Transformer Question

On Sat, 4 Feb 2017 20:35:40 -0800 (PST), Phil Allison
<pallison49@gmail.com> wrote:

>John Larkin wrote:
>
>>
>> >> 
>> >> 
>> >> A dial-primary (120:240 to whatever) transformer makes a good
>> >> isolation transformer. Use the two primaries and ignore the secondary,
>> >> unless you have some use for it too.
>> >>
>> >
>> >** Fraid that idea is not safe to recommend - as the two primaries may well be bi-filar wound. 
>> 
>> They can stand 120 and 240 and transients reliably already. It takes a
>> huge voltage to punch through enameled magnet wire.
>> 
>> >
>> >That is not adequate insulation for a mains isolation tranny, it could not pass safety standards anywhere.
>> 
>> A one-off home project doesn't need to pass safety standards.
>> 
>
>
>** Fraid that is a complete irrelevance. 
>
>The OP needs the isolation to be there to protect him from electrocution. 

Actually, we don't know what he wants it for.

>
>Your attitude is *criminally irresponsible*.

Your attitude is fraidy-cat.

-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

On Sunday, 5 February 2017 00:23:19 UTC, Spehro Pefhany  wrote:
> On Sat, 4 Feb 2017 15:49:14 -0800 (PST), the renowned Klaus Kragelund
> <klauskvik@hotmail.com> wrote:
> >On Sunday, February 5, 2017 at 12:27:49 AM UTC+1, Spehro Pefhany wrote:
> >> On Sat, 04 Feb 2017 13:53:14 -0800, the renowned John Larkin
> >> <jjlarkin@highlandtechnology.com> wrote:
> >> >On Sat, 4 Feb 2017 00:21:41 -0800 (PST), klaus.kragelund@gmail.com
> >> >wrote:
> >> >
> >> >>You should not make an isolation transformer your self if you don't have extensive experience 
> >> >>
> >> >>Isolation transformers must have double insulated design which involves special copper wire,
> >> >
> >> >Special copper wire? 
> >> 
> >> He's probably thinking of triple-insulated wire, and I don't think
> >> you'll find that in any 50/60Hz isolation transformers. It's useful in
> >> SMPS transformers where you want to put the windings as close together
> >> as possible to link all the flux, but you don't care much about
> >> primary-secondary capacitance. 
> >> 
> >Nope, for a transformer the basic insulation in case of an earthed laminated core or the double insulation in case of no earth depends on the wire classification
> >
> >Typical class F wire, which is approved for 155 degrees C.
> >
> >See for example section 7 in this:
> >
> >https://www.indiannavy.nic.in/sites/default/files/tender_document/Transformer.pdf
> >
> >Or first table on this link:
> >
> >https://en.wikipedia.org/wiki/Insulation_system
> >
> >During maximum power through the transformer or shorting of the secondary side, the winding gets hot, and must stay below 155 degrees to still have the insulation system in place
> >
> >Cheers
> >
> >Klaus
> 
> 
> Insulation between primary and secondary is **not** dependent on the
> wire insulation. It's provided either by bobbin design (split bobbin)
> or by the UL/CSA approved (north america) tape between primary and
> secondary. 
> 
> That's true whether the wire is class F or lower temperature rating. 

True for bobbin types. Not so for Chinese specials that are just enamel wire on enamel wire. The slightest scratch...


NT

John Larkin wrote:

> 
>
> >
> >> 
> >> > 
> >> >Relying on testing insulation is venturing on a slippery slope
> >> >
> >> > 
> >> I assume the op wants to hack one isolation transformer for personal
> >> use. I don't think he intends to get UL or VDE certification.
> >> 
> >
> >** But a single point failure of the enamel, likely from excess pressure,
> > a defect or continuous corona discharge over time would make the unit
> > lethal. 
> 
> 120 volts is no big deal. I wire everything hot.


** But you area reckless maniac who treats NG posting as a joke. 

 Advising others to do the same as you chose to is criminally irresponible. 


> 
> And 120v is not going to make corona.
>

** It can, and the secondary side of the tranny can be floating at some higher voltage. 

 You advise is criminally reckless. 



> 
> Don't be such a wuss.
> 

 ** Don't be such a cunt. 



> >An isolation transformer for bench work on live electronics is a SAFETY device, protecting human life and it is not rational to make or use a hazardous one. 
> >
> >Rational advice is not your forte - is it ? 
> 
> Silly fears sure aren't.
>


** More criminal advice for a notorious asshole. 

   Larkin is quite proud of being one. 




....  Phil 

John Larkin wrote:

>
> Transformer winding machines count turns exactly.
>


** I'm sure they do.

  But counting errors still happen for other reasons. 

  Fuckhead. 



