[Amps] soft start, how to determine if needed?

[Alex Eban]

Yes, there is.
The most endangered part are the rectifiers. The specification includes a
current value called " non repetitive peak current", usually with a time
limit of about a cycle or so. Use that value, assume a dead short at the
capacitors and calculate a value for the resistor, such that the peak
current at the peak of the input waveform voltage is less than this current.
Keep in mind that the transformer action changes the current so that 1
ampere at 2500V translates to 10 amperes at 250V!
At 240 VAC, the resistor comes out around 1 ohm or less so that it can be
wired in series and left there, even without a shorting relay. Use a wire
wound resistor, such as Dale's and install on a heat sink.
Alex	4Z5KS

-----Original Message-----
From: Felipe Ceglia [mailto:felipeceglia at gmail.com] On Behalf Of Felipe
Ceglia - PY1NB
Sent: Wednesday, February 24, 2010 2:22 PM
To: Edward Swynar
Cc: Alex Eban; Amps at contesting.com
Subject: Re: [Amps] soft start, how to determine if needed?

Folks,

Thank you for your replies.

Is there a way to calculate what R values and relay contact Amp rate should
I need?

Also, if the primary is feed with 110+110 volts, I should use one R on each
primary leg winding, right?

73 tu,

Felipe - PY1NB




Edward Swynar wrote:
> Hi Guys,
>
> FWIW, I had to re-build my rectifier stack at least twice before I 
> finally incorporated a soft-start / step-start scheme in the primary 
> of my B+ transformer...
>
> The p.s. is a full-wave rectifier job, applying 2.5 KV to a pair of 813s.
>
> Since incorporating the scheme, I have had no further troubles in this 
> regard.
>
> As someone said before me, it's "...cheap insurance", and not all that 
> daunting a task to add-in, even after the fact.."
>
> ~73~ de Eddy VE3CUI - VE3XZ
>
>
> *******************************
>
> ----- Original Message -----
> From: "Alex Eban" <alexeban at gmail.com>
> To: <felipe at dxwatch.com>; <Amps at contesting.com>
> Sent: Wednesday, February 24, 2010 3:39 AM
> Subject: Re: [Amps] soft start, how to determine if needed?
>
>
>   
>> As far as possible, USE ONE!!!!!
>> First, the cold resistance of a tube's filament is as low as one 
>> tenth of the warm filament, so inrush currents can reach 10 times the 
>> operating value.
>> Second, inrush current of a HV power supply can reach a hundred 
>> amperes, measured with a Tektronix current probe. If nothing else, 
>> that current can weld the switch contacts!
>> I don't have to tell you that the stresses on the rectifiers don't do 
>> any good and the capacitors are also badly stressed.
>> Today, almost all integrated circuits intended for power supply 
>> control incorporate some form of soft start circuitry, precisely for 
>> reducing
>>     
> these
>   
>> stresses.
>> Use step start or soft start, it's very cheap insurance.
>> Alex 4Z5KS
>>
>> -----Original Message-----
>> From: amps-bounces at contesting.com 
>> [mailto:amps-bounces at contesting.com] On Behalf Of Felipe Ceglia - 
>> PY1NB
>> Sent: Tuesday, February 23, 2010 3:34 PM
>> To: Amps at contesting.com
>> Subject: [Amps] soft start, how to determine if needed?
>>
>> Hi folks,
>>
>> Regarding this recurring topic about soft starting...
>>
>> How can one determine if it is needed or not?
>>
>> Should HV be soft-started as well?
>>
>> What would be the best math to determine the soft-start dumping
resistors?
>>
>> 73,
>>
>> Felipe - PY1NB
>>
>> --
>> Felipe Ceglia - PY1NB
>> ---------------------------------------------------------------------
>> -----
>>     
> --
>   
>> ---------
>> PR1T team member /// Rio DX Group member /// Araucaria DX Group 
>> member http://www.dxwatch.com /// http://reversebeacon.net /// 
>> http://riodxgroup.dxwatch.com
>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>     
>
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>   

--
Felipe Ceglia - PY1NB
----------------------------------------------------------------------------
---------
PR1T team member /// Rio DX Group member /// Araucaria DX Group member
http://www.dxwatch.com /// http://reversebeacon.net ///
http://riodxgroup.dxwatch.com