Fusing the K3 Power Line

Reading the manual....it says that two 25 amp fuses should be in both the
positive and negative leads going to the K3 from the battery.  Now, what about
AC supply like and Astron 35M.  Should you also have the same thing - two fuses
inline from the PS to the K3.  The manual talks about a "battery" but doesn't
address that specifically (or you could infer) for a AC power supply.  Or, am I
just loosing my mind?

Lee


 In our day and age it seems that Common Sense is in short supply.  If you don't
have any Common Sense - get some Common Sense and use it.  If you can't find any
Common Sense, ask for help from somebody who has some Common Sense.  Is Common
Sense divine?

Common Sense is the image of the Creator expressing revealed truth in my mind.
-  John W. (Kansas)

Never interfere with anything that isn't bothering you.
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[mzilmer]

Hi Lee,

The manual (rev D10) doesn't really say 25A fuses, just that the power supply should be rated 25A and that two fast-blow fuses should be used in the supply cabling for protection.  I use 30A fast-blow fuses, one in each of the pos and neg lines.  Power comes from a battery, and the battery is solar-charged.

Matt Zilmer
Consultant - Product Management Dept.
Magellan Navigation / MiTAC Digital Corp.
Tel: [phone]
Cell: [phone]
Si fractum non sit, noli id reficere


-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Lee Buller
Sent: Tuesday, June 26, 2012 1:57 PM
To: Elecraft Reflector
Subject: [Elecraft] Fusing the K3 Power Line


Reading the manual....it says that two 25 amp fuses should be in both the positive and negative leads going to the K3 from the battery.  Now, what about AC supply like and Astron 35M.  Should you also have the same thing - two fuses inline from the PS to the K3.  The manual talks about a "battery" but doesn't address that specifically (or you could infer) for a AC power supply.  Or, am I just loosing my mind?

Lee


 In our day and age it seems that Common Sense is in short supply.  If you don't have any Common Sense - get some Common Sense and use it.  If you can't find any Common Sense, ask for help from somebody who has some Common Sense.  Is Common Sense divine?

Common Sense is the image of the Creator expressing revealed truth in my mind.
-  John W. (Kansas)

Never interfere with anything that isn't bothering you.
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[Fred Townsend]

Lee your K3 is protected from over current in a number of ways. The worst
case I can imagine in your shack is a heavy metal object falling across and
shorting the unprotected power leads to the K3. I have had this happen. To
protect against this you place fuses at the battery. Your Astron has
foldover current limiting so it is also self-protecting but if it is
connected directly to the battery you will need a second set of fuses at the
battery to protect the charging circuit from reverse feeding a shorted
cable. I think the Astron primary is already fuse protected.

You have already indicated you have grounded everything in your shack. If
that includes the negative of your battery then there is no need to fuse the
negative since you have provided a shunt path around the negative fuse.

A word about fuses and fuse holders. Buy the best quality available and that
usually means buy American. Fuse holders are probably the least reliable
component in your system. Fuse are the second least reliable. Use only spade
type fuses (that's called a faston connector). Protect the assembly from
heat and moisture. Clean up any corrosion with a baking soda paste and a
toothbrush. Remember a bad fuse is one that doesn't fuse at its rated
current. A good fuse is one that fuses at its rated current. No wonder there
is so much confusion about fuses.
73, Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Lee Buller
Sent: Tuesday, June 26, 2012 1:57 PM
To: Elecraft Reflector
Subject: [Elecraft] Fusing the K3 Power Line


Reading the manual....it says that two 25 amp fuses should be in both the
positive and negative leads going to the K3 from the battery.  Now, what
about AC supply like and Astron 35M.  Should you also have the same thing -
two fuses inline from the PS to the K3.  The manual talks about a "battery"
but doesn't address that specifically (or you could infer) for a AC power
supply.  Or, am I just loosing my mind?

Lee


 In our day and age it seems that Common Sense is in short supply.  If you
don't have any Common Sense - get some Common Sense and use it.  If you
can't find any Common Sense, ask for help from somebody who has some Common
Sense.  Is Common Sense divine?

Common Sense is the image of the Creator expressing revealed truth in my
mind.
-  John W. (Kansas)

Never interfere with anything that isn't bothering you.
______________________________________________________________
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Home: http://mailman.qth.net/mailman/listinfo/elecraft
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[Carl W Clawson]

A better way to say it would be "A good fuse is one that meets its written
specifications." They aren't all guaranteed to ever blow at their rated
current. Some are, some aren't. Looking one up at random on littelfuse.com
just now, I found "time to open" specified as:

150% of rating, max 30 minutes
300% of rating, max 10 seconds

Another one says

100% of rating, min 4 hours
135% of rating, max 1 hour
200% of rating, max 1 second

Circuit breakers are rated similarly. Remember, nothing is 100% accurate or
100% perfect, so there has to be some "slop" somewhere.

73 and thanks for listening,
Carl WS7L
"Mr Pedantic"

> -----Original Message-----
"A good fuse is one that fuses at its rated current. No wonder there
is so much confusion about fuses. "

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