Physically silencing coil whine?

[lpc32]

I have a consumer device with inductors that make a high pitched noise. A cotton wool cover around the inductors helped some, but not enough, and it's messy.

What are common physical ways to silence coil whine? Are silicone sealants a good idea? Candle wax? What doesn't work at all? Are there any substances to avoid due to potential PCB or component damage? What's more difficult/easier to remove if needed?



BTW, there's already some white glue/substance around the inductors. Was this only to help with noise?

[wraper]

Are you completely sure it's a coil whine, not ceramic capacitor whine?

[Marco]

In the end the only way I found to truly silence my PC was 10 meter cables and some intervening drywall.

[lpc32]

I can't fully pinpoint the source of the noise, but I think "open" inductors are a common culprit?

Do you mean SMD caps? If so, that'd be easier to cover.

Moving noise sources to another room is not that practical. Luckily, I don't think my PCs whine, not appreciably anyway. Sadly, they make other annoying noises.

[wraper]

Do you mean SMD caps? If so, that'd be easier to cover.

Yes, sometimes they sing like hell.

If they are the culprit, you could also just try to change them. If they are of crappiest type like Y5V, Z5U, changing them to X7R or X5R will significantly reduce or completely eliminate the noise.

[PeterFW]

I can't fully pinpoint the source of the noise, but I think "open" inductors are a common culprit?

Take a bit of rubber hose and if you have a piece of tube, put the hose on the tube, but the hose in you ear.

That makes a perfect "near field sound probe", you can pinpoint were the sound comes from nicely that way.

You can use a solid piece of metal tubing as well but the rubber part makes it more mobile and comfortable.

[wagon]

A thick layer of varnish might help.

[T3sl4co1l]

Often the problem is *striction (electro- or magneto- for caps and chokes respectively), which is a bulk expansion phenomenon.  Glue won't help because it's not rattling and loose.  The vibration is transmitted through the material and substrate bulk (and, as with high frequency radio waves: it radiates easily as well, hence the audible sound).

I'd be tempted to hack the circuit itself.  Shitty controller designs sing (pulse modulated, or badly compensated and oscillating).  Only occasionally do quality controllers sing (usually because they are pulse skipping, which is efficient, but hopefully, done at a low current too, where magnetostriction is least).

Tim

[lpc32]

I'd rather not attempt to rework it before trying to just dampen the sound with something. I'll try to find some better foamy material to stick in there. Hopefully the heatsink won't be a problem.

Even if the caps are a possibility, is there a reason to rule out the inductors right away? Anyway, I'll see if I can pinpoint it better.

What sort of varnish?

[wagon]

I've used old fashioned shellac before on coils.  Also, normal oil-based varnish for wood might work.  Even a thick application of a clear sprag enamel my help.

[Canobi]

Plasti-Dip liquid rubber is what you need

Spongey foam just won't cut it unless it's fairly dense, and even then there's no guarantees otype work satisfactorily.

Plasti-Dip is the same as electric tape but in a liquid form that cures when exposed to air to a firm rubber which is much better at deadening high pitch whines.

[lpc32]

Plasti-Dip looks interesting. Is it a viable heatshrink-equivalent (for hard to reach places)?

I improved the situation some. Not perfect, but better than the first attempt. I didn't check what helped more (if at all):
2 layer of transparent nail polish/sealant on the inductors. Not sure what's it made of, but plastic didn't like it. The PCB survived.
I chamber the inductors, around and on top, with a plastic foamy packing material sheet. It's quite stiff, and somewhat thick. I added some cotton wool inside the chamber.
Two small transformers got the same chamber treatment, sans cotton wool. I couldn't quite pinpoint the noise source, but maybe they contributed too.

BTW, the noise appears to be harmonics of 1kHz that come and go to a certain degree, plus a stronger and constant ~13.2kHz. I'm not sure if I can infer that there are at least two noise producers.

[Canobi]

Plasti-Dip looks interesting. Is it a viable heatshrink-equivalent (for hard to reach places)?

