This is interesting information, together with the later note from Will
suggests a real need to be cautious about equipment designed for 60Hz only
supplies when run pretty much anywhere other than in the US, maybe a couple
of other places that use 60HZ?
Ok, the Alpha 78 has a transformer with two 120 volt windings on the primary
side. Wired either series or parallel they allow connection to either 120
volt or 240 volt systems. Looking at the manual for the Alpha 78 the
specification page states 220-250 V @ 10A max or 110-130 V @ 20A max., 50-60
Hz single phase. I guess that means it should be okay on 50Hz.
Right now I am more concerned as to why on load the AC side of the secondary
drops about 90 volts but the DC sags 350 volts. That seems a big difference.
73
Martin
-----Original Message-----
From: KD7QAE [mailto:KD7QAE@ARRL.NET]
Sent: 05 March 2006 21:56
To: Martin Sole
Cc: amps@contesting.com
Subject: Re: [Amps] Alpha 78 voltage sag
Martin,
If the XFMR is designed for 60Hz only, you will hae excessive core losses
and high primary current as the core is being driven too close to saturation
on each cycle. The primary current will manifest itself in both heating and
voltage drop. The core losses will cause core heating. All in all a bad
setup. If this is the case, you will have to lower the primary voltage to
5/6 of a 60Hz standard value and run on the matching tap the primary has
(208, 230, 240) or you could buy a 50Hz rated transformer.
Tomm
Martin Sole wrote:
>I had a good number of replies to my questions concerning likely output
>for the Alpha 78 and in the process uncovered what is clearly a problem
>here with the AC supply line. The distribution is done from the breaker
>panel to the wall outlet with 2.5mm. Breaker panel to main breaker is
>35mm and the feed from the street is in what looks like the next size up
from that.
>
>Measured about 10 volts sag in the AC line at the wall outlet with the
>amp key down 1.5K out. Sag drops to 2.5 volts when I use 6mm cable Also
>measured about 90 volts AC sag on the secondary of the transformer in
>the SSB position. Seeing approximately 350 volts sag at the output of
>the power supply filter. Why so much?
>
>Measured the ripple by looking at the voltage across the 180K HV
>metering resistor. Saw approx 8 volts pk-pk off load rising to approx
>25 volts pk-pk at full output. Added a bank of 6x470uF capacitors and
>the ripple reduced to approx 6 volts off load and neglible on load, can
>see the 20 metre RF getting in the scope but that's all. DC still sags down
350 volts on load.
>Changed the diodes out replacing the RCC1733 with a string of
>3x1N5408's in each case, no difference, DC still sags 350 volts.
>
>If this is about right can anyone explain why? Others have indicated to
>me that they see approximately 200 volts of drop between no and full load.
>Think I could maybe accept that but not yet cofortable with 350 volts
>drop, Any ideas?
>
>Just as a thought , not that it would make that much difference but I
>really couldn't say. Electrical supply here is 50Hz not 60Hz, would
>that be enough to render the transformer a Peter Dahl 2.4KVA Hypersil
>meant for 60 Hz, a little on the wimpy side?
>
>
>73
>Martin
>
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