Heater Switch Fried

[YukonJack]

Converted my 47 to 12 volts a few years ago. Ran my 6 volt heater on 12 volts. Worked ok, just ran very fast. Last winter the switch gave out, you had to wiggle it to get the heater to come on. The original switch was mounted to the front of the heater, not the control panel. Went to Napa, got a universal 12 volt under dash switch. Hooked it up and it worked fine, on high. On anything lower than high the rheostat in the switch would start smoking. Ran the heater today (a little cold in Chicago) for about 15 minutes and the fan started slowing down on its own. Finally quit working. Any thoughts on this. I would really like to get the heater working again.

[Plymouthy Adams]

if you did not smell anything smoking, the bushing are probably dried out due to the extra heat generated by the 12 volt operation..possible you may disassemble and relube for continued operation..

[greg g]

I was for some reason thinking on this the other day, those littel clip on reostat switches are not robust enough to deal with the draw. Would a balast resister in the line drop the volage enough to get a workable fan speed with 12 volts going in to the resistor???? They are cheap enough, and easy to mount, and would drop the voltage to 8 9 volts. wonder what their reliablity would be. Still probably cause a lot of heat.

[Don Coatney]

Would a balast resister in the line drop the volage enough to get a workable fan speed with 12 volts going in to the resistor????

I have not tried it but I dont think a ballast resistor has enough ampacity to run a DC motor. Even using a ballast resistor to drop voltage across my ignition coil heats the resistor to the point it will burn your fingers. Using a ballast resistor on a coil where it is only moving electrons is no where near the load requirement of spinning a motor to drive a fan blade.

[bob westphal]

You need to buy a 12-6 volt reducer. These will get hot and need to mounted away from wiring etc. Thankfully the 6 volt windings are heavier than 12 volt or you would have cooked the motor.

[Plymouthy Adams]

just keep in mind that if you do use the Runtz type dropper..the motor will surge before returning to the slower speed..you may or may not notice this...if you do..this will be normal..

[YukonJack]

just keep in mind that if you do use the Runtz type dropper..the motor will surge before returning to the slower speed..you may or may not notice this...if you do..this will be normal..

I used the Runtz reducer on my gas gauge when I first did the conversion. It lasted about a day, then burned out. Seemed like a waste of money. I've been running 12 volts to the gas gauge ever since without a problem.

[grey beard]

My feeling is that Mr. Adams is correct - the higher speed of the motor from 12 volts of electrical pressure has sorta' been hard on the bushings - mebby the windings, too. When you run a six volt system on 12 volts, you don't have to worry about cutting down the amperage - you've already cut it in half. That's why 12 volt wiring is smaller gauge than six.

The analogy of six volt starters cranking on 12 volts comes to mind. They sure do crank their hearts out, and many of them will last for years, The undeniable truth of the matter is that that high speed engagement is a little tough on starter drives and ring gears, and eventually the bushings peter out due to the excessive rpm, but no one has ever had to install a voltage or amperage reducer in their craking circuits. Methinks the same logic applies to our friend's heater motor that's been running on 12 volts very happily for some time - and at a quite higher speed than originally. JMHO

[Plymouthy Adams]

Alrighty now...I just got in from the laboratory..(shop in my case)...here are the specs from using a 6 volt fresh charged battery..12 volt fresh charged battery..one 6 volt heater motor and my clip on amp meter prope and digital (110 volt) multimeter..zero'd the meter to the probe...also I check this against direct analog reading on the 10 amp scale just to bench mark the set up.

6 volt...surge to 7 amp start current and runs on 4.79 amp constant draw at speed. analog with 7 start and 5 run show on the digital.

12 volt...surges to 17 amps start current and runs on 9 amps constant speed and may I add very high speed...

using a 2 ohm dropping risistor rated at 25 watts..when connected to 12 volts will surge to almost 5 amp on start and run at 3 amps constant and just under speed..and in four minutes the resistor is quite warm..

using a Chrysler ballast resistor on 12 volt it will surge to 7 amp start current and runs constant at 5 amp draw...and runs very much to speed as that of the normal 6 volt operation..after about 4 minutes run time the resistor is warm to touch and feels about the same temp as the 25 watt'er did...

