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Grabatire Regular
Joined: 05 Mar 2009 Posts: 212
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Posted: Mon Dec 10, 2012 9:05 pm Post subject: 8N Ford 6Volt to 12 Volt Conversion 


I'm doing the 6V to 12V conversion on an 8N with front mount distributor and bought a 12 volt coil.
My question is: Does anyone know if the 12V coils have a built in resistor, or do I need to add one? There wasn't any information that came with with the coil. 

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Dell (WA) Tractor Guru
Joined: 21 Sep 1998 Posts: 25117
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Posted: Mon Dec 10, 2012 9:30 pm Post subject: Re: 8N Ford 6Volt to 12 Volt Conversion 


grabatire..........ALL squarecan ignition coils need the "infamous ballast resistor"........NO ARGUE!!!!
They do NOT have a builtin resistor.
Surprizingly enuff, both the points (0.015") and the condenser work just fine on 12V. Same with the OEM 6Vstarter motor. Works fine on 12V, positive or negative ground. .......Dell, a 12V advocate for the right reasons, who knows 8ways to convert to 12V and they all work right the first time 

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souNdguy Tractor Guru
Joined: 20 Aug 2002 Posts: 57613
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Posted: Tue Dec 11, 2012 12:49 pm Post subject: Re: 8N Ford 6Volt to 12 Volt Conversion 


keep the oem ballast resistor with the newer 2.5 ohm ( usually ) square coil. 

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Grabatire Regular
Joined: 05 Mar 2009 Posts: 212
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Posted: Tue Dec 11, 2012 7:28 pm Post subject: Re: 8N Ford 6Volt to 12 Volt Conversion 


Thanks soundguy and Dell.
The new 12V coil is a square coil like the original 6V. I was hoping it had a builtin resistor because the oem resistor is toast, but if I read you right soundguy, the oem resistor would do the trick if it was OK?
My neighbour has an early 8N, so I can measure the resistance of its oem resistor and see how it compares to a resistor from a 1980 Dodge truck. I suppose I can run two of them in series if one isn't enough. 

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Dell (WA) Tractor Guru
Joined: 21 Sep 1998 Posts: 25117
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Posted: Tue Dec 11, 2012 7:59 pm Post subject: Re: 8N Ford 6Volt to 12 Volt Conversion 


grabbatire........NO....NO....NO......the "infamous ballast resistor" is a special kind of resistor that changes value with heat. It starts out about 0.5ohms and as it heats up (inna'bout 2mins) it INCREASES in value to about 2ohms. This is something you can NOT measure with common ohmmeter. But you can measure the effect on the top of your 1terminal squarecan ignition coil with yer VOLT meter. Ittza LAW, Ohms Law.
The "infamous ballast resistor" is like yer lightbulb, it either works or it don't. So iff'n yer tractor starts, guess what??? Yer ballast resistor is working. .........Dell, yer selfappointed sparkiemeister 

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Grabatire Regular
Joined: 05 Mar 2009 Posts: 212
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Posted: Tue Dec 11, 2012 9:38 pm Post subject: Re: 8N Ford 6Volt to 12 Volt Conversion 


OK guys, I'll try to find an oem resistor. The owner of this tractor had put a jumper across the terminals of the resistor when it burned out so he could feed his critters, but the points didn't like it and eventually gave up. That's when he asked me to convert it to 12V. I've worked on the engines of these little tractors quite a bit, but never did a 12V conversion on one.
I guess I should ask; What is the voltage I should be shoot'n for when measured at the terminal on top the coil? It's my understanding that the original 6 volt system was reduced to near 4 volts at the points by the oem resistor. Would that be a bit too much to expect on a 12 volt system.
I found some 12 volt conversion information on the 'net' that showed a second resistor in series with the oem resistor but it didn't say whether the coil was still 6V or had been changed to 12V. 

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souNdguy Tractor Guru
Joined: 20 Aug 2002 Posts: 57613
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Posted: Wed Dec 12, 2012 6:24 am Post subject: Re: 8N Ford 6Volt to 12 Volt Conversion 


the oe resistor is commonly available.. get it. otherwise you will be playing hide and go seek matching up a fixed ressitor value.
new 2.5 ohm coil and old oe resistor tend to play well together.
soundguy 

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JMOR Tractor Guru
Joined: 13 Aug 2007 Posts: 18998
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Posted: Wed Dec 12, 2012 6:48 am Post subject: Re: 8N Ford 6Volt to 12 Volt Conversion 


Grabatire wrote:  (quoted from post at 01:38:19 12/12/12) OK guys, I'll try to find an oem resistor. The owner of this tractor had put a jumper across the terminals of the resistor when it burned out so he could feed his critters, but the points didn't like it and eventually gave up. That's when he asked me to convert it to 12V. I've worked on the engines of these little tractors quite a bit, but never did a 12V conversion on one.
I guess I should ask; What is the voltage I should be shoot'n for when measured at the terminal on top the coil? It's my understanding that the original 6 volt system was reduced to near 4 volts at the points by the oem resistor. Would that be a bit too much to expect on a 12 volt system.
Don't shoot for a voltage. What you are after is 4 amperes steady state coil current (engine stopped/points closed/ign on). Now, IF, I said IF, the coil is 2.5 ohms, that will yield 10 volts across the coil.
I found some 12 volt conversion information on the 'net' that showed a second resistor in series with the oem resistor but it didn't say whether the coil was still 6V or had been changed to 12V.
IF you use the 6v coil, its resistance is a nominal 1 Ohm (they vary from as low as 0.47 up to 1.5), so when used on 12 volt system, you need to add the second resistor, exact value depends on exact coil, but typically about 1.5 to 2.0 Ohms.



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Dell (WA) Tractor Guru
Joined: 21 Sep 1998 Posts: 25117
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Posted: Wed Dec 12, 2012 9:11 am Post subject: Re: 8N Ford 6Volt to 12 Volt Conversion 


grabatire.........many times, instead of replacing the burned points, shadetree mechanics will "jump" the ballast resistor for hotter sparkies and eazier starting. Unfortunately, they fergitt to remove the jumper and MELT the insulative tar inside the squarecan coil and will no longer start 'cuz you end up with weak sparkies and BAD coil.
Heres the deal on extra resistor. Many "bubba" conversions are done on the "cheap". Use the original ballast resistor plus a 12Vto6V conversion resistor in series like flashlite batterys. (resistors are cheaper than new 12V coil)
As fer voltage readings, about 4volts at top of the 6V squarecan coil and about 10volts at top of new 12V squarecan coil (with the points CLOSED) .........Dell, yer selfappointed sparkiemeister 

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Mimos Guest
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Posted: Thu Dec 13, 2012 4:47 am Post subject: Re: 8N Ford 6Volt to 12 Volt Conversion 


Where can I find the manual that has Ittza LAW Ohms chart ? 

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JMOR Tractor Guru
Joined: 13 Aug 2007 Posts: 18998
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Posted: Thu Dec 13, 2012 6:17 am Post subject: Re: 8N Ford 6Volt to 12 Volt Conversion 


Mimos wrote:  (quoted from post at 08:47:53 12/13/12) Where can I find the manual that has Ittza LAW Ohms chart ?  Same place you get the "8 ways to convert & they all work first time" list. Elusive. 

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