A little electrical help please

[Edward B.]

Re: A little electrical help please

Well, I had my son go check the voltage using your method (he's home today), but I'm not sure he did it right. He says with the car on and the switch in the LOW position, he's getting 4.5 volts between terminal 2 and 3. That can't be right can it???

Ed

[Joe R.]

Re: A little electrical help please

Well, I had my son go check the voltage using your method (he's home today), but I'm not sure he did it right. He says with the car on and the switch in the LOW position, he's getting 4.5 volts between terminal 2 and 3. That can't be right can it???

Ed

Hi Ed,

That sounds a lot more reasonable to me. You probably would not want to drop 10 Volts across the resistor, that only leaves 4 Volts for the motor. So, I would use a 10 Watt wirewound resistor (that old resistor looks like it has a lot of inductance because of how it's wound). Here are some choices for you:

http://www.mouser.com/Passive-Components/Resistors/_/N-5g9n?P=1z0x70qZ1z0wt4w

I think it comes down to mechanical considerations now (package size and mounting). 5 % tolerance or less is probably fine. By the way, the motor is drawing a little over an amp of current on low speed (I = V / R = 4.5 Volts / 4 Ohms).

Joe

[Edward B.]

Re: A little electrical help please

EXCELLENT Joe! Thank you VERY much.

Looks like they don't have one that's really small (like the original), so I'll probably have to go with one a little bigger, but since it's hidden, it shouldn't be a big deal.

My last question would be about heat. Some of them show in the graphs that they generate a LOT of heat! Up to 150 degrees. I don't remember the old one generating that much, but then again, I never really paid that much attention. Should I be concerned with how much heat these things are putting out? I want to make sure I don't burn something up after I get it all put back together again!

Ed

[Joe R.]

Re: A little electrical help please

EXCELLENT Joe! Thank you VERY much.

Looks like they don't have one that's really small (like the original), so I'll probably have to go with one a little bigger, but since it's hidden, it shouldn't be a big deal.

My last question would be about heat. Some of them show in the graphs that they generate a LOT of heat! Up to 150 degrees. I don't remember the old one generating that much, but then again, I never really paid that much attention. Should I be concerned with how much heat these things are putting out? I want to make sure I don't burn something up after I get it all put back together again!

Ed

Ed,

You're welcome! I must admit I didn't look at the graphs. But since the resistor will actually dissipate around 5 W in circuit, a 10 W resistor should be as cool as a cucumber. Well, maybe not that cool, but I would imagine that it should not be very warm to the touch. I would recommend seeing how hot it gets before you stick it in the torture chamber.

Good luck and may the force be with you!!! Please let us know how it turns out.

Joe

[Edward B.]

Re: A little electrical help please

I would recommend seeing how hot it gets before you stick it in the torture chamber.

Good idea.

Please let us know how it turns out.

I'll certainly do that Joe, and MANY thanks again!

Ed

[Joe R.]

Re: A little electrical help please

Ed,

You're welcome! I must admit I didn't look at the graphs. But since the resistor will actually dissipate around 5 W in circuit, a 10 W resistor should be as cool as a cucumber. Well, maybe not that cool, but I would imagine that it should not be very warm to the touch. I would recommend seeing how hot it gets before you stick it in the torture chamber.

Good luck and may the force be with you!!! Please let us know how it turns out.

Joe

Ed,

I had another thought. Assuming it runs fairly cool in free air, mount the panel, run it for a while, then pull the panel to see if the resistor is hot or discolored (a sign of being hot).

Joe

[Edward B.]

Re: A little electrical help please

"Discolored"

You mean like this? (see attached)



(That's a picture of my 68 roadster that burned to a crisp many years ago. The sordid details can be found HERE.)

So you can probably guess why I'm so concerned with heat!!

Ed

[Joe R.]

Re: A little electrical help please

"Discolored"

You mean like this? (see attached)



(That's a picture of my 68 roadster that burned to a crisp many years ago. The sordid details can be found HERE.)

So you can probably guess why I'm so concerned with heat!!

Ed

Ed,

Hopefully not discolored like that!!! That is a bummer and a half!!! Yes, heat is always a concern. I try to be very conservative in my designs. I will be very surprised if that resistor runs hot. Give it a shot, I think you will be fine.

By the way, I did not mean to insult you. Many people don't know that with electronics, a good visual inspection should be the first step when there's trouble. It has saved my bacon in the past!!!

Joe

[Edward B.]

Re: A little electrical help please

No, you didn't insult me at all. I really appreciate your help.

I'll see what my local Radio Shack has and go from there. If I can find something local, that would be great. There's also a "mom-n-pop" electronics store not too far away, so they may have something too.

Ed

[Joe R.]

Re: A little electrical help please

No, you didn't insult me at all. I really appreciate your help.

I'll see what my local Radio Shack has and go from there. If I can find something local, that would be great. There's also a "mom-n-pop" electronics store not too far away, so they may have something too.

Ed

Hi Ed,

OK, good deal. Keep in mind that if you want the resistor to run as cool as possible, you could approach it from the angle of trying to fit the highest wattage resistor possible in the space available. I will pretty much guarantee a 25 or 50 W resistor will run cool for you. Also, if space is tight, here's a 20 watt resistor in a TO-220 package that I've used in the past:

http://www.ohmite.com/cat/res_tah.pdf

I don't think it would have near the inductance of the original, but I doubt that is very important here.

