another bad amp guage

B

bobmc

Member
This is for all the electrical professionals out there. I purchased this 1931 slant window last May, 2017. It was restored by a gentleman that has since passed on, no way to pick his brain. It is running a original 6 volt positive ground electrical system. Since owning this car I have gone through 2 amp meters. Both of them were new purchased from a known supplier. They are the 0 to 20 amp scale. When I install the gauge it works fine. Depending on how much I drive the car determines how long the gauge last. The original and the two I replaced all did the same thing. Worked fine when installed, after some service time they stop working. At this time in the off position of the motor the gauge reads -10. Upon starting the car up and increasing the RPM of the motor the gauge never moves to the charge side of the meter. It does move to the o position but never goes to the charge side. Using my fluke multi meter I am able to check the volts at various positions in the system. All is fine and the gen is working as it should. At the dash it reads 7.5 volts with a slight increase in RPM. This reading is taken while the gauge read -10 to 0. Any suggestions would be appreciated Thanks
 
With the car running and the bad amp gauge connected, the gauge shows -10 and touching the Fluke to the terminals on the back of the gauge the fluke registers 7.5 more or less depending on the rpms
 
If you are using an original generator, your description sounds a bit like your cut out on top of the generator is not working properly. If you take the top off and pop the contacts apart with an insulated tool, your amp meter should/might go back to zero. Ernie
 
Don't blow the fuse in your Fluke. It only reads milliamps. But I'd complain to the vendor. With voltage readings all good, I'd say your ammeter is lying.
 
Last edited:
Ernie Vitucci said:
If you are using an original generator, your description sounds a bit like your cut out on top of the generator is not working properly. If you take the top off and pop the contacts apart with an insulated tool, your amp meter should/might go back to zero. Ernie
Click to expand...

7.5 volts indicates the cutout is closed, engine running. If the contacts were welded, the battery would go flat in less than an hour. But engine off, cutout disconnected (wire end insulated!), it should read 0 amps.
 
It is an original cut out. My confusion is with the car running using the Fluke set to volts at the cut out I get the same reading all along the circuit. Starting at the cut out through the terminal block to the back of the amp gauge it reads between 6.5 and 7.5 at an idle.


It seems to me that something is causing the gauges to go bad in a relative short period of time. Taking an old gauge apart (not much to them) all there is in them is a round bar shape magnet. Could something be causing the magnet to lose polarity? or become weakened?


also I have the safety fuse mounted on the starter. When car is parked I pull the fuse. when I reinstate the fuse there is no spark leading me to believe there is no direct short.
 
Does the meter read zero when the fuse is pulled - if so, then you probably have a weak battery. If not, the ammeter is bad.

The ammeter reads only battery charge/discharge current, nothing else.
 
Pulling the fuse or turning on the lights have no effect on the gauge. It remains in the -10 position until the engine is started. with increase rpm the gauge will increase to just below the o scale. Also with the gauge removed from the car in my hand not wires attached it is in the -10 position


I believe it is a defective gauge, my original question is what is making the gauge malfunction after working perfect when installed. After several months of starting and driving the gauge just stops working. This will be the 4th gauge in about one years time.


thanks for everyone taking the time to respond!
 
Since I have the gauge out of the dash now, I have noticed that the parts tray on my bench that has a magnetic base has an effect on the needles movement. Moving the gauge across the magnet will cause the needle to move form -10 to +10. This is what leads me to believe the gauge is now defective. With that being said, it takes me back to a previous question. What would cause the magnet in the gauge to become demagnetized?


thanks
 
While not original but much safer for touring vehicles is to replace the AMP meter with a volt meter. Voltage is a better indicator of battery condition and you are not pushing all the amp. draw through a delicate instrument which can lead to shorts and fires. Leave the org. in the dash and bypass the gauge. with proper gauge wire. Install the volt meter elsewhere.
I have not done this but will consider it if quality AMP meters are not available or a good original gauge.
 
imported junk! possibly someone on the barn can supply you with a original gauge,i have same gauge for 35 years and no problem!
 
OK just a guess here, is it possible you have a wire of high amps near the rear or your amp meter that might be demagnetizing your meter ? I have to agree with Dave a volt meter rather than a amp meter is a more accurate measure of Battery condition, I have changed to a volt meter on every car I owned. Don't forget your test meter is registering in volts and your amp meter is measuring amps naturally. Another thing to try is to run 2 jumper wires to the meter, both ground and hot to see if a defective wire is causing problems for you.
 
Bobm90
That is an interesting thought. The only wire added to the back of the instrument panel is for the exterior dash light mounted above the cluster. It's an armored cable and I am in unaware of the gauge.


I will look at the location of the red wire going to the key switch, if memory serves me correctly ( I am not at the car now) it comes from the coil, which could have a much higher current.


thanks
 
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