B7100 regulator test

[nevertoolate]

I'm in the final stages of rehabbing a B7100D and need to resolve an issue with the charging system. At the battery terminals I read the battery voltage only regardless of engine speed. I have 29.8 V AC coming to the regulator which I understand from reading other posts indicates the dynamo is OK. I have 0 V DC when I check from the the regulator output wire to ground. Pretty sure that means the regulator is toast but wondered if I am missing anything.

Thanks in advance.

 

[ShaunBlake]

Something smells fishy. Even though you have a dynamo, it's like an alternator in that it doesn't generate its rated output at idle; the higher the RPM, the greater the output voltage (so the voltage should increase with an increase in RPMs) ... and I don't believe any of these old tractors can generate almost volts -- and dynamos generate DC, unlike alternators, which generate ... drumroll ... alternating current (the AC you've recorded).

As for testing regulator output, I'd want to ask how you performed the test before sticking my foot in any deeper.

 

[kubotasam]

I'm in the final stages of rehabbing a B7100D and need to resolve an issue with the charging system. At the battery terminals I read the battery voltage only regardless of engine speed. I have 29.8 V AC coming to the regulator which I understand from reading other posts indicates the dynamo is OK. I have 0 V DC when I check from the the regulator output wire to ground. Pretty sure that means the regulator is toast but wondered if I am missing anything.

Thanks in advance.

You seem right on target. The dynamo should produce around 30 volts AC current at full rpm. If no DC current on the output side then the regulator/rectifier is bad. You did check that the ground wire from the regulator/rectifier is attached and with a clean connection?

 

[North Idaho Wolfman]

dynamos generate DC, unlike alternators, which generate ... drumroll ... alternating current (the AC you've recorded).

Negative on the "Dynamos Generate DC"
Dynamos produce Pulsed AC across the 2 leads.
So 15V per lead and 30V across both leads.
The Difference between a Dynamo and an alternator lies in the Magnetic field. A dynamo uses permanent magnets and an alternator uses an electrically induced magnetic field.

 

[nevertoolate]

You seem right on target. The dynamo should produce around 30 volts AC current at full rpm. If no DC current on the output side then the regulator/rectifier is bad. You did check that the ground wire from the regulator/rectifier is attached and with a clean connection?

I've taken all the electrical connections apart and cleaned them hoping that would resolve the problem. It did not. Thanks for the confirmation.

 

[nevertoolate]

Something smells fishy. Even though you have a dynamo, it's like an alternator in that it doesn't generate its rated output at idle; the higher the RPM, the greater the output voltage (so the voltage should increase with an increase in RPMs) ... and I don't believe any of these old tractors can generate almost volts -- and dynamos generate DC, unlike alternators, which generate ... drumroll ... alternating current (the AC you've recorded).

As for testing regulator output, I'd want to ask how you performed the test before sticking my foot in any deeper.

I could have been clearer, 29.8 V at max RPM output increases with RPM.

 

[ShaunBlake]

Negative on the "Dynamos Generate DC"...
The Difference between a Dynamo and an alternator lies in the Magnetic field...

Blast! I found something I knew a little about, and it was wrong! <blushing>