Repairing A Variac

Guest
Got this nice 0-140 5 amp variac that started arcing. Iunplugged it immediately of course.

It had been repaired before. When I first got it the wire feeding from the AC input had pulled the turn of the winding off, soldering took care of that. There was a little catch right at that point but it wasn't bad. Months, maybe about a year ago that "catch" got worse and I reworked it, tightening up the winding and making sure it was smooth. It was fine.

Then about last week I was using it to boost voltage to a car battery charger to feed something a tad over its usual output, which was working fine. And no overload at all, the drain was about 2.5 amps at 16 volts or so, so that was well within spec for the variac. Later I turned it down because it was time to test the UUT with lower voltage. (this is an intermittent overheating problem in the DC/DC convertor of an AC/DC version of the Tek 422)

Then I noticed that at the end, above where the line goes in, it was arcing between the windings.

I don't have nor want to find the magnet wire to rewind or partially rewind this thing. Is there a chemical solution to this problem ? (pun intended)

Perhaps our resident thaumaturge Jeff Lieberman has some idea, or anyone. I don't use it enough to buy another one but when I need variable AC I need variable AC. I might have to add some boost/buck transformers to my newly kludged bohungus isolation transformer. It even has a fan.

http://usr.audioasylum.com/images/7/71823/badazzis01.jpg

As you can see there is plenty of room for a few smaller transformers, but I would need them to be able to handle the current of the main one, right ? Otherwise an overload could be a catastrophe, and I have had enough of those in my life.

But is there a way to fix the variac ? I'm thinking a solvent, then enamel, then filing it down for the wiper to contact and ??? Maybe. I don't know if I can find such chemicals, or if they even exist. And how would I keep the windings on place once they're stripped ?

Any ideas ?

Also, I am not all that worried about the boost end of it, ans I am not concerned with ground faults because I can just always run it off isolation. It will almost fit n that cabinet but not with the knob in front, and I don't want it on top. But then it might be ready for the dump anyway.

Thanks in advance.
 
On Monday, 30 April 2018 13:50:53 UTC+1, jurb...@gmail.com wrote:
Got this nice 0-140 5 amp variac that started arcing. Iunplugged it immediately of course.

It had been repaired before. When I first got it the wire feeding from the AC input had pulled the turn of the winding off, soldering took care of that. There was a little catch right at that point but it wasn't bad. Months, maybe about a year ago that "catch" got worse and I reworked it, tightening up the winding and making sure it was smooth. It was fine.

Then about last week I was using it to boost voltage to a car battery charger to feed something a tad over its usual output, which was working fine. And no overload at all, the drain was about 2.5 amps at 16 volts or so, so that was well within spec for the variac. Later I turned it down because it was time to test the UUT with lower voltage. (this is an intermittent overheating problem in the DC/DC convertor of an AC/DC version of the Tek 422)

Then I noticed that at the end, above where the line goes in, it was arcing between the windings.

I don't have nor want to find the magnet wire to rewind or partially rewind this thing. Is there a chemical solution to this problem ? (pun intended)

Perhaps our resident thaumaturge Jeff Lieberman has some idea, or anyone. I don't use it enough to buy another one but when I need variable AC I need variable AC. I might have to add some boost/buck transformers to my newly kludged bohungus isolation transformer. It even has a fan.

http://usr.audioasylum.com/images/7/71823/badazzis01.jpg

As you can see there is plenty of room for a few smaller transformers, but I would need them to be able to handle the current of the main one, right ? Otherwise an overload could be a catastrophe, and I have had enough of those in my life.

But is there a way to fix the variac ? I'm thinking a solvent, then enamel, then filing it down for the wiper to contact and ??? Maybe. I don't know if I can find such chemicals, or if they even exist. And how would I keep the windings on place once they're stripped ?

Any ideas ?

Also, I am not all that worried about the boost end of it, ans I am not concerned with ground faults because I can just always run it off isolation. It will almost fit n that cabinet but not with the knob in front, and I don't want it on top. But then it might be ready for the dump anyway.

