How to check for non-working amp meter?

J

Jim Kroeger

Member
I own a '30 Town Sedan and run a 6-volt alternator but it seems like the amp meter is not registering. Everything is hooked up properly but I don't see the needle budge with the motor running. Using my test meter where are the correct points that I should hook up to so I can see if it is the alternator or meter that is malfuntioning? Thanks. Jim
 
Jim,

Keep it simple. With the car not running, turn on the headlights. Did the amp meter turn to the left ?

If so, it's working.

Marc
 
hook up a volt meter at the battery posts or the alternator output terminal and engine head nut. you should read more than battery voltage with the engine running. i have seen bad ammeters that would stick to the neg with car off and lights on, but not to the pos side when running so the best way to ck is with an ext meter.
hold the rpms up to ck
 
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The only way these ammeters can show negative but not positive is physical damage. These aren't thermocoupled.

If the meter moves with motor off and switching lights on/off, then the ammeter works. If not, then it doesn't.
 
Do you have a fairly large 6V battery charger, like 15A or more with a working meter?

1)Engine and ignition key OFF, lights OFF: Disconnect the output lead from the back of your alternator.
2)Attach the (-) lead from the charger to the wire(s) that you just removed from the alternator output stud.
3) Attach the charger (+) to a nut on the top of the cylinder head.

Turn the charger on- look at the charger's meter reading.
The dash panel meter is now passing that same current and should read the same.
 
All good responses. Some people become concerned when they don't see the ammeter needle move quite a bit to the right, as it does with an unregulated charging system. When everything is charged and normal, the needle should be very close to the 0 mark in the center. In a regulated system, as a generator with an EVR, or an alternator, if the needle stays a fair amount to the right, then you need to worry. It could be a bad battery, or a bad regulator.
 
Also, not to insult your intelligence, but are you aware that you must "excite" the alternator by revving the engine to get it to charge before the ammeter will show charge? Or, in other words, just starting the car and increasing the idle a little the ammeter will just sit there and show no change because the alternator hasn't "kicked in".
 
Thanks for all the tips guys on the amp meter. I will try your suggestions to help remedy the situation. Learning as I go. Love the hobby.
 
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