Today's Message Index:
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1. 09:01 AM - RX-7 Alternator mod - negative spike diode needed? (Finn Lassen)
2. 10:40 AM - Re: Shunt Questions (Steve Williams)
3. 10:41 AM - Re: Re: Questions about Architecture Design (Robert L. Nuckolls, III)
4. 11:03 AM - Schottky diode voltage drop. (Sam Hoskins)
5. 02:10 PM - Re: Schottky diode voltage drop. (Robert L. Nuckolls, III)
6. 04:09 PM - Re: Crowbar let the smoke out (Finn Lassen)
7. 04:47 PM - Re: Schottky diode voltage drop. (user9253)
Message 1
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| Subject: | RX-7 Alternator mod - negative spike diode needed? |
I modified the RX-7 Mitsubishi alternator (reman 14910?) to require
external field voltage.
Connection between three small rectifier diodes and the internal
regulator unsoldered, regulator tab bent up and covered with heat
shrink, just for good measure.
Very, very simple modification and the internal regulator is still used.
Sorry for they very poor picture from the Haynes RV-7 manual.
So, I feed the field winding from main bus, via a 5A alternator
pull-breaker to the EM-36 spade terminal on the alternator.
After my OV crowbar blew up, I took a closer look and am now wondering
if I should add a diode from ground to the EM-36 field winding terminal
to curb any negative spike.
Normally, without the mod, any negative spike resulting from powering
the field winding would be absorbed by the three small diodes and
rectifier diodes going to ground.
And perhaps I should also a diode in series with the wire from the
breaker to the alternator field terminal so a positive spike from the
field winding won't trigger the OV module?
BTW, the alternator does have a built-in capacitor over the output (B+)
not shown on the schematic, but visible to the right in the photo and
from the outside of the alternator, but doesn't affect the voltage
regulator.
Finn
Message 2
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| Subject: | Re: Shunt Questions |
Bob and Eric, thanks for pointing out a much more elegant solution than
a shunt farm!
Bob, I re-read the section of Chapter 7 on Hall effect sensors. I'm
sure I read it around 30 years ago, but I had forgotten.
One way this is more elegant is that it can be inserted into the ground
path without disrupting the ground, which makes the physical wiring
safer. (The shunt and fuse block in my van's wiring closet are a bit
vulnerable right now.)
The microcontrollers I'm planning to use have lots of A/D pins, so
that's not a problem. They're Arduino compatible, but at 3.3V, so I
wonder whether the LTS 6-NP must have a 5V supply voltage? If so,
that'll factor in to the multiplier produced by the parallel wires, to
make full scale no more than 3.3V.
I skimmed the data sheet on the LTS 6-NP. I'll have to read it more
closely before I'll be able to put it to use! I believe I understand
how the six primary leads are configured to the application, but not so
much passing a conductor (or turns!) through the aperture.
Other than your clever 10X scaling, how does one choose between a
conductor through the aperture vs. the primary leads?
And I'll want to understand more about the physical considerations: Does
this device require some minimum clearance from other wiring/components?
I assume you specify a 1 foot length for each of the parallel 22AWG and
10AWG wires because 10AWG has a cross section about 9X 22AWG? Why 1
foot? What about just a shorter length of each, from one side of the
sensor to the other? (I'm picturing a printed circuit board with the 22
AWG soldered near Fast-Ons or threaded studs to attach the 10AWG and the
wires to ground and load/battery. Or, heck, just a bolt through to the
chassis, like the ground block.)
I wonder whether one could achieve the same multiplier (and current
capacity) using a shorter wire through the aperture together with a
generous area of printed circuit foil to carry the other 90% of the
current? (I've never learned anything about the current capacity of
printed circuit foil or how to predict its resistance.) Could that
assembly be calibrated somehow? Would it be stable?
Thanks, as always, for being so generous with your time!
On 5/25/2020 7:38 AM, Robert L. Nuckolls, III wrote:
> I have all but abandoned metallic shunts for current
> measurement - especially when the millivolt data
> is to processed in low level digital electronics.
>
> We can revisit your shunt questions but I'll
> suggest you consider this product:
>
> https://tinyurl.com/yaxv58ax
>
> These are closed loop, hall-effect sensors priced
> about the same as the metallic shunts. Beauty
> of these critters is total isolation, very
> good linearity, repeatability and accuracy.
>
> Best yet, one device can measure a huge
> range of currents.
>
> I stock the 6A version for about all applications.
> I can run 5 passes of 22AWG wire through the
> aperture and get plus/minus 1.2A full scale.
> Alternatively, a single pass of 22AWG 1 foot
> long through the aperture spliced in parallel
> with 10AWG 1 foot long outside the aperture
> gives me approx 10x multiplier for plus/minus
> 60A full scale.
>
> You can situate the sensor local to the stimulus
> of interest and extend the leads on a shielded,
> twisted pair for direct interface with your
> a/d converter. You don't need those high common
> mode gain chips to do achieve an interface.
> You WILL need some a/d ports to process your
> hall sensor data.
>
> I've acquired high quality data at the ends
> of 40' leads in all manner of noisy environments.
> The attached photo is one example of one
> application. This board includes a 5v, 3-terminal
> regulator enabling me to use the device
> 'barefoot' with a digital VOM at the observation-
> end of the leads. For applications such as yours,
> I'd probably solder a shielded pair directly to
> the module pins and 'pot' the connections with
> E-6000.
