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I have a 49 1/2 ton that i rewired last year.
(12 volt) The only thing i did not replace was the blower toggle heater switch which is original. I used the heater for the ist time yesterday. I reached down to oggle the switch from high to low. Being dark I grab the back of the switch and burnt my fingers. The wires were HOT. When i got home i seen where the back of the switch has some type of wire coil which i believe has ceramic in the coil. My question is what is this coil and is this suppose to get hot?

49dream,

Think of that little coil as a toaster and your fingers as the toast.

The coil is a resistance in the line which "holds back" the electricity so the heater motor speed can be varied.

More voltage..fan runs fast. Less voltage..fan runs slower.

The pregnant question (actually two questions) is did you change the heater motor to 12 volts when you did the swap. Are you sure the switch was on the HIGH setting when you cooked your pinky's. The little rheostat should not have been red hot on HIGH, but might have been on LOW.

The heater switch wouldn't be voltage sensitive, but would be rated for current. I actually don't know if a 6 volt motor that is run on 12 volts draws less amperage than a 6 volt motor on 6 volts..I think it would draw less, so that's why I wonder about the heater switch being hot when the fan was on high.

Maybe Mr.Ohm and his pie chart will be along soon.

Stuart

Now this was one of the 1st questions I asked about with my truck. When you run the heater motor on high it will be warm, when you run it low it will be hot. If you touch the back of it itll burn you, it did me...

In idiot terms (how I understand it) the heater motor uses a lot of power, the coil on the back of the switch turns that excess power to heat, therefore your sending less power to the heater motor so it turns slower and vice versa. High setting puts more power to the motor and less to the coil on the back of the switch so it stays cooler.

Let us know what you find. Jeff

Yep

It's the Law of Conservation of Energy in action.

Thanks everyone for your input. To answer Stuart questions. I might of not had it on high and was it changed over to 12 volt? All i can say is I hope so. The truck was converted to 12 volt when I got it. The person that had it before me did't know anything about wiring. I had a real mess and tore everthing out and put a EZ wire kit in. I replaced all the switches except the heater one. If I were to replace this switch does anyone have a reconmendation.
Marcus

Marcus,

I'm pretty sure the switch would be the same regardless of 6 or 12 volts (I think). It is the heater motor that is usually changed with the swap to the higher voltage.

I think the very best advice would be don't change anything now...just be aware of the hot coil and your fingers.

As was noted above, that thing is suppose to get hot..it's OK if it is hot. The prudent thing to do would be to make sure there is a fuse in the heater motor circuit. A 15 amp inline dude ahead of the hot thing would be just ducky.

Stuart

If you put a rheostat control on you'll have nearly infinite fan speeds at your fingertips.

AD-52,

Although this is someone else's thread, this deals with the same topic...so here are some thoughts.

The 6 volt heater blower motor will run on 12 volts, but will run proportionatly faster. This increase can sometimes be noisy, and at full blast might stress the motor to a point of no return.

Previous posts show folks do run it this way for years. If you buy the proper voltage reducer and install it ahead of your variable switch in the motor circuit, you can retain both the switch and the motor and have them perform as they should.

I have enclosed a link showing the reducer. Good luck.

http://www.fifthaveinternetgarage.com/parts/parts_counter_2.html

Stuart

I'm thinking that a 6 volt switch coil/resistor would be overloaded after time and may burn up. The resistor is desiged to disipate a certin amount of heat at 6vdc not 12vdc.

Beaver53,

Generally speaking, a 6 volt switch should be rated for twice the current as a 12 volt switch. They probably aren't dialed in this way, but from the standpoint of Ohms Law, the math says 'twice the voltage..half the current'.

Running the 12 volt motor at a comfortable speed might require the switch to be running like a little toaster most of the time, but it should handle it...the main concern would be having one of the grand kids grabbing it..OUCH!

Just remember the battery cable thing. Modern 12 volt cables are the size of a straw. Old fashioned 6 volt cables are the size of a elephants trunk. With only half the 'pressure' they have to be twice as big to get all those little 'amperes' shoved through to Mr. Starter.


Stuart

Atmo, Is it the volts or amps that turn the motor? Would a 12 volt 100 amp generator run a 24 volt 50 amp motor at half the speed with no damage?

Beaver53,

I don't know the answer to your question. This is how I understand it. Voltage is the power, or potential that powers a device. Amperes are not something supplied to a device, but a measurement of the current used by the device to create work.

The heater motor can have 12 volts ready and waiting to do work...but until the motor turns on, no work is being done..no current is flowing.

Regarding your hypothetical generator, my guess would be, yes, it would run the motor. Although I am not a electrical engineer, I think the current draw of the motor is a function of the voltage supplied, but also of its construction.

Electric motors, both AC and DC are a science in themselves.

Electrical concepts are tough to visualize. It is possible to prove them using Ohms Law, but that does little for the person like me that needs to see and touch things to really understand them.

This topic has come up before and turned into a biggest bag of worms the world has ever seen.

Maybe someone will show up that can explain this clearly to both of us.

Stuart

Thanks

There is a basic problem when trying to apply Ohm's law to the analysis of a circuit with a rotating machine in it. The problem being the round thing with the shaft sticking out of it.

The current draw of a motor is determined by the voltage applied to it and THE MECHANICAL ENERGY DELIVERED TO THE LOAD by the shaft.

A motor running with NO mechanical load will draw a very small amperage. As you apply mechanical load to it, the amperage will increase rapidly as the motor slows down.

If we had a test motor and were able to have a variable speed 'load' attached to it, as you increased the speed of the variable speed 'load', you would see the current in the circuit actually drop to zero. If you continued to increase the speed, the current would reverse and our test motor would become a test generator. The key is MECHANICAL energy flow. As we speed up the 'load', we reverse the flow of mechanical energy from out of the test motor to into the test motor at the same time reversing the flow of current from into the motor to out of the motor.

Any motor that is turning either from the electrical energy supplied to its terminals OR from the mechanical energy supplied to its shaft is generating an internal voltage called a 'back EMF'. If the motor is being turned by the supplied voltage, then back EMF will tend to OPPOSE the supplied voltage.

In plain English, the motor behaves like a variable voltage generator that is directly tied to the speed the motor is turning. The voltage OPPOSES the voltage applied by the vehicle battery. The motor will accelerate until a balance is established between the applied voltage and the internal voltage at which point the motor will run at a steady speed.

If you apply twice as much voltage to the motor, the motor will have to turn twice as fast in order to reach this balance point.

If you stick a resistor in the supply circuit, then some of the supply voltage is 'dropped' across it and the motor runs at a slower speed.

Whats the current? That depends on the amount of mechanical power required to turn the fan, the speed of the motor, the battery voltage, the size of the voltage dropping resistor and a couple of other minor things.

The ceramic encased wire coil on the heater switch is a voltage dropping resistor used to provide slower speeds for the fan. It is normal for it to be VERY hot when running the fan at one of the slower speeds. In high fan position, there is normally not be a resistor in the circuit and the switch shouldn't be more than just warm on high speed.

This gentleman from Walla Walla is a veteran of the first great Heater Switch War of '06.

As they say on the reservation, "he speak truth".

Stuart

With all that great information now out in the open,will the life of the 6 volt heater switch be the same as a 12 volt heater switch on a 6 volt heater motor? Hmmm