Slant Six Bumblebee
Well-Known Member
What is the ideal resistance for ammeter my old ammeter had 9 ohms and a spare one i have is 1 ohm is that still to much?
Ammeter voltage drop
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What type of ammeter?
Nothing in the system should show any measureable resistance.
If there's a 0.1 ohms in the whole line between the battery and main splice, I'd say that's not a good start.
Measured three in this post.
Charging system road rage
My terminology may not be correct. It may not really be an internal 'shunt'. Those ammeters work on magnetic field created by the current through the metal plate. I think more properly a shunt type has a parallel path. Regardless, an in-line ammeter should have no resistance.
Nothing in the system should show any measureable resistance.
If there's a 0.1 ohms in the whole line between the battery and main splice, I'd say that's not a good start.
Measured three in this post.
Charging system road rage
My terminology may not be correct. It may not really be an internal 'shunt'. Those ammeters work on magnetic field created by the current through the metal plate. I think more properly a shunt type has a parallel path. Regardless, an in-line ammeter should have no resistance.
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Slant Six Bumblebee
Well-Known Member
It’s the stock ammeter for my 72 slant six dart. I calculated the meters ohms into the .9
So what are you basing this calculation on?
Slant Six Bumblebee
Well-Known Member
My multi meter with the ohms of the leads subtracted
Something is not right. Whether its the ammeter, or the multimeter (Digital or analog) I don't know.
Check the multimeter ohms setting against a known resistor.
You could use the ballast resistors. If your car has just one, its probably around 0.6 to 0.7 Ohms. See if the multimeter ohms setting gets anything close to that.
If the car has a dual ballast resistor, one is 0.5 ohms and the other is 5.0 ohms
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Digital multi-meter with the alligator clips together. 0.1 to 0.2 ohms. So that's baseline reading.
Hawk gage set.
Same with the RAC gage set.
And the here's the rally ammeter.
Here's a back view.
Hawk gage set.
Same with the RAC gage set.
And the here's the rally ammeter.
Here's a back view.
67Dart273
Well-Known Member
The thing is you CAN NOT accurately measure low values of resistance with a multimeter. This varies with the quality of the meter, but below two or one ohms, you are getting flakey, and something like Horrid Freight/ other Chinese import, maybe higher than that
The only real thing you need to be concerned about is total voltage drop when charging hard, AKA with 20, 30, 40 A going through the circuit, THE ENTIRE CIRCUIT, which includes the fuse link----the connection at the start relay "big stud"---the wire end terminals----the bulkhead connector terminals---the wire terminals at the ammeter---of course the ammeter itself, and so on
This figure varies with opinion, but "Let's say" you have a 50A alternator operating at that output, you have a load on the battery to simulate heavy load, if you have anything less than 2V between alternator output stud and the battery POS stud, I'd say "call er good."
The bit issue with the ammeter is that the studs are not soldered/ brazed/ welded to the shunt/ guts. These connections can get hot with extreme current especially with something "got loose" and a little corrosion, etc. If you want to improve this, take it apart, clean it up and using proper flux, solder the studs to the shunt with silver based solder
The only real thing you need to be concerned about is total voltage drop when charging hard, AKA with 20, 30, 40 A going through the circuit, THE ENTIRE CIRCUIT, which includes the fuse link----the connection at the start relay "big stud"---the wire end terminals----the bulkhead connector terminals---the wire terminals at the ammeter---of course the ammeter itself, and so on
This figure varies with opinion, but "Let's say" you have a 50A alternator operating at that output, you have a load on the battery to simulate heavy load, if you have anything less than 2V between alternator output stud and the battery POS stud, I'd say "call er good."
The bit issue with the ammeter is that the studs are not soldered/ brazed/ welded to the shunt/ guts. These connections can get hot with extreme current especially with something "got loose" and a little corrosion, etc. If you want to improve this, take it apart, clean it up and using proper flux, solder the studs to the shunt with silver based solder
Just did a live test.
13.48v supply while load applied
12.3ohm load
1970 dart ammeter
14 awg wire
0.1v voltage drop across ammeter
1.1A in cir.
Gives 0.091ohm for the ammeter.
