How to test a voltage regulator

[mike.smith]

How would I physically go about testing the AeroVee voltage regulator? I suspect mine might be bad, but I have no idea how to check. I know almost nothing about using a multi-meter other than checking continuity, so if anyone can tell me how to test, and what values I'm looking for, I would appreciate it.

[n982sx]

Just curious as to what makes you think it may be the regulator.

I don't have a method for testing, but by recording the voltage levels for a whole flight, (it looks like you have an EFIS that will do this) you may be able to better describe and then diagnose your issue.

If you have a plot of voltage levels during your flight, post it here and maybe we can help.

[radfordc]

I once saw low voltage indications on the EIS and thought it was a bad VR. Turned out to be a loose/dirty battery connection.

[gammaxy]

I don't think you'll get far with just a multimeter. You might be able to connect a variable power supply in place of the alternator, but I haven't tried it myself so am hesitant to say exactly what I'd do.

I believe our regulator uses a design similar to the one in the following patent:
http://www.google.com/patents/US4220909
Notice how one of the alternator outputs is directly connected to + on the battery, just like in our application.

Apparently, small engine repair guys have the equipment to test these types of regulators, so you might call around and see.

[mike.smith]

Just curious as to what makes you think it may be the regulator.

I have a 30 amp fuse on the 10AWG wire from the voltage regulator to the + terminal of the battery. Twice it has blown, most recently on a runup yesterday. There are at least 2 things that can do this: a bad regulator or a bad stator (though one of the jobs of the v.r. is to stop power surges from getting to the battery). The stator is brand new. Since a regulator is essentially a couple of diodes, a multimeter should be able to test if the power is being allowed to flow in one direction only. It's a starting point. As soon as I started the runup I began to notice the voltage decreasing. After I found the blown fuse that made sense, since no power was getting past the blown fuse.

[gammaxy]

Here's what I believe is likely the schematic (or close to it) of our voltage regulator. The actual schematic doesn't seem to be published anywhere that I can find, but this one seems to work with the same style alternator and has one alternator lead directly connected to the battery just like ours.



It's a little more complicated than a couple diodes inside, so the best I think you can do with a simple multimeter is probe the alternator inputs and measure the resistance. A simple resistance measurement between the alternator inputs should be infinity because the voltage drop of diode 32 will prevent any current from getting through. Your multimeter might have a diode mode, but off the top of my head, I'm not sure what that does when measuring through a diode and resistors 22 and 24. Likewise, the current between case ground and the alternator inputs will also be infinity.

If you had a variable power supply, you could connect it in place of the alternator (12) and measure the current it delivers as you crank the voltage up. Should be 0 until around .7volts where it will be basically the current through resistors 22 and 24 (milliamps?). That will tell you those 3 components are working correctly.

I think you can simulate your airplane's electronics by connecting a multimeter in voltage mode between the voltage regulator's case ground and where you typically connect the battery (the tab that connects to one of the alternator wires). To be super realistic, you might use a light or something that draws several amps between the multimeter probes (to simulate actually running things in the airplane). Now, as you crank up the voltage on the power supply, the voltage on the multimeter will indicate the same voltage as the power supply until you cross ~14 volts or whatever the charging voltage is set as. Then it should stay constant while the current delivered by the power supply continues to rise (and the regulator heats up), showing the path through circuit elements 34,28,30,and 20 is working.

Of course, all this should be done with the regulator not connected to the airplane.