nuckolls.bob(at)aeroelect
Guest
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 Posted: Mon Aug 29, 2022 11:46 am Post subject: 30A PM alternator and Z101? |
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| Quote: | 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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