EMC problems on High Voltage's DC motor

where is 60 and 70 MHz coming from in the system?

are there electronics in the motor?

are there brushes sparking in the motor?

is the motor driven by an electronic PWM supply?

Mark

dumb question What do the motor manufactures say?

martin

After the first death, there is no other. (Dylan Thomas)

These 3300uF are hardly good for 60MHz. Get Something smaller in parallel, say 10nF

Rene

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I presume you meant to write commutator....

perhaps the OP is using a brushless electronically commutated motor...

3300uF caps, if thats what youve really got, are electrolytic (I assume!!) and all wound caps are inductive. You need flat plate caps, eg ceramics, for the hf stuff. Try .01uF ceramics

(Just trying to imagine the OP with 3300uF paper caps...)

NT

A DC motor tends to have a collector which fires on the shorts and gaps. Some winding capacitances together with the winding inductivity could create a resonating circuit in whatever frequency range.

Rene

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A brief overview of DC brush commutated motors.

On page 16 the schematic shows a standard EMI filter known from 12V DC motors. (Found this typical EMI circuit only in a 42V/PWM article.)

Dieter

Yes.

I never heard of them in this voltage range. There are synchroneous motors in this voltage range which require a hefty frequency converter.

Rene

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Thanks for all reply.

I think I have a typing error as 3000uF must not correct. My meaning is using a 3000pF capacitor. And I will try on the following setting.

o--------[ choke, 8uH ]--+--------+-------+ | | | | | --- capacitor | | --- 10nF | | | capacitor --- [Rotor] +------- GROUND 470nF --- | | | | --- capacitor | | --- 10nF | | | o--------[ choke, 8uH ]--+--------+-------+

Hope that I can solve the problems.

the circuit is good, but the physical arrangment of the components is also very important at 60 MHz.

Look up the term "feedthu" or "feedthrough" capacitors.

You need to have a very low inducance RF path to the metal case of the motor.

Mark

following setting.

what type of caps r they?

NT

Should it be cerematic capacitor? Any suggestions?

Assuming the 3300uF is a typo. Probably 3300pF.

To reduce EMI on the incoming power cables you might consider a capacitor (or two capacitors) on the left hand side of the inductors. Perhaps also use twin screened power cables.

--
Tony Williams.

I have tested with the 10nF ground capacitor adding on the motor for suppression. The result is not so obvious. Of course, to increase the capacitor from 10nf to a bigger one, the performance may improve. However, I would like to ask:

Because I am followed EN55014 for EMC testing, may I know that is there any limitation on capacitance of live / ground capacitor on using? As I remember that there is some requirement on selecting the cap. value for suppression. Anyone can give me a actual figure that what values that cannot be over?

Thnaks a lot.~

I read in sci.electronics.design that Electronic Swear wrote (in ) about 'EMC problems on High Voltage's DC motor', on Wed, 27 Apr 2005:

The maximum value is not in EN 55014-1 (I hope you are not looking at an out-of-date EN55014!) but in whichever safety standard applies to your product. A maximum value of current in the protective conductor is specified. It varies with the type of product.

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