typical voltage and amperage across a spark plug ??? - Fuelly Forums

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Old 07-20-2006, 08:53 AM   #1
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typical voltage and amperage across a spark plug ???

hey guys...
i've been 'disconnected' for some time now
motor swapping and out of work
i'm back surfing wifi in the car
getting about 35mpg...bah

anyway

none of my manuals talk about distributor output
and i dont really want to burn out my only dmm
so i figured someone in the group would know 'roughly' how much volts and amps is put out by a stock honda coil to the plugs...

thanx fellas
i will be around a bit more

peace
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Old 07-20-2006, 09:23 AM   #2
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looks like 8000-10000 volts roughly
still looking for amperage
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Old 07-27-2006, 10:05 AM   #3
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nobody knows...?
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Old 07-27-2006, 10:06 AM   #4
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Something tells me Diemaster will know, or Dax. They both seem to have all of the Helms manuals.
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Old 07-27-2006, 10:26 AM   #5
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Just a guess here but 10000V is very dangerous. The current would have to be infinatesimal for it to be used in a consumer product such as a car. I have been shocked by a spark plug wire and I didn't get electrocuted.
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Old 07-27-2006, 10:51 AM   #6
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Proper term is didn't go into cardiac arrest . . . that takes about 0.100 amps . . . if you take the 12 to 14 volts charging the primary at about 4-6 amps and multiply them then divide by the output voltage you get the current plus or minus a duty cycle correction factor so for a long spark 0.00875 amps for 10% discharge duration maybe 0.0875amps (10 times greater current for 1/10 the time). You really need to measure the discharge on the primary side with a Scope to figure the spark duration and then calculate the current.
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Old 07-27-2006, 03:54 PM   #7
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thank you jangeo

as far as high voltage
a high power stungun has 750,000 volts
running on 4 9volt batteries
it wont kill you
the amperage isn't there...
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Old 07-27-2006, 09:03 PM   #8
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Spark plugs work on high-frequency, so peak current and voltage wouldn't be as important as the wave shapes. The idea is that you charge the coil with low voltage, then open it across a capacitor (an LRC circuit). It then oscillates at high frequency, which causes a pretty healthy voltage on the primary, and high voltage on the secondary. I think they're wound 100:1 or so.

I think the current would be mainly set by the plug wire resistance. You would get a high voltage until the arc is struck, then it would decrease to maybe 100 volts. Lower pressure means higher voltage. They absorb the rest of the voltage in the plug wires. I'd guess hundreds of mA peak.

Probably the best way to get an idea of this is to measure low-side current on either a plug or the coil. You would need a scope for sure.

So why are you interested in the plug current anyway?
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Old 02-10-2012, 10:57 AM   #9
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Re: typical voltage and amperage across a spark plug ???

From http://home.earthlink.net/~jimlux/hv/igncoil.htm:

Up to 45,000 volts and 50-75 amps at cranking time, so roughly 2,000,000 watts at crank. The guy above must not have been cranking the car when he was "shocked by a spark plug wire and I didn't get electrocuted", because if it had been during the ignition cycle he would be dead. Other times there is a resistor that whacks the voltage down to about 12V and about 12A, or about 144 watts during engine operation.
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