New ballast resistor trick

Electrical issues
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kell
Posts: 369
Joined: Sat Jun 19, 2004 2:58 am

New ballast resistor trick

#1

Post by kell » Tue Aug 24, 2004 4:44 am

I found a way to use a 1.2 ohm coil... with points! Just get a halogen headlight element (the little doohickey in the center, not the whole headlight) at any auto parts store and use it as a ballast resistor.
When you first kick the bike to start it, the halogen element will be cold and have a resistance of only about an ohm. So you will have total primary resistance of only about 2.2 ohms, giving you a lot of current, and a hot spark. When the bike's running the bulb starts to glow, the resistance goes up to several ohms, limiting the current. I measured the current with this setup and it's very close to the current I get using a 5 ohm coil.
Years ago in a small independent auto parts store I found a ballast resistor the did the same thing. It had an exposed wire element; cold, an ohm or less (for starting); then during running the element got hot went up to a couple ohms resistance. I don't have the part number, unfortunately. It was used in some Chryslers.
Of course, a glass bulb is not the perfect ballast resistor, because it could break. But I was kind of wowed by how well it works.



Billy
Posts: 719
Joined: Tue Mar 23, 2004 6:57 am

Re: New ballast resistor trick

#2

Post by Billy » Tue Aug 24, 2004 5:35 am

Kell, I remember those exposed Chrysler ballast resistors. Usually mounted to the Chrysler's firewall.
I do believe that JC Whitney still sells them.
In Fact I'm almost positive they do.

http://www.jcwhitney.com" onclick="window.open(this.href);return false;

57pan
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Location: Michigan, USA
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Re: New ballast resistor trick

#3

Post by 57pan » Tue Aug 24, 2004 4:44 pm

Kell, you just keep coming up with these cool ideas.

How long does it take to cool back down again?

Hot starts have always been my main problem - like when you turn it off at the gas station to refuel and then try to start it again. I suspect that the halogen element may not have cooled sufficiently during that time since it is somewhat insulated inside the glass bulb. Maybe the exposed wire ballast resistor would cool off quicker though.

kell
Posts: 369
Joined: Sat Jun 19, 2004 2:58 am

Re: New ballast resistor trick

#4

Post by kell » Wed Aug 25, 2004 3:39 am

I realized the bulb is not gonna work, because...
As soon as you turn the ignition on, it likely will be in dwell, meaning the bulb will get hot before you even get a chance to kick it, because the bulb gets hot real fast, like in a second or two.
The Chrysler ballast resistor takes more like a minute to heat up or cool down.
The ballast resistor would be more workable all around, since it gives you time to kick the bike, and it's not made of glass!
If the exposed element ballast resistors are too hard to find a guy could use a common ballast resistor and put a switch that jumpers across it to use while starting. A 2.3 ohm coil and the 2.5 ohm ballast resistor from some old car should be pretty easy to get. All you gotta do is find a place on your bike to put the chunky resistor and a switch.

mbskeam
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Re: New ballast resistor trick

#5

Post by mbskeam » Wed Aug 25, 2004 4:44 am

hello, what is up with the ohm ratings on coils? please learn me
mbskeam

King
Posts: 373
Joined: Fri Apr 02, 2004 5:05 pm

Re: New ballast resistor trick

#6

Post by King » Wed Aug 25, 2004 2:22 pm

Me too. And how do you test them??

King

kell
Posts: 369
Joined: Sat Jun 19, 2004 2:58 am

Re: New ballast resistor trick

#7

Post by kell » Thu Aug 26, 2004 2:34 am

First up a lot of cheap ohmmeters don't measure low resistance in the range of a few ohms accurately.
I know one that does give good measurements is the Radio Shack auto-range digital multimeter that folds up, about $25. You can measure a coil's resistance accurately with that; just set the dial on the ohm symbol (looks like the omega in alpha-and-omega) and touch the leads to the primary terminals on your coil.

Ohms are resistance to current. More ohms means more resistance, and thus less current. With points, you have to keep the current fairly low or they will burn up, so points bikes use 5 ohm coils, or in the case of cars with points -- about 2.5 ohms in the coil and a 2.5 ohm ballast resistor.
Transistorized ignitions can be made to carry more current than the old points ignitions could handle. So you use a lower resistance coil. The advantage with having more current flowing in the coil, of course, is that when it comes time to fire the spark, the coil has more energy built up as a result of the high current and you get a bigger spark.

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