Engine charging AGM Deep Cycle

[T210DRVR]

I did some search and didn’t find anything so here goes. I have a 1973 GB 42 with the original electrical system. Each engine has it's own battery bank which is an 8D AGM deep cycle battery. I’ve been reading battery forums and their seems to be a question about a standard alternator’s ability to properly charge deep cycle batteries, both flooded and AGM. In your experience is this a problem with the normal alternator found on a Lehman?

One 8D bank is tired. I can’t fit two group 27 or 31 batteries in the 8D battery box, but three group 24’s will fit. I’m not looking forward to putting in another 8D. They are just too darned heavy! Any issues with using three group 24’s in parallel?

 

[DavidM]

Well the problem with most alternators is not specific to AGMs; it affects all battery types. Most engine alternators are like the one on your car- it is regulated at a fixed voltage. This works fine for replacing the small charge that starting usually takes. And if you don't use either bank for house uses at anchor you should be fine with the standard engine alternator.


But high output, externally regulated alternators charge batteries much, much faster if they have been significantly depleted.


It sounds like you do not use the batteries much at anchor so you should be fine.


Finally three G24s wired in parallel is a little strange but I don't see why it wouldn't work. The jumpers you find at WM are smaller gauge. Use the same gauge as the main cable to the engine's starter for jumpers.


David

 

[FF]

"I’ve been reading battery forums and their seems to be a question about a standard alternator’s ability to properly charge deep cycle batteries, both flooded and AGM."

If the alt is rated high enough to refill a 50%= discharged batt in modest time ,one hang up is always the auto style Voltage regulator.

As about 1/2 the energy is lost in the alt. a lot more heat is created in the one that is charging at 14+V.

All small alts produce reduced output at higher temperatures.

Cars get by as most times the car batt is pretty well charged and starting ' take much out.

The car V regulator will attempt to replace about 1/2 of the battery needs per hour .

If a big batt like an 8D needs 100A , 50A will be done in the first hour , 25 in the second 13 in the third. Not a big deal when the batt is 95% charged but not good for a batt needing a bunch of amps.

A marine style 3 or 4 stage (any brand) V regulator is built to maintain much better charge rates until the batt is 85 or 90% charged , where it too slows down, to keep from boiling the batt.

Changing to a 3 or 4 stage charge regulator is good , but do not be surprised if the output is low from operating hot , or if it wears out rapidly.

The only simple answer is a large frame truck sized 135-150A alt with a 3 or 4 staged V regulator. About a buck an amp.

Not expensive at truck shops , but get a dual belt pulley and fit it if you can.

 

[T210DRVR]

BTW, on the hook I have a marine “smart” inverter/charger and the charger component is rated at 80 amps. When on the hook I can use the gen set to recharge. I suppose my concern was more towards any chance of overcharging with the engine alternator. I suppose the internal regulator set at +/- 14.5 volts from the alternator won’t overcharge?

 

[DavidM]

BTW, on the hook I have a marine “smart” inverter/charger and the charger component is rated at 80 amps. When on the hook I can use the gen set to recharge. I suppose my concern was more towards any chance of overcharging with the engine alternator. I suppose the internal regulator set at +/- 14.5 volts from the alternator won’t overcharge?

Engine alternators are set much lower, usually in the mid 13s. They will never overcharge at that voltage.


David