Thanks in advance.

Variacs are never ready for the dump.
If you can get all traces of the carbon out from the gap, you're most of the way there. If not, and I expect you won't, I'd cut the wire and unwind half a turn each side. Put a turn of new wire on & solder its ends to the old ends where they're not in the way. With 2 half turns out the way it should be easier to remove any carbon.


NT
 
http://www.directindustry.com/prod/electrolube/product-6210-169678.html?utm_source=ProductDetail&utm_medium=Web&utm_content=SimilarProduct&utm_campaign=CA

Used its equivalent - it works.

Peter Wieck
Melrose Park, PA
 
On 30/04/2018 13:50, jurb6006@gmail.com wrote:
Got this nice 0-140 5 amp variac that started arcing. Iunplugged it immediately of course.

It had been repaired before. When I first got it the wire feeding from the AC input had pulled the turn of the winding off, soldering took care of that. There was a little catch right at that point but it wasn't bad. Months, maybe about a year ago that "catch" got worse and I reworked it, tightening up the winding and making sure it was smooth. It was fine.

Then about last week I was using it to boost voltage to a car battery charger to feed something a tad over its usual output, which was working fine. And no overload at all, the drain was about 2.5 amps at 16 volts or so, so that was well within spec for the variac. Later I turned it down because it was time to test the UUT with lower voltage. (this is an intermittent overheating problem in the DC/DC convertor of an AC/DC version of the Tek 422)

Then I noticed that at the end, above where the line goes in, it was arcing between the windings.

I don't have nor want to find the magnet wire to rewind or partially rewind this thing. Is there a chemical solution to this problem ? (pun intended)

Perhaps our resident thaumaturge Jeff Lieberman has some idea, or anyone. I don't use it enough to buy another one but when I need variable AC I need variable AC. I might have to add some boost/buck transformers to my newly kludged bohungus isolation transformer. It even has a fan.

http://usr.audioasylum.com/images/7/71823/badazzis01.jpg

As you can see there is plenty of room for a few smaller transformers, but I would need them to be able to handle the current of the main one, right ? Otherwise an overload could be a catastrophe, and I have had enough of those in my life.

But is there a way to fix the variac ? I'm thinking a solvent, then enamel, then filing it down for the wiper to contact and ??? Maybe. I don't know if I can find such chemicals, or if they even exist. And how would I keep the windings on place once they're stripped ?

Any ideas ?

Also, I am not all that worried about the boost end of it, ans I am not concerned with ground faults because I can just always run it off isolation. It will almost fit n that cabinet but not with the knob in front, and I don't want it on top. But then it might be ready for the dump anyway.

Thanks in advance.

Does it have the correct width of brush? it must not be able to contact
more than 2 turns at any time. The proper ones look suspiciously unmanly
for the job.
 
On 2018/04/30 6:17 AM, pfjw@aol.com wrote:
http://www.directindustry.com/prod/electrolube/product-6210-169678.html?utm_source=ProductDetail&utm_medium=Web&utm_content=SimilarProduct&utm_campaign=CA

Used its equivalent - it works.

Peter Wieck
Melrose Park, PA

Peter, does that have a suitable breakdown voltage for 130 - 150VAC? I
didn't bother sending the manufacturer my email address so they would
send me the docs to verify. However the ad says it is suitable for LEDs
and circuit boards, doesn't mention higher voltage applications.

For the OP be really sure to clean between the windings where the arcing
occurred, you want to remove any sharp edges or points on the wire or
any carbon residue. There are dialectic varnishes designed for higher
voltages such as MG Chemicals Corona Dope:

https://www.mgchemicals.com/products/insulating-coatings/super-corona-dope-4226


John :-#)#
 
On Monday, April 30, 2018 at 8:50:53 AM UTC-4, jurb...@gmail.com wrote:
Got this nice 0-140 5 amp variac that started arcing. Iunplugged it immediately of course.

