Transformer temperature

[Phil WhitleyParticipant @philwhitley94135]

Sorry Russell Eberhardt, but you are wrong, any type of transformer or power supply which is dissipating Watts as heat, and not as electrical output is inneficient by the very nature of the fact that it is not a heater! The heat is an unwanted by product, which shortens the life of the power supply and the more heat it produces, the more Watts it is dissipating as heat, and the more inneficient it is. There is always some heat, but they are not "designed to run hot", more they are designed to cope with the heat they produce due to their inneficiency, usually caused by them being built down to a price, rather than up to a standard. The thought that anything from China complies with BS EN 60065, is frankly laughable! I know it is supposed to (or it used to be in pre EU days) comply, but thanks to the good old CE standard , it will be about as compliant as the (also CE marked) panels on the Grenfell tower block! In a previous life running a wireless ISP company which I also started, we installed thousands of wireless access points with the wall wart type power supplies, all CE and BS marked, and got into the habit of switching them off before unplugging them as the pins usually stayed in the 13A socket, as the heat had completely destroyed the plastic. Some had been installed for a matter of weeks! we sent hundreds of these power supplies back for replacement, and the survival rate of the replacements was little better. We offered some of these power supplies to the BSI for testing, but withdrew when they told us they would charge us for it, although they would do it for free for an end user.

Phil

[Mike PooleParticipant @mikepoole82104]

Industrial spot welding transformers and electrodes are water cooled. Controlling temperature rise is critical to weld quality. Water flow failure will soon cause problems so pressure, temperature and flow are monitored.

Mike

[Neil WyattModerator @neilwyatt]

> The thought that anything from China complies with BS EN 60065, is frankly laughable!

Really?

Have you actually thought about what is made in China these days?

Neil

[SillyOldDufferModerator @sillyoldduffer]

Phil,

I wonder if you took advice about your responsibilities as a distributor of CE marked equipment before your company installed all those unsatisfactory power supplies?  "If you are a distributor you must check the presence of both the CE marking and the necessary supporting documentation. If you are importing a product that is from a third country you have to check that the manufacturer outside the EU has undertaken the necessary steps. You must check that the documentation is available." I'm guessing you didn't check.

Then in a post mentioning the Grenfell fire, you confess to installing over-heating equipment that you believed to non-compliant. And furthermore that the company for which you were responsible decided not to have the power supplies checked because BSI charge a commercial rate. 

Good job no-one got hurt, you might have had an exciting brush with the law.

Dave

Edited By SillyOldDuffer on 28/06/2017 22:12:23

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Phil Whitley on 28/06/2017 20:51:37:

Sorry Russell Eberhardt, but you are wrong ——— but they are not "designed to run hot",

Every process that converts energy from one form to another has less than 100% efficiency. So heating is inevitable. The degree of heating allowed is one of the many parameters to be considered when doing the design calculations, so it is part of the design process. There always has to be a trade off between the different design parameters some have more weight than others. Safety should have the highest priority. Another parameter that must have a high priority is the market price. If it is too high the product will not sell and the business is no more. That is a fact of life.

The safety standard I quoted is not a pre-EU standard but the BSI published version of the EU standard and compliance with it is one of the requirements for the CE marking of many electronic products intended for domestic use.

You do seem to be a little confused over the CE marking process. The responsibility for CE marking a product lies with whoever places the product on the market within the EU. Thus, if you import a product and sell it on within the EU you are responsible for the conformity, not the manufacturer. You may pass on some responsibility to the manufacturer outside the EU in your contract with him but you cannot avoid your responsibility. You can of course ask him to affix the CE mark on your behalf.

Russell

[not done it yetParticipant @notdoneityet]

Sorry Russell Eberhardt, but you are wrong ——— but they are not "designed to run hot",

I agree wholeheartedly, Phil. Radiant electric fires are designed to run hot while infrared versions are designed to run much cooler. The thermal losses of any (properly designed) electrical devices (other than a heater) are manufactured to lose as little thermal heat as practical. Unless it is a cheap chinese wall wart. The windings and insulation has to be chosen around the best the designer can manage for temperature rise in the component. A subtle difference!

