Ammeter issue

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Russ T Fender
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Ammeter issue

Post by Russ T Fender » Fri Aug 05, 2022 9:49 pm

The needle on the ammeter on my '27 moves to the charge side when the lights are turned on and the engine is off so I reversed the wires but when I reversed the wires the lights don't go on and the needle doesn't move. I put the wires back the way they were and the lights work again and the ammeter still shows positive when the lights are on and the engine is off. Is the ammeter bad? I would assume that if it works with the wires one way it would with them reversed as well. Any suggestions?


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Re: Ammeter issue

Post by TXGOAT2 » Fri Aug 05, 2022 9:53 pm

That's strange. I suspect that the ammeter was wired backwards, and that it also has a loose internal connection. I'd replace it.


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Re: Ammeter issue

Post by MichaelPawelek » Fri Aug 05, 2022 10:04 pm

The reason it registers backwards is that it was probably made for the positive ground Model A. Why it does not work I do not know.


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Re: Ammeter issue

Post by Moxie26 » Fri Aug 05, 2022 10:05 pm

Is your battery installed with a negative ground, or a positive ground??

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Re: Ammeter issue

Post by JohnH » Sat Aug 06, 2022 12:02 am

There is nothing inside the ammeter that will prevent it working only with one polarity. It's just a current shunt which actuates the needle. It should work both ways round, although of course the discharge/charge indication does depend how it is wired. Model T and A ammeters are the same.
Reversing the wires causing it to become inoperative suggests some physical problem with one of its terminals. Particularly with repro ammeters, the terminals can be problematic. Paul Shinn, of Model A fame, addresses this in one of his videos https://www.youtube.com/watch?v=n85WuQa ... =PaulShinn

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Re: Ammeter issue

Post by TRDxB2 » Sat Aug 06, 2022 2:45 am

Is your ammeter an original or a reproduction, would help to know. Since the ammeter is connected in series with the load on the system it measures the direction the current is moving through its terminals. So it is strange that it works in one direction and not the other because its using the same terminals.

Would like to know what the ammeter shows when its connected with the engine running and the lights on and then also with the lights off. By the way what kind of cutout do you have a diode or solenoid?

If its a repro buy another at your local Auto parts or Farm Supply they are only $10-$14. They are all the same ones so it makes no difference there is no ground just need to be wired in the correct direction. But check that you tube video
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TWrenn
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Re: Ammeter issue

Post by TWrenn » Sat Aug 06, 2022 8:11 am

Moxie26 wrote:
Fri Aug 05, 2022 10:05 pm
Is your battery installed with a negative ground, or a positive ground??
Being a model T it better be negative ground!

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Re: Ammeter issue

Post by John.Zibell » Sat Aug 06, 2022 8:31 am

I had a conversation with John Regan several years ago when restoring my 26. Basically these small ammeters for the 26/26 cars at the low price are basically junk. They are not accurate at all. A good one would cost 60 to 70 dollars retail but since the cheapest thing in a model T is the owner they aren't made. Fortunately when setting up the 3rd brush on my generator to work with the voltage regulator John kindly loaned me a good ammeter to set it up correctly. The ammeters for the older cars are much better than the small ones.
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Re: Ammeter issue

Post by Norman Kling » Sat Aug 06, 2022 9:11 am

The correct connections are to have the battery negative ground and the positive goes from the battery positive terminal to the starter switch. At the starter switch on the same side of the switch with the battery cable is a yellow wire which goes to the terminal block on the firewall. From there it goes to the ammeter. And from the ammeter the terminal block and then to the cutout. I have not included all the wires to lights and coil box etc. But have given the direct route from the battery to the generator. Everything else is connected to the wires which go through the ammeter in such a direction that if you are using the battery the ammeter shows discharge but with the generator turning, it shows a charge. Note, depending on how many amps the generator is set to charge, you might show a discharge with the lights on, but less discharge than they would show with the generator not running. Now that I have confused you thoroughly, Hopefully, someone will post a wiring diagram for your year car.
If either the battery is connected backward or the ammeter backward, it would show discharge with the engine running, or charge when the lights are on without the engine running.
The Model A ammeter looks like a T ammeter, however it reads opposite a T and if used, the wires should be reversed at the ammeter.
Norm


