To: <amps@contesting.com>
>Date: Fri, 28 Mar 2003 09:00:31 -0600
>To: "Ian White, G3SEK" <g3sek@ifwtech.co.uk>
>From: dj2001@mn.rr.com
>Subject: Re: [Amps] Filament Inrush Control
>Cc:
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>Thanks for the good explaination Ian, this is the first time I've
>fiddled with step start. I'll leave it alone for now, but the next
>time I open it up maybe I'll try a 12v dc relay which I already have.
>
>73
>Dale K9VUJ
>
>
>
>>>I'm using a 40 ohm and it seems to pull in almost right away. I
>>>still hear a thump when the power is turned on which leads me to
>>>think it's not delaying enough. I wonder if a 100 ohm might be a
>>>better choice. It's a AL80A amp.
>>>
>>>>Depends on the size resistor you use and how big the filter cap
>>>>is in the supply. I select resistor size so that it pulls in
>>>>after a short delay of a second or so. Too large a resistor and
>>>>the voltage will never get high enough to pull the relay in.
>>
>>The delay isn't really a key parameter. The big current surge is
>>over within a 3-4 mains cycles. After that, the current slowly
>>ramps down, so you can short out the series resistor as soon as you
>>like. When the relay pulls in, there is a second current surge - a
>>step-up in current to the normal standby level.
>>
>>The optimum is probably to make the first and second steps about
>>equal. If the series resistor is too low, the first step is too
>>big, but the second step is only small because the capacitors are
>>already almost charged up. If the series resistor is too big, the
>>first step is small but there's a big thump when the resistor is
>>shorted out.
>>
>>A good rule of thumb is to limit the first step to about the normal
>>operating current, which all the components should be rated to
>>handle comfortably. For example, if an amp runs from 230V and draws
>>up to 13A, the surge resistor could be as low as 230/13 = 18 ohms,
>>or maybe 22 ohms. So even at worst, the first surge can never
>>exceed the normal operating current. You might go up to 30 or even
>>50 ohms, but there's no point in going as high as 100 - that only
>>increases the size of the second step.
>>
>>In an SB-1000 (fraternal twin to the AL-80A) I've had good results
>>with a 47 ohm resistor, shorted by a 12V DC relay connected to the
>>existing 12V rail. This is a version of Rich's step-start - it
>>works very well and it couldn't be simpler.
>>
>>No timing components are needed. Everything is supplied from the
>>one big transformer, so whenever the 12V rail comes up far enough
>>to operate the relay, that will be the right time to short out the
>>resistor. In practice this is a small fraction of a second.
>>
>>If I'd had a suitable 33 ohm resistor handy, I might have used that
>>in preference to the 47 ohms - but definitely not 100 ohms.
>>
>>The amp is permanently wired for European 230V mains, and is
>>protected by a fast 10A fuse which never blows.
>>
>>
>>--
>>73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
>> Editor, 'The VHF/UHF DX Book'
>>http://www.ifwtech.co.uk/g3sek
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