Alan Ibbetson wrote:
>>This requires a larger resistor - such as a 10W surge protection type
>>of approximately 10 to 15 ohms.
>
>The 10 or 14 watt ones commonly available from the big UK supply houses
>are wire wound vitreous enamel types, with a maximum voltage rating of
>only 500 or 750v. I guess I'll need several of these in series, not so
>much for the power rating as for a breakdown voltage safety margin.
>Messy, but just doable within the rather cramped confines of the L-4B PSU.
>
The voltage rating on these components is a continuous rating. The green
Welwyn 14W resistors will handle higher voltages for a short time in
glitch resistor service. Three of these 10 or 15 ohm resistors in series
will comfortably handle 3.5-4kV in a crowbar short.
Also remember that the glitch resistor is only one half of the
protection. As Rich says, it's only there to absorb the initial surge
out of the reservoir capacitor. The other half is a fast fuse or circuit
breaker to disconnect the mains.
To adapt a rock-climbers' saying: "If you're scared to crowbar your
power supply, then you don't have real protection."
--
73 from Ian G/GM3SEK
http://www.ifwtech.co.uk/g3sek
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