Brush or Brushless DC motor

Thread Starter

Vincenzo1309

Joined Dec 28, 2008
57
Dear all,

I have a cheap and typical remote controlled car which has two DC motors.
How do I find out that these motors are brush or brushless type without dismantling the motor?

Kindly advise


Thanks and Regards
 

gerty

Joined Aug 30, 2007
1,250
Typically brush type motors have two plastic screws or caps over the brushes . they insulate them from the case. On some motors there are cutouts that let you see inside the motor.
 

Thread Starter

Vincenzo1309

Joined Dec 28, 2008
57
Beside these observations, can I say that only brushed motors are prone generate electrical noise?

Brushless motor typically don't have this problem.
 

jpanhalt

Joined Jan 18, 2008
7,699
Brushless model motors typically have 3 power leads. Brushed motors have just 2 power leads.

John
 

Von

Joined Oct 29, 2008
65
Brushed DC motors have brushes that contact the commutator portion of the armature and perform the "timing" of the magnetic fields (on - off) to cause repulsion (i.e. rotation). Speed can be varied by varying the voltage to some extent or by PWM.

Brushless motors use an "electronic speed controller" (ESC) to electronically perform the commutation function using the three wires previously cited. This set-up also allows almost infinte speed control upto the motor's kV or rpm-per-volt rating.

Since there is no sparking with a brushless motor it could be said brushless motors are "quieter" but the ESCs (and wiring) can be a source of noise due to the fast switching times if not properly implemeted.
 
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Thread Starter

Vincenzo1309

Joined Dec 28, 2008
57
Dear all,

I know that there is a need for a resistor to be connected between the pin out of a PIC and the base terminal of the transistor. The resistor is to limit the base current and prevent the transistor from damage.

So exactly how much base current will damage the transistor? is it indicated in the datasheet of the transistor?

I saw in the BD679 datasheet that puts Base current = 1A. Does it mean that 1A supply to the base terminal will damage this transistor?

Kindly advise.

Thanks alot!
 

jpanhalt

Joined Jan 18, 2008
7,699
Your PIC can output 25 mA per pin at most. Think about protecting the PIC. The transistor can probably handle it.
John
 

Thread Starter

Vincenzo1309

Joined Dec 28, 2008
57
Hi,

In what way do you mean by protecting the PIC?
From what I know is, we shouldn't allow too much current to flow to the base terminal, we should limit it to 10- 15mA.
But what happens to the PIC if I allow, say 18mA, to flow to the base terminal?
Kindly advise
 

jpanhalt

Joined Jan 18, 2008
7,699
I saw in the BD679 datasheet that puts Base current = 1A. Does it mean that 1A supply to the base terminal will damage this transistor?
My comment was based on the assumption that you were using a power transistor that could use up to 1 A of base current. I was simply pointing out that the PIC can only supply 25 mA, and if you try to drive something of such low impedance (say, the gate of a large mosfet), you may need a current limiting resistor to protect the PIC.

John
 
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