Can a 75 HP Outboard charge a deep cycle battery

Submitted: Tuesday, May 21, 2013 at 16:34
ThreadID: 102334 Views:2044 Replies:2 FollowUps:2
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I would like to put my old (10 years ) 60 lt Evakool fridge in my new boat, the boat has a generic battery set up and I would like to put a duel battery system ( my 2 year old gel deep cycle 100 amp hour ), with these specs Alternator (Electric Start) 44-Amp (554 watt)
Battery Charging Power 35 Amp for the out board would a 75 hp keep up the charge to the battery over a week or so, taking into account that in the evenings I can put the fridge on a gen set most times.

Thanks in advance

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Reply By: Member - Scrubby (VIC) - Tuesday, May 21, 2013 at 18:59

Tuesday, May 21, 2013 at 18:59
G`day Phil,
Only being a self eddicatid bush 12 volt sparky this is what I reckon.
I may well be wrong.
Others may explain it better.

Depending on how long the outboard is running, and at sufficient RPM, its inbuilt charger will replace up to approximately 35 a/h per hour of running.

The fact that the motor is 75hp is basically irrelevant, it is the output of the alternator in the amount of amps to the battery multiplied by the amount of time it`s running.
The amps will vary for several reasons so the "35 amp" figure is the maximum obtainable.

A clamp meter to measure the actual amps will assist, and a volt meter to determine the level of charge of the battery is important.

There are too many variables to give an answer, it will be a matter of trial it and measure.

AnswerID: 511535

Reply By: gbc - Wednesday, May 22, 2013 at 06:06

Wednesday, May 22, 2013 at 06:06
A couple of hours running during the day plus a genset as backup is verging on overkill. Being a new boat, I wouldn't trust the dealer setup as far as I could throw it, and have an auto sparky check the charge/isolator system off the motor as a matter of course.
I have the same fridge and run a twin battery system in my boat with a manual isolator. I use one battery for the boat, one as a house battery. I only recharge the house battery when underway, and the boat battery is happy. I've never run the fridge like that for more than 2 days, but the smart guages tell me I could go pretty much indefinitely. My 135 h.p. probably puts out a little more current too though.
AnswerID: 511554

Follow Up By: Aussi Traveller - Wednesday, May 22, 2013 at 06:56

Wednesday, May 22, 2013 at 06:56
HI gbc

I got the specks off the Honda web site, I was going to use a isolator as well, where we go we is a private area on the coast and we can use a gen set without disturbing the peace so running a lead to the boat wouldn't be a problem.
I was thinking it would be ok but thought there was no harm in asking, as my mechanic always says I shouldn't touch electrics. LOL

Thanks Phil
FollowupID: 789821

Follow Up By: gbc - Wednesday, May 22, 2013 at 07:07

Wednesday, May 22, 2013 at 07:07
We must have the same bloody mechanic! I am banned from playing with electric string as well :(
FollowupID: 789822

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