12 volt conversion harness question
- Thread starter AZ Chris
- Start date
Bruce Lancaster
Member Emeritus
6v circuits use twice the amperage of 12v equivalents, so stock haress in good shape or repro made for 6v gives you wiring with a big safety margin. 12V Ford generator parts from the basic '56-63 generator generally raided for conversion pieces wire up using same harness as the 6v.
Bruce Lancaster
Member Emeritus
Just use the original harness and figure out what alternator needs and all will look stock...there will be an output wire, affix it to B terminal on regulator using the old regulator as just a terminal block and object to make firewall look right. Second wire can be spliced and run back to idiot light, resistor, or whatever alt needs and harness will look stock.
Dave in WY
Member
Bruce, Using ohm's Law, would a 6 volt heater switch work okay for a 12 volt heater motor?? I tend to think it would, but not sure if the resistors will hold up.
Dave
Dave
COE Dan
Senior Member
Dave,
I know I’m not Bruce but I think this answers your question.
First, my assumptions:
1) The 12V motor does the same work as the 6V motor (i.e. it spins a fan/moves air at the same speed).
2) If the motors do the same work, the power consumption will be the same. (This is probably not entirely true in reality due to lots of variables but close enough to approximate here.)
3) The resistor(s) are switched in series with the motor to give the motor multiple speeds.
Next, if the 6V and 12V motor power consumptions are the same, this means electrically they consume the same wattage.
Ohm’s Law converted for power is: Watts (W) = Volts (V) X Current (A)
Doubling the voltage (from 6V to 12V) halves the current required to produce the same work (wattage):
Example: Wattage = (6V) x (1A) = 6W = (12V) x (0.5A)
Switches are not really susceptible to voltage variations (especially differences as small as 6V). Voltage failure in switches occurs when you approach the design limits of the internal parts (i.e. switch will arc internally, arc to ground, dielectric breakdown, etc.). We’re talking hundreds of volts or more usually.
However, current limiting capacity (usually the size of the switch contacts/wiring) is the greatest concern – they must be able to handle the current required by the circuit.
Since 6V motors need double the amperage of a 12V motor to do the same work, you can usually assume anything wired for 6V will handle the current needed for 12V operation. Therefore, as long as your 6V switch can handle the same or more current than your 12V motor draws, you’ll be fine.
Lastly, the resistors placed in the motor switch circuit for speed control work as follows:
Electrically, current flow sees the motor as a resistor (which just happens to dissipate energy by rotation rather than purely heat). The voltage is distributed across both the motor and the resistor in proportion to their individual resistances, effectively dropping the voltage and the current across each. The partial voltages across the resistor and the motor will sum to 12V and individually always be less than 12V. This causes the motor run slower than a motor without a resistor because the voltage and current across it will be lower. Further, a circuit with the resistor will draw less current than one without. Therefore, your resistors won’t generate as much heat during 12V operation vice 6V due to less current flow which means they shouldn’t be damaged.
Bottom line, make sure your switch/resistors can handle the max rated current draw of the 12V motor and you’ll be fine.
Dan
(Hopefully any simplifications I made here for clarity don’t confuse anyone…)
I know I’m not Bruce but I think this answers your question.
First, my assumptions:
1) The 12V motor does the same work as the 6V motor (i.e. it spins a fan/moves air at the same speed).
2) If the motors do the same work, the power consumption will be the same. (This is probably not entirely true in reality due to lots of variables but close enough to approximate here.)
3) The resistor(s) are switched in series with the motor to give the motor multiple speeds.
Next, if the 6V and 12V motor power consumptions are the same, this means electrically they consume the same wattage.
Ohm’s Law converted for power is: Watts (W) = Volts (V) X Current (A)
Doubling the voltage (from 6V to 12V) halves the current required to produce the same work (wattage):
Example: Wattage = (6V) x (1A) = 6W = (12V) x (0.5A)
Switches are not really susceptible to voltage variations (especially differences as small as 6V). Voltage failure in switches occurs when you approach the design limits of the internal parts (i.e. switch will arc internally, arc to ground, dielectric breakdown, etc.). We’re talking hundreds of volts or more usually.
However, current limiting capacity (usually the size of the switch contacts/wiring) is the greatest concern – they must be able to handle the current required by the circuit.
Since 6V motors need double the amperage of a 12V motor to do the same work, you can usually assume anything wired for 6V will handle the current needed for 12V operation. Therefore, as long as your 6V switch can handle the same or more current than your 12V motor draws, you’ll be fine.
