I want to understand how my UPS inverter works

Thread Starter


Joined May 17, 2016
Hi everyone,

This is my first post on the forum. I'm a computer programmer who has a fascination with learning!

I won't go into depth at the moment as to why, as it's a long story... But I want to understand how the inverter works - to a high level. I've tried to learn about it already, but I need more help.

This is my understanding up to now:

1: 24v power comes in through the anderson connector.
2: It seems to then go through a 40v, 2700uf capacitor. (why?)
3: It then goes to the two heatsinks and the middle legs of four mosfets. (H-bridge)
4: Something happens here (???) and then current flows through 4 63v, 1uf capacitors (why?)to the right legs of four more mosfets.
5: The mosfets give the charge to the outer two heatsinks of the h-bridge. The result is that the current is now AC (but for some reason only 12v instead of 24v - how/why?).
6: From here, the two heatsinks give the charge to a huge transformer.
7: The transformer dups.jpg oes its thing (fairly simple) and the output is three lives and a neutral. (Three taps?) The highest one seems to be 230v ish.
8: Something happens here which I don't understand - but it seems to involve mosfets, film capacitors, relays and transformers. I haven't got a clue what happens here...
9: There's a three pin socket, the middle socket isn't used but the outer two supply live and neutral.
10: The cable which takes those connections seems to have some small capacitors. (smoothing maybe?)

Ok, so the reason why I want to know about this is because I want to upgrade it, maybe run two together in parallel, or do whatever else to double or triple the watt capacity of the inverter. I have a few of these units and I want to make a 3kw, 24v - 240v inverter.

Can you add any details to this?

I'd greatly appreciate anyone's help with this!

Thanks, Antony



Joined Feb 5, 2010
You need to read the data sheet or spec sheet on you UPS. "Sync" ability is what you are wanting. Each UPS will output it's AC, but they will not be in phase with each other. Bridging the outputs will result in smoke and or fire and destruction of the units.
Units that can be synchronized are more expensive and not very common.


Joined Jun 22, 2012
You wont understand anything unless you have the circuit diagram, its just an oscillator using a transformer and push/pull transistors stepping up the dc voltage to AC, so you cant parallel two together unless they are inphase

Thread Starter


Joined May 17, 2016
Thanks, how can I get them in phase? Surely, the mosfets do the phasing? Why couldn't I join two boards together pre-phase then link the outputs together?