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UPS Transformer Details

Suraj143

Active Member
Why computer UPS transformers using 6.5V & some other UPS using 7.5V-0-7.5V on its driving side.

Why it is not rated for 12V? But its driving circuit using 12V DC supply (batteries).

Can I use 12V modified square wave 50Hz circuit to drive above UPS transformers using Full bridge or Push pull circuit?
 

rjenkinsgb

Well-Known Member
Most Helpful Member
A 12V battery at high load may only give around 11V or even less, then there are resistive losses in the low voltage wiring and components that reduce the final voltage even further.

Also, the output is likely synthesised by a PWM signal and controlled with feedback to maintain the correct output voltage, and enough "headroom" in the duty cycle so the power devices never lock on from cycle to cycle (100% duty cycle).
 

Suraj143

Active Member
Ok thanks.Will the low voltage tapping on the transformer (7.5V-0-7.5V) gets heated if I drive it from a 12V source?

All the DIY push pull inverters using 12V transformers.But in every UPS it has low voltage 7.5V transformers...!!

Because on my testing there will be no load.Just to make sure the correct voltage is producing.Also feedback is not available.

1649894797189.png
 

rjenkinsgb

Well-Known Member
Most Helpful Member
That totally depends on the rest of the unit circuit & how it is built? Is it an off-line or on-line design?
(Switching in with a clunk when AC fails, or permanently stabilising the power through it?)
 

Suraj143

Active Member
That totally depends on the rest of the unit circuit & how it is built? Is it an off-line or on-line design?
(Switching in with a clunk when AC fails, or permanently stabilising the power through it?)
Those are offline UPS.650VA & 1.2KVa the most cheap domestic models.It operates when AC fails.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
If you are using the transformer without connections to the original electronics it should be OK, at least for a short time to test the output & see what you get?
 

ChrisP58

Well-Known Member
Most Helpful Member
The transformer in a typical modified sinewave UPS does not directly make the output voltage. It makes a single DC rail that is the peak output voltage.

4 mosfets in a full bridge configuration then are switched on in timed sequence to create the positive. zero, negative, zero, repeat, output waveform.
 

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