How to bench test voltage regulator?

[ScoopMan]

Is this possible with a digital multimeter and nothing else? My dmm has a diode setting, and I get a voltage drop between the red lead on the Marelli VR and its case no matter which way I connect the test leads. Same deal when I switch the dmm to ohms. Shouldn't the current only flow in one direction? Every other way I hook up the leads, green to case (and vice versa), green to red (and vice versa), I get an open circuit.

I have been googling away and the bench tests I find require a variable voltage source. I guess I got the cheap entry level 'Mr. Science' kit because I do not have one sitting around. Then again I might try to dig out my old model train transformer and see what kind of voltage that sucker cranks out...

Any quick and torment free ideas? Thanks in advance....

[vandor]

If you install it in an alternator most auto parts stores can test it.

[majicwrench]

Best test is on car with engine running. Why try to bench test it?
Keith

[ScoopMan]

Keith, I DID test with the car running, and the charge light on the dash never turned on, and the voltage at the battery never increased. The bulb is fine, and there is no lack of continuity from the exciter wire to ground. Seemed easier at that point just to take the alternator out to try to find out if it is the VR or the alt. I have a reman alt sitting here that I am comparing it to. If it is only the VR, I can get a new one for $10 and get back my $ for the reman alt. Plus, the dumb thing came without a pulley, and it is a Bosch, while the old one is a Marrelli, so there are some differences with the casing.

[majicwrench]

I'm thinking you must have the old VR on the firewall system?? If so, have you checked for voltage at terminals key on engine off??
Not sure what you are testing, the exciter wire probably shouldn't be grounded.

YOu can rig up a bench test for almost any kind of regulator, you just mimic the arrangement under the hood.
Keith

[ScoopMan]

The VR is on board the alternator. As far as the exciter wire, I set my multimeter on ohms and connected one lead to the connector on the exciter wire and the other to ground. I got measurable resistance, which I assume is the bulb, so I am assuming that is OK.

Anyway I just tested the alt with a new VR, and I get voltage drops no matter how I switch the leads, so unless the new VR is bad, I am guessing some diode in the alternator must be fried.

[Danno]

I'm following this because I posted this week on Mira with a similar question. Initially, the question was about how valid the alternator test at Autozone was if I just take in my alternator. the consensus was that it would be a waste of my time because they are idiots.

The second part of the question was about bench testing the regulator. nobody had an answer other than "checking it's performance while driving is the only real way to know." I can dig that as a solution, but I dislike the idea of using a complex system as a gauge for a part. But then again, I dislike the idea of taking the whole alternator out and finding out that it's not the problem and something within the complex system is messed up. It was suggested that reading volts while driving is important because you don't want to 'splode your battery, nor do you want to get a dead battery while away from home. Obviously, one good way to check this is one of those cigarette lighter voltage meters.

Anyway, continue on. I'm back to observing your thread to see where you go with all of this...

[ScoopMan]

Well here is a typical easy bench test
http://www.youtube.com/watch?v=rWl9Ejiyyxw

The on board test with the car running IS very easy, but it did not give me any final answers, so I had to start taking things apart...