It had been repaired before. When I first got it the wire feeding from the AC input had pulled the turn of the winding off, soldering took care of that. There was a little catch right at that point but it wasn't bad. Months, maybe about a year ago that "catch" got worse and I reworked it, tightening up the winding and making sure it was smooth. It was fine.

Then about last week I was using it to boost voltage to a car battery charger to feed something a tad over its usual output, which was working fine. And no overload at all, the drain was about 2.5 amps at 16 volts or so, so that was well within spec for the variac. Later I turned it down because it was time to test the UUT with lower voltage. (this is an intermittent overheating problem in the DC/DC convertor of an AC/DC version of the Tek 422)

Then I noticed that at the end, above where the line goes in, it was arcing between the windings.

I don't have nor want to find the magnet wire to rewind or partially rewind this thing. Is there a chemical solution to this problem ? (pun intended)

Perhaps our resident thaumaturge Jeff Lieberman has some idea, or anyone. I don't use it enough to buy another one but when I need variable AC I need variable AC. I might have to add some boost/buck transformers to my newly kludged bohungus isolation transformer. It even has a fan.

http://usr.audioasylum.com/images/7/71823/badazzis01.jpg

As you can see there is plenty of room for a few smaller transformers, but I would need them to be able to handle the current of the main one, right ? Otherwise an overload could be a catastrophe, and I have had enough of those in my life.

But is there a way to fix the variac ? I'm thinking a solvent, then enamel, then filing it down for the wiper to contact and ??? Maybe. I don't know if I can find such chemicals, or if they even exist. And how would I keep the windings on place once they're stripped ?

Any ideas ?

Also, I am not all that worried about the boost end of it, ans I am not concerned with ground faults because I can just always run it off isolation. It will almost fit n that cabinet but not with the knob in front, and I don't want it on top. But then it might be ready for the dump anyway.

Thanks in advance.

Remember the Mitsubishi deflection yokes that used to arc over on the PTVs? Back in the old days, I'd just kind of gently pick apart the area where the arcing occurred, clean as best I could, and dose it with several layers of thin cyanoacrylate. That stuff penetrates almost like Kroil. Of course, those windings were much thinner and easier to move around. Not advice really, just reminiscing.
 
On Monday, 30 April 2018 18:57:01 UTC+1, John Robertson wrote:
On 2018/04/30 6:17 AM, pfjw@aol.com wrote:
http://www.directindustry.com/prod/electrolube/product-6210-169678.html?utm_source=ProductDetail&utm_medium=Web&utm_content=SimilarProduct&utm_campaign=CA

Used its equivalent - it works.

Peter Wieck
Melrose Park, PA


Peter, does that have a suitable breakdown voltage for 130 - 150VAC? I
didn't bother sending the manufacturer my email address so they would
send me the docs to verify. However the ad says it is suitable for LEDs
and circuit boards, doesn't mention higher voltage applications.

For the OP be really sure to clean between the windings where the arcing
occurred, you want to remove any sharp edges or points on the wire or
any carbon residue. There are dialectic varnishes designed for higher
voltages such as MG Chemicals Corona Dope:

https://www.mgchemicals.com/products/insulating-coatings/super-corona-dope-4226


John :-#)#

removing every little trace of carbon is vital IME


NT
 
On Monday, April 30, 2018 at 1:57:01 PM UTC-4, John Robertson wrote:

Peter, does that have a suitable breakdown voltage for 130 - 150VAC? I
didn't bother sending the manufacturer my email address so they would
send me the docs to verify. However the ad says it is suitable for LEDs
and circuit boards, doesn't mention higher voltage applications.

John:

I must admit I am not sure. I used its functional equivalent on a Hot Tub control board switching 240 VAC heater and 120 VAC pump circuits without any problems - but for the heater on one just failed this weekend. Not the board, the heater itself. I suspect that the material you linked might be more suitable given its brush applicator and specific prescribed uses.

