Today's Message Index:
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1. 08:58 AM - Re: 30A PM alternator and Z101? (user9253)
2. 09:53 AM - Re: 30A PM alternator and Z101? (johnbright)
3. 03:41 PM - Re: Re: 30A PM alternator and Z101? (Robert L. Nuckolls, III)
4. 05:01 PM - Re: Re: 30A PM alternator and Z101? (Robert L. Nuckolls, III)
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| Subject: | Re: 30A PM alternator and Z101? |
If it is desired to shut off the alternator during flight and there is concern
about causing an over voltage event, just close the throttle first.
Speaking of a thermos bottle, never fill one with boiling hot coffee that is intended
to be opened during flight. Due to the lower atmospheric pressure at altitude,
the very hot coffee
will turn to instant steam, burning the pilot and filling the cockpit with fog
which fogs the windows.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=507153#507153
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| Subject: | Re: 30A PM alternator and Z101? |
I created a new pdf file (Elec Schem with Monkworkz MZ-30L as backup and Z101 as
a template rev draft 4.pdf, too large to attach so https://drive.google.com/file/d/1Pg2Jg5Q-qNAFjQ4kux7Ugcsj3QxKQv74/view?usp=sharing)
with five configurations
for brainstorming. The configuration I posted on June 6, 2022 (Elec Schem
with Monkworkz MZ-30L as backup and Z101 as a template rev draft 3.pdf) is now
called Configuration 1.
Bob:
I don't understand why the regulator would generate a voltage spike if disconnected
from the battery while delivering a significant level of current.
Bill Judge of Monkworkz said "It's possible that the OVP would be triggered by
switching off the relay when there is significant current flowing. No damage will
occur but you only get three of those per engine start. Around 15.3 V is where
an OV event is registered, and the duration needs to be on the order of 10
ns or more, way faster than DO-160 requires."
I was trying to address his concern by adding the diode across the relay.
The voltage spike has not been demonstrated on the bench to my knowledge.
Alternator backup mode:
I understand that it's not necessary.
The crew will get an indication on the EFIS or panel light if the alternator wakes
up from backup mode when the voltage drops to 13.7. Ref the Active High connection
on the regulator.
The only configuration that has any sort of switch sequencing SOP is Configuration
1 where the progressive battery alternator off / connect / on switch should
not be moved quickly from on to off in order that the hypothetical voltage spike
would not be created. If this switch is moved quickly from on to off and
if the hypothetical voltage spike is a real thing, the diode across the relay
will shunt said spike to the battery.
Joe: AFAIK the 1N5822 diode is rated at 3A (IF(AV) under certain standard conditions)
which is OK because the alternator is off when the relay contacts are open.
I don't have a Monkworkz alternator to experiment with rather I'm trying to plan
ahead in case this product proves itself in the field. I see it as being in
the early adopter stage at present.
--------
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
https://drive.google.com/folderview?id=1u6GeZo6pmBWsKykLNVQMvu4o1VEVyP4K
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=507155#507155
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| Subject: | Re: 30A PM alternator and Z101? |
At 10:57 AM 6/8/2022, you wrote:
>
>If it is desired to shut off the alternator during flight and there
>is concern
>about causing an over voltage event, just close the throttle first.
>
>Speaking of a thermos bottle, never fill one with boiling hot coffee
>that is intended
>to be opened during flight. Due to the lower atmospheric pressure at
>altitude, the very hot coffee
>will turn to instant steam, burning the pilot and filling the
>cockpit with fog which fogs the windows.
Airplanes I fly don't achieve that kind of
atmospheric delta-p. Further, in recognition
of McD's famous pension for serving drive-up
coffee capable of bodily harm . . . I don't
bottle it up that hot for terrestrial travel
much less at 10K (boiling point 195F).
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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| Subject: | Re: 30A PM alternator and Z101? |
>Bob:
>I don't understand why the regulator would generate a voltage spike
>if disconnected from the battery while delivering a significant
>level of current.
