PWM - Mosfet/motor introducing noise

[DynamoBen]

Here is a working schematic.

I'm sharing a common between the 12V and 5V rail. I haven't looked at the 5V rail yet.

[mackrackit]

Try a 4700 or greater cap across the motor leads?

[DynamoBen]

I tried a 2200K, no change.

Here are some scope shots of the 5V and 12V rails with the motor running.
5V = motor controller2 sml
12V = motor controller 12sml

2ms/div, 1V/div (x10 probes)

[DynamoBen]

After some thought I may just leave things as they are. To get it perfect will require a major redesign which I don't have time for. At this point I'm not sure that this will be a big deal. Agreed?

[Acetronics2]

Hi,

First ...

Your diode parallelled to the mosfet must be paralleled to the MOTOR ... that will GREATLY limit the spikes ( 1N400x seems a bit Weak for this kind of motor ... try better 1N540x or a fast recovery TO220 model )

Now,

1) place a low ESR 1000µF or + capacitor as close as possible to the motor ... to lower the 12v power source impedance. ( by the way, I'm saying the mosfet could be placed close to the motor ...and the diode between motor terminals ...)

2) place a .1µF on your motor terminals

3) place a 10nF between each motor terminal and motor frame which has to be connected to circuit ground.

4) you can place a core coil ( 1mH range "big value" ) in series beetween 12 v and your 5v reg input

Alain

[DynamoBen]

Your diode parallelled to the mosfet must be paralleled to the MOTOR ... that will GREATLY limit the spikes ( 1N400x seems a bit Weak for this kind of motor ... try better 1N540x or a fast recovery TO220 model )

The schematic isn't correct in this case, the diode seems to be drawn wrong. However I will try moving the diode up to the motor. I will try to located a different diode...

1) place a low ESR 1000µF or + capacitor as close as possible to the motor ... to lower the 12v power source impedance. ( by the way, I'm saying the mosfet could be placed close to the motor ...and the diode between motor terminals ...)

The mosfet can't be moved. I don't know if I have a low ESR cap. I can dig through my parts bin. Anything specific I should be looking for?

2) place a .1µF on your motor terminals

Is this in addition to the above cap?

3) place a 10nF between each motor terminal and motor frame which has to be connected to circuit ground.

Will try.

4) you can place a core coil ( 1mH range "big value" ) in series beetween 12 v and your 5v reg input

I don't have anything like this lying around.

[Acetronics2]

QUOTE=DynamoBen

The mosfet can't be moved. I don't know if I have a low ESR cap. I can dig through my parts bin. Anything specific I should be looking for?

> IF I tell you BC Components (ex. Philips ) Series 136 ... ESR <= 22 mOhms ( Milli ...yes ! )


Is this in addition to the above cap?

> The .1µF capacitor must be soldered ON the motor terminals ...


Will try.

> The 10nF are also necessary.


I don't have anything like this lying around.

> Not compulsory, yes ...but highly recommended !!!

Alain

[DynamoBen]

1N400x seems a bit Weak for this kind of motor ... try better 1N540x

I picked up a 1N5406 at Radio Shack last night.

1) place a low ESR 1000µF or + capacitor as close as possible to the motor ... to lower the 12v power source impedance.

I was unable to locate a low esr cap, so this one can't be done.

place a .1µF on your motor terminals

done

place a 10nF between each motor terminal and motor frame which has to be connected to circuit ground.

done, frame of motor is connected to common

you can place a core coil ( 1mH range "big value" ) in series beetween 12 v and your 5v reg input

Still no luck locating a coil.

In the end my "issue" still exists. *sigh*