"Hybrid" Power Supply--is this a bad idea?

[Douglas Furton]

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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[Julian, G4ILO]

Since you're using CW, I think the only possible ill effect of the voltage variation could be a pulling of one of the VFOs causing a chirp  on your signal, if the K2 voltage regulation isn't good enough to take care of it (which it probably is.) The best way to be sure is just to listen to your signal in another receiver.

[Guy, K2AV]

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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[P.B. Christensen]

> "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..."

It should be possible to parallel another 5 Farad of C by adding a DC
connector to the Gamma supply.   For higher duty cycle operations, just plug
the added C into the new DC jack.   For lower duty cycle, the added C would
be left unplugged.

Real estate is pretty tight inside the Gamma supply.  Probably the best
attempt may be a coaxial DC jack and it cannot be accidentally reversed with
the existing Molex output connector.   The Gamma supply works very well with
the K3 and the inclusion of more C would probably make it even better under
higher duty cycle operations.

Paul, W9AC

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[Douglas Furton]

Guy --

> 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.
>

You're right on with the 30 watts key down; I just did the experiment.

It's nice that the KAT100 tunes with 20 watts, and quickly at that.

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[Reinaldo Leandro]

>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.

I have been using the small supply with my K3 all the time. No distortion or
clicks heard or reported on SSB and CW at 100 watts out.
A very neat package when combined with the SPE 1KFA lineal amplifier, that
needs so little input power that even RTTY at 500 W out is of no consequence
to the Gamma Research power supply limitation.

73

Reinaldo, YV5AMH    

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[4Z5TO]

Hi,
The Gamma is my primary PS on my K3 (don't own a K2). Never had a problem with it since I've been using it almost a year now. That being said, you have to understand its limitations: SSB, it's great and gets out 100w; AM, reduce power down to 70w-80w; Digital modes & some high speed CW can drag it down if you don't lower your ERP a bit. You might try uping your CW speed if you can ! Once again this is with my K3, K2 might be different.

The dual voltage capability of the Gamma was one of its biggest selling points for me.

A side note - 25 amp breakers/fuses are a good idea to install on the power lines to the radio since there is no breaker/fuse in the unit itself.