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12v coil with tag saying use with a resistor

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PDB

05-28-2003 08:07:13




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A previous post said these are 8 volt coils. Should the voltage be 8 volts at the coil with one of these? I have one of these coils but I measure 12 volts at the terminal.




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yes . . . Dell (WA)

05-28-2003 08:27:29




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 Re: 12v coil with tag saying use with a resistor in reply to PDB, 05-28-2003 08:07:13  
PDB..... ....alotta 12 volt ignition systems use a resistor to drop the 12 volts to 8 volt during normal running, BUT when starting, a special switching scheme BYPASSES the resistor for a hotter sparkie during starting, and the moment you stop twisting the ignition key to START, the resistor is automatically re-connected to the ignition coil.

So yes, unless you have a resistor from the ignition switch ON, you will have 12 volts at coil terminal and will eventually "toast" your coil..... ..... Dell

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JerryU

05-28-2003 10:04:21




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 Re: Re: 12v coil with tag saying use with a resis in reply to yes . . . Dell (WA), 05-28-2003 08:27:29  
The bypass scheme was addressed in the N Newsletter eons ago. There were a number of schemes. Easiest, for what its worth, is to go to NAPA and get an oil pressure switch made to open (means needs a set of normally closed contacts) on sensing oil pressure. Most switches are reverse of this. It is simply wired to jumper out the resistor as Mr. Dell has said. Upon sensing oil pressure it opens up and the resistor is in the circuit. It is easily mounted using a tee in the line right behind the oil pressure gauge where no one will even know you have it there.

JU

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souNdguy

05-28-2003 11:05:12




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 Re: Re: Re: 12v coil with tag saying use with a r in reply to JerryU, 05-28-2003 10:04:21  
That NC, open w/ pressure switch sounds like the kind NH is using on the newer tractors.... with the key on the oil light glows.. after starting, it goes off.
Not a bad idea for an ignition resistor bypass based on oil pressure...

Soundguy



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Jim Cox

05-28-2003 09:35:48




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 Re: Re: 12v coil with tag saying use with a resis in reply to yes . . . Dell (WA), 05-28-2003 08:27:29  
Most excellent post Mr Dell. I have often wondered why there was not an ignition bypass setup on these here antique machines. Doubt I take time to work one in either. I wonder if my 12V 54 ford would actually start without it.
jim cox



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Rob

05-28-2003 08:24:08




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 Re: 12v coil with tag saying use with a resistor in reply to PDB, 05-28-2003 08:07:13  
There are two voltages on the coil. One points-open which will be the battery voltage regardless of resistors and another lower, points-closed voltage. Bump the starter once and read the other voltage.
On a 12v system that lower voltage should be 7.5v to 8v. Don't know for sure about an 8v coil but if it had like 6v and started good I'd leave it. I might even leave it well enough alone if it had 7.5v, don't know.

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