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Ford 9N, 2N & 8N Discussion Forum

12V Frontmount Coil Wiring

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Brads8N

03-24-2004 09:46:11

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I have a 48 8N with a 12V conversion. The 12V Frontmount coil says to limit the voltage, probably 13 Volts or so. I'm using the ballast resistor mounted to the dash, and have another resistor (forgot the value) wired in series before it goes to the coil. I'm afraid I don't have enough Volts at the coil, after reading thru some of the recent posts.

Everything seems fine, coil runs cool, starts and operates fine. I want to make sure I have full ignition power, without frying the coil.

What voltage should I see at the top of the coil with the points closed and open?

Couldn't find what I needed in the archieves.

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DavidO

03-25-2004 05:53:58

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Re: 12V Frontmount Coil Wiring in reply to Brads8N, 03-24-2004 09:46:11

Brad, SouNdguy is right. The reason your new 12V square coil says to limit the voltage to 13V is because experience has taught the coil makers that higher voltage than that will cause that particular coil to overheat and fail. Remember that the alternator was designed for a car with a different type of coil. The alternator is regulated to 14+ V. On the type of coil that you have, I would put a resistor of about 1/2 ohm, 10 watts or better in series with the coil. Remove/disconnect any OTHER resistors in that circuit. That should give you a reading of "battery" voltage with the points open and approx 10-12V with the points closed at the terminal on the top of the coil. If that checks out, you should be good to go. If not, you need to check wiring, points, condensor, etc. to determine why not.

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Charles (in GA)

03-24-2004 14:42:20

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Re: 12V Frontmount Coil Wiring in reply to Brads8N, 03-24-2004 09:46:11

With the points open, there is no load on the circuit, so the ballast resistors will not drop the voltage (the voltmeter does not exert any measurable load on this circuit) and so you should see the same or very close to the same voltage you see at the battery terminals. When the points close you have created a ground for the circuit and the coil is energized, placing a load on the circuit and with current flowing the ballast resistors will cause the voltage downstream of them to drop.

If these 12V coils have an internal resistor that is correct (and drops the voltage to about 6), you are supposed to be able to place 12 volts directly to the coil. Apparently the "12V" coil really cannot stand 12V if they overheat and the points burn up, etc. so you would want to limit the voltage with the external ballast resistor you have. I cannot imagine you would want to see less than 5-6 volts at the coil with the points closed.

Charles

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guess? . . . Dell (WA)

03-24-2004 10:28:18

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Re: 12V Frontmount Coil Wiring in reply to Brads8N, 03-24-2004 09:46:11

Brad..... ...why guess, even the cheapest $10 voltmeter will tell you exactly what yer volts are. $10 cheap, hardware store..... ..Dell

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Dell.... I have a Voltmet

03-24-2004 13:04:47

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Re: Re: 12V Frontmount Coil Wiring in reply to guess? . . . Dell (WA), 03-24-2004 10:28:18

I have a volt meter. That's why I asking what voltage a 12V Frontmount coil should have with the points closed (for maximum performance and coil life). Should see battery voltage with the points open, right?.

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old

03-24-2004 10:04:22

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Re: 12V Frontmount Coil Wiring in reply to Brads8N, 03-24-2004 09:46:11

Well if I remember right it should be 12 volts with points open and about 3-4 volts with them closed

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souNdguy

03-24-2004 12:02:36

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Re: Re: 12V Frontmount Coil Wiring in reply to old, 03-24-2004 10:04:22

If he is using a 12v front coil.. I would think he would want more than 3-4volts on the coil with the points closed... I'm guessing closer to 9-10-12. Just enough resistance to make the coil happy.

Now if it were a 6v front coil, using the ballast resistor, and dropping resistor, then 3.5 to 4.5 on the coil with points closed would be a good target.

My guess is he has way way too much resistance in line with a 12v front coil... ( not that that it is going to hurt anything.. until he starts getting some wear in the system, and has insuficient secondary voltage available due to too low of primary voltage )

Soundguy

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