Test Generator Voltage Regulator

LSK

Filing Flight Plan
Joined
Aug 23, 2020
Messages
26
Display Name

Display name:
Rowdy
What is the procedure to test a generator VR suing a multimeter?

Problem is the gen light inside comes on dimly sometimes, and goes off and on when landing or hitting a bump in taxiway -
All the wire terminals are tight at the connection - still need to spend some time to verify that the crimps are still tight -
 
What is the procedure to test a generator VR suing a multimeter?

Problem is the gen light inside comes on dimly sometimes, and goes off and on when landing or hitting a bump in taxiway -
All the wire terminals are tight at the connection - still need to spend some time to verify that the crimps are still tight -
Might be that the bulb is loose in the light assembly. Does the light stay off when the RPM is up, as in flight?
 
We had to re crimp a ground that looked fine. Cured a similar problem. Might help and takes seconds.
 
The generator light is connected one terminal to switched battery voltage and one terminal to generator output voltage. It illuminates when the generator voltage is below the battery voltage and the cutout relay (part of the VR) is open. When the generator is at charging speed the cutout relay closes, the battery and generator voltage becomes equal, and the light goes out. That said, I have had three vehicles with generators and idiot lights. The '64 Triumph's light worked properly. The '69 MG's light always glowed slightly. However, the battery kept charged and the electrical system operated properly so I didn't worry about it. Same thing with the '65 C172, light glows dimly but ammeter shows correct operation and battery keeps charged; it has been this way for the past 19 years.
Does your plane have an ammeter? If so, pay attention to it and ignore the idiot light. If no ammeter, you should probably look into the light problem. Start by measuring the voltage drops a) between the VR GEN terminal and the generator output terminal and b) between the VR BATT terminal and the battery positive terminal. Anything over about 0.2V is cause for concern and the source should be located and fixed.
 
It sounds to me like there are possibly two separate concerns. The first is how the generator light is supposed to operate, which has already been explained. The second is that going over bumps appears to be affecting the light, which sounds less like a regulator problem and more like a poor light connection to me.

Does the ammeter show that the generator is functioning properly? Does the battery stay charged? Under some normal conditions the generator light may be illuminated so this should not be an immediate cause for concern unless other charging system problems accompany it.
 
Back
Top