1972 Johnson 50ESL72c charging issue

[RCAUTO]

Hello all, Iam a new boat owner of the 30 year old engine (1972 Johnson 50hp 50esl72c), thanks to a relative. I dont know whether it is charging or not. I took a reading with a volt meter at the battery, in the water, at over 3500rpm. It showed about 12.6 volts. Didnt seem like enough. I took the rectifier out and checked the ohm reading both ways on each lead. ZERO / ZERO No reading with either polarity on all three leads. Sooo I bought a new rectifier. It tests ok with about 1.5 - 7 on way on each lead and zero reading the opposite. When I put this new rectifier on my motor, started the engine for a brief moment, I still got about 12.6 volts at the battery. The book says to test with the propellor in the water but I dont know what difference that would make. But ... thats why Im here, I KNOW NOTHING. smile!!

 

[Barnacle_Bill]

Re: 1972 Johnson 50ESL72c charging issue

You won't see much of an increase until about 2K RPM. You don't want to do that high very long with just muffs.

 

[phatmanmike]

Re: 1972 Johnson 50ESL72c charging issue

go to radioshack, throw down 3 dollars, and get a 25 amp, full wave bridge rectifier. boom, problem solved. have a nice day.

 

[Seasport]

Re: 1972 Johnson 50ESL72c charging issue

12.6V sounds too low - should be over 13V - but as IB says you need to rev the motor a bit to get the full current (& voltage). The reason they say that the propeller should be in the water is that it is bad for the motors to rev with no load.<br /><br />The best way is to check the current directly with a DC ammeter. That alternator shouldn't put out much current. An ammeter which can handle 10A would be OK. You need to put the ammeter in line (series) with the circuit.