Coil whine - is CA superglue safe on inductors - Page 1
Forum section: electronics / projects

author: TruslowPJ
author_rank: Contributor
timestamp: February 04, 2023, 01:25:40 pm
content: I have been working on modifying a tripplite su2200rtxl2ua online UPS to go in my office. So far I have replaced the batteries with lifepo4 and swapped the fans for quiet ones. Unfortunately the 18khz PWM of causes one of the inductors to whine substantially. I have used a microphone as well as a paper cone and my ear to confirm which inductor is making the noise. Before anyone says it is not the inductor, it is definitely the inductor. There are no ceramic caps nearby that could be making the noise, and the relay next girl the inductor is definitely not the source.My plan is to start with some sort of rigid glue to stop the windings from moving on the core, then maybe apply some hot glue (depending on how hot that inductor gets) or electronics grade silicone.My question is will CA based superglue (thin or medium) damage the coating on the inductor turns? I do not know who made the inductor or exactly what the insulation is. All I can tell is it has a blue toroidal core, and two windings (so I guess it is a 1:1 transformer) with about 30 turns of 18awg wire each, and one winding has an orange color while the other is a deeper red. The inductor/transformer in question is near the second one from the back along the middle of the inverter with the visible blue core.Thank you to anyone who is able to provide advice.

author: xrunner
author_rank: Super Contributor
timestamp: February 04, 2023, 01:37:48 pm
content: I doubt CA will damage the inductor coating - it's enamel. But you can buy small bottles of transformer varnish that would work.

author: jonpaul
author_rank: Super Contributor
timestamp: February 04, 2023, 01:40:36 pm
content: cause is poorly designed converter, subcycle oscillatons or,unstable loop.No ammount of adhesive will fix the noise.the APC UPS seem better design and quality than trip liteJon

author: TruslowPJ
author_rank: Contributor
timestamp: February 04, 2023, 01:53:16 pm
content: Whether or not an APC UPS would be better isn’t quite relevant for me. I have two of these I got for a song, so my goal is to make it quiet enough to live in my office. I know I can’t fully eliminate the whine, but I am sure I can at least attenuate it some. It is mechanical movement after all.If I could I would use one of the APC xl units as they can have their charge voltage adjusted and my bank could do with just a bit more voltage but i can’t find one local to me and shipping one would cost nearly what I have in this project.

author: wraper
author_rank: Unknown
timestamp: February 04, 2023, 01:59:59 pm
content: Quote from: jonpaul on February 04, 2023, 01:40:36 pmAPC is an overpriced trash buld from trash parts, usually with trash batteries included. I'm talking overall, not just cheap consumer models.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 04, 2023, 03:13:18 pm
content: Quote from: jonpaul on February 04, 2023, 01:40:36 pmChoice of 18kHz PWM might be suboptimal if audible noise is important, but it is not "poor design" per se. Especially if the UPS is old and thus limited to the technology of that era. One can't know from the whine alone if the product otherwise has good performance or lifetime.

author: Zoli
author_rank: Frequent Contributor
timestamp: February 04, 2023, 05:27:59 pm
content: Typically, for silencing the TV fly-backs a silicon conformal coating spray was used; that would be my first choice instead of CA.

author: JacobPilsen
author_rank: Regular Contributor
timestamp: February 04, 2023, 05:41:35 pm
content: Cured CA is too brittle.I wouldn't try it.

author: TruslowPJ
author_rank: Contributor
timestamp: February 04, 2023, 06:22:19 pm
content: Quote from: Zoli on February 04, 2023, 05:27:59 pmI just happen to have a spray can of MG chemicals 422c I can borrow so I will give that a shot. Without having to buy anything, my options are hobby grade 30 minute epoxy and CA, 422C, hot glue (inductor gets too hot for that) and shower caulking(may cause corrosion due to acetic acid so too risky)I understand the proper things would be a varnish made for motor or transformers, or electronics grade silicone but I have neither. That silicone-acrylic conformal coating is worth a shot and might be the ticket to help at least to a degree.I will mask as well as I can and just hit the inductors though. I’ll probably do them all rather than just the one in question.

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 04, 2023, 10:42:41 pm
content: Quote from: Siwastaja on February 04, 2023, 03:13:18 pmI agree, although I would classify parasitic noise in the "performance" category for any product that is meant to be used in a home or office environment.If it's meant to be used in a basement or an industrial environment, obviously not.

author: jonpaul
author_rank: Super Contributor
timestamp: February 05, 2023, 12:17:52 am
content: Hello again:18 kHz is above the range of human hearing for those older than a Teen.A 1/2 sub cycle will b e9 kHz, check the frequency of the while with a mic and smartphone SA.Crazy glue has very active chemicals that may attach copper.Easy to pur a wrap of fiberglass around the transformer and see if the noise is less.Jon

author: coppercone2
author_rank: Super Contributor
timestamp: February 05, 2023, 01:53:53 am
content: you can try to build a dam around it and pour in flowable silicone, then hit it with a vacuum

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 05, 2023, 06:46:25 am
content: CA is fine for what it is, but I would be worried the operating temperature will simply melt/release it. Epoxy will hold up to the rating of the part.Or electrical varnish, which they probably already used.But if you're certain it's the blue thing, that's interesting as those are probably Sendust, a material with low magnetostriction. The wire is tightly wound, unlikely to shake; more likely the core itself expands due to this effect. Perhaps that's not what it is (core colors aren't the most consistent thing); I've seen ferrites coated in blue before, and ferrite has notable magnetostriction.You'll do better (and make less of a mess) by adding acoustic damping to the panels around it, I think.Tim

author: Zoli
author_rank: Frequent Contributor
timestamp: February 05, 2023, 07:41:07 am
content: Quote from: TruslowPJ on February 04, 2023, 06:22:19 pmA few(4-6) application may be required; is recommended to blow ALL the dust out of the supply before applying the conformal coating. Sometimes the noise is generated by a wrongly placed speckle of dust...

