Reply by John Larkin February 6, 20172017-02-06
On Sun, 5 Feb 2017 11:07:28 -0800 (PST), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>Den s&#2013266168;ndag den 5. februar 2017 kl. 19.54.10 UTC+1 skrev John Larkin: >> On Sun, 05 Feb 2017 19:28:19 +0100, Jeroen Belleman >> <jeroen@nospam.please> wrote: >> >> >On 05/02/17 16:48, John Larkin wrote: >> > >> >> Transformers, absent thermal overload or soaking in salt water, are >> >> amazingly reliable. Using a dual-primary tranny as an isolation >> >> transformer will be no less reliable. >> >> [..] >> > >> >I wish! I'd *expect* transformers to be amazingly reliable, but in >> >my experience they aren't, even under moderately light loads. >> > >> >Jeroen Belleman >> >> I've used thousands of 120:240 power transformers, and none have >> failed in the field from defects of design or construction. We did >> have one toroid that ran into saturation, and got hot, at maximum line >> voltage and 50 Hz, at a UL test lab. The manufacturer had to modify >> the design; I think they changed the core material. >> >> There are no doubt cheap, nasty transformers around; don't buy >> transformers from chop shops. >> > >http://s240.photobucket.com/user/inspector72/media/funny%20stuff/thirdworldarcwelder3.jpg.html
Is that a CE sticker that I see on the side? -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by February 6, 20172017-02-06
On Sunday, 5 February 2017 22:41:45 UTC, Judges1318  wrote:
> On Fri, 03 Feb 2017 16:36:30 -0800, tabbypurr wrote: > > On Friday, 3 February 2017 21:58:31 UTC, Judges1318 wrote: > > > >> Basically, the VA of the transformer is the max voltage you possibly > >> have at the secondary for any type of load, times the max current you > >> can possibly have in the secondary on a permanent basis for any type of > >> load. > > > > I always thought it was the nominal V & I. And the rating is on the > > basis of a certain level of MTTF, one can certainly exceed it when less > > MTTF is acceptable. > > > > > > NT > > Well, you are right for most practical purposes. My formulation is more > cautious. > > VA of a core is a practical way to express the ability of > that core to carry over energy i.e. power. But that may be not > the power that is used at the secondary. What if the load on > the secondary is purely inductive? No ACTIVE power is used, > but the voltage may be high, the current may be great, and the > flux in the core must be able to produce these high values at > the secondary. Plus, of course, to cover for any losses. > > What you call "nominal" is "on a permanent basis" in my formulation. > As with most limits, excesses above nominal values may be tolerated > if not too large and never for long periods.
I'm not clear what point you're trying to make here. NT
Reply by legg February 5, 20172017-02-05
On Sat, 04 Feb 2017 19:23:16 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> 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. > >--sp
The OP was working with a transformer with 480V/240V labeled primary. Providing it was a listed part, or constructed using a listed supplier under an OEM license, it will serve adequately as an isolation transformer for 480V inputs or lower, so long as the primary is connected to the line and the output is taken from the secondary. A standard isolation transformer is likely only to differ in that an electrostatic screen is usually present in layered E or toroidal parts. Most commercial types expect a safety earth connection to the core. The screen would share this connection. RL
Reply by Phil Allison February 5, 20172017-02-05
dca...@krl.org wrote:

> > > > > > If you are making a 1:1 transformer using a couple of MWT's > > > ( MicroWave Tronsformer ), You do not use the secondary windings. > > > > > > > ** THAT is a COMPLETELY DIFFERENT story to what you posted previously. > > > > YOU need to be WAY more careful with what you post !!!!!!!!!!!!!!! > > > > W what you posted before was DANGEROUS advice - anyone reading it would think you meant to use the two transformers as they were. > > > > You need to go back and retract that post NOW. > > --------------------------------------------- > >
> > If you go back and read my previous post, you will see that I never > said to use the secondary windings. >
** "What you posted before was DANGEROUS advice - anyone reading it would think you meant to use the two transformers as they were. " You are one stubborn fuck. .... Phil
Reply by Julian Barnes February 5, 20172017-02-05
On Sun, 05 Feb 2017 11:07:28 -0800, Lasse Langwadt Christensen wrote:
 
