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Old 06-25-2010, 04:12 PM   #1
jzmuda OP
JZ
 
Joined: Jul 2008
Location: Sandpoint, ID
Oddometer: 66
Voltage Regulator Alternator Check

As some of you may recall I have been having some electrical issues as described in the following thread:

http://www.advrider.com/forums/showthread.php?t=584397

I have gone through my entire wiring harness and think I have corrected all harness related issues. After replacing my starter relay (which was horribly corroded inside) I show no voltage drain on the system when the ignition is switched off.

I just dropped 90 bucks on a new Panasonic battery so I wanted to check that my alternator and regulator were functioning properly. I turned to my "sometimes trusty" Clymer manual for advice.

In the manual it directs you to disconnect the B+ terminal on the diode board and measure between the B+ terminal on the diode board and the D+ post on the alternator brush assembly. The reading should be between 13.5 and 14.25 with the engine running a little above idle.

My reading is about 0.5 volts.

If the reading is low (as mine is) the manual directs you to inspect the alternator.

Not knowing how to check the alternator (and no guidance in the manual) I performed the following.

If I measure the voltage on my battery with the engine turned off the voltage is about 12.67 volts. If I start the bike, the reading is about 13.5. If I disconnect the B+ terminal and measure across the battery with the bike running the voltage is about 12.5 (because it is running as a total loss system). This all seemed reasonable.

Any ideas why my reading from the B+ terminal to the D+ post could be so far off? Or, any guidance on doing a better alternator check?

I've had cases where my Clymer manual led be astray in the past, so I wanted to check with the experts.

Thanks in advance.

J
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1985 Honda Magna (first bike) 98k miles
1972 Kawasaki H1 engine - cafe modification
1997 Ducati
1983 Suzuki DR 250
BMW R65 (modified - wants to be GS)
1973 Bridgestone TMX100 ("my wifes bike")
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Old 06-25-2010, 04:34 PM   #2
bpeckm
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Joined: Apr 2008
Location: Road Island
Oddometer: 5,705
It sounds as though your alternator is putting out... the diode board is there to "rectify" the alternator output into a battery-friendly dc current.

Not sure about your D+ reading, but the fact that you are getting above 13 volts while the engine is running indicates that the alternator is, in fact, putting out.

The voltage regulator is what controls the current going to the alternator field, thus the out put voltage.... if I were you, I would do the following:

1. Check battery with everything off. Should be just above 12 vdc.
2. Start engine, check battery voltage at idle.
3. Slowly rev engine, and keep an eye on voltage readings. Should go up to perhaps 13.5 volts, but not a lot higher than that.

Ideally, you want the voltage to come above the static voltage (engine off) when the engine speed is slightly above idle. As you rev the engine, the voltage should go up, BUT, never really beyond a certain point in the low-13v range, regardless of rpm.

The voltage regulator has three posts: one is battery + voltage, one is battery -, the third one has a variable output. You can test your alternator output by "jumping" full battery voltage to the "variable output": this should peg your alternator output, even at idle. (Do not do this for long, as the battery and other electrical things will not like 14+ volts that you might see...)

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Old 06-26-2010, 06:06 AM   #3
jzmuda OP
JZ
 
Joined: Jul 2008
Location: Sandpoint, ID
Oddometer: 66
Ok. Thanks for the thoughts; this gives me a little peace of mind. I think I might just do a bench test on the regulator; call me chicken.

Has anyone successfully done the procedure in the Clymer manual and had success? I'm still curious about my results being so far off.

J
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JZ

1985 Honda Magna (first bike) 98k miles
1972 Kawasaki H1 engine - cafe modification
1997 Ducati
1983 Suzuki DR 250
BMW R65 (modified - wants to be GS)
1973 Bridgestone TMX100 ("my wifes bike")
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