83 Mercury 35hp outboard, charges but not much

[Commerce Steve]

Bought an old pontoon with an '83 35hp Mercury outboard a couple years ago, runs and starts ok but battery will run down after about 4-6 weeks of use during the summer.
If I take it out at night and use the running lights it will run down much quicker. Charges but not much, bought a new battery last year but didn't really help.
What are the most likely causes of this?
Was thinking maybe dirt corrosion on the magnets/pickups but I read about some issues here with regulators and rectifiers.
New to working on outboards so any help would be greatly appreciated.

 

[Barnacle_Bill]

Check your charging output. With the motor off, the battery should read at least 12.6 VDC. Start the motor and slowly increase the RPMs to about 2000 RPM. Voltage should go up to 14-15VDC. You will get very little charging at low RPMs.

 

[Commerce Steve]

Thanks, assuming I should check this at the battery connections where I checked the battery voltage?
Will need to get after this on the weekend when I have some daylight to work with,

 

[Chris1956]

Yes, put the voltmeter on the battery and note voltage. Now start motor and rev it to 1500 RPM or so. The voltage should rise.

That motor likely has a 6Amp or 9Amp charging system. Your running lights could use that much current or even more. If you use more than the motor puts out, the battery will discharge.

 

[Alumarine]

Are you running a sound system? They can draw a lot too.

 

[merc850]

Put the VM on the bat. and then turn on your usual loads and note the V drop then turn them off and see if the V returns to unloaded V, just to see if the battery is good. Fix the problem and switch to LED running lights - they are way brighter and you can leave them on for 24 hrs and not dent the bat voltage.

 

[Barnacle_Bill]

BTW, do not exceed 2000 RPM with just the muffs on. You can ruin your day big time.

 

[Commerce Steve]

OK,finally got her up and running, 12 VDC at battery, when running at approx. 1500rpm( no RPM gauge), still 12 VDC at battery connections.
Got a fly wheel puller, wondering do I start at the fly wheel and pick ups and work my way to the battery? Looking to try the easiest/most likely causes first.
Electrical diagnosis is my weakest area.

 

[MH Hawker]

i would do that last, first test the rectifier and see if you have voltage from the stator, you should have 13 plus AC volts from the stator going in the rectifier then 13 plus DC out

 

[Commerce Steve]

Got nothing going into the rectifier. Fly wheel time?

 

[Commerce Steve]

Looks like the next element in the circuit is the "switch box", it is under the fly wheel. How so I test that with the fly wheel off?

 

[Barnacle_Bill]

Switch box has nothing to do with it. Have you tested the rectifier?

 

[Commerce Steve]

With the engine running at rpm, I have no voltage going to the rectifier. Looking at http://www.marineengine.com/parts/m...ifier-and-wiring-harness-electric-only.Trying to figure out what is next?

 

[Commerce Steve]

Latest update, figured out that I tested the input to the rectifier incorrectly, with engine at approx. 1500RPM,(no tach so not sure) getting 11 V AC to the rectifier. Seems low, anyone know how much the voltage should be?

 

[Commerce Steve]

Anybody that needs to work on older outboard electrical should check out http://www.cdielectronics.com/ ! They have an awesome troubleshooting guide that is free online. All older models and up to recent model years. Great for some one electrically challenged like me.