I improved the situation some. Not perfect, but better than the first attempt. I didn't check what helped more (if at all):
2 layer of transparent nail polish/sealant on the inductors. Not sure what's it made of, but plastic didn't like it. The PCB survived.
I chamber the inductors, around and on top, with a plastic foamy packing material sheet. It's quite stiff, and somewhat thick. I added some cotton wool inside the chamber.
Two small transformers got the same chamber treatment, sans cotton wool. I couldn't quite pinpoint the noise source, but maybe they contributed too.

BTW, the noise appears to be harmonics of 1kHz that come and go to a certain degree, plus a stronger and constant ~13.2kHz. I'm not sure if I can infer that there are at least two noise producers.

Crud! Why wasn't I notified of a reply dammit, I'm going to have to wake up the dead on this one, sorry.

Did you ever sort the whine out?

And yes, PlastiDip is an isolator so can be used instead of heatshrink.

[Chris C]

A bit late for the original poster, but most common hardware store silicones emit acetic acid as they cure.  And tend to trap it in the component or joint you've sealed.  Not very electronics-friendly.

[lpc32]

Crud! Why wasn't I notified of a reply dammit, I'm going to have to wake up the dead on this one, sorry.

If not thread subscription alerts, there's always the "Show new replies to your posts" link, at the top of forum pages.

Did you ever sort the whine out?

Just what I did in the last post. It's mostly good enough, though still not silent.

most common hardware store silicones emit acetic acid as they cure.

Any way to tell apart the ones that don't?

[technix]

In the end the only way I found to truly silence my PC was 10 meter cables and some intervening drywall.

For quite a while in my home there is no computer new enough to use a few new apps I use daily other than a server. Then I set up virtual machines on that server and access them using my iPad over VNC over Wi-Fi. That was mess-free and noise-free definitely.

[jitter]

most common hardware store silicones emit acetic acid as they cure.

Any way to tell apart the ones that don't?

Yes, they should be labeled and marketed as "acid-free".

[T3sl4co1l]

most common hardware store silicones emit acetic acid as they cure.

Any way to tell apart the ones that don't?

Yes, they should be labeled and marketed as "acid-free".

Read the label, if it says something like "diacetoxydimethylsilane" (or anything with "aceto" in it), it's the vinegary stuff.

Not all "acid free" is safe for electronics: the "amide" variants produce ammonia on curing, which is also very corrosive to copper.

The "methoxy" kinds, or RTV kinds that don't cure on atmospheric exposure at all (two parts), are preferred.

Tim

[lpc32]

Wikipedia claims (but no citations ),  that some RTV types release acetic acid.

[jitter]

most common hardware store silicones emit acetic acid as they cure.

Any way to tell apart the ones that don't?

Yes, they should be labeled and marketed as "acid-free".

Read the label, if it says something like "diacetoxydimethylsilane" (or anything with "aceto" in it), it's the vinegary stuff.

Not all "acid free" is safe for electronics: the "amide" variants produce ammonia on curing, which is also very corrosive to copper.

The "methoxy" kinds, or RTV kinds that don't cure on atmospheric exposure at all (two parts), are preferred.

Tim

Tomorrow I will check what we use, but I don't think it's anything special. We've been using this stuff for as long as I work there without any adverse effects. Perhaps the limited curing time in combination with the solder resist on the boards prevents problems from occurring. Exposed pads are never bare copper but either have a HASL or ENIG finish.

[Tandy]

If the device didn't make a noise to start with it is usually a sign of a problem. Just covering it up may not be the answer as the circuit is probably under undue stress and may fail prematurely as a result. Often I find a singing coil is in fact the result of a failed electrolytic capacitor that is not smoothing the power supply properly causing the coil to resonate.

[jitter]

Tomorrow I will check what we use, but I don't think it's anything special. We've been using this stuff for as long as I work there without any adverse effects. Perhaps the limited curing time in combination with the solder resist on the boards prevents problems from occurring. Exposed pads are never bare copper but either have a HASL or ENIG finish.

I must correct myself. The stuff we use is not just "something that'll do".
It's Dow Corning 744 which is formulated for use on electronics (among other things) after all.
Product information here and safety sheet here.

[penfold]

When ever I have had problems with whining from a magnetic component, it turned out to be two halves of the core clattering together, which i solved by clamping the halves tighter

[lpc32]

...

Thanks.