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1985 50hp Merc Charging?

D

d18

Member
I just bought a 50 Merc, 1985 I think.

I suspected that the battery was not charging,
so I checked the voltage with out the motor
running, it was 12.7v on the meter. When running at
full throttle, it was still at 12.7v.

Shouldn't the voltage be slightly higher when at full Throttle?
 
Re: 50 Merc Charging?

Not necessarily. These are not sophisticated charging systems. Try this: Run the battery down some with a light bulb, measure the voltage, then fire the motor up and measure it again. That will tell you.

Jeff
 
Re: 50 Merc Charging?

I'll try that, but I thought that as you say, they're not
that sophysticated, and that the charging voltage
should be slightly higher than the normal battery
voltage at full charge, 12.8V
 
Re: 50 Merc Charging?

That's about what most of mine do. WHat counts is that it is doing SOMETHING, hence my test.

jeff
 
Re: 50 Merc Charging?

Making "12.7 volts at WOT" and (say) 12. 5 volts at idle is normal charging on old Mercs. Long as the voltage rises--even a 1/10 of a volt--as you rev the motor, it's charging.

We aren't talking about a sophisticated system here! If the alternator puts a few amps back in the motor will run fine and start next time. Hell; I can fire up my 4 cylinder Merc 50 times on a lawn mower battery without any recharging whatsoever.

Merc knew that and, to avoid battery damage, they made the alternator into a trickle charger, which is all you need since most Mercs back then ran without a battery.

Jeff
 
Re: 50 Merc Charging?

I finally got back to the charging issue,
the rectifier was Kaput, replaced it and now
the voltage was 12.7 with engine not running,
and went to 13.2 at idle...perfect...
 
Re: 50 Merc Charging?

Not sure on the 2000 model, but mine was on the starboard side, near
the rear of the engine, a little square block, 2 or maybe 3 of them are
coming from the magneto. I think my Merc is 2 wires, my old Johnson was 3.
 
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