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12 volts coil

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Luc Perron

11-04-2004 06:20:03

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Dear list members,

I got stuck in the trail to my little piece of land on my first ride of a Farmal super A 1950. I figured out that the coil was dead by testing the quality of the spark. A poor yellow and short light. The tractor is 12 volts converted.

I tried an spare 12 volts coil from my volkswagen bus. This coil was matched with a points distributor on the original VW engine. The "new" coil" is longer than the one that was on the farmal (maybe not an original one anyway). Now the engine never stops anymore.

I read that it is a must that a resistor balast has to be there, in serie with the coil primairy current. There is no one the VW, I put no one with the farmal as well and everything is working. But for how long? This is my question, any problems to comes without a balast?

Luc

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Spongetires

11-04-2004 16:12:05

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Re: 12 volts coil in reply to Luc Perron, 11-04-2004 06:20:03

If you use a Mopar ballast resistor make sure it is bolted to a good heat sink, such as body sheet metal. If you don't the resistor will burn up quickly, or get so hot the spark will be reduced to a point where the tractor will not run well. Mopar resistors can cause a lot of trouble, they often burned out in their cars. After burning up several ballast resistors I put a resistor coil and haven't had any trouble since. Spongetires

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MN Charlie

11-04-2004 11:03:16

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Re: 12 volts coil in reply to Luc Perron, 11-04-2004 06:20:03

If I remember correctly did"t the VW bus use a 6 volt battery? It"s been a few years since I was in the "hippy" mode of transportation. I can also remember that they were still positive ground. Like I said this was a long time ago and maybe your bus is newer and VW swithch to 12 volt and Neg ground. Maybe somebody will chime in and help this brain to remember. Good luck

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ironhead

11-04-2004 15:11:16

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Re: 12 volts coil in reply to MN Charlie, 11-04-2004 11:03:16

i have a few vw sitting around and all are 12v neg. ground. maybe in the early years they were 6v. not sure though

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Doug in OR

11-04-2004 08:58:19

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Re: 12 volts coil in reply to Luc Perron, 11-04-2004 06:20:03

Some "12 volt" coils require a ballast resistor, some do not. Measure across the two terminals with an ohmmeter. If it reads about 1.5 ohms, you will need a ballast resistor. If it reads about 3.2 ohms, you can run it stock with no ballast resistor - the resistor will be in the coil. Be sure the coil is disconnected when you make this measurement. Any MOPAR ballast resistor will work, if needed.

A weak yellow spark usually indicates other problems. Are your points good? Do you have a solid ground connection to your points? (No rust or grease or anything). Are all your connections between the coil and the ignition switch good and solid? A leaky condensor could cause this too. Your coil could be bad, but I would check all other connections first.

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Luc Perron

11-04-2004 09:04:12

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Re: 12 volts coil in reply to Doug in OR, 11-04-2004 08:58:19

Thanks Doug in Or!

This procedure and the precise technical info will help me a lot. I'll check everything and I'll start making a grossery list of parts that will include condensor, new points, etc.

Luc In Qc

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captaink

11-04-2004 08:31:59

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Re: 12 volts coil in reply to Luc Perron, 11-04-2004 06:20:03

If the coil from the bus was 12 volt, make sure that you have 12 volts getting to it. If there is a resistor on the tractor to lower the voltage to 6 for the original 6 volt coil, you need to get rid of it or you can have touble starting in cold weather when the starter takes more juice. Voltage can get so low on a 12 volt system during the extreme starting load that the voltage going through a resisitor will bee too low to get a good spark.

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Red Dave

11-04-2004 06:54:51

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Re: 12 volts coil in reply to Luc Perron, 11-04-2004 06:20:03

Some coils have the resistor inside and don't need one externaly.
I have no idea whether a VW coil has an internal resistor or not. Maybe a VW service manual or parts book could tell you.

About the worst thing that would happen anyway without a resistor is rapid points burnout. If your points aren't pitting and burning, you may just be OK with what you have as it is.

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