The Ford Barn

daveymc29 · 11-07-2023, 12:23 AM

my amp meter is showing a constant charge, I'd guess about 6 amps, but that is all it does, key on or off, motor running or not, the needle fails to change position. This in a negative ground, 12V set up which I installed to facilitate A/C unit. It worked when I first put everything together and honestly I don't know how long ago it quit, as the engine ran fine and the battery stayed charged. I noticed it at some point and ignored the issue for a couple of years, but now I have installed a new battery and may as well fix it, but, not being electrically proficient I haven't a clue where to begin. I'm running an alternator that puts out plenty of juice for all my elecrical needs, tho the amp needle seems to never feel it necessary to tell me anything. Any suggestions for the electrically challenged?

nkaminar · 11-07-2023, 07:31 AM

Your ammeter is defective. Aside from that, your alternator will charge the battery after you use it to start the car and then not keep charging it like the stock generator will. Your best bet is to install a new ammeter and a volt meter. The volt meter is a better tool to monitor the battery health. Your alternator will charge the battery to about 14 volts when you drive the car and then the ammeter will show zero amperage. When you first turn on the ignition the volt meter will show the battery voltage which should be around 12.6 volts before you start the car.

daveymc29 · 11-07-2023, 03:43 PM

So my amp meter is defective? I thought that and luck has it that I have several. So, short of hooking them up and starting the vehicle, is there a quick test to determine whether they register or not? Jumper wires, or some such?
Thanks in advance

Marshall V. Daut · 11-07-2023, 03:56 PM

Try tapping on the ammeter's glass face with your finger a few times. That often frees up a "stuck" needle and brings it back to the neutral position.
Marshall

rotorwrench · 11-07-2023, 04:30 PM

The meters can be disassembled. If original, it will have the special round slotted brass nuts. I made a tool to remove those. They have a C-shaped magnet in them that fits in the inner circumference of the housing. Like any magnet, it can lose it's residual magnetism. The needle is mounted to a spindle that sets in the frame with rudimentary bearings to support it. Like anything, this stuff can get damaged or wear out. I still see repairable units on flea pay or check the swap meet section.

The needles are very sensitive to movement when in good condition. Blow on one that's disassembled and the needle will move a lot. Jostle it a little and it will wiggle easily.

Herb Concord Ca · 11-07-2023, 04:47 PM

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Dave make sure you install a 30A ammeter. You need the extra range for your A/C.

Paragon · 11-07-2023, 05:28 PM

OK, I have a crazy issue. For my 30 coupe, i'm assembling the dash components on the bench and have installed the NuRex replacement ignition switch and the speedometer. The 30 A amp meter reads "zero" before I install it, but when I place it in the dash and make metal to metal contact, the meter reads discharge 3 to 6 amps (one to two marks to the left). I have a second meter with a scratched up glass doesn't move when I install it. What do you think is happening?

rotorwrench · 11-07-2023, 09:18 PM

There is a process of elimination that can be done to see where the parasitic current draw is coming from. Check your ignition circuit first. There are several ways it can be connected. Alternators can also have diode bridge problems. Brake light switches are another source to check.

nkaminar · 11-08-2023, 08:02 AM

An ammeter, especially a modern replacement, will be effected by a magnetic field nearby. Is there a magnet near the ammeter?

Bob Bidonde · 11-08-2023, 09:01 AM

For a 12V electrical system with an alternator, you need a 30Amp Ammeter.

Badpuppy · 11-08-2023, 09:21 AM

12V system uses 1/2 the current of 6V for the same power. Unless you intend to power a heavy load with your battery with the engine off, a 20A meter should do just fine. In the other direction it should show a battery charge of only 1-2A most of the time.

The ammeter originally was intended only to show if the battery is charging or not.

Big hammer · 11-08-2023, 09:26 AM

Quote:

Originally Posted by Paragon

OK, I have a crazy issue. For my 30 coupe, i'm assembling the dash components on the bench and have installed the NuRex replacement ignition switch and the speedometer. The 30 A amp meter reads "zero" before I install it, but when I place it in the dash and make metal to metal contact, the meter reads discharge 3 to 6 amps (one to two marks to the left). I have a second meter with a scratched up glass doesn't move when I install it. What do you think is happening?

Hopefully your not doing any electrical work with the battery connected !

Paragon · 11-08-2023, 11:22 AM

The dash is on the bench, front facing down and not wired to anything at this time. The speedometer is installed. Could the magnet in the speedo be the source "pulling" the amp meter indicator? Appreciate all the help/responses.

rotorwrench · 11-08-2023, 12:48 PM

The rotating magnet sets inside the drag cup that moves the needle then the whole thing sets inside a steel case. The speedometer magnet would have little effect on the amp meter. The amp meter has it's own internal magnet that is mounted on the needle spindle on the reproduction units. The original C shaped magnets from the model A days were a much better set up.

