Can anyone think of any problem with adding another diode bank to my
90hp Merc 2cycle so that it could charge another different battery?
I assume that the diodes are nothing more than a bridge rectifier
setup so adding another set of diodes would just provide another
parallel load to the alternator stator coil. I assume that since the
alternator is by and large a current source anyway that the only
effect of adding another bridge rectifier is that some of the charging
current that normally goes to the starting motor would now get
directed to this other battery.

I know that there's other ways of doing this, battery isolators etc,
but it would seem that if I have space under there and have the
diodes that this would be a reasonable way to go about it.

Any reason why not? I'm no longer under warranty. Worst case if
there were excessive loading I could burn the stator coil of the
alternator if the current were not limited.

tks
Don

On Jun 26, 5:21 pm, wrote:
Can anyone think of any problem with adding another diode bank to my
90hp Merc 2cycle so that it could charge another different battery?
I assume that the diodes are nothing more than a bridge rectifier
setup so adding another set of diodes would just provide another
parallel load to the alternator stator coil. I assume that since the
alternator is by and large a current source anyway that the only
effect of adding another bridge rectifier is that some of the charging
current that normally goes to the starting motor would now get
directed to this other battery.

I know that there's other ways of doing this, battery isolators etc,
but it would seem that if I have space under there and have the
diodes that this would be a reasonable way to go about it.

Any reason why not? I'm no longer under warranty. Worst case if
there were excessive loading I could burn the stator coil of the
alternator if the current were not limited.

tks
Don

I would think that adding another diode block to the coils to charge
another battery would be the best answer, if you can get them wired to
the coils correctly.

It is the best way to maximise and equalise the charge to both
batteries. It is also the best way to overwork the charging coils in
your engine.

Terry K

Terry K brought forth on stone tablets:
On Jun 26, 5:21 pm, wrote:

Can anyone think of any problem with adding another diode bank to my
90hp Merc 2cycle so that it could charge another different battery?
I assume that the diodes are nothing more than a bridge rectifier
setup so adding another set of diodes would just provide another
parallel load to the alternator stator coil. I assume that since the
alternator is by and large a current source anyway that the only
effect of adding another bridge rectifier is that some of the charging
current that normally goes to the starting motor would now get
directed to this other battery.

I know that there's other ways of doing this, battery isolators etc,
but it would seem that if I have space under there and have the
diodes that this would be a reasonable way to go about it.

Any reason why not? I'm no longer under warranty. Worst case if
there were excessive loading I could burn the stator coil of the
alternator if the current were not limited.

tks
Don


I would think that adding another diode block to the coils to charge
another battery would be the best answer, if you can get them wired to
the coils correctly.

It is the best way to maximise and equalise the charge to both
batteries. It is also the best way to overwork the charging coils in
your engine.

Terry K


I would think that this would be fruitless. If the alternator is
running flat out into one battery bank, it is not the diodes which are
the pinch point for electrical flow, it is the gauge of the wire in the
stator coils and/or the rotor (if it is not a PM alternator). Adding
another diode trio won't make any difference.

The alternator stator is a current source - but not a textbook one. It
has internal resistance - derived from the gauge and length of wire in
the coils.

bob
s/v Eolian
Seattle

On Jun 27, 9:33 am, RW Salnick wrote:
Terry K brought forth on stone tablets:



On Jun 26, 5:21 pm, wrote:

Can anyone think of any problem with adding another diode bank to my
90hp Merc 2cycle so that it could charge another different battery?
I assume that the diodes are nothing more than a bridge rectifier
setup so adding another set of diodes would just provide another
parallel load to the alternator stator coil. I assume that since the
alternator is by and large a current source anyway that the only
effect of adding another bridge rectifier is that some of the charging
current that normally goes to the starting motor would now get
directed to this other battery.

I know that there's other ways of doing this, battery isolators etc,
but it would seem that if I have space under there and have the
diodes that this would be a reasonable way to go about it.

Any reason why not? I'm no longer under warranty. Worst case if
there were excessive loading I could burn the stator coil of the
alternator if the current were not limited.

tks
Don

I would think that adding another diode block to the coils to charge
another battery would be the best answer, if you can get them wired to
the coils correctly.

It is the best way to maximise and equalise the charge to both
batteries. It is also the best way to overwork the charging coils in
your engine.

Terry K

I would think that this would be fruitless. If the alternator is
running flat out into one battery bank, it is not the diodes which are
the pinch point for electrical flow, it is the gauge of the wire in the
stator coils and/or the rotor (if it is not a PM alternator). Adding
another diode trio won't make any difference.

