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KB2VXA > TECH 27.11.03 08:06l 59 Lines 2970 Bytes #999 (0) @ WW
BID : 16045_WT3V
Read: DB0FHN GUEST OE7FMI
Subj: Re: DC2FR > 12VDC lamp inverter
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<7M3TJZ<JE7YGF<LU6DTS<N1UAN<WB1CHU<
K1UGM<W1ON<W1ON-5<K1UOL<K1UOL<WA2SNA<KC2COJ<WT3V
Sent: 031127/0153 16045@WT3V.#CNJ.NJ.USA.NOAM $:16045_WT3V
From: KB2VXA@WT3V.#CNJ.NJ.USA.NOAM
To : TECH@WW
Hi Wolfgang and readers,
I agree with everything but one, there has never been a need to preheat
(or heat) the electrodes provided the starting pulse is of sufficient
voltage to arc the lamp. Once ignited the arc heats the electrodes as it
does in any arc lamp, carbon or metallic vapor. Maybe I should say carbon
vapor because that's what the hot glowing plasma is anyway. (;->) Then to
in high pressure sodium vapor lamps (HPS) the electrodes are "cold",
simply platinum buttons. They contain a small bit of metallic mercury
deposited on the electrodes and a 4KV pulse arcs the lamp flashing the
mercury and striking the arc. It operates as a mercury vapor lamp until
it gets hot enough to vaporize the sodium coating also on the electrodes.
You may have noticed them starting up looking a sputtering blue until
they start to turn yellow. When power is removed and the lamp cools,
first the sodium is redeposited on the electrodes and then the mercury
being it has no other metal to attatch itself to, the envelope being
fused quartz. I hope this explanation of the HPS lamp helps you to
understand the operation of the mercury arc lamp (flourescent or HID) to
which it is related.
The only difference with the "standard" flourescents operated from
inverter ballasts is the operating frequency which is usually between 100
and 200Khz. This HF operation allows greater ionization with far less
current for economical purposes. Otherwise, like at AC mains frequency
the actual operating voltage is essentially zero, it's all current. Any
arc is about the closest thing to a short circuit as you can get which is
why inductive (reactance) ballasts are most commonly used. An inductor by
it's nature is the most efficient way of limiting AC current.
Now if you really want an education by way of comparison, go down to your
local auto shop and see the spark analyzer in operation. For those who
lack the "motorhead" mentality (;->) it's a specialised oscilloscope that
displays the waveform across the spark plugs. It looks like a huge spike,
20 to 50KV worth which when the arc is struck flattens to a couple
hundred volts and ends in a damped wave when the arc extinguishes. Now if
you put a scope with a HV probe across a flourescent lamp you;ll see
something similar but not nearly so dramatic.
Ah, electric arcs are so much fun! I think I'll go play with my Jacob's
Ladder and if I really want to drive the neighbors batty I'll switch on
the Tesla coil. MUA HA HA HA HAAAAA! Igor, what did you do with the kites
THIS time? Now go get them out of the tree, we have WORK to do!
73 de Warren, KB2VXA@WT3V.#CNJ.NJ.USA.NOAM
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Message timed by cesium laser: 02:01 on 2003-Nov-27 GMT
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