1989 MerCruiser 3.7L Over-Charging Problem

[Barkentine]

Doing some searches and reading on this forum about the OEM alternator (MC #6231A10, with volt reg. #99502A9), I have not come across an over-charging system.

Connecting a multi-meter to the battery indicates 14 - 14.5 VDC at idle (700 RPM).

At 1,500 RPM the volt reading goes to 16-17 VDC. This is too high and will probably damage the coil, points, condenser, etc.

Any feedback on this one? And what would be the fix?

New or used OEM regulators are a source of "sticker price" shock.

I should probably make sure the regulator is wired properly, but don't have a diagram.

Thanks ahead of time for your help.

 

[Scott Danforth]

I would assume your regulator went belly up.

 

[Bt Doctur]

The reg most likely went bad and you will overcharge everything. You do not have a traditional alt system. You have a stator system. A series of coils with rotating magnets to generate AC voltage that is rectified and regulated to 12 volts.
Some have used Harley Davidson rectifier/regulators that are used on the larger machines. The AC output is about the same and the max Amps output is around 30. Wire hookup is simple. The yellow wires from the reg go to the input wire of the motorcycle reg and one wire to the battery
Breezeworks has a standard GM alt conversion for those motor and is the best way to go.

 

[QBhoy]

If it’s the standard system...on that engine it’s a stator and rectified system. One of the many weak points of that engine. There is an alternator conversion kit. We did it with a friends 3.7 the other year. Really simple to do.
Perhaps you already have this, when you refer to a regulator ?

 

[muc]

The 3 times I have seen this in the past it was the stator.
2 of the times the customer didn't pay attention to the volt gauge and the batteries blew up ----- big mess to clean.
Ohms test the stator. Pay close attention to either of the yellow wires being slightly shorted to ground.
If you got sticker shock on the voltage regulator, the stator isn't any better.
​​​​​​​The alternator conversion kit will start looking pretty good.

 

[Barkentine]

Thank you for the responses.

The ohm test on the stator and the regulator indicate both are good, as far as those checks go.

02Mar2018 Ran ohm tests on voltage regulator per info from iBoats.com:

***********THE TEST PER FORUM:

The left connector and middle-right connector should have yellow-red leads, these are the two wires going to the stator.

If you have an ohm meter, check resistance between these two leads

(while disconnected from the regulator).

If resistance exceeds 1 ohm the stator needs replacement.

Also check resistance between each of the yellow-red connection studs

and the regulator case (dm comment: or ground) with an ohm meter,

replace the regulator if either reading is near zero.

**********
Results:

Ohm resistance is ZERO thru the stator: (Ohm meter connected to yellow leads.)

Ohm meter between stator posts and ground: No continuity, no reading. Okay.

Both these checks indicate the voltage regulator is good. But apparently, there may be something else wrong.

Checked for continuity between red wire on top of regulator and where the red wire terminates at the main engine connector, near the trim solenoids.
No resistance, good continuity according to the ohm meter.

Plugged everything back up, turned on the water and ran the engine.

Checked battery voltage soon after start-up: 13.6 VDC at idle: This is good.

Checked voltage at battery at approx. 1200-1500 RPM: 14.0 VDC. This is good.

Ran engine for (5) minutes and rechecked voltages at battery:

13.5 VDC at idle: OKAY.

16.5 VDC at 1500 RPM: Too high.

*******
It appears the problem has to do with temperature in the regulator or stator.
After 15 minutes of running the engine, the battery was not warm at all. I expected it to be, but it wasn't.

I plan on looking into the H-D fix. The conversion looks like the way to go, though.