Clay,
Unless things have changed since I tested the Caddock Thick Film Power
resistors of other than 50 ohms, I would not parallel 20 1000 ohm
resistors to produce a 50 ohm load. Values other than 50 ohms are not
guaranteed to be non-reactive.
I would put 4 strings of 4 50 ohm resistors in series in parallel. Each
resistor mounted with leads as short as possible.
I don't know about the dissipation characteristics of those resistors
mounted in oil, and I suspect it depends on the heatsinking ability of
the resistor mountings when immersed in the oil.
20 100 watt resistors *should* produce a 2000 watt load, but as I
indicated, it depends on the dissipation of the individual resistors and
how fast they can transfer their heat to the oil. It may be necessary
to attach the resistors to a heat sink and immerse those heat sink
assemblies into the oil.
For all those who are looking for a suitable dummy load for high power,
you usually do not have to be concerned about measurement quality
impedance. Something adequate to provide a suitable load for the
amplifier may be all that is needed. Having a precision 50 ohm load is
a requirement for measurement, but not for routine amplifier tuning and
general operating procedures.
73,
Don W3FPR
73,
Don W3FPR
On 12/27/2016 7:16 PM, Clay Autery wrote:
Makes me curious about designing with these TO-220 resistors in the 1000
Ohm size of appropriate power rating... Parallel 20 of them like folks
do on the axials that they put in the can type dummy loads with oil.
Options:
1) 20 in parallel on a finned copper or bare aluminum sink of sufficient
size and then entire assembly in a oil wetted container.
2) Same, but only the finned side of the finned/pinned heat exchanger in
a coolant bath.
I'd like to have a rugged, high power, key down load built from easily
obtainable and replaceable parts.
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