Lazy Ammeter
 

Since everything on my 29 coupe is highly suspect because of the previous owner, I was wondering about seemingly low indications on my ammeter. I've redone the gen. and I'm still getting an output on the guage of only 2 or 3 amps. Question: Can an ammeter actually get worn out? Are my readings correct? I don't want to keep advancing the 3rd brush until I fry something.
Thanks for any comments or thoughts
Peter

Re: Lazy Ammeter
 

Peter J - Your amp reading is too low, and ammeters can wear out. Two areas of wear are: 1) the needle movement (there may be something preventing the needle from full travel), and 2) the ammeter's magnet may be getting weak.

The ammeter is not hard to inspect. First, unhook the battery, next take all the screws out of the dash. , and then unhook and remove the ammeter. The outer bezel or ring is a compression fit and can be removed with gentle taps. Now you can inspect the needle movement for restrictions. As for testing the magnet's strength, that takes more equipment than the average A owner has.

Do you belong to a Model A Club? If so, ask if a member has a known spare working ammeter, and try it on your car. Also, ammeters are not expensive, and you could order a new one from one of the vendors.

Good luck solving the problem,

Re: Lazy Ammeter
 

Before you tear everything apart find an electronics friend with an ammeter (or buy one, cheap ones are about $10) and check the current by removing the wire going to the battery at the starter post and putting the ammeter into the circuit. Remember don't run the car without a complete circuit.

Charlie Stephens

Re: Lazy Ammeter
 

be carefull of the new ones from the vendors they are junk

Re: Lazy Ammeter
 

A cheap ammeter will not work unless it is a anologue one . There is to much interference from the gen to make the digital ones work properly. just my 2 cents

Re: Lazy Ammeter
 

http://i118.photobucket.com/albums/o...AmpGuage-1.jpg

Most of the meters just need to have the cover removed, then use a toothpick and carefully put a drop of heavy oil on each of the two pivots for the needle.

If you take the amp meter completely apart, make sure the magnet goes back the same way it came out. The heavy wire ring is the magnet, and if you suspend it by a thread one side will point north.

Some people solder the studs to the buss bar for a foolproof connection inside the ammeter, but the main thing is to be sure the connections are clean and tight. I made a special wrench to tighten the nuts on the back of the original ammeter. ALL connections must be clean and tight.

If you suspect a bad meter, connect a volt meter across the two terminal box wing nuts. If the terminal box nuts are tight and the 2 wires going to the ammeter are good, and the meter is good, then you should show less than .1 volts. To make this measurement you need current flowing, so turn the engine off and the lights on. Now, what does the voltage read across the 2 terminal box wing nuts? Also, what does the ammeter read?

Re: Lazy Ammeter
 

Hey guys, that's great. I didn't know all that could go on with an ammeter. I was regestering good voltage from the gen. to the cutout and 8v from the batt. side of the cutout. Better not mess with the 3rd brush huh? Thanks for the pics. Tom.
Thanks Again !!
Pete

Re: Lazy Ammeter
 

http://i118.photobucket.com/albums/o.../AmpGuage1.jpg
http://i118.photobucket.com/albums/o.../AmpGuage2.jpg
http://i118.photobucket.com/albums/o.../AmpGuage3.jpg

Here's 3 more pictures with the first 2 showing an original guage, and the last showing a repro guage.

Many repro guages are aluminum, and none of the repro's I've seen have the studs and top half of the bussbar painted flat black. When you look through the slot for the needle, anything you see should be flat black, and not shiney brass.

Re: Lazy Ammeter
 

Sure doesn't look like their's much to go wrong with them. Shouldn't be a problem to check out the spring and solder connections. Great info and more keepers.
thanks Tom

Re: Lazy Ammeter
 

Re only using analogue to check amps. I've experienced no problems checking amps with my digital ammeter/multimeter.

Re: Lazy Ammeter
 

Tom,
On the bench, can I use a VOM? What should the reading be?
Thanks, Dudley

Re: Lazy Ammeter
 

I've got my doubts that the ammeter is the problem. Ammeters can go bad from over charging but what i've seen, they either work or they don't. If adjusting the third brush doesn't change the charging rate, the brush wires are reversed. It will motor and charge even if the brush wires are reversed but adjusting the third brush will make no change in the rate of charge. look at the left lower corner of page 66 of the new Brattons catalog for the internal wire hook up legend for the tube type model A generator. If the wires are reversed, like I suspect, it will burn out the field coils if allowed to operate in this condition for an extended period.

Re: Lazy Ammeter
 

Purdy,

I have a bunch of ammeters(original)that I'm restoring and looking for a
way to test them on the bench....too sort the good from the bad.

Re: Lazy Ammeter
 

Dudley,

The voltage Tom is referring to is the voltage drop across the ammeter due to the resistance of the ammeter "shunt" while current is running through it.

Ohms law....V=IR

Hard to do on the bench unless you have a current going through the ammeter on the bench.

Marc

Re: Lazy Ammeter
 

Purdy, that is what I was thinkin too. Another good posibility to check. Great thread!

Re: Lazy Ammeter
 

Re: Lazy Ammeter
 

I've seen a few generators that had the brush wires reversed by an electric motor shop nearby. When I saw them they would only charge 3 or 4 amps and brush adjustment did nothing. I like generator threads. I rebuild my own tube type generators. I don't know anything about the power house generators.

Re: Lazy Ammeter
 

Dudley, I do just as Mike K. said. I have a quality amp meter and put it in series with the Model A ammeter and put a 10 amp load in the circuit.

I also put a drop of heavy oil, like gear oil, on each of the 2 meter pivot points.

Re: Lazy Ammeter
 

Tom,

Are you saying, use a 10 amp battery charger?
Damn, I don't electricity well...if you catch my drift!

Got a photo or a print?.....if I can see it...I can do it.
Thank you!

* Tom, if it's "yes" to the battery charger...I can do that.*

Re: Lazy Ammeter
 

You can use the battery charger as your power supply, but not as your load. Something like 2 headlamp bulbs would make a good load. They would be about 5 amps each for a total of 10 amps. You could even use a couple metal plates in salt water to make a load for the circuit.