Just bought a never used, new in box isolation transformer from local tech surplus shop for about $50 US, the seller claimed its rated 1000 VA. The reason they offered this price level was because it was mishandled during shipping and the unit's case is somehow deformed at the bottom, check photo "02. Current Condtions.JPG' for the detail of the defect.
The physical looks very new without any dents or scratches, and no dust at all and came with box. I was allowed only to test it briefly with their cheap dmm for resistance checking between primary and secondary windings just in case there is an internal short, also a very brief 5 minutes load testing on a PC with crt monitor to check the input vs output voltage, thats all.
There are no descriptions nor labels at all at the unit's front/rear plate, the only label printed at the box is just the words "Isolation Transformer" and without any brand either
, while internally there are only two labels indicating its "1000 VA" and 220 Volt rating on primary & secondary termination, detail on photo "03. Terminations.JPG".
I used to have a smaller one rated at 200 watt was used for working with high voltage measurements like probing with scope on switching power supplies and etc, but unfortunately I never did open it up to see how its wired inside, and don't have it with me now.
Appreciate any help or advise on modding this into technician isolation transformer, so far I've been reading at the net and also watched the great tutorial like the one from toddforfun's video on youtube. Although the connections are very simple, its just I want to be really sure since this is a high voltage stuff that must be taken very seriously.
Made the the schematic below after dismantling the whole unit, traced all connections, and also made few measurements on the transformer windings electrical properties :
Questions :
1. Is that the right modification just by cutting the ground connection to the Neutral at secondary, to turn this transformer into a technician version of isolation transformer ?
2. How about the connection from the Ground to the iron core ? Just leave it as is ?
3. You can see for yourself that the unit is just so plain without on/off switch, indicator light and fuse like the one I used to have. Where is the best place in the circuit to put those additional components ?
4. At this price and with very minimal labeling or description, from the detail photos below and the measured electrical properties, does this transformer really rated at 1000 VA ?
5. I'm planning to do a load test, and I have a killawatt to measure watt consumption, is it safe to use a high wattage load like hair dryer, an iron or even my rice cooker to test loading it.
6. What happened if an isolation is overloaded ? Symptoms ? What kind of measurements should I check to see if it reached it's max rating ?
....or any other suggestions or considerations that I missed.
Pictures below show the current conditions of the unit when I brought it home, planning to hammer that case to straighten it's base, also as you can see the space inside is quite empty even with the transformer in it.
Included few closeup shots to show the built quality of that transformer, really like to hear your comment about the transformer built quality as well, one thing for sure, this thing is damn heavy.
Thanks in advance & Happy New Year !