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Re: Ammeter issue

Post by TXGOAT2 » Sat Aug 06, 2022 10:08 am

This ammeter must have a bad connection between the terminals and the conductor inside the case. Disturbing the terminals causes the ammeter to fail to function. It may be a cheap, general replacement unit that lacks quality, and it may have been subjected to an overload at some point. The solution is to replace it. The charge/discharge problem is a matter of switching the wires. An ammeter made for a Model T will read correctly as to charge/discharge if the wires are connected correctly. A general replacment ammeter may need the wires reversed to read correctly. As mentioned above, none of the commonly available ammeters that will fit in the later T cluster are accurate. One that is working properly will indicate charge/discharge with reasonable accuracy and will give a general indication of charge/discharge rate. Really cheap ones are no bargain. They are likely to be very inaccurate and failure prone, and may lack the correct current-carrying capacity. They are apt to have poor quality internal construction that is subject to corrosion, dust intrusion, and overheating, even at normal loads.


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Russ T Fender
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Re: Ammeter issue

Post by Russ T Fender » Sat Aug 06, 2022 10:36 am

The battery is set for negative ground and has been in the car that way for years. I have an original Ford cut out and what is a Ford script ammeter but I don't know if it is Model A or Model T. With the engine running the needle does not move but when the lights are turned on it moves to the charge side. The battery is fully charged and on a trickle charger and I crank start so there is no appreciable drain on it when starting. Wiring is as Norm described. I will try to add a picture of the ammeter in case someone can determine if it is correct for a T.
BD42D48C-B514-44C3-BEA2-01840FB5F530.jpeg


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Re: Ammeter issue

Post by Norman Kling » Sat Aug 06, 2022 10:56 am

One possibility could be if the cutout stuck and the battery voltage went directly to the generator when the car was not running, the weakest point in the path would be the ammeter. In that case it would burn out like a fuse. However, I have never heard of one doing that and then showing charge with the lights on. Similar problem could happen if the battery cable came off or became so corroded to open the circuit while the generator was charging The ammeter could blow and if the lights were on, it could blow the light bulbs.
Did you own the car when this change in the ammeter occurred? Or was it this way when you bought the car? If it happened while you had the car, try to think back to what you were doing when you first noticed it? Maybe you can figure out what happened. Anyway, I think the ammeter is shot and needs replacement. But if you can find the cause, you might be able to avoid a repeat.
Norm


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Re: Ammeter issue

Post by J1MGOLDEN » Sat Aug 06, 2022 12:00 pm

Those ammeters are so close to junk that some dealers will not even sell them.

If you are reading 5 amps with a light on and reverse the wires, you may be reading 10 amps in the other direction then.


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Re: Ammeter issue

Post by TXGOAT2 » Sat Aug 06, 2022 2:24 pm

It's possible that it doesn't show a charge when hooked up correctly because the generator is not charging, or that the charge rate is at or below any load from the ignition system. (1) With the engine off, the ammeter should show 0. Turning on the lights with the engine off should cause it to indicate a discharge of several amps. (2) With the engine running at about 1,000 RPM or more, or about 25 MPH in high, the ammeter should show at least some charge. (3) You can often tell if the generator is working at all by running engine at slow idle after dark and turning on the lights, then speeding the engine up to 1200 to 1500 RPM. The lights will usually get a little brighter when this is done. (4) A better way to check the generator is to check the voltage at the cutout terminal that is connected to the car's wiring. With the engine running at about 1200 RPM and the lights off, you should get a reading of 7 to 8 volts or more on a DC voltmeter connected to the output terminal on the cut out (wire side) and a good ground.

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Re: Ammeter issue

Post by JohnH » Sat Aug 06, 2022 7:08 pm

Russ T Fender wrote:
Sat Aug 06, 2022 10:36 am
The battery is set for negative ground and has been in the car that way for years. I have an original Ford cut out and what is a Ford script ammeter but I don't know if it is Model A or Model T.
The T and A versions of these parts are the same thing. Neither the mechanical cutout or ammeter are polarity conscious.

