I have a 120v APC backup UPS that I brought from the USA. I also have a 500watt rated step-down transformer 220->120.

Would plugging my UPS after the step-down transformer work so my devices receive 120 volt battery backup?

And if it works are there any drawbacks?

cant see any reason why not

Do bear in mind that unless your UPS is a true on-line unit that the devices will be receiving power at 110V 50Hz when on mains and 110V 60Hz when on UPS.

I don't foresee any significant issues but it's something worth thinking about.

Do make sure your 110V plugs are well marked to prevent someone inserting them into a 220V outlet.

An interesting question. A 60 Hz off-line UPS, the type sold in the USA for household use, would be operating outside acceptable pass through frequency deviation limits when on 50 HZ. This may cause it to switch to internal battery back-up mode 100% of the time. The off-line UPS was not designed to operate this way. The good news is that the step-down transformer won't mind just as long as it's not overloaded (including any harmonics from the UPS).

It should all work, but having been here for a few years, I am wondering what devices require UPS back-up. 500W is not a lot of power.

It should all work, but having been here for a few years, I am wondering what devices require UPS back-up. 500W is not a lot of power.

How about a desktop computer.

It should all work, but having been here for a few years, I am wondering what devices require UPS back-up. 500W is not a lot of power.

How about a desktop computer.

When we run everything connected to our UPS we're pulling just over 1kW (1250VA @ 0.9 measured Power Factor). That's 4 PCs (2 are headless [no monitors]), 46" TV, home theatre, 50W of LED lighting, 2 fans and 3 fish tanks (lights, air and water circulation).

Good point about the 50 / 60 Hz issue IO, it may not work at all

Probably but:

1. Remember P=IxE. Power=Current x Voltage

Is the transformer you are using big enough to handle the current load? At 220 volts you will exceed the trasformers wattage rating at about 2.3 amps of current. Now I know transformers are normally made to exceed their stated wattage rating...but I don't know by how much...especially the one you plan to use. At 3 amps of curent into the transformer your transformer will be handling (3 amps times 220 volts equals) 660 watts. Even if it works, it's going to get hot. If your load is pulling 4 amps of current through the transformer your 500 watt transforemer is going to have to handle 880 watts through it (and dissapate that heat somehow). So the question is: Will it be able to handle that power without getting to hot?

2. I would guess that whether the UPS can survive the 50Hz vs 60Hz depends on what type of UPS it is. If it merely rectifies the incoming AC to DC which it then uses to charge a battery in the UPS...I guess it won't hurt the UPS. But if he UPS is a switching type of UPS, and it is sensitve to the incoming frequency...that might not be so good.

Probably but:

1. Remember P=IxE. Power=Current x Voltage

Is the transformer you are using big enough to handle the current load? At 220 volts you will exceed the trasformers wattage rating at about 2.3 amps of current. Now I know transformers are normally made to exceed their stated wattage rating...but I don't know by how much...especially the one you plan to use. At 3 amps of curent into the transformer your transformer will be handling (3 amps times 220 volts equals) 660 watts. Even if it works, it's going to get hot. If your load is pulling 4 amps of current through the transformer your 500 watt transforemer is going to have to handle 880 watts through it (and dissapate that heat somehow). So the question is: Will it be able to handle that power without getting to hot?

2. I would guess that whether the UPS can survive the 50Hz vs 60Hz depends on what type of UPS it is. If it merely rectifies the incoming AC to DC which it then uses to charge a battery in the UPS...I guess it won't hurt the UPS. But if he UPS is a switching type of UPS, and it is sensitve to the incoming frequency...that might not be so good.

1. Somewhere in all this discussion power factor (PF) needs to be included since we are talking about alternating current (AC). P=IxE is DC power.

2. The UPS input would need to be rated for 50/60 Hz for it to work at all. See post #4.