Choosing the Best DC Motor Brush Material: Tips and Recommendations

In summary, the receiver won't turn on with less than 5.5 volts, but it can be powered with 6 volts on a separate input.
  • #1
William123
39
0
Hello there

Building DC motors has sort of become a hobby lately and I'm about to build the best version yet. However, I have a few questions when it comes to the brushes.

I salvaged a couple of brushes from an old electric saw that my dad was throwing away but the resistance of those are much too high for what I'm going to use the motor for. The biggest battery I have is at 11.1V so I can't have brushes with a resistance of almost 10 ohms each. I have read that high resistance brushes gives better commutation but still :eek:. I also read that carbon graphite brushes can handle a current density of 7 amps/cm^2, which seems low to me. What material are the brushes made of in start motors? (low voltage high current)

What do I search for on fleabay if I want brushes with a maximum resistance of 1 ohms each and that can handle a higher current density?

Your answers are appreciated as always :)

Edit: I've been using copper brushes until now
What I've found so far is that Electrographitic and Metal graphitic brushes are good for what I'm going to use them for but there are so many grades that it's hard to find the right ones on ebay (or any at all).
 
Last edited:
Engineering news on Phys.org
  • #2
What kind of current do you think an automotive starter takes? I doubt the current you require will exceed that in a starter.
 
  • #3
Averagesupernova said:
What kind of current do you think an automotive starter takes? I doubt the current you require will exceed that in a starter.
No, I won't be close to those currents. But if my motor would draw more than 5A under load then I would need brushes that can handle a higher current density that 7A/cm^2. Is there a name for low resistance brushes?
 
  • #4
William123 said:
No, I won't be close to those currents. But if my motor would draw more than 5A under load then I would need brushes that can handle a higher current density that 7A/cm^2. Is there a name for low resistance brushes?
This might help you with a starting point :smile:

http://www.astroflight.com/781
 
  • Like
Likes William123
  • #5
RonL said:
This might help you with a starting point :smile:

http://www.astroflight.com/781
Silver is somehow the key word here. I can't order from the US though because of the shipping cost to Sweden so I searched on ebay (for silver brushes) and found these:

http://www.ebay.co.uk/itm/Tamiya-53...028429?hash=item3ad6092bcd:g:phYAAOSw2xRYYsjB
http://www.ebay.co.uk/itm/Tamiya-Racing-Motor-Brush-Set-Standard-Type-53581/371827349600?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=20140122125356&meid=7524c5f15f8c434cbcc58416556621a1&pid=100005&rk=1&rkt=6&sd=252699028429

Since tamiya makes RC related stuff I'm assuming that these brushes must have a low resistance in order to work with low voltage battery-driven motors.
Thanks!
 
  • #7
RonL said:
Here is a link that might help when you are looking for materials or shape and function.

http://www.kjelectric.com/pdf_files/carbone/514_3-brushes-for-electrical-machines-en.pdf

Yes that might actually come in handy.

I have another question but it's on another topic. Maybe you can help me again.
I disassembled and old electric scooter today to salvage parts when I got the idea to build a radio controlled car using that 250W motor. My receiver can be powered on channel 2, which also controls the motor. The motor controller puts out 4.9V for the throttle signal (not sure about the terms here) but my receiver won't turn on with any less than 5.5V it seems. However, the receiver also has a separate power input so I could make a 6V battery pack and power it from there. So my question is this, what happens when you power the receiver with 6V on the separate input while it also gets 4.9V on channel 2?

I could do a test. If the receiver blows up I only lose about $4.

The throttle used to be controlled with some kind of magnetic component based on what I could see. It was really small, smaller than any potentiometer I've ever seen. Any idea what this could be?

Edit: Turns out it's a hall effect sensor. I wonder how different the signal output is compared to my receiver..
Edit 2: The signals are quite different. What are my alternatives then? Radio controlling the pot with a servo?
The 24V RC ESC's on ebay are very expensive.
 