The alternator stator is a current source - but not a textbook one. It
has internal resistance - derived from the gauge and length of wire in
the coils.

bob
s/v Eolian
Seattle

Yes, just like a battery is not a perfect voltage source the
alternator is not a perfect current source either since they both
have internal resistance. The main point was that if an alternator
acts like a current source then overloading it shouldn't cause it to
overheat, I suppose it depends on how much internal resistance there
is. Now underloading should make the voltage go way high which is why
you never want to run without a battery. Anyway, I'll look into it.
All this stuff may well be molded into epoxy where I can't get to the
stator output windings anyway which would make all this discussion a
mute point.

In any case, the lowest resistance path and the lowest charged battery
will win the lions share of the charging current but at least the
batteries wont' directly be connected to one another. In my case we
are only talking about a 7.5A alternator charge anyway.

Do they use a diode trio now with 3 phases these days or is it a
simple bridge rectifier on one single winding? I'm talking about the
real simple kind of alternator on a lower Hp outboard not the kind
that look more like what you'd see on a car or 200hp fuel injected
30A baby.

best regards
Don

brought forth on stone tablets:
On Jun 27, 9:33 am, RW Salnick wrote:

Terry K brought forth on stone tablets:




On Jun 26, 5:21 pm, wrote:

Can anyone think of any problem with adding another diode bank to my
90hp Merc 2cycle so that it could charge another different battery?
I assume that the diodes are nothing more than a bridge rectifier
setup so adding another set of diodes would just provide another
parallel load to the alternator stator coil. I assume that since the
alternator is by and large a current source anyway that the only
effect of adding another bridge rectifier is that some of the charging
current that normally goes to the starting motor would now get
directed to this other battery.

I know that there's other ways of doing this, battery isolators etc,
but it would seem that if I have space under there and have the
diodes that this would be a reasonable way to go about it.

Any reason why not? I'm no longer under warranty. Worst case if
there were excessive loading I could burn the stator coil of the
alternator if the current were not limited.

tks
Don

I would think that adding another diode block to the coils to charge
another battery would be the best answer, if you can get them wired to
the coils correctly.

It is the best way to maximise and equalise the charge to both
batteries. It is also the best way to overwork the charging coils in
your engine.

Terry K

I would think that this would be fruitless. If the alternator is
running flat out into one battery bank, it is not the diodes which are
the pinch point for electrical flow, it is the gauge of the wire in the
stator coils and/or the rotor (if it is not a PM alternator). Adding
another diode trio won't make any difference.

The alternator stator is a current source - but not a textbook one. It
has internal resistance - derived from the gauge and length of wire in
the coils.

bob
s/v Eolian
Seattle


Yes, just like a battery is not a perfect voltage source the
alternator is not a perfect current source either since they both
have internal resistance. The main point was that if an alternator
acts like a current source then overloading it shouldn't cause it to
overheat, I suppose it depends on how much internal resistance there
is. Now underloading should make the voltage go way high which is why
you never want to run without a battery. Anyway, I'll look into it.
All this stuff may well be molded into epoxy where I can't get to the
stator output windings anyway which would make all this discussion a
mute point.

In any case, the lowest resistance path and the lowest charged battery
will win the lions share of the charging current but at least the
batteries wont' directly be connected to one another. In my case we
are only talking about a 7.5A alternator charge anyway.

Do they use a diode trio now with 3 phases these days or is it a
simple bridge rectifier on one single winding? I'm talking about the
real simple kind of alternator on a lower Hp outboard not the kind
that look more like what you'd see on a car or 200hp fuel injected
30A baby.

best regards
Don


In small outboards, typically the device works like this: There are
magnets embedded in the inside edge of the flywheel for the use of the
magneto ignition. A second coil can be located anywhere it will fit,
and will also be a source of power. The module the OB manufacturers
typically install is a combination of coil and bridge rectifier.

In this case, presuming you can find a place where it will fit, yes,
installing another coil/rectifier would double the electrical output of
the motor.

I guess I am surprised that a 90 hp outboard would not have a
conventional alternator.

bob
s/v Eolian
Seattle

In article ,
RW Salnick wrote:

In this case, presuming you can find a place where it will fit, yes,
installing another coil/rectifier would double the electrical output of
the motor.

I guess I am surprised that a 90 hp outboard would not have a
conventional alternator.

bob
s/v Eolian
Seattle

and loosing that power, from moving the vessel....