>>>I just helped a friend install Whelens on a LongEZ. The
>>>Whelen book said these exact things. Use the strobes
>>>regularly or the capacitor may need to be reformed.
>>>Instructions are included for reforming.
Larry, can you quote us the specific instructions that
Whelen publishes for "reforming"
>>I have read the same thing. I think it even says this in the
>>owners manual or warrenty info you get with your strobes.
>> I had mine stored for about 3 yrs and they still worked OK so I
>>don't think it is a major problem.
>>This is the classic case of 'use it or loose it'.
> Where did you get your facts for this piece of information? I have a set of
> new Whelan's that won't be used for a while yet. I've never heard of this.
> Maybe Bob Nuckolls would care to comment?
Sure. This is a piece of hagar-lore that has been fertilized too much.
Strobe light systems in airplanes and cameras are brothers. They utilize
a hollow tube filled with xenon gas and fitted with electrodes at each
end of the tube. A high (300-500 volt) dc potential is placed on the
two electrodes. A third electrode is not even stuck through the glass,
it's simply a wire or band wound around the outside of the glass. The third
electrode is "spiked" with a 2,000 to 5,000 volt pulse (from a tiny coil
that acts like an ignition coil for a VERY small engine) the xenon gas is
driven into conduction and begins to emit an intense, white (acually multi-
colored) light.
The ENERGY in that flash of light is determined by the size of an
electrolytic
capacitor and the voltage to which it is charged. The general equation for
energy in a capacitance storage system is C*E*E/2=J where C is capacitance
in Farads, E is volts and J is watt-seconds or Joules. Let's say we're
going to charge a 100 microFarad capacitor to 330 volts. 330 squared times
100 times 10 to the minus 6th power divided by 2 is 5.45 Joules. If the
capacitor is allowed to charge completely between flashes -AND- if the
tube is in good shape, one may expect a 5 joule flash per ignition.
Further,
if one wished to get 10 joules per flash, either the size of the capacitor
has to be doubled -OR- the voltage must be raised by about 40%.
Electrolytic capacitors have been around for about 60 years. Back in the
vacuum tube days, all electronic devices required elevated voltages in
the 100 to 300 volt range and capacitors with high voltage ratings were
very common for power supply hum filtering. Nowadays, photoflash systems
are one of the very few systems that still use this venerable technology.
The capacitors are formed by winding two long, thin strips of alluminum up
in a jelly-roll like configuration with a chemical coating between the
layers.
When the assembly is complete, a voltage is applied which causes chemical
changes to take place making one connection (+) and the other (-) with
respect to applied voltage. The chemistry also becomes the media in which
electrons are stored. It is true that LONG periods of inactivity should
be avoided for this chemistry to achieve and maintain peak performance.
Back in my early amateur radio days, it was not uncommon to find an old
capacitor whos value had dropped by 50% or more due to inactivity. Further,
it's leakage (losses) current went up.
The fix was to apply rated voltage to the capacitor through a large (100,000
ohm resistor) for up to a day. The resistor would limit current flow
while the power supply gently stirred the chemistry back to life. In a
period of time ranging from hours to days, the capacitor's leakage will
have gone down and it's capacitance would be up.
Modern electrolytics have a "shelf life" rated in years. When I fire
up a stobe system who's vintage and utilization are unknown, I'll run
some quick leakage checks on the capacitors just to be sure they're
not going to overheat. Then, I might cycle the strobe system up with
low bus voltage (9-10 volts) for a few hours and then raise it up to
normal over the next four or five hours. This is an EXTREME measure
that I've seldom had to apply. For the most part, if I know a strobe
system has been inactive for many years . . . I'll simply replace the
capacitors. They're probably dried somewhat and they DO have a service/
storage life limit.
For a new system to require monthly attention is absurd. If a manufacturer
recommends this, you need to write and question their capacitor source.
I suspect it's easier to predict the worst and require the most of customers
for care and feeding of their product - it may help at warranty adjustment
time but if I were building stobe systems, I'd use a good quality photo
flash capacitor and ask my customers to put their system into service
within two years.
Any new system should come out of the starting gate just fine from a
storage period of 2 years. If one measures the light output from
a strobe system that's been in storage, the light output may be down
a few percent but it will recover nicely in the first few hours of usage.
Hope this helps chase a few "gremlins" from the workshop.
Regards,
Bob . . .
AeroElectric Connection
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