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Can I use my old 6 volt heater switch with my 12 volt system? This is the switch that bolted under the dash of a 1952 chevy 1/2 ton truck. On the back of the switch is what looks like a coil winding that may dissipates heat and a 20 A glass fuse.

It will work, but it will get hot as H, especially when run on partial speed.

An electronics person will correct/confirm/clarify. My comment is based on personal experience.

I would love to hear a solution to this. I have a box of these switches, and I want to use them with my 12 volt systems for aesthetic reasons. Is there a resistor change that is available or what can we do to make them work just as they did with a 6 volt system. The aftermarket ones do not look the same.

I use the factory correct toggle switch on 12 volts and a 12 volt motor, and it works fine. I don't think that it gets any hotter than when I was running 6 volts on a 6 volt motor.
It is a switch with resistance coils in it.
The switch does not know whether it is a 6 volt or 12 volt switch.
Just don't tell it.
Carl

Hey Tim, what's wrong with your web site, can't access it this morning.

dg

Yep, must have been someone messing with the server.
Need to go and spend the morning at your place and
see what kind of new stuff you've added.
Thanks.
DG

Deve & Carl,

Good to know thank you. My ceramic on the back is not in good shape. I've seen somewhere a picture of an updated switch with a larger heat sink. Is there a source for those?

T

I didn't know 6 or 12v would make a difference in a rheostat switch. Any rheostat switch will get really hot at partial speed. I am no expert so I learned something today I reckon. FWIW 12v rheostat switches are available through the vendors. I always thought that was just marketing (6 or 12v) but I guess not eh?

Its a 4 position paddle switch with 3 pickoffs on the resistor that is on the back of the switch beside a fuse holder. OFF-LOW-MED-HIGH.

If the motor amperage is 2 amps, if the battery voltage is 6v, that's 12 watts. If it's 12v, it's 24 watts. (P=IE) They get hotter than blazes with a 12v input. I have 5 of them and all have very badly cracked and discolored resistors and blown fuses. I would just like to get a 3-pickoff resistor that is rated for 12 volts. I have not been successful yet.

https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=1014407&page=all

This is a great thread about these switches. The thing that isn't mentioned is what happens when you put 12 volts to it. In that case, Power comes into play, not just Ohms Law. The 6 volt resistor wattage rating is half that of what is required for 12 volts, thus why it gets so hot. I am looking into a more optimal ohm value when using a 12v motor (12v system) and a higher wattage solution so you can feel safe using the stock switch.

Thanks Dave,
If you find a source or solution let us know.

The problem is a unique one. If you install a 12 volt heater motor on a 12 volt system, there is NO resistor needed at full blast. But to get medium and low, THAT is a different story. To do that, you have to lower the voltage to 9.8 volts at Medium, and 6.2 volts at low. With a 12 volt system, two one ohm resistors ganged together will do exactly that. Problem is, we have the Power Formula to contend with. The Siemens 12 Volt replacement motor takes 3.94 amps at full speed. I tested that myself. Now I have one problem left to figure. What wattage resistors do I use? Research is still ongoing.

The power formula, wattage equals amperage times the voltage, seems easy. But I am stepping down so it would be the difference. Its a little confusing for this old brain.

Or you could stop over thinking it and build a tray to go under the stock switch for making toast while operating the heater in the low position. You will have to drive around all day before its ready...

Then again..

The motor does pull around 50 Watts at full voltage, which is not 12 volts, it's 13.8 volts. As you put the Voltage Dropping Resistors in series with the motor you get the confusing part.

The Current that is drawn changes as each of the added resistors cause the voltage to decrease.

In low speed you have a total series resistance of 5.7 ohms. I=E/R so you will have I=13.8/5.7 which = 2.4 amps. P=E, 13.8 x2.4 = 32.64 Watts.

The Power that is lost to the motor is due to the resistors and their voltage drops. Remember as you change series resistance the motor current changes!!