....  Phil 

On Sat, 4 Feb 2017 22:00:42 -0800 (PST), the renowned
tabbypurr@gmail.com wrote:

>
>True for bobbin types. Not so for Chinese specials that are just enamel wire on enamel wire. The slightest scratch...
>
>
>NT

The last design I ordered from China has a split bobbin (PA66 94V-2
plastic from Dupont or an alternate Chinese supplier, both UL file
numbers), insulation on wires is 130�C with UL file numbers. Both
types of tapes are 130�C, both UL with file numbers in our records. 
UL thermal fuse included. 

No quality problems whatsoever. 

I've seen some pretty scary stuff from India, not so much from China
these days. We're showing them how to make 1st world quality. Of
course if you go onto Ali or worse, you might find some shockingly bad
product. 

--sp 

-- 
Best regards, 
Spehro Pefhany
Amazon link for AoE 3rd Edition:            http://tinyurl.com/ntrpwu8

Spehro Pefhany wrote:

> 
> >
> >True for bobbin types. Not so for Chinese specials that are just enamel wire on enamel wire. The slightest scratch...
> >
> >
> >NT
> 
> The last design I ordered from China has a split bobbin (PA66 94V-2
> plastic from Dupont or an alternate Chinese supplier, both UL file
> numbers), insulation on wires is 130°C with UL file numbers. Both
> types of tapes are 130°C, both UL with file numbers in our records. 
> UL thermal fuse included. 
> 
> No quality problems whatsoever. 
> 
> I've seen some pretty scary stuff from India, not so much from China
> these days. We're showing them how to make 1st world quality. Of
> course if you go onto Ali or worse, you might find some shockingly bad
> product. 
>


** The last toroidal tranny I replaced was an 800VA job from China. The primary had failed, layer to layer and would blow an AC fuse at switch on. 

Some time later, I decided to unwind the tranny, take a look at the damage and get some free copper wire to boot. 

This was very tedious as it meant removing the secondary first, lots of poly tape and then most of the primary to find the problem area. The primary was bi-filar wound as was the secondary. 

I finally found carbonisation of adjacent turns and traces of melted copper concentrated near the inside corner of the core, where winding pressure would naturally accumulate. 

After unwinding all the wire, I got down to the steel core where a nasty surprise was waiting for me. 

Unlike any other toroidal I had ever seen, the core was not wound with a single strip of tape nor had its sharp edges covered with plastic caps. About twenty scrap pieces of core material of slightly varying widths had been spot welded together, end to end, to make the final core. It looked like shit.

The centre hole was dead round, having been fitted onto a mandrill for winding, but the outside diameter varied by 3mm or 4mm around the circumference. 

This precluded the use of end caps so the maker has simply ground the sharp edges down a bit by hand and then applied adhesive cloth tape along each of them. Grinding the inner hole was more difficult, so not done very evenly. 

The tranny was bound to fail and I understand a large percentage of them did.

If you think it must have come fitted inside some flea-bag Chines product - it did not. The tranny was in a Crown Audio (of the USA) professional power amplifier model XLS602. See internal pic.

 http://cdn.avsforum.com/3/38/38365662_vbattach143596.jpeg


Understandably, I was very reluctant to buy another example and luckily had on hand a suitable toroidal of Italian manufacture that was close enough in ratings to do the job.




....  Phil 


 

whit3rd <whit3rd@gmail.com> wrote:
> 
>  **note, Tripp-Lite sells "isolation transformers" with the neutral of the secondary
> bonded to ground/case.   That is NOT what you want, if you might be poking into a live
> circuit.   If the specs mention "Neutral to ground bonding at the secondary"
> it means you can get a shock from isolated HOT to ground.
> 

Yeah, got caught by that one once on a Hammond isolation transformer.
Plugged a scope into the isolation transformer to float it, hooked up the
ground lead of the scope probe and shorted my circuit to ground. As per
CSA, the ground pin in the receptacle of an isolation transformer must be
connected to ground (which kinda ruins the "isolation" function of the
device).

On Sunday, 5 February 2017 06:22:02 UTC, Spehro Pefhany  wrote:
> On Sat, 4 Feb 2017 22:00:42 -0800 (PST), the renowned
> tabbypurr wrote:
> 
> >
> >True for bobbin types. Not so for Chinese specials that are just enamel wire on enamel wire. The slightest scratch...
> 
> The last design I ordered from China has a split bobbin (PA66 94V-2
> plastic from Dupont or an alternate Chinese supplier, both UL file
> numbers), insulation on wires is 130°C with UL file numbers. Both
> types of tapes are 130°C, both UL with file numbers in our records. 
> UL thermal fuse included. 
> 
> No quality problems whatsoever. 
> 
> I've seen some pretty scary stuff from India, not so much from China
> these days. We're showing them how to make 1st world quality. Of

they smile politely, promise quality, and deliver it at first. Then the corner cutting happens and you get crap. All nicely polished of course.

> course if you go onto Ali or worse, you might find some shockingly bad
> product. 

The thing with Chinese goods is that while a lot is good, much is lousy quality, too much is noncompliant, and the only way to know is a complete teardown.


