[Heathkit:Yahoo] How much capacitance

[Bob Burns]

Hi Paul
 
Perhaps I can offer my own thoughts from a slightly different  perspective?
 
In principle I agree with what you have said. I also think that any item  
with a large switch on surge should be protected regardless of whether the  
electrolytics have been increased in value or not. Older units are 
increasingly  difficult to maintain because of poor availability of replacement parts 
and I  have a number of Heath SB-Line units that I want to keep running as 
long as  possible.
 
Perhaps what is needed is a low cost surge protector that can either be  
mounted and wired inside the PSU enclosure or outside in a protective case  
with its own mains switch and fuse if you are a purist and do not want to  
change the original wiring or mechanics in any way. All that is needed is  an 
optional enclosure/fuse/switch, a large wattage series resistor, a relay and  
a simple network to provide the equivalent of a few seconds delay. The  
series resistor and fuse would need to be appropriate to the final load.  The 
delay mechanism could be as simple as detecting when the mains on the load  
side of the series resistor had risen to say 50% of normal when the resistor  
could be shorted out by the relay energising so no actual timer would be  
required. This could be accommodated in a small die cast box as an external 
unit  or a PCB to be mounted internally. The series resistor may need some 
cooling in  the event of a fault condition or an overheat detector with a 
power off.  Whatever is considered safe and appropriate.
 
Anyone up for a quick design job?
 
73

Bob 

G3OOU
G-QRP  6907
Joint site with Crystal Palace Radio & Electronics Club: _www.g3oou.co.uk_ 
(http://www.g3oou.co.uk/) 
My technical site: _http://www.qsl.net/g3oou/_ (http://www.qsl.net/g3oou/) 

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