I have two motors from the back wheels of an old Rollin' Rambler kids powered car (https://www.amazon.com/12V-Rollin-Rambler-Ride-On/dp/B00S713PW4). Unfortunately, I didn't get the wiring harness and controls out before it was thrown away. I'm thinking of using one of the motors to make a vibrating parts cleaner, but want a way to power it without having to use the battery. The car had a slow and fast speed, so I'm assuming it supplied maybe 6 or 8 volts to the motors for slow speed and 12 volts for fast speed. However, I don't really know how many amps the motor pulls. I can't find an exact one online using the numbers on the motor housing, but I think this one is similar: https://www.amazon.ca/SODIAL-15000-Electric-Motor-Spare/dp/B078CR3P86
That description has 35-45 W. If I understand it correctly, that equates to 2.9-3.75 A.
I also have an old laptop charger that outputs 19.5 V and is rated for 3.33 A. I'm wondering if there's any reasonable way I could use this charger and a resistor or something to power this motor at 12 V (or even less volts if that will reduce the current to an acceptable level for the charger).
From what I can figure, to use this charger to power the motor at 12 V and 3.75 A (I know it might even pull more amps on startup), I would need a 2 Ohm resistor:
- (19.5-12)/3.75 = 2
But then I think that would require the resistor to be rated for almost 30 W:
- (19.5-12)*3.75 = 28.125
And that just doesn't seem right/logical to me, but I've only really done anything with lower voltage and small watt resistors.
So, is there a reasonable way to power the motor using the charger, and are my calculations correct?
Here are pictures of the actual motor and charger.
Best Answer
Yes you can. It will however rotate at a higher speed and will get a lot hotter. Also if the now hotter motor is stopped abrupt, it might serve thermal damage (so its a good idea to use a speed regulator and to let it cooldown at a lower rotating speed). Also the lifetime of the commutator will drop.
But these cheep motors like the one on the picture are robust. So it will work for some while I guess...
And if you only turn it on for a short time, lets say a minute, it shouldn't get this hot and work well. Using Motors with higher power than rated - in the thermal limits - is normal e.g. for trains when they start rolling.