Last edited:
  • #8
My background in electronic component circuit speed control is very limited, I do have a few units that have been burned because of improper current and amperage loads during operation, so IMO there is little room for error in regard to voltage input.
Most of my setups involve larger (up to 5 hp) DC motors and router speed control 120 AC/volt units, converted to DC using full wave bridge rectifiers.
Below are a couple of links to one of my favorite sources of info.

https://en.wikipedia.org/wiki/AstroFlight

http://astrobobb.com/electric_motor_handbook.pdf

Bob Boucher's book gives information you need to understand what is involved in the speed/power relationship of any electric motor.

Look for small electric motors ( DC/AC and universal types) and speed controllers in hand tools, household appliances too numerous to list.
If your thread continues for a while, I might have an idea to pass on...
Best wishes on your learning.

Ron
 
  • #9
RonL said:
My background in electronic component circuit speed control is very limited, I do have a few units that have been burned because of improper current and amperage loads during operation, so IMO there is little room for error in regard to voltage input.
Most of my setups involve larger (up to 5 hp) DC motors and router speed control 120 AC/volt units, converted to DC using full wave bridge rectifiers.
Below are a couple of links to one of my favorite sources of info.

https://en.wikipedia.org/wiki/AstroFlight

http://astrobobb.com/electric_motor_handbook.pdf

Bob Boucher's book gives information you need to understand what is involved in the speed/power relationship of any electric motor.

Look for small electric motors ( DC/AC and universal types) and speed controllers in hand tools, household appliances too numerous to list.
If your thread continues for a while, I might have an idea to pass on...
Best wishes on your learning.

Ron

Thank you for linking astroflight again. I found this http://www.astroflight.com/rcpwm2v. Ingenious. These are very cheap on ebay aswell. A cheap solution would be a PWM to constant voltage signal converter and a motor controller that uses a pot. I will look into this tomorrow.
 
  • #10
RonL said:
If your thread continues for a while, I might have an idea to pass on...
Best wishes on your learning.

Ron
I thought I'd give you an update. My Arduino UNO arrived shortly after my last post and I realized that I can use that to read the receiver's PPM signal and convert that into PWM and feed it into an H-bridge to power the motor. So this is where I am now: https://www.physicsforums.com/threads/making-an-arduino-controlled-h-bridge.906028/
 

1. What is the purpose of the brush material in a DC motor?

The brush material in a DC motor serves as the contact point between the rotating commutator and the stationary parts of the motor. It helps to transfer electrical current from the power source to the armature, allowing the motor to rotate.

2. What are the most commonly used materials for DC motor brushes?

The most commonly used materials for DC motor brushes are carbon and graphite. These materials have high electrical conductivity, low friction, and good heat resistance, making them ideal for use in motors.

3. How do I know when the brush material needs to be replaced?

You will typically notice a decrease in motor performance or unusual noises coming from the motor when the brush material is worn out. You can also visually inspect the brushes for any signs of damage or excessive wear.

4. Can I use any type of brush material in my DC motor?

No, the type of brush material used in a DC motor is specific to the motor's design and intended use. Using the wrong type of brush material can result in poor motor performance and potential damage to the motor.

5. How often should I replace the brush material in my DC motor?

The frequency of brush material replacement will depend on the motor's usage and operating conditions. In general, it is recommended to replace the brushes every 6-12 months or when there is a noticeable decrease in motor performance.

Similar threads

  • Electrical Engineering
Replies
5
Views
2K
  • Electrical Engineering
Replies
12
Views
13K
Replies
2
Views
913
Replies
11
Views
3K
  • Electrical Engineering
Replies
2
Views
2K
  • Electrical Engineering
Replies
5
Views
2K
  • Electrical Engineering
Replies
13
Views
2K
Replies
5
Views
3K
  • Electrical Engineering
Replies
1
Views
1K
  • Electrical Engineering
Replies
5
Views
1K
Back
Top