Connect capacitor parallel with DC motor

Hell every one

I have wheelchair (Brushed dc motor) (200 watt, 24 volt), I will control with it by arduino PWM signal,

I want to know what is the preferred capacitor size I should connect it parallel to the motor to decrease the noise?

Thank you.

Connect a .01uF from each lead to the motor frame, NOT parallel across the two wires.

Paul

This tutorial shows you how reduce motor electrical noise.

Thank you all,

Dear jremington, I checked the Pololu site, it is very useful thank you so much.

I think you need to explain what the "noise" is that is concerning you.

Paul__B:
I think you need to explain what the "noise" is that is concerning you.

Brushed motors produce copious high frequency noise from the arcing of the brushes,
so a ceramic capacitor across the brush leads is normally needed to cut this down to
prevent RFI.

All that is OK, but I was questioning what noise was actually concerning the OP. :grinning:

The question here is very often, what the actual question is. :astonished:

Thanks Mr. MarkT for this explain,

I read very nice article about the noise reasons and your information meet one point of this article, If any one interested to understand the noise reasons of the dc motors, I suggest him to follow this link:

Why Capacitor is connected with DC Motor? Explained - ETechnoG.

Dear Paul__B, actually I don't turn on the motor yet, I just want make professional motor operation. no noise, soft running by using PWM and increase the speed gradually to decrease the stall current, and use a diode in order to cancel the motor stop current ( the generated current that happen when stop the motor)

Also I was going to use NTC to control by inrush current and decrease it, I choose the value of this NTC after good study, But I can't find this value in the locale market.

Thank you all.

AMER_ALAHMAD:
I just want make professional motor operation. no noise, soft running by using PWM and increase the speed gradually to decrease the stall current,

Fair enough, but I am none the wiser as to what sort of noise you have in mind. And for such a motor, you will require more than a couple of capacitors. :astonished:

AMER_ALAHMAD:
and use a diode in order to cancel the motor stop current ( the generated current that happen when stop the motor)

That very much depends on how or why you propose to "stop the motor". Do you actually intend to use this on a wheelchair or what else? Does it need to reverse?

AMER_ALAHMAD:
Also I was going to use NTC to control by inrush current and decrease it, I choose the value of this NTC after good study, But I can't find this value in the local market.

For a 200W motor, I don't think a NTC thermistor is very practical.

Dear Paul,

thank you for your support and sorry for the late response, don't use any NTC, every thing going well,

Thanks again.

AMER_ALAHMAD:
Dear Paul,

thank you for your support and sorry for the late response, don't use any NTC, every thing going well,

Thanks again.

Brushes need to wear to fit the armature segments of your motor. New motors need time to allow the brushes to wear or what is called to be "seated". Old motors may have worn out brushes so only a small part of the brush is in contact with the armature segments. This also reduces the power the motor can supply.
All of the above can produce noise. All brushed motors produce noise because the current arcs from the brush to the copper armature segment as it makes the contact and as the contact is opened.
Paul

Also I was going to use NTC to control by inrush current and decrease it, I choose the value of this NTC after good study, But I can't find this value in the locale market.

NTC thermistor definition An NTC thermistor is a thermally sensitive resistor whose resistance exhibits a large, precise and predictable decrease as the core temperature of the resistor increases over the operating temperature range. Characteristics of NTC thermistors

I fail to see the connection between inrush current and an NTC. Sensing inrush current is typically done with a current shunt , an op amp amplifier and an A/D, read by a microprocessor which then reduces the motor controller signal, although discrete components performed this function pre-microprocessors. (since inrush current has always been around, unlike microprocessors). Using a thermister seems like it would be slower since it is dependent on
thermal transfer. Where were you thinking of putting the NTC ?

I have a couple of thoughts..

  1. What frequency are you planning for the PWM?

  2. If you are much above 1K and using a diode across the motor you should be aware some general purpose have a long trr (reverse recovery time). A high trr will allow the diode to conduct in the reverse direction for a small time then the motor drive mosfet(?) is turned on.

  3. If you are planning on using a diode across the motor I suggest you look at "synchronous switching" type of output. I'm not 100% sure this is the correct term. In essence the diode is replaced by another Mosfet. The mosfet across the motor is turned on when the lower mosfet is off. This drops the power dissipated from the "motor current X diode voltage" to "motor current x mosfet on voltage"

As the mosfet voltage is much lower than the diode voltage there is a power savings and reduction of heat generated.

So in short this is not a simple straightforward discussion for a motor of this size. :astonished: