Today's Message Index:
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1. 12:46 PM - Re: Re: flyback diode across fuel pump (Robert L. Nuckolls, III)
2. 12:46 PM - Re: Re: 30A PM alternator and Z101? (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: flyback diode across fuel pump |
>Hi Bob,
>
>The VAF thread started as =9Clocal ground or
>forest of tabs for fuel pump ground?=9D, EFI
>fuel pump, and drifted at post 9 to someone
>recommending a diode across the pump motor to
>protect the pump switch. I had never heard of this so I asked here on AEL.
>
>https://vansairforce.net/community/showpost.php?p=1629894&postcount=9
>
>--------
>John Bright, RV-6A, at FWF, O-360
Good show
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 2
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| Subject: | Re: 30A PM alternator and Z101? |
>Hi Bob,
>
>I have communicated by email and telephone with Bill Judge of Monkworkz.
>
>I passed along your offer of doing performance testing and
>evaluation of the spike that trips OV protection if the B lead is
>disconnected under load. At present Bill plans to keep testing in house.
I am in contact with Bill . . . we're discussing
ways in which I might be of service.
Why would the b-lead contactor be opened under load?
Sounds like the rather sophisticated ov management
system described in the Monkworkz literature is
being presented with the equivalent of a load-dump
event. We're not privy to the functional dynamics
of the sensor.
MOST legacy ov protection devices are too 'twitchy'.
The very first project I did for Electro-Mech back about
1975 was a solid state replacement for the
RBM controls RBM138-1 electro-mechanical ov relay
http://aeroelectric.com/Pictures/Relays/RBM138-1_A.jpg
http://aeroelectric.com/Pictures/Relays/RBM138-1_B.jpg
This device was widely used in Cessna Prospect Plant
airplanes (310, 320). My replacement was solid
state sensing, 1/4th the weight and volume and per
customer's wishes, would trip in about 50 mS
responding to a step from 28 to 32 volts.
Much faster than suggested by Mil-STD-704
description for DC system performance.
See figure 14 of
http://aeroelectric.com/Reference_Docs/Mil-Std-704/704_excerpts.pdf
Design rules tell us that a 32 volt transient
in a 28v system can be EXPECTED to last up to 1
second. DO-160 qualification testing requires us
to DEMONSTRATE an ability to stand off 40V for
one second in 28v system; 20V in a 14V system.
I've designed many ov management devices to customer
procurement specs that were MUCH faster.
Today, I would design to tolerate a bus in excess of
16 volts for 500 milliseconds. If voltage drops
below 16 volts, the timer resets and starts awaits
a new trip decision if the voltage goes back
up.
This protocol is 99.999% immune to all common
transient excursions including alternator
load-dump . . . but will perform as needed
to mitigate an alternator runaway event.
I'll inquire of Bill what his ov detection/
reaction philosophy is next time we talk.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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