Question about polarizing

54robbie · May 26, 2019

I have a MF 35 diesel with a 12 volt positive ground system. The generator has 2 terminals which have no markings. One is a small tab and the other is a much larger tab both on the back end. It has a VR that is buried in behind the console. I had the gen. rebuilt. When running it charges fine. When not running it kills the battery. Do I need to polarize the gen and what is the proper procedure?
The only reason for rebuilding the gen is that the bearing seized otherwise everything was working fine.

teddy52food · May 26, 2019

No need to polarize if it charges fine. The points in the cut out are stuck closed causing the dead battery.

54robbie · May 26, 2019

Is that why my ammeter shows a discharge when not running?
How could this suddenly happen when everything was working fine?

M-MAN · May 26, 2019

Replace the voltage regulator. You could
polish the points inside but that's a
band aid.

John T · May 26, 2019

If its charging its likely already polarized properly. HOWEVER when it shuts down the Cutout portion of the Voltage Regulator is supposed to open otherwise the battery discharges rapidly and the genny will get hot. I suspect a sticking cutout relay if it discharging fairly fast. If the belt were real loose or removed and the cutout relay is stuck closed upon shutdown the genny will spin.

John T

John T PS · May 26, 2019

To answer your question (but see my post below) to Polarize a Generator: Do that BEFORE starting.

1) If you have easy access to the VR use a jumper wire to momentarily flash/jump from the BAT terminal over to the GEN/ARM terminal and you should get a small spark.

2) If you cant get to the VR but can the genny, use a jumper wire to momentarily flash/jump a hot ungrounded battery voltage source (such as its ungrounded post) direct to the gennys ARM post.

On many gennys with two base insulated posts out the side where wires from the VR attach (Im NOT talking about a case ground stud) the bigger post is ARM and the smaller is FLD.

John T

JMOR · May 28, 2019

(quoted from post at 11:04:40 05/26/19) Is that why my ammeter shows a discharge when not running?
How could this suddenly happen when everything was working fine?

t was likely working fine before it was removed and replaced. Then when replaced, it had been polarized opposite the previous polarity and upon starting the cut out closed with opposing voltages and the resulting arc and current welded contacts together. Polarization is fine now but VR, not. Note inJohns instructions. "Polarize BEFORE starting".

JMOR · May 28, 2019

(quoted from post at 09:42:10 05/28/19)

(quoted from post at 11:04:40 05/26/19) Is that why my ammeter shows a discharge when not running?
How could this suddenly happen when everything was working fine?

Click to expand...

t was likely working fine before it was removed and replaced. Then when replaced, it had been polarized opposite the previous polarity and upon starting the cut out closed with opposing voltages and the resulting arc and current welded contacts together. Polarization is fine now but VR, not. Note inJohns instructions. "Polarize BEFORE starting".

54robbie · Jun 1, 2019

Thanks for the help. Tough lesson learned. The cut out contacts were welded.

Question about polarizing

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teddy52food

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JMOR

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54robbie

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