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...