Lastly, the resistors placed in the motor switch circuit for speed control work as follows:
Electrically, current flow sees the motor as a resistor (which just happens to dissipate energy by rotation rather than purely heat). The voltage is distributed across both the motor and the resistor in proportion to their individual resistances, effectively dropping the voltage and the current across each. The partial voltages across the resistor and the motor will sum to 12V and individually always be less than 12V. This causes the motor run slower than a motor without a resistor because the voltage and current across it will be lower. Further, a circuit with the resistor will draw less current than one without. Therefore, your resistors won’t generate as much heat during 12V operation vice 6V due to less current flow which means they shouldn’t be damaged.
Bottom line, make sure your switch/resistors can handle the max rated current draw of the 12V motor and you’ll be fine.
Dan
(Hopefully any simplifications I made here for clarity don’t confuse anyone…)
Drbrown
Well-known member
When converting 6 to 12 volts, I understand one must install a 1 Ohm ceramic reducer/resistor between the existing heater switch and the 6v heater blower motor, which in certain installations such as mine may be a four speed motor (2 forward/2 reverse). I recommend you ID your specific heater type and determine the need. See AutoReWire.com
Voltage reducers are available at inexpensive prices at various electrical internet sites and at Radio Shack.
Voltage reducers are available at inexpensive prices at various electrical internet sites and at Radio Shack.
Last edited:
Dave in WY
Member
Dan, Thank you VERY MUCH for your detailed information. I will study this and see what happens. I pick up my new 12 volt heater motor today, so will check the amps it draws. My hopes were to be able to use an old original type heater switch with a 12 volt system. I also have just seen there are new 12 volt switches that look like the old switches, so I could go that route if needed. Again, THANKS for the explanation!!!
Dave
Dave
COE Dan
Senior Member
Drbrown brings up a good point. If you are going to use a 6V motor in a 12V system you need to add resistance. Here’s why:
Ohm’s Law is: Resistance = Volts/Amps
Ohm’s Law Power equation again is: Watts = Volts x Amps
Thus, substitution gives the following relationship: Resistance = Volts2/Watts = Amps2 x Watts
Again, assuming the same amount of work (power) is being done we find that the resistance in a 6V system will be ONE- FOURTH that of a 12V system consuming the same power:
(Resistance for 6V circuit) = (Resistance for 12V circuit) / 4
This occurs due to the square that shows up in the equation above.
Here’s an example why you need that resistor in series with a 6V motor when using 12V:
1) Assume a 6V heater motor draws 1A.
2) Using Ohm’s Law, the heater motor has a resistance of 6-ohms.
3) Note circuits only draw as much amperage as they need to operate. Voltage and resistance do not change.
4) Applying 12V across the 6-ohm motor resistance then creates a draw of 2A.
Thus, applying 12V will possibly draw more current than a 6V motor is designed to handle. Adding an appropriate resistor into the circuit drops the voltage across the motor and will bring the current draw within design limits.
Further, I agree with Drbrown that you need to analyze the specific circuit application to determine the correct resistance to place in series when using 6V parts.
Dan
Ohm’s Law is: Resistance = Volts/Amps
Ohm’s Law Power equation again is: Watts = Volts x Amps
Thus, substitution gives the following relationship: Resistance = Volts2/Watts = Amps2 x Watts
Again, assuming the same amount of work (power) is being done we find that the resistance in a 6V system will be ONE- FOURTH that of a 12V system consuming the same power:
(Resistance for 6V circuit) = (Resistance for 12V circuit) / 4
This occurs due to the square that shows up in the equation above.
Here’s an example why you need that resistor in series with a 6V motor when using 12V:
1) Assume a 6V heater motor draws 1A.
2) Using Ohm’s Law, the heater motor has a resistance of 6-ohms.
3) Note circuits only draw as much amperage as they need to operate. Voltage and resistance do not change.
4) Applying 12V across the 6-ohm motor resistance then creates a draw of 2A.
Thus, applying 12V will possibly draw more current than a 6V motor is designed to handle. Adding an appropriate resistor into the circuit drops the voltage across the motor and will bring the current draw within design limits.
Further, I agree with Drbrown that you need to analyze the specific circuit application to determine the correct resistance to place in series when using 6V parts.
Dan
Ross F-1
Well-known member
These resistors are about the right resistance, and are very heavy duty. They are used in German OEM applications to provide two speeds on radiator fan motors that draw more like 5 amps @ 12v. I measured 1.3 ohms.
Search on eBay for "Porsche 944 radiator fan resistor". They come as shown, two on a heat sink. About right for my F-1's electric wipers, too.
Search on eBay for "Porsche 944 radiator fan resistor". They come as shown, two on a heat sink. About right for my F-1's electric wipers, too.
