How many amp battery charger ?

[K-2]

I have two 8D starting batteries and four T105 golf cart batteries, 6 volt each, wired together to give me 12V for house power, how many amp charger do I need to charge these ? Is there a formula for sizing charger to batteries?
I would like a 3 battery "smart" charger, any specific brand, model recommendations would be great!
Feel free to post an iboats link and say "buy this one"
I want to plug into shore power and keep my batteries fully charged.

 

[alldodge]

Re: How many amp battery charger ?

Off the cuff I would lean toward a 80 to 100 amp 3-bank, 3-stage charger. Before I suggest would like to know, how do you use your boat? What is the temperature where you hang out most times? Do you run your generator most time while out or do you run on an inverter for long periods? I take it your generator starts off one of your 8D batteries, correct?

 

[UncleWillie]

Re: How many amp battery charger ?

Off the cuff I would lean toward a 80 to 100 amp 3-bank, 3-stage charger...

I hope you meant an 80 to 100 WATT charger! ???

A 5 to 10 AMP charger will do the job in a reasonable amount of time. Well under 24 Hours.
Anything over 15 amps is just bragging rights. The Amp rating of the charger is the MAX it CAN produce, but not how much it WILL deliver.
No mater how big of a charger you get, the chemistry of the battery will ultimately determine how much current it will absorb.
The majority of the charging time will be spent at under 10 amps much of that will be at 5 or less.

Do you need to charge all the batteries at the same time? A Multi-bank Charger will be needed.
If you can make use of a single charger, SCHUMACHER makes a nice line of chargers at reasonable prices.
They are available almost everywhere.

 

[K-2]

Re: How many amp battery charger ?

It's a commercial fishing boat, most of our season is 72 hours of fishing per week, the rest of the week in town plugged in.
No generator, just an inverter that runs a microwave. I usually run the engine at high idle when using the microwave.
Only thing on the house batteries is the fridge and the inverter, the fridge is fairly new and uses very little power compared to the old Norcolds. Temps run from the 40's to high 70's. Twin engines so 2 alternators, one charges the 8D's the other the house bank.
I now have an old (1989) CONSTA VOLT, it makes a lot of noise and if the batts' are low it cycles on and off a lot, takes forever to charge and I don't trust it enough to keep it plugged in overnight. In the spring, after sitting all winter the batteries are very low and it takes forever to charge them. I do have a Honda EU2000 just for emergencies.
Thanks!

 

[alldodge]

Re: How many amp battery charger ?

I hope you meant an 80 to 100 WATT charger! ???
.

No, I said and meant amps not watts.
An 80 amp 3-bank charger can charge each bank around 25 amps (100 amp about 30). Batteries listed by the OP indicate they can take that and more.

It's a commercial fishing boat, most of our season is 72 hours of fishing per week, the rest of the week in town plugged in.
No generator, just an inverter that runs a microwave. I usually run the engine at high idle when using the microwave.
Only thing on the house batteries is the fridge and the inverter, the fridge is fairly new and uses very little power compared to the old Norcolds. Temps run from the 40's to high 70's. Twin engines so 2 alternators, one charges the 8D's the other the house bank.
I now have an old (1989) CONSTA VOLT, it makes a lot of noise and if the batts' are low it cycles on and off a lot, takes forever to charge and I don't trust it enough to keep it plugged in overnight. In the spring, after sitting all winter the batteries are very low and it takes forever to charge them. I do have a Honda EU2000 just for emergencies.
Thanks!

Since you spend most time at the dock or fishing you could get by with 50 to 60 amp 3-bank 3-stage charger. Any or the Charles, Pro Mariner and Xantrex should do fine. IMO you need enough power to do bulk absorption to brings batteries up then scale back to maintain. If you have one to small it may have to work full out which could cause other reliability later. Nothing wrong with getting one a bit larger then needed but not the reverse. I had a pro mariner in mine and changed it out to a Charles due to going to AGM batteries and the Pro was not switchable.

Edit: Forgot, you either may have some batteries going out or something as your charger draining the batteries.

 

[UncleWillie]

Re: How many amp battery charger ?

It looks like you are in the market for a quality 3 bank charger. 10 amps per bank if it is in the budget.
However, do not expect to recharge extremely low batteries in just an hour or two.
5 to 10 hours plus is not unreasonable if you do not want to be buying new batteries 3 time a year.

If you want to charge them in under an hour, Lithium Batteries, and a 100 amp charger would be needed.
A second mortgage on the boat may be required to fund that project. :facepalm:

 

[UncleWillie]

Re: How many amp battery charger ?

No, I said and meant amps not watts.
An 80 amp 3-bank charger can charge each bank around 25 amps (100 amp about 30). Batteries listed by the OP indicate they can take that and more...

I was not familiar with the 8D batteries. At 250Ah and 140lbs, they are on the hefty side.
Even at 25 amps initially, on a low battery, the charge time is going to be in the 5 to 12 hour range.

 

[bruceb58]

Re: How many amp battery charger ?

Dual Pro are one of the makers that are approved for Odyssey batteries. That is what I run now on my AGMs.

Pro Charging Systems