Joe

[Edward B.]

Re: A little electrical help please

Joe, that does look very promising, but I just noticed at the bottom of the page it says (in BIG BOLD RED LETTERS!!!)

THIS PRODUCT IS DESIGNED FOR USE WITH PROPER HEATSINKING.

Since there's no heatsink on the switch, do you think that could be a problem?

Also, I noticed you mention inductance again, so I did a little Google searching last night and from what I can see, it appears this device isn't really a "resistor", but an "inductor" coil. At least that's what it looks like to me. Am I wrong about that? It's just a single wire wrapped around and around several times inside a ceramic (?) tube. I'm a little confused on what this thing really is! I was under the assumption that the ceramic (?) tube was just to protect the wire from touching the housing and shorting out, or some kind of heatsink (or both), but if it's part of the resistor (or inductor), and it's now missing, then would my original readings be skewed?

Ed

[Joe R.]

Re: A little electrical help please

Joe, that does look very promising, but I just noticed at the bottom of the page it says (in BIG BOLD RED LETTERS!!!)

THIS PRODUCT IS DESIGNED FOR USE WITH PROPER HEATSINKING.

Since there's no heatsink on the switch, do you think that could be a problem?

Also, I noticed you mention inductance again, so I did a little Google searching last night and from what I can see, it appears this device isn't really a "resistor", but an "inductor" coil. At least that's what it looks like to me. Am I wrong about that? It's just a single wire wrapped around and around several times inside a ceramic (?) tube. I'm a little confused on what this thing really is! I was under the assumption that the ceramic (?) tube was just to protect the wire from touching the housing and shorting out, or some kind of heatsink (or both), but if it's part of the resistor (or inductor), and it's now missing, then would my original readings be skewed?

Ed

Hi Ed,

OK, I would recommend following the manufacturer's recommendation and use a clip on TO-220 heat sink like one of these (with some thermal grease):

http://www.mouser.com/Thermal-Management/Heat-Sinks/_/N-5gg0?P=1yz8nmlZ1z0yxmxZ1yzvl0j

That's assuming it all fits, of course.

The voltmeter doesn't care if it's a resistor or an inductor, it just measures the voltage for you. I don't think the inductance is important here. I suspect that's just the way the resistor was wound to get it to fit in the package they planned to use. It looks to me like the purpose of the resistor is to slow down the motor by limiting the current supplied to it. An inductor in series with a motor in a DC circuit does not do anything. The inductor is a short to DC.

Joe

[Edward B.]

Re: A little electrical help please

Perfect. Thank you again Joe. Your assistance is GREATLY appreciated!

Ed

[Edward B.]

Re: A little electrical help please

Rich, from my research, and as far as I can tell from the documentation, the 1968 to late 1973 system was the same (a two wire switch with a resistor built in to reduce the voltage on the low side).

It changed sometime in late 1973 or early 1974 to the resistance wire you refer to, which now used the three prong switch with no resistor that you and Tom (above) mention.

The switch for 1968 was originally P/N 3861697 and changed in the AIM to 3942696. I can't make out the exact date, but it looks like ?-2-68. (The early 3861697 switch was also used from 1965 - full size and Chevelle - through 1968 - full size, Chevelle, Camaro, Nova and Corvair).

The 1969 Corvette AIM shows the part number as 3942696, and this changed ONLY for the Corvette.

(Note that the 1973 P&A 30B (dated October, 1972) shows the switch for 1969 through 1973 as the same for the late 1968, P/N 3942696.)

However, this is where it starts to get cloudy. The 1979 P&A 14 (dated 14 June, 1979) shows the 3942696 being used from 1969 to 1973 like the other P&A does, but it also shows P/N 410202 for the switch for 1974 through 1976. The problem here is that this is a plastic, 3 prong toggle switch and I KNOW there was a 3 prong "rotary" switch used in late 1973 or early 1974 because of the pictures attached.

I believe this 3 prong rotary switch isn't mentioned in any of the P&A's, but it MIGHT be mentioned in the 1973 or 1974 AIM (of which I have neither).

1st picture - Late 1973 or early 1974 3 prong ROTARY switch (front) - (No clue what the part number was)
2nd picture - Late 1973 or early 1974 3 prong ROTARY switch (rear) - (Again, no clue what the part number was)
3rd picture - Mid 1974 (?) 3 prong TOGGLE switch (front) - (Part number 410202)
4th picture - Mid 1974 (?) 3 prong TOGGLE switch (rear) - (Again, part number 410202)

Sorry guys. I just noticed I made a mistake in terminology. The above should read "3 prong ROCKER switch", not "3 prong TOGGLE switch". It's too late to edit the original post unless a moderator can do it.

And by the way, does anyone have a 1973 or 1974 AIM they can check to see if that 3 prong rotary switch is listed? It may be in the Revision Record at the bottom right of the page.

Ed

[Jeffrey S.]

Re: A little electrical help please

Ed,
Here is a photo of the switch from my Oct '68 car. As you can see there is no resistor. On the photo of the switch plugged in you can see an inline fuse. Hope this helps.
Jeff

Mike, it's a 1969 roadster and the switch is in the driver's side front console trim panel.

Ed