[Amps] Alpha 78 voltage sag

[Will Matney]

*********** REPLY SEPARATOR  ***********

On 3/5/06 at 11:50 PM Martin Sole wrote:

>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?


Most all European countries are 50 Hz if I recall. Japan is also I think, but I think they use a different line voltage.


>
>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.


Most likely. However, I'd check the back of the amp as most of the time they'll put a sticker or label saying which it's for. The manual could be written for both, and still have a 60 Hz one in it. However, you mention it has a Dahl transformer. They had a red tag on the transformer which told what it was, line voltage and frequency. Has this transformer been replaced, or is it the original one? I noticed the regulation by the varied line voltage don't give anything for low line voltage, only high. Generally, a transformers primary is designed to run in between the low and the high. What is the line voltage there, or is it less than 220 or 110 Vac? The filter capacitance has something to do with the regulation too and the total current drawn by the whole supply itself. There is a variance on power supply formula over this. Some say to multiply the total needed current by 1.6, and some say to multiply it by 1.8. A current rise means a voltage drop.

>
>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 at ARRL.NET] 
>Sent: 05 March 2006 21:56
>To: Martin Sole
>Cc: amps at 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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>>  
>>
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Best,

Will