Obviously, you don't do it because you'd have to buy a vacuum pump that is rated for continuous duty, like a Gast. I have one. You'd also need a clear container with an air tight lid that is big enough to hold the transformer and strong enough not to crush under vacuum. A large glass jar with a screw on lid might be ok. The lid has to have an adapter installed that can accept the hose from the pump. The rest is straight forward. Put the transformer in the container, fill with varnish or poly to cover the transformer, install lid, connect vacuum pump and turn it on. Keep the pump on until there are no more bubbles coming out of the transformer. I don't know how long that takes. The pro shops use heat to reduce the viscosity of the poly or varnish.
When I paid a shop to do this in the past, it was a motor rewinding shop for really big motors and they just put it in with the motor windings since the transformer was relatively small. It was not $2 or $3 though. Much more than that but it was years ago and I can't remember now. Maybe $20?
how about chassis?
big transformer do vibrate even a little but the chassis should be enough to handle it.and how about pads or rubber that are used to surpressed the vibration when mounting the transformer?
regards,
joel
big transformer do vibrate even a little but the chassis should be enough to handle it.and how about pads or rubber that are used to surpressed the vibration when mounting the transformer?
regards,
joel
Ever seen how pre-preg airplane wings are made or continuous vacuum infused yacht hulls ?
Good comments Michael. Everything is based on cost nowadays days and it seems to hell with everything else.
Re transformer vacuum impregnated. Just make sure when you order you specify this otherwise If you have to DIY it you only need to created a low pressure differential between the outside air pressure and the impregnation tank. You just need the air bubles to burst to ensure the varnish really gets into every nook and cranny. Once done, bake at c. 150c for a few hours and you are done.
Years ago I worked at a company that wound all their own trannies. The vacuum impregnation tank was a fish tank with a lid that had a rubber sealed lid and a small vacuum tank. Something that could be lashed up in a few hours. The transformer were rated for 5kV isolation.
Re transformer vacuum impregnated. Just make sure when you order you specify this otherwise If you have to DIY it you only need to created a low pressure differential between the outside air pressure and the impregnation tank. You just need the air bubles to burst to ensure the varnish really gets into every nook and cranny. Once done, bake at c. 150c for a few hours and you are done.
Years ago I worked at a company that wound all their own trannies. The vacuum impregnation tank was a fish tank with a lid that had a rubber sealed lid and a small vacuum tank. Something that could be lashed up in a few hours. The transformer were rated for 5kV isolation.
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I used a Triad 1kVA on my e-Amp and it is very quiet. Not as good as the 2KVA Airlink custom wound used on my Ovation 250, but still remarkably good. $140 excl. shipping from Mouser.
Yes. They put the whole damn boat or wing into a big freaking bag and attach a vacuum pump and walk away for a while. I do that for veneering wood.
Do not bake this in your kitchen oven. Not only will your wife hate you but you will probably poison all of your food that you would bake in there in the future. Baking is optional anyway. It just speeds up the curing.
There is an other impregnation method called VPI. Is it more effective?
http://www.solidstatecontrolsinc.com/techhpapers/pdfs/vpisystem.pdf
http://www.solidstatecontrolsinc.com/techhpapers/pdfs/vpisystem.pdf
Using a classic "Bell Jar" as a chamber for maintaining vacuum would seem a good idea. Everything is visible but finding same is not so easy. Using a large jar might be suspect too, as modern thin-walled containers don't inspire confidence. Worse still, the openings are seldom big enough for power transformers.
The thought of a large jar imploding with 90kPa air pressure should also concern you if you you have no means of regulating vacuum. I've seen the results many times and it's most likely to occur when being handled.
Industry generally uses large steel vessels with safety glass "portholes" to see what's happening. If anyone was serious, this is the way to go, using steel pipe as a vessel. The ends can be gasket sealed to flat steel plates and clamped with long bolts. The details need only be basic, requiring a little turning but welding should not be needed for a budget, occasional use item.
This is well and good but for a home DIY of just mechanical damping, heating the transformer to around 75C and submerging in varnish should be adequate. Leave 'til cold and drain, dry and stove the long, unfriendly way.
The thought of a large jar imploding with 90kPa air pressure should also concern you if you you have no means of regulating vacuum. I've seen the results many times and it's most likely to occur when being handled.
Industry generally uses large steel vessels with safety glass "portholes" to see what's happening. If anyone was serious, this is the way to go, using steel pipe as a vessel. The ends can be gasket sealed to flat steel plates and clamped with long bolts. The details need only be basic, requiring a little turning but welding should not be needed for a budget, occasional use item.
This is well and good but for a home DIY of just mechanical damping, heating the transformer to around 75C and submerging in varnish should be adequate. Leave 'til cold and drain, dry and stove the long, unfriendly way.
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ah hah, pre-heating the device and submerging !
