Question: Testing a generator

Unknown
Unknown
edited November -1 in HUDSON
First off, thank you all for the tips on the 12 volt conversion. So far so good. Park Waldrop sent me a very well researched data sheet from when he did his. I'll add to it as I continue my work. I'm going to experiment with a 6v switching power supply for some of the heavier components, like the radio.



This question seems straightforward, but I just need a reality check.



I have a 12v generator (not altenator) from a late 50s Hudson, which I got on eBay a while ago. It's condition is unknown. It has 2 screw terminals, with a component (perhaps a capacitor) going from one terminal to the body of the generator.



I simply installed this into my car, leaving it electrically detached, and fired up the engine just to spin it. I expected to see some reasonable fraction of 12volts accross the two terminals. Instead I see noise, nothing about 0.10 volts. Maybe the idle speed was too slow.



Did I conduct a valid test? Is this unit bad? And what the heck is the component (capacitor?) there for anyway?



Maybe I should have this thing rebuilt. For that matter, anyone have a known good 12v generator? Maybe I'll just break down and find an altenator that will fit a 308. Suggestions?



Thanks agian;

-Chris

Comments

  • Unknown
    Unknown
    Hudson308 wrote:
    If you can figure out which wire is the "field" wire, this needs to be grounded for the generator to produce. As an added bit of info, the regulator grounds and ungrounds this terminal to turn the generator on and off in response to battery voltage. The other terminal is the armature (output) wire. This may be the the one with the capacitor on it. That would make sense, to clean up the switching noise from the generator brushes.





    So simply spinning up the generator won't tell me if it's working or not, because the field is not grounded. Looks like I either need to run a line between field and the case of the generator, or just hook up the whole system and test it that way.



    I seem to recall on my 6v, there was a tiny F printed in the case. I'll look for that on the 12 v (which I just painted... oops). If I can't see a mark, how else could I tell which terminal is F and which is A? The generator doesn't look very hard to take apart.



    One hint, one screw terminal is larger than the other. Can I assume consistancey between the 6 and 12 v generators? If say the large screw terminal on the 6V is Field, is that the case for the 12v?





    Thanks;

    -Chris
  • Park_W
    Park_W Senior Contributor
    Chris,

    The field terminal does indeed need to have a path to ground for the generator to produce normal output. But be careful ... with the field connected directly to ground, and no load on the generator, the voltage will get pretty high if the RPM is run up a bit. Best to have the engine at idle, then connect the field to ground, then carefully run the RPM up to see if the output voltage comes up nicely to 15v or so, and don't go much further. The armature and field terminal studs usually are of a different size, with the armature (output) terminal being larger. The condenser is for radio noise suppression, and should be connected to the armature terminal. There are strong warnings in the book against connecting it to the fireld terminal, but I've never thought through or read what the result of that would be. As an aside, a quick way to test one of these generators off the car is to connect the field terminal to ground, then connect a battery of the appropriate voltage to the generator, and it should turn at a moderate rate, as if it were a motor. Generator shops typically do this right off, to see if there's anything seriously wrong with the unit. (Note that for most GM/Delco gen's, you short the field terminal to the armature terminal rather than grounding it)
  • MikeWA
    MikeWA Senior Contributor
    If everything is hooked up in the car, to test the generator you have to ground the field terminal (as already stated), but you should also put a jumper wire across the BAT and ARM terminals on the voltage regulator (to take the voltage regulator out of the circuit). Then, the amperage on the amp gauge should increase as the engine RPM is increased, and vice versa. If it does, your generator is good. Then remove the jumper and the ground from the field terminal, and if you still get a charge at the ammeter, your regulator is also OK. If no charge, replace voltage regulator. BTW, the other posts on identifying the terminals are correct- field may be marked with an F; field terminal will be smaller than armature terminal; and capacitor should be on armature terminal (function is to ground out any alternating current produced, which is the cause of radio interferance. Capacitors are a dead short for alternating current, but will not pass direct current).
  • Unknown
    Unknown
    Excellent suggestions! I'll try this out again this weekend.



    Thanks all;

    -Chris
  • Park_W
    Park_W Senior Contributor
    A couple of clarifications on the above ... Mike is using the term "voltage regulator" to refer to the whole regulator "box." Grounding the field terminal bypasses the voltage regulator unit within that box. Shorting ARM to BAT bypasses the "cutout" contacts, to ensure they're not affecting the readings. One more caution would be to not leave the ARM to BAT jumper in place if you shut the engine down. If you do, you're pretty nearly shorting the battery directly to ground, and some wires are going to get hot! Finally, the amount of AC current a capacitor (condenser) passes depends on the frequency of the AC and the capacitance value of the capacitor. It can vary between almost nothing to almost a dead short depending on these two factors.
  • bobbydamit
    bobbydamit Expert Adviser
    One last item is to be careful of is that you don't change the polarity of the generator while doing all this jumping stuff. You won't know it until you shut off the car and take the key out. The points in the regulator will stick closed and the gen. will drain the battery. Just keep this in mind if, when all done, the system drains the battery when off because the battery is now trying to run the gen. as a motor. I know, old car electrical is fraught with gray areas.
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