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ZS6CFC > HELP 23.08.07 13:45l 54 Lines 1793 Bytes #999 (0) @ WW
BID : 993875ZS6CFC
Read: DG5YM GUEST
Subj: Re: Switch mode ?
Path: DB0FHN<DB0FOR<DB0MRW<DB0ERF<DB0FBB<DB0IUZ<DB0OVN<DB0GOS<DB0RES<TU5EX<
KB9MMA<CX2SA<ZS0MEE<ZS0DLD
Sent: 070823/1213Z @:ZS0DLD.PTA.GAU.ZAF.AF #:38755 [PRETORIA] $:993875ZS6CFC
From: ZS6CFC@ZS0DLD.PTA.GAU.ZAF.AF
To : HELP@WW
Hello
Especially OM John , about VDRs = Voltage dependend
resistors.
And thats what they are. They change apruptly their
resistance towards zero if their set voltage is approached.
Therefore clamping the voltage on the protected device to a
safe level.
They are designed to "Fail-Safe" and deliver a short when
they go...have expired their useful live.
There is a lot to be had here , but that might be to much
what John wants to know.
As far as I have seen there is no colour code used on them.
They came in red, blue, black and grey as body colour.
They should have stamped on them the working voltage.
The working voltage is the safe one, AC or DC, to put them
across the device. E.G. 220 or 240 for the usual mains
Voltage. Their clamping voltage is much higher, but still
safe for the protected device.
Their phisical size can come in less than a small ceramic
capacitor or in a disk the size of a 2 Euro pice or so.
This determens their clamping power, resistance to repeated
stress.
First determine the operating voltage E.G. Mains
Or say, 16 to 18 volts for a cars 12 Volts system.
They come in a range of about 16 volts to 400 or so.
They should be available at any good components store.
If you have the place in the set choose a bigger one, the
price for one or two should be no objection.
Check olde used Computer power supplies for theese thingies.
And yes, I remeber the real cats whisker.
Ask for a VDR , 240 volts (presumably) and use a bigger one
than was inside.
In the circuit it is assumed that there are fuses ore other
protection devices installed b4 the vdr.
Any questions , ask !
73 DE Sten ZS6CFC@ZS0DLD.PTA.GAU.ZAF.AF
Message timed : 13:35 on 23 Aug 2007
Computer , the species of Calculus Interruptus
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