Hi Chris,
I have a tool by DJ5IL here which predicts around 60°C for the cores
(excluding heat caused by the winding)
and ca. 480 Gauss flux density.
73
Clemens
DL4RAJ
>-----Original Message-----
>From: [email protected]
>[mailto:[email protected]] On Behalf Of Chris Wilson
>Sent: Saturday, May 13, 2017 12:26 PM
>To: [email protected]
>Subject: LF: Combining LF amps revisited
>
>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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