[Elecraft] In Line Power Pole Fuses

[Dave B]

> Dave and all,
>
> Placing the fuse near the power supply end is the way to do it.
> In the event of a short, the power wire can spew metal and start a fire.
> Always fuse near the power supply.? A fuse at the equipment end will 
> only protect the equipment, but will expose the wire from the power 
> supply to hazards.
>
> 73,
> Don W3FPR
------------------------------------------------------------------------

Also, if at all possible, do not connect directly to the Negative side
of the battery without a fuse.

In the event of a (not uncommon) fault with the batteries own ground
strap, your radio etc will try to conduct a large proportion of the
engine cranking current, that doesn't end well.  (I have seen CB sets
explode under such conditions!)

Sketch out the starting circuit, then include your radio's power wiring
and you'll see the problem.  (Include the antenna ground connection!)

With some modern vehicles, such a connection can also affect the battery
charging system behaviour, as a bulk current sensor could be bypassed by
your wiring resulting in overcharging the battery under some conditions.

Some vehicles also use the alternator to provide extra engine breaking,
resulting in large charging currents and voltage changes for short
periods (seconds) while overall the battery is never "fully" charged, to
accommodate such short term usage without damage.

For Safety, it is best to connect the radio -ve direct to the vehicle
chassis ground, not the battery negative.

If you do have to connect directly to the vehicle battery negative (for
a temporary install, during an EMCOM event for example) then check the
condition of the vehicles battery ground strap first, AND use a Fuse in
the radio -ve lead.  (If you ever find that fuse has failed for no
"apparent" reason, you need to check the health of vehicle battery
cabling in detail.)

Always check the vehicle handbook for advice about such things too.

Having suffered a vehicle electrical fire* while driving, I can tell
you, you do not want that experience.

(* Unrelated to any amateur radio matters, it was due to a "money saving
feature" by the vehicle maker, that over time eventually caused a short
to ground of a lighting circuit, that was also not fused!)

Take care.

Dave G8KBV



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