Amp gauge
- Thread starter KarlJS
- Start date
deuce_roadster
Well-known member
With the battery disconnected, take the wires off the amp meter, clean them and put them back on snugly.
GB SISSON
Well-known member
I have two trucks that show charge and discharge, and two that don't. They are all 12 negative ground. I have reversed the direction through the hoops on the back, but am running modern 8 or 10 gauge wire. Is the insulation too good on the modern wire? Hoping this isn't a hijack, but it could be the OP's problem too.
Insulation is not a factor. Is it the kind with 2 terminals or does the wire just go through a little hoop? The force to move the needle is small so any stickiness might keep it from moving but yes, you should see movement in the negative direction with lights on and engine off, if its wired correctly. A voltmeter will tell if the generator is charging the battery.
I understand, like me with major engine or even more scary a transmission. But this ones easy! A voltmeter is a great thing to have around and you can get a decent one cheap. I have a great one and one that was a giveaway somewhere. The latter is so cheap the switch doesnt work half the time. Anyway all you need to do is put it on volts, one lead on each battery terminal. If its just 6V or below, the generator is not charging. You should see something higher like 6.5-7V if the battery needs a charge (Im not sure how the old cutouts work, maybe they shut down the generator when the battery is fully charged but I doubt it, modern alternators keep about 14V across the battery all the time the engine is running.) You will find the voltmeter handy even if you are not an electrical guy.
If the lights are on (with the engine off) and the amp shows no movement, either the amp is shot or the amp is not wired correctly. Except for the connection going to the starter solenoid, the amp should measure all the current flowing to or from the battery. Hence the wire from the battery must pass through the ammeter before it is connected to anything else. If the wiring is correct and your lights work but the ammeter shows no movement, then the gauge must be bad.
V8COOPMAN
Well-known member
Go ahead and wire it up EITHER way ..... you won't hurt it if it's the WRONG way. With the engine NOT RUNNING, turn the headlights on. If the gauge shows a DISCHARGE with lights ON, you got it right. If the gauge shows a CHARGE, reverse the two leads. Easy, peasy!
Coop
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glennpm
Well-known member
Right on Coop!
petehoovie
Well-known member
rotorwrench
Well-known member
Ammeters are connected into the line to the battery from the generator. They take a bypass sample of what is moving through the circuit. Volt meters are connected between a hot wire in a circuit and any convenient part of the ground plain of the car. They don't work like an ammeter.
On a 1939 vehicle, it could have an old 3-brush generator with just a cut out or it can have a 2-brush generator with a 3-pole voltage control unit otherwise referred to as a regulator. The old 3-pole VRs control the system "coming on line function" with a cut out pole and then have the separate two poles for voltage regulation and current limiting.
The old 3-brush only has the battery to regulate it's voltage within a range depending on amperage output. The 3rd brush is manually adjusted to get the proper amperage of output. The generator has to have the pole shoes polarized with a residual magnetic gauss in order for it to generate enough voltage to close the cut out relay so that the generator can come on line. Once it's on line it then generates what ever amperage it is manually set to operate at. The output voltage varies with the amperage output but it can't overwhelm the battery as long as it is well connected to it and the battery is in good condition.
Test an ammeter with some jumper leads and a battery. Connect the battery hot wire post to the discharge side and then connect in a load such as an electric motor or a high output 6-volt light bulb like an old sealed beam headlamp bulb. Connect the ground side back to the battery ground and watch the ammeter indication. It should show a discharge. If it doesn't then find an ammeter that will. A lot of the modern reproduction ammeters have a rare earth magnet on their armature and they can be damaged. Some D'arsonval meter movements can be fried since they have very fine windings. The Model T and A type ammeters had a big semi-circular horse shoe type magnet inside the meter and they could take most of what an old 3-brush generator could throw at them.
The ammeters with the loop are the inductive type. Amperage has to flow one way or the other through the hoop to get a reading. If it doesn't move with high amp discharge or charge then it never will again. It would be time to look for another one or make sure the battery and electrical wiring are good and proper.
If the vehicle has an alternator then every thing depends on it's internal electronic output controller. Voltage output had to be checked with a volt meter across the battery posts. Ammeter readings will only be noticed right after a start till the battery is back to normal state of charge. If the alternator controller is functioning then it may never show a discharge until the engine is at rest with no alternator function.
On a 1939 vehicle, it could have an old 3-brush generator with just a cut out or it can have a 2-brush generator with a 3-pole voltage control unit otherwise referred to as a regulator. The old 3-pole VRs control the system "coming on line function" with a cut out pole and then have the separate two poles for voltage regulation and current limiting.
The old 3-brush only has the battery to regulate it's voltage within a range depending on amperage output. The 3rd brush is manually adjusted to get the proper amperage of output. The generator has to have the pole shoes polarized with a residual magnetic gauss in order for it to generate enough voltage to close the cut out relay so that the generator can come on line. Once it's on line it then generates what ever amperage it is manually set to operate at. The output voltage varies with the amperage output but it can't overwhelm the battery as long as it is well connected to it and the battery is in good condition.
Test an ammeter with some jumper leads and a battery. Connect the battery hot wire post to the discharge side and then connect in a load such as an electric motor or a high output 6-volt light bulb like an old sealed beam headlamp bulb. Connect the ground side back to the battery ground and watch the ammeter indication. It should show a discharge. If it doesn't then find an ammeter that will. A lot of the modern reproduction ammeters have a rare earth magnet on their armature and they can be damaged. Some D'arsonval meter movements can be fried since they have very fine windings. The Model T and A type ammeters had a big semi-circular horse shoe type magnet inside the meter and they could take most of what an old 3-brush generator could throw at them.
The ammeters with the loop are the inductive type. Amperage has to flow one way or the other through the hoop to get a reading. If it doesn't move with high amp discharge or charge then it never will again. It would be time to look for another one or make sure the battery and electrical wiring are good and proper.
If the vehicle has an alternator then every thing depends on it's internal electronic output controller. Voltage output had to be checked with a volt meter across the battery posts. Ammeter readings will only be noticed right after a start till the battery is back to normal state of charge. If the alternator controller is functioning then it may never show a discharge until the engine is at rest with no alternator function.
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Very interesting thanks. I’m using the original 2 post gauge out of my 49 F3. All it shows is if it’s charging or discharging. Hope that helps. I believe me hooking it up to my battery charger was a bad idea. I installed the cab on a 91 dodge D250 with a Cummins in it if that helps.
