Coil Voltage
Joined: Jun 2008
Posts: 8,376
Likes: 28
From: Chino Hills, CA
Measuring coil voltage on a running motor with a digital meter can be misleading.
Make sure you're not measuring across the coil; measure from the coil's positive lead to a solid ground point (like battery negative). Should be equal to supply voltage, as that's where it's coming from.
If it's lower, you have a less-than-perfect connection or switch contact somewhere between the coil and the battery.
You can verify a lossy connection by measuring from the battery's positive post to the coil's positive terminal with the ignition on; this is called measuring for voltage drop in your supply wiring, and it tells you if you are losing voltage due to a resistance somewhere.
You should see either a very small voltage or ideally no voltage; if you're dropping more than a volt you have contact issues that need remedying.
The negative lead on the coil is constantly being switched away from ground in order to collapse the primary field and generate the HV in the secondary, once per firing cycle. So the apparent voltage across the coil's terminals is constantly varying, and appears to drop as the RPMs rise and the coil cycles faster.
Make sure you're not measuring across the coil; measure from the coil's positive lead to a solid ground point (like battery negative). Should be equal to supply voltage, as that's where it's coming from.
If it's lower, you have a less-than-perfect connection or switch contact somewhere between the coil and the battery.
You can verify a lossy connection by measuring from the battery's positive post to the coil's positive terminal with the ignition on; this is called measuring for voltage drop in your supply wiring, and it tells you if you are losing voltage due to a resistance somewhere.
You should see either a very small voltage or ideally no voltage; if you're dropping more than a volt you have contact issues that need remedying.
The negative lead on the coil is constantly being switched away from ground in order to collapse the primary field and generate the HV in the secondary, once per firing cycle. So the apparent voltage across the coil's terminals is constantly varying, and appears to drop as the RPMs rise and the coil cycles faster.
ok well looks like he needs a better alternator...with the efan on and the car idling the coil is not getting 12v...i dont even measure 12v at the batter positive and negative...and when you rev it with just the efan on the voltage never goes above 12.5...a worn out 50 amp alternator isnt doin the job anymore i guess
thanx
thanx
I had to upgrade my ign switch to relays and upgrade alternators to get proper voltage. In a perfect world there should be no voltage drop to the coil. It should see battery voltage with the key on. Worn out bat cables, alternator, worn out ign switch, wiring etc will cause the voltage to drop by the time it gets to the coils.
I think alot of the coil upgrades would make an even bigger difference if the typical voltage drops have been repaired.
I think alot of the coil upgrades would make an even bigger difference if the typical voltage drops have been repaired.
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