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Biuld UPS...

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An entire schematic with parts would fill several pages.
The basics of a UPS are just a two units.

- a charger to keep the batteries topped off.
- a Inverter to change the power from DC to AC.

The charger isn't to complex.

The Inverter is the tricky part.

All an inverter does is create a sine wave (usually 50/60hz)
then feed that sine wave into a very high power amplifier.

If you want 120V AC at 60Hz then build a push/pull (Half bridge)
amplifier that can supply the needed current (or wattage)

The trick is to drive the amp with only the battery power.

A hint, Most UPS systems use 48V batteries (Four 12V's in series)

If you swing that through a transformer forward then negative you can
get 48Vpp or 73Vac.
If your transformer can handle bumping that up 3:5 ratio then you have

If this still sounds like something you REALLY want to try then you will need
to define a few basics first. How much power do you need. How long does the UPS need to run, Is the UPS a pass-though or a fail over design, Will you be driving resistive or inductive loads, and why would you want to build a UPS in the first place?

Answer these and I'll help some more.


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  • 2 months later...

Woirking in the Power Electronics and Power Quality field, I deal with UPS's all of the time.

Even a small 500VA UPS is a very complicated machine.

It is not designed in two parts, it actually has many more pieces than that. Since most modern UPS's are "online" I will include a block diagram for one.


This diagram is over simplified. It is missing the boost circuit and all of the PWM control. Not to mention the fact that the rectifier is a 12 pulse SCR bridge.

Good Luck :)

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