Battery to Battery charger as best solution- reality check

[Pete7]

Originally Posted by john61ct

That is not the OP's situation though.

True, John on SV Libby wants to control the float voltage:

Originally Posted by sv Libby

Unfortunately the 14.2V output cooked my last set on a long motor. The new ones want 13.4 float in the tropics

So, given the proposed future move to LFP, what cost effective solution can we suggest for the new AGM batteries which are about to be fitted?

Is the answer something cheap and cheerful with the idea that in say 3 - 4 years scrap it and the AGMs then start again. Or try to aim off buying kit, which is more expensive, now that might suit a future LFP solution with the risk that something better may come along?

Pete

[john61ct]

As I suggested a Sterling BB.

Modding the alt setup is #2.

There are cheaper solutions but not suitable IMO.

[KadeyKrogen38]

I use the Balmar Digital Duo Charge for B to B charging. Very happy

[john61ct]

Duo Charge is not actually a DC/DC battery charger with step-up or down capability, no independent output, dropping to Float

yes in a way acts as a regulator, at least in setting min/max, will step voltage down

but still a "voltage follower" in that it has no independent intelligent charge management.

Does not actually limit current, its maximum is 30A, but a big design flaw, it will **shut down** completely if a load of more than 30A is drawn, rather than just limiting the output current.

There **are** use cases where it is very suitable for splitting output between a Starter and House, can be more sophisticated for that usage than a VSR/ACR,

but really its functionality has nothing to do with the OP scenario.

[sv Libby]

Originally Posted by Pete7

Me too, there are thousands of yachts happily using AGMs with ordinary automotive alternators.

You motor almost everywhere up here in Asia and it is 30deg C. We killed our batteries on a 2 day motor. 14.0 - 14.1 Float was enough to do it. I don't want to do it again.

[Dockhead]

Originally Posted by sv Libby

You motor almost everywhere up here in Asia and it is 30deg C. We killed our batteries on a 2 day motor. 14.0 - 14.1 Float was enough to do it. I don't want to do it again.

Been there, done that. My sympathy. Even open lead-acid batts can be cooked to death like that.


That's why you need an external regulator like the Balmar MC-612, which not only will drop to a real float voltage, but also has a battery temperature sensor.

[smac999]

Originally Posted by sv Libby

You motor almost everywhere up here in Asia and it is 30deg C. We killed our batteries on a 2 day motor. 14.0 - 14.1 Float was enough to do it. I don't want to do it again.

And millions of cars do this every day.

Charging agms at 14v is not going to kill them in a couple days.

[ben2go]

Battery to battery? We call'em jumper cables down here in tha south.

[john61ct]

Experiment: one big LFP bank, fully charged, another well depleted.

Join in parallel with jumper cables from your favorite big box or automotive retail.

You first 8-)

[skenn_ie]

I use a DC-DC buck-boost converter that I bought on eBay. One with current and voltage adjustments is best.

[tgrimmett]

If you are getting most of your amps from solar, you'd want to at least make sure you've got good MPPT controllers (like Victron) to manage their charge. We do this, and the charge goes directly into the house bank, with a Balmar Digital Duo Charger bleeding off amps from the house bank to keep the engine battery charged up. Works great. Even though you said you don't rely as much on the alternator, I would suggest completing the solution on that end too, with either an external regulator (we have a Balmar ARS 5 but the M614 would work fine too), and preferably a heavy duty alternator (we've used both the Balmar units and more recently the Valeo alternators that come stock on the new Yanmars, modified with the Balmar Smart Ready Retrofit kit), so that you can get full benefit out of the engine charge potential. We send our alternator amps into the house bank as well, and the Duo Charger tops up the engine battery as needed. This is the second boat we've done this setup on, and we've been very happy with it. We also use a battery to battery converter/controller, made by Sleipner, but this is solely to convert from 12 to 24 volts to charge the bowthruster bank.

[ben2go]

Originally Posted by tgrimmett

If you are getting most of your amps from solar, you'd want to at least make sure you've got good MPPT controllers (like Victron) to manage their charge. We do this, and the charge goes directly into the house bank, with a Balmar Digital Duo Charger bleeding off amps from the house bank to keep the engine battery charged up. Works great. Even though you said you don't rely as much on the alternator, I would suggest completing the solution on that end too, with either an external regulator (we have a Balmar ARS 5 but the M614 would work fine too), and preferably a heavy duty alternator (we've used both the Balmar units and more recently the Valeo alternators that come stock on the new Yanmars, modified with the Balmar Smart Ready Retrofit kit), so that you can get full benefit out of the engine charge potential. We send our alternator amps into the house bank as well, and the Duo Charger tops up the engine battery as needed. This is the second boat we've done this setup on, and we've been very happy with it. We also use a battery to battery converter/controller, made by Sleipner, but this is solely to convert from 12 to 24 volts to charge the bowthruster bank.

Does Victron charge controller pick a source to charge the batteries or does it combine all sources to charge the batteries? What model charge controller?

[tgrimmett]

Originally Posted by ben2go

Does Victron charge controller pick a source to charge the batteries or does it combine all sources to charge the batteries? What model charge controller?

No the Victron controller we use is strictly for solar. It is an mppt controller that maximizes the output of the solar panel. They are really the way to go these days. We use the Blue Solar 75/15 (max 75 volts and 15 amps) but they make lots of sizes. While you can combine panels in series, we've chosen to use one controller for each panel to minimize the amp loss due to shading. So the output from all the controllers goes to the house bank, as does the externally regulated alternator output.

[ben2go]

Originally Posted by tgrimmett

No the Victron controller we use is strictly for solar. It is an mppt controller that maximizes the output of the solar panel. They are really the way to go these days. We use the Blue Solar 75/15 (max 75 volts and 15 amps) but they make lots of sizes. While you can combine panels in series, we've chosen to use one controller for each panel to minimize the amp loss due to shading. So the output from all the controllers goes to the house bank, as does the externally regulated alternator output.

I feel like an idiot. I read that you said it was an MPPT. I was thinking of a charge controller or combiner further down the path from the MPPT.

[tgrimmett]

Originally Posted by ben2go

I feel like an idiot. I read that you said it was an MPPT. I was thinking of a charge controller or combiner further down the path from the MPPT.

No worries. Downstream from the solar MPPT controllers, that's where we use the Balmar Digital DuoCharger, to charge the engine bank (or theoretically any other bank of the same voltage level) from the house bank. When the house bank is receiving current at 13.2 volts or higher, whether that is from solar, alternator, shore power, or any other source connected to it, it sends amps to the engine bank to keep it charged up. Where we are in the eastern Med, we've done a lot more sailing than motoring. So the engine battery doesn't always get much of a charge up because the boat was originally designed with the alternator output going to the engine bank onlyl. The setup we have takes care of that issue by sending some amps from our solar array that is charging the house bank, over to the engine battery. And we moved the alternator output to the house bank, where there is the greatest demand for recharging, again with the DuoCharger siphoning off some to keep the engine battery ready for the next start.