Trick APC UPS

[boelle]

basicly i want to trick an apc ups so i can use it as a kind of home battery controller

so i need to able to control when the battery is charged and when the battery is used to drive things, for fun and giggles lets say a fridge

so electricity is cheap during the night and most expensive during the afternoon and evening

my thought was to expand the battery capacity so i could run without mains for 18 hours at 100W load, and then charge them during the remaing 6 hours

ideal i want mains to be connected at all times and only have the alarm go off if mains to the house goes away, and then simply control/tricking the UPS

i found one schematic and still eyeballing it for ways to hack it without the ups know that something is off

pointers and constructive critism welcome

[coromonadalix]

normally many smps have monitoring / supervisor ic's,  you need to hack them / reprogram them ....   but mostly you need code ...

because  if you have say 2 batteries for a 24vdc system inside, the ups know how to calculate power, remaining time etc ...

putting many in parallel  will change the calculations ...

if it was doable we should have already heard about it ...  sorry .. if it was already done, never heard about it

[boelle]

yeah, this is why i'm asking

the calculated runtime does not matter to me as i would do a test to confirm the run time is enough

but yeah, it would require some hacking, i think i will just put a relay in front of the mains input and do a hack to disable the beeper, that i can figure out at least

of course an inverter and batteries could do the same thing, but these APC ups's come up second hand all the time and for far cheaper than inverter+battery+charger would cost

[CaptDon]

Even though night time electricity is cheaper, do you really save anything with the inefficiency of the battery charge cycle plus the inefficiency of the inverter itself while converting battery energy to mains equivalent energy? Sounds like an over engineered net loss to me.

[boelle]

well the savings between the high peak during late afternoon / evening and night is arround 0.50 dkk each kwh, and arround 0.12 DKK the rest of the time

of course its not 100% effective since we have conversion involved and i knew that from the start, but you save a little, the batteries will be replaced with lifepo4 cells so they last longer, but yes higher up front cost

the goal is to save in the long run, and as inflation goes these days every little bit counts