Hi, There!!
I have changed my 52 ford to 12 Volts system, but there are a couple of devices that I keep without modification. One of them is the Windshield wiper and the other one is the heat fan. I connected a resistor to low the voltage but when it is working, it gets red and too hot. (I think it is not the best way to reduce voltage)
Does anybody knows how I can do this?
I´ll really appreciate your help!

Nacho Salazar

 

You need a solid state fifteen amp voltage reducer. Ron Francis wire works has a pretty nice one. The URL is:

http://www.wire-works.com/D5.asp

 

You may want to try this Battery


12/6 Battery: Convert your 6 volt car to a 12 volt and tap off 6 volts for your accessories. Available in all group sizes. You must have a 12 volt charging system

http://antiqueautobattery.com/prod011.htm

Dick C
Erie, PA

 

Ignatio, there is nothing wrong with using a resistor on a constant current device such as your motors.
In your case the resistor appears to be underated in its wattage.

Here are some formulas to use:

R=E/I where R=Resistance; E=Voltage drop desired; I= current in amps drawn by the motor.

As an example lets assume that you will be dropping from 14 to 7V and the motor draws 5 Amps.

So we have a 7V drop; 7/5 = 1.5 Ohms for the resistor.

Next we need to calculate the power in watts required.

There are a few ways to do this but lets use:

E(squared) divided by R

7x7= 49/1.5 = 32.7 Watts.

In this example you could use a 1.5 Ohm (standard stocked value)50W aluminum encased resistor mounted to a bare metal surface on the firewall and with a thin coat of thermal paste available at Radio Shack.
The resistor is available at www.mouser.com for $2.75 and they do not have a minimum order. The 50W size is only about 2" long so it is quite compact and unobtrusive.

You can determine the current required by measuring in series with the load.

The next size power rating resistor is 100W.

If you need more help or getting the part let me know, I have a business account with Mouser.