Testing the Stator / Rectifier

[bucchb]

I have a 1973 85hp Merc.

I have experience with stators from motor cycles and ski mobiles. Ussually 1/2 the stator is for running the engine, and the other 1/2 is for charging the battery. Do I have this right on an old Mercury?

I ran the boat for about 5 gallons at an average speed of about 30mph, and my battery was down to 90% charge.

If I disconnect the battery, the motor quits. Only tried that one time for fer of an arc. This ussually means the stator is shot?

Someone meticulously recoated the 2 wires from the stator to the rectifier?

I could post some pics on this motor.

 

[Chris1956]

Re: Testing the Stator / Rectifier

If that 850 is truely a 1973 model it will have a single ignition coil and a distributor. The stator's only function is to charge the battery.

Now since you disconnected the battery while the motor was running, and your battery runs down while running the motor means that the rectifer is likely bad. You can buy a merc replacement for $50 or a radio shack 25Amp full wave bridge rectifier for $3. The radio shack product is vastly superior to the OEM, but requires you change the ring terminals to spade terminals. The -DC terminal on the Radio Shack rectifier is grounded. The AC terminals are connected to the two stator wires.

Check the stator with a ohmmeter. There should be continuity between the two stator wires, but no continuity to ground from either wire.

 

[bucchb]

Re: Testing the Stator / Rectifier

Thanks, just tested and have continuity thru the stator but no leakage on either wire to ground.

Let me make sure I understand. The 2 wires from the stator are AC, and inbetween them on the rectifier must be 12V to the battery.

With the Radio Shack unit it is not self grounding like the OEM? There must be a DC / + and - and I obviously connect the - to a grounding point on the engine, and the center wire to the +.

 

[Laddies]

Re: Testing the Stator / Rectifier

Heres the simple OHM test for the rectifier

 

[Chris1956]

Re: Testing the Stator / Rectifier

I think you have it. The two yellow stator wires go to the two AC terminals on the rectifier. One of these is also the signal lead for the tach. The -DC terminal is grounded to the frame of the motor and the +DC terminal is connected to the red wire that goes to the battery amd switchbox.

 

[bucchb]

Re: Testing the Stator / Rectifier

That fixed it, thanks.
Tested according to instructions an it was blown diodes.

Didn't really believe you, that a part from Radio Shack for $3.25 would work, but it sure does. I was able to use the hole for where I think a heat sink could go, as a mount with a small 1" angle bracket.

Thanks again, you really help a lot of people in this forum.

 

[j_martin]

Re: Testing the Stator / Rectifier

That fixed it, thanks.
Tested according to instructions an it was blown diodes.

Didn't really believe you, that a part from Radio Shack for $3.25 would work, but it sure does. I was able to use the hole for where I think a heat sink could go, as a mount with a small 1" angle bracket.

Thanks again, you really help a lot of people in this forum.

The mercury version is a cheap press in pushed into a plate and potted. Way too little heat dissipation for what it's expected to do. Failure by design.

John

 

[Faztbullet]

Re: Testing the Stator / Rectifier

You got lucky!!! That is a battery style ignition and the reason the motor died when cable was removed is that 12vdc was dropped at switchbox. This is sometimes instant death to trigger. Highly recomend that you dont remove cables while running on old or new style systems a system surge can pop a rectifer...

 

[Codeman96]

Re: Testing the Stator / Rectifier

I know this is an old post but thanks for the info on the rectifier. The 3.25 Radio Shack part worked like a charm. Saved me $30.00 basically.

 

[j_martin]

Re: Testing the Stator / Rectifier

I know this is an old post but thanks for the info on the rectifier. The 3.25 Radio Shack part worked like a charm. Saved me $30.00 basically.

More than that. You'll never go back there (rectifier change) again.

John