For the OP be really sure to clean between the windings where the arcing
occurred, you want to remove any sharp edges or points on the wire or
any carbon residue. There are dialectic varnishes designed for higher
voltages such as MG Chemicals Corona Dope:

https://www.mgchemicals.com/products/insulating-coatings/super-corona-dope-4226

The 'thing' about AC arcing is that once an arc is struck, the plasma generated helps sustain it. Hard to strike, but once struck not hard to maintain if there is a source for the plasma. Just a few weeks ago, a large Norway maple tree behind us started rubbing against a 13,200 primary. Those arcs made 6-8 inches until sufficient of the tree was eroded that the distance eventually was too much. PECO took nearly a week to get to it as the heavy snow and wind that caused the condition in the first place did far more damage elsewhere. 90 houses around us were without power for 4 days. We were exceedingly lucky not to.

When PECO did come, they worked from our back yard, and I got 'the dope' on arcing from their engineer on-site.

Peter Wieck
Melrose Park, PA
 
On 2018/04/30 11:39 AM, pfjw@aol.com wrote:
On Monday, April 30, 2018 at 1:57:01 PM UTC-4, John Robertson wrote:

Peter, does that have a suitable breakdown voltage for 130 - 150VAC? I
didn't bother sending the manufacturer my email address so they would
send me the docs to verify. However the ad says it is suitable for LEDs
and circuit boards, doesn't mention higher voltage applications.

John:

I must admit I am not sure. I used its functional equivalent on a Hot Tub control board switching 240 VAC heater and 120 VAC pump circuits without any problems - but for the heater on one just failed this weekend. Not the board, the heater itself. I suspect that the material you linked might be more suitable given its brush applicator and specific prescribed uses.

For the OP be really sure to clean between the windings where the arcing
occurred, you want to remove any sharp edges or points on the wire or
any carbon residue. There are dialectic varnishes designed for higher
voltages such as MG Chemicals Corona Dope:

https://www.mgchemicals.com/products/insulating-coatings/super-corona-dope-4226

The 'thing' about AC arcing is that once an arc is struck, the plasma generated helps sustain it. Hard to strike, but once struck not hard to maintain if there is a source for the plasma. Just a few weeks ago, a large Norway maple tree behind us started rubbing against a 13,200 primary. Those arcs made 6-8 inches until sufficient of the tree was eroded that the distance eventually was too much. PECO took nearly a week to get to it as the heavy snow and wind that caused the condition in the first place did far more damage elsewhere. 90 houses around us were without power for 4 days. We were exceedingly lucky not to.

When PECO did come, they worked from our back yard, and I got 'the dope' on arcing from their engineer on-site.

Peter Wieck
Melrose Park, PA

A Jacob's Ladder is an excellent example of how an AC or DC arc plasma,
once started, can more than double its initial width as the plasma
climbs up the wires...

https://www.youtube.com/watch?v=0ioHlYCmu_A

https://www.popsci.com/how-to-build-jacobs-ladder

I had one in my parents home where I had a fat 5KV Neon sign Xformer -
which made nice fat arcs, but that was way back in the 60s...

John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
 
On 4/30/18 7:50 AM, jurb6006@gmail.com wrote:
Then I noticed that at the end, above where the line goes
in, it was arcing between the windings.

How does it do that?
The voltage from one winding to the next is pretty small.

don't worry about carbon tracks, if you ppur this stuff
<https://www.ebay.com/itm/152789446463>
over the part that's arcing, the carbon will be encapsulated.

Give it 2-3 days to completely dry and get hard.

It if still arcs, throw it in the trash.


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com
 
On Mon, 30 Apr 2018 15:45:19 -0500, Fox's Mercantile <jdangus@att.net>
wrote:

don't worry about carbon tracks, if you ppur this stuff
https://www.ebay.com/itm/152789446463
over the part that's arcing, the carbon will be encapsulated.

I don't know how it's possible to arc between windings with only
117/220VAC. My guess(tm) is that there's arcing between the contact
brush and the windings caused by a layer of filth on the windings or
contact brush.

