help needed to undurstand the online ups & off line ups

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pradeep.g.belchada

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hello everybody i wanted to design myself a online ups 5kva. the offline ups is a one which iam using for
the computer. in which relay is used for transfer of mains to battery mode. i have a question is online ups is having any internal relay.and i learnt that online ups always takes the power from battery. if mains present then also it takes the power from battery. my question is how it is possible to charger of
ups to charge the battery as well as to give the power to the inverter(converter which is igbt based)
what will be the wattage of the charger. how much current it gives e.t.c
 

It all depends on your recovery time (time between blackouts). If you load is 1 KW, then the charger has to produce 1.1 KW, the odd .1 KW will then charge the battery up again in about 10 Hrs (8?). One thing to be very careful about is that the charger has to have very low ripple voltage, else you get micro charging which ages the battery.
Frank
 

hello chuckey, thanks for your reply.
But still i have one question. is the charger of online ups is smps based or linear transformer based? & in onlineups of 5kva how it is possible to build a 5kva smps using tl494 . i mean the charger section which will deliver the power to the load as well
as charge the battery.

and can somebody give me the usefull links for this online ups like project work and schematic
 

At this power level a SMPS would be a better choice. You would need to have a small linear PSU to fire up the TL494, which would then power the hi power high voltage inverter which is then transformered down and rectified to charge the batteries. Which reminds me, a good choice of voltage for the batteries is 48V as its a "safe" voltage, even though 400V would be technicaly better. Unless your batteries are in a safe interlocked area, they, and their charger should be completely isolated from the incoming mains.
Frank
 

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