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12 Volt or 6 Volt Coil for '48 8N? Dell?

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Brads8N

08-09-2001 08:16:12

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I think my coil is bad. Have the 12 Volt Conversion. I did not use a resister in-line with my Coil. Question is should I go with a 6 Volt Coil and the RU-100 Resister or another 12 Volt Coil ( I don't know what size resister I would need with the 12 Volt Coil) Would the 6 volt coil be more reliable? And what are the plus and minus of using either Coil? Thanks in advance.

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Dell (WA)

08-10-2001 10:34:10

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Re: 12 Volt or 6 Volt Coil for '48 8N? Dell? in reply to Brads8N, 08-09-2001 08:16:12

Brad..... ...If'n it was me, I'd use a 12 volt frontmount ignition coil and 2 OEM "ballast resistors" in parallel (side by side). If'n you're electrically challenged and don't understand what parallel means electrically, THEN DON'T USE 12 VOLT COIL.

If you are electrically challenged, I'd recommend you use the OEM 6 volt frontmount ignition coil with electrical power coming thru BOTH a 12 to 6 volt converting resistor AND the OEM ballast resistor (on the back side of your dash panel). Connect BOTH resistors in series (like flashlight batterys) starting with power from the ignition switch and going to the coil terminal..... ...Dell

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CDA

08-10-2001 17:42:04

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Re: Re: 12 Volt or 6 Volt Coil for '48 8N? Dell? in reply to Dell (WA), 08-10-2001 10:34:10

Be careful Brad putting resistors in parallel as that decreases the overall circuit resistance below that of the value of just one resistor. If you put two 1.5 ohm resistors in parallel that leg of the circuit has only .75 ohms of resistance defeating your purpose.

The other posts offer very good advice.

Good Luck

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Dave Smith

08-10-2001 18:39:58

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Re: Re: Re: 12 Volt or 6 Volt Coil for '48 8N? Dell? in reply to CDA, 08-10-2001 17:42:04

CDA, What I think Dell was trying to say is that less of a voltage drop is needed with a 12 volt coil with external resistance. Unfortunatly most coils are not marked whether they need external resistance or not. I think you better be ready to drag out the formulas for parallel and series circuts. Dave <*)))><

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Mountainman

08-11-2001 14:04:08

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Re: Re: Re: Re: 12 Volt or 6 Volt Coil for '48 8N? Dell? in reply to Dave Smith, 08-10-2001 18:39:58

I don't think there are any front mount coils of either 6 or 12 volts that don't require some external resistance.

Mountainman (CA)

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CDA

08-11-2001 14:39:49

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Re: Re: Re: Re: Re: 12 Volt or 6 Volt Coil for '48 8N? Dell? in reply to Mountainman , 08-11-2001 14:04:08

Generally that's true Mountainman. The whole of idea of the resistance is prevent excessive amperage through the coil frying the windings. Total circuit resistance of 2.7 to 3.3 ohms is usually recommended. Some 12 volt coils have internal resistors others do not. Just check the resistance of your primary winding. If it is less than 2 ohms some sort of external resistor is required to get it in the right amperage bracket.

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Mountainman

08-11-2001 22:40:02

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Re: Re: Re: Re: Re: Re: 12 Volt or 6 Volt Coil for '48 8N? Dell? in reply to CDA, 08-11-2001 14:39:49

Seems the concensus on this board that measuring voltage at the top terminal of front mount coils is the easiest way for the electrically challenged (like me) to get it right and not, as you said, "fry the windings." I suspect it's partly due to the fact that many of us are not real comfortable checking ohms resistance on a coil as they are known to make your hair stand on end if you make a wrong move.

Mountainman (CA)

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CDA

08-12-2001 07:27:22

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Re: Re: Re: Re: Re: Re: Re: 12 Volt or 6 Volt Coil for '48 8N? Dell? in reply to Mountainman , 08-11-2001 22:40:02

I haven't got enough hair to stand on end anyway! The only reason it is good to know your coils primary resistance is to determine the need for an external resistor. The aim of the game is to get around 4 amps of current flowing through the coil. This is determined by taking the voltage and dividing the resistance into it. So, if you have a coil with a primary resistance of 3 ohms, and you have 12 volts to the top of the coil, that gives you 4 amps for the circuit, PERFECT! But, most front mount coils have only .5 ohms of resistance and you have 12 volts at the top, FRY CITY 24 AMPS. I have 2.45 volts at the top of my 6 volt coil which has .5 ohms of resistance and it works great (12 volt conversion). Most automotive coils have about 8-12 volts at there input because they have internal resistors.

Remember that during all resistance checks the power must be OFF so that you don't fry your meter. And, with the power off there is no danger of your hair going vertical. It is good to be accurate so that you have a balanced system and will work well for years to come. Otherwise, premature coil and points replacements are sure to be the case.

Sorry for the long post Mountainman, but I have dealt with this stuff for a long time and seen a lot of basic mistakes cost people plenty of dough.

Take care!

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Mountainman

08-12-2001 12:26:59

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Re: Re: Re: Re: Re: Re: Re: Re: 12 Volt or 6 Volt Coil for '48 8N? Dell? in reply to CDA, 08-12-2001 07:27:22

Long posts are fine � that's how we learn. In all the years of (mostly 12 volt) auto electrical work I've done, I've rarely had to do much troubleshooting requiring a meter (other than the dwell, tach and timing light of course); most problems were obvious I guess. Six volt positive ground is a whole new world and I remember well the costs of fixing the unfixable system in my 53 GMC years ago. It simply wasn't made to go over 45 mph and I did, of course, being young.
The memory of the GMC was part of my reason to convert the tractor to 12 volt but I knew the coil had to have a resistor because I previously had a resistor wire (part of the harness) deteriorate in my Chevelle. I replaced it with a standard wire and a resistor from a '57 Chevy, which is how I came to use the same thing on the 8N. Then I found this board and started measuring and found I'm getting 7.5 volts to the top of my 12 volt coil and good spark at the plugs so I left well enough alone. I have no idea how many amps that is or if the resistance is the same (or double or half) for 6 and 12 volt coils. Maybe each is slightly different if not manufactured to exact standards.
It probably is a good idea to do a resistance test to ensure long term performance and that might well be a winter project.

Thank's for the info.

N � joy your Sunday.

Mountainman (CA)

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Mountainman

08-09-2001 12:19:43

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Re: 12 Volt or 6 Volt Coil for '48 8N? Dell? in reply to Brads8N, 08-09-2001 08:16:12

I'm not Dell, and don't pretend to be an expert, but I did convert to 12 volts and used a 12 volt, front mount coil. I got a ceramic resistor like one used in a '57 Chevy and I get 7.5 volts at the top of coil with engine off, key on. That's a little low but I get good spark and it runs great.
If you use a 6 volt coil, you should use the original resistor plus a 12 volt to 6 volt resistor (in series).

Hope this helps.

Mountainman (CA)

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Mark *8N126925*

08-09-2001 12:16:23

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Re: 12 Volt or 6 Volt Coil for '48 8N? Dell? in reply to Brads8N, 08-09-2001 08:16:12

I also have a 12 volt conversion.I have used both types of coil (depending on supplier availability at that time) and found no difference in their performance.when using a 12 volt coil, simply jumper around the extra resistor.Use an indelible paint pen to mark them however, the little sticker will fall off making it indistinguishable from a 6 volt.

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