Large transformers are designed to run as cool as practicable, given other manufacturing constraints. The necessary design features incorporated are to avoid damaging the item by overheating. If they were designed to run 'hot', they would never sell them in front of the better designed item which minimised the thermal losses.

[John HaineParticipant @johnhaine32865]

Radiant electric fires are designed to run hot while infrared versions are designed to run much cooler.

Hmmmm……….not sure how they manage this, black body radiation being what it is………

[SillyOldDufferModerator @sillyoldduffer]

Posted by not done it yet on 29/06/2017 13:22:34:

…

Large transformers are designed to run as cool as practicable, given other manufacturing constraints.

…

Could this debate be built on the quicksand that is the English Language? Terms like 'hot', 'cold', and 'cool' are relative, all of them meaningless without a reference point.

Russell says 'transformers are designed to run hot'. In support of his opinion my design book (published in 1941) quotes operating temperatures between 65C and 140C. The higher temperatures are made possible by the development of improved insulation. Anyway, I think 65C is 'hot' relative to taking a shower..

On the other hand, NDIY says 'Large transformers are designed to run as cool as practicable…'. My question to NDIY, is what temperature do you think that is ? Compared with a radiant electric fire, 65C is 'cool'. On that basis it's possible that NDIY and Russell are in violent agreement.

One feature that's not been mentioned is the duty cycle. Depending on what it's for, a transformer may spend much of it's time lightly loaded with only intermittent bursts of high demand. As it's expensive to provide a transformer rated for a continous maximum load that rarely happens, it's not unusual to install a smaller transformer in the expectation that it will 'run hot' during the bursts. For example the 1.5kW transformer in my Microwave oven is less than half the weight of a 300W continuous duty transformer. Might be interesting to take the MOT's temperature next time I bake a potato. (Danger! Please don't.)

An interesting feature of Transformer Design is the number of factors that might have to be taken into account. Operation indoors or outdoors; operation in hot countries, a coal mine, or ship; balanced and unbalanced loads; expected variation in load; third harmonic suppression; short circuit protection; surges, and much else. Operating temperature doesn't come over as being controversial. Maximum operating temperature was set by British Standard. Judging by my book the main temperature concern is avoiding 'hot spots' in the windings rather than keeping the whole transformer 'cool' . Of course the need to save energy may have changed design thinking since the book was written.

Being into electronics I never throw old wall warts away: I have a box full going back to when they first appeared. None of mine, well into double figures, have ever overheated in use. Perhaps I've just been lucky!

Dave

[Phil WhitleyParticipant @philwhitley94135]

Russel Eberhardt,

My post was somewhat misunderstood. We did not import the product, the product was imported by our supplier (who also handled replacements) and was CE marked by the original manufacturer. in China/Taiwan etc There was plenty of paperwork available, and we had sight of it. The reason that I would give no credence whatsoever to any paperwork issued by the manufacturers was based on the experience that the equipment did not anything like perform as specified in the paperwork, and I would also guess that the quality and safety claimed on the documents was also wildly exagerrated. I remember at one point we were building wireless mesh boxes based on a mini atx computer and a wireless card . as you can imagine we were buying large amounts of wireless cards , in batches of 50 at about £35-00 each. We were having many poor performance problems, so we got the spec sheets from our suppliers, and started testing the wireless cards. Fully 90% were performing well below their rated output, and also producing vastly more noise than specified outside the frequency they were supposed to transmit on > this was not a bad batch, or limited to one supplier, it was universal across different makes and suppliers, and for several months we sent hundreds back, to the point where we were searching the world for wireless cards which actually did what the manufacturers spec claimed they did! The problem with CE is quite simp[le, there is no independant testing, it is all done by the manufacturer, it is a paperwork exercise in which the EU states what is required to comply, and the manufacturer provides paperwork to assure the EU that their product complies with this "standard"

What I took exception to was the "designed to run hot statement" which is electrical nonsense. You have now provided a concise and correct explanation!

