Float voltage for Firefly batteries

[jkleins]

I have two of the Magnum inverter chargers (I love redundancy). They put out about 220 amps for a while into our 700+ bank. It was as cheap to buy the inverter as it was a plain 100 amp charger and it allows me to change them out if one breaks. The magnums have a constant voltage mode that works well to keep the second charger from moving to float too early when one is cycled on and off for some reason.

[mitiempo]

Originally Posted by a64pilot

Another way is an inverter / Charger. I have a Magnum MS2812 at 125 amps, it along with my 60 amp Sterling gives me 185 amps, and that is about all my 30 amp Boat can support.

The Victron Multiplus 12/3000 is an inverter charger. 3000 watts inverting and 120 amps charging. The op is planning on switching to this as stated in his first post.

[john61ct]

Bruce's public pronouncements and current official documentation may be a compromise with the Indian co's marketing staff.

My understanding from past discussions, with longevity a priority and assuming fully programmable charge sources,

in order of preference:

1. Bank isolated from Float once full, "just stop" as with LFP best practice

2. 13.2V Float setpoint

3. Higher is "acceptable", up to 13.5V maximum, but lower the better

[Wild Cherry]

I have recently purchased 2 Victron 220AH AGM batteries for my house bank. There are 2 90 ah batteries for the windlass and bowthruster and another to start the engine and generator. I have a 40amp Dolphin charger and a 6,5kw Onan generator. Just before launch 3 weeks ago I could charge the batteries fully with shore power. Now that I have been away from shore power for about 2 weeks I find I cannot get the absorption rate of charge above 13volts. I am switching off the other batteries with their isolator switches and only charging the 2 victron batteries with the gennie and charger. Why can I not get the batteries fully charged again? After running the generator for a couple of hours I get them up to say 12.6volts and when I swith off the charging the voltage falls back to 12 - 12.2Volts. What do I need to check or test? Thank you for any advice.

[hellosailor]

So,
2x220h Victron AGM new house.
2x 90 Ah old for motors
1x 90Ah old engine SLI

And the change is that you've gone from shore power to generator power for charging.

I would first actually TEST and VERIFY that the other three batteries are actually isolated. There may be some loop in the wiring that is still connecting them, i.e. perhaps someone wired the bilge pump or another item to multiple power sources. Perhaps they are not really disconnected.

If you can eliminate that, then either:
1-You are making a measurement error. Are you using a calibrated voltmeter or other device to measure this voltage?
2-There are still loads on the new AGMs when you think you are charging them? (again, verify and confirm)
3-The generator setup is putting out insufficient voltage, or not running long enough. Output settings must be, yes, tested and verified.
4-Cabling issues. If the generator output to the batteries is going through too much cable, too thin cable, corroded cable fittings, etc. that's all it takes to eat the power before it is getting to the batteries.

Assume *nothing*. Be relentlessly logical and skeptical, and you'll find (as Sherlock Holmes said) that whatever remains, no matter how improbable, is the culprit.

[Wild Cherry]

Thanks Hellosailor for that excellent response - all taken on board and I think a thorough investigation is required. The volt readings seem correct at the battery and I am relying on the Beneteau multi levels display meter for volt readings. I reckon this calls for a Victron battery monitor as well to be sure. I am on anchor around Corfu and will be looking for an electrician first thing Monday. Thanks again.

[smac999]

40a charger is pretty small for your needs. you have gone from running the charger 24/7 on shore to only running it for short periods when the gen is running. likly you are not running the gen long enough each day to get enough charge back in. look towards a 100a charger.

note that turnning off the battery switches of the other batteries likly does not stop charging. the chargers should be direct to batteries.

if your 440ah house bank is down to 12v. you have removed over 220ah. of charge.

the 40a charger is putting maybe 25a into the batteries because 15 is likly consumed by things already running.

so you'd have the run the gen for ~ 10 hours to get 220ah back into the batteries at 25a

with a 100a charger you'd be putting 85a in and run for 3 hours

[Wild Cherry]

You are absolutely correct smac999 and thank you for that input. In fact I had a good technician on board today and he has also suggested an 80amp charger (if we went to 100amp it would mean changing the cables to a bigger gauge as well which was not necessary). I am now trying to source a Victron 80amp or Mastervolt 75amp charger here in Corfu which is proving challenging. I wish Europe could be more like the US when it comes to buying things - quick, easy and fast!

[RickG]

Wild Cherry, looking at the Victron charger/inverter you can limit the number of amps the charger will put out. I'll be upgrading the charger and inverter DC cables to the maximum output to prevent any surprises.

Cheers, RickG

[john61ct]

Sterling or Magnum should be as good, maybe quicker to source.

[mitiempo]

Originally Posted by Wild Cherry

You are absolutely correct smac999 and thank you for that input. In fact I had a good technician on board today and he has also suggested an 80amp charger (if we went to 100amp it would mean changing the cables to a bigger gauge as well which was not necessary). I am now trying to source a Victron 80amp or Mastervolt 75amp charger here in Corfu which is proving challenging. I wish Europe could be more like the US when it comes to buying things - quick, easy and fast!

So have you given up on the Victron inverter/charger?

[a64pilot]

Even with an unlimited charge source, it’s going to take at least five hours of charging, probably longer to fully charge the batteries. Of course that means five hours or more of generator run time every day

[a64pilot]

Originally Posted by smac999

with a 100a charger you'd be putting 85a in and run for 3 hours

For a Lifepo bank yes, but it doesn’t work like that for lead acid, due to declining charge acceptance rate, at three hours your going to be 85% or 90% charged just as a guess, and it’s going to take pretty much an additional three to be fully charged.

If your going to be charging off of a generator only, you do not want AGM batteries, you want inexpensive flooded and expect to replace them every few years, and do a lot of short cycling them, but it makes more sense than running the generator all day long, every day.

[Wild Cherry]

Originally Posted by mitiempo

So have you given up on the Victron inverter/charger?

I already have a separate inverter - an Enag 2000 watt. Definitely I'd get an inverter/charger but already I'm tossing the Dolphin 40 amp charger.

[Wild Cherry]

Interesting dilemma I'm faced with re lengthy charging times and cost benefit ratios brought up by my many learned friends on this forum. A 100amp Mastervolt charger costs around 1600 euros and an 80 amp charger around 1200 euros. Should I not rather spend that cash on solar panels? The thought of several hours of generator noise every other day is not appealing.