Coil vaoltag #'s
Thread Starter
Melting Slicks
Joined: Mar 2008
Posts: 2,023
Likes: 6
From: Austin Tx
Coil voltage #'s
Can anyone confirm that this is correct for me?
I have a 72 with breaker points ignition system. And this is what I have oberved, and want to confirm that this is normal.
With ignition key just in the 'on' position
When everything is hooked up, + side of coil shows 6 volts.
When resistor wire, and wire from started removed from coil, that terminal shows 12 volts.
Negative side of coil shows 0 volts.
The coil gets hot to the touch - this concerns me.
When the car is running
Positive side of the coil shows 10 volts. I thought that the higher voltage should only be when starting. The voltage goes up when starting, and stays there even after the car is running.
Negative side of coil shows 6 volts.
I guess my main concerns are, when the key is in the 'ON' position, should the resistor wire show 12 volts? And, should the coil get hot with the ignition on? And, should the voltage on the positive side of the coil drop back down after the car is running?
Thanks,
Matt
I have a 72 with breaker points ignition system. And this is what I have oberved, and want to confirm that this is normal.
With ignition key just in the 'on' position
When everything is hooked up, + side of coil shows 6 volts.
When resistor wire, and wire from started removed from coil, that terminal shows 12 volts.
Negative side of coil shows 0 volts.
The coil gets hot to the touch - this concerns me.
When the car is running
Positive side of the coil shows 10 volts. I thought that the higher voltage should only be when starting. The voltage goes up when starting, and stays there even after the car is running.
Negative side of coil shows 6 volts.
I guess my main concerns are, when the key is in the 'ON' position, should the resistor wire show 12 volts? And, should the coil get hot with the ignition on? And, should the voltage on the positive side of the coil drop back down after the car is running?
Thanks,
Matt
Last edited by Mashman; Jul 16, 2009 at 05:53 PM.
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Can anyone confirm that this is correct for me?
I have a 72 with breaker points ignition system. And this is what I have oberved, and want to confirm that this is normal.
With ignition key just in the 'on' position
When everything is hooked up, + side of coil shows 6 volts. With the points closed, that's correct.When resistor wire, and wire from started removed from coil, that terminal shows 12 volts. That's correct, too, assuming you're talking about the harness terminal, not the coil terminal.
Negative side of coil shows 0 volts. Correct, as the points are closed and there is no positive connection anywhere.The coil gets hot to the touch - this concerns me. How hot? Realize that when everything is hooked up, and the key is on, that there is probably about four amps going through the coil. At six volts across the coil (as you measured earlier) that is 6V X 4A = 24Watts. That will warm things up.
When the car is running
Positive side of the coil shows 10 volts. I thought that the higher voltage should only be when starting. The voltage goes up when starting, and stays there even after the car is running. You're not going to get an accurate voltage with a voltmeter when the engine is running, but look at it this way. When the points are closed, you'll get 6 volts, as you did before. When the points open, you'll get 12 volts, just the same as when you disconnected the wires. The points are opening and closing, meaning that the current is flowing and stopping. Your voltmeter can't keep up, and it's just giving you a rough average of the changing instantaneous voltages.Negative side of coil shows 6 volts. Yes again, for a similar reason as above. When the points are closed, the voltage will be zero. When the points open the voltage jumps to a couple hundred volts for a brief moment, then settles down to 12 volts. Your voltmeter is just giving you a rough average voltage again.
I guess my main concerns are, when the key is in the 'ON' position, should the resistor wire show 12 volts? Yes, with the wire disconnected or with the points open. And, should the coil get hot with the ignition on? It'll get warm, for the reason stated above. And, should the voltage on the positive side of the coil drop back down after the car is running? It's constantly bouncing around, but your meter will give you a reading slightly less that 12 volts. Remember, it's not an accurate reading if done with a voltmeter while the engine is running.
Thanks,
Matt
I have a 72 with breaker points ignition system. And this is what I have oberved, and want to confirm that this is normal.
With ignition key just in the 'on' position
When everything is hooked up, + side of coil shows 6 volts. With the points closed, that's correct.When resistor wire, and wire from started removed from coil, that terminal shows 12 volts. That's correct, too, assuming you're talking about the harness terminal, not the coil terminal.
Negative side of coil shows 0 volts. Correct, as the points are closed and there is no positive connection anywhere.The coil gets hot to the touch - this concerns me. How hot? Realize that when everything is hooked up, and the key is on, that there is probably about four amps going through the coil. At six volts across the coil (as you measured earlier) that is 6V X 4A = 24Watts. That will warm things up.
When the car is running
Positive side of the coil shows 10 volts. I thought that the higher voltage should only be when starting. The voltage goes up when starting, and stays there even after the car is running. You're not going to get an accurate voltage with a voltmeter when the engine is running, but look at it this way. When the points are closed, you'll get 6 volts, as you did before. When the points open, you'll get 12 volts, just the same as when you disconnected the wires. The points are opening and closing, meaning that the current is flowing and stopping. Your voltmeter can't keep up, and it's just giving you a rough average of the changing instantaneous voltages.Negative side of coil shows 6 volts. Yes again, for a similar reason as above. When the points are closed, the voltage will be zero. When the points open the voltage jumps to a couple hundred volts for a brief moment, then settles down to 12 volts. Your voltmeter is just giving you a rough average voltage again.
I guess my main concerns are, when the key is in the 'ON' position, should the resistor wire show 12 volts? Yes, with the wire disconnected or with the points open. And, should the coil get hot with the ignition on? It'll get warm, for the reason stated above. And, should the voltage on the positive side of the coil drop back down after the car is running? It's constantly bouncing around, but your meter will give you a reading slightly less that 12 volts. Remember, it's not an accurate reading if done with a voltmeter while the engine is running.
Thanks,
Matt
Thread Starter
Melting Slicks
Joined: Mar 2008
Posts: 2,023
Likes: 6
From: Austin Tx
Yes!
Thanks you so much!
I would say the heat generated by the coil when the ignition is on - I can leave my hand on it, but would call it hot - kind of like the bottom of my laptop when it's been running for a while. I'll get an ir temp reading later.
This all came about because I started to have an issue where after the car was warmed up, it would start to idle a bit rough, and would stall when left in gear and stopped at a light.
I found the vacuum advance had a leak, and replaced it. The problem persisted, and I figured maybe the coil was going bad - replaced both the coil, and the capacitor in the distributor. The problem went away, and the car now runs great - but I was afraid that there was a continuing problem that would cause the new coil/capacitor go bad also, or something worse.
So, if everything looks normal, I will just assume that there was nothing that 'caused' the coil/capacitor to go bad, it just did.
Thanks you so much!
I would say the heat generated by the coil when the ignition is on - I can leave my hand on it, but would call it hot - kind of like the bottom of my laptop when it's been running for a while. I'll get an ir temp reading later.
This all came about because I started to have an issue where after the car was warmed up, it would start to idle a bit rough, and would stall when left in gear and stopped at a light.
I found the vacuum advance had a leak, and replaced it. The problem persisted, and I figured maybe the coil was going bad - replaced both the coil, and the capacitor in the distributor. The problem went away, and the car now runs great - but I was afraid that there was a continuing problem that would cause the new coil/capacitor go bad also, or something worse.
So, if everything looks normal, I will just assume that there was nothing that 'caused' the coil/capacitor to go bad, it just did.
