[Elecraft] K3: Power cable question

[d.cutter at ntlworld.com]

A regular fuse should blow at 2.6 x the rating within 30s, in other words very slowly.  It's only a short circuit that will normally blow a new fuse.  Have not seen any data on old fuses which might get metal fatigue.  There are faster fuses, but the fastest are rf transistors - on three legs anyway...

David
G3UNA
> 
> From: "Ron D'Eau Claire" <ron at cobi.biz>
> Date: 2008/06/16 Mon PM 06:52:16 BST
> To: "'Elecraft Discussion List'" <elecraft at mailman.qth.net>
> Subject: RE: [Elecraft] K3: Power cable question
> 
> Hi Julius:
> 
> I measure just over 20 Amps under some bands and conditions running the K3
> at 100 watts. Like the K2, I suspect the current draw varies a bit depending
> upon the rig, the actual parameters of some of the transistors, etc. That's
> normal, according to the K3 specs, which rate the current demand at 17-22
> amps at 100 watts in transmit
> 
> IMX fuses have a nasty habit of suddenly opening after being cycled a number
> of times near their rated limit, even the 'slo-blo' type that are supposed
> to offer a little resistance against sudden failure when their current limit
> is reached will sometimes open unexpectedly.
> 
> I've seen fuses operating near their current limits develop cracks so they
> act like thermal switches, causing power to go off suddenly then, after a
> few seconds (while the fuse cools) suddenly come back on, then switch off
> again as soon as a higher current is drawn such as for transmitting.
> Eventually they fail completely, but in the meantime the symptoms can be
> pretty confusing.  
> 
> As a matter of practice I try to allow significant headroom between the
> rating of any fuses and the actual current draw, and I always have spare
> fuses on hand since they can and do fail over time, even if not subjected to
> excessive current. 
> 
> Ron AC7AC
> 
> 
> 
> -----Original Message-----
> 
> Ron,
> 
> I've been using my K2 cable with my K3, including
> contests, without an issue. 
> 
> Considering what the KPA100 will do with my 160M
> setup, in the way of drawing current, I think there is
> enough wiggle room not to worry too much.
> 
> The K3 barely gets warm when I run :o)
> 
> 73,
> Julius
> 
> 
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