Today's Message Index:
----------------------
1. 06:02 AM - Re: Re: Wiring / Relay Question (Robert L. Nuckolls, III)
2. 06:26 AM - Re: Diode across main contactor fat terminals (Robert L. Nuckolls, III)
3. 09:05 AM - Circuit for driving LED warning lights from differential pressure transmitter? (DCS317@aol.com)
Message 1
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| Subject: | Re: Wiring / Relay Question |
At 02:50 PM 3/1/2009, you wrote:
><hammer408@comcast.net>
>
>Bob
>
>I've placed my Battery Bus Firewall forward next to the Battery Contactor,
>just above the 60 amp current limiter. I have a 14 g (15 amp) wire going
>from battery bus thru firewall to a 7104 relay, as per the Heavy Duty E bus
>configuration.
I'm not sure I'm seeing a good mental image of
your installation. I presume the 60A limiter is
your b-lead protection, normally this goes next
to the starter contactor which is usually on
the upper port corner of the firewall co-located
with a loadmeter shunt (if you have one).
>My question, should I use an additional relay or "something" between the
>Battery Bus (15amp - 14 g wire)-firewall forward - and the relay which is
>next to my E-Bus - mounted on sub-panel - for added safety?
If you have a relay mounted next to the e-bus
inside the aircraft, then you have it on the wrong
end of the wire. The purpose of the e-bus
alternate feed relay is to serve as a sort of
mini-battery contactor for this feed line . . .
it should be mounted as close as practical
to the battery bus fuse that feeds it.
Do I interpret correctly that your battery bus
is under the cowl?
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
Message 2
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| Subject: | Re: Diode across main contactor fat terminals |
At 08:55 AM 3/1/2009, you wrote:
>
>On May 23, 2008, I posted a hypothetical question about Z-19 main
>battery charging current back feeding through the endurance bus and
>blowing fuses in the event that the main battery contactor fails and
>the pilot closes the endurance bus alternate feed switch.
>http://forums.matronics.com/viewtopic.php?p=184591&sid=86e2d2ac21d95a18ce267b57c4fcd85e
>To prevent the above scenario, what if a diode were placed across
>the main contactor fat terminals? If the contactor fails, this
>diode would prevent the main battery from discharging. What are the
>disadvantages?
The only time you can back-feed the e-bus to the battery
with energy from the main bus is if the alternator is running.
The progressive transfer switch used to orchestrate main
battery and alternator operations precludes having the
alternator ON with the battery OFF.
> If this diode shorted out (diode failures are rare), then the
> pilot would lose the ability to shut off the master switch in case
> of an electrical fire. However, current would be limited by the
> lead size of the diode, similar to a fusible link. The chances of
> an electrical fire and the diode failing on the same flight are
> extremely remote. If one is concerned that the diode failure would
> go unnoticed at engine shut down, then a warning chime could be
> connected to terminal 3 of the master switch. I think the odds of
> the main contactor failing and associated pilot error (with
> dangerous consequences) are greater than the odds of a diode
> failing (with minimal consequences). What are your thoughts?
>Joe
Adding a diode across the contactor defeats the purpose
of the contactor which is to provide complete disconnect
from the system when in the OFF position. Given that
your hypothesis for back-feeding the alternate feed path
is addressed by the configuration of the DC POWER MASTER
switch, I think your concerns are without foundation.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
Message 3
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| Subject: | Circuit for driving LED warning lights from differential |
pressure transmitter?
aeroelectric-list:
I need a circuit (the receiver) for driving LED warning lights from
differential pressure transmitter. The differential pressure transmitter has
an
output of at the low pressure end of 4 mA varying continuously to 20 mA at the
high end. 12 volt DC system (aircraft battery) is the power supply. The
transmitter can withstand 35 volts DC. The total circuit (receiver) resistance
should be 100 ohms, given by the formula R Max = (V of power supply minus
10.0) divided by 20 mA DC . I would like to have the circuit (the receiver)
with flashing superbright red LED on at the lower range (adjustable "ON point"),
flashing superbright yellow at mid-range (adjustable "ON point"), and
superbright green at high range (adjustable "ON point"), each lit only when the
pressure is in its respective range. A dimmer sub-circuit would also help!
One terminal of the pressure transmitter connects to the positive terminal of
the 12 volt power supply (aircraft battery) and the other terminal of the
pressure transmitter connects to the receiver ("circuit") and from the receiver
to the negative terminal of the 12 volt power supply. I.e., simple series
arrangement.
Any help would be appreciated. Point me to sources (books or articles or
posts) or email me a circuit? I have a basic knowledge of electronics.
Don Schmiesing RV-8 N417DS
Any
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