Repurposing Reillo Dialogvision 1500VA UPS as Inverter Using IR2153 or TL494 Driver?

I have two 2006 vintage Reillo Dialogvision 1500VA UPSs that have failed. Far as I can tell it’s the processor side that is faulty and not the power electronics. Am wondering if I can repurpose them as battery to  mains inverters, ditching all the USB comms, battery charging,  LCD display, mains synchronization, etc.

If I strip out most of the control side can I use a simple inverter driver chip such as IR2153 or TL494 to feed the MOSFETs,? Maybe with some driver transistors between, although these should be already present. Problem Is that I can occasionally mend UPSs and inverters but have never designed one so am not that skilled at this.
From attached pic you can see the switching FETS on large heatsinks at bottom centre. Bottom right is a SMPS for powering control circuits which may have to stay. Top right is transformer which only has 3 leads but think the primary and secondary share one lead. Its leads are labelled AVR which is strange. Unless it is Italian I make that Automatic Voltage Regulator. 48V battery and LCD panel on left. Control circuits are on daughterboards on their edge at right of main PCB.
Rest of main PCB is manly chokes, relays, current transformer  and capacitors.

Found that it contains a KA3525A chip which
is similar to an IR2153 and believed same as SG3525. The circuit around it is similar to  http://www.circuitsgallery.com/2014/01/sg3525-inverter-circuit-pwm.html
but more complex as it's much higher power, with parallel FETs. Also EMC complaint,
which adds chokes and capacitors.  Perhaps
all I need to do is to find the enable line to the IC and turn it on. Also may need
to disconnect the synch line as that will be making sure the IC is synched with
the incoming mains, but not needed in my simple inverter.



All that saves me the difficult job of AC design.

Edward,
I think you are on the right track.I found this data sheet for the KA3525A
https://www.mouser.com/ds/2/149/KA3525A-1010657.pdfPin 10 is the /shutdown which you have to pull high to start it up.Let us know how you get on with this.

Thanks. Somewhat reluctant to
dive in a turn it on and cause a meltdown until I
better understated how the circuit works.I am puzzled that the 30A running
current of the FETs does not seem to carry to the big transformer on any PCB
tracks that I can find that could take that amount of current. Neither are any
of the 5 relays rated that high. So am wondering if some of the other chokes or
transformers are performing a voltage multiplication function despite them not
being very large. The only ones with wire thick enough for 30A are the inductor
second up from bottom and the medium sized (only 42mm wide) transformer at the lowest point, but with a
ferrite core does not seem suitable for 50Hz at 1500VA. It does seem to be wired
much like the transformer in http://www.circuitsgallery.com/2014/01/sg3525-inverter-circuit-pwm.html
   





Am now wondering if in fact this transformer runs
at kHz and charges a 300V capacitor. Then using the HV set of 4 FETs on same heatsinks as a bridge it converts that 300VDC to 230VAC. As that set appear to be controlled
off the processor and not using another KA3525 type device I think I am
against a brick wall as it will be difficult to replicate the processor’s outputs.
I suppose another KA3525 could be used but it would be challenging to get the timing
right so all 4 don’t turn on at once. Also I'd have to find a way get a feedback of the 230VAC to regulate the PWM.

Edward,You might be right about the voltage being converted to 300VDC than to 230VAC. As you said, getting the timing right if the processor is dead would be difficult...

The
2 pairs of HV FETs are run by 2 IR2104 half bridge drivers https://www.infineon.com/dgdl/ir2104.pdf?fileId=5546d462533600a4015355c7c1c31671.
Which only need a logic 1 to turn on a pair of FETS. If I have a simple circuit
that alternately enables one then the other, with a small gap in between, this should
output a modified square wave as in https://www.homepower.com/ac-output-wave-forms
. I don’t need voltage feedback in this arrangement as the KA 3525 has feedback
to ensure the 300VDC (actually 325) is stable. The FET bridge will then convert
this into a hopefully stable 230VAC irrespective of load current as the peak
voltage will always be 325V. Suspect not quite stable as these are not true
sine waves.

Can’t do a stepped
sine wave as the bridge can’t be half on, as far as I can see. But can PWM the bridge
with wider off periods when the sine wave is less high. The chokes will smooth
out the gaps. I can program PIC processors so could arrange this although it’s
a lot of work compared with an off the shelf KA3525 type device.

This discussion has helped me investigate
the faults with the units and found that one has a failed FET. Replacing it with
a different type restores 90% of the functionality so I have ordered new FETs
and will see what that does. Even with the unit working as it is now I can put
a scope on the IR2104 half bridge and find out what waveform
is being driven. 

Great suggestion,Usually I never comment on blogs but your article is so convincing that I never stop myself to say something about it. You’re doing a great job Man,Keep it up.

Very valuable information, it is not at all blogs that we find this, congratulations I was looking for something like that and found it here.

You might be right about the voltage being converted to 300VDC than to 230VAC. As you said, getting the timing right if the processor is dead would be difficult.

Any suggestion? cleanmaster

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