No way am I going to pay $18 for 2 oz of Q-Dope.
Q-Dope is polystyrene disolved in MEK.
<http://www.gcelectronics.com/order/msds/101.pdf>
Make your own from packing peanuts and MEK:
<https://www.youtube.com/watch?v=ANn6hti35Zc>

Maybe some anti-corona goo will provide some better arcing protection:
<https://www.mgchemicals.com/products/insulating-coatings/super-corona-dope-4226>
<https://www.amazon.com/MG-Chemicals-Corona-Liquid-Applicator/dp/B008OA7CAE>

Variac cleaning videos:
<https://www.youtube.com/watch?v=5vKHOSpynM8>
<https://www.youtube.com/watch?v=xPdIrzw2kko>
<https://www.youtube.com/watch?v=Mbbght6HIxM>
etc...

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
On Mon, 30 Apr 2018 18:43:11 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
(...)

This kinda sounds like the arcing problem as described. The arcing is
from the winding to the carbon brush wiper:

Variac Repair using DeOxit:
<https://www.youtube.com/watch?v=qRTKHNoiRQI>

However, I'm not sure that's such a great idea. It looks like he
managed to burn up the Variac:
<https://www.youtube.com/watch?v=po5Xxl_Syxg>


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
>"This kinda sounds like the arcing problem as described. The arcing is from the winding to the carbon brush wiper: "

No, the wiper was nowhere near it. It is either between the windings or from the windings to the core.

From what I see there are probably 100 turns, if not there must be at least 50. That means only a couple volts between each turn. This is not hopeful.

Since it all seems to be at the boost end, maybe I can eliminate that part and just have something that will cut the line voltage. It beats nothing.

There is another possibility, I could put the rectifiers back in the "isolation transformer" cabinet and use the DC supplies which are + - 90 volts to power a class D amp. I know they can get hairy to design like for high fidelity audio but for these lower frequencies it should not be all that difficult. Or I could tap off an existing class D amp before the output filter (except for certain Crowns et. al.)and use that to drive bigger transistors, set up a feedback attenuator to match the level and make a bigger output filter. It would be easier than designing from scratch. It would also automatically be isolated.

But honestly that is a pipe dream. Maybe I should just think about eliminating that part of the winding and hope the rest is alright. Seems like that would be the hottest part of the winding and would fail first, no ? For the amount of time I use it...

Soon, I'll take the cover off and have a closer look at this arcing. But I am sure it is not to the wiper.
 
On Tuesday, 1 May 2018 04:26:18 UTC+1, jurb...@gmail.com wrote:

"This kinda sounds like the arcing problem as described. The arcing is from the winding to the carbon brush wiper: "

No, the wiper was nowhere near it. It is either between the windings or from the windings to the core.

From what I see there are probably 100 turns, if not there must be at least 50. That means only a couple volts between each turn. This is not hopeful.

Since it all seems to be at the boost end, maybe I can eliminate that part and just have something that will cut the line voltage. It beats nothing.

There is another possibility, I could put the rectifiers back in the "isolation transformer" cabinet and use the DC supplies which are + - 90 volts to power a class D amp. I know they can get hairy to design like for high fidelity audio but for these lower frequencies it should not be all that difficult. Or I could tap off an existing class D amp before the output filter (except for certain Crowns et. al.)and use that to drive bigger transistors, set up a feedback attenuator to match the level and make a bigger output filter. It would be easier than designing from scratch. It would also automatically be isolated.

But honestly that is a pipe dream. Maybe I should just think about eliminating that part of the winding and hope the rest is alright. Seems like that would be the hottest part of the winding and would fail first, no ? For the amount of time I use it...

Soon, I'll take the cover off and have a closer look at this arcing. But I am sure it is not to the wiper.

if it's a small section of winding, how hard is it to rewind that bit?
 
