Thanks for the many good information that I have received so far.

Sound like the 16-amp stator is just enough to charge one battery, two
is pushing it, and four is not practical. Good to know this "rule of
thumb" guide line. This means I will have to recharge at least three
if not all four batteries when I get back home if a boating / fishing
trip. I will know whether I need to recharge 3 or all 4 batteries
when I start getting real experience in using my boat.

This also means I really don't need to worry about the issue related
to using the alternator to charge the pair of AGM trolling motor
batteries; I will not be able to use the alternator to charge the AGM
trolling motor batteries anyway. I will have to recharge them at home
using a 3-stage charger. With this understanding, I am certain that I
will buy AGM batteries (instead of flood batteries) to take advantage
of the fact that I will not need to pull them out from the boat every
winter to refill water (like what we need to do for flood batteries).

Thanks again.

Jay Chan


On Mar 22, 10:44 am, "Tim" wrote:
Jay, If I remember correctly, your boat has a Mercury outboard[?]

16a. is about all you're going to get out of it total. and as far as I
know,t here isn't any performance stator to give you more power.

In a nutshell, the outboards charging system will charge all your
batteries, but it will take quite a while. You can't expect automotive
performance with that small of output.

A basic rule of thumb is that if you take a 650 CCA battery that is
flat dead (or almost), it will take a 10 a battery charger a good 6
hr.s to recharge it. That rule is a bit inefficient, but gives you an
idea on how battery charge rates work.

Of course you're not taling charging 4 dead batteries on 16a either.
Another thing to consider, is that the stator builds up a lot of heat
under the enclosed flywheel, and doesn't have any fan cooling. It
will usually handle what it's intended for, but under extended hard
loads, the Stator gets really hot, and burns off the enamel insulation
on the stator wires, and shorts them out, then it doesn't charge at
all untill you get the Stator replaced.

Not handy, and not cheap.

But if you really feel you need to go this rout, instead of going with
a battery isolator I'd go with a battery switch where you can pick and
choose which set of batteries you need to charge . the problem with
battery isolators, is that because they use heavy diodes, is that you
have a voltage drop due to the power absorbtion of the diodes
themselves. and with only 16a (possibly 20a peak) you need all the
help you can get.

Honestly, I think you are going a bit of over kill by adding the extra
batteries, but then again, it's your boat.

Good Luck.



wrote:
My boat has an alternator that has a 16-ampere stator (and voltage
regulator). Is there a formula to calculate the number of batteries
that the alternator can charge? Can it charge two or four batteries
all at the same time?

I am asking this because my boat already has two dual purpose group-24
batteries (for starting battery and house battery), and I will add two
deep-cycle batteries for trolling motor. I think this will be nice if
I can use the outboard motor to recharge all four batteries when I am
done with fishing and heading home. And all four batteries will be
ready for next day boating/fishing trip without worrying about
recharging them at night.

Can this alternator handle AGM batteries instead of flood batteries?
I am under the impression that AGM batteries may be accepting charge
too fast that they may over-stress the alternator and overheat it (or
something like that if I understand this correctly). I am wondering
if this is relevant to my alternator.

I am asking this because the batteries-storage area in my boat is very
difficult to reach (tiny room with a tiny access door). Seem like AGM
batteries will be suitable for me because they don't need as much
maintenance as flood batteries - at least I don't need to physically
pull them out to add water. But if they could overheat the alternator
in my outboard, I would have to pass on them and choose flood
batteries instead (and relocate the batteries to some place more
accessible).

Thanks in advance for any info on this issue.

Jay Chan- Hide quoted text -

- Show quoted text -