Ammeter acting funny

Barber31

Barber31

Well-known member
I searched on how to polarize a generator because I was suspicious that maybe that's what it needed. The ammeter seems to work because it moves when lights are on or starter is engaged. The only 2 problems are when the engine is running the needle is just bouncing back and forth non stop. With the engine off I can turn the headlamps on and the ammeter shows a charge. I touched both ends on the diode cutout but it didn't seem to do anything. I actually touched them 3 or 4 times and it stayed the same. Any ideas ?
 
I agree with Farrell. If it shows charge with the lights on and the engine off, the ammeter is hooked up backwards. I suspect that there are other problems with the generator as well. A weak brush spring or an out of round commutator on the armature will cause the needle in the ammeter to bounce. I would clean up the commutator with fine sand paper and undercut the mica between the segments of the commutator with a hack saw blade. You really need testing equipment such as a growler for any serious generator repair work.
 
The ammeter showing a charge with the lights on indicates the ammeter wires are backwards. However, how is the battery connected ? It should be positive [+] ground. How is the diode installed ? Does the generator motor when power is applied ? When trying to polarize is the engine running ?
 
I know I put the wires on the correct terminals because I had the wiring diagram in front of me so I wouldn't think that's it. The system is wired with a positive ground and when I polarized it the vehicle was not running. A search on here said it didn't have to be but if it does I will try that if need be. I'm not sure about the motoring issue. How do I check to see if it does that? And the diode is mounted correctly with the wires connected up front and the gen connected on the back unless there's something I don't know of.
 
The wiring diagrams don't apply to some of the reproduction ammeters. Some if not most venders sell the 26-27 model T ammeter that is negative ground but looks the same as the model A positive ground ammeter. Again, if the ammeter registers charge with the engine off and the lights on, the ammeter is connected backwards. To motor the generator, the fan belt needs to be removed or loose enough that the pulley can turn without trying to turn the water pump and engine. Touch a hot wire from the post on the starter switch to the terminal post on the generator. If you make a good connection, the generator will turn like an electric motor if the generator is good. If the internal ground from the field coils are reversed , the generator will motor backwards but won't charge.
 
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I would suggest that you reverse the wires on the ammeter anyway, even though you followed the diagrams, because it isn't hard to do and might fix the problem. The bouncing ammeter needle can also be cause by loose wiring. Make sure you're wires are tight everywhere in the charging circuit. Purdy's suggestions about the generator are also good. If the brushes are not making good contact the needle will be erratic; look at the spring that holds the brushes against the armature. You might also have a cracked brush.
 
Alrighty. Good to know about the ammeter. Ill definitely do that then. So when I try to motor the gen, how will I know if its going backwards? So let's say I switch the wires on the meter, it should now be operating normal. So when I motor the gen if its operating normal it should show a charge? If its not operating normal and going backwards it will show a discharge? Is that correct?
 
The generator should motor in the same direction that the engine turns when it is running, it should motor in the clockwise direction. Reversing the wires behind the ammeter won't reverse the direction that the generator motors. The reason that I mentioned the direction of rotation was that the generator can motor but still not charge if the internal connections at the field coils is reversed.
 
Barber31 said:
Alrighty. Good to know about the ammeter. Ill definitely do that then. So when I try to motor the gen, how will I know if its going backwards? So let's say I switch the wires on the meter, it should now be operating normal. So when I motor the gen if its operating normal it should show a charge? If its not operating normal and going backwards it will show a discharge? Is that correct?
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Yes, driving with nothing on, to the right, with the headlights on, to the left
 
I have been having battery issues as well. My new exide battery never seems to get charged which i assumed was because of the gen not polarized but this last time my brother charged it for me, as soon as I put it on it was acting like it was drained. The following morning it wouldn't even move the starter. It only had enough to turn on lights. And I didnt leave it connected overnight so the car couldn't have drained it. I've been using a jumper box to get her started lately. Today ill pick up my charged battery and try the reverse wire thing.
 
If you are sure the ammeter is hooked up correct, check you terminal connection.
Using an analog voltmeter check how much your generator output is.
 
The no start problem was a false alarm. It was a bad connection at the starter switch. I got the fully charged battery to crank it and I switched the terminals so the ammeter reads correctly now. The needle is still jumpy and I'm not sure if the battery is charging so ill try to do those gen checks.
 
To check for charge, with the engine running at enough rpm for the generator to begin charging, you can loosen and quickly remove the negative cable from the battery post and if the engine continues to run, the generator is charging. Only do this for a few seconds or damage can occur. If you are running a can style regulator don't try it.
 
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