Third test put the 25 watt resistor and the ballaster in parrallel to each other and in series with the motor yields a current draw of 6 amps..slighly higher speed and after 4 minutes the combination of the reisistor was just warm.

As the ballast resistor is about 1.3 ohms I feel if you go to your local electronics friendly and get a ceramic housed wire wound resistor in the neighborhood of 50 watt or better and then mount that on a piece of aluminum as a heat sink..you should be on the money with speed and current draw equal to stock while running 12 volt and the added heat sink further increase life of resistor..

I imply no guarantees on your configuration or results as that is outside of my ability to look over your shoulder..

HAVE FUN

[Norm's Coupe]

If I recall correctly, I think blueskies (Pete) just had the same problem with his heater motor that was 6 volt, running off 12 volts.

As for adding one of those reducers, I'm no expert. However, in the catalogs I have for them, they all say, "not for use with any type of motorized accessories". Just for use for radio, gages etc.

As for Tim's solution. Sounds logical and maybe worth a try, if you can get the old motor to run again. If the motor needs repairing though, I would just have it rebuilt to a 12 volt motor since the car has already been converted.

[Don Coatney]

Alrighty now...I just got in from the laboratory..(shop in my case)...here are the specs from using a 6 volt fresh charged battery..12 volt fresh charged battery..one 6 volt heater motor and my clip on amp meter prope and digital (110 volt) multimeter..zero'd the meter to the probe...also I check this against direct analog reading on the 10 amp scale just to bench mark the set up.

6 volt...surge to 7 amp start current and runs on 4.79 amp constant draw at speed. analog with 7 start and 5 run show on the digital.

12 volt...surges to 17 amps start current and runs on 9 amps constant speed and may I add very high speed...

using a 2 ohm dropping risistor rated at 25 watts..when connected to 12 volts will surge to almost 5 amp on start and run at 3 amps constant and just under speed..and in four minutes the resistor is quite warm..

using a Chrysler ballast resistor on 12 volt it will surge to 7 amp start current and runs constant at 5 amp draw...and runs very much to speed as that of the normal 6 volt operation..after about 4 minutes run time the resistor is warm to touch and feels about the same temp as the 25 watt'er did...

Third test put the 25 watt resistor and the ballaster in parrallel to each other and in series with the motor yields a current draw of 6 amps..slighly higher speed and after 4 minutes the combination of the reisistor was just warm.

As the ballast resistor is about 1.3 ohms I feel if you go to your local electronics friendly and get a ceramic housed wire wound resistor in the neighborhood of 50 watt or better and then mount that on a piece of aluminum as a heat sink..you should be on the money with speed and current draw equal to stock while running 12 volt and the added heat sink further increase life of resistor..

I imply no guarantees on your configuration or results as that is outside of my ability to look over your shoulder..

HAVE FUN

Tim;

Thanks for posting. There for a while I thought I was the only one with a meter here.

[Jim Saraceno]

As Tim's research tells us, if you double the voltage you will double the current. In a resistive load (lights) it will be a direct correlation - I=ExR, with an inductive load (motors) it is a little less direct as what limits the current in a motor is counter electromotive force which will change with speed.

Many 12 volt devices will take 1/2 the current because they will be made with twice the resistance. A 35 watt 12 volt bulb will have twice the resistance as a 35 watt 6 volt bulb and use 1/2 the amperage. However, you put 12 volts on that 6 volt bulb and it is now a 70 watt bulb burning real bright for a short amount of time because it is now carrying twice the current that it was made for.

I'm not real sure about how dc motors are made. I don't know it they make 12 volt motors with a heavier wire that will take the higher current or if they do something to limit the current so they are still using the same amount of power.

