I added step 4.5, you're right
I haven't yet added a means for vibration, but I had a thought. I'm going to be using a large piston style compressor to drive the vacuum pump. If I can securely place the chamber on top of the compressor, it can kill two birds with one stone... heat up the varnish a bit, and also vibrate the heck out of it.
So today was the first trial. I didn't have the oven yet, so I preheated the transformer in the normal oven, to 65C, on a disposable tray.
The vacuum chamber is cool, it works as advertised. I cut a plastic milk carton as a liner for the chamber, and filled it with varnish. I then degassed the varnish by drawing a vacuum, and it swelled up with bubbles like a beer with too much head. It then settled down. Then I placed in the pre-heated transformer, and drew a vacuum again. This time lots of bubbling, from every pore of the transformer. After half an hour it was settled down to nothing, I let the air in, and pulled out the transformer. As the oven is not yet ready, I suspended it in front of an electric heater. So far, so good!
The vacuum chamber is cool, it works as advertised. I cut a plastic milk carton as a liner for the chamber, and filled it with varnish. I then degassed the varnish by drawing a vacuum, and it swelled up with bubbles like a beer with too much head. It then settled down. Then I placed in the pre-heated transformer, and drew a vacuum again. This time lots of bubbling, from every pore of the transformer. After half an hour it was settled down to nothing, I let the air in, and pulled out the transformer. As the oven is not yet ready, I suspended it in front of an electric heater. So far, so good!
Q-Dope vs. Varnish
I had posted a bit back that I made Q-Dope by dissolving polystyrene packing peanuts in a solvent, but I named the wrong solvent. It should be toluene. Toluene is still available at local hardware and big box stores, but bear in mind that it is not terribly good for your health so use it with proper ventilation.
But I have a question. Ham radio operators seem to swear by Q-Dope for their projects (mainly RF coils) since polystyrene is low dielectric. I suspect that that doesn't matter for a transformer, but would appreciate hearing from the experts on that issue. As a second issue, I expect that heat is probably more of a problem in a transformer than an RF coil. Would a typical varnish withstand heat better than polystyrene? For reference, polystyrene has a melting point of 240 C, but a glass transition point of about 100 C. I can't find similar information for varnishes, but polyurethane, phenol and alkyd based varnishes are all touted as having "high" heat resistance. (since I switched to water based finishes I have a whole bunch of old -but still useable-oil based varnishes in my shop so I would be happy to use them).
If anyone has information on what the real heat resistance of various varnishes is, I would appreciate hearing about it.
On an entirely other matter, does anyone have any experience using an old woofer to make a vibration table?
Thanks.
I had posted a bit back that I made Q-Dope by dissolving polystyrene packing peanuts in a solvent, but I named the wrong solvent. It should be toluene. Toluene is still available at local hardware and big box stores, but bear in mind that it is not terribly good for your health so use it with proper ventilation.
But I have a question. Ham radio operators seem to swear by Q-Dope for their projects (mainly RF coils) since polystyrene is low dielectric. I suspect that that doesn't matter for a transformer, but would appreciate hearing from the experts on that issue. As a second issue, I expect that heat is probably more of a problem in a transformer than an RF coil. Would a typical varnish withstand heat better than polystyrene? For reference, polystyrene has a melting point of 240 C, but a glass transition point of about 100 C. I can't find similar information for varnishes, but polyurethane, phenol and alkyd based varnishes are all touted as having "high" heat resistance. (since I switched to water based finishes I have a whole bunch of old -but still useable-oil based varnishes in my shop so I would be happy to use them).
If anyone has information on what the real heat resistance of various varnishes is, I would appreciate hearing about it.
On an entirely other matter, does anyone have any experience using an old woofer to make a vibration table?
Thanks.
This morning it was totally dry, and really glossy. Everything is evenly covered, but I noticed that there's not a lot of mass on the windings, it got a fairly thin coat. The laminations are totally saturated however, and the screws are completely glued in with varnish. I did some small transformers and chokes at the same time, which did not get the pre-heating or heat to dry, those were done only with the varnish.
The acrylic lid of the vacuum chamber exhibited some crazing due to the solvent in the varnish. I am getting the vendor to send me a tempered glass lid, since it will be more resistant to solvents.
