Board index Flathead Power-Technical Questions, Answers, and Suggestions Knuckles 6 volt coil in 12 volt system ?????

6 volt coil in 12 volt system ?????

Post Mon May 18, 2009 9:12 pm

Posts: 5
Hi, May be a dumb question and I may be hoping for an answer that is self evident but you never know? right? My replica 12 volt coil went to heck and I have a 6 volt coil and am wondering what would hapen if I ran the 6 volt coil in the 12 volt system, would spark be hotter or would coil just burn up or will it work ok in the real world as many thing do Thanks Tom

Post Mon May 18, 2009 9:44 pm

Posts: 2688
Location: Los Angeles, CA
Burn up the coil

Post Tue May 19, 2009 7:54 am

Posts: 5
thanks, that's what I figured

Post Tue May 19, 2009 10:44 am

Posts: 1676
Location: Interlaken, NY USA

Right, and would burn up your points as well. However, to "get you home", put a taillight bulb in series with the coil, and you'd make out o.k.
DD

Post Tue May 19, 2009 1:26 pm

Posts: 62
Location: Texas' Big Bend country
You could also use a ballast resistor; should be available at the auto parts store.
--- Randall

Post Tue May 19, 2009 2:36 pm

Posts: 5
That resistor sounds interesting, cheaper than a new coil- is there a certain one I should get? thanks

Post Tue May 19, 2009 4:00 pm

Posts: 121
I think ballast resistors only bring it down to 8volts on most auto applications.

Post Wed May 20, 2009 12:53 am

Posts: 1654
putting a ballast resistor in series with a 6v coil sounds a pretty stupid way of saving a trivial amount of money, to me. If you need that kind of savings you'd be better off selling your Harley and buying a Honda 90, you'll have less problems and not be living on baked beans
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Wed May 20, 2009 7:21 am

Posts: 5
Yeh, i'ts more trouble than it's worth but it is always fun to play with stuff and learn , my initial question was valid though- I do have the origiional coil and wanted the wisdom- don't want to ruin a nice old part

Post Wed May 20, 2009 7:23 am

Posts: 5
incidently, I have a yamaha trial 90 in my stable and it is a blast-especialy at swap meets

Post Wed May 20, 2009 7:40 am

Posts: 1654
I've had several junior speedway and grasstrack bikes over the years with Honda engines ranging from 90, 125 and 185cc and they have generally been a hoot.

I had one in particular, an overbored 100cc which did at least 16 rides with 3 different riders in the same meeting. By the end of the day it was so hot you couldn't touch any part of the engine, the exhaust had fractured in two places, the clutch springs were so soft that it had to be pushed off in a rolling start - but it was still running....
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Wed May 20, 2009 12:54 pm

Posts: 62
Location: Texas' Big Bend country
In regards to ballast resistors; in the years after 12-volt systems were first introduced on cars and trucks it was common for them to be fitted with a 6-volt coil and a ballast resistor. It was a winding of wire about 2 inches long in a porcelain insulator, usually mounted on the engine compartment firewall. I don't know why they used the 6-volt coils, maybe they had a lot of them on hand. I used to convert quite a few 50's vintage cars and trucks to 12 volts and would install a ballast resistor because it was cheaper than buying a new coil. It would make for a messy wiring set-up on a bike, but it would work and that was the question.
--- Randall

Post Wed May 20, 2009 1:12 pm

Posts: 1676
Location: Interlaken, NY USA

GM used the ballast resistor so that they could start with 12 volts across the coil, then switch to running with the voltage dropped across the ballast resistor to 6 volts. Got you a hotter spark for starting. Or, in reality, after the battery voltage was dropped by the starter draw, probably about 8-9 volts at start.
DD

Post Thu May 21, 2009 4:07 am

Posts: 1654
there is a 'fix' sometimes seen on old British bikes, involving using a resistor to increase the output of the old 6v, 60W Lucas dynamo to 12v 90W. It 'sort of' works but doesn't last very long...
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Thu May 21, 2009 4:31 am

Posts: 1676
Location: Interlaken, NY USA

That D*&^mn Lucas generator is the basis of 90% of the bad "Lucas, Prince of Darkness" jokes. What a POS. Who the F%$#CK would try to build a Generator with only one field pole/winding and whose armature windings were actually a fusible link. Don't get me started :x That little C&%$Ksucker is one third the size of a 32E and was expected to to the same work. Totally underengineered for the task at hand.
By the way, that resistor was meant to reduce the current to the field winding when you threw a 12 volt regulator on one of those things and hoped to run some 12 volt lights.
DD

Post Thu May 21, 2009 7:11 am

Posts: 641
Location: Wisconsin, USA
Come on Dick, don't hold back, tell us how you really feel about the Lucas gen. My earliest Triumph was a 62 650 single carb job. If my memory serves correct it had an alternator? When I was living in Phoenix, I took a weekend ride to Flagstaff and was on my way home when I noticed the machine losing speed. The geography in the mountains can mess with your head sometimes, as far as being able to determine visualy if you are going uphill or down. I just cranked up the throttle more and more as I slowed. When I realized it was mechanical, I looked down to see smoke pouring out of the breather. When I backed out of the throttle, the motor locked up. I thought I had overheated and melted motor parts together. When I started to tear it apart, I found the alternator fused into a solid lump. Removing that mess turned out to be one of the toughest repair jobs ever. I might have cussed Lucas a bit too.

Post Thu May 21, 2009 7:37 am

Posts: 1654
those generators aren't very clever, and I DID say the 12v 'conversion' didn't work very well.....
Last edited by 45Brit on Thu May 21, 2009 5:01 pm, edited 1 time in total.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Thu May 21, 2009 1:21 pm

Posts: 1676
Location: Interlaken, NY USA

45Brit, don't worry, nobody's holding you responsible for Joesph Lucas's unconscionable plundering of poor working folks hard earned money. He probably laughed all the way to the bank, in his MERCEDES.. :D :D
Kyle, I had to cut one of those off with the torch, after cracking the cases trying to press it off. Personally, I think Joe Lucas had the English channel dug to cut off his fellow countrymen from the rest of the world, so they wouldn't know equipment existed that didn't fail if not ministered to every weekend!
I'm done, and that's why I switched to H-D.
DD

Post Thu May 21, 2009 5:03 pm

Posts: 1654
those 6v-to-12v conversions were a classic early 70s idea...
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun May 24, 2009 9:50 pm

Posts: 646
Location: Detroit
To get home you can use any 12 volt coil.
New Knuckleheads? Thank, you, Jesus!!

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