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Old 19-12-2015, 06:44   #16
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Re: Battery Bank Amp - Hour Requirements (Confused again)

Originally Posted by ontherocks83 View Post
37 amps is not even at 10% of the rated ah. I would say 15-20% of rated ah so you can charge from 50% of discharge and be able to run electronics comfortably. Also if you dont have a shore charger or other means of charging besides your alternator you are going to have to run the engine for really long periods of time to get over 80% charged.
A$$... you beat me by 8min...

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Old 19-12-2015, 09:54   #17
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Re: Battery Bank Amp - Hour Requirements (Confused again)

Originally Posted by Maine_bill View Post
Thanks for all the advice...lot to absorb, but in the end I think I've decided on four (4) 6volt T105's ....

My next question ...
Will my current alternator be adaquate to charge them

I "think" it is a Motorola Y3N3S..rated at 37 was rebuilt by the PO in 2012
The engine is a 24 hp Universal

That sounds like a stock alternator for that engine. 24 hp? Universal made an M25 and an M25XP at 21 and 23 hp. What specific engine model?

I have an M25 in our '86 boat and replaced the stock Motorola 55A alternator with a 100A aftermarket alternator with an external regulator, Balmar MC-612 (now the 614 model). Skippers use belt (or amp) manager and Small Engine Mode features of the regulator plus temperature sensing of both battery bank and alternator to de-rate the alternator output to avoid overheating. A bigger alternator running at less than its max output will work just fine and better and cooler than trying to max out any alternator. Do a Google search on this forum for many detailed discussions of those features. Our 100A alternator works just fine a 60A continuous output for a while until the battery acceptance reduces the amp flow. Search around on battery acceptance, too.

Don't use your stock alternator with an external regulator, it won't work, it will overheat the alternator, which is too small for your system.

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Cowichan Bay, BC, (Maple Bay Marina) SR/FK, M25, Rocna 10 (22#) (NZ model)
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Old 19-12-2015, 14:04   #18
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Battery Bank Amp - Hour Requirements (Confused again)

A Stock Alt even if it is a 100 amp or so will only output 13.8 To 14.2 volts, essentially trickle charging the battery. That is fine to keep a battery that is fully charged from discharging, but won't charge one well at all.
If your regularly at the slip plugged in, you'll be fine until the kitty can afford a real Alt and external regulator, if your only charge source is the Alternator, then you'll need to do something, may even be more cost effective to buy a Honda to charge batteries and run other AC devices than a high output alt and external regulator.
I believe many have successfully used an external reg with an ambulance or other automotive larger than normal alternator.
I'm going out on a limb here, but I believe almost all Marine high output alternators are based on automotive ones.

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