author: TruslowPJ
author_rank: Contributor
timestamp: February 07, 2023, 04:41:04 pm
content: well, after many, many coats of conformal coating, I don't think it made much difference. I have attatched a frequency graph before and after, but you can't really tell which is which.It looks like it did damp a 9khz subharmonic, but not the massive spike at 18khz.out of curiousity, I passed a single loop of wire through the transformer and connected a scope to get an idea of the signal passing through that transformer. looks to me like an 18khz square wave with varying duty cycle to approximate a sine wave, which i guess gets smoothed out by the inductor above and some caps that follow before the output, which I suppose is about how i figured it worked. given the lack of a big chunky 60hz transformer, it appears to be using the equivalent of a class D amplifier to drive a transformer. with the output being filtered to remove most of the 18khz ripple.If only this thing would go into eco(bypass) mode. from what I can tell by heat, most of the energy is lost in this transformer and the associated inductor, so they are definitely switching that part of the circuit off in eco mode, sadly even tripp-lite support couldn't figure out how to enable eco mode, as my unit just ignores the command from their software.maybe my next thing to try is silicone. I don't think I should totally pot the thing due to it already running around 150F under full load, but maybe smearing it into the gaps between the windings and core will help without causing it to heat up much more.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 07, 2023, 04:53:03 pm
content: 150°F, that's it? That's...still touchable. Electronic components handle on the order of 150°C, not 150°F. Are you sure about "full load"? It should run for some minutes to heat up; maybe it's not finished heating up yet? (If it can't run for long enough... great, no need to worry about excess temperatures anyway!)You're sure you don't want to consider acoustic damping before making the thing utterly unserviceable (and changing thermal performance -- mind that silicones generally have quite poor thermal conductivity, get an appropriate formulation)?High frequencies like that are either carried on the air (straight line paths, think optics) or solid materials, generally things either that are flexible (so air couples into it easily), or rigidly attached to things (so the vibrations in a dense object conduct through them all). The same principles that apply to electronic filters apply here: alternate high ("inductive") and low density ("capacitive") elements to make a lowpass filter. Add damping (fiber, foam, rubber) to absorb energy. Seal off openings if you can, and make circuitous paths (galleries lined with damping material) where you can't.Tim

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 07, 2023, 05:46:28 pm
content: I'd be thinking about vacuum impregnating it with epoxy.

author: jonpaul
author_rank: Super Contributor
timestamp: February 07, 2023, 05:52:45 pm
content: I would check the input/output power with an AC line monitor, at max load to find the efficiency.Most PSU parts are rated 85..105 dec C.Ferrite and bobbin hotspot and insulation are class 130 or 155C.Use thermocouple not temp gun for accuracy, all T in C not F.Jon

author: james_s
author_rank: Super Contributor
timestamp: February 07, 2023, 05:54:04 pm
content: I've used CA for this purpose and never had any trouble with it. YMMV.

author: TruslowPJ
author_rank: Contributor
timestamp: February 07, 2023, 06:42:40 pm
content: Quote from: T3sl4co1l on February 07, 2023, 04:53:03 pmyeah I was surprised too. it was touchable, but definitely uncomfortable eventually.as for the load, it was powering a 1400W space heater for 15 minutes before exhausting the batteries. i immediately pulled the cover and checked temps all over with an IR gun, sorry to say I had it in Farenheit. It is a 1600W, 2200VA unit. I think they built in a healthy amount of safety margin given it can support an unlimited number of external batteries, and being online, the only part of the circuit not in the path all the time is the boost converter that powers the high voltage rail from the batteries in battery mode. I'm not sure how long I can power a 1400W space heater through the UPS on the circuit it is connected to. it's a pretty long run and the input voltage sags to 105V, but the output is rock steady at 119.8-120V, so the input current sits at around 16A on a 15A circuit. I don't have a Kill-a-watt so I was using a pair of smart plugs with power monitoring. maybe I will do an extended load test on mains power with the heater on half power, as I doubt I will ever run this thing at 1600W continuously, more like 3-400w with peaks at 1000W tops.vacuum impregnating it with epoxy sounds great, but I think it's impractical. I don't feel like pulling the inverter board from this unit, let along removing the transformer to make the job easy. also the amount of silicone conformal coating I have applied will probably make the epoxy not bond to the surface, but it will at least be held in place from being in between the windings. The epoxy I have I know from experience softens at pretty low temperatures so I would need to get something else.I'll see about putting a thermocouple on it. i was using an IR gun because I can scan all over easy, and putting a thermocouple in a mains referenced circuit needs to be done with care. don't want it coming loose as I put the top cover on and it short something out.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 07, 2023, 07:50:51 pm
content: Decent epoxies will do far better than 150F. Heck that's the cure temperature for many that we use. That said, if you can't remove the part I don't think any treatment will be super effectiveOne hint with IR measurements. Watch out for emissivity. I typically use some flat black paint to put a good measurement spot on critical components if they're made of metal. Otherwise you just can't trust the readings.

author: james_s
author_rank: Super Contributor
timestamp: February 07, 2023, 10:07:30 pm
content: Quote from: Conrad Hoffman on February 07, 2023, 07:50:51 pmThat seems to be especially true of aluminum. IR thermometers are all but useless for measuring the temperature of a bare aluminum surface.