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Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I've started using melted wax instead of oil wherever I can. It's much more tidy, but you'll never be able to repair it again afterwards. For insulating high voltage resistors it's pretty much ideal, as you'll never be able to repair a burnt out resistor anyway.
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
Uzzors wrote ...
I've started using melted wax instead of oil wherever I can. It's much more tidy, but you'll never be able to repair it again afterwards. For insulating high voltage resistors it's pretty much ideal, as you'll never be able to repair a burnt out resistor anyway.
So do I , actually I only lately acquired some mineral oil so I was using synthetic (paraffin) candles before:
But why do you say you can't repair it? Melting the wax is very easy, depending on how much it is: 1) use a hairdryer - works great if the wax layer is thin 2) use a gas/electric oven, place the waxed module on a plate, and set the temperature to lowest.
The melted wax flows away, and the components remain cleaner than when using oil.
EDIT: there are some (minor) problems with paraffin: - it reduces its volume when it solidifies - it melts and flows on relatively low temperatures - it develops superficial cracks around components (not a very good adherence) that can lead to electrical problems (so when it cools down, one needs to make sure he's done with moving the parts around)
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Regarding internal pressure from thermal expansion of the oil: If the enclosure is a round pipe, the thinner the wall the lower the pressure. Figure the bulk expansion of oil, subtract the bulk expansion of the enclosure, then do the elastic cylinder under pressure calculation (with modulus reduced by temperature).
A rigid vessel filled with oil at room temperature would develop a partial vacuum in cold weather. How does that affect the HV dielectric behavior of the oil?
How 'bout this for an inexpensive "expansion bellows"? Start with thin-wall-schedule PVC pipe, of larger diameter than you need. Soften it with heat and partly flatten it. That will greatly reduce the slope of internal pressure vs. stretched volume (and, indirectly, vs. temperature).
Kluge time: Hot-form the pipe to be flat and also curved lengthwise. Now you have a Bourdon tube, which will straighten as the oil expands.
p.s. I think we've seen reports here that ordinary hot melt glue eventually dissolves completely in hydrocarbon oils.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Klugesmith wrote ...
Regarding internal pressure from thermal expansion of the oil: If the enclosure is PVC pipe, the thinner the wall the lower the pressure. Figure the bulk expansion of oil, subtract the bulk expansion of the enclosure, then do the elastic cylinder under pressure calculation (with modulus reduced by temperature).
How 'bout this for an inexpensive "expansion bellows"? Start with thin-wall-schedule PVC pipe, of larger diameter than you need. Soften it with heat and partly flatten it. That will greatly reduce the slope of internal pressure vs. stretched volume.
Kluge time: Hot-form the pipe to be flat and also curved lengthwise. Now you have a Bourdon tube, which will straighten as the oil expands with temperature.
WOW! you have quite the brain in your head kluge, thats some real smarts i see here.
Klugesmith wrote ...
p.s. I think we've seen reports here that ordinary hot melt glue eventually dissolves completely in hydrocarbon oils.
YES, i do not think it dissolves per se, as it is PE... but liquids have a bad habit of getting into the interface between Hot glue and the original surface, thus liberating both.
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Making liquid tight or silicone resistor containers....
