[Premium-Rx] Surges and spikes

[Rick]

G'day from Cairns,
Interesting to read the problems with inrush, surges and spikes being of
concern. Having spent many years in a dirty and uncontrolled electrical
environment I have to admit that inrush damage has always related to the
power section of most equipment, and that many assemblies that need inrush
has NTC resistors or switched series current limiting.
Most modern SMPS are very tolerant of both long term surges and sags due to
their mode of operation. Spikes are their worst enemy.

The problems of sag and surge are both best solved by a true online UPS, one
which rectifies, stores and regenerates a new sine wave for the equipment.
In PNG we used these in a variety of ways including an application in a
remote area where American health researchers had dammed a stream to allow
themselves 4 hours of hydro a day. This "240VAC mains" charged the batteries
in an online UPS (it weighed about 300Kg) that allowed them to run their
PC's for the rest of the day. The UPS was only rated at 750VA, BUT it was a
pure sine wave and lasted for many hours even with this short charge.
Re spikes etc, there was never a connection between the hydro mains and the
equipment.
TRUE ONLINE UPS are now quite rare and most are usually bypassed on overload
or failure by a bypass circuit which may include triacs and relays to
minimize load transfer time and losses. These are an expensive alternative,
but what's being protected is usually worth it.

Most cheap UPS these days have just a simple spike filter in the circuit
MOST of the time and a trickle charger for the battery. They usually produce
a poor sine wave with lots of distortion and VLF noise. In general they
filter the mains no better than a simple LC and MOV filter you might buy for
less than $50. Their backup time is minimal and maybe 10 minutes at half
load is average. They also take maybe 24 hours to re-charge.

MOV's and gas discharge tubes provide fast (nS) reponses and can divert
large energy pulses, but not forever. They should be changed / thrown away
after a storm if you suspect being hit ! MOV's are cheap and can handle huge
energy's but there is a voltage vs diversion current graph that still
impresses plenty of over-voltage on the load equipment. They can be wired
across a mains plug (A-N and A-E) and shoved into the wall socket next to
the appliance for reasonable protection at very low cost.

A very good option is to get a sine tracking filter which clips spikes that
are instantaneously a few volts greater or less than the value of the sine
wave at that time. I can't say how they work, BUT they do and I have used
these in all my workshop's to protect test gear for many years. In Aussie,
Total Power Systems made them, but they have now been bought out by one of
the giants - EATON Powerware.
These aren't too expensive, but work very well - I have always had one on my
WJ. That PSU got to be so old, the electro's failed instead !

Rick