Motor noise suppression

[kybert]

Hi


I have a 12V winch connected to a car battery. The winch is drawing about 30Amps when in use.

I have a 433MHz remote that i build for it, and a 17cm antenna, however, the range is about 1 metre.

If i disconnect the motor, the range is 25m. This is still very poor (manufacturer of the Tx and Tx quote 100m), however, at the moment im just trying to solve the motor noise issue.

How can i stop the motor from interfering with the receiver? I thought a large cap accross the motor, but as the motor reverses, i cannot use electrolytic caps (polarity sensitive)

Any ideas?

I already have 2x 470uF caps and a 0.1u disc cap near the Rx supply rail.

 

[MikeMl]

Likely the noise is coming off the motor brushes. Put two 470pF or 1000pF 1kV disc ceramic capacitors (with leads as short as possible, 1/4" is ideal) between each brush holder and the motor frame. Moving the 433Mhz antenna as far as possible from the motor will help, too.

 

[kybert]

I cant open up the motor, its a sealed unit.

Can i place one cap from each of the power terminals to the motor case? The case is not connected to any power rail, should it be?

 

[MikeMl]

I cant open up the motor, its a sealed unit.

Can i place one cap from each of the power terminals to the motor case? The case is not connected to any power rail, should it be?

You can try connecting the capacitors to the leads going into the motor, but the connection should be as close to the motor housing as possible. The other ends of both capacitors go to the motor housing. The motor housing should be grounded to the battery negative, normally happens naturally when the winch is bolted onto a car.

 

[kybert]

Thanks for the advice, i'll ground the casing, and get some caps ordered up monday.

 

[Sceadwian]

Posted in the wrong thread ignore.

 

[kybert]

its possible for me to open the motor and add the caps right on the base of the brushes, where the power cable and spring is soldered to the brush.

Is this beneficial or should i place them on the power terminal bolts the protrude from the motor?

 

[MikeMl]

Inside is better. The leads of the ceramic caps must be as short as possible. The inductance of ~1/4" of wire makes a series resonant circuit with the 470pF capacitor (series trap) to suck out VHF and UHF frequencies (100 to 500 MHz).

 

[ikalogic]

hmm.. i am not that good with EMC... but did you try shielding the motor? some aluminum foil, grounded to cover all the motor... just thinking out of the box

 

[kybert]

I havn't tried wrapping the motor, will try the caps first, and some additional smoothing on the Receiver power supplys.

I bought 1nF cer disc 1kV caps, not 470pF.

 

[MikeMl]

I havn't tried wrapping the motor, will try the caps first, and some additional smoothing on the Receiver power supplys.

I bought 1nF cer disc 1kV caps, not 470pF.

Wrapping the motor is not as good as just making sure the motor's frame is grounded. Aluminum foil self-oxidizes; Aluminum Oxide is a good insulator. Besides, the motor will likely overheat if covered.

1000pF or 470pF will work...

 

[Sceadwian]

Not to mention it won't help much at all, the noise is on the electrical lines themselves which act as an antenna, it's not coming from holes in the grating of the motor casing. You could try a ferrite core wrapped a few times on the main line as well as a capacitor. You'll have to have to avoid creating a resonant frequency anywhere near where the noise is occurring.

 

[ikalogic]

Not to mention it won't help much at all, the noise is on the electrical lines themselves which act as an antenna, it's not coming from holes in the grating of the motor casing. You could try a ferrite core wrapped a few times on the main line as well as a capacitor. You'll have to have to avoid creating a resonant frequency anywhere near where the noise is occurring.

Thanks for the correction, as i mentioned, i am not that good with EMC.. but it's good to learn!

 

[ljcox]

Many years ago, I bought a surplus World War 2 radio transceiver.

Inside the case, it had "feed through" capacitors so that the DC supply could be passed into the screened box in which the RF components were housed.

They mounted in a hole in the screened box with a tag on both sides so that the DC connection went through one of the cap plates. The other plate was connected to the cap mounting screw and was thus connected to gnd.

Hence, there was virtually no series inductance only capacitance to gnd.

Does anyone know if these can be purchased these days?

 

[Damo666]

As an hf, vhf and uhf enthusiast i find that " ferrite cores/beads " eliminate almost all of my problems. A brushless motor would also be an option, and would last much, much longer than a brushed variant.

 

[MikeMl]

...

Does anyone know if these can be purchased these days?

Bulkhead feed through filter capacitors