Ballast failures

Some months back, the issue of electronic ballast reliability came up,
and I said we lose quite a few at work. Yesterday, I got talking with
the engineer who replaces them all. He has a box of the failed ones
which he opens out of curiosity to see what went. We rummaged through
them, and the most common failure by far (75%) was not one I had
expected at all. It is that the PCB tracks have flashed over on the
circuit board. This seems to happen in a variety of different places
on the circuit boards. Perhaps a third of them are around the bridge
rectifier diodes, but the others are all in different places, and
not necessarily anywhere near the mains side of the circuit.
Initially I though it might be a short to the case through the plastic
insulator film all the ballasts wrap around the circuit board, but I
took several of them out and the plastic is undamaged and the arcing
hasn't gone to the metal case - it's between tracks on the PCB.
There are several different makes and models of ballast, all
similarly affected. They are around 6 years old. We lose around 2/week.

The second most common is a burned out component on the board, either
a non-polarised capacitor on the output side or the transformer
itself.

In a small number of cases, there is no physical damage visible.

There are also lights in the building with magnetic ballasts.
None of those has ever failed.

 

A good possibility is the use of water based flux for the soldering. That's
basically a weak acid - like citric acid. It's supposed to be rinsed off
after the soldering is done. If traces of it remain, and there's enough
moisture in the air, it's possible for a conductive path to be created -
especially where there's several hundred volts to follow the path.

 

This is a common thing with "switch mode power supplies" which share common
design ideas with electronic ballasts as opposed to analogue or linear
designs or in the case of lamps, magnetic ballasts. My experience over 40
years is that yes, they are more efficient , more compact but if you want
reliability go linear in power supplies and magnetic for ballasts.

 

Come to think of it, I've had a switched mode PSU board in a
video recorder do this. I cleaned it all up, and it's been
working OK for about 10 years since then (but now gets very
little use.)

 

This harks back to the earlier days of electronic ballasts when
manufacturers with little experience with PCBs or semiconductors tried to
learn a lot in a short time. Unfortunately, there were several business
failures in the process as lightning bolts, line surges, overheating and
incorrect applications caused electronic ballasts to fail by the
building-full. It may be comforting to return to the simpler design of
magnetics; but, of course, there's a 30-40% adder in energy costs these days
for the same illumination.

As one who was formerly involved in lamp and ballast product service, I can
say that this situation is scary for the ballast manufacturer; but it's time
for a "six sigma" approach to find out what's wrong. My first thought is
that line surges or overheating are at work and that can go to improper
circuit design or improper application -- or both (which is the worst case).

Potentially, there's a product service claim, of course. What's the
warranty situation? Every ballast manufacturer has a Failues vs. Time curve
for production ballasts. Match that with your installation experience and
that becomes the basis for warranty negotiations. Fortunately, someone has
kept the failed ballasts (hopefully with the install and failure dates).
Not so good is that they've already been tampered with so the manufacturer
won't be able to analyze them properly.

Terry McGowan

 

| This is a common thing with "switch mode power supplies" which share common
| design ideas with electronic ballasts as opposed to analogue or linear
| designs or in the case of lamps, magnetic ballasts. My experience over 40
| years is that yes, they are more efficient , more compact but if you want
| reliability go linear in power supplies and magnetic for ballasts.

Got any URLs to linear power supplies for my PC?