Hi Guys,
Just a quick question.
Is the 'sellotape' that holds on the outer insulation of clear cellophane looking stuff on a toroidal transformer anything special?
That is to say is it anything other than plain old sellotape?
Also bonus round, what is the cellophane looking stuff?
Many Thanks
Sadface
Just a quick question.
Is the 'sellotape' that holds on the outer insulation of clear cellophane looking stuff on a toroidal transformer anything special?
That is to say is it anything other than plain old sellotape?
Also bonus round, what is the cellophane looking stuff?
Many Thanks
Sadface
It is mylar (PETP), not cellophane. It is much more robust, withstands high temperatures and has a high dielectric strength
The little piece of sticky tape used to keep the Mylar wrap from coming unwrapped isn’t anything special. I prefer stuff that doesn‘t get tacky or gooey over time and has similar dielectric properties - because in a pinch it can be used as the actual wrap. Or as the final layer. I still don’t have a good steady source of the non-adhesive wrap, and I can always get the adhesive variety (the yellow stuff, intended for SMPS trafos) from Mouser.
3M 1350F - available in black or yellow, various widths. It’s mylar, adhesive, but only 1 mil thick. Real toroidal trafo wrap is 3 mil thick. THAT’s the tough part. Even the non adhesive stuff you can get from Tape-Rite is only still 1 mil thick. Getting any sort of build up at all gets expensive.
Even my source of black cloth friction tape has dried up recently. At some point I may just go back to using 100 polyurethane dips, followed by 1 layer of 1350F. I’ll still be using that for insulation between layers of salvaged/rewound EIs.
Even my source of black cloth friction tape has dried up recently. At some point I may just go back to using 100 polyurethane dips, followed by 1 layer of 1350F. I’ll still be using that for insulation between layers of salvaged/rewound EIs.
Thanks Guys,
That's enough info to get me started.
I want to split a centre tapped secondary into to separate secondaries so I am trying to think ahead to the other side of the process.
That's enough info to get me started.
I want to split a centre tapped secondary into to separate secondaries so I am trying to think ahead to the other side of the process.
My plan would be to resuse the old mylar wrap.
It seems as though 3M #56 is something of an industry standard tape for transformers.
Perhaps a layer of #56 over the reused mylar for good measure?
It seems as though 3M #56 is something of an industry standard tape for transformers.
Perhaps a layer of #56 over the reused mylar for good measure?
Provided that it’s not too mangled from heat shrinking. Some manufacturers do that, others don’t. When they don’t, it comes off in good enough condition to re-use.
G'day Guys,
I've finally received all the bits and had some time and patience to do this one.
Everything went well. the old insulation behaved nicely and rewound back on without too much difficulty.
I did a horiztonal layer of #56 around the outside just to make sure all of the old insulation wasn't going to move.
I would still like to do a full layer of #56 just to make damn certain the insulation wont fail. However I have a dilema.
As can be seen from the photo, the roll of $56 tape clearly won't fit through the centre of the donut.
The best I've come up with so far is to simply uncoil the required length of tape and feed it through in the same way I had to with the original clear insulation.
This seems unlikely to work as the chances of NOT creating a sticky mess seem incredibly low.....
Anybody have any suggestions for how I might get around this?
I've finally received all the bits and had some time and patience to do this one.
Everything went well. the old insulation behaved nicely and rewound back on without too much difficulty.
I did a horiztonal layer of #56 around the outside just to make sure all of the old insulation wasn't going to move.
I would still like to do a full layer of #56 just to make damn certain the insulation wont fail. However I have a dilema.
As can be seen from the photo, the roll of $56 tape clearly won't fit through the centre of the donut.
The best I've come up with so far is to simply uncoil the required length of tape and feed it through in the same way I had to with the original clear insulation.
This seems unlikely to work as the chances of NOT creating a sticky mess seem incredibly low.....
Anybody have any suggestions for how I might get around this?
Rewound piece of tape on a smaller core, perhaps on a strip of cardboard or squash it and use as a shuttle.
Because that yellow tape is adhesive, you can wrap it a couple of turns at a time. That stuff will stay, especially when stuck to itself. It takes more time and a little more material than doing it as a single piece but you don’t have to fight it.
Great suggestions Tony and Naresh.
Sadly a day late as I got 3/4 of the way through last night using 1m or so sections of tape.
I should have the job finished tonight if there aren't too many interruptions.
Sadly a day late as I got 3/4 of the way through last night using 1m or so sections of tape.
I should have the job finished tonight if there aren't too many interruptions.
Job done!
Any appropriate testing that should be done prior to powering up?
Continuity would be the obvious one to me. Anything else?
Any appropriate testing that should be done prior to powering up?
Continuity would be the obvious one to me. Anything else?
Ideally, Hi-pot between primaries and secondaries, but you are probably not equipped for. If you have a megger, make an insulation test at the maximum voltage, generally 500V.
The resistance should read ~infinity.
If you don't have access to a megger, test the resistance at 20Meg, and if it's infinite measure the leakage current between all the primary wires shorted and secondary idem, connected each to the mains (with due precautions, of course). Depending on the capacitance, you shouldn't read more than some tens of µA
The resistance should read ~infinity.
If you don't have access to a megger, test the resistance at 20Meg, and if it's infinite measure the leakage current between all the primary wires shorted and secondary idem, connected each to the mains (with due precautions, of course). Depending on the capacitance, you shouldn't read more than some tens of µA
Thanks for the advice Elvee,
I finally got back around to this project. I have an old analog megger my dad made some 40 years ago.
I had to replace the battery holder which had corroded terminals after these decades.
Calibrated to read 0R with the leads shorted. I tested with a 2M2 resistor to verify it still works and reads properly.
Across all combinations of primary to secondary or secondary to secondary, I get circa 50M at 690vdc.
I am thinking that means I am good to go. I believe the standard is >1M @ 230/240vac.
I finally got back around to this project. I have an old analog megger my dad made some 40 years ago.
I had to replace the battery holder which had corroded terminals after these decades.
Calibrated to read 0R with the leads shorted. I tested with a 2M2 resistor to verify it still works and reads properly.
Across all combinations of primary to secondary or secondary to secondary, I get circa 50M at 690vdc.
I am thinking that means I am good to go. I believe the standard is >1M @ 230/240vac.