Phil

[Phil WhitleyParticipant @philwhitley94135]

Silly old duffer,

Yes, we took our responsibities very seriously, but we were not selling unmarked non compliant equipment, we were selling fully marked, supposedly compliant equipment supplied by the importer.

"You have to check that the manufacturer outside the EU has taken the neccasary steps."

How? They are in China, typical EU buck passing. surely the people setting the standard should also test for compliance, thats what the BSI used to do!!

"You must check that the documentation is available"

We did check, it was available., the fact that the paperwork was a work of pure fiction seems to matter little to the EU or the manufacturers, as the seem to have conspired to make the supplier responsible! That would not have been us, but our supplier, who was also the importer.

My point about mentioning the Grenfell tragedy was that it is a current example of something made in another country, sold in Europe (so it must be CE marked) and is obviously not fit for purpose, and non compliant with current regulations The building regs have a catch all regulation, which states basically that any work done to a building must not leave it in a less safe condition than it was before in the work was done………….fail.

"Then in a post mentioning the Grenfell fire, you confess to installing over-heating equipment that you believed to non-compliant. And furthermore that the company for which you were responsible decided not to have the power supplies checked because BSI charge a commercial rate"

WOT? When we bought it, it was fully documented and CE marked as compliant, after we had experienced the failures, all the PSU's were replaced FOC by our supplier, with more corectly marked and supposedly compliant psu's which also began failing. At this point the supplier recalled and replaced all the WAP units, and supplied a different type. We assumed that the BSI would be interested to know that an item marked as compliant to their standards seemed to be underperforming to the point of being dangerous, basically, they weren't, unless we paid them (A LOT). In the situation of an end user submitting a faulty or dangerous item to BSI, they would (at that time) have tested it free. Today they seem to be in the business of selling very expensive deemed to comply documents.

My whole point in this post was to try to illustrate that the Chinese will stamp their goods with any mark or number that is needed in the UK and Europe in order that it can be sold. They will also provide the neccasary paperwork on the same basis. To attach any credence to the validity of this marking and specification is the part that is laughable! There is no independant testing!! CE seems to make BSI more or less redundant, perhaps it will change when we eventually get out.

Phil

[Neil WyattModerator @neilwyatt]

Ten years of iPhones and their PSUs being made in China.

My Japanese Canion camera has a Chinese charger. My Nikon and its charger are both made in China.

My Binatone DECT phone and its charger (both made in China) have been running as cool as the ordinary 13A plug in the next socket for ten years.

Ditto my LOGIK DAB radio and its PSU, and my Toshiba laptop and PSU, but not the DELL laptop that preceded it (Made in Ireland, according to the label) which always ran hot.

I'm sure that if I went around the house I could triple or quadruple that list. yes some, crap does come from China, but they also make electrical goods that are as good as those made anywhere else.

Buying cheap generic stuff of eBay is not a fair way to judge everything that comes out of the country.

Neil

P.S. I know for a fact that some importers go to great lengths to make sure that the CE stuff they get from China is backed up by valid paperwork and tests and is NOT just a stick on label.

[Russell EberhardtParticipant @russelleberhardt48058]

I'm finished with this thread having designed transformers and had them made in both the UK and the Far East in their hundreds of thousands I have nothing more to say.

Just an aside before I go, one example of a world recognised test house in China: **LINK**

Russell

[michael howarth 1Participant @michaelhowarth1]

I received an e-mail from Interpet/Blagdon today stating that their display models have a transformer operating temperature of between 30 and 40 degrees. They have asked me to record temperatures over this weekend and get back to them.

Russell ……Thank you for your interesting contribution to this thread.

Mick

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