Posted by
Guy, K2AV on
Jan 25, 2010; 1:33pm
URL: http://elecraft.85.s1.nabble.com/Hybrid-Power-Supply-is-this-a-bad-idea-tp4453756p4453917.html
Key-down tuning for QRO is a no-no, as is RTTY. They spec the power
supply at 22 amps -->> 25% duty cycle <<-- or 5 amps continuous. 12.5
volts times 5 amps is 62.5 watts. If one figures in the usual 50%
efficiency of transistor rigs, that's 31 watts brick on key, a figure
that will be need to set as a tuning power limit in an auto-tuner rig.
Probably better to say 25 watts continuous and enough to drive an amp
that drives with 50-60 watts, IF the amp can be tuned at half power.
Otherwise, tuning the amp would require a pulser or string of dits.
For a suitcase situation it would be ideal, just back the power off.
What I don't understand is why they didn't double up on the cap,
upsize a few things and get it to 22 amps 50% duty cycle.
But in its current miniature version, I've toyed with the idea of
deconstructing the power supply and reconstructing it inside an EC2
with a KPA100 as a companion to my going-to-stay-that-way 10W battery
K2.
73, Guy
K2 #1239 K3 #1239
On Mon, Jan 25, 2010 at 7:55 AM, Douglas Furton <
[hidden email]> wrote:
> I've been running my CW only K2 using the "hybrid" power supply designed by Fred (K3GQ) at Gamma Research. This tiny power supply packs a big punch because it is loaded with about 5 farads of capacitance. The capacitors provide the high current surges needed during the high-power portions of the duty cycle, but recharge during low-power portions of the duty cycle. You can read more about this thing at <
http://www.gammaresearch.net/hps-1a.html>. In all ways, I've found this power supply to be an excellent piece of work (and I haven't noticed any RF hash).
>
> Now that I've added the KPA100/KAT100, in a separate EC2 enclosure, I'd like to continue to run this power supply. But I'm wondering if anyone thinks this is a bad idea.
>
> The potential problem lies in the fact that the power supply is in a sense not well regulated. While it never provides a voltage > 13.6 V, the voltage sags on TX as the capacitors discharge. Fred has designed this power supply so that it can power most rigs at 100W (CW or SSB, but my work is only CW) before the voltage sags below ~12V for normal CW/SSB duty cycles.
>
> I've measured the voltage sag at the output of the power supply with an oscilloscope and find that when I send CW at 15 WPM into a dummy load at 100W with my K2, the power supply sags as low as about 11.9 volts on TX. Of course, the voltage recovers quickly between the dahs and dits as the caps recharge, but again, never even momentarily goes below ~11.9 volts. Also, as I noted above, the power supply never provides a voltage > 13.6 volts.
>
> I could acquire and attach an o-scope trace, if that would help anyone make up their mind.
>
> I'm wondering how this rapid supply voltage variation might affect the K2? I've not noticed any problems, but I'm not that bright.
>
> Doug
> K8EXB
>
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