The warmed air cools and contracts, sucking in the liquid. The sucked in liquid is heated slightly reducing viscosity and making for easier penetration through narrow gaps. Then, capillary action takes over, while the liquid is still warm. Nice non technical way of avoiding a vacuum procedure.
EXACTLY - This is the method of desperation that does work with experience, particularly the minimising of varnish with a close fitting container and covering adequately to ensure you impregnate with varnish, not just more air or froth, which can occur when higher preheat is used.
Anyone trying hot immersion should be aware of the possibility of reaching the flash point of solvents like Xylene in varnishes and alkyd (polyester) types commercially used. This is not the temperature of combustion, only the minimum vapour temperature which will allow it if a spark, flame etc. is present - Just play safe and well away from such ignition sources.
A depressing possibility is that, due to the materials or method, you may have to repeat this to get sufficient damping which is quite a different matter to the main intent of improving insuation resistance.
Anyone trying hot immersion should be aware of the possibility of reaching the flash point of solvents like Xylene in varnishes and alkyd (polyester) types commercially used. This is not the temperature of combustion, only the minimum vapour temperature which will allow it if a spark, flame etc. is present - Just play safe and well away from such ignition sources.
A depressing possibility is that, due to the materials or method, you may have to repeat this to get sufficient damping which is quite a different matter to the main intent of improving insuation resistance.
Yes, absolutely agree. Best option is to get an old oven and keep it in the garage. One of those table top ones would do just fine for DIY.
You do not need a huge vacuum to get the varnish into the transformer! Preheating is a great idea also.
I have no problems with curing polyurethane based resin in the oven. (2-component epoxy resin might raise some food health issues 
)
Back in highschool days, a DIY vacuum pump was easily built with a fridge compressor on a piece of floorboard.
(the link Tommy posted states 30 inches of mercury, one almost thinks they do it in outer space)
)Back in highschool days, a DIY vacuum pump was easily built with a fridge compressor on a piece of floorboard.
(the link Tommy posted states 30 inches of mercury, one almost thinks they do it in outer space)
Is this necessary , sonic differences or just to eliminate transformer noise, what about potting ..?
From MPOV it's nothing to do with sonics. Just to stop it buzzing and rattling. I think from the sonics aspect, you need to spec a decent transformer, antd make sure it does not go anywhere near saturation. I bought a 1KVA from RS that buzzes like a chainsaw (and it's not because of DC on the mains) and runs very warm. I put it down to the fact that it is 1KVA by the skin of its teeth. The Triad I am using on my e-Amp is a world away in terms of noise and it runs cool also. Interestingly, the Triad is about 2Kgs heavier than the RS transformer which I now use for stepping 110 to 220 in my office/workroom. It's not much use for anything else.
Btw if you want to test for noise, power the transformer up with it on a wooden table then put your ear to the table. You can quickly sort out the good from the bad. My Airlink is almost inaudible, the Triad very good and the RS very bad.
chassis...
I have repaired some of those commercial brand amplifiers mostly japanese.when you removed the base plate still the power transformer will remain inside the chassis screwed on a thick bracing or plate.I have seen most of the amplifier enclosure here and most of them without proper bracing.when you mount those big transformer on the base plate specially on the middle part the base plate will act as a trampoline causing the whole unit to vibrate.
I have seen the goldmund casing and notice the footings of the enclosure.I think they have used rubber bushing to lessen the vibration.I have opened a washing machine and i have noticed that it is using rubber bushings then the motor are mount on top of it to lessen of course the vibration.
And notice also that transformer are mounted usually at the side close to the corner or fold of the chassis coz this where the strongest part and most stable(COMMERCIAL BRANDS).
regards,
joel
I have repaired some of those commercial brand amplifiers mostly japanese.when you removed the base plate still the power transformer will remain inside the chassis screwed on a thick bracing or plate.I have seen most of the amplifier enclosure here and most of them without proper bracing.when you mount those big transformer on the base plate specially on the middle part the base plate will act as a trampoline causing the whole unit to vibrate.
I have seen the goldmund casing and notice the footings of the enclosure.I think they have used rubber bushing to lessen the vibration.I have opened a washing machine and i have noticed that it is using rubber bushings then the motor are mount on top of it to lessen of course the vibration.
And notice also that transformer are mounted usually at the side close to the corner or fold of the chassis coz this where the strongest part and most stable(COMMERCIAL BRANDS).
regards,
joel
Attachments
Speaking of highschool, laboratories used to be equipped with water ejector pumps which could pull up to 13" (330mm) vacuum, simply by the force of mains water supply. I would love to show an image, but these were a simple, small assembly of chromed brass gas fittings fittings, incorporating a Venturi which provided the vacuum when a pressure differential was created across the internal jet nozzles.
The ultimate cheap vacuum pump, these would be fine for the job. I had a souvenir that was probably souvenired again by persons unknown but I did use it for small bag and tank impregnation of boat timbers for several years. It would work fine and safely for transformers too.
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