> http://s240.photobucket.com/user/inspector72/media/funny%20stuff/
thirdworldarcwelder3.jpg.html "Afro-engineering" LOL!
Reply by John Larkin February 5, 20172017-02-05
On Sun, 5 Feb 2017 21:50:16 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

>On Sun, 05 Feb 2017 07:58:10 -0800, John Larkin wrote: > >> How would that happen? > >All sorts of improbable circumstances can occasionally conspire to create >a lethal situation.
Certainly. And that fact can make you afraid of everything. There is a fix for that. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by Judges1318 February 5, 20172017-02-05
On Fri, 03 Feb 2017 16:36:30 -0800, tabbypurr wrote:

> On Friday, 3 February 2017 21:58:31 UTC, Judges1318 wrote: > >> Basically, the VA of the transformer is the max voltage you possibly >> have at the secondary for any type of load, times the max current you >> can possibly have in the secondary on a permanent basis for any type of >> load. > > I always thought it was the nominal V & I. And the rating is on the > basis of a certain level of MTTF, one can certainly exceed it when less > MTTF is acceptable. > > > NT
Well, you are right for most practical purposes. My formulation is more cautious. VA of a core is a practical way to express the ability of that core to carry over energy i.e. power. But that may be not the power that is used at the secondary. What if the load on the secondary is purely inductive? No ACTIVE power is used, but the voltage may be high, the current may be great, and the flux in the core must be able to produce these high values at the secondary. Plus, of course, to cover for any losses. What you call "nominal" is "on a permanent basis" in my formulation. As with most limits, excesses above nominal values may be tolerated if not too large and never for long periods.
Reply by dcas...@krl.org February 5, 20172017-02-05
On Sunday, February 5, 2017 at 4:38:01 PM UTC-5, Julian Barnes wrote:

> What is this shit? Afro-engineering?? Seriously, fork up for a properly > made tranny (unless your life has no value whatever of course, in which > case, go nuts).
There is no fun in buying things. I kind of believe if you did not make something, it really isn't yours. Dan
Reply by Cursitor Doom February 5, 20172017-02-05
On Sun, 05 Feb 2017 07:58:10 -0800, John Larkin wrote:
 
> How would that happen?
All sorts of improbable circumstances can occasionally conspire to create a lethal situation.
> Use a GFD if you are afraid of 120 volts.
WADR I think you're dishing out some very questionable advice here, John. People who need to be told how to build an isolation transformer really need to forget the whole idea and buy a decent proprietary one.
Reply by Klaus Kragelund February 5, 20172017-02-05
On Sunday, February 5, 2017 at 7:54:10 PM UTC+1, John Larkin wrote:
> On Sun, 05 Feb 2017 19:28:19 +0100, Jeroen Belleman > <jeroen@nospam.please> wrote: > > >On 05/02/17 16:48, John Larkin wrote: > > > >> Transformers, absent thermal overload or soaking in salt water, are > >> amazingly reliable. Using a dual-primary tranny as an isolation > >> transformer will be no less reliable. > >> [..] > > > >I wish! I'd *expect* transformers to be amazingly reliable, but in > >my experience they aren't, even under moderately light loads. > > > >Jeroen Belleman > > I've used thousands of 120:240 power transformers, and none have > failed in the field from defects of design or construction. We did > have one toroid that ran into saturation, and got hot, at maximum line > voltage and 50 Hz, at a UL test lab. The manufacturer had to modify > the design; I think they changed the core material. >
Thousands of power transformers.... That what we use in just about 6 hours of production, if your really want to bring in numbers. I really don't care. Your suggestion is deadly and plain wrong. I would expect you to be better than that, and know when you are wrong Cheers Klaus