For the test piece, I'm not going to give it a second coating before I check it for vibration, and see how well the impregnation effort worked. I think for the RCA transformers though, I will do two or three dips, just to make sure it's absolutely perfect.
Another issue is my vacuum pump can't get to -30 inches of mercury, it can get only to -26. I think it may not matter though, a huge quantity of air escapes at this vacuum level.
It was fun to make a tiny bit of shaving cream fill a whole glass, or take the fizz out of carbonated water, when I was playing with it before I started the transformer experiment.
The acrylic lid of the vacuum chamber exhibited some crazing due to the solvent in the varnish. I am getting the vendor to send me a tempered glass lid, since it will be more resistant to solvents.
For the test piece, I'm not going to give it a second coating before I check it for vibration, and see how well the impregnation effort worked. I think for the RCA transformers though, I will do two or three dips, just to make sure it's absolutely perfect.
Another issue is my vacuum pump can't get to -30 inches of mercury, it can get only to -26. I think it may not matter though, a huge quantity of air escapes at this vacuum level.
It was fun to make a tiny bit of shaving cream fill a whole glass, or take the fizz out of carbonated water, when I was playing with it before I started the transformer experiment.
Well, it's hardly original research, but I think probably there aren't too many people vacuum impregnating old transformers, as opposed to new ones using easily obtainable equipment, as part of restoring vintage equipment. So long as it's interesting to the forum, I may as well post what's happening, and hopefully it will help someone in the future.
I'm already blown away by how well the vacuum works at removing air from the transformer. The first five minutes are quite turbulent, as you can see by my short video I linked above. It then settles down to 15 - 20 minutes of fizz, followed by occasional bubbles, and eventually nothing.
What was really impressive, is how much air came out of the varnish before I put the transformer in.. it foamed up so high, I was worried I would start sucking varnish out of the container along with air. If someone is doing this, definitely make a point of degassing the varnish before putting the transformer in.
At this point I'm not totally convinced vibration is necessary, the vacuum alone was very effective, and allows the whole process to take place safely on my work bench.
One thing I will also mention, is I didn't thin the varnish, and was able to recover about 80% of it after the work was done. Some was lost to the container being impossible to fully empty, but a lot ended up in the transformers too. I started with a 1 quart can.
I'm already blown away by how well the vacuum works at removing air from the transformer. The first five minutes are quite turbulent, as you can see by my short video I linked above. It then settles down to 15 - 20 minutes of fizz, followed by occasional bubbles, and eventually nothing.
What was really impressive, is how much air came out of the varnish before I put the transformer in.. it foamed up so high, I was worried I would start sucking varnish out of the container along with air. If someone is doing this, definitely make a point of degassing the varnish before putting the transformer in.
At this point I'm not totally convinced vibration is necessary, the vacuum alone was very effective, and allows the whole process to take place safely on my work bench.
One thing I will also mention, is I didn't thin the varnish, and was able to recover about 80% of it after the work was done. Some was lost to the container being impossible to fully empty, but a lot ended up in the transformers too. I started with a 1 quart can.
I am not at all an expert in polymers, resins or varnishes. In the past I had some good help from very talented chemists and my experience is on getting resin into small cavities.
As I see maxhifi's challenge, it is to mechanically stabilize elder 50/60Hz transformers and coils such that they leave a minimum of audible noise and are protected against humidity and other corrosive agents for several decades.
Given this particular task, adhesion and rugged flexibility are crucial qualities. The resin used must be such that none of the initial materials are harmed.
For dielectric qualities, I do not see them as critical because the transformers and coils already have the insulation needed. The transformers and coils are used at low frequencies in low-impedance circuits such that a lowered resonance frequency is unlikely to be an electrical problem. Adding a bit more insulation will only leave further insulation margins.
The heat resistance, I also do not see as a problem. The items to be treated are some 40-70 years old and, with the technology in those days, hardly designed to operate at high temperatures. In those days electromagnetic quality components were made a bit like buildings - find out what is likely to be needed and then add generous margins to be sure it will never fail. Today, all is about price and the components are taken to the limit. The transformers and coils maxhifi are treating will hardly get to 80 degrees Celsius. The varnish used for maritime purposes can no doubt stand 100 degrees Celsius. You know how hot items that are left in strong sun can become. And, you know how tough the ultra-violet radiation of the sun can be on any oil-based product. It is rugged stuff.
