varnish type for buzzing transformers? *fixed* - Page 1
Forum section: electronics / repair

author: coppercone2
author_rank: Super Contributor
timestamp: April 18, 2021, 08:25:49 am
content: So I have a nother HP harrison, this one is buzzing at the transformer. I used my mini microphone on a stick probe to trace it down to the area where the transformer bolts to the PCB. Prying and clamping near it does not work and the bolts appear to be super tight.I found this list of possible candidateshttps://www.electro-wind.com/media/files/dolph's/literature/varnish-resin-guide.pdfI wonder which one of these has the highest possible chance of success?My plan was to dip it in hot varnish after baking it, maybe try doing something with the vacuum (I hate this), then bake it more with a bunch of clamps on it

author: jonpaul
author_rank: Super Contributor
timestamp: April 18, 2021, 08:57:18 am
content: Hello the buzz is due to a loose core piece, excess gap or high exitation.Varnish needs a vacuum oven to effectively fill every airgap.Beware many of the Dolph etc are not available in some locations due to VOC regulations.Easier to tighten the lam bracket or screws, and to vibration isolate the transformer off the chassis.Good luck,Jon

author: coppercone2
author_rank: Super Contributor
timestamp: April 20, 2021, 09:53:47 pm
content: I bought mg chemicals red transformer varnish because usually they have good things, i could not make a decision based on that tableits small so I will try out my cooking pot vacuum chamber, it does work, just I hate the cheap pump from HFdo I still need to do all the baking since this is an old transformer? do i need to heat the varnish on a hot plate before the dip ? on one hand it decreases solubility of gas (so the trapped air can not dissolve as easily, if it does), but on the other hand it should reduce viscosity.my vacuum chamber has vacuum adjust so I can prevent it from boiling it

author: floobydust
author_rank: Super Contributor
timestamp: April 20, 2021, 10:12:05 pm
content: Another cause of noisy, buzzing power transformers I have seen is the lamination bolts end up making a shorted turn, if people reef them tight and break the insulator washers.I would check the transformer's mounting hardware is right.Some bigger transformers (1000VA) I ended up mounting them on rubber standoffs, because they just vibrate and possibly their leakage flux is attracting nearby steel. The transformer is quiet on it's own but the vibration is transferred to the chassis. Have you tried running it alone on a bench?I haven't tried redoing varnish on an old transformer. The heating I thought is to lower curing time and lower viscosity to get the foam out easier.Problem is heating the transformer's core, that's a lot of work and hot varnish on a cold core might be a problem.

author: coppercone2
author_rank: Super Contributor
timestamp: April 20, 2021, 11:00:21 pm
content: yea the transformer would be preheated.I did not think of a shorted turn, the bolts are like... fake trick bolts, they have phillips, its not worn out, but its too shallow for my screwdrivers to work with it, I thought it would take 2 seconds and I keep running into bull shit problems, maybe its so people in the factory cannot destroy it in the first place, but who knows it could have failed its ancientwell since I already bought the varnish a few days ago, when i am ready to undertake this I will try those things out before soaking itwhen I reinstall it I can cut a strip of rubber under the transformer I guessI run it with only the chassis outline (the sides) without top and bottom, it makes the same noise, getting the sides off requires desoldering. i can do that since i invested in some PACE stuff without cursing but i need to ready myself up for that job, the last harrison kept having problems so my 2 hour trimpot restoration idea turned into 12 hours work, but I usually improve it, like desolder the transistors and add thermal compound and new pads under them and stuff like thatprobobly should desolder the screw terminals and ultrasonic clean them for a long time and shine that old shit up

author: coppercone2
author_rank: Super Contributor
timestamp: April 24, 2021, 10:48:06 pm
content: OK, I baked it for 1 hour at 110C in my PID oven, when it cools down some what I will dip it in a beaker of varnish that I pull a vacuum on, my vacuum chamber can do ~24 inches of mercury because the seal leaks, its made really bad with some kinda sticky rubber I found in the trash and rubbed down with vacuum grease, unfortunatly it hisses, but I understand you don't want the vacuum to be too strong with a varnish that uses a solvent. I can adjust the vacuum level with some needle valves and a omega digital vacuum gauge.I will degas it in a beaker sitting in the cooking pot then put the transformer in and pull a vacuum and see what happens.its a real half assed implementation but I guess we will see what happens, I see they want more vacuum and some kinda varnish thats not solvent based that costs 200$ a gallon and vacuum baking but I am not gonna be able to do that

author: floobydust
author_rank: Super Contributor
timestamp: April 24, 2021, 10:55:39 pm
content: Uh I think 110°C is really hot, no need for that as it will melt plastics and existing wire varnish in the transformer.

author: coppercone2
author_rank: Super Contributor
timestamp: April 24, 2021, 11:26:59 pm
content: I think the transformer should be able to take like 130C for a class BI see there are transformers that go down to only 90C. Well it looks OK and does not smell or anything like that, I hope its ok.

