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

That's really a very small alternator. I would suspect that while running
you don't have much more that 8 to 10 amps available for charging. The
alternator has to supply the power to operate the boat as well as to charge.
I would not plan on being able to bring two trolling batteries up very far
at the end of the day with that configuration. I suggest you mount a good
electornic charger capable of charging your both your trollling batteries at
the same time you install them. Then simply plug it in when you get home.
If you are going to have 2 dedicate trolling batteries you really don't need
to have two additional batteries for the regular operation. One regular
battery will suffice to operate the boat. You can add a simple switch to
use the trolling batteries for starting in an emergency.

wrote in message
ups.com...
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

On 21 Mar 2007 18:34:42 -0700, "
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?

No.

You will have to either up the amperage (which may not be possible) or
charge the trolling batteries onshore with an external charger.

As to the dual boat battery system, it won't charge both of them
simultaneously - you will probably have to install an A/B switch and
use one as a spare using the other as the boat battery.

The start/run battery will probably draw at least 8/10 amps for the
equipment on the boat plus the engine. That's doesn't give you a lot
of amperage to work with for battery charging - one is about the
limit.

Trolling motor batteries are pretty stable over time and unless you
are looking to use the trolling motor on constant duty, they will last
you a good time on the water - 8 hours or so. I have a 24 Vdc system
on the Ranger and the shortest I've ever had on constant duty was
about six hours and that was right before I changed them.

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

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 -

Sorry, I missed one point that you had mentioned in your post. You
are saying that I really don't need the extra two batteries. I would
like to learn more. If I really don't need them, I will be able to
cut down at least one hundred pounds from the load, and this would be
a very good thing.

In order not to get the extra two batteries, I will need to use the
current two dual purpose batteries to do the following things:

o First dual purpose battery: I will need to use it to crank the
outboard and use it to power fishfinder, GPS, VHF radio,
livewell for baits, and _may_be_ a pair of trim tabs. I have
a feeling that one battery cannot handle that many tasks,
and I may need to split the tasks into two batteries.

o Second dual purpose battery: I will need to use it strictly for
trolling motor. This also means that I will need to pair it with
a 12-volt trolling motor, and this is limited to no more than
55-lb thrust.

Based on West Marine recommendation, 55-lb thrust should be enough for
a 18-ft 2000-lb fiberglass boat. But based on tech support in a
trolling motor company, they recommend 70-lb thrust for that size of
boat, and that will require a 24-volt system and two 12-volt
batteries. This makes me a bit confused. If I interpret this
correctly, this means more is better, and less is OK if I am not using
it in strong current or high wind situation. If I understand this
correctly, 55-lb thrust probably is OK for me, and this also means
that I probably only need one battery for the trolling motor.

In summary, I may only need totally 3 batteries instead of 4 batteries
as what I originally thought. This is good because I can cut down at
least 50-lb to 60-lb from the boat load. Thanks for getting me
thinking along that line.

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 -

On 22 Mar 2007 09:50:20 -0700, "
wrote:

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).

Batteries that are kept fully charged will not freeze so there is no
need to pull them from the boat. AGMs and gel cells require special
charging precautions that I prefer not to deal with, not to mention
the additional expense. The best $$$ value for trolling batteries (or
any other deep discharge application) is 6 volt golf cart batteries
wired in series to yield the proper voltage. Approximately $50 each
at Sam's club, years of reliable service.

On 22 Mar 2007 10:21:07 -0700, "
wrote:

Sorry, I missed one point that you had mentioned in your post. You
are saying that I really don't need the extra two batteries. I would
like to learn more. If I really don't need them, I will be able to
cut down at least one hundred pounds from the load, and this would be
a very good thing.

In order not to get the extra two batteries, I will need to use the
current two dual purpose batteries to do the following things:

o First dual purpose battery: I will need to use it to crank the
outboard and use it to power fishfinder, GPS, VHF radio,
livewell for baits, and _may_be_ a pair of trim tabs. I have
a feeling that one battery cannot handle that many tasks,
and I may need to split the tasks into two batteries.

o Second dual purpose battery: I will need to use it strictly for
trolling motor. This also means that I will need to pair it with
a 12-volt trolling motor, and this is limited to no more than
55-lb thrust.

Based on West Marine recommendation, 55-lb thrust should be enough for
a 18-ft 2000-lb fiberglass boat. But based on tech support in a
trolling motor company, they recommend 70-lb thrust for that size of
boat, and that will require a 24-volt system and two 12-volt
batteries. This makes me a bit confused. If I interpret this
correctly, this means more is better, and less is OK if I am not using
it in strong current or high wind situation. If I understand this
correctly, 55-lb thrust probably is OK for me, and this also means
that I probably only need one battery for the trolling motor.

In summary, I may only need totally 3 batteries instead of 4 batteries
as what I originally thought. This is good because I can cut down at
least 50-lb to 60-lb from the boat load. Thanks for getting me
thinking along that line.

