[sdiy] blowing fuses

ColinMuirDorward colindorward at gmail.com
Mon Feb 17 16:43:50 CET 2020


Thanks, Richie, for the detailed explanation, and everyone else. That's
helpful.
Since it's -40 here, I'm just leaving that PSU on while I wait for my slow
blow fuses to arrive! A little extra heat won't hurt.
I'm still lost re Teddy Salad, but google says something about Monty Python.
Colin

On Mon, Feb 17, 2020 at 8:49 AM Sarah Thompson <plodger at gmail.com> wrote:

> Yep, linear supplies can eat current like it went out of fashion. Go for a
> slow blow and you should be fine.
>
> On Sun, Feb 16, 2020 at 9:45 PM Richie Burnett <
> rburnett at richieburnett.co.uk> wrote:
>
>> > How does this magnetized transformer problem work? Doesn't that
>> magnetism dissipate after a short time?
>>
>> If the AC mains voltage happens to be crossing through zero at the
>> instant when the transformer is connected to the mains line, then the
>> transformer core sees asymmetric magnetisation and soon saturates.  This
>> means it loses most of its inductance and the primary current is limited
>> only by the winding resistance.  The larger the transformer the bigger the
>> current surge due to this effect because the windings are thicker and have
>> lower resistance. Low resistance makes the current surge larger and last
>> longer before the transformer core moves out of saturation and returns to
>> normal operation.
>>
>> Some additional resistance in series with the primary of the transformer
>> reduces the magnitude of the current surge and also makes it go away
>> quicker. This resistance can be bypassed to minimise losses once the Inrush
>> event has passed. An NTC thermistor in series with the transformer primary
>> is another common method to limit Inrush.
>>
>> -Richie,
>>
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>>
>
>
> --
> [s]
>


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