Too big a battery harmful?

[p10]

I recently got my hands on a 2009 Suzuki DF 50 for my 18 feet boat. I'm planning to have a 50ah starter battery and a 90ah auxiliary battery. I'm hoping to tie them together using one of those automatic charging relays that disconnect the two batteries when the engine is turned off.

However, I was told by a friend that I shouldn't hook both batteries to the engine, because the combined ah size would probably be too much for the engine alternator and that I risk damaging the engines charging circuits if I do it?

 

[tpenfield]

Sounds like a made-up story. The starter will draw what it needs. The only thing with 2 batteries is that the voltage drop while cranking will probably be less than with just the one, which can be a good thing.

Many boat electrical system are set-up with just that . . . a way to use more than one battery during cranking of the engine.

 

[boscoe99]

Yamaha for one lists minimum and maximums for batteries. Seems to be based on the type of alternator being used.

Looking at a DF50 owner's manual I see only a minimum specification. With mention of paralleling multiple batteries. But no caution as to there being too many.

 

[dingbat]

You will have no problems charging both with an ACR

 

[KD4UPL]

I see no problem with your plan. Your friend may be thinking of lithium batteries.

 

[99yam40]

best thing to do is keep the batteries charged up
do not expect a dead battery to be charged up from the outboard itself
it will do its best to try ,but that can over task it

 

[cyclops222]

If you run batteries down to 1/2 capacity ? You COULD possibly damage a O B alternator. YOU are responsible for correctly running ALL of your boat systems. Not someone else. Never Lie to yourself that boat systems are as reliable as any car.

 

[dingbat]

If you run batteries down to 1/2 capacity ? You COULD possibly damage a O B alternator.

Please explain the mechanism for this damage.

 

[cyclops222]

Some O B Chargers Are simple AC Volts generators with a DC rectifer circuit feeding the battery.
Without a voltage regulator for limiting MAXIMUM CURRENT out to a very run down battery. There is a excellent chance the motor alternator windings - rectifier - electronics - battery will be cooked to death. Older motors are of that type of risk.
The new LIFEPO4 batteries are just like a piece of Copper wire when run way down. They will burn out UN REGULATED chargers in motors.
My older Evinrudes are of the UN REGULATED types. If not watched during a long high speed run. They battery is being charge to 15 or 25 volts. Some electronic equipment have no protection to those bad voltages.

 

[boscoe99]

best thing to do is keep the batteries charged up
do not expect a dead battery to be charged up from the outboard itself
it will do its best to try ,but that can over task it

best thing to do is keep the batteries charged up
do not expect a dead battery to be charged up from the outboard itself
it will do its best to try ,but that can over task it

Why not?

That is the purpose of having an alternator. To charge up a battery, or batteries, and to provide current to electrical devices on the boat. As well as providing current to electrical components on the outboard motor itself.

Talking of over tasking an alternator is similar to over tasking the motor itself. One can run a motor wide open throttle all of the time as well as an alternator. Recognizing of course that additional wear and tear may ensue.

 

[boscoe99]

If you run batteries down to 1/2 capacity ? You COULD possibly damage a O B alternator. YOU are responsible for correctly running ALL of your boat systems. Not someone else. Never Lie to yourself that boat systems are as reliable as any car.

If you run a motor at WOT you COULD possibly damage it. Same with an alternator. Just comes with the territory.

I could not agree with you more about boat systems never being as reliable as automotive systems.

 

[Ackevor]

the combined ah size would probably be too much for the engine alternator and that I risk damaging the engines charging circuits if I do it?

Like most have already said, the size or capacity of the battery is not a concern, the voltage is. Just don't wire them in series.

 

[99yam40]

Why not?

That is the purpose of having an alternator. To charge up a battery, or batteries, and to provide current to electrical devices on the boat. As well as providing current to electrical components on the outboard motor itself.

Talking of over tasking an alternator is similar to over tasking the motor itself. One can run a motor wide open throttle all of the time as well as an alternator. Recognizing of course that additional wear and tear may ensue.

I thought they are designed to keep up with the needs of a vehicle and motor to keep the battery from being drained while running not charge it from dead.
if it is dead there is a good chance the battery is bad to start out with.
heck even in automotive they say not to jump off a dead battery with some vehicles..
so it is best not to let dead batteries be in anything.
if the battery is dead replace it or see if you can charge it up before starting a motor.
heck back in the good old days you could do just about anything, but with the new things full of electronics controlled stuff it is not wise.

I had a generator on my old 64 Galexie 500 lock up on a trip.
I rigged up an idler pully in place of the generator so the fan belt could still run the water pump.
by the time I got where I was going not much would run, the battery was so low.

My brother had a battery go bad in the toyota during a trip,
vehicle just died on the highway.
he had to get towed into a shop.
they had to replace the battery and the alternator

 

[mike_i]

You can't have a "too big" of a battery as in capacity just size and weight.