Help with motor noise Please

Thread Starter

chico1st

Joined Mar 12, 2010
2
I have an issue with motor noise on one of my projects.
I am running the motor through an H bridge and controlling it with a PWM at 250 Hz (tried 4 KHz same thing). Its a 6V motor that we run in various directions using the HBridge.

When the motor is on, our analogue sensors signal has large noise spikes (see picture):


We have 10nF ceramic caps on the + and - of the motor to ground.

But they didnt seem to do anything. Anyone have an idea on what we should do? I saw the 10nF cap number going around a lot for spike reduction.
 

someonesdad

Joined Jul 7, 2009
1,583
Divide and conquer: is the noise inherent to the motor? If you can, put it on a simple, clean source of power. This will help you decide whether your control circuitry is causing the noise problem or not.
 
First a LC mains filter for the PWM control is a must have device. Next, mount the filter and PWM control in a mild steel box w/ conductive gasket for the door. Add 2-pass ferrites to each output wire before exiting the box. A double shielded cable to the motor is last. This should kill the noisemakers.

Cheers, DPW [ Everything has limitations...and I hate limitations.]
 

hgmjr

Joined Jan 28, 2005
9,027
In addition to the schematic that has already been requested, I would ask you to take a few digital pictures and post them here also. It could help us spot a weakness in the layout of your system.

hgmjr
 

SgtWookie

Joined Jul 17, 2007
22,230
Divide and conquer: is the noise inherent to the motor? If you can, put it on a simple, clean source of power. This will help you decide whether your control circuitry is causing the noise problem or not.
If it's a brushed motor being driven by PWM at any speed, there will be more noise than a punk band concert in a library. :eek: ;)
 

SgtWookie

Joined Jul 17, 2007
22,230
First a LC mains filter for the PWM control is a must have device.
I think you meant a low-pass LC filter or low-pass RC filter for the current monitoring?

A simple toroidal ferrite would kill EM interference back-feeding to the mains; were the power connections wrapped through the toroid 10 times or so.

Next, mount the filter and PWM control in a mild steel box w/ conductive gasket for the door. Add 2-pass ferrites to each output wire before exiting the box. A double shielded cable to the motor is last. This should kill the noisemakers.
That might do it; but it's getting a tad pricey, too. Have you priced that sort of thing lately?
 

Thread Starter

chico1st

Joined Mar 12, 2010
2
ok all the info is very helpful.
Sorry I cant post a schematic right now but I will.

I know its not just an unclean power source. If I just have the motors running near my sensors from a different supply and holding them in my hand not on our PCB the sensors still get noise.

It is brushed DC under PWM, but the noise exists even without the PWM.

How do i make multiple RC filters? My signal is a step every 1ms (like a stair case) so I guess I would want the cutoff just over 1 KHz, then do i just put like 4 of those rc filters in parrallel... series makes more sense to me.
 
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