The Murphy Builders Site

Hi Dan

I agree the switch should be replaced.

I would however expect the switch to have 2 contacts minimum. It is very
unlikely to have the mounting lug as a ground connection - never seen one
like that anywhere.

I would expect the switch to be carrying only the solenoid operating
current, and that will be a lot less than 35 amps :-)

Nig
745E



-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
leinadair
Sent: 31 July 2010 14:32
To: rebel-builders@dcsol.com
Subject: [rebel-builders] Master Lever Switch problems

Lately (on startup from Niagara Falls Intl. NY) My Rebel Amphibian Master
(lever/toggle switch) would not engage unless I move the lever/toggle ever
so slightly down or up.

It definitely needs replacement as I fear over time the contacts inside the
switch may have began to burn out with use. I have flown over 100 hrs since
I bought the A/C over a year ago. The A/C now has a total of 320 hrs.

I believe the Master is a SPST (ON/OFF) . I reached behind the panel and
found/felt only one heavy wire connected to the Master switch. The switch
body is definitely larger than all other lever/toggle switches. I believe
this switch completes the Ground (negative) circuit to the Solenoid relay
which then energizes the (HOT) side of the bus? The other terminal has no
leads coming out and must somehow be the ground to the BUS through the
switch body ?

Master Breaker is rated for 35 amps. Aircraft Spruce has a Lever switch
rated at 20 amps for 12/24 volts and looks sturdy enough.

Any advice ?, Do I really need a 35 amps (or more) rated switch? If so where
can I find one ?. Will a good 20 amp switch do the trick? Would it be
better that the switch have the same military specification as the certified
airplanes? Or does it really matter?

Regards

Dan (0178 R) GGNB




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Dan

If the switch is grounded to the panel that could be the issue right
there. Properly rated switches in aircraft usually suffer from corrosion
issues long before contact failure.

If there is a battery contactor it will not draw more than an amp
however there should be a diode across the coil or across the switch to
prevent arcing at the switch contacts when it is turned off. Almost any
switch would last almost forever with the diode.

Some aircraft are wired with a heavy switch instead of a battery
contactor though which implies a heavy wire compared to using a
contactor. At least 10 awg and preferably 8awg as opposed to the typical
22awg for grounding a solenoid. If that is your situation with only one
heavy wire then yes you need a 35amp or higher rated switch. However
that implies the switch grounds the battery and the starter is grounded
separately which would be a dangerous system from almost any
perspective. ie any positive wire will always be a fire risk if it
grounds to the airframe even when the master switch is off. You would
not have the ability to kill power to it unless you have a master
solenoid or a master (200 amp) switch. The point of a battery
contactor/switch is to kill all non essential power. If your system is
really as you describe, I would strongly suggest that you rewire the
master switch with two wires to cut +12 volt power to everything.
Everthing else would be permanently grounded as per every other aircraft
that I'm aware of.

Ken

N.Smith wrote:

Hi Dan

I agree the switch should be replaced.

I would however expect the switch to have 2 contacts minimum. It is very
unlikely to have the mounting lug as a ground connection - never seen one
like that anywhere.

I would expect the switch to be carrying only the solenoid operating
current, and that will be a lot less than 35 amps :-)

Nig
745E



-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
leinadair
Sent: 31 July 2010 14:32
To: rebel-builders@dcsol.com
Subject: [rebel-builders] Master Lever Switch problems

Lately (on startup from Niagara Falls Intl. NY) My Rebel Amphibian Master
(lever/toggle switch) would not engage unless I move the lever/toggle
ever
so slightly down or up.

It definitely needs replacement as I fear over time the contacts inside
the
switch may have began to burn out with use. I have flown over 100 hrs
since
I bought the A/C over a year ago. The A/C now has a total of 320 hrs.

I believe the Master is a SPST (ON/OFF) . I reached behind the panel and
found/felt only one heavy wire connected to the Master switch. The switch
body is definitely larger than all other lever/toggle switches. I believe
this switch completes the Ground (negative) circuit to the Solenoid relay
which then energizes the (HOT) side of the bus? The other terminal has no
leads coming out and must somehow be the ground to the BUS through the
switch body ?

Master Breaker is rated for 35 amps. Aircraft Spruce has a Lever switch
rated at 20 amps for 12/24 volts and looks sturdy enough.

Any advice ?, Do I really need a 35 amps (or more) rated switch? If so
where
can I find one ?. Will a good 20 amp switch do the trick? Would it be
better that the switch have the same military specification as the
certified
airplanes? Or does it really matter?

Regards

Dan (0178 R) GGNB




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