>> Here's a simple one for ya. I have been looking for listings on the split
>> Main Power switch (battery/altenator). I find it listed in Aircraft
>Spruce and Wicks catalog, says Cessna type. Bob's webb site doesn't list
any. Is
>> that what you guys have been using, or is there a better one, or way, and
>> available where?
The whole concept behind the "split rocker switch" for DC power
master was created at Cessna about 1965 when the switch from
generators to alternators was in full swing. Generators would
run self-excited and did not need a battery on line to be a useful
source of power. The battery master and generator switches
could be separate, unrelated controls.
Not so the alternator. Alternators would not come on line by
themselves nor were they particularly stable without a battery.
We needed a way to insure that the alternator would never be
on by itself but still allow the battery to be on by itself.
The style of switches used in Cessnas and most other singles
was evolving to rockers so the interlocked split rocker switch was
born. Over the decades, that switch has been endowed with some
sort of mystical properties. I've seen hundreds of airplanes
with every other kind of control switch where the red split
rocker holds court from a prominant place on the panel looking
like no other switch in the airplane.
I personally object to rocker switches because they need a
rectangular hole, they're style critical with respect to the
original manufacturer (you can only replace the thing with
exactly the same brand) and much more labor intensive to install.
Further, in decades since the split rocker was birthed, RG
battery performance for cranking engines has totally
overshadowed an earlier requirement for relieving as much
load on the battery as possible during cranking.
Hence, our present recommendations for battery and alternator
control is to use the simpler, less expensive and more widely
manufactured 2-pole rocker switch to bring battery and
alternator OFF and ON together. See:
http://www.aeroelectric.com/errata/z8_0299.pdf
All of our power distribution concepts use crowbar ov
protection which suggests use of a breaker rather than
fuse for field supply. If this is a pullable breaker,
then the very rare cases where an alternator needs to
be off line while only the battery is on can be accomodated
by pulling the breaker. That's why we don't offer
this device from our website catalog.
For those interested in independent yet interlocked
toggle switch control of the alternator could consider
a switch like our S700-2-10 that can be wired so that
down is both OFF, mid position is battery only ON, and
upper position is both ON.
In any case, I cannot recommend the split rocker found
in almost everybody's electrical parts catalog unless
you're planning to use the same brand and style of
rocker switch for all other applications and you'd like
your panel to take on the look of a 1965 Cessna . . .
Bob . . .
--------------------------------------------
( The only time you don't fail is the last )
( time you try something, and it works. )
( One fails forward toward success. )
( C.F. Kettering )
--------------------------------------------
http://www.aeroelectric.com
|