No capacitors soldered onto motors of toy car

Dear all,

I find something weird. Why are there no capacitors soldered onto the DC motors of a remote controlled toy car, yet the toy car works just as fine?

I had used the chassis of a remote controlled toy car as the chassis of my wheeled robot.
Only the DC motors of the car were used. So I took out the toy’s controller board, and I used the micro dual serial motor controller to control the motors. I use a 9V battey to control the motors.

When I tested the robot, the electrical noise from the motors had impaired my motor controller.

Therefore I solder capacitors across the terminals of the motors to reduce the effects of the noise. The problem was solved.

Why are there no capacitors soldered onto the motors of the toy car in the first place? Somehow without the capacitors, the toy car can work!

My guesss:
Is it due to the battery supply, since the toy car only requires around 3.6V to run the motors. Whereas in my case, I had used a 9V battery.
Kindly advise…


There are several reasons they might not have soldered capacitors on to their motors. Maybe the toy’s controlling board already had capacitors on the motor outputs. Maybe the electronics used on the toy’s controller board is quite different than the microcontroller on your motor controller, and it is less vulnerable to motor noise effects.


I think your guess is largely correct. Motors running at 3.6V will generate less noise than if they were running at 9V. Also, part of the problem could be your power source itself. Were you using a single 9V alkaline cell battery?

- Ben

Dear all,

Thanks for your replies.

To Ben:
Yup, I am using a single 9V alkaline cell battery.

So that explains everything!

Thanks for your enlightnment once again!

In general, you should not use 9V batteries for high-current applications such as powering motors. This could also partially explain your problem. 9V batteries have very low capacities and cannot provide much current. You should try to use higher-capacity alkalines (e.g. AAs) or, even better, rechargeable NiMH or NiCD batteries.

- Ben

Hi Ben

Actually I am also using the 9V battery to power up a solenoid actuator and the 2 DC motors.
So when choosing the batteries, you were saying that this 9V battery is unable to supply alot of current

What do you mean by higher capacity alkalines?
These batteries supply more current? Then is the voltage rating of the batteries important? Can I choose a 6V battery to supply my soldenoid actuator and DC motors?
(the voltage rating of the soldenoid actautor is 6V to 12V)

Kindly advise…

The higher a battery’s capacity, the more current it can supply (or, put another way, the longer it can supply a particular current before it goes dead). AA cells have higher capacity than AAAs, C cells have higher capacity than AAs, D cells have higher capacity than C cells, etc. You should generally avoid using a 9V battery to power motors (unless they are tiny and have miniscule current draw), and ideally you would use NiMH cells. You should select a battery pack (or battery holder filled with individual batteries) that provides a voltage that your system can tolerate.

- Ben

Hi Ben,

Thanks alot! I shall work on finding a suitable power supply.