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Re: Ammeter issue

Post by TRDxB2 » Sat Aug 06, 2022 7:26 pm

Russ T Fender wrote:
Sat Aug 06, 2022 10:36 am
The battery is set for negative ground and has been in the car that way for years. I have an original Ford cut out and what is a Ford script ammeter but I don't know if it is Model A or Model T. With the engine running the needle does not move but when the lights are turned on it moves to the charge side. The battery is fully charged and on a trickle charger and I crank start so there is no appreciable drain on it when starting. Wiring is as Norm described. I will try to add a picture of the ammeter in case someone can determine if it is correct for a T.BD42D48C-B514-44C3-BEA2-01840FB5F530.jpeg
An ammeter isn't grounded unless it has an internal bulb that is connected to a switch. AGAIN the ammeter is connected in series (minus to plus) to the electrical system to indicate the current load on the system. The terminals in the back need to be connected correctly such that when the indicator arrow moves it matches the face plate as charging or discharging. So as the wiring diagram goes one terminal is from the generator and the other to the battery. When these connections are correct the arrow should show a negative reading with the lights on if non-led lights are used regardless of the engine running or not. It should show a positive reading with the engine running and the light off.

The ammeters current behavior is an indication that it needs to be replaced. It is likely that something is restricting its movement to the negative side of the scale Replacements are available most everywhere. If not I have repros & originals that I'll be glad to sell you
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Re: Ammeter issue

Post by paulmikeska » Sun Aug 07, 2022 5:32 pm

I found this some time ago and thought that this may be the answer to the junk ammeters. An expensive answer but still an answer. Look to the right side of the page on the top line.
https://www.westach.com/ammeters

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Re: Ammeter issue

Post by John.Zibell » Sun Aug 07, 2022 5:54 pm

paulmikeska wrote:
Sun Aug 07, 2022 5:32 pm
I found this some time ago and thought that this may be the answer to the junk ammeters. An expensive answer but still an answer. Look to the right side of the page on the top line.
https://www.westach.com/ammeters
Have you tried one of these meters? It would be worth the price if accurate.
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Re: Ammeter issue

Post by paulmikeska » Sun Aug 07, 2022 6:01 pm

Westach is a reputable company and I have used their products in the past without issue. I have a small stash of good original ammeters, so I don’t need to buy one of these. If I was, I would call their tec support and ask them about the unit and find out what kind of movement they are using before shelling out that much cash.

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Re: Ammeter issue

Post by John.Zibell » Mon Aug 08, 2022 9:01 am

paulmikeska wrote:
Sun Aug 07, 2022 6:01 pm
Westach is a reputable company and I have used their products in the past without issue. I have a small stash of good original ammeters, so I don’t need to buy one of these. If I was, I would call their tec support and ask them about the unit and find out what kind of movement they are using before shelling out that much cash.
So what type of movement would be desirable?
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Re: Ammeter issue

Post by Moxie26 » Mon Aug 08, 2022 10:21 am

20 - 0 - 20 amp


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Re: Ammeter issue

Post by Russ T Fender » Mon Aug 08, 2022 10:43 am

I had an earlier Ford script larger ammeter that I hooked up temporarily and it worked fine so I guess the ammeter was the culprit. I have another original ammeter in Florida and will replace the defective one with that when I get back to Florida in the fall. In the meanwhile I will just live with what I have as it seem to be functioning except for showing charge when it is actually discharging. Thanks again for all the help.

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Re: Ammeter issue

Post by paulmikeska » Mon Aug 08, 2022 12:09 pm

The original amp meters used a D'Arsonval analog movement.

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Re: Ammeter issue

Post by John.Zibell » Mon Aug 08, 2022 1:17 pm

paulmikeska wrote:
Mon Aug 08, 2022 12:09 pm
The original amp meters used a D'Arsonval analog movement.
Thanks for the information.
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Re: Ammeter issue

Post by paulmikeska » Mon Aug 08, 2022 5:45 pm

If you can live with a 30-0-30 here is a link to one with a D'Arsonval analog movement. I would be tempted to put a 20-0-20 face plate in it and just know that if it shows 10 it is actually 15 amps and so on.
www.nurex.com/30-30-ammeter


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Re: Ammeter issue

Post by Moxie26 » Mon Aug 08, 2022 6:27 pm

Nu-Rex is a quality and reliable company for Model A cars.. and I wonder why they have the 30-0-30 ammeter for the Model A when Ford in production supplied the 20-0-20 unit ??


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Re: Ammeter issue

Post by J1MGOLDEN » Mon Aug 08, 2022 6:43 pm

That is so you can install an alternator capable of providing a 50 amp battery charge.

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