I just use a 20 Ohm 50W resistor on my 2M amp but the relay is a 40A
contactor <G> It goes "thud" rather quick and not a gradual closing. It
keeps the 3CX1000A7 (5V/30A filament) contented as well as the 36 uF
(3x12uF) of 4KV oil filled caps.
Carl
KM1H
----- Original Message -----
From: <TexasRF@aol.com>
To: <paul.kelley.n1bug@gmail.com>; <amps@contesting.com>
Sent: Saturday, March 07, 2009 9:07 AM
Subject: Re: [Amps] Step-start; improved circuit.
>
> Also, there is a series of Dayton timer modules in the W.W. Grainger
> catalog. Most are adjustable over a 10 to 1 time range. 120vac on the
> input terminal
> delivers about 119 vac to the output terminal when the time has
> elapsed.
> They are rated for a 1 A load so driving a relay or even a modest
> sized filament
> transformer is no problem.
>
> The modules are encased in plastic, about 2 inches square and maybe 1
> inch
> thick with a single mounting hole in the center.
>
> I have used many of them for step start as well as warm up timers and
> have
> never had a failure.
>
> Cost is about $20. It doesn't get much easier than this!
>
> 73,
> Gerald K5GW
>
> In a message dated 3/7/2009 6:56:13 A.M. Central Standard Time,
> paul.kelley.n1bug@gmail.com writes:
>
> Mark K5AM wrote:
>> Some step-start circuit troubles have been reported recently.
>>
>> The step-start circuit usually seen can sometimes cause trouble; the
>> problem is that the relay coil is part of the RC timing circuit.
>> This
>> means that as the capacitor charges it first reaches a point where
>> the
>> relay armature just begins to move slowly, and then finally the
>> relay
>> closes. Not a snap-action arrangement. This slow closing can cause
>> contact burning and eventual failure.
>>
>> To avoid such troubles, I use a step-start circuit with an op amp
>> timer. After a one second delay, full voltage is instantly applied
>> to the relay.
>>
>> The circuit is described in a web article
>> "Overload Protection for High Voltage Power Supplies"
>> posted for download at www.zianet.com/k5am. The article
>> also includes ideas for other aspects of high voltage power
>> supply design.
>
> I have to agree whole heartedly. While many conventional step start
> circuits have worked flawlessly for years, even decades, I was never
> completely satisfied with any arrangement that had the relay voltage
> slowly ramping up. It just didn't seem right to me.
>
> Eventually I came up with an op amp timer very similar to that in
> Mark's excellent article, and have been using it ever since, in
> several HVPS projects. This also makes it easy to customize the step
> start delay for any given situation. I actually used a 1M trimmer
> where Mark has the 680K resistor, so the delay is adjustable.
>
> 73,
> Paul N1BUG
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