This is an oft cited but seldom encountered
condition which the automotive circle call an
"alternator load dump" event. The worst-case
pre-event condition is as follows:
You have a really robust alternator (modern
vehicle loads often call for alternators in 100A
class!).
Your battery is badly discharged . . . maybe you
ran it down having left something on over night.
You get the car started and the alternator goes
to work stuffing energy back into the battery . . .
i.e. regulator running nearly full field in
an attempt to get things back in order.
So now we have a BATTERY demanding alternator
output while vehicle demands are low.
Now . . . for what ever reason . . . the battery
becomes disconnected from the vehicle's distribution
system. The alternator suddenly becomes lightly
loaded and the battery's willingness to absorb
alternator transient surges is gone.
Take a peek at this document from Texas Instruments:
https://tinyurl.com/2ymdwrcj
Figure 4 illustrates the automotive load dump
parameters, this is an analog to the DO-160
40v surge favored by aviation in 14v systems.
Figure 3 illustrates the condition that precipitates
the event.
Figure 8 illustrates performance of a over-voltage
disconnect circuit (figure 6) when placed in
the supply lead of an at risk product.
We had a hopeful supplier to Beech offering
heated seat inserts being proposed for some of
our high-end heavy-iron. They were unable to
pass the 80v surge for qualification on our
28v aircraft. I suggested and almost identical
but simpler h.v. disconnect circuit which they
incorporated with success . . . don't know if
they ever made it onto our airplanes.
Long story short, what is the likelihood of
suffering a disconnect of depleted battery
at rpms high enough to be producing heavy output
thus setting up an alternator load-dump event?
Further, the automotive load-dump ALWAYS involves
a wound-field alternator driven by a regulator
with a purposefully limited response struggling
to bring a fully fielded, suddenly unloaded
alternator back under control while it's
b-lead is still connected to potential
victims of the o.v. event.
It's not clear to me how a PM alternator's
rectifier/regulator would suffer a similar
characteristic with the 'b-lead' relay.
>Bill Judge of Monkworkz said "It's possible that the OVP would be
>triggered by switching off the relay when there is significant
>current flowing. No damage will occur but you only get three of
>those per engine start. Around 15.3 V is where an OV event is
>registered, and the duration needs to be on the order of 10 ns or
>more, way faster than DO-160 requires."
This makes no sense to me. Switching off the
'b-lead' relay can suddenly unload the alternator
which will undoubtedly experience some magnitude
of load dump surge. But where will it go and
what risk for damage exists? He of all people
should know.
>I was trying to address his concern by adding the diode across the relay.
>The voltage spike has not been demonstrated on the bench to my knowledge.
Perhaps it would be well for him to explore this
question?
>Alternator backup mode:
>I understand that it's not necessary.
>The crew will get an indication on the EFIS or panel light if the
>alternator wakes up from backup mode when the voltage drops to 13.7.
>Ref the Active High connection on the regulator.
>
>The only configuration that has any sort of switch sequencing SOP is
>Configuration 1 where the progressive battery alternator off /
>connect / on switch should not be moved quickly from on to off in
>order that the hypothetical voltage spike would not be created. If
>this switch is moved quickly from on to off and if the hypothetical
>voltage spike is a real thing, the diode across the relay will shunt
>said spike to the battery.
I'm concerned that any such band-aid would be
useful along with any requirement placed on
the pilot for positioning of switches.
>Joe: AFAIK the 1N5822 diode is rated at 3A (IF(AV) under certain
>standard conditions) which is OK because the alternator is off when
>the relay contacts are open.
If it's 'off' where does the surge come from,
how high, how long and if the diode were not
there, what are the risks?
>I don't have a Monkworkz alternator to experiment with rather I'm
>trying to plan ahead in case this product proves itself in the
>field. I see it as being in the early adopter stage at present.
If you're being recruited as part of the Monkworkz
product development team, then one would want to
do some bench testing to confirm/deny the hypothesis.
I've got a AN20000 drive pad test stand whereupon
such questions could be explored.
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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