K3: Power cable question

[Julius Fazekas n2wn]

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




Julius Fazekas
N2WN

Tennessee Contest Group
TnQP http://www.tnqp.org/

Elecraft K2/100 #3311
Elecraft K2/100 #4455
Elecraft K3/100 #366
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[David Cutter]

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" <[hidden email]>
> Date: 2008/06/16 Mon PM 06:52:16 BST
> To: "'Elecraft Discussion List'" <[hidden email]>
> 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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[Brian Lloyd-6]

On Jun 16, 2008, at 9:59 PM, <[hidden email]> <[hidden email]
 > wrote:

> 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...

Most people don't know that the purpose of a fuse or circuit breaker  
is to protect the power distribution wiring, not the electronic  
component itself. Wire will carry a surge without too much temperature  
rise. The idea is that the fuse will blow or the breaker open before  
there is any chance of damage to the wire.

This means that a fuse or breaker cannot protect your active devices.  
If you want that level of protection you need something like a power  
supply with fold-back current limiting.

Brian Lloyd
Granite Bay Montessori School          9330 Sierra College Bl
brian AT gbmontessori DOT com          Roseville, CA 95661
+1.916.367.2131 (voice)                +1.791.912.8170 (fax)

PGP key ID:          12095C52A32A1B6C
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[David Cutter]

Glad you raised that point, Brian.  In my Sunday school classes I ask the
question: "what does the fuse protect?"  It's  a revelation to all when I
give the right answer.

On our 240V distribution system, a melted cable can lead to a severe shock
hazard and I'm guessing that in the 110V centre-tapped system since the
shock hazard is so much less, the next major hazard is fire, so, I've often
thought that we are protecting against 2 hazards, each with a different
emphasis in each case.

In a 14V dc distribution system there is no real shock hazard (SELV), so the
remaining hazard has to be fire, so, a slow fuse is not a problem, since
heating effect in the wiring is so much slower.

Anyone care to comment/add?

David

>
> On Jun 16, 2008, at 9:59 PM, <[hidden email]>
> <[hidden email]
> > wrote:
>
>> 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...

>
> Most people don't know that the purpose of a fuse or circuit breaker  is
> to protect the power distribution wiring, not the electronic  component
> itself. Wire will carry a surge without too much temperature  rise. The
> idea is that the fuse will blow or the breaker open before  there is any
> chance of damage to the wire.
>
> This means that a fuse or breaker cannot protect your active devices.  If
> you want that level of protection you need something like a power  supply
> with fold-back current limiting.
>
> Brian Lloyd

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[WILLIS COOKE]

--- David Cutter <[hidden email]> wrote:

> Glad you raised that point, Brian.  In my Sunday
> school classes I ask the
> question: "what does the fuse protect?"  It's  a
> revelation to all when I
> give the right answer.
>
> On our 240V distribution system, a melted cable can
> lead to a severe shock
> hazard and I'm guessing that in the 110V
> centre-tapped system since the
> shock hazard is so much less, the next major hazard
> is fire, so, I've often
>

You are right David.  110 VAC is much safer than 240V,
it can just barely kill you.

Cookie, K5EWJ

Willis 'Cookie' Cooke
K5EWJ
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