Small Project: AC Mains Isolation Transformer from Two Broken UPSs (1/2)

From cannibalizing two UPSs to proof of concept and load test …
↓↓↓ Complete description, time index and links below ↓↓↓

Warning: This video involves mains AC, which can cause serious injury or death!

I had two dead APC Smart-UPS 750s lying around and was in need of an isolation transformer. Knowing what’s inside such an UPS (link below) an idea formed in my head.

At the heart of such an UPS is a transformer. It can transform AC mains to low voltage for charging the battery. It can also be driven with low voltage from the battery to create AC mains voltages. I just put one and one together.

00:00 Intro – one warning, two dead UPSs, one wish and two reasons
02:11 Two UPSs – teared apart to get to their hearts
03:30 Two UPS transformers – make an isolation transformer (maybe)
06:12 Transformers’ windings– which high voltage side tap is what
08:46 Transformers’ isolation – resistances at low (DMM ohmmeter) voltages
11:02 Transformers characterized – somewhat (winding resistances and voltages)
12:49 Transformers tested – the isolation that is (not to any norms or standards!)
17:23 Design consideration – keeping the low voltage side current low
20:17 Proof of concept – cobbled everything together and did some measurements
24:30 Load test – a drop of 7V at 100W, not great, not terrible

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