Can an Ammeter be fixed?

[Idaho Brett]

I know reproduction Ammeters can be bought for about $8.00 from the vendors, but I'd like to keep using the one in my Model A for sentimental reasons.

Any way....... My Ammeter will show a charge of 4 Amps with the battery disconnected and the needle is pegged at full charge 20 amps with the engine running at high idle. I put my Multi-meter on it and it showed a 10 amp charge during high idle. So I'm pretty sure my ammeter gauge is wrong.

I tried wiring it backwards to try fixing it by swinging the needle the opposite direction. It didn't fix it.

Like I said before; I know ammeters are cheap enough but can they be tweeked, fixed or adjusted? Or should I just get over it, give up and get a reproduction Ammeter. Thanks.

 

[Tom Wesenberg]

Unless you have an aftermarket electronic voltage regulator you should NEVER run a 3 brush generator with the battery disconnected. When you have an open in the unregulated charging circuit the generator can put out up to 40 volts and cook the generator, as well as blow bulbs.

Where does you meter set with the engine off?

 

[MikeK]

Do not buy a repop POS. Easy fix, next to nothing inside. Straighten needle, recharge ring magnet if necessary, bend adjusting wings inside. Clean and tighten everything. Tom W has some dandy pix in this thread: LINK

 

[Idaho Brett]

Unless you have an aftermarket electronic voltage regulator you should NEVER run a 3 brush generator with the battery disconnected. When you have an open in the unregulated charging circuit the generator can put out up to 40 volts and cook the generator, as well as blow bulbs.

Where does you meter set with the engine off?

I should have clarified that it shows a 4 amp charge with the battery disconnected AND the engine is not running. I get a 20 amp charge with the engine running and high idle. I would not even consider running my engine with the battery disconnected.

Do not buy a repop POS. Easy fix, next to nothing inside. Straighten needle, recharge ring magnet if necessary, bend adjusting wings inside. Clean and tighten everything. Tom W has some dandy pix in this thread: LINK

Thanks for the LINK. I'll give a try.

 

[MikeK]

Could you give more information on bending adjusting wings. I have seen wings on repo ammeters but I cannot find the wings on original ammeters. So far all my original ammeters have been accurate after cleaning and centering the needle.

They swing with the needle. Originals are triangle points that go out sideways from the pivot. Some of the repops have them both pointing down. Bending them closer or farther from the brass shunt affects the inductive couple between the magnetic field of the current passing through the shunt and the emf induced in the needle which reacts against the ring magnet field. Clear as mud?

 

[Tudortomnz]

My original gauge/gage [ but not guage] also gave up the ghost but I did not want to continue using a repro one.
Found an older aftermarket gauge, prised off the rim & glass & put my 84 year old rim & face on it. The latest type repros appear to have the rim bonded to the body.
Now I still have my old worn & faded ammeter to look at.

 

[MikeK]

I understand the shunt effect, but I am not clear on exactly which part to bend, all the ones I have looked at were perfectly flat, I have never seen one with a bend in it. I see a brass triangle and a steel triangle.

The magnetic steel triangles are what need to move. They are actually one piece, kind of shaped like this- < > with the needle pivot through the center. It's been several years, but I believe the brass piece is a clip that holds the aluminum needle to the steel < > and pivot pin assembly.

None of them ever came bent from the manufacturer. Nor were they individually calibrated. Likely a fixed assembly fixture was used to precisely set the height of the steel < > above the base of the pivot pin. To make it read higher I bent the tips of the < > down. It may also be possible to slide the entire < > assembly down/up on the pivot pin, I have not tried that.

 

[bogiediver]

FWIW...

I've attached a couple of PDFs.

'Lazy Ammeter' is a compilation of this thread and the thread linked in post #3, including pictures

'Reading the Ammeter' is info taken from another ammeter thread somewhere along the line (don't remember...)

If you think they help - it was worth it...

If you don't - then disregard...