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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Herr Zapp wrote ...
... If you've actually found silicone RTV sealants at your local (California) hardware stores that DO NOT use the "standard" corrosive acetic acid cure system, please share the information....
ive been to the hardware store, ive gone through half the labels, but i think it must be GE Silicone II, that i was thinking of, becuase i dont see acetic acid on the label, and i think this uses the methanol/ammonia cure process.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
If you use resin/epoxy in sachet/resin pack form, e.g. it will mix with NO air bubbles.
Liquid solvent based polyurethane varnish also produces no air bubbles but can take a looong time to cure where air doesn't reach, e.g. inside a capacitor or transformer.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Thanks for that tip Sulaiman Wasn't there an article a while back about some early NSTs being cured by shorting the output and using a variac to heat it up internally while dipped in resin/varnish ?
This approach can also be applied to homemade transformers, and also allows it to be checked for imminent breakdowns using a longwave radio.
Registered Member #3343
Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311
Microwatt :
You have wrote:" a vacuum pump cost money. I am doing the project right now with bubbles"
Good.
I have design and built my HV caps CONSIDERING AIR BUBBLES inside, and between the foil and the solid dielectric material.
So, the dielectric is considered as a solid with small portions of air.
Glass capacitors, oil impregnated paper caps, even dry Mylar caps following the assumtion that there are small air bubbles inside the dielectrc, the result: the cap works fine without corona .
Some were constructed 2006 and are working 8 hours a day whithout any failure. Some glass caps working at 5000V in discharging ckt.
The concept is not allows the voltage gradient in the air bubbles reache the starting corona voltage.
I have used the same concept when winding my hi voltage transformers and HV flyback.
See " Calculation of corona starting voltage in air-solid dielictric systems", AIEE TRANSACTIONS, April 1956.
Maybe Patric can get a free download from the library of University and post in this forum.
The impregnation is just a means to assure mechanical strengt. Alkid vernish, (Very used by General Electric under the name of Glyptal, clear outdoor vernish or "carriage vernish" from Canadial Tire ) or even clear Epoxi vernish bought at boat repair supply are fine.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Haven't heard of the pulled syringe trick, thanks for that!
This might be relevant to my current project of making transparent EL, as it seems that the secret of a good display is to 1) ensure even coating of the SrS:Ce or ZnS:Cu and 2) make sure there aren't any air gaps. 2) is essential as with air gaps it won't work at all. Seems that the best method is to use two identical sheets of patterned ITO glass and then coat one with phosphor, then use the "blade trick" to get an even coating of UV setting adhesive. Put it in a near vacuum so that no air gets in between the plates then press together with about a 0.05mm gap.
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epoxy high voltage strength
