charge the house bank underway?

Many have no need of the power source, the others may be more than enough.

But yes, **if** alt input is significant enough to justify fitting a good external VR, it should be wired directly to House.

[john61ct]

Originally Posted by expozen

LA battery wired in parallel to your LFP battery?

Only so long as that bank' input buss is connected to allow it to be charged from the alternator circuit.

The lead batt stays on the alt side, hardwired circuit.

[Mike Banks]

You could run two alternators--a smaller one that does nothing but charge an entirely separate starting battery --and a second heavy duty alternator to charge your battery bank. That smaller alternator just needs a hinged mounting plate and adjuster--and a separate set of pulleys. It will probably max out at fifty amps. Three times that, about 120 to 150 amps, will serve most high-load battery bank systems. It is not so much how big the thing is, it is how long it is practical to keep a diesel engine running with very little load..

Having said that--I also had a Honda petrol gen-set aboard. It allowed fans to be run for long periods as well as charge batteries through a 240 volt to 30 amp 12 volts DC charger when sitting out a cyclone in some mangrove creek.

[Q Xopa]

Originally Posted by john61ct

DCDC

Exactly the best practice recommended from the start.

Without searching back, werent you saying the opposite about charging the starter batt from the alternator then the house via the DCDC to not overload the alternator?

[Q Xopa]

Originally Posted by Mike Banks

You could run two alternators--a smaller one that does nothing but charge an entirely separate starting battery --and a second heavy duty alternator to charge your battery bank. That smaller alternator just needs a hinged mounting plate and adjuster--and a separate set of pulleys. It will probably max out at fifty amps. Three times that, about 120 to 150 amps, will serve most high-load battery bank systems. It is not so much how big the thing is, it is how long it is practical to keep a diesel engine running with very little load..

Having said that--I also had a Honda petrol gen-set aboard. It allowed fans to be run for long periods as well as charge batteries through a 240 volt to 30 amp 12 volts DC charger when sitting out a cyclone in some mangrove creek.

Can certainly do it that way with a dedicated Start batt Alternator. Many do.
But to me it seem like a bit of a waste having it not do much a lot of the time.
Particularly when the House batts need more than they are getting from one Alternator.
What I have done is to share the load of charging the House batts between 2 largish Alternators, 24V 110A.
Then trickle charge the Start batt with a B2B.
Just the option I have gone with.

[john61ct]

Originally Posted by Q Xopa

Without searching back, werent you saying the opposite about charging the starter batt from the alternator then the house via the DCDC to not overload the alternator?

No, my point often is to take the variable factors of the specific use case into account.

As opposed to those blindly advocating for a single approach without remaining open to the (many) possible alternatives.

Perhaps in the past thread you recall, people were claiming it's OK to attach a LFP bank to a stock alternator without fitting a current limiting VR?

[ranger58sb]

Originally Posted by mvweebles

For the comments about using engine alternator omly for engine start battery, how do you charge the house bank underway? There are three hi amp charging sources: solar (800w = 60a), inverter/charger for shore power or generator (125a), and an engine alternator (could be balmar 150a, but even if stock 70a).

OP didn't ask that...

But FWIW, in our case, when necessary or useful... we just crank up the genset and turn on the battery chargers.

-Chris