To figure the "voltage drop" across each resistor I had to figure total series resistance for the low and medium settings. LOW has a total series resistance of 3.7 ohms (motor), and 1.0 for the LOW speed resistor and another 1.0 ohms for the MEDIUM resistor. This all figures out to about 2.4 amps drawn in LOW speed, 2.8 amps drawn in MEDIUM, and 3.8 amps drawn in HIGH speed. Series circuit amperage is the same through all the series components.

Use E=I/R, and you'll see the various voltage drops as the resistors are added and removed. POWER dissipated by each resistor must be calculated individually as they are added or removed because the amperage changes and thus, the voltage also changes going thru the resistor!

So, making a long story short: In low setting 5.6 Watts will be dissipated in "both" the 1 Ohm resistors, and in high setting (Remember you have only one resistor in series now.) The medium resistor will dissipate 7.8 Watts. The best way to handle this is to get two 1 ohm, 10 watt power resistors. Axial, Cement Wire Wound. Mouser Electronics and sometimes Ebay are good choices for finding them.

The one that has three leads that comes on the original switch has a 5 watt power rating. THAT is why they burn up when applying 12 volts to them. This is not over because now I have to figure out a way to hide these two (larger) 10 watt resistors. Rather than wasting my time on an AD Toaster, I think I will concentrate on a good place to hide the resistors. Any ideas?

Anyone else out there burning up AD toggle switches on 12 volts other than Deve?

I had one back in the 70s, when I briefly converted from 6v to 12v. It glowed under the dash (as best as I can remember).

One thing that they do with modern switches is they separate the switch from the resistor. Picture
The selector switch is mounted on the dash and the resistor is mounted inside the heater duck work. Picture
The fan circulates air pass the hot resistor, cooling it down.
Which may make it last longer.
Also adds a little heat to the circulating air.

I was thinking that this could be done with the older Delco or ARC-LES switches.
Use the same switch and remove the resistor on the back and mount it inside the heater box.
But then it wouldn't be stock.

I like this idea. I think we can make it look stock anyway. I think if it were done right, nobody could see the modification and a person could even make kits for everyone else to make it easier. The entire reason for the effort is to use a stock switch for aesthetics. The heat coming out of the core wouldn't effect the thermal characteristics of the resistors anyway.

I know almost nothing about amperage, etc, and 12v to 6v resistors.

From the information posted above, about the original 6v system, the heater/switch draws less than 3 amps?
- Here is a 4 amp load 12v-6v voltage reducer.
- here is a 6 amp load 12v-6v voltage reducer

The confusion here for some of you is we are using a 12 volt motor, 12 volt system and need to switch to 12 volt rated power resistors so that we can maintain the stock appearance.
The resistors are about $2 each.

If you keep your stock 6 volt motor, there are stepdown resistor solutions available from the vendors that remove this issue entirely as you mention above.

A thing to keep in mind. In a "Series" circuit, the voltage drop at each "Load" adds up to the total volts available. So if Deve's numbers are good(I have no reason to doubt them) you will get something like the following.
High speed. 13.8 V. across the motor. That gives you 3.7 Amps to run the motor at 13.8 V.
When you add a 1 Ohm resistor(medium speed) you have a total of 4.7 Ohms. The Resistor(1 Ohm) and the motor(3.7 Ohm) you get 2.9 Amps to run the motor and drop 13.6 Volts across the motor. The other .5 volts is dropped at the Resistor. That Resistor now has .5 Amp to convert to heat.
With the other Resistor in place(slow speed) Resistor1(1Ohm) Resistor2(1 Ohm) and the motor(3.7 Ohm) you get 2.4 Amps to run the motor. And the Voltage drops to 8.8. With 3.2 Volts dropped across both Resistors, about 1.6 Amps across each one. The Amps is how you make "work"(speed) more Amps is more speed. In this case "work" equals fan speed. The Amps at each Resistor in slow speed is about 1.6 Amps that must become heat. The only issue that could come from a 6 Volt control at 12 Volts would be a High speed, almost High speed and a very fast low speed control.
The thing that happens in a 6 Volt system, is that 2 times the Amps are needed to do the same "work". So consider the following, 6 Volts and the same motor Resistance. High speed Amps is 1.9. The 6 Volt motor must have a lower Resistance or it would be slow and slower. With the same Amps(3.7) a 6 Volt motor would have to be close to 2 Ohms.

