I recently came across an uninterruptable power supply my EE department was throwing out due to bad batteries. Everything else in it is good though. However there is not a large transformer inside like I am used to seeing (to step up the 24V modified sine wave from the batteries to the 120V output).

Instead there are two giant inductors (10A, 2.5 mH) and two giant capacitors that look like they are wired in series (4700uF, 250V).
There are also two gigantic BJTs connected to a heatsink (the package has screw terminals, so they are real high current).
A few relays and such as well.

No sure how this thing operates. if you look at the LC resonant frequency of the two big inductors and caps, depending on whether you assume they are two separate tank circuits, or various series/parallel combinations, you can get pretty close to 60Hz.

I am thinking that they are using a tank circuit to provide power, and switching in one of the capacitors or inductors to power the load while charging the other cap/inductor? does this make sense?

 

it's most likely a switch mode power supply. try googling it.

 

it's most likely a switch mode power supply. try googling it.

I am only familiar with "switch mode" power supplies referring to DC supplies or dc/dc converters.

This is a battery (DC) to 120V AC output used to keep equipment running in the event of a power outage or brownout.

I did a little googling on power inverter topologies and came across a patent for ones using a tank circuit where some of the elements were switched in and out of the tank, at least I think. I was only able to view the abstract.

 

What's the make & model?