new brand new voltage regulator/rectifier only gives 8 volts

[astampfel]

I have a 1990, 90 Hp Johnson VJ90TLESB. I noticed that my battery was always dying. So, I checked out the voltage regulator/rectifier and stator using a SELOC repair manual. From my multimeter readings, it looked like the stator was fine but my voltage regulator was bad. My tachometer also seems to be good. So, I bought a new voltage regulator/rectifier. After an arduous process (removing the flywheel, ughhhhhhhhhhhhhhh) I installed the new rectifier. While in the water, I wanted to see if it was working, so I disconnected the batter and hooked up my multimeter. To my surprise, the reading was 8 volts at 4000 rpm! Shouldn't it be somewhere around 12-13 volts? Could my permanent magnets be weak?

 

[ezeke]

Re: new brand new voltage regulator/rectifier only gives 8 volts

You probably cooked the rectifier testing it in that manner; the way to test it is to read the voltage on the battery with the engine off and then while running.

 

[bktheking]

Re: new brand new voltage regulator/rectifier only gives 8 volts

Don't disconnect the battery to test, no load, connect the battery and retest at the terminals with it running.

 

[metriccrescentwrench]

Re: new brand new voltage regulator/rectifier only gives 8 volts

YIKES - don't EVER run an engine with a charging system without a battery connected, it acts as a huge capacitor to smooth out the voltage coming out of the rectifier. Without it the AC voltage can get pretty high, 50 or 60 volts, and that's enough to kill the rectifier.

Nowthen, I'm a EE and I know for a fact that those rectifiers could be built to withstand that kind of voltage, but it would cost a bit more to manufacture. But it is what it is, and we just need to make sure we don't do things like that.

 

[astampfel]

Re: new brand new voltage regulator/rectifier only gives 8 volts

If i leave the voltage regulator hooked up to the battery when I read the voltage with my multimeter, how do I know if I am reading the battery voltage or the rectifier voltage? Should I connect a 12 volt load instead of the battery?

 

[bktheking]

Re: new brand new voltage regulator/rectifier only gives 8 volts

Test it with the battery connected (good battery) running and post the results.

 

[wilde1j]

Re: new brand new voltage regulator/rectifier only gives 8 volts

The voltage (with a good battery) measured across the battery terminals will be what ever the R/R is putting out. Typically with a good R/R, you should see ~ 13.5 to 14 vdc. Don't overthink this. Expensive lesson, don't re-learn it.

 

[astampfel]

Re: new brand new voltage regulator/rectifier only gives 8 volts

At idle, I was getting 13.1 volts. I didn't have time to run it up to 5000 RPM, but I guess 13.1 volts is better than 7 volts.

 

[metriccrescentwrench]

Re: new brand new voltage regulator/rectifier only gives 8 volts

13.1 volts at idle is perfect.

 

[ezeke]

Re: new brand new voltage regulator/rectifier only gives 8 volts

What was the battery voltage with the engine not running? It's the difference between that and the voltage with the engine running that lets you know the rectifier is working. You could easily read 13.1 on a freshly charged battery with the engine off.