DC UPS vs AC UPS efficiency issues

[neazoi]

Hi there, I have owned two UPS at the past. The one was a small 600va with AC in and AC out (mains)
The other was a DC UPS, meaning AC mains in and DC 12v out.
https://www.plaisio.gr/anavathmisi-diktia/asfaleia-trofodosia-pc/ups-power-supply/Turbo-X-DC-UPS.htm

Even though the second UPS had a much smaller battery and it cannot power up big loads, it kept my router up and running for longer than the first one.

Why is that?

I suspect it has to do with efficiency and losses, as in the first case AC is converted to DC and then DC is converted to AC to power the plugs, Which is then re-converted to DC by the router PSU.
Whereas at the second case it is only AC that is converted to DC and that's it.
(the second case UPS has a DC-DC converter inside to convert the 6V battery to 12v)

 

[badea]

DC 12v output UPS is more efficient than one due to AC==>DC==>AC losses in first inverter
you can use internal batteries of your ups to directly connect your router (only if your router supply is 12v and batteries in ups is 12v) in this situation you got maximum efficiency of AC==>DC==>AC UPS

 

[neazoi]

DC 12v output UPS is more efficient than one due to AC==>DC==>AC losses in first inverter
you can use internal batteries of your ups to directly connect your router (only if your router supply is 12v and batteries in ups is 12v) in this situation you got maximum efficiency of AC==>DC==>AC UPS

I am talking about a huge difference in efficiency!
The AC UPS kept my 5W load for one hour max.
The DC UPS with a much lower Ah and V battery is keeping the same load for 4 hours according to the manual.
This is a huge difference!

 

[KlausST]

Hi,

I assume the 5W is far away from the rated power. But the given efficencies are at (or close) to the rated power.

With that low load you should better look for "no load power consumption" ... if given.

You may expect a longer back up time with a more suitable (rated power closer to load power) UPS.


Klaus

 

[FvM]

It's just expectable that a 600 VA UPS isn't effective in supplying a router with 5W. I guess it can be explained by looking at the technical data, the latest by measuring the no-load current consumption.

These PC UPS are designed to deliver relative large power for a short amount of time, e.g. 5 or 10 minutes, efficiency with small or effectively no load isn't a design goal, and not easily to achieve.

Choosing the right UPS is probably not well supported by the bold and simple advertising statements, it needs quite a bit thinking of yourself.

 

[neazoi]

Thank you all for your informative replies!
It seems I made the right choice (by luck) with the DC UPS, for my low power consumption load.
Have a happy new year!

 

[c_mitra]

... I have owned two UPS at the past. The one was a small 600va with AC in and AC out (mains)
The other was a DC UPS, meaning AC mains in and DC 12v out.

To be called an UPS, it must have an energy storage device (a battery) that can take over when the mains is down. It is the battery performance that determines the final overall efficiency.

If your "DC UPS" is only taking 230V AC in and putting out 12V DC, it is simply a basic power supply. It should not be called an UPS.