MEOPTA 87328 16mm projector supply

 I have a solder station which I use daily. It is fantastic with it's finely adjustable tip temperature and vacuum system to remove the fumes produced when soldering. But sometimes the big guns are required to melt solder in tube style radios that use wire wrap methods to solder joints. I have found that the Weller solder gun is ideal for that.

It produces instant heat at the touch of a button and with 200 Watts of power it will melt anything you are likely to come in contact with. Especially solder joints that attach to the metal chasis of a radio.

Sadly, this unit does not come in a 220V version (at the time of writing), so European users are a little left out.

So I researched eBay for a step down transformer that provided the necessary power at 120V. There are many items offered but not so many that can provide the punch required for instant turn on. I had bought a cheaper transformer in the past and witnessed first hand what happens when these transformers are driven to their limits. A thick choking smoke from the windings and a flash fire. I had to open all the windows in the appartment for several hours (whilst going for a walk) to clear out the stench of burnt out windings. So this time I wanted a little more power than was required.

I came accross a rather interesting beast. A power supply from the former Czechoslovakia which was used to power halogen projector lamps in the days when soviet CZ was prone to brown outs. It accepted 220V or 127V input and provided 220V, 120V, 110V and 75V output options at an impressive rating of 1,000 VA. A huge rotary knob on the front allowed the operator to compensate for low line input voltages.

An fantastic break down of what is contained inside and a circuit diagram can be found in this excellent article from Bogin, Jr.

Given today's very stable 220V line voltage, I really do not recommend turning the knob on the front panel. Doing so, would result in oversaturation of the transformer and will result in lots of smoke and unpleasant smells.

For those of you thinking this might be an option for an isolation transformer, forget it now. The input and output windings are both earth referenced. 

So, upon receipt of the beast, I attached it to my isolation transformer and current limited supply and slowly turned up the volts. As I wanted 120V out, I set the knob on the rear to 120V.

On my multimeter, I read 220V - not good. Obviously someone had changed the wiring on the inside of the transformer. So the case was removed.

Upon inspection, it was hard to see just how the last owner had wired the output cable. As you can see below:

So the cable clamps were removed and it became clear that the last user had connected the output to the 220V pre-projector connections.

So I removed the connection from tag 6 to tag 5, which is the variable output selector on the rear side.

Immediately, I had a variable output supply.

On further testing of all output settings, I discovered that the 120V winding was somehow damaged. It was only producing 97V. So I placed the output selector to the 110V winding and this produced a healthy 110V which is enough for my solder gun.

The take-away from this article is, never trust a 2nd hand item. Always test it first. Connecting my 120V solder gun to 220V would have resulted in a big mess. Always check that what is written on the tin is what it actually delivers before connecting any equiptment.

I am very happy with the purchase, as it does what I need. Instant heat!