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55v + 55v testing Transformer
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55v + 55v testing Transformer
I describe here, the process of converting an existing bar lighting transformer into one designed to supply power for testing pneumatic solenoid valves. I include it here, partly as a reference for my own use and partly to show the stages of conversion that may help others to carry out similar conversions.

Safety is important... If you are not competent to carry out this work, then please consult a trained electrical engineer, who will be able to follow the directions on this page to produce similar articles.

Design considerations... I was looking to provide an 110v ac source from 230v 50 Hz domestic mains supply. This is provided as two independent and identical 55v windings to give added versatility.

Choosing a suitable transformer to modify was simple... I had to hand a couple of enclosed transformers, with switch and fuses, originally intended to supply 12v to illuminate bar top beer dispensers. These were continuously rated at 18 VA and known to run cool at this, indicating a conservative rating. The solenoids that I was intending to power were between 7 VA and 23 VA and would only be "on" about 1 second in ten.

Disassembly In this particular case I stripped everything and cleaned each component as there were some sticky deposits left over from the previous usage.

After cleaning the outside of the lamination stack, I removed the clamping screws and pulled the stack to pieces wiping each lamination with a damp cloth.

Recalculating for our desired output
[find notes]

Rewinding the secondary...

Turns and voltages
Although this was a little tedious, it was simple enough... Each layer of turns was controlled and insulated using strips of 'double sided' adhesive tape. Hand winding allows the turns to be laid precisely side by side, but can make you fingers a little sore, due to the tension that should be sustained while doing so. The tappings shown in the winding schematic are for fine tuning as the exact turns per volt ratio was unable to be precisely established.

Re-coring is the process of interleaving the "E"s from each side alternately, then filling each "I" shaped space with an "I". Once all spaces are filled then the core should be laid on a hard, flat (preferably metal) surface and the sides of the stack tapped lightly with a hammer to ensure that all the gaps between "E"s & "I"s are as small as possible.

Terminating the conductors and the rest of the wiring is done, following the schematic diagram at right, Insulating terminals and joints with sleeving. Schematic Diagram of completed unit

Testing the unit

Final tweaks

Feeding the transformer from an energy reducer or dimmer

Electrical interference (EMC)

I am a qualified electrical and electronic engineer and as such I take precautions to ensure my own safety and the safety of others. I cannot be held responsible for the work of others that are not under direct supervision.

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Written... Summer 2001, Revised... 12 October 2001, New Domain... 21 April 2004,

Electronics Favicon Coding Standard 2003 Issue 5