What is a good resistor size?

Lochlin

All,

I have a 1.4 ohm ballast resistor on each of my carts to help keep the electronic ignition modules, coil and plug cool. The resistor is between the module and the coil.

I was chatting with a Harley motorcycle guy over the weekend and he said that he converted his vintage bike from points to electronic. In talking, he mentioned that, in his opinion, the 1.4 ohm resistor is not enough and suggested going as high as 3 ohm which seems a little to much to me. Then again, I suppose if the plug is fires with a bigger resistor then the lessened current can only help to keep things cool. To get a bit more detailed, the bike guy mentioned that, like carts, his bike's generator puts out out right around 14 v when operating property. He said that ignition modules / coils shouldn't be subjected to much over 10v hence the need for bigger than 1.4 ohm resistor. Yes, I realize that I am switching between amps and volts but it's the same logic in this scenario.

Anyone have any thoughts on this?

BGW

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tew45

I think the current limiting (Ballast) resistors come in around 1.5 ohm and a 3 ohm. If you get e good spark with a 3 ohm resistor it will give you longer coil life. Check the site (Ignition Solutions for Small Engines) They give you some very good info on point and electronic systems!

73eldo

Its a pretty poor design if they can't take 14 volts since most 12v systems run in that range. If it needs such a device it should be included with the kit or they should at least specify what is required. Some coils have built in resistors so are clearly identified as such and others not so much. Having the resistor at the coil will do different things than having it in the feed of the module. Most cases you don't want it on the module feed but in some cases it is needed. I think the 70's Chrysler system used one in both sides. The GM HEI of the 70's used a micro processor as part of the module so they didn't need a resistor. If GM had that technology in the early 70's I would think a cart module designed at least in the 80's could easily have something similar.

For being a simple device what the resistor is doing is fairly complicated. In this case its being used as a current limiting device. It can be a little hard to wrap your brain around because its somewhat of a dynamic process.

Here is a bit of info on the concepts.
https://en.wikipedia.org/wiki/Current_limiting

tew45

Also be sure to check the ( Ignition solutions for small engines ) it goes into most all of the ignition systems. I think some of the electronic systems on the site are going to need a voltage inverter. There are prints on construction of the inverter somewhere on the forum.

johnny reb

out of curiosity i havent seen a point elimination set for harley carts. do they make such a thing? i put one on a cb 750 i had and i loved it, no more popping in the rain.

Lochlin

The electronic module for the 86 and later carts can be put into the earlier carts. The ignitor will be the same for all years but the rotator will be different depending on what year crankshaft you have.

Warning, these modules are $150 - $175 plus another $30 for the right rotator. Hence why I want to make sure to protect them with a $10 resistor.

My carts have never run better though.

73 Eldo homemade a system for much less that I intend to try at some point.

tew45

Does the rotator have 2 magnets in it? (One for each direction or?)

johnny reb

i found it. for that price points run fine. ew45 it looks like 2 magnets http://www.vintagegolfcartparts.com/...idson_ignition
here is the ignition too
http://www.vintagegolfcartparts.com/...idson_ignition

tew45

I am trying to find an alternative for the hall effect ignition system that is affordable and workable. Any input is helpful.

73eldo

Interesting that there is 2 magnets and they are 180 off from each other. Hard to tell where they are based on the offset of the hole in the photo. It must be sparking twice? Once that would be slightly advanced for forward and then again at what would be advanced for reverse?

If you are willing to spend in the $200 range you can pick up an MSD6 capacitive discharge ignition box. Those things generate a crazy hot spark and will trigger off points. With that like my conversion you are only using the points for a trigger for the electronics so you don't have wear issues and the gap adjustment is not critical.