The switching relay on the input side of the battery-protected circuit on my Off-Line type of Belkin UPS which supplies my desktop with power has decided that now is the time to go on the blink - literally. With the AC power on, and a load on the battery protected circuit, the relay continually switches between AC mains power and battery. The desktop powers up OK, but the Belkin software is showing AC failure and the input power gauges are going up and down like Tower bridge.

If I turn the power off at the mains, and apply a load to the the battery supported circuit it works perfectly.

Similarly, with the AC power on, the surge protected circuit i.e. the one which is unsupported by battery, works fine.

Unit is five years old. Showed no prior symptoms of failure. Can't believe that the relay points have just suddenly gone.

Any ideas,

Nick,

6/06/08

Problem solved.

It appears that since last using the desktop on Thursday, the mains plug connected to the UPS had become marginally dislodged from its socket and in effect was just siting on its three-pin socket ?

I'm not sure what caused this to happen, perhaps it had worked loose over a period of time.

In consequence it was making intermittent contact so that the mains supply became discontinuous. The UPS was detecting the intermittent supply and so was switching back and forth between mains and battery supply.

Pushing the mains plug in so that the socket fully gripped the pins (Only an eighth of an inch) solved the problem.

Anyway, I, of course, didn't spot this first off because the plug was connected to a plug extender, and had its pins facing toward the ground, so that the very slight gap between plug and socket wasn't visible.

I suspect the fault lay in the design of the plug, which allowed the pins to ease out over time. All of the plugs and sockets foreign sourced - an object lesson, if you want quality and reliability buy MK.

All very annoying !

Nick,

7/06/08

The problem has reoccured.

All the mains-in AC power cable connections check-out OK, so the problem appears to be inside the UPS.

Basically, on this Belkin unit (FSH500uk unv) power from the mains enters the unit via a single cable and then the circuit divides. One side supplies 3 unswitched

AC power sockets, which are surge protected and always on. The other side feeds through a rocker switch to a further 3 AC power sockets which, in the event of AC mains failure are switched onto a rectified internal DC supply from a battery.

The three AC ouput sockets on the unit which are powered by an unswitched line are OK and the LED which is powered from this line is on (green) to indicate that surge protection is in operation. However, the three sockets running off the switched AC (Battery protected) line are dead, even with the AC-in switch positioned "On", and the "Power on" LED which should be illuminated green is dead.

Taking the back-off the unit, I found that the battery, which is rated 7.2AH 12v, delivered 12.5v and 1.89A with a multimeter across the terminals.

Are these levels indicative of a failed cell(s) in the battery ? - its a sealed unit so a hydrometer can't be used, or is the failure on the switched cicruit electronics ?

-the instruction manual says the battery charges as long as AC mains is live.

Nick,

11/06/08

Might be best to get a new one. They don't last forever.

I doubt it's a failed cell.

The battery will be gel anyway, so no hope for a hydrometer.

Sounds like the sensing electronics have packed in. Since it all works on battery power, the inverter is OK.