REFLECTOR: SuperSwitch starter control

Fri Apr 13 10:20:21 CDT 2007

 Anybody know anything about the new Lamar Technologies ( 
http://www.lamartech.com/ ) Master Control Switch called SuperSwitch? I saw 
an ad GA News. It's all solid state and is smaller/lighter that a std AC 
starter solenoid. It is also programable for max current and resets 
automatically. It is for the experimental market, and is sold thru std AC 
parts distributors. Don't know cost. They also make lightweight starters and 
electrical parts for the big jets.

This might handle the concern Dave had about a massive short to ground.

----------------------------------------
>
> My theory is that I can turn off the battery contactor (in the nose, near
> the batteries) if the #2 wire should short to ground somewhere between the
> battery and the starter.
>
> Dave Scharfenberg
>
>
> On Jan 29, 2007, at 10:37 AM, Scott Derrick wrote:
>
> Terry,
>
> This conversation about protecting the "big" wire that runs to the rear of
> the plane to power the starter and to provide for the alternators charge
> circuit got me interested in possibly protecting it with a big fuse or
> breaker.  200 Amp or so... Starters draw a huge current.
>
> I'm not talking about protection for the alternator, this being the short
> #10/8 or so wire that connects the alternators charge circuit(B lead) to 
> the
> supply side of the main starter relay(big wire from main relay to starter
> relay).  That small wire should have a fuse or resettable breaker. I think 
> a
> fuse would be the right choice.
>
> I searched the Aero-Electric list and found this... Its not for a canard 
> but
> it is about a battery lead from the rear of a tractor style airplane to 
> the
> firewall.  Similar application..
>
>>
>>Bob and everyone else ...
>>When considering a ground fault, what is best used to protect a #4 cable
>>run, from the rear battery, in an RV, while powering a bus?
>>
>>What is best used to protect this same #4 cable, when it is in parallel
> with
>>the front battery and charging current is flowing to the rear batt?
>>Thanks ...
>>Jerry Grimmonpre'
>
> Fat wires in light aircraft are not, as a rule, "protected".
> If you study the wiring diagrams for light airplanes going
> back to the first generator and battery installations
> (mid 40's), things like fuses and circuit breakers do not
> appear in the fat feeders. Let's see what the certified guys
> design to by reading from FAR23.
>
> Sec. 23.1357 Circuit protective devices.
>
> First, keep in mind that I quote this document only as a means
> of illustrating thought processes for crafting the most trouble
> free system . . . and in no way am I suggesting that these
> words be treated as a "requirement" that should flow down into
> the OBAM aircraft community.
>
> (a) Protective devices, such as fuses or circuit breakers, must be
> installed in all electrical circuits other than--
>
> (1) Main circuits of starter motors used during starting only; and
>
> (2) Circuits in which no hazard is presented by their omission.
>
> I can tell you that these paragraphs describe the portion of the
> architecture you are asking about. Fat feeders in light aircraft
> are seldom if ever involved in a hard fault situation because of
> the extra care we take in securing such wires and thoughtfulness
> for installation to keep them clear of moving parts that might
> pose a threat.
>
> When a fat feeder suffers compromised insulation, it's generally
> against thin sheet metal and the fault tends to be "self clearing",
> i.e., it take a lot of force designed to drive the faulted conductor
> to ground such that the conductor is now at-risk for catastrophic
> failure due to high currents. Relatively light, passing contacts
> tend to burn open with little or no effect on the rest of the system.
>
> (b) A protective device for a circuit essential to flight safety may not 
> be
> used to protect any other circuit.
>
> Common sense. A fuse or breaker for every accessory. Don't stack
> multiple accessories on a single breaker/fuse whether "essential"
> or not. Of course, this begs for a definition of "essential" which
> is a topic for a who chapter. The government position on aviation
> is to build ever more goodies into the essential category . . .
>
> As I've described in Chapter 17 . . . it's up to YOU to decide
> what's "essential" based on your understanding of personal
> and mechanical limits based on proposed missions.
>
>
> (c) Each resettable circuit protective device ("trip free" device in which
> the tripping mechanism cannot be overridden by the operating control) must
> be
> designed so that--
>
> (1) A manual operation is required to restore service after tripping; and
>
> (2) If an overload or circuit fault exists, the device will open the
> circuit regardless of the position of the operating control.
>
> Common sense.
>
> (d) If the ability to reset a circuit breaker or replace a fuse is
> essential to safety in flight, that circuit breaker or fuse must be so
> located and identified that it can be readily reset or replaced in flight.
>
> Yup, good thing to do. Now, I've suggested for years that there's
> no good reason for ANY single piece of equipment to become so
> "essential" that it qualifies for special treatment of access to
> fuses or breakers. There are hundreds more things that cause
> an accessory to fail that DOES NOT open a fuse compared to
> failures that DO open a fuse. Focusing on the ability to restore
> a fuse or breaker circuit is non-productive. These are
> a tiny proportion of all failures and likelihood of getting
> a system back by replacing the fuse is nil.
>
> It stands to reason then that if any one SYSTEM is so
> desirable, then there had better be a backup SYSTEM.
> Once this condition is achieved, there is no reason for
> making ANY fuse or breaker accessible in flight.
>
> (e) For fuses identified as replaceable in flight--
>
> (1) There must be one spare of each rating or 50 percent
> spare fuses of each rating, whichever is greater; and
>
> (2) The spare fuse(s) must be readily accessible to any
> required pilot.
>
> As thoughtful designers and users of OBAM aircraft, we're
> able to craft flight systems that completely negate any
> reason to observe this requirement . . . we can design
> so that there is no need to reach any fuse/breaker because
> there are no singular, "essential" systems likely to be
> resurrected by replacing a fuse or resetting a breaker.
>
> This is the general answer on circuit protection . . . the
> short answer to your specific question is that experience
> and common sense have shown that there is no value in
> adding "protection" to long battery feeders (other than
> the locally situated battery contactor). This includes
> the generally smaller but still quite robust feeder from
> the cranking circuit to the main bus.
>
> Bob. . .
>
>
>
>
> -- 
>
> -
> The only security of all is in a free press. The force of public opinion
> cannot be resisted when permitted freely to be expressed. The agitation it
> produces must be submitted to. It is necessary, to keep the waters pure.
>
> Thomas Jefferson to Lafayette, 1823. ME 15:491
>
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