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6 Volt to 12 Volt Conversion ?

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Triumph

09-27-2004 15:24:52

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Hello Everyone
I converted An Allis WD 45 from 6V to 12V. Just one Problem, What ignition coil should I use? I ask this question because I am burning up points extremly fast. I am told that some coils have an internal resistor and some do not. At this time I have a generic 12V coil that must not have an internal resistor. Anyone have any part numbers or application information for a 12 Volt coil with an internal Resistor ? Thanks for your help Best Regards John

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buickanddeere

09-29-2004 05:30:46

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Re: 6 Volt to 12 Volt Conversion ? in reply to Triumph, 09-27-2004 15:24:52

Purchase an ignition coil with 3.l0 ohms primary resistance. The old one is likely about 1.5 ohms if it hasn't started shorting out from over heating. The origional 6V system didn't use a ballast resisitor so we won't confuse the issue by adding a ballast and by-pass starting. Goes to show the simple cheap fix of purchasing a $39.99 12V alternator when the 6V generator needs rebuild is not the simple, fast easy repair it appears to be.

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Mike M (RI)

09-27-2004 17:20:13

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Re: 6 Volt to 12 Volt Conversion ? in reply to Triumph, 09-27-2004 15:24:52

On my '59 D14 I used a NAPA IC-14 coil 12v with "internal" resister $42 4 yrs ago. It just went bad & I replaced it with a Standard STD-UC15 coil, 12v, with internal resistor...$40. Hope this helps.

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tlak

09-27-2004 17:25:17

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Re: 6 Volt to 12 Volt Conversion ? in reply to Mike M (RI), 09-27-2004 17:20:13

Autozone has one for $14

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TomH

09-27-2004 16:57:48

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Re: 6 Volt to 12 Volt Conversion ? in reply to Triumph, 09-27-2004 15:24:52

Get a voltmeter and check the resistance across the + and - terminals of the coil. If it's less than two ohms, you need the ballast resistor, if it's around three you have another problem (maybe the condensor?)

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Sam#3

09-27-2004 16:35:15

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Re: 6 Volt to 12 Volt Conversion ? in reply to Triumph, 09-27-2004 15:24:52

Define "Burning up." A lack of dropping resistor will cause blue overheated contacts. From all the reports I've read the coil will get HOT and maybe melt it's dielectric.
If the contacts are transfering material(forming pits) it's the capacitor. The capacitor's mission in life is contact protection.

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tlak

09-27-2004 15:42:07

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Re: 6 Volt to 12 Volt Conversion ? in reply to Triumph, 09-27-2004 15:24:52

70s VW coil

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Jon H

09-27-2004 16:18:43

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Re: 6 Volt to 12 Volt Conversion ? in reply to tlak, 09-27-2004 15:42:07

There are no coils with a built in resistor,only coils with a 6V primary winding or 12V primary winding.There are 12V coils designed to work with an external resistor,and are marked as such on the case. These have a primary winding very close to that of a 6V coil. You need to add an external resistor to the wire feeding the coil you have now. Auto parts stores should have the resistor.

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tlak

09-27-2004 17:01:06

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Re: 6 Volt to 12 Volt Conversion ? in reply to Jon H, 09-27-2004 16:18:43

The coil i got said internal resister. Going on a year same set of points with no inline resister.

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Jon H

09-27-2004 17:36:10

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Re: 6 Volt to 12 Volt Conversion ? in reply to tlak, 09-27-2004 17:01:06

Hmm, I don't understand what the point would be of an internal resistor. The last thing that oil filled coil needs is an internal resistor generating more heat ??. The coil is an induction coil,not a transformer, so the number of turns in the primary winding (6V vs 12V) in relation to the secondary winding should have little effect. An induction coil builds a magnetic field using dc power which when turned off collapses the magnetic field and generates a voltage spike of about 20-30,000 volts in the secondary winding and several hundred volts in the primary winding which is absorbed by the condenser to prevent arcing and burning of the points.
Maybe one of the others (B&D or Bob?) can add their knowledge of battery ignition systems to settle this.

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Jon H

09-27-2004 18:12:14

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Re: 6 Volt to 12 Volt Conversion ? in reply to Jon H, 09-27-2004 17:36:10

I did a web search on ignition coil design and found that some coils do use an internal iron resistance wire to limit primary current at low rpm. I stand corrected. Internal resistor coils do exist.

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Dave Wis

09-28-2004 03:39:22

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Re: 6 Volt to 12 Volt Conversion ? in reply to Jon H, 09-27-2004 18:12:14

It may be just different wording. All the coils I have used over the years say 6volt or 12volt and then "for use with external resistor" or "not for use with external resistor". They didn't say internal resistor but most people probably assume that's what it infers. I guess it doesn't matter about the wording, the bottom line is to have the correct resistance to make the points live longer.

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Jon H

09-28-2004 06:51:35

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Re: 6 Volt to 12 Volt Conversion ? in reply to Dave Wis, 09-28-2004 03:39:22

Yes Dave,The tech papers I found online do indicate that the coil with internal resistor still has a 6V or 12V primary winding and that the internal resistor will only limit primary current at low rpm for less load on the points. It is not a full 12V to 6V drop like an external ballast resistor which allows a 6V coil to work on 12V. I just wanted to correct my statement that there is no such thing as a coil with internal resistor. There is,but the internal resistor will not replace an external ballast resistor as needed on a 12V with 6V coil system.

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