The difference is 12 Vdc and 24 Vdc. 12 Vdc systems have reduced run
times as they will draw more current doing any task. With 24 Vdc
systems, that current draw is spread across two batteries increasing
efficiency and run times. Put another way, the higher the voltage the
less current draw.

For example, on my Princecraft, a 14 foot aluminum boat, I have a
single 12 Vdc battery to power the 45 lb. thrust trolling motor. It
does quite nicely in a wind situation and moves the boat along
quickly, but it will only last a half day's fishing is I'm on a small
pond and has zero power for cutting weeds. The 24 Vdc system (67 lb
thrust) on the Ranger runs all day pushing a boat 4 times the weight
of the Princecraft and I have reserve power up the ying yang.

Holding a boat against a wind or wave action with a 12 Vdc trolling
motor is going to tax your patience because you will not have the
power necessary to properly move the boat.

I would definetly opt for the higher thrust and 24 Vdc system.

Fwiw, I'd be tempted to move the items that I will use when trolling over to
the trolling batteries along with the trolling motor. The fishfinder and
livewell. That way your primary run battery is not in use much while the
outboard is not running. You can pull 12v off the first of the two trolling
batteries for accessories even though you have them wired in series for a
24v trollling motor. An a-b switch correctly added would also give you the
ability to start from the first trolling battery in case your primary run
battery goes down. There are some really nice electronic chargers that can
be mounted with your agm batteries. You'll be able to simply plug them in
when you get home. Pricey though. Unless there is a big price difference
I'd go for the 70lb motor. The battery draw is more a function of how the
actual load on the motor than it is on the motor's maximum thrust.

wrote in message
oups.com...
Sorry, I missed one point that you had mentioned in your post. You
are saying that I really don't need the extra two batteries. I would
like to learn more. If I really don't need them, I will be able to
cut down at least one hundred pounds from the load, and this would be
a very good thing.

In order not to get the extra two batteries, I will need to use the
current two dual purpose batteries to do the following things:

o First dual purpose battery: I will need to use it to crank the
outboard and use it to power fishfinder, GPS, VHF radio,
livewell for baits, and _may_be_ a pair of trim tabs. I have
a feeling that one battery cannot handle that many tasks,
and I may need to split the tasks into two batteries.

o Second dual purpose battery: I will need to use it strictly for
trolling motor. This also means that I will need to pair it with
a 12-volt trolling motor, and this is limited to no more than
55-lb thrust.

Based on West Marine recommendation, 55-lb thrust should be enough for
a 18-ft 2000-lb fiberglass boat. But based on tech support in a
trolling motor company, they recommend 70-lb thrust for that size of
boat, and that will require a 24-volt system and two 12-volt
batteries. This makes me a bit confused. If I interpret this
correctly, this means more is better, and less is OK if I am not using
it in strong current or high wind situation. If I understand this
correctly, 55-lb thrust probably is OK for me, and this also means
that I probably only need one battery for the trolling motor.

In summary, I may only need totally 3 batteries instead of 4 batteries
as what I originally thought. This is good because I can cut down at
least 50-lb to 60-lb from the boat load. Thanks for getting me
thinking along that line.

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 -

On Mar 22, 1:27 pm, Wayne.B wrote:
On 22 Mar 2007 09:50:20 -0700, "

wrote:
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).

Batteries that are kept fully charged will not freeze so there is no
need to pull them from the boat. AGMs and gel cells require special
charging precautions that I prefer not to deal with, not to mention
the additional expense. The best $$$ value for trolling batteries (or
any other deep discharge application) is 6 volt golf cart batteries
wired in series to yield the proper voltage. Approximately $50 each
at Sam's club, years of reliable service.

Actually, I was referring to pulling out the flood batteries in order
to examine the water level, and also for refilling the water. In my
boat, the batteries compactment has a tiny access door. If I need to
check the water level of the batteries without pulling out the
batteries, I will have to have half of my body inside the battery
compactment, and my face will be dangerously close to the acidic water
in the batteries. I really don't want to do this. But pulling the
batteries from that tiny battery compactment is really a struggle.
That is the reason why I am looking for AGM batteries that I don't
need to check the water level, and I can leave them inside the battery
compactment without doing that annual exercise of pulling them out and
putting them back.

I have another alternative to the use of AGM batteries to solve this
problem. I can relocate the batteries to under the deck with a large
access door right on top of the batteries. But I don't want to
greatly change the boat layout just yet. If charging AGM batteries is
really difficult, I may have to stick with flood batteries, and I will
have to relocate the batteries.

The idea of using 6-volt batteries is interesting. But I am afraid
that the total weight of batteries will be much higher than using 12-
volt batteries, and I really want to keep the weight down. If I had a
bigger boat, I probably would take your advice.

Jay Chan