# Variable Power Supply?



## Who. Me? (Jan 12, 2007)

I'm in the process of renovating the upstairs of our house at last, and with most of it plastered, I'm finally getting to the point where I'll have a clean, quiet space to work on some of my projects, so I'm starting to bring some tools together.

One item I reckon I'll need is a 0-2V variable power supply to mimic a cell.

I've seen pics on the web of a analogue multimeter type watch-tester that has a variable output allowing the user to power a movement for 'bench' running electronic movements.

Anyone know who actually makes one? (Am I allowed to post a link to the page on pmwf?)

Searcing for a 0-2V supply, all I can find are the Bulova one, which was designed to setup accutrons for 1.35v mercury cells, needs modifying to output >1.7V (and I can't find any), Omega's Alitest and the various branded equivalents (ESA Metre etc) which are half as common as hens teeth and twice as expensive, or laboratory power supplies which are 0-50V (pointless and risky IMO).

I've got one of the bulova movement holders that you can fit a cell in to power the movement, but that supplies the constant voltage of the cell you put in it.

Any suggestions? I keep an eye on ebay, but most of the older, Bulova kit seems to be in the states, so shipping virtually doubles the price.


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## zozur (Dec 3, 2011)

Hello

Maybe this ?

Only over ten elements + multimeter.


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## Silver Hawk (Dec 2, 2003)

Andy,

I have a couple of boxes that will go from between 0.8 to about 1.95 volts...both were made by the same guy and he might be willing to make another if you're interested....

This is Mark 2:










And this is Mark 3 with a few improvements:


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## Who. Me? (Jan 12, 2007)

Bugger, I just bought the bits online.

Found this website with instructions... http://www.pocketwat...pwr-supply.html (Mods, apologies if the link breaks any house rules - feel free to chastise me if I have).

Thought I'd have a go, as the instructions are pretty step by step, which is easier for me than following the basic circuit diagrams I found elsewhere.

It doesn't have the built in meter like yours, but does have binding posts to connect a multimeter as well as the outputs to the movement holder.

If I mess it up, I'll ask if you can put me in touch though.

Thanks

Andy


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## Who. Me? (Jan 12, 2007)

Well, I've surprised myself.

A handful of components from ebay (Â£23) and one Wilkinsons variable voltage power supply (Â£5), coupled with the Lidl soldering iron out of the garage, a copy of the Collins Complete DIY Manual and a couple of hours work later and...



















One (apparently working properly) variable voltage power supply.

As witnessed by the second photo above, it outputs up to 3.5V, so I'll need to mark the housing and/or put a safety stop in place to make sure I don't overload the movements, but I'm quite surprised and very pleased that it works, especially because...


I haven't soldered any electronics since GCSEs 25 years ago

The easy step-by-step instructions were no use to me as they're based around a Radio Shack 'experimenters board', which has lots of helpful copper tracks and isn't available in the UK, so I had to work with a basic matrix board

I was working hunched over the coffee table (with the Collins DIY Manual acting as a heat-resistant pad) as the house is a bomb-site due to all the decorating


I'm not going to show you the back of the board as it's smothered with solder - I definitely need to get a new tip for this soldering iron and/or use a bigger matrix board if I make another - but it looks OK from this side.

Just need to get a bigger project box as the one that came with the matrix board is way too small, then I'll solder in the on/off switch and the binding posts for the output. Might also get a double pole double throw switch so I can connect an Ammeter and Voltmeter at the same time, but I've only got the one Multimeter at the moment, so I may just go with one set of terminals for now.

Anyhow, if anyone needs one of these supplies, I'd definitely recommend having a look at the linked PDFs above and having a go.

The only iffy bit was soldering the voltage regulators as their pins are so close together. The Radio Shack board used in the PDFs would make that a whole lot easier as you can space the other components, while I had to place them butted up to each other and use solder to bridge between them (very messy and very frustrating).


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## Silver Hawk (Dec 2, 2003)

Nice job Andy. Can you read microAmperes with your set up? I find this quite important / useful when working with Accutrons.


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## Who. Me? (Jan 12, 2007)

Hi Paul

Thanks for the feedback.

Is there a need to simultaneously read current and voltage on the one box?

I've been thinking of using the multimeter to check supply voltage, then connecting the supply to the movement holder, then switching the multimeter to microamperes and testing. The cheapo multimeter in my pics has a 200 microampere range setting, but I can't remember the precision.

Haven't looked at the current/voltage testing procedures yet (aside from the basic 'is the coil good or not' tests that I've done up to now).

I don't think it's an issue to add one (the second and third PDFs in the above links explain how to make a tester that looks very similar to your Mk2 & Mk3 above). A panel-mount 0-30 microampere ammeter won't be massively expensive (and a panel-mount voltmeter would be very cheap to add), but I'm not sure how the panel-mounts are zeroed. Can you zero the Ammeter on your boxes?

Thanks

Andy

P.S, anyone know what the ASCII code is for 'mu'? Would be much easier than typing microampere every time.


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