LiFePO4 House; AGM Engine - how to charge?

[mvweebles]

I am installing a 500AH LiFePO4 House battery bank with 800W solar plus a Magnum 3000W hybrid inverter/charger. Any informed suggestions on charging my Engine Start and Generator Start/Thruster AGM batteries? I found a Renogy DC-DC charger but cannot figure out if it is acceptable to go between different battery chemistries (LiFePO4 >>>AGM). Thoughts on this or other solutions?

Peter
(apologies if this is a repeat - I tried searching the archives but did not find a good match).

[expozen]

I'm pretty sure that charging between different battery chemistry's is one of reasons they exist.

Sterling Power also offers the same:

https://www.sterling-power-usa.com/s...rycharger.aspx

[john61ct]

Yes. Best practice is, all significant energy inputs go to House directly, regulation set to their ideal profile.

Starters get charged by the DC-DC.

Alternator input only is sufficient for those, so wire IGN to turn on the DCDC.

[expozen]

Originally Posted by john61ct

Yes. Best practice is, all significant energy inputs go to House directly, regulation set to their ideal profile.

Starters get charged by the DC-DC.

Alternator input only is sufficient for those, so wire IGN to turn on the DCDC.

Why is alternator input required? I would think a 500ah bank would be able to run a 20amp charger without a problem?

[john61ct]

Originally Posted by expozen

Why is alternator input required? I would think a 500ah bank would be able to run a 20amp charger without a problem?

You don't pull charge energy from one bank to another.

The actual charge sources, besides alts, are solar, shore power or genset (+AC charger), wind, hydro etc.

The DCDC charger should only be running while such a charge source is active.

Sterlings have VSR/ACR functionality built in, usually run that way from any source automatically.

Renogy requires a separate switch trigger.

Starters actual input needs are trivial, so up to you, but IGN is the usual.

[expozen]

Originally Posted by john61ct

You don't pull charge energy from one bank to another.

The actual charge sources, besides alts, are solar, shore power or genset (+AC charger), wind, hydro etc.

The DCDC charger should only be running while such a charge source is active.

Sterlings have VSR/ACR functionality built in, usually run that way from any source automatically.

Renogy requires a separate switch trigger.

Starters actual input needs are trivial, so up to you, but IGN is the usual.

Got it. I got confused because I've only one I've ever looked at was the B2B, which as you say already has VSR/ACR built into it. So I only imagined it on when a charge source was available. Without VSR/ACR wiring to IGN is a good call.

[mvweebles]

Originally Posted by john61ct

Yes. Best practice is, all significant energy inputs go to House directly, regulation set to their ideal profile.

Starters get charged by the DC-DC.

Alternator input only is sufficient for those, so wire IGN to turn on the DCDC.

First, thanks to all who responded. Ver helpful.

Second, why is it best practice to run primary charge leads to house bank? That sounds intuitively correct in my mind, but friend who is also extremely knowledgeable and has been an engineer for one of the marine propulsion OEMs for decades says primary charging leads should go to engine start first, then distribute to other banks. Reason being is criticality of engine start. Thoughts?

[john61ct]

The high current inputs. should be directly connected where they are needed.

Starter batteries do not get depleted, their Ah per day energy input is trivial, easily satisfied by an inexpensive combiner device e.g. Echo Charge.

[tanglewood]

Originally Posted by mvweebles

First, thanks to all who responded. Ver helpful.

Second, why is it best practice to run primary charge leads to house bank? That sounds intuitively correct in my mind, but friend who is also extremely knowledgeable and has been an engineer for one of the marine propulsion OEMs for decades says primary charging leads should go to engine start first, then distribute to other banks. Reason being is criticality of engine start. Thoughts?

That is certainly the past practice. But with the advent of large house banks that require much longer charging than a start battery, the practice has been reversing. Then add in LFP requiring a different charge protocol, and it becomes even more compelling.

[CatNewBee]

Originally Posted by mvweebles

First, thanks to all who responded. Ver helpful.

Second, why is it best practice to run primary charge leads to house bank? That sounds intuitively correct in my mind, but friend who is also extremely knowledgeable and has been an engineer for one of the marine propulsion OEMs for decades says primary charging leads should go to engine start first, then distribute to other banks. Reason being is criticality of engine start. Thoughts?

Exactly, this is the way to go.

Charging the LFP from alternator is not worth it. LFP have higher resting voltage, so the difference between alternator output and house bank is too insignificant to drive a high current, except your battery is either empty or you have high loads on it like an inverter under full load. Then you may fry your alternator.

Keep the engine wiring as_is, if you want to charge the LFP from the alternator too, use a B2B charger that limits the current and increases the voltage, it also allows LFP friendly charge profiles, what an alternator usually does not. .

[tanglewood]

Originally Posted by CatNewBee

Exactly, this is the way to go.

Charging the LFP from alternator is not worth it. LFP have higher resting voltage, so the difference between alternator output and house bank is too insignificant to drive a high current, except your battery is either empty or you have high loads on it like an inverter under full load. Then you may fry your alternator.

Keep the engine wiring as_is, if you want to charge the LFP from the alternator too, use a B2B charger that limits the current and increases the voltage, it also allows LFP friendly charge profiles, what an alternator usually does not. .

Or just install an external regulator on the alternator and put it to full use charging your house bank. Why reduce it's output capacity by running it through a DC/DC converter/charger?

[ranger58sb]

Originally Posted by mvweebles

I am installing a 500AH LiFePO4 House battery bank with 800W solar plus a Magnum 3000W hybrid inverter/charger. Any informed suggestions on charging my Engine Start and Generator Start/Thruster AGM batteries?

Let the engine alternator recharge the engine start battery, and let the genset alternator recharge the genset start battery.

There's so little demand during starting, and AGMs don't self-discharge very much...

So treat 'em like car batteries: start up when you need to, and otherwise forget 'em.

Maybe carry a set of jumper cables onboard just in case.

-Chris

[CatNewBee]

For protection from overheating.

[john61ct]

Originally Posted by tanglewood

Or just install an external regulator on the alternator and put it to full use charging your house bank. Why reduce it's output capacity by running it through a DC/DC converter/charger?

^^^^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.

[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.