For maxhifi's needs, I am convinced it will work.
You mention a different need and suggest a solution (Q-dope) that is probably very suited. For HF there is no risk of audible vibrations so the adhesion and physical strength is less important. But, the frequencies are high and the impedance likely to be high as well. Then, the dielectric properties of the insulation and encapsulation become important as they are likely to influence the electrical operation significantly. What you propose is probably a very useful "resin" for that need.
If you have needs somewhat similar to maxhifi, I would use the oil-based varnish you have in stock. For transformer renovation it will probably do very well. For HF-use, the varnish may fail but you know a better solution.
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Well. I came home and it was totally dry, so let's try it!
Hum is 99% gone, this thing used to hum so you could hear it across the room, now the ear has to be closer than 30cm in a silent room.
Of course, 99% is not 100%. Ideas for improvement include better varnish, using multiple coatings, and trying to achieve a better vacuum. I think - 26inhg is only an okay vacuum.
All the same, I am very encouraged by the first trial.
Hum is 99% gone, this thing used to hum so you could hear it across the room, now the ear has to be closer than 30cm in a silent room.
Of course, 99% is not 100%. Ideas for improvement include better varnish, using multiple coatings, and trying to achieve a better vacuum. I think - 26inhg is only an okay vacuum.
All the same, I am very encouraged by the first trial.
Attachments
Top effort, and quite within the realms of diy.
Can you conceive a way to suspend the transformer above the resin and pump both down prior to then lowering the transformer in ? That may achieve a better wicking in to a higher % of available space, although trying to make a comparison would be fickle.
Given that vintage transformers would be a target application, it would be interesting to get some views on cleaning away as much surface contamination as practical first, especially for transformers without bell-ends, or without full taped covering of windings.
Did any of your smaller test transformers come with mounting holes in the core? Plugging holes, or avoiding varnish buildup that caused hassles with fitting bell-ends again or removing clamping bolts to remount a transformer, may be a hassle in some situations.
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Thanks for the encouragement. I am not sure of an easy way to lower the transformer after pumping down, but I will think about this. There has to be something.
See my post just above yours for a pic of the test mule.. This one is too new to have end bells. When I pumped it down, you could see the air coming out of the bolt holes, I suspect it is all one big blob of varnish now.
before dipping in varnish, what i do is the ensure that the laminations sit tight with the bobbin, to test this i use a flat screwdriver, if i am able to wedge that in, then shimming is indicated, like i mentioned before, i use popsicle sticks for wedging...
99% of the traffo buzz can be cured this way....and varnishing considered the last step can be done...
buzzing can not be helped in an overloaded traffo, when it is near or at saturation points... and the cure for this should be obvious, remove the overload...
99% of the traffo buzz can be cured this way....and varnishing considered the last step can be done...
buzzing can not be helped in an overloaded traffo, when it is near or at saturation points... and the cure for this should be obvious, remove the overload...
On the cheap transformer I just used as a trial, I believe the issue is it was never impregnated, just a quick dip at the factory. It has a plastic bobbin and no gap or looseness I can find. All buzz is gone now, just a tiny bit of hum left, not more than may amps have. I think not bad for something I did in my garage!
With the RCA, the chokes buzz at the air gap, and in the laminations. It is a choke input with 230mA DC, and 113V of AC across the choke, so very demanding application. I already tried shims, at this point the strategy is just make it as good as possible. Plus this is kind of fun. I want to make sure I give it my best effort before giving up.
With the RCA, the chokes buzz at the air gap, and in the laminations. It is a choke input with 230mA DC, and 113V of AC across the choke, so very demanding application. I already tried shims, at this point the strategy is just make it as good as possible. Plus this is kind of fun. I want to make sure I give it my best effort before giving up.
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Toluene, also called toluol, is a generic industrial solvent. Best known as the solvent in glue for plastic (polystyrene) model cars/planes. Also for huffing (inhalation "high"). Apparently used in some real-airplane paints-- that's where I found it online. Use in small-scale painting is rare, there are much less toxic paint chemistries available. One member in South America says it is highly restricted, perhaps because it is the preferred solvent for cocaine extraction.
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