Let's just say for the sake of argument, a 12 volt motor is built to use the same amount of power as a 6 volt motor. So a switch that is used for a 12 volt motor is made to carry 1/2 the current as a switch for a 6 volt motor. Now you take that 12 volt switch and put it in the circuit that is running a motor made to run on 6 volts but is now running on 12 volts. You now have a switch that is made to carry 1/2 the current, actually running twice the current which means it is running 4 times the current it is designed for.

You may need to figure out how much current your motor is drawing and find a switch that is not only rated for 12V but the proper current (or wattage, depending how it is rated).

[jd52cranbrook]

Truck parts and service places offer 12 to 6 volt drops encased in ceramic . They are rather cumbersome, but they offer one lead in for the 12 volts, and two 6 volt outputs. Made for larger than a dash gauge load. I use one on my wiper motor for the last two years of winter driving, never had a problem. Bolted it to the firewall and have forgotten all about it till now. I would not use a Runtz type that I use on my fuel gauge and dash clock. I don't think it would hold.

[Merle Coggins]

As Tim's research tells us, if you double the voltage you will double the current. In a resistive load (lights) it will be a direct correlation - I=ExR, with an inductive load (motors) it is a little less direct as what limits the current in a motor is counter electromotive force which will change with speed.

Actually, you got your formula wrong. the The current in a circuit will have an inverse correlation to the load and voltage. The correct formula is E (voltage) = I (amperage) X R (resistance). If you are calculating amperage it would be I = E/R. Pushing 12 volts through a 6 volt motor will draw fewer amps, even though it'll spin faster.

Merle

[greg g]

I think if you look at the way 12V heater motors operate, they ae switched through a resistor switch to modify the motor speed. I believe if you put a meter on the output, you wil find something like 6, 8 10, and then 12 volts as full speed is an unresisted circuit. So in the switch circuit doesn't halving the voltage to a device cause its current draw to go up? And wouldn't that require a more robust implement that one running on 12V alone?????

[Plymouthy Adams]

Actually, you got your formula wrong. the The current in a circuit will have an inverse correlation to the load and voltage. The correct formula is E (voltage) = I (amperage) X R (resistance). If you are calculating amperage it would be I = E/R. Pushing 12 volts through a 6 volt motor will draw fewer amps, even though it'll spin faster.

Merle

That is why I did not quote any formula's as most folks can read a meter and hook up a wire..if you go back and read my findings..you will find that the current did jump higher...in the 12 volt pushing the 6 volt motor the current was quite bit higher...using your own formula above..we have...(motor read about 1.9 ohm vlaue..and will be constant regardless of applied voltage)

12.62 volt divided by 1.9 ohm for a current of 6.64 amps which is close to the 7 amp listed above in my finding for run current..remember the surge will be greater

6.2 volts divided by 1.9 ohm for a current of 3.26 amps

slighlty less than the 4amp shown om my digital meter as I posted but remember..we dealing with benchtop wiring and non calibrated instruments..but the theory proves itself..push the voltage..you push the amperage...

As stated earlier..the winding of the 6 volt motor compared to a 12 volt motor is the difference in the amperage...wish I had a 12 volt motor winding I could get to real easy..

Also using the dropping resistor of 1.3 ohms with the 1.9 ohm motor pushed by 12.62 volts gives you current of 3.94 amps...again where my test setup ball parked the reading

[Jim Saraceno]

I = E/R. Pushing 12 volts through a 6 volt motor will draw fewer amps, even though it'll spin faster.

Merle, thank you. You are half correct. I=E/R not I=ExR. And I am half correct. Double the voltage will double the current. Either by ohms law or by Tim's research.

I think if you look at the way 12V heater motors operate, they ae switched through a resistor switch to modify the motor speed. I believe if you put a meter on the output, you wil find something like 6, 8 10, and then 12 volts as full speed is an unresisted circuit. So in the switch circuit doesn't halving the voltage to a device cause its current draw to go up? And wouldn't that require a more robust implement that one running on 12V alone?????

