Posted for "John Richardson"
<
n16dx@comcast.net>:
Hi
Valin and LML
I have been using a prototype version of the
Lamar "Super Switch" in my 28V
legacy. I'm using the
uni-directional version as a starter contactor. I've
got about
300 hours on the plane now and this "contactor" has never failed. I
must tell you that I got onto Lamar initially because of their starter
which
is a direct drive (no planetary gear reduction drive like the Iskra)
due to
the bad reports about starters that do not release the Continental
starter
drive adapter spring. I subsequently found out after
talking to their lead
engineer working on the Super Switch that it uses
the new P-channel MOSFETs (I
think several in parallel) as a high side
switch just like a solenoid
contactor. (you put the contactor
between the battery and the input to the
starter and the other lead of the
starter is internally grounded) . Also, I
have had starter
traditional aircraft contactors fail (on a Cessna) where it
sticks closed
even though you release the ignition key from the "start"
position. So I figured it's time to get rid of the traditional
contactor, at
least when switching high current. Just as
background, high current MOSFETs
have always been N-channel up until just
a few years ago so high side
switching of very low impedance loads was not
very simple. Now the P-channel
devices (which make high side
switching simple) are almost as good and rated
at incredible high peak
current. We'll see how well they hold up. I test it
each time I
start the engine. I"m flying the engineer's second prototype
switch and gave them early feedback. I learned that Cirrus was
thinking about
using several of these switches in a centralized switching
matrix to control
all the high current circuits like flaps, landing lights
etc. Don't know if
that
happened.
I have chosen to limit my exposure to
this new technology and do not use the
bi-directional super switch in the
master contactor application. One is
enough. However, there are, I think, better solutions than just
using the
standard aircraft solenoid contactor. I decided to
use the Tyco EV-200 high
current relay as a master
contactor. There has been some discussion on the
LML about the
EV-200. It is more expensive than the standard aircraft
solenoid, Tyco has a very complete spec sheet on the unit, and these specs
are
great. Also, the master contactor usually does not have to
actually switch
(make or break) high current like a starter
contactor. Plus the EV-200 has a
spec for number of on/off
cycles. When not switching high current, this spec
is very
high. I forget the actual number, but I could not find meaningful
specs for the typical aircraft contactor. One last plus for the
EV-200....it
draws only about 70 mA hold current. Weight is 1
lb. Bob Nuckolls was going
to analyze one about a year ago but
I've not seen that report.
Hope this helps.
John Richardson
Legacy N16DX
-----
Original Message -----
From: Valin & Allyson Thorn
To: lml@lancaironline.net
Sent: Monday, February 22, 2010 5:09
AM
Subject: [LML] Solid State Contactors --
SuperSwitch?
Hey LML gang,
Has anyone had experience
with these Lamar Technologies solid state
contactors (see info from ACS
below)? I know they're expensive - but, we're
already in that
category of contactor with the need for 28V high continuous
current
contactors (100 A alternator, all electric A/C). We already have
these very nice Blue Marine high capacity contactors that are hermetically
...snip...