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### Author Topic: DC brushless motor not getting enough voltage  (Read 984 times)

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#### x1222

• Beginner
• Posts: 3
##### DC brushless motor not getting enough voltage
« on: October 22, 2011, 01:29:34 AM »
Hello everyone,

I'd really appreciate some help. I'm trying to get my 6V DC brushless motor to push some tray on a track. I connect it directly to some power supply (has dials that go up to 4A and 20V, so 80 W?), no resistor. I can get it up to 6v and get the motor running, but once I try to get it to push the tray the voltage drops too low (below 3v) and is unable to push the load. I can't seem to get it higher, even if I crank the voltage dial up. What's the reason for this? Do I need to build a circuit to get motor to stay at a fixed voltage, or is the motor too weak?

Also, the motor uses 6v and 0.50A draw. Without the resistor and a load the motor will actually start moving at 0.1V because the amps raise fast. I'm guessing I need to add a resistor, but how can I calculate and get 0.50A? With 6V, to get 0.50A, it means 12 ohm resistor is needed. However they seem to burn up at 6V. Thanks.
« Last Edit: October 22, 2011, 01:30:50 AM by x1222 »

#### Soeren

• Supreme Robot
• Posts: 4,672
##### Re: DC brushless motor not getting enough voltage
« Reply #1 on: October 22, 2011, 05:54:30 AM »
Hi,

I'm trying to get my 6V DC brushless motor to push some tray on a track. I connect it directly to some power supply [...] What's the reason for this? Do I need to build a circuit to get motor to stay at a fixed voltage, or is the motor too weak?
You need gear reduction to get more torque. What you have now is rotational speed with less "muscles" - with gearing you get the speed down but it will be able to move a higher load.
So, no circuit, just gearing.

BTW. I assume you by "motor direct to power supply" mean "motor controller directly to power supply"?
A brushless motor won't run without a controller (but it may be built in).

Brushless motors are very fast, compared to brushed motors. The gear reduction needs to convert perhaps 10000 to 20000 RPM at a low torque, to some usable speed at a much higher torque.
Do you have any data on the motor, or a link to where you got it?

Also, the motor uses 6v and 0.50A draw. Without the resistor and a load the motor will actually start moving at 0.1V because the amps raise fast. I'm guessing I need to add a resistor, but how can I calculate and get 0.50A? With 6V, to get 0.50A, it means 12 ohm resistor is needed. However they seem to burn up at 6V. Thanks.
No resistor needed. A motor drawing 0.5A at 6V is the equivalent of a 12 Ohm resistor, but with a 6V supply you don't need a resistor.

The reason a small (1/4W) 12 Ohm resistor burns is that it will see 3W when connected to a 6V source.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Engineering is based on numbers - not adjectives

• Beginner
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