The speed of todays modern fan is controlled by adding resistance, however the speed of a motor can also be controlled by how it is manufactured. I believe if they change the winding ratio, they can change the speed of the motor and in the end, it is the speed of the motor that changes the counter electro motive force (cemf) and that will limit the current. If you add resistance to a circuit, it may decrease the voltage on the motor, making it go slower but you have increased the resistance of the circuit so I would think you would decrease the current. But it may be awash, in the end the added resistance and the lowered cemf may just add up to the same amount of power being used.

[YukonJack]

That is why I did not quote any formula's as most folks can read a meter and hook up a wire..if you go back and read my findings..you will find that the current did jump higher...in the 12 volt pushing the 6 volt motor the current was quite bit higher...using your own formula above..we have...(motor read about 1.9 ohm vlaue..and will be constant regardless of applied voltage)

12.62 volt divided by 1.9 ohm for a current of 6.64 amps which is close to the 7 amp listed above in my finding for run current..remember the surge will be greater

6.2 volts divided by 1.9 ohm for a current of 3.26 amps

slighlty less than the 4amp shown om my digital meter as I posted but remember..we dealing with benchtop wiring and non calibrated instruments..but the theory proves itself..push the voltage..you push the amperage...

As stated earlier..the winding of the 6 volt motor compared to a 12 volt motor is the difference in the amperage...wish I had a 12 volt motor winding I could get to real easy..

Also using the dropping resistor of 1.3 ohms with the 1.9 ohm motor pushed by 12.62 volts gives you current of 3.94 amps...again where my test setup ball parked the reading

My original thought was that the fan switch in lowest speed position I would be operating the motor at a speed equal to high when it was 6 volts. The original 6 volt switch lasted a while with 12 volts and did control speed. The rheostat on the back eventually burned out. The new 12 switch only allowed high speed and when I tried to turn the speed lower the rheostat would start to smoke.

I did stick my finger in in heater (power off) and the fan does have some resistance when I spin it. I don't think it is a factory heater as the switch was originally mounted to the front of the heater and had a red illuminated know that has ARVIN written on it. Am I going to need to remove the heater from the car to oil the bushings or will the cover come off with the heater still mounted?

[Plymouthy Adams]

right you are but boy the cost of the motor with three seperate windings versus using a dropping resistor..and a good resistor network will be internal to the ducting where the fan is cooling it as it drops the voltage...would not want it anyother way...

[windsor8]

Truck parts and service places offer 12 to 6 volt drops encased in ceramic . They are rather cumbersome, but they offer one lead in for the 12 volts, and two 6 volt outputs. Made for larger than a dash gauge load. I use one on my wiper motor for the last two years of winter driving, never had a problem. Bolted it to the firewall and have forgotten all about it till now. I would not use a Runtz type that I use on my fuel gauge and dash clock. I don't think it would hold.

Do you have a part number or name of dealer or manufacturer of this part?

[Plymouthy Adams]

My original thought was that the fan switch in lowest speed position I would be operating the motor at a speed equal to high when it was 6 volts. The original 6 volt switch lasted a while with 12 volts and did control speed. The rheostat on the back eventually burned out. The new 12 switch only allowed high speed and when I tried to turn the speed lower the rheostat would start to smoke.

I did stick my finger in in heater (power off) and the fan does have some resistance when I spin it. I don't think it is a factory heater as the switch was originally mounted to the front of the heater and had a red illuminated know that has ARVIN written on it. Am I going to need to remove the heater from the car to oil the bushings or will the cover come off with the heater still mounted?

on my BF Goodrich aftermarket heater assembly I used to bench test with, yes the cover does come off and giving you access to the motor without having to pull the entire unit from the car...actually the motor can be removed from the base after the cover covers off leaving the back case and heater coil in position..

[Merle Coggins]

OK. I stand corrected. I knew my formulas were correct, but I didn't think all the math through. Tim's findings would be right.