On 2018/04/30 8:26 PM, jurb6006@gmail.com wrote:
"This kinda sounds like the arcing problem as described. The arcing is from the winding to the carbon brush wiper:"

No, the wiper was nowhere near it. It is either between the windings or from the windings to the core.

From what I see there are probably 100 turns, if not there must be at least 50. That means only a couple volts between each turn. This is not hopeful.

Since it all seems to be at the boost end, maybe I can eliminate that part and just have something that will cut the line voltage. It beats nothing.

There is another possibility, I could put the rectifiers back in the "isolation transformer" cabinet and use the DC supplies which are + - 90 volts to power a class D amp. I know they can get hairy to design like for high fidelity audio but for these lower frequencies it should not be all that difficult. Or I could tap off an existing class D amp before the output filter (except for certain Crowns et. al.)and use that to drive bigger transistors, set up a feedback attenuator to match the level and make a bigger output filter. It would be easier than designing from scratch. It would also automatically be isolated.

But honestly that is a pipe dream. Maybe I should just think about eliminating that part of the winding and hope the rest is alright. Seems like that would be the hottest part of the winding and would fail first, no ? For the amount of time I use it...

Soon, I'll take the cover off and have a closer look at this arcing. But I am sure it is not to the wiper.

I trust the variac is grounded, so this may be an arc to the case...or
failing insulation on the power cord. How OLD is this variac anyway?

John :-#(#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
 
On 4/30/18 11:14 PM, John Robertson wrote:
I trust the variac is grounded, so this may be an arc to
the case...or failing insulation on the power cord. How
OLD is this variac anyway?

Since it's on the "hgh" (boost) of the variac, He's got
between 120=135 vac to gound at that point.

And knowing Jurb, it's probably something he fished out of
a dumpster 30 years ago.
He's already admitted to "fixing" it twice already.
I doubt he did a good job either time.


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com
 
On Tuesday, 1 May 2018 05:55:01 UTC+1, Fox's Mercantile wrote:
On 4/30/18 11:14 PM, John Robertson wrote:

I trust the variac is grounded, so this may be an arc to
the case...or failing insulation on the power cord. How
OLD is this variac anyway?

Since it's on the "hgh" (boost) of the variac, He's got
between 120=135 vac to gound at that point.

And knowing Jurb, it's probably something he fished out of
a dumpster 30 years ago.
He's already admitted to "fixing" it twice already.
I doubt he did a good job either time.

Variacs are all (or almost all) many decades old.


NT
 
On 2018/04/30 10:20 PM, tabbypurr@gmail.com wrote:
On Tuesday, 1 May 2018 05:55:01 UTC+1, Fox's Mercantile wrote:
On 4/30/18 11:14 PM, John Robertson wrote:

I trust the variac is grounded, so this may be an arc to
the case...or failing insulation on the power cord. How
OLD is this variac anyway?

Since it's on the "hgh" (boost) of the variac, He's got
between 120=135 vac to gound at that point.

And knowing Jurb, it's probably something he fished out of
a dumpster 30 years ago.
He's already admitted to "fixing" it twice already.
I doubt he did a good job either time.

Variacs are all (or almost all) many decades old.


NT

Not all are decades old:

https://www.circuitspecialists.com/variac-tdgc2-2.html

John ;-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
 
On 5/1/18 12:20 AM, tabbypurr@gmail.com wrote:
On Tuesday, 1 May 2018 05:55:01 UTC+1, Fox's Mercantile wrote:
On 4/30/18 11:14 PM, John Robertson wrote:

I trust the variac is grounded, so this may be an arc to
the case...or failing insulation on the power cord. How
OLD is this variac anyway?

Since it's on the "hgh" (boost) of the variac, He's got
between 120=135 vac to gound at that point.

And knowing Jurb, it's probably something he fished out of
a dumpster 30 years ago.
He's already admitted to "fixing" it twice already.
I doubt he did a good job either time.

Variacs are all (or almost all) many decades old.


NT

Not off them are fished out of a dumpster either.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com
 

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