how to test a generator

jacob smith

jacob smith

Senior Member
I am adjusting my 3rd brush on my 36 ford. I what to find out how many amps the generator is putting out. Were should the multimeter be attached to and what should the reading be at idle.
 
You can safely use your car's ammeter to judge amps output. You probably shouldn't try to use a multimeter as an ammeter in the generator circuit attached to your battery since it can alter the overall generator circuit resistance among other undesirable things.

However, you can safely use a multimeter to measure voltage at the generator output terminal or at the battery negative terminal with one multimeter probe on the terminal and the other to ground.

At idle, the current should probably be just slightly charging on the car's ammeter (slightly above 0) with no lights or other electrical equipment turned on.


Jack E/NJ
 
Jacob - The installation instructions for the Fun Projects regulator will answer your charging question. Be sure to follow the instructions to the letter and if you have a good generator, battery, proper sized cables, and good connections, the charging system should work as advertised. I installed a Fun Projects voltage regulator and I used one of their Model T ammeters to set my 3rd brush and I am pleased with the results. After starting with a fully charged battery, the generator puts out around 6 volts and after about 5 minutes of re-charging the battery, the charge rate drops down to and stays at about 2 amps.
 
Does the Fun Projects voltage regulator have any identifying marks on it to differentiate it from a regular Ford script cutout???
 
Peter
No it looks just like the cut out even has ford on it. You can get it without ford on it to save a little money
 
Jacob, Whatever you do don't set the third brush generator output any higher than 15 amps total. This will show as about 12 amps charge on your cars ammeter allowing for the 3 amps drawn by the ignition coil. The generator will not charge at engine idle speed (approx. 500 RPM) but has to be revved up a little. Contrary to what the FUN PROJECTS instruction sheet shows, this setting may not quite cover the draw of the headlights when on, depending on the wattage of the headlight bulbs. So your ammeter may show a discharge of a couple of amps or so in this case. If you set much higher than 15 amps then you risk overheating and burning out the generator armature, which may already be a very old winding and somewhat fragile. Regards, Kevin.
 
I had a problem with my rebuilt three brush generator when I set the 3rd brush to 15 amps maximum on the car instrument ammeter going by the Fun Projects instruction sheet, I burnt out the the 3rd brush contact on the armature as well as the holder, it was lucky this was the only damage I done so I replaced these parts and had the automotive electrician reset the third brush to 10 to 12 amps on his machine,
Apparently you can not set the charging rate on the car instrument ammeter properly as it gives a different reading to an individual reading from a separate ammeter.
 
thanks for the info. We i started the car up after the 24 hours of not being started asper the instructions my charging rate at when i was giving it gas was at 17 so that means i have to adjust the 3rd brush down. The instruction say not to adjust the 3rd brush with the regulator installed. do i need to start from the beginning and install the cut out again to reset the charging rate or can i just adjust the 3rd brush
 
Don't know if it would help you at all but there is a Ford Service Bulletin that specifies various generator maximum amp outputs at a specific rpm. However, would need to know the Ford Part Number of your generator to look it up.
 
Jacob, If you have set your third brush at 17 amps charge on your dash gauge (which may not be an accurate gauge) then you have to allow approx. 3 or 4 amps current drawn by the ignition coil that draws negative on your ammeter, this is what you are forgetting !!. Therefore your total generator output could be 21 amps or more, TOO HIGH !! As I said earlier set your third brush at NO MORE THAN 12 AMPS charge showing on your dash ammeter with the engine revs up somewhat. That then is about 15 or 16 amps TOTAL out of the generator. You should be able to knock the third brush back a little without unmounting the fun projects regulator off the generator. If you like disconnect the negative (power) battery cable first. FUN PROJECTS are just trying to cover their arse so you don't short something out while you are doing the adjustment. All ford V8 generators 1934 to 1938-39 are happy with 15 amps SAFE output and no more. Regards, Kevin.
 
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