Below are Ohms readings & pictures of a (ARK LES) 6 volt, 3 speed switch resistor.

Below is a resistance TEST going thru the switch.
Switch position OFF open circuit,-------------------- no reading
Switch position HIGH closed circuit, no resistance,-0 ohms
Switch position MEDIUM closed circuit,-------------- 1.1 ohms
Switch position LOW closed circuit,------------------ 1.7 ohms

Below is a resistance TEST of the resistor.
Resistor tap 1 to Fan motor lead ------ 0 ohms
Resistor tap 2 to Fan motor lead ----1.1 ohms
Resistor tap 3 to Fan motor lead ----1.7 ohms

Switch Photo Album
How electricity works. Ohm's Law clearly explained. The Ohm guy is the resistor.
Ohm's Law Calculator and all Formulas

Does 52pu have a 6v or 12v heater-blower motor in his 12v electrical system (and 6v heater switch)?

Happy Birthday, Steve_H

Jorb, I used those numbers when looking into all this. Thanks! It turns out that the 12 volt motor behaves a little differently and two 1 ohm resistors are all that is needed. Just at a more suitable power rating.

I have a 6 volt to 12 volt motor conversion on my web site here:

http://devestechnet.com/Home/HeaterRestore

I did NOT have the switch solution figured out at the time, so I have yet another tech article to amend. I am trying to get completely away from 6 volts having no part of the electrical system stepped down with step-down resistors. As I have more time, I will address every electrical system and how to do that. Not enough hours in the day!

BTW, I have 6 of these heater switches and 5 of them are ARK-LES.

I don't really trust those switches. They give off more heat than the heater. I have the heater on full speed or not at all.

I'm also changing from 6v to 12v, purchased a reducer for the heater motor, but not for the switch..........hope this works!.....any suggestions/advise?

I am not an electrician, but I do not see where it matters whether the reducer is upstream or downstream of the switch. (Upstream/downstream?! I told you that I am not an electrician.)
Carl

Put the voltage reducer you got before the switch so that it also gets the benefit of the reduction. If you don't you will have a very hot switch and the same problem I have been talking about. Does that make sense?

Thanks Dave!

The reason that it does not matter where the reducer goes is because it is the electric motor that dictates the amperage draw. The sum of the voltage reducer resistance plus the resistance in the heater switch is the only thing that matters.
Look at it this way. Lets say that you have two resistors inline between a battery and a motor. One is 2 ohms and the other is 5 ohms. Does it matter which resistor is closer to the motor? No, it does not.
Carl

It matters Carl because he is changing the voltage of the entire system. He wants to keep his 6 volt heater motor and all that that entails. Part of the entailment is the resistors and switch that are only rated for 6 volts. It has to do with wattage.

If the 6 volt stream starts before the resistors on the back of the switch, the entire system will think its 6 volts, not just the motor. I know its confusing. If volts and amps were all we had to contend with, it would make sense, but we also have watts.

There are two ways to do this. Go with a 12v motor and higher wattage resistors, or the way bjs went. Stepping down the heater circuit. Part of that circuit is the switch and the resistors.

I know this thread is an old one but thought I would post an update in case anyone else searches for answers to this question. I have a recirculating dealer installed Harrison heater in my 54 3100. I replaced the 6v motor with a 12v motor. I took the truck on a 1 1/2 hour ride with the 4 position (OFF-LOW-MED-HIGH) original rheostat switch set to LOW. It worked perfectly. I did not increase the size of the fuse. I stayed with the original 20 AMP size. To be clear, I did then try the other speeds and the switch performed as it should.

I am running the 6 volt switch with a 12 volt motor on a 12 volt system on my '49 1/2 ton. Switch gets a bit over warm in the low and medium position after 2 hours of running, but not hot. I'm with dgrinnan and 52Carl on this one....so far.

Tim

Another data point on the blower........

Running a 6 volt blower motor on 6 volts draws about 8 amps runs normally.
Run a 6 volt blower motor on 12 volts is draws 17 amps and runs about twice the normal speed.