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Re: Copper Coupler Temp (SG)
Ted,
It ultimately depends on how much airflow you use to cool them. The heat
generated by your gaps is a function of peak tank current, operating
frequency, the effective break rate of your system, and how well it's
quenching. The power that's dissipated by the sparkgaps goes up linearly
with tank current, break rate, and spark duration (i.e., lower operating
frequency) - and all of these tend to scale upward as you make your
system larger.
Each firing spark gap behaves much like an arc discharge, dropping
around 100-200 volts once heavy tank current begins flowing. So,
doubling the tank current or breakrate, or halving the operating
frequency will cause about a 2X increase in gap power dissipation. For
planning purposes, you can assume that roughly 15-25% of your system's
input power will be "burned up" as waste heat in your spark gaps. This
estimate reflects efficient power transfer to the secondary with
quenching occuring on the 1st or 2nd notch. However, if your system's
not "breaking out", then this may jump to over 90% as the bang energy
cycles between primary and secondary and back, heating your gaps instead
of incinerating the air with streamers. The heat from the gaps must be
removed at a comparable or faster rate in order to keep your gap
electrodes from cooking.
A static vacuum gap which forces high-velocity air between the adjacent
copper tubes can run for extended periods with the electrodes only
getting moderately warm to the touch. However, forget to turn on the
vacuum cleaner motor and they'll overheat in 5-10 seconds on a 3 KVA
system. A TCBOR gap (cylindrical in PVC Pipe with a muffin fan for
cooling) will begin overheating at a power level of 2-3 KVA, since the
relatively low amount of cooling air is insufficient to take away the
heat generated by the gaps. And, if you turn off the muffin fan the gap
electrodes will overheat in seconds.
You CAN run static gaps at very high power levels - the trick is simply
to remove the heat at a faster rate than it's being generated. Larger
diameter copper tubes have more surface area that aids in cooling (the
same principle as adding fins on heatsinks), so gaps made from larger
tube diameters will tend to run somewhat cooler. A properly designed
static gap should see relatively little temperature rise (perhaps 30-50
degrees F). A rise of several hundred degrees implies that the gaps are
not getting sufficient air cooling.
Hope this helps, and safe gappin' to you, Ted!
-- Bert --
--
Bert Hickman
Stoneridge Engineering
http://www.teslamania-dot-com
Tesla List wrote:
>
> Original Poster: "Ted Rosenberg" <Ted.Rosenberg-at-radioshack-dot-com>
>
> Hi all:
> I am not sure if anyone has asked the following:
>
> What is the typical operating temperature of 3/4" or 1" or 1.5" or 2" copper
> coupling tubes used in a static gap?
> More or less than, say 500 degrees F? I'm assuming operation for 5-10
minutes.
>
> Thanks
>
> Curious in Cowtown
>
> Ted