Noisy motor

[jwax]

I have an application for controlling a small DC motor by a 430 MHz digital-encoded transmitter/receiver. On-off control only, and reversible.
Original problem was that the motor noise would interrupt the digital signal, the receiver would see an incorrect code train, and stop. Then, receiving good code, would run again, but then stop again because of the noisy signal. Chatter, if you will.
Finally fixed this, but I don't understand why this fix works.
Tried .01 MFD across the motor, no help. Tried 0.1 MFD, showed some improvement! Finally connected two 10 MFD tantalum electrolytics in series, but -/+/+/- configuration across the motor. That works!
Did not want to place one electrolytic across the motor, because half the time it would be reversed polarity. Essentially, I made a non-polarized capacitor, but what's happening here? Are non-polarized caps used to quiet motor noise in other applications? Is this a good design?
BTW, I tried many combinations of inductors to reduce noise with zero effect.

[Edd]

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Meeeester J wax. . . . . . . .

And apparently . . . . . that's not Johnson's Wax

Some how. . . . . I want to believe that you were trying a poly family or paper capacitor.
If that was the case, NOW try a disc ceramic cap in the .1 ufd range.
As per my experiences with the very LOW ESR exhibited by that family of caps in bypassing applications.


73's de Edd
[email protected] . . . . . . . . (Interstellar~~~~~Warp~~~~Speed)
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Any time things appear to be going better . . . . . you have overlooked something..




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[Externet]

Hi John.
The unknown is if the offending interfering signal enters the receiver via its antenna or backwards by the motor connection. -or both-

The motor is causing the interference by either path above; the capacitors are clipping/smoothing/diminishing the spikes and thus the emission of spikes, like a filter. I would not be concerned in using a larger capacity non polar in parallel as being 'bad design'
You see old tape players, turntables, cd players with capacitors in parallel to their mechanism motors to lower noise in the power rails and preventing such from interfering with audio.

Interesting the inductors in series with the motor feed lines is not helping. That could point the noise spikes are entering the receiver via its antenna and explaining why the inductors fail to choke their effect. Have you monitored the noise with an oscilloscope, in motor feed lines and with an 'antenna' to the scope probe ?

Try shielding the motor from radiating spikes too.

Miguel

[haklesup]

Is the ground return of the motor seperate from the digital ground of the control circuit? If they are the same, then the big caps just act like big springs on the suspension (or maybe likeness to a water hammer supressor). It slows the ground bounce so that the digital circuit moves with it and is not glitched. If you already have a seperate ground return for the motor (perhaps becuase it has a different supply) then the cap is supressing EMI emissions and then a smaller ceramic cap should have done the job. If you must have a common ground between the motor and the circuit try speerating the motor with a coil. The inductor will maintain a DC connection but supress any current spikes trying to raise ground on the digital side. The ground return for the motor may not be one of its leads but possibly a point further back at the head of the driver ccircuit.

Polarized caps don't so much care about the direction of the noise signal dv/dt but they definately care about the DC bias. Since motors generally do have a significant DC component, you either needed to do what you did or use a non polarized variety.

[gerty]

Are you using this rf receiver by any chance?
http://www.digikey.com/product-detail/e ... -ND/340079

I used one for a motor control project, and the motor was remote mounted, about 10' away.
The receiver was 2' from a pwm control board and refused to run properly until I put the pwm unit in a metal enclosure. after that all was good.

[jwax]

Thanks for all the input guys. It runs fine with the back-to-back tantalums, so I'll leave it at that.
Some small DC motors run electrically quiet, while some are serious generators!
No gerty, mine are different 433 MHz units.