I would say that the shunt is 0.1 ohms +/-10%
13.48v supply while load applied
12.3ohm load
1970 dart ammeter
14 awg wire
0.1v voltage drop across ammeter
1.1A in cir.
Gives 0.091ohm for the ammeter.
I would say that the shunt is 0.1 ohms +/-10%
Slant Six Bumblebee
Well-Known Member
ok ill give this a try i got a wiring diagram and was tracing the voltage drop everywhere and the only places that there were any were the link and the ammeter. Is there a better option than the fuseable link?
67Dart273
Well-Known Member
THat's a tough question. The fuse link is darn poor protection, and yes!! LOL!!1 I have a story about that. But a breaker might be worse. A breaker small enough to protect the wire might nuisance trip under high charging loads
Just where are you measuring the drop, under what kind of conditions (electrical load/ charging current) and how much is it showing?
Just where are you measuring the drop, under what kind of conditions (electrical load/ charging current) and how much is it showing?
Slant Six Bumblebee
Well-Known Member
no load just my battery plugged in. i bolted the two ammeter terminals together for testing. I measured at the ammeter terminals and the alternator with the car off and all the voltage drop comes from the link with no ammeter in the circuit.
What he wrote.^^^^.
1. Is the meter and probes providing consistant and relatively accurate readings? Compare the voltage measurements against some known voltages. Compare the measurement readings against some known resistances.
Wait. Maybe this is it. Lets go over using the multimeter.
The resistance setting should only be used when the power is disconnected.
The voltage setting is used when the power is connected.
2. Voltage should be the same everywhere when everything is off.
This is a the basic scheme of standard 1972 Valiant.
Everything connected to the battery positive is hot.
Key off, lights off, dome light off, brakes off;
Ammeter should show ZERO.
Voltage between battery positive terminal and ground should be the same as voltage to ground at any point that is hot.
For example if its 12.8 Volts across the battery, it should be 12.8 Volts at the dome light socket.
If you think of current like a river of electrons flowing, with all the switches off, the river is blocked. Pressure behind the blockage is the same everywhere. That pressure is the voltage.
1. Is the meter and probes providing consistant and relatively accurate readings? Compare the voltage measurements against some known voltages. Compare the measurement readings against some known resistances.
Wait. Maybe this is it. Lets go over using the multimeter.
The resistance setting should only be used when the power is disconnected.
The voltage setting is used when the power is connected.
2. Voltage should be the same everywhere when everything is off.
This is a the basic scheme of standard 1972 Valiant.
Everything connected to the battery positive is hot.
Key off, lights off, dome light off, brakes off;
Ammeter should show ZERO.
Voltage between battery positive terminal and ground should be the same as voltage to ground at any point that is hot.
For example if its 12.8 Volts across the battery, it should be 12.8 Volts at the dome light socket.
If you think of current like a river of electrons flowing, with all the switches off, the river is blocked. Pressure behind the blockage is the same everywhere. That pressure is the voltage.
Voltage drop in the wiring can also be measured directly.
With no current flowing, there can be no voltage drop.
For example if the battery has 12.8 Volts, the voltage at the alternator's output terminal better be the same.
Measuring directly looks like this.
If you want to measure resistance for hunting really poor connections or broken circuits.
Disconnect the battery, set the meter to ohms, and check this will indicate major problems in the wiring between the probes.
If all that checks out, then go on to measuring voltage drop by putting a load on the circuit.
For example to check the line from the battery positive to the main splice, with the engine off, turn on the parking lights and headlights.
About 12 amps will flow through the wires.
If the meter shows 0 Volts, that portion of the circuit highlighted is pretty good.
With no current flowing, there can be no voltage drop.
For example if the battery has 12.8 Volts, the voltage at the alternator's output terminal better be the same.
Measuring directly looks like this.
If you want to measure resistance for hunting really poor connections or broken circuits.
Disconnect the battery, set the meter to ohms, and check this will indicate major problems in the wiring between the probes.
If all that checks out, then go on to measuring voltage drop by putting a load on the circuit.
For example to check the line from the battery positive to the main splice, with the engine off, turn on the parking lights and headlights.
About 12 amps will flow through the wires.
If the meter shows 0 Volts, that portion of the circuit highlighted is pretty good.
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