Lately I've become aware of increasing
numbers of equipment failures in respect of mains supply problems.
Why should this be so?
Years ago, before the National Grid,
UK mains voltage depended on where you lived, so one are might
receive 250 volts DC and your neighbour might be getting 120
volts AC. To cater for the variations one had to firstly ensure
that an AC/DC type equipment was purchased, if in fact you received
DC mains, or if you were on an AC supply (or DC supply) you had
to ensure the voltage tapping arrangement at the rear of the
TV set, for example, was set correctly.
Nowadays, nearly all equipment is for
use on AC mains only.
Now, to consider the harmonisation of
European mains and the unforeseen consequences that have arisen...
Designers of electrical equipment, who used to be familiar with mains circuitry, and the old standards, seem to have been caught a little bit wrong-footed. Once these chaps retire and their old ideas retire with them, all should be well.
. I repaired several
light units designed in Germany and being used by Hampshire Local
Authority. These light units employed a varistor (a protection
device for preventing damage from spikes and transients in mains
Recently I found a wall-mounted "intelligent"
telephone switchboard or PABX had failed after a mains failure.
When the power supply board was removed it was discovered that
the varistor rated at 250volts was short-circuit.
A couple of other points . Equipment using switching power supplies will continue to work normally even when some of their component parts have degraded beyond serviceability but.... cut their mains voltage and turn them on and they will not work. Ostensibly these equipments failed when the mains supply failed, BUT they had already potentially failed, maybe six months earlier.
Finally computer power supplies. These are always of the switch-mode variety and often will cater for virtually ANY mains voltage from around 100 up to 270. They include a circuit which detects whether the incoming mains is like the US type, say 115volts or European 230volts and switch automatically to the correct level. Jolly useful because there's no little setting switch needed and a common design can perform worldwide. Unfortunately, if there's a "brownout" or a period when our UK mains voltage is very low immediately before being restored the circuit which has dutifully selected 115-volts will explode when 230volts suddenly appears across its input.
I wonder how the consequences of the recent mains failure (Jan2009) in nearby Bransgore is managed. From the evidence quite a large voltage suddenly appeared at local mains sockets, and this destroyed all sorts of equipment. In one shop the PABX, one computer, the electric blind, the burglar alarm and the transformer supplying a LAN switch all failed.
How many equipments have YOU got that are permanently connected to 13-amp sockets just waiting for a similar mains problem?
Harmonization of European mains has meant that light bulbs are a problem. The tungsten or halogen types anyway, if not these new fangled low energy or "green" lamps.
Use a UK lamp in France and it will be dim. It'll last a long time but it will be dim. Use a French lamp in England and it'll be very bright. Unfortunately it won't last very long.
If you buy a filament lamp in the UK make sure its designed for use in the UK. In the case of tungsten lamps you may find it pretty difficult in fact to buy such a lamp as they're being outlawed by governments.
If you live in France however, get a UK lamp and it'll last for ages.
These low energy lamps were absolutely useless when first introduced. They took ages to warm up and after stumbling through semi-darkness to find something you'd sometimes turn round and exit empty handed or look for a torch.
Lately designers seem to have solved the problem and most lamps are bright enough straight away.
What about reliability?
These low energy lamps use switching power supplies and if they use capacitors (most, if not all do) this is the weakness as cheap capacitors dry up with heat and fail.
I suspect that capacitors are the salvation for many manufacturers as when they fail one is left with little option, but to throw away and buy new.
This goes for computers, modern TV sets, set-top boxes, DVD recorders as well as low energy lamps.
Repair price: new capacitor 10 pence, labour £75.
Is this built-in obsolesence or what?
The monitor on which I'm looking at this typing has had its capacitors changed once under warranty and once by myself.