HPS-1a Gamma Hybrid,Communications Power Supply

[Doug Phillips]

Is anyone using the HPS-1a with their K3?

73, Doug W7RDP
K3 1937
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[Leigh L. Klotz Jr WA5ZNU]

It works at 100W SSB with 10-20dB compression.
For CW at 20WPM you need to go down to 70W or so.
It would not be good for RTTY or MFSK or other 100% duty cycle modes
past 20W or so.  Think of it as a 5A switching supply if you're usign
100% duty cycle.
Leigh/WA5ZNU
> Is anyone using the HPS-1a with their K3?
>
> 73, Doug W7RDP
> K3 1937
> _____

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[Dick Dievendorff]

I have one for casual portable operation. I hear it just a little bit, so I
wouldn't use it at home where a full-sized linear supply is available.

Dick, K6KR



-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Doug Phillips
Sent: Saturday, December 06, 2008 3:48 PM
To: [hidden email]
Subject: [Elecraft] HPS-1a Gamma Hybrid,Communications Power Supply

Is anyone using the HPS-1a with their K3?

73, Doug W7RDP
K3 1937
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[Jim AB3CV]

I use one with my K3/10.

 

73

 

jim ab3cv

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[P.B. Christensen]

> It works at 100W SSB with 10-20dB compression.
> For CW at 20WPM you need to go down to 70W or so.

I've been testing the Gamma supply with my K3 on CW.   It works very well at
95W down to about 15 WPM.  I rarely send below 20WPM and at that speed, the
rig's full 100W can be expected.  Even with this limitation, it's a
remarkable device, given its size.

I'm a bit leery of the over-voltage protection circuits built into these
small supplies.  I added a Vishay 1.5KE15A 15-volt transient suppressor,
reverse-based across the DC output (Mouser P/N 625-1.5KE15A).  The diode is
in parallel with the DC output terminals but a series fuse is inserted just
ahead of the diode.  This is essentially a zener crowbar device that upon
reaching 15 VDC will conduct and blow the DC fuse before any damage is done
to the rig (or one hopes!)

My only nit with the supply is that the AC line cord is hard-wired into the
unit.  An IEC receptacle would have been a nice addition. But in all
fairness to the designer, there's almost zero room inside the enclosure for
the receptacle.  One alternative is to cut the line cord ~ 6-inches from the
cabinet and add an IEC pig-tail.  This offers the benefit of being able to
use an IEC RFI/EMI filter as part of a disconnecting pig-tail assembly.

Paul, W9AC
.

 

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[David Cutter]

Paul

I'm always a little wary of this scheme since using it myself a while ago
and not getting the results I expected.  I would call it a limiter not a
crowbar.

I'm guessing these supplies have a relatively high (compared to conventional
linear regulator) output resistance and when I've done this with other
supplies it doesn't actually blow the fuse.  I'm sure it would still protect
your rig, but simply act as a peak limiter using the fuse and holder and
output resistance to pull the output below the clamping level.  Don't know
what fuse you are using: say it's an ordinary "fast" blow 20A, then you will
need >40A for 30s to blow it by which time the transient has long gone.  The
clamping voltage also depends on the current drawn and could be as high as
21.2V according to the spec. I would have to draw a load line to find out
how that would perform with the supply but that would be only static
conditions.

David
G3UNA

>

>
> I'm a bit leery of the over-voltage protection circuits built into these
> small supplies.  I added a Vishay 1.5KE15A 15-volt transient suppressor,
> reverse-based across the DC output (Mouser P/N 625-1.5KE15A).  The diode
> is in parallel with the DC output terminals but a series fuse is inserted
> just ahead of the diode.  This is essentially a zener crowbar device that
> upon reaching 15 VDC will conduct and blow the DC fuse before any damage
> is done to the rig (or one hopes!)
> >
> Paul, W9AC
> .
>

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[P.B. Christensen]

> output resistance to pull the output below the clamping level.  Don't know
> what fuse you are using: say it's an ordinary "fast" blow 20A, then you
> will need >40A for 30s to blow it by which time the transient has long
> gone.  The clamping voltage also depends on the current drawn and could be
> as high as 21.2V according to the spec. I would have to draw a load line
> to find out how that would perform with the supply but that would be only
> static conditions.

Agree with all your statements.   I tested the circuit ahead of time with a
variable switching supply and a 25A fast-acting fuse (a value I am currently
using with the K3).  At about 15.5V the diode clamped, the fuse blew and the
circuit opened up as intended.  The diode remained good after that fault
event.  Now, how fast did the fuse blow?  According to the info I've
gathered from the Littelfuse and Bussman 3AG fuse datasheets, not fast
enough to ensure 100% protection.   Also agree that some switching designs
will limit current ahead of the zener device and that may preclude the fuse
blowing.  I don't particularly care as I still want that fuse there for
safety purposes.  Again, all this may be trivial in the grand scheme of
things if the Gamma OVP design actually works.

But consider this: as long as the diode is clamping, even if we're waiting
for the fuse to blow or the current of the supply to self-limit, the diode
should still be performing a reasonably fast protection function.  OTOH, if
the diode fails while we're waiting for the fuse to open or the circuit to
self-limit, all bets are off on the usefulness of the diode.

A fast-acting circuit breaker may be better -- or not.  I need to research
the available types of CBs a bit more, including the Airpax types.

Paul, W9AC

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