DC Motor Noise?

[Benta]

Nice plots, thanks.
The effect of the filtering is very obvious.

[Paul Ebert]

I've got a similar problem, though my motor is quite small (somewhere between 3 and 10 watts). I'm also pretty much a software guy. What size inductors should I try. I'd rather not use ferrite beads because I have essential tremor so holding such things stable for soldering is a challenge (any soldering is a challenge). Is there some sort of nice small (non-SMT) component inductor I can buy from Digikey or something like that?

I'm controlling my motor by using an arduino controlling a DAC feeding into a TI OPA548. The op amp has current limiting. Can I use that as a basic soft start? If not, could someone please suggest an appropriate simple circuit?

[shabaz]

Hi,

What's the precise issue you're experiencing?

In general, the capacitor(s) are highly recommended by default.
You might not need wound inductors per se (sometimes it can indeed be useful) you might just need ferrites, such as the clip-on variety, it would cause no harm, and could be effective.
If not a toroidal ferrite (sometimes also called a bead, although it's larger), then you could pick any clip-on ferrite (several loops through it will be more effective).
If issues are still experienced after this, then some further thought/experimentation will be needed.

However, you may have an unrelated issue, so it's worth describing it, in case any other suggestion springs to mind. A circuit diagram and maybe a photo of the setup if possible, may also help.

[Refrigerator]

I've got a similar problem, though my motor is quite small (somewhere between 3 and 10 watts). I'm also pretty much a software guy. What size inductors should I try. I'd rather not use ferrite beads because I have essential tremor so holding such things stable for soldering is a challenge (any soldering is a challenge). Is there some sort of nice small (non-SMT) component inductor I can buy from Digikey or something like that?

I'm controlling my motor by using an arduino controlling a DAC feeding into a TI OPA548. The op amp has current limiting. Can I use that as a basic soft start? If not, could someone please suggest an appropriate simple circuit?

High current opamps are such an unusual concept to me 
But yes, this will work just fine, you can even put an RC circuit in there, or interpolate in SW.
This IC has thermal shutdown and current limit, so there's pretty much no way you can kill it. This also works as a protection for the motor in case it stalls or burns out, which would cause sustained high dissipation in the IC.

Also wouldn't winding a couple loops of wire around a ferrite ring be easier than soldering? There are even clamp style ferrite rings that are even easier to use.
I'm not familiar with tremors.

[shabaz]

If you can share your use-case, that would be helpful. What are you using the motors for? It's unusual to use a DAC + Op Amp to control the motor, normally it's approximated by using PWM and a H-bridge instead (and possibly an inductor too), and it's usually cheaper/simpler/efficient to do this. This is not quite related to this thread though.

[Paul Ebert]

Hi,

What's the precise issue you're experiencing?

In general, the capacitor(s) are highly recommended by default.
You might not need wound inductors per se (sometimes it can indeed be useful) you might just need ferrites, such as the clip-on variety, it would cause no harm, and could be effective.
If not a toroidal ferrite (sometimes also called a bead, although it's larger), then you could pick any clip-on ferrite (several loops through it will be more effective).
If issues are still experienced after this, then some further thought/experimentation will be needed.

However, you may have an unrelated issue, so it's worth describing it, in case any other suggestion springs to mind. A circuit diagram and maybe a photo of the setup if possible, may also help.

First, a bit about the application.  This is for a DIY turntable motor controller. The provision of DC is as described. To control it, I've got a disk with alternating "pie slices" of white and black mounted to the underside of the platter. An optical sensor detects the edges as the platter spins.  Software detects the time between edges and adjusts the DC voltage accordingly. This issue I was having was that the time between edges was quite variable. On the order of a few percent. Clearly not going to do for playing a record. I jumped into this thread because of this issue and the fact that I don't have any equipment (other than a cheap DVM) for hardware debugging. I, too, was struggling with the question if I should spend $400 or more on a scope that I might very well use once.

Anyway, I've largely solved my problem (for now anyway). I was able to determine that the strobe disc I made wasn't very accurate. When I look at the same slice as the platter spins, the time is stable to a tenth of a millisecond or so. Not great, but maybe not a problem. The second realization was that I was only measuring with a microsecond resolution and this wasn't sufficient. When I switched it to microsecond (a simple SW fix), it was clear that the stability was an order of magnitude better than I could detect previously.

Part of me still wants to get a scope. I could always sell it if I find I'm never going to use it again. On the other hand, the money would be better spent on a better cartridge.

[Paul Ebert]

High current opamps are such an unusual concept to me 
But yes, this will work just fine, you can even put an RC circuit in there, or interpolate in SW.
This IC has thermal shutdown and current limit, so there's pretty much no way you can kill it. This also works as a protection for the motor in case it stalls or burns out, which would cause sustained high dissipation in the IC.

Also wouldn't winding a couple loops of wire around a ferrite ring be easier than soldering? There are even clamp style ferrite rings that are even easier to use.
I'm not familiar with tremors.

LOL (at myself). I was showing my ignorance here. I have a several decades recollection of ferrite beads being actual beads - about a millimeter or two - soldered directly to IC chip pins. I wasn't thinking about something that could be easily clipped around a pair of leads.

Essential tremor looks like the tremor one often gets from Parkinson's, but doesn't have the other eventually fatal symptoms. It's an annoyance. Difficulty soldering is where I bump into it most impactfully.