11-07-2023, 12:23 AM	#1
daveymc29 Senior Member Join Date: Sep 2010 Location: Danville, CA Posts: 1,554	amp meter question my amp meter is showing a constant charge, I'd guess about 6 amps, but that is all it does, key on or off, motor running or not, the needle fails to change position. This in a negative ground, 12V set up which I installed to facilitate A/C unit. It worked when I first put everything together and honestly I don't know how long ago it quit, as the engine ran fine and the battery stayed charged. I noticed it at some point and ignored the issue for a couple of years, but now I have installed a new battery and may as well fix it, but, not being electrically proficient I haven't a clue where to begin. I'm running an alternator that puts out plenty of juice for all my elecrical needs, tho the amp needle seems to never feel it necessary to tell me anything. Any suggestions for the electrically challenged?

11-07-2023, 07:31 AM	#2
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,897	Re: amp meter question Your ammeter is defective. Aside from that, your alternator will charge the battery after you use it to start the car and then not keep charging it like the stock generator will. Your best bet is to install a new ammeter and a volt meter. The volt meter is a better tool to monitor the battery health. Your alternator will charge the battery to about 14 volts when you drive the car and then the ammeter will show zero amperage. When you first turn on the ignition the volt meter will show the battery voltage which should be around 12.6 volts before you start the car. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past.

11-07-2023, 03:43 PM	#3
daveymc29 Senior Member Join Date: Sep 2010 Location: Danville, CA Posts: 1,554	Re: amp meter question So my amp meter is defective? I thought that and luck has it that I have several. So, short of hooking them up and starting the vehicle, is there a quick test to determine whether they register or not? Jumper wires, or some such? Thanks in advance

11-07-2023, 03:56 PM	#4
Marshall V. Daut Senior Member Join Date: Apr 2011 Location: Davenport, Iowa Posts: 2,112	Re: amp meter question Try tapping on the ammeter's glass face with your finger a few times. That often frees up a "stuck" needle and brings it back to the neutral position. Marshall

11-07-2023, 04:30 PM	#5
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,436	Re: amp meter question The meters can be disassembled. If original, it will have the special round slotted brass nuts. I made a tool to remove those. They have a C-shaped magnet in them that fits in the inner circumference of the housing. Like any magnet, it can lose it's residual magnetism. The needle is mounted to a spindle that sets in the frame with rudimentary bearings to support it. Like anything, this stuff can get damaged or wear out. I still see repairable units on flea pay or check the swap meet section. The needles are very sensitive to movement when in good condition. Blow on one that's disassembled and the needle will move a lot. Jostle it a little and it will wiggle easily.

11-07-2023, 04:47 PM	#6
Herb Concord Ca Senior Member Join Date: May 2010 Location: Concord CA Posts: 637	Re: amp meter question Sponsored Links (Register now to hide all advertisements) Dave make sure you install a 30A ammeter. You need the extra range for your A/C.

11-07-2023, 05:28 PM	#7
Paragon Member Join Date: Jul 2017 Posts: 30	Re: amp meter question OK, I have a crazy issue. For my 30 coupe, i'm assembling the dash components on the bench and have installed the NuRex replacement ignition switch and the speedometer. The 30 A amp meter reads "zero" before I install it, but when I place it in the dash and make metal to metal contact, the meter reads discharge 3 to 6 amps (one to two marks to the left). I have a second meter with a scratched up glass doesn't move when I install it. What do you think is happening?

11-07-2023, 09:18 PM	#8
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,436	Re: amp meter question There is a process of elimination that can be done to see where the parasitic current draw is coming from. Check your ignition circuit first. There are several ways it can be connected. Alternators can also have diode bridge problems. Brake light switches are another source to check.

11-08-2023, 08:02 AM	#9
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,897	Re: amp meter question An ammeter, especially a modern replacement, will be effected by a magnetic field nearby. Is there a magnet near the ammeter? __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past.

11-08-2023, 09:01 AM	#10
Bob Bidonde Senior Member Join Date: May 2010 Location: Long Island, NY Posts: 3,470	Re: amp meter question For a 12V electrical system with an alternator, you need a 30Amp Ammeter. __________________ Bob Bidonde

11-08-2023, 09:21 AM	#11
Badpuppy Senior Member Join Date: Dec 2017 Location: Guthrie, OK Posts: 1,145	Re: amp meter question 12V system uses 1/2 the current of 6V for the same power. Unless you intend to power a heavy load with your battery with the engine off, a 20A meter should do just fine. In the other direction it should show a battery charge of only 1-2A most of the time. The ammeter originally was intended only to show if the battery is charging or not.

11-08-2023, 11:22 AM	#13
Paragon Member Join Date: Jul 2017 Posts: 30	Re: amp meter question The dash is on the bench, front facing down and not wired to anything at this time. The speedometer is installed. Could the magnet in the speedo be the source "pulling" the amp meter indicator? Appreciate all the help/responses.

11-08-2023, 12:48 PM	#14
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,436	Re: amp meter question The rotating magnet sets inside the drag cup that moves the needle then the whole thing sets inside a steel case. The speedometer magnet would have little effect on the amp meter. The amp meter has it's own internal magnet that is mounted on the needle spindle on the reproduction units. The original C shaped magnets from the model A days were a much better set up.