Dear Andy, Mal, LF Group,
At 11:32 11/06/2002 +0100, you wrote:
A T200 core does intuitively seem a bit small, but the theory says it should
work
Well, up to the point that it won't saturate - but that is just the first
hurdle. I was slightly amazed to find the micrometals catalogue at work in
my filing cabinet, containing core loss data for -2 mix amongst other
things. There are 2 versions of the T200 toroid, one is 14mm thick, the
other is 25mm. Lets assume Mal is using the big thick one. The area of this
is 2.32cm^2, using Andy's figures, the flux density works out to 50mT or
500 gauss. At 136k this results in core loss of 0.44W/cm^3, and with a
volume of 30cm^3 the total core loss is about 13W. The thinner core is
about double this. By itself, the 13W will result in a temperature rise of
about 50 or so degrees C - the resistive loss in the windings will add at
least a few watts and another 20deg C or so to this. By the time you have
added some more temperature rise due to being in a box and the insulating
effect of the PCB, the actual operating temperature will be way over 100deg C.
I think stacking 2 of these cores would give a more reasonable temperature
rise - but the power dissipation would still be more than the original
air-cored coil - take your pick!
Cheers, Jim Moritz
73 de M0BMU
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