Passive high-voltage dummy load

[pwdrive]

Thanks for posting that up Al, it looks as though it will get a lot of use with all those transformers you have.

Lawrence.

[Robert G0UHF]

Hi Al,

Thanks for posting all the diagrams and explaining further the theory and operation of the unit.

First, I must compliment you on the standard of your diagrams. They are very clear and easy to follow, and along with your text make the concept of the project easy to understand.

I haven't that many transformers lying around to justify building one of the units myself, but I can see for anyone that does have a largish number how useful having your unit would be.

I imagine without the fan the case can become way too hot even at low current settings! As Michaelr has already mentioned, some sort of temperature monitoring of the transformer under test would seem to be the next enhancement to consider if you wished to develop the concept further. Although the unit is excellent 'as-is' in my opinion.

Great work, very well done!

Kind regards

[AlanBeckett]

One possibility is eBay Item 250783963726.
I've bought a couple for the greenhouse, but you could equally lay one on top of the TUT.
Alan

[Skywave]

Thank you for your kind words Robert (G0UHF).

At present, the drawings are really 'final provisionals'. As a design develops, a drawing often gets to the point where there is so much 'Tippex' on it, the sheet stands upright, all by itself :omg: - that it's time to do a re-draw. I then scan that re-draw into the computer (as a master) and then issue it, via the printer, as the next issue, and go back to the bench with it. And so on, ad nauseum. That way, you can always keep track of what was before, should the next 'revision' turn out to be a non-starter. When the item is finally declared finished, I then produce a manual for the item - including operating instructions. This approach is simply a by-product of a life-time spent in electronic engineering. Despite every effort that should render future access to such documentation unnecessary, experience shows that there will come a day when a repair or modification will be required - hence a decent set of drawings, etc. Years ago, my attitude was "O.K., that's done. I'll never need to worry about how it works, what I did or what it does". Wrong: there is always a 'next time'. In a phrase, 'the job isn't complete 'till the paperwork is done'.

As for the degree of complexity in the unit, it could be drastically simplified for anyone who has fewer transformers to test or just needs something for occasional use. The initial block diagram illustrates the basic concept, in which the two meters could easily be replaced by a.c. measuring voltmeter and ammeter (single range for each) and only a few dummy load resistors included. My design was simply geared to what I had available.

I claim no intellectual property rights for this item, so if anyone wishes to build their own - please go ahead.

Al.

[Skywave]

Thanks for that suggestion, Alan. I suppose it measures the air temperature in the room where it lives. Laying it on top of the TUT wouldn't tell me its real temperature. As such, that's not quite the beast for the job: what I really need is a temperature probe - like a thermocouple - that I can firmly attach to the core of the transformer under test - for example between the core windings and the laminations, where the temperature rise will be the greatest. And now you've got me thinking. Could I make my own? :idea: Two dissimilar metal wires, suitably chosen and twisted together, will develop a p.d. across their junction that is a function of their temperature. Use that resultant p.d. to drive a high-gain amplifier that drives a moving-coil meter. But hang on a tick. I'm sure that somewhere I have a thermocouple attachment for my Fluke 77 DMM. But then perhaps that's 'cheating': it's not D-I-Y. But I could use that as a calibration standard for a home-brew analogue thermometer. Hmm; food for thought here . . . .

We'll see.

Al.

[Tedzed1]

This may sound like a silly idea, please tell me if it is, but how about adapting one of these to measure the temperature of a Transformer?

http://www.amazon.co.uk/LUPO-Digital-The..._2?ie=UTF8&qid=1323299538&sr=8-2

[Mark Hennessy]

An even better idea - measure the change in resistance of a winding as a result of the heating. I forget what the temperature coefficient of copper is, but it's pretty well documented...

[AlanBeckett]

In a previous lifetime that's exactly how we used to do it. The problem is that you need some very accurate Ammeters and Voltmeters to get an accurate answer.
In the 'normal' world what you need to know is the core temperature. That's what a 'sit on the top' thermometer tells you.
Alan

[Yorkie]

As to measuring temperature, Maplin have an infra red thermometer on offer at present, normally £39.99, reduced to £19.99. I bought one a year or so ago when they were on offer before, primarily to balance the thirteen radiators on our central heating system, but the thermometer has obvious use in electronics for such things as checking the temperature of transformer cores, heat sinks, high wattage resistor, particularly to note any rises in temperature. It’s a pistol grip type infrared thermometer which has a laser and backlight for easier targeting and operation. The temperature range is large -35°C to 365°C temperature, and it gives real time maximum reading and has power saving auto shutoff. I’ve found it excellent, and the laser is useful as it enables accurate targeting of the infra red beam.

The features, as outlined at the link below, are:

Compact thermometer with a wide -35°C to 365°C temperature range
Built-in laser pointer for accurate readings
Automatic data hold and real-time MAX temperature reading
Last measurement memory recall
Large, easy to read display with 15-second hold
Fixed emissivity (0.95) covers 90% of surface applications
Distance to spot ratio: 8:1
Auto shut off
Large LCD screen with backlight
°C/°F selectable
Uses 2 x AAA batteries (supplied separately - order code L42AL)

http://www.maplin.co.uk/infrared-thermom...05?c=found&u=tools&t=infrared%20thermometer&utm_source=google&utm_medium=cpc&utm_campaign=test%20equipment&utm_term=infrared%20thermometer%20-e&gclid=cmrypnin8qwcfcsmtaodi1yhqa

They also have a 50 Watt soldering station on offer, one of which I bought about a month ago, and have used extensively since. The tip temperature can be controlled from 350°F (180°C) to 900°F (480°C) without the need to change the tip or heating element. Additionally, a pack of three assorted tips for this solder station can be purchased separately (Order Code: N79AR).

Normally £32.99, offer price till 24 Dec £14.99. Nice stocking filler! (admittedly not as nice as Kylie!)

http://www.maplin.co.uk/50w-solder-station-35016

I’ve got no connection with Maplin, other than as an occasional customer. (Most of my needs for the sort of stuff that Maplin used to stock are met by Rapid, ESR, and Spiratronics).

[Skywave]

Lots of useful ideas there chaps, thanks: all now filed for reference.

Al.