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 In the trenches.
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 Return to top of page · Post #: 1 · Written at 7:40:32 PM on 25 January 2015.
Labrat's avatar
 Location: Penrith, NSW
 Member since 7 April 2012
 Member #: 1128
 Postcount: 300

Dear Members.

I thought that I would relate to all this story, because it is nowadays quite rare to experience this situation.

During the week I was called to attend a site with, “Issues.”
I found the equipment exhibiting a fault that I have never before encountered during the past seven years of servicing said equipment over hundreds of sites.

At first I was a little taken aback to be presented by such a fault, but I gathered my composure and replaced the one piece of equipment that could be accessed and seemed to be capable of producing the symptom. This did indeed improve matters but was still far short of the performance that I expected. As the Abloy keys that I have did not fit the riser door I had to wait until I could arrange for someone to open it for me. Once I did have the door open, as a first step measured all the voltages that I could. The results were mixed. Some were spot on, others low, but not real low.

Trusting ones test gear is the best way known to man to get egg on ones face, and as my multi-meter is thirty years old,
(a transitional model Fluke, the one between the side mounted push buttons and the ones with the push button in the middle of the rotary switch) I figured it prudent to measure a known good reference, the mains.

This I measured twice as it measured 167.3 volts, about seventy-three volts low. No wonder things were bad. The pieces of equipment that were switch mode operated quite happily. The other equipment struggled on and gave near correct output voltages until loaded. They then dipped and tried to recover. I would never have thought that the equipment would perform so well with such a low input.

Because I could not correct the incorrect mains voltage I reported the matter to the person responsible for the management of the building. Then I went to inform the client. In her unit I measured the mains voltage, which was 254vac. Fourteen volts high.

When I was growing-up, from time to time, we would have brown-outs and would and would watch the TV as the picture became smaller and smaller until the picture broke up and disappeared.


 Return to top of page · Post #: 2 · Written at 7:48:32 PM on 25 January 2015.
Brad's avatar
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6573

254 volts isn't uncommon in Australia and is only a volt outside tolerance. I'd be more worried about the 167 volt scenario. Either the circuit involved there is suffering a big voltage drop (perhaps from being overloaded or the circuit's wire gauge is too small) or there is a poor joint somewhere.

Modern switchmode power supplies are set to operate between 100 and 250 volts, covering the nominal mains voltages of most countries. Most sense the voltage automatically and adjust themselves as necessary and most don't even have a voltage selector switch anymore.

A valve a day keeps the transistor away...

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