1937 Heater Motor

Thread Starter

Steve_R

Joined Oct 18, 2020
17
I have a 1937 Plymouth. The voltage has been converted to 12vdc from 6vdc.
I want to wire up the original heater motor to my 12 volt supply. There are no markings on the motor to tell me what amperage it is. How can I find the best way to install this motor?
 

AlbertHall

Joined Jun 4, 2014
12,345
Do you have a suitable 6V supply to power the motor?
Do you have a meter that measure perhaps 10A - 20A?
If so connect the motor to 6V with the current meter in series to get how much current the motor needs.
I presume the motor has a fan attached and it should be attached for the current measurement.
 

DNA Robotics

Joined Jun 13, 2014
647
Some may say it will be an unbalanced load on the battery but the heater won’t always be on and the battery will balance when its off.
If you have room, you could use two 6 volt batteries in series to make 12 volts and take 6 volts off the grounded one.

6 volts from 12 battery.jpg
 
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Ian0

Joined Aug 7, 2020
9,671
If you measure the DC resistance that will give you its stall current, or it startup current, not its running current.
Do you have a few 12V lamps? Pick one about 30W and put it in series with the motor, and measure the motor voltage and current. If the voltage is nowhere near 6V try a different lamp.
 

jpanhalt

Joined Jan 18, 2008
11,087
I have 2 leads from the motor. Would I put my meter on these leads to measure the resistance?
Yes. Since it is old and probably brushed, you may need to wiggle the shaft to get a reliable reading. Assuming it is not permanent magnet, there are two basic configurations plus combinations:

1603028028000.png
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
I have 2 leads from the motor. Would I put my meter on these leads to measure the resistance?
But it is not a reliable way to measure a motor resistance, you need to place an ammeter in series with one of the leads at a known small DC voltage and lock the rotor, and measure calculate the resistance.
But this does not give you the operating current, just the initial inrush.
Just measure the current when ran at the normal operating rpm on 6v. .
Max.
 

Thread Starter

Steve_R

Joined Oct 18, 2020
17
Ok I have put my test leads on the motor. Turning the fan I read 9-13 ohms. Can I use ohms law to figure my amperage?
At 12vdc Which would be 0.9 -1.3 amps
At 6vdc 0.046 -0.66 amps
Or am I missing something?
 

Thread Starter

Steve_R

Joined Oct 18, 2020
17
Ok I have put my test leads on the motor. Turning the fan I read 9-13 ohms. Can I use ohms law to figure my amperage?
At 12vdc Which would be 0.9 -1.3 ohms
At 6vdc 0.046 -0.66 ohms
Or am I missing something?
Sorry I mean 0.9 -1.3 amps for 12 vdc and
0.046 - 0.66 amps for 6vdc
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Ok I have put my test leads on the motor. Turning the fan I read 9-13 ohms. Can I use ohms law to figure my amperage?
At 12vdc Which would be 0.9 -1.3 amps
At 6vdc 0.046 -0.66 amps
Or am I missing something?
The resistance when stationary is of no use in this case.
If this is a fan, the ideal way is to measure current when operating at its normal voltage and rpm.
Which appears to be the way you did it in #11?
IOW you need to use the ammeter method.
Max.
 

Ian0

Joined Aug 7, 2020
9,671
So, we have an upper limit on the motor current. Isn't that all we need?
To make it run at 6V from a 12V supply, just switch it on and off with a MOSFET with a 50% mark-space ratio, at a few kHz.
So long as the MOSFET and its flyback diode are rated for at least a couple of Amps, it's going to work.
(Unless of course we are limited to the use of 1937 technology).
By the way, is that the said car in your little picture?
 

jpanhalt

Joined Jan 18, 2008
11,087
So, we have an upper limit on the motor current. Isn't that all we need?
https://electronics.stackexchange.c...ance-in-a-dc-motor-constant-if-the-voltage-is

That was my thought too, but the calculated current seems low for a modern blower putting out a lot of air. I have no idea what the blower in a 1937 car did. If its series wound and the brushes have poor contact, that might explain the high resistance.

At this point, I would give it a spin with 6V or 12V with a 6Ω resistor in series. That resistor will need to be a few watts, or simply immerse it in water. What's the highest wattage you can find? Two, 1/2 watt, 12Ω in parallel might work in water.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
The semi-device is a good solution, but for many decades the heaters (blowers) in autos were controlled by a series resistor for various speeds.
Usually a radial cage fan.
The alternative is to drive the Mosfet with a 555 for variable PWM.
Max.
 

Thread Starter

Steve_R

Joined Oct 18, 2020
17
So, we have an upper limit on the motor current. Isn't that all we need?
To make it run at 6V from a 12V supply, just switch it on and off with a MOSFET with a 50% mark-space ratio, at a few kHz.
So long as the MOSFET and its flyback diode are rated for at least a couple of Amps, it's going to work.
(Unless of course we are limited to the use of 1937 technology).
By the way, is that the said car in your little picture?
Hi Ian0 yes that our Miss Daisy. Last year she was in a movie called Das Boot Season 2. It was filmed in Liverpool England. Her are a few photos of the inside.

Now I am more of a mechanical engineer that knows a bit about electronic. What would I need to fit this MOSFET and flyback diade?
 

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Thread Starter

Steve_R

Joined Oct 18, 2020
17
https://electronics.stackexchange.c...ance-in-a-dc-motor-constant-if-the-voltage-is

That was my thought too, but the calculated current seems low for a modern blower putting out a lot of air. I have no idea what the blower in a 1937 car did. If its series wound and the brushes have poor contact, that might explain the high resistance.

At this point, I would give it a spin with 6V or 12V with a 6Ω resistor in series. That resistor will need to be a few watts, or simply immerse it in water. What's the highest wattage you can find? Two, 1/2 watt, 12Ω in parallel might work in water.
I did hook it up to my 12vdc supply in the car and the fan turned, not fast but it did turn, maybe about 700rpm. I am thinking that it is not a high speed fan. I also cleaned the com and checked the brushes which had very little wear.
 
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