Need help getting high current DC motors to work

djsfantasi

Joined Apr 11, 2010
6,338
I don't know why it seems so unbelievable that I don't have a car. Is this an American thing? As a student in Germany you just don't need a car to get around and I currently don't have access to any of my friends' cars.
One last idea in desperation. Is there an auto repair facility nearby. They may let you connect up the motor to a battery for a quick test. I don’t know about Germany, but here in America, a crisp bill discreetly passed to the mechanic would get you the help you need :rolleyes:
 

MisterBill2

Joined Jan 23, 2018
5,785
Shouldn't a battery rated at 10000 mAh (which to my knowledge is its capacity and not its power output) and at 10C discharge output at max. 100A and not 10A. Please tell me where my calculations are off.:)

I don't know why it seems so unbelievable that I don't have a car. Is this an American thing? As a student in Germany you just don't need a car to get around and I currently don't have access to any of my friends' cars.
I guess I will just have to buy a power supply rated at 30A or 40A.


The Li-po battery pack I used isn't the newest and I hardly used it but this might explain it.

Thank you all for your replies.
That same increase of internal resistance is found in almost all the types of batteries.
 

MaxHeadRoom

Joined Jul 18, 2013
20,430
I have an electric car seat laying around at home which has a couple brushed DC motors inside.
I was going to buy an external power supply to connect to the seat but it confuses me that the battery doesn't seem to be powerful enough.:)
If the idea is just to experiment with DC motors, I suggest buying some of the cheap DC brushed motor that are out there rather than putting the money into external power supplies that may not even then, do the trick with the seat motors.!
Max.
 

MrSoftware

Joined Oct 29, 2013
1,742
Power seat motors aren't going to take much current. A 10aH 10C battery should deliver 100A, so if the battery is in good shape then current is not the problem. Measure the actual current going into the motor. It's possible the motor is damaged or frozen.

This probably isn't your specific motor, but is a seat motor and according to the spec sheet it requires less than 3A unloaded and max of 12A when stalled. I wouldn't expect much more from an average seat motor:

https://andymark-weblinc.netdna-ssl.com/media/W1siZiIsIjIwMTkvMDEvMjIvMTUvNDAvMDgvNDE1ZWE5ZmUtZjA4Ni00M2MxLWE1YjMtYThhNzJhZWE0NmMxLzIwMTYtMTItMjEgc3BlYyBzaGVldCAtIEJvc2NoIEZSQyBtb3RvciA2IDAwNCBSQTMgMTk0LTA2LnBkZiJdXQ/2016-12-21 spec sheet - Bosch FRC motor 6 004 RA3 194-06.pdf?sha=42a181c2a13b270e
 

MisterBill2

Joined Jan 23, 2018
5,785
I have another set of suggestions that do not require another battery. The very first is to check that the motors can spin freely by hand. It is entirely possible for them to bind quite tightly if not aligned perfectly. Then, if the motors do turn freely, connect an ohm meter across the power leads and verify that the motor has continuity through. It should be less than 2 or 3 ohms. And rotate the motor so that you get to check the resistance of each section on the commutator. It is possible to have one failed segment and then some times the motor will not start. Finally, as a third check, switch the meter to a low DC voltage range, 1- or 20 volts full scale, and spin the motor rapidly by hand. It should generate at least a volt when you spin it. If it passes all three of these tests then the problem is not in the motor, but some place in the power to the motor.
Consider that if the powered seat is just sitting around it may be that there is some part that has failed and is the reason why it was not in use.
 
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