NT

On Sunday, February 5, 2017 at 1:23:19 AM UTC+1, Spehro Pefhany wrote:
> On Sat, 4 Feb 2017 15:49:14 -0800 (PST), the renowned Klaus Kragelund
> <klauskvik@hotmail.com> wrote:
> 
> >On Sunday, February 5, 2017 at 12:27:49 AM UTC+1, Spehro Pefhany wrote:
> >> On Sat, 04 Feb 2017 13:53:14 -0800, the renowned John Larkin
> >> <jjlarkin@highlandtechnology.com> wrote:
> >> 
> >> >On Sat, 4 Feb 2017 00:21:41 -0800 (PST), klaus.kragelund@gmail.com
> >> >wrote:
> >> >
> >> >>You should not make an isolation transformer your self if you don't have extensive experience 
> >> >>
> >> >>Isolation transformers must have double insulated design which involves special copper wire,
> >> >
> >> >Special copper wire? 
> >> 
> >> He's probably thinking of triple-insulated wire, and I don't think
> >> you'll find that in any 50/60Hz isolation transformers. It's useful in
> >> SMPS transformers where you want to put the windings as close together
> >> as possible to link all the flux, but you don't care much about
> >> primary-secondary capacitance. 
> >> 
> >Nope, for a transformer the basic insulation in case of an earthed laminated core or the double insulation in case of no earth depends on the wire classification
> >
> >Typical class F wire, which is approved for 155 degrees C.
> >
> >See for example section 7 in this:
> >
> >https://www.indiannavy.nic.in/sites/default/files/tender_document/Transformer.pdf
> >
> >Or first table on this link:
> >
> >https://en.wikipedia.org/wiki/Insulation_system
> >
> >During maximum power through the transformer or shorting of the secondary side, the winding gets hot, and must stay below 155 degrees to still have the insulation system in place
> >
> >Cheers
> >
> >Klaus
> 
> 
> Insulation between primary and secondary is **not** dependent on the
> wire insulation. It's provided either by bobbin design (split bobbin)
> or by the UL/CSA approved (north america) tape between primary and
> secondary. 
> 
> That's true whether the wire is class F or lower temperature rating. 
> 
Partly true

When it comes to the direct winding, yes tape or triple insulated wire is used (beware UL recent rules does not allow for usage of triple insulated wire alone)

But when the wire exit the bobbin and is wound onto the pins clearance and creepage distances comes into play. The wire insulation reduces the requirements for clearance distances

For triple insulated wire the wire must be tested during wire production for 5.5kV, and finding a wire that can comply to that is difficult (I have never found one that does)

Cheers

Klaus

On Sunday, February 5, 2017 at 1:28:46 AM UTC+1, John Larkin wrote:
> On Sat, 4 Feb 2017 15:52:41 -0800 (PST), Klaus Kragelund
> <klauskvik@hotmail.com> wrote:
> 
> >On Saturday, February 4, 2017 at 9:18:22 PM UTC+1, John Larkin wrote:
> >> On Sat, 4 Feb 2017 11:58:08 -0800 (PST), tabbypurr@gmail.com wrote:
> >> 
> >> >On Saturday, 4 February 2017 18:30:34 UTC, John Larkin  wrote:
> >> >> On Sat, 4 Feb 2017 09:32:13 -0800 (PST), tabbypurr wrote:
> >> >> >On Saturday, 4 February 2017 17:16:45 UTC, John Larkin  wrote:
> >> >
> >> >> >> A dial-primary (120:240 to whatever) transformer makes a good
> >> >> >> isolation transformer. Use the two primaries and ignore the secondary,
> >> >> >> unless you have some use for it too.
> >> >> >
> >> >> >as long as you don't want too much isolation. What voltage breakdown do you get with the 2 primaries wouund one directly on the other?
> >> >
> >> >> Kilovolts, probably. Test it for margin if you plan to float the load
> >> >> way off ground.
> >> >
> >> >that's at odds with my experience of hipot testing transformers. Enamel on enamel failed below 1kV. Unfortunately I don't remember what voltage it managed. Probably over 500v, but that's not a comfortable margin.
> >> >
> >> >
> >> >> It will have more inter-winding capacitance than one of those
> >> >> extreme-expense isolation things.
> >> >
> >> >Yes. I don't know how much shock current that lets through.
> >> >
> >> >
> >> >NT
> >> 
> >> I made a twisted pair of #36 magnet wire and applied DC until it
> >> arced. 1400 volts.
> >> 
> >> Somebody should test a few ordinary dual-primary transformers for
> >> breakdown. 
> >> 
> >Relying on testing insulation is venturing on a slippery slope
> >
> >Then you need to do 100% production testing and getting approval from UL or VDE is VERY difficult and time consuming
> >
> >Cheers
> >
> >Klaus
> 
> I assume the op wants to hack one isolation transformer for personal
> use. I don't think he intends to get UL or VDE certification.
> 
If he does what you say, he is still required to do it according to the standards. What happens if he gets a visitor that is electrocuted?

Cheers

Klaus