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12v replacement for 6v round duoglide coils

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panhead_kicker
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12v replacement for 6v round duoglide coils

#1

Post by panhead_kicker » Fri Sep 18, 2009 3:26 am

I've looked over several aftermarket vendors, but have not seen anyone sell a 12v version of the dual 6v round coils found on late dual point duoglides. Has anyone found a decent replacement?



Schwee
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Re: 12v replacement for 6v round duoglide coils

#2

Post by Schwee » Fri Sep 18, 2009 1:52 pm

I converted my dual point to 12 volt years ago and continue to run the "6 volt" coils. They work just fine and I've never had any one explain to me why it would be a problem (I'd like to know).

The only trouble I've had is once I left the ignition on all night and the next morning one of the coils was toasted - cracked down the side and no more spark. Don't know if that would have happened if the battery were 6 volt.

I bought new (6V) coils from J&P three or four years ago. Expensive (about $100 each), but working great.

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Re: 12v replacement for 6v round duoglide coils

#3

Post by panhead_kicker » Sun Sep 20, 2009 5:03 pm

panhead_kicker wrote:They work just fine and I've never had any one explain to me why it would be a problem (I'd like to know)
While my education is in the ee field, my actual line of work doesn't exercise it. But , from what I do remember, I would think that running your 6v coils on 12v would cook your points in short order and eventually the coils themselves, as the secondaries would now be pumping out a considerably higher voltage than the system was designed for. You would have been less likely to have toasted the coil when you left your ignition on all night if the battery had been 6v.

I guess I could run an inline resistance to the stock 6v coil and cut the voltage down. That would be the least expensive way to go , if I am thinking things through right. But I 'd still like to know if their are any bolt-in replacement 12v coils out there as an option. Anybody?

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Re: 12v replacement for 6v round duoglide coils

#4

Post by kell » Sat Oct 03, 2009 12:40 am

A friend of mine has a 12 volt BSA with round coils. You could look into it. I don't know if they're the same size as Harley coils but hey, you might get lucky. I'm a big believer in adapting parts from other vehicles to work on Harleys.

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Re: 12v replacement for 6v round duoglide coils

#5

Post by RUBONE » Sat Oct 03, 2009 12:58 am

Lots of American vehicles used 6V coils with 12V sytems in the '50s and 60s when 12V became prevalent. They use inline ballast resistors to drop the voltage.
Robbie

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Re: 12v replacement for 6v round duoglide coils

#6

Post by panhead_kicker » Sat Oct 03, 2009 3:04 am

Thanks for the responses guys. I figured this one died quietly. I am going to take one of my 6v to NAPA tomorrow and see what they might turn up, resistor or coil wise.

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Re: 12v replacement for 6v round duoglide coils

#7

Post by panhead_kicker » Sun Jun 06, 2010 7:14 pm

I am getting ready to try and run my 64. I don't want to have to fight more than one thing at a time, so I was wondering if, rather than swap out my single point with a dual point circuit breaker, if I can run my two 6v coils, with the negatives both driven by the single point circuit breaker lead. I've run this breaker before, so it will be a known good, while I work out any issues with a new Linkert. Any ones see any issues with this?

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Re: 12v replacement for 6v round duoglide coils

#8

Post by panz4ever » Sun Jun 06, 2010 8:45 pm

If this can be done, can someone post a pic of how this should be wired and if a resistor is used, what type and how to/where to connect it. Have a OEM dual point set (6v) along with a dual point timer I was thinking to use on a 56 project but keep it 12v w/ 6v coils.

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Re: 12v replacement for 6v round duoglide coils

#9

Post by panhead_kicker » Tue Jun 08, 2010 1:24 am

Here is what I plan to do. In pic is a 12 to 6v resistor , that I believe will work for this application. It will go in line with the positive B wire from the battery in the schematic to reduce my 12v battery to 6vs to make the coils happy. The positive terminals on the coils will be tied together as shown. Rather than the B and Y wires from the circuit breaker, I will have the single circuit breaker wire feed tied to both coil negative terminals.
Anyone see any issues with this?
Eventually I'll swap out the circuit breaker with the correct dual point. I plan to keep the resistor. The metal mounting stud comes off with a little persuasion. The remaining ceramic is pretty small, and can be stashed about anywhere.
12v_6v.JPG
12v_6v.JPG (281.36 KiB) Viewed 1751 times

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Re: 12v replacement for 6v round duoglide coils

#10

Post by Dave_R » Tue Jun 08, 2010 2:36 pm

Years ago running 6V coils on a 12V system was considered a "trick" to get a hotter spark, since the spark voltage (secondary) became double of what it used to be.

The drawback was that the coils usually did not last as long (A few years instead of many years) due to the insulation break-down. The insulation rating on the secondary conductors get "stressed-out", and can lead to "flash-over" (Where one winding arcs over to another winding). This can also be caused by the windings actually moving a little, rubbing against each other. This is more apparent with greater voltages (picture striking an arc with an arc welder, and seeing the cables "jump" at first contact).

Also, like some have said, your points do not last as long either. I used to run (and still do) the heavy duty blue-streak points that fit a 6 cyl chevy (Single point set-up).

This is because the current on the primary increases. I = E / R

Since Coil Resistance (R) is the same, doubling voltage (E) results in doubling current (I) through the primary, which is what your points control.

Hence, the resistor you have is a real good idea for any coils that you want to last, or have any age on them.

Anyways, this is how I understand it.

- Dave

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