Hello rsgb,
I finally had the right combination of time and assistance to get my
huge Farnell linear variable voltage and current power supply
upstairs into my shack in the last 3 days. I have always had a
sneaking worry that some of my blown FET issues when running at the
limit were perhaps due to the SMPS doing odd things when the load
was suddenly relinquished.
I decided to try the W1VD Wilkinson combiner again on this PSU and
was pleased to see no blown FET's! I think it's "softer" in
transition between load on and off than the big server SMPS which
probably was never intended to serve hard switched loads. Just
guessing though.... I managed 60V at near 40 Amps on the two amps,
but have now hit a new snag. In the combiner the output transformer
is three stacked FT-240 77 material toroids, wound with 2 mm OD
enamelled wire (12 AWG) in a 5 turns primary, 7 turns secondary
configuration, and it gets damned hot. I chickened out at 75 degrees
Celcius on my infra red thermometer. I am unsure if it's the
windings or the cores getting hot, it's hard to tell as each heats
the other of course. The ferrite beads on the Teflon co-ax don't
even get warm. Only other downside to combining is the drain
waveforms are a bit more spiky. Jay, W1VD stated this combiner was
designed to combine two 500 Watt amps, I am trying to combine two of
his 1kW ones, albeit I will run them at a reduced drain voltage in
that format
So, to my questions please. How can I tell if the combiner's
transformer is heating due to core losses, or wire heating? If it's
the stacked core what do you suggest i use instead, I like to
de-rate things as much as possible, even if I go a bit OTT in the
process :) What about wire type and gauge?
Andy G4JNT mentioned abandoning the Wilkinson combiner and using a
single transformer with coupling windings one from each amp's
output, and a single secondary to the LPF. I don't see an earlier
post i made asking what the turns ratio needs to be for this, but I
do occasionally seem to miss posts from Blacksheep. If anyone can
assist in this and suggest a conservatively sized and type of core
to wind it on, with suggested wire type and gauge I'd be very
appreciative.
The amps being combined: http://www.w1vd.com/137-500-KWTX.html
The combiner: http://www.w1vd.com/137-500-500WCombiner.pdf
The LPF: http://www.w1vd.com/LPF.html
Thanks
--
Best regards,
Chris 2E0ILY mailto:[email protected]
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