48 volt uninterruptible power supply

Have you tried putting a small load (5 watts, maybe) on the output? Perhaps it doesn't switch on if it doesn't detect any connected equipment. If that doesn't do it, try a little more load, but at a guess, it should work with half its rated load (18 watts or so).

If it was meant to be used with equipment that was also supplied from a 48 V battery bank, it might want to see some voltage on its output before it turns on. The idea being that when everything is working, the external battery bank is being charged by another charger and the system voltage is maybe 54 V. When mains power fails, the other charger quits, and the external battery drops to maybe 50 V. As it discharges, maybe to 46 V, this UPS detects it and kicks on to supply power. If the voltage gets too low, it might shut off automatically.

Are there any labels on the strip? If so, what are they?

Since this sounds like phone gear, you might also ask over in comp.dcom.telecom.tech .

Matt Roberds

HI Matt

Thanks for the reply..

Yes - I did wonder about that. ISTR that the switchers in PC PSUs won't run without a load on the output..... I'll try that & report back

Hmmm - I'm not sure about that. I think ths box is certainly from the telecomms field, but I'm guessing that the -48v is intended to replace the usual line voltage from the exchange.... but I'm guessing.

Now that'd be far too easy . Actually - they are labelled - 1 through to 8 - where 7 is also a black label and 8 is also a red label

- so it looks as if they might well be the -48V connections.

That's a good idea - I'll go there in a day or too and see what they have to say on the matter.

Many thanks Matt

Adrian Suffolk UK ======return email munged================= take out the papers and the trash to reply

Hi Matt

Just to follow up on my earlier post - and in case anybody else is searching in thre future for the answer to the same question :-

It seems that this UPS wants to see a link between pins 1 and 6 on the terminal strip. I think this is a kind of 'UPS enable' link - which prevents the UPS from functioning during shipping.

It also wants to see some kind of a load on the 48v terminals (I used a 470R / 2W resistor.

If both of thesethings are present, AND mains is applied, then 48v appears at the output terminals. Subsequently, if the mains then drops, the unit goes into UPS (battery backup) mode.

In short, it works ! - but only if the above conditions are satisfied, and in the right sequence........

cunning, eh ?

Thanks all Adrian ======return email munged================= take out the papers and the trash to reply

Glad to hear you worked it out! (Did you find documentation, or just start playing with it?)

I bet if you start playing with a voltmeter or ohmmeter you will find that some of the other terminals open and close with the mains, and possibly open and close with a good/discharged battery.

Did the red and black terminals (1 and 8) turn out to be the 48 V terminals?

Matt Roberds

Both ! There's a similar unit on the web at

- and it sort of mentions that there's a need for a link between 1 and

But the sequence of operations turns out to be critical..... which caused me some confusion (doesn't take a lot, these days !)

Correct - as per the weblink above

Many thanks for your input - it does help to be able to 'bounce' ideas off another person - my 2 dogs are clueless when it comes to electronics !

Thanks Adrian

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