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2021, 12:09:15 am
content: alright I poured 400ml into a beaker, degassed it (it did not degas much) for a few minutes, then I dipped the transformer in on a wire and turned it on for maybe 5 min. It gassed alot, I think it was air leaving the transformer, not stuff in the varnish. The pressure reached was 26 inches of mercury.Now I took it off and hung it under a tray lined with aluminum foil off a vise so it catches the drips. This stuff is pretty thick, maybe it should have been thinned, its like thin batter for crapes.It seems to be mostly retained but its skidding off the sides of the transformer, and it got under all the tape for protecting the wire, but I think it will be OK. I am going to hang it for a while, I don't think I will bake it because the shitty vacuum pump already made way too much smoke and I think it will smell bad. The transformer looked like there was 'voids' in the winding, when looking from the top so that looks filled. before i dipped it I wiped it down with isopropyl alcohol and task wipes, maybe it could have used a light sanding on the sides, I suppose they were still well varnished so the new stuff did not want to stick to the slick surface too much.I have to say it looks pretty bad but from what I understand it should increase thermal dissipation by filling in those voids seen from the top I don't like the red color.I kind of wonder if turning them on under load while in the varnish would help the varnish get into shit thats deflecting because of magnetic fields but it seems like a good way to start a fire, I would need single part non flammable epoxy. Like if you turned it on near max load while its submerged in the varnish under vacuum. It can probobly break the seal, suck in oxygen and make a spark and blow the fuck up though.When its dry I will put it over the edge of a table and apply paint stripper gel on the wires with a q-tip to clean the varnish off of them then solder it back into place. Hopefully it will be quieter.

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2021, 02:55:58 am
content: Ok, if you do this, the best thing you can use the clean the varnish off something like a transformer lead before heat cure (after an hour or 2) is called Goof-Off. Magical product, its a few dollars for a tin with a very good squirt nozzle (like lighter fluid). I think it has THF in it, anyway it does a fantastic job of getting the varnish off of everything, including glassware on the final wipe after alot of mineral spirits, the plastic funnel (nalgene), small spots that the gloves missed, etc. It gets into tape real good.If you soak it into a kim wipe or blue shop towel and gently pull it over the transformer leads it cleans right up.I am going to do a bake now at 80C. I drizzled a little bit on top of the transformer because there was a slight cavity there, not sure how it formed, unless the stuff continued to flow inside of the transformer after a while of being out of the bath. I would probobly recommend if you care about cosmetics to do a 2nd standard dip after its cured if that works to make it look better, after a light sanding, but I don't think I will go that far until I test it and get a feel for if it works.I did lose the transformer number, so be sure to write it down if you do this.I used a large spaghetti pot for this, make sure its smooth onthe inside and the handle is welded to the outside instead of riveted on the inside. The lid I made from maybe 3/8 plexiglass with soft rubber glued around the rim, with silicone caulk at the interface of the rubber and plexiglass, the other parts are swagelokI would highly recommend buying a vacuum chamber on ebay, everything but the plumbing is great on those, they have a real gasket, it can probobly pull a much harder vacuum. I put a normal glass beaker and used nalgene funnel and recycled the left over varnish back into the bottle, if it gets too tacky I will buy their varnish thinner and dilute it a little. If you 'fill' the area on top of the transformer where the windings are, it looks much better. When its dried and I handled it I think overall it is a better transformer, I feel more confident in the assembly.

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2021, 05:12:25 am
content: the pitch of buzzing changed and I can localize it now. It looks like both the transformer and some capacitors were buzzing, I replaced all but the axial ones, so I will get those in on monday.I put a tube into my ear and when I move it near the transformer its more quiet then when I move it near the capacitor it gets distinctly loud. Before I could not tell and it sounded like the whole area was buzzing uniformly .Old sprague axial capacitors. One is in spec but the other one has slightly higher ESR and deviated capacitance, I thought it was within spec but I guess not.I think it did silence the transformer though.On my lambda, just replacing the capacitors made it quiet. In this case I think it there are two problems.

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2021, 10:38:08 pm
content: I found the problem, it was.. everythingAfter I varnished the transformer and cut out the axial caps and replaced the sprague filter caps, it was still buzzing, near the transformer. But I decided to cut out the disk caps, and replace them with small foils that are similar size to the same voltage the rail is on. Totally solved the problem, have a tiny bit of buzz if I put my ear right to the transformer but its fine. I just need to probe them with a scope during turn on to see why they had 500V caps, but it seems to run fine with 63V caps, because the measured AC voltage is around 50VAC.I would say 25% of noise was from transformer, like 25% from the spragues and50%from the disc caps. Those things are fucking loud!So if you are doing this yourself, don't be too scared of varnish if you think the setup needs to be hardcore. I got it down to a WAY lower level thats almost unnoticeable with only a basic setup. If I did the whole vacuum baking single part epoxy expensive transformer resin 24 hour crazy procedure, it could not have made it more then a few percent quieter. Of course it could be my luck but I have a feeling if you do it for your lab equipment, it will be more then enough of a improvement.