Electronics > Beginners
UPS transformer with 3 wires altogether
max.wwwang:
Another beautiful thing is it seems like the UPS I have here has the very similar topology and uses the similar technology as described in this patent document --
https://patentimages.storage.googleapis.com/fb/75/34/13fab3664adb39/WO1993012570A1.pdf
which is a highlight of Dave's video in my opinion!
One thing that I don't understand is that when I was very excited and tried to hook the two wires of the second biggest transformer in this unit (the two wires the opposite side of the battery wires), the main switch of my house immediately tripped. It didn't work as I thought.
I can see clearly a H bridge with 12 MOSFET in 4 groups (3 in each group wired in parallel), right next to the two fat battery wires, and I don't see an apparent diode rectifier bridge or a charging transformer as Dave said in this video.
Any idea?
ArthurDent:
The "second biggest transformer in this unit" isn't a transformer at all but probably a dual inductor in series with the A.C. line and has almost zero voltage drop so you put a dead short across your A.C. line, tripping your breaker.
Here's two drawings showing how I think your backup unit works. I didn't show the switching/relays involved but this is a crude diagram of how the charge and carryover functions work. Your backup unit may have separate diodes but the patent shows using the internal diodes in the MOSFETs so I just copied that schematic to illustrate the point. There would also be some sensing circuits and current limiting but this is basically how I think it works. By combining the two windings as an autotransformer they saved some money and because everything is totally enclosed you don't need any line isolation.
In the top drawing the 240V comes and is stepped down to about 24V and the diodes rectify this voltage to charge the batteries. In the bottom drawing things are switched around when the loss of line voltage is sensed so the battery is powering the inverter circuit and you get 240V out of the transformer.
SeanB:
The transformer also looks like the low current section of the windings is done in copper wire, but those parallel pairs used for the 24VAC section look suspiciously like CCA wire, the curse of modern electronics and motors, as it fails quite quickly from insulation failure, breaking from fatigue at the ends, or simply corroding away from the terminals.
Otherwise the transformer at least has a thermal fuse, and also has double insulation between the winding sections, and probably will actually work with the thinner winding disconnected from the thick, though it will definitely run hot.
max.wwwang:
Obviously the circuitry should not be that simple. Fortunately my house wiring is idiot-proof to some degree!
Had a bit more reading of the patent document and more tracing of the PCB, and its topology becomes clearer to me. Overall the unit is faulty but it may still be perfect to be salvaged as a high power inverter with my own Arduino PWM input to the H-bridge. (It seems a bit too complicated to me to re-engineer it with external sensing and signalling circuits based on Arduino, etc.)
It's amazing that the patent document is so well-written and so instructive, so good that it is a perfect reference for anyone who wants to understand how a UPS works in general ("prior art", without this invention) and the new idea of this invention as well!
I hope Dave will make another video dedicated to this patent idea.
max.wwwang:
--- Quote from: ArthurDent on February 17, 2020, 02:56:07 pm ---The "second biggest transformer in this unit" isn't a transformer at all but probably a dual inductor in series with the A.C. line and has almost zero voltage drop so you put a dead short across your A.C. line, tripping your breaker.
Here's two drawings showing how I think your backup unit works. I didn't show the switching/relays involved but this is a crude diagram of how the charge and carryover functions work. Your backup unit may have separate diodes but the patent shows using the internal diodes in the MOSFETs so I just copied that schematic to illustrate the point. There would also be some sensing circuits and current limiting but this is basically how I think it works. By combining the two windings as an autotransformer they saved some money and because everything is totally enclosed you don't need any line isolation.
In the top drawing the 240V comes and is stepped down to about 24V and the diodes rectify this voltage to charge the batteries. In the bottom drawing things are switched around when the loss of line voltage is sensed so the battery is powering the inverter circuit and you get 240V out of the transformer.
--- End quote ---
Thanks very much for the effort you have taken in drawing this up and explaining. I see what you mean. By saying the "second largest transformer" I mean the lower left one in the photo of the PCB. Not the common mode (or differential mode?) noise filter at the right hand side of the photo.
[Based on what I understand from here https://techweb.rohm.com/knowledge/emc/s-emc/01-s-emc/6899 and the wiring, it's common mode.]
Indeed the Brown/Blue wires are connected to the mains input via a relay and it seems like the 24V AC is used somewhere. There are 8 IRF740 MOSFETs close to the traces of this voltage but it doesn't seem like they are in a formation of an H-bridge (with each pair in parallel). It's very clear, however, that another 8 IRF3205 MOSFETs (at the left hand side) are directly hooked up with the battery wires (and the second largest transformer) which I have identified are in a formation of an H-bridge (each pair in parallel).
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