Protect alternator in Lithium/FLA system

[john61ct]

Originally Posted by Newcruiser311

John, I had considered that. Was trying to figure the best way to connect it. Come off one of the start batteries? Wouldnt the alternator still run just as long and hot?

Can choose any robust connection point in the alt - to - Starter batt circuit as input to the BB, read its docs.

And no, the BB cannot pull more than its maximum, and it can be adjusted to pull less, aka derate it.

I believe 60A is the current biggest one, but they can be stacked for someone putting in a big HO alt.

The BB can front-end for the bank, condition the power from any old "dirty" charge sources.

[john61ct]

Originally Posted by tanglewood

I have a hard time getting too excited about alternator surge protection

I'm not sure which issue you are referring to with that phrase

Fitting an external VR to manage the alt - protect from the LFP pulling too much current - is a big expensive job, and may not even be possible.

BB is much better value because of the future-proof flexibility, not alt-specific, not vehicle-specific.

Disconnecting the LFP from the charge source is not IMO an issue here.

And per-cell functionality can also be set aside for now.

The first most critical issue is protecting the stock alt setup from the LFP demanding current production it's not capable of producing safely.

[Newcruiser311]

Ya, battleborn recomeded that isolator. I was trying to figure out how to deal with 3 batteries. I guess I could wire the two starter batteries in parallel.

[john61ct]

Ignore BB wrt the combining, not relevant, any good one will do.

Focus on charging their LFP well.

Starter batt should be dedicated to cranking only, and if so then need very little charging and care, not fussy.

Why do you have two?

[Newcruiser311]

What do you mean any good one will do? The isolator? In regards to 2 batteries, there is a starter battery for each engine.

[john61ct]

Originally Posted by Newcruiser311

What do you mean any good one will do? The isolator?

The term isolator usually implies an old-fashioned diode-based device.

More modern ones without the voltage drop problems go by the terms

VSR / ACR or combiner, essentially the same functionality, just different ampacities, build quality maybe some added features.

Some like Echo Charger or DuoCharge are unique.

Then DC-DC chargers, completely different.

> In regards to 2 batteries, there is a starter battery for each engine.

Better to use a VSR than parallel them full-time.

Plus the ability to start either engine from either battery would be ideal, but separate topic.

[john61ct]

https://battlebornbatteries.com/shop...ation-manager/

> the BIM will connect for 15 minutes, disconnect for 20 minutes, and repeat this cycle until the coach battery is charged

That's just nuts.

OK I suppose, **if** your charge source is running daily for long periods for other reasons, like a trucker on the road all day, but the bank can get recharged back to full in just a few hours.

But if running just for charging purposes, that behaviour will double the charging time!

[Newcruiser311]

Ok, thanks John. I am going to look at the BB chargers. Got to figure out how to deal with two alternators but maybe I will answer my questions when I look at the install manuals. Tha is again.

[smac999]

on a recent build with 2 engines with non controllable internal alts (outboards) we ran each to own start battery. then each start battery feed the lifepo bank with a steerling BBW12120 dc to dc charger (two of them). these have a lifepo charge mode. and also an ign turn on input. which we ran through the BMS. so the BMS could shut off the dc to dc charger, charging to the house bank, but the engine would continue to charge the engine battery. (and the alts wouldn't blow up from the shut down)

all 3 banks still needed dock charging inputs. as the DC to DC was fed from the ign source (then through BMS). I guess if you wanted you could only charge the engine batts from shore and feed the ign inputs with constant 12v instead. so the dc to dc always charge the house. but we did it with an inverter / charger instead at dock.

this is not going to prevent the alts from getting hot. they will still each be putting the whole 70a each into the house bank. if you got a lower current version, it would likly just limit current between batteries and not have an issue. but then your charging will be slower.

the best way to limit the alts is with a external regulator and then you can set the max output of the alt lower.

[tanglewood]

I guess I don’t see what the big deal is with installing and external regulator that will back off if the alt gets too hot, and use the field output to drive both alternator field inputs in parallel, running them in tandem as a big 140a alternator.

[smac999]

Originally Posted by tanglewood

I guess I don’t see what the big deal is with installing and external regulator that will back off if the alt gets too hot, and use the field output to drive both alternator field inputs in parallel, running them in tandem as a big 140a alternator.

there is the odd special reg that can do 2 alts. but normally you just need 2 regulators.

you still have the isolation issue to deal with the 3 banks. and different charge profiles

[tanglewood]

Originally Posted by smac999

there is the odd special reg that can do 2 alts. but normally you just need 2 regulators.

you still have the isolation issue to deal with the 3 banks. and different charge profiles

If the two alternators are charging the same battery bank(s) and driven by the same engine, then one regulator works fine and eliminates the challenge of getting the settings the same and balanced between two regulators. I’ve run like this for years, and explain it in my blog.

[Jon Hacking]

Originally Posted by tanglewood

I guess I don’t see what the big deal is with installing and external regulator that will back off if the alt gets too hot, and use the field output to drive both alternator field inputs in parallel, running them in tandem as a big 140a alternator.

Al Thomason's Very Smart Regulator will source (or sink) 30A of field current, which is plenty to drive multiple alternators. But they may not share that field current equally, even if they're the same model. Also, if the alternators are on different engines, then an alternator on a non-running engine will get field current but won't be able to use it, so it will get hot. Yes, you can weave a web of switches & such to handle these situations, but at $125/reg, why bother? The regs talk to each other over the CAN-Bus when both alternators are running, so they don't argue. Redundancy is good, which is why the OP (& I) have multiple alternators & multiple start batteries.

[john61ct]

Yes, those with high-level DC electric skills and DIY experience with VR/alternators,

can easily optimize that one charge source category for their LFP bank at a pretty reasonable cost.

However, for those not so technical, who would need to hire those skills - if even reliably available nearby - such a project would cost **a lot**, for just those alts, on just that boat.

And then the other perhaps more significant charge sources, switches, other infrastructure will likely also need tweaking / replacing.

My point here wrt the Sterling BB unit,

(and I don't recommend their BBW line for LFP, but that can be discussed later)

is that you just buy that **one** "middleware" solution, and from then on, that LFP bank can be reliably and safely charged from **any** old nominal 12V charge source

without making **any changes** to the existing infrastructure.

Not just stock alts, but old & primitive mains chargers, cheap solar controllers, whatever.

Including moving to a new boat in a few years, or living in an off grid cabin, traveling in an expedition camper rig, whatever.

The charge time question is valid, but is very likely NBD compared to the bad old lead bank days, especially for such a small bank

and if that does become an issue, just get a bigger BB, or stack them.

[Newcruiser311]

Sorry for all the questions John, as you can tell I am new at trying to DIY. I really want to learn it myself so I can work on it or under way. I agree your idea seems like the simplest solution. Do you think the best way would be to attach the BB charger to just one of the starter batteries? I have a diagram but not sure how to upload it. Basically as it is the two alternators both plug into the guest isolator. The isolator has three outputs. On these outputs there is a T-type connector that connects the outputs of the isolator and also the outputs from the shore battery charger. Then all three lines each run to a battery. So although the battery charger connects at the isolator, it doesn't actually run through the isolator. Only the alternators do. Hopefully that makes sense. If I placed the BB charger after the isolator I am not sure how that may interfere with the sensing the isolator diodes do. I'd prefer to just get rid of the isolator but that starts to exceed my know how. Sorry for all the questions and feel free not to answer if your tired of this...lol..