I'm working on an older build, the owner wants to retain as much of the original flavor as possible, this includes running the resistor that was on it. it's a tubular wire wound unit, maker unknown. the rest of the ignition is stock '57 Chevrolet, stock single point distributor, stock (replacement) coil. only upgrade are some fancy plug wires. looks like you move the lug along the tube to get desired resistance. any information would be helpful
I don't think it's adjustable.... That green stuff is a ceramic coating protecting the wire, unless there's a bare 'stripe' on the back, I don't know what the 'clamp' is for... Maybe repairing a crack?
search: wire wound adjustable resistor just wondering if anybody here has experience using one and wisdom to impart.
measure the resistance of the thing, let us know what it is. and for fun, you could take it off the car and take a picture of the back side of it.
The back side has a strip of the wire winding exposed with the adjustable strap contacting it. Much like a rheostat only instead turning a knob to adjust you move and set the strap. I'll do some testing and post findings tomorrow.
The way it works, is you figure out what resistance you need, then you move the band to where it needs to be to get that resistance (relative to one end of the resistor). then connect one wire to the correct end, and the other to the band. Pretty simple, and probably what you already thought?
A search and some interesting gives me the notion that it wasn't originally intended as a ballast resistor and was probably for some electronic item that needed exact voltage. Probably stuck on there by an electronic tech that owned the car at some time in the past when the original ballast resistor gave up the ghost. If it works and puts out the correct voltage to the coil I'd say leave it as part of the cars history and replace it with a correct one if it ever craps out. One of the things the article said is that they are pretty stout and stand up well.
Recalling the 'transfer' between the points, and a proper ballast R prevented this. (Possibly same R as the coil & wiring?)
Vintage adjustable resistor. As others have said, loosen, slide to dial up your required resistance and then reclamp. Connections are at one end and the central slide (like ya hadn't figured that out already). Popular in old radios and TV's. If it was working before, you prolly don't need to mess with it. Does it have a cover? These are not meant to be in dirty areas. Are there any numbers on the unit? It would be a good idea to check to power rating just to be on the safe side.
The power rating is closely related to size...it's a big'un, so as long as it has a low enough overall resistance, I wouldn't worry about that.
We used adjustable resisters all over the older power plants I worked in for 45 years. A wire was always connected to the tap when the needed resistance was found. Not that you couldn't but I never found one on a car and if the resistance was correct with out the tap clamp I would just remove it. They are always mounted in open air for cooling purposes.
Yes, that is just a "tapped" resister, they were used on old radios/tv's back when they used tubes. If you have an Ohm meter you could check the resistance of it. I think you want something less than 3 ohms, maybe even 1.4 ohms for a ballast resister. It looks like it mounts on that one end and if it does, it may bounce around a lot. If I was you I would just get a real ballast resister.
I've never seen one used for a ballast resistor before, but they were pretty common on early electric trailer brake controllers
Sure you did ! Get rid of it. The white ceramic ones are period correct for that car. Sent from my iPad using H.A.M.B.
The first setting where it's 1.4 ohms is probably where you want it. Or you could leave the band off, and run it at 1.7 ohms, it will still probably work. Or leave the band on, and just connnct to the ends. The reason you don't see any voltage drop by connecting the volt meter to it, is that the resistance of the volt meter is much higher than the resistance of the resistor. I don't really feel like trying to teach electrical theory, but if you were to connect an ignition coil through the resistor to the battery, you would see the voltage drop. A voltage dropping resistor only works under load.
thanks Jim, that helps. I am relatively ignorant when it comes to testing and understanding electricity, it usually ends up being if it's broke replace it with what I believe to be a reasonable replacement..
most folks have no clue about dealing with electricity, no worries. Hopefully you know enough to understand what this part does, and how to make it work for what you want it to do.
It just looks like someone replaced a fixed value ballast resistor with a variable one, because that's what was available at the time. The value was dialled up, installed, then, because it worked, was left there. Sort of like your "temporary roadside fix" that becomes permanent. When I see those old ceramic jobs, reminds me of working on tube equipment from the 30's.
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