Thanks to everyone for your imput.
As i sayd i do not want to complicate stuff too much so i will most probably go with a combination between voltage and current reading on the battery charging device, maybe an adjustable max voltage and a current shunt witch will trigger charger cutoff at some set vallue, i will maibe go for i verry small shunt and amplify it's voltage with a OA witch i can also set it to have an adjustable current threshold for the cutoff and maybe some histeresis if needed, i'll decide when i'll get to that, what i understand from your imput is that i must make sure i do not allow the car battery ( if used ) to discharge too much, and i think it can be done easy enough since i only require a few mins of backup.
Now about the UPS's mods, i was thinking of something that might seam strange but still... the UPS will only power switching supplyes ( PC main unit and LCD display ) so i was thinking of dropping the "H" bridge on the outputs, i do not need a 50Hz output, actually do not need AC at all, so i was thinking of just rectifying the power transformer output and maibe a small capacitor after that and go for some 300 or so Vdc on the output, that way i eliminate a stage and so some important looses, what do you think?
As i sayd i do not want to complicate stuff too much so i will most probably go with a combination between voltage and current reading on the battery charging device, maybe an adjustable max voltage and a current shunt witch will trigger charger cutoff at some set vallue, i will maibe go for i verry small shunt and amplify it's voltage with a OA witch i can also set it to have an adjustable current threshold for the cutoff and maybe some histeresis if needed, i'll decide when i'll get to that, what i understand from your imput is that i must make sure i do not allow the car battery ( if used ) to discharge too much, and i think it can be done easy enough since i only require a few mins of backup.
Now about the UPS's mods, i was thinking of something that might seam strange but still... the UPS will only power switching supplyes ( PC main unit and LCD display ) so i was thinking of dropping the "H" bridge on the outputs, i do not need a 50Hz output, actually do not need AC at all, so i was thinking of just rectifying the power transformer output and maibe a small capacitor after that and go for some 300 or so Vdc on the output, that way i eliminate a stage and so some important looses, what do you think?
If your PC power supply is of the active PFC sort, and expects to sync a
resistive ripple current behavior to your 50Hz alternating Voltage. If you
feed it DC, the lack of expected reference frequency might be confusing
to the circuit trying to fix a problem that isn't there.
Active power factor correction is usually to 390VDC with about 10VAC
ripple (due the deliberate ripple current is more than a reasonable cap
size can completely hide). DC voltage similar to your suggestion (after
the PFC) wouldn't appear strange in most supplies.
resistive ripple current behavior to your 50Hz alternating Voltage. If you
feed it DC, the lack of expected reference frequency might be confusing
to the circuit trying to fix a problem that isn't there.
Active power factor correction is usually to 390VDC with about 10VAC
ripple (due the deliberate ripple current is more than a reasonable cap
size can completely hide). DC voltage similar to your suggestion (after
the PFC) wouldn't appear strange in most supplies.
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Shame on me, i have forgot about the PFC...
The PC supply doesn't has PFC so there would be no issue, but i do not know anything about the LCD's supply, it is still in it's waranty so i cannot mess around with it. So it seams either i go for the "H" bridge or i power only the PC's supply from the UPS, it would have been nice to save an entire stage not neccesarily for the simplicity but rather for energy saving...
Thanks for the head's up.
regards.
The PC supply doesn't has PFC so there would be no issue, but i do not know anything about the LCD's supply, it is still in it's waranty so i cannot mess around with it. So it seams either i go for the "H" bridge or i power only the PC's supply from the UPS, it would have been nice to save an entire stage not neccesarily for the simplicity but rather for energy saving...
Thanks for the head's up.
regards.
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