Is this normal for an ammeter?

30cabriolet

30cabriolet

Senior Member
With the key off the ammeter shows zero, but when I turn the key to on my ammeter shows a slight discharge. Is this normal?

Background:
I have been fighting an intermittently poor running/stalling/backfiring car for about a week. I changed the carburetor(no help). Got a spark tester and the car would die before I hit 10000 volts. So I changed the coil(no help), I cleaned the paint from the base of the distributor(slight increase in volts), I swapped out the condenser(modern points) and I got a much better spark; although the car/spark was still intermittent. Finally, I changed out the ignition switch and everything seems much better. I now have a strong 20000volt spark, but I still think that I have a problem because the car stumble one time during a test run after all the work.

I noticed that my ammeter does not react the way it did before I did all the work. I have one of Tom's EVR's and the ammeter used to show a good charge after start-up and then it would drop down near zero. Now, when I turn the key, the meter shows a slight discharge and a strong charge after starting, but at idle I now see the meter going negative instead of settling around zero. I am worried that the new to me ignition switch, cutout, or something else may be shorted slightly to ground causing some of my problems. I did run the battery down during troubleshooting and it still may need more charging.

Any thoughts?
 
Yes, it is normal for the ammeter to show a slight discharge with the key on and the engine not running. This is because the points are usually closed and therefore you see the current draw of the ignition circuit. Tom is the expert on his EVR but I would test the battery voltage at the battery with a digital volt meter. If the battery voltage is below 6.35 I would charge the battery and then retest the operation of the ammeter while the engine is running.
 
First put a 3 to 6 amp charger on the battery to bring it up to full charge ASAP. This may take 6 hours or so.

Engine stopped and key on the ammeter should show discharge of 2 to 4 amps ONLY if the points are closed, otherwise the ammeter should remain at zero.

The ignition switch connects the coil ground side primary to the points if you have it wired the original way. Check to see if one or both of the switch terminals are touching the gas tank. This has happened to me and others when a repro switch is used. With an original popout switch, if you still have the original wire inside the steel cable, it may be shorting to ground due to bad insulation.
 
I will charge the battery as soon as I get home today. I will also look to see if the points are closed or open and if it makes any difference on the discharge. This is an old repro switch that may or may not be any good, but I did cover the terminals on everything when I had the instrument panel off yesterday.

Tom, is there any problem when the meter shows discharge at idle with the EVR?
 
Its easy to tell if its the points causing the current draw with key on... move the spark lever and you will see the opening/closing of the points on the ammeter. I have an EVR and at idle it shows just a tich above zero on the ammeter. Once the battery is charged, the ammeter goes back to almost zero, no matter what the RPMs are. If you look real close you can see that the meter is slightly positive. I haven't used a digital ammeter to actually see for sure how much its charging but my battery stays up real nice so no reason to worry about it. As soon as you hit the horn the meter jumps negative then centers while the horn is running, then positive for a few seconds after you release the horn button, then back to just above zero.
 
rusted said:
What is this evr you guys keep talking about? Where can someone get one?
Click to expand...

GeneratorEndPlate.jpg


There are three of us that I know of making voltage regualtors for the Model A and B generators. This shows the one that I make and sell.
The upper right is just an exploded view of the adjustable brush holder parts, as pictured below it. You remove the adjustable brush and it's holder and screw the EVR in it's place. You can send me a PM for my address or more information. Thanks
 
I have the one from Mac's that looks like a cutout. Tom's looks like a better idea though....
 
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