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One for the New Year

kellys_eye

Jun 25, 2010
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I enjoy watching Youtube videos by The Tech Guy (he repairs hi-end test equipment) and have always admired his variable AC power supply that he often uses to power up equipment that have PSU problems.

He did a video showing the innards of this variable AC power supply and despite its relative complication (seemed awfully more intricate than it really needed to be imho) it is something I intend to reproduce as a New Year project for my own workshop.

I was fortunate enough to purchase a (very) cheap variable low voltage AC supply unit - an ex-schools laboratory unit that delivered 0-28V AC at up to 10A. It is a simple variac powering a standard AC transformer so lends itself to adaptation to a full-scale 0-280V AC supply by the simple addition of another 28VAC secondary mains transformer wired in reverse!

This gives a nice ISOLATED supply that can vary from (as good as) zero right up to past 240V (the UK mains supply) and at a total power of around 250W - more than sufficient for most electronic equipment that I repair, especially TV's and the like.

Some additions I will be making include an interlock to prevent the high voltage side being switched on unless the variac starts at 0V, metering for Volts, Amps and Watts (Chinese all-in-one module), current trip etc.

The finished version will have:

Variable AC 0-28V @ up to 10A - metered V and I
Variable DC 0-40V @ up to 6A (simple BR and smoothing, so unregulated) - metered V and I
Variable AC 0-280V @ up to 1A - metered V, I and W (cumulative too!)

Various switching arrangements will ensure only one type of output can be used at any one time, thermal detection for transformer overheating and, as already mentioned, full mains isolation!

I don't know how much Tech Guy paid for his unit but mine (so far) has cost £10..... another £15 for the second transformer and (say) £15 for the metering. I have all the sundry parts to finish.

Anyone got a New Year project they want to mention? Note, this is not a 'resolution' - I'm useless at those!
 

Arouse1973

Adam
Dec 18, 2013
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Mine is a simple one. Its an ECG using the AD8232. I have the PCB and electrodes just need to wire it up and put it in a box. Need to build a small regulator PCB as it runs from 3.3 Volts and I plan to power it from a USB battery bank. Then I can connect the circuit to my PICO scope and see my heart response on my TV.
Thanks
Adam
 

kellys_eye

Jun 25, 2010
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I'm undecided on the practicalities of homebrew medically-orientated devices given that the information they might produce could be easily mis-interpreted.

If it's purely for experimental use then excellent - there is a lot to be learned from such interfacing.

I'd be too concerned that reading the data incorrectly would cause undue worry! and, potentially, inconvenience to the medical services that would be called in to verify such results.

Will you be comparing your output with data from a 'legit' source?
 

Arouse1973

Adam
Dec 18, 2013
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I already have the worry LOL. I have AF and yes I have had two ECGs so got a rough idea of what I am looking at. The AD8232 is the type of device they use in loop recorders for monitoring your heat beat. With me I have an extra beat in my heart rhythm. The reason I am doing it is because I want to know if it still does it when I think it's not or is it so mild that I am used to it and don't notice it. Bit of nerdy fun really.
Adam
 

kellys_eye

Jun 25, 2010
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Addendum - the guy I refer to in post #1 isn't the 'Tech Guy' but is on Youtube as 'The Signal Path' (my bad) and the variable AC supply is this one:

 

kellys_eye

Jun 25, 2010
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I have AF and yes I have had two ECGs so got a rough idea of what I am looking at.
Whilst I can't show any 'happiness' at your answer it does please me that you are familiar with the issues and therefore less prone to making inappropriate decisions based on the results!

We can all equate with 'nerdy desire' though :p
 
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