>
> If you'd like some boards to mount and terminate
> the wires in a connector, I think I've got a
> few laying around. Also, if you'd like to
> go for the metalic shunts, I think I've
> got a few dozen 20A shunts available for the
> asking . . . but you don't want to overload
> these things by much . . . maybe 50%. They're
> easy to 'smoke'.
>
> LONG time no hear my friend! Pleased to know
> that you're still alive, kicking and curious!
>
>
> Bob . . .
>
Message 3
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| Subject: | Re: Questions about Architecture Design |
>
>How many devices on your clearance delivery
>bus?
>
>Four, Primary EFIS, GPS, Comm and strobes so I don't forget to turn
>off the clearance delivery switch.
Do your strobes have their own power
switch? If there is risk that the
CD switch is inadvertently left on
at shutdown, how is there less risk
that the strobes are not independently
shut off and the CD switch is now
un-monitored?
Checklists are a time honored, legacy
proven hedge against human weakness
of the gray matter. The FARS require
a single-stroke feature for making the
aircraft electrically 'cold' . . . in
the case of multiple, dual-feed buses
it's easily managed with a 'crash bar'
over the row of switches.
Sorry if I seem 'fussy'. I cannot help
being extra attentive to things done to
mitigate 'forgetfulness'. Airplanes
are not SAFE. They are exceedingly
unforgiving as demonstrated in countless
NTSB incident/accident narratives . . .
the vast majority of which have foundation
in over confidence/forgetfulness.
>What is the 'down side' for having 'all that stuff
>running' during start? Z101 as depicted supports all
>auxiliary busses with independent feed paths. What
>are your plans for an avionics bus?
>
>OK, I gave my avionics wiring diagram a hard look. If I eliminate
>the avionics bus and move those devices to the main bus, I only have
>two items that might reboot during start, they are the Garmin
>GMC-507 auto pilot head and the #2 MFD. The rest are on the TCW IBBS
>6ah back-up battery.
With Z101 you have probably the most failure
tolerant architecture flying . . . and you've
still got a back-up battery?
>You make them from fuse link wire. Where do you
>plan to incorporate them?
>
>I currently show a 16awg fuselink on the ALT 'B' line just before
>the starter solenoid.
Trying to accurately describe an architecture
with words leaves much to be desired. If
you're basing your plans on Z101, then
exactly how do you plan to modify that
drawing?
Those remote relays for alternate feed
paths allow clustering major components
together on short (*) leads making
fault protection easier. There are several
instances of fuse-link wire illustrated
on Z101.
Bob . . .
Message 4
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| Subject: | Schottky diode voltage drop. |
Long story short, my Dynon display reads low voltage due to the isolation
diode. Is there a better choice?
I have had my Essential buss installed for 10? years now. My Dynon takes
it's power from the E buss and uses that to display the system voltage. My
Q-200 is all electric and I really want to see what the actual voltage is
there. Unfortunately, the voltage drop across the Schottky diode seems to
be almost a volt. So, when flying I mentally add a volt to the display, but
I would really prefer not to, especially times when I might have other
electrical issues going on.
Is there another diode product I could use that would reduce the drop?
Thank you.
Sam Hoskins
samhoskins.blogspot.com
Message 5
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| Subject: | Re: Schottky diode voltage drop. |
At 01:00 PM 5/26/2020, you wrote:
>Long story short, my Dynon display reads low
>voltage=C2 due to the isolation diode. Is there a better choice?
>
>I have had my Essential buss installed for 10?
>years now.=C2 My Dynon takes it's power=C2 from the
>E buss and uses that to display the system
>voltage. My Q-200 is all electric and I really
>want to see what the actual voltage is
>there.=C2 Unfortunately, the voltage drop across
>the Schottky=C2 diode seems to be almost a volt.
>So, when flying I mentally=C2 add a volt to the
>display, but I would really prefer not to,
>especially times when I might have other electrical issues going on.
>
>Is there another diode product I could use that would reduce the drop?
Isn't the Dynon programmable as to what it
calls 'low voltage'?
You can go with a Schottky diode which will
drop less voltage . . . but it's not going
to be zero . . . so you still have to do the
mental exercise to deduce main bus voltage.
But what's the motivation for concern? Under
what circumstances would you need to know
the main bus voltage? In any case, you can
fly with the e-bus alternate feed switch
closed . . . which would cause the instrument
to read very close to bus voltage and probably
turn the warning off.
Bob . . .
Message 6
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| Subject: | Re: Crowbar let the smoke out |
Exactly what I did. zip-tied (and siliconed) it to top of breaker, with
very short thick wires to ground (ring around breaker mounting neck) and
to breaker terminal screw.
So, shorter and thicker wires is not always better :(
This is a 60 - 70 amp alternator, so I figured would need at least 5
amps or approx 10% for field winding?
Not expecting to ever use that much current, but didn't want to pop the
breaker in case of a nearly discharged battery.
So use 22 awg the 30" from breaker to alternator? And a bigger SCR?
Finn
On 5/25/2020 6:28 PM, Robert L. Nuckolls, III wrote:
> I've had
> customers install their AEC fabricated
> modules right at the breaker on a legacy
> bus bar . . . they even shortened the
> factory supplied leads. Their modules
> suffered the same fate the first time
> they tripped.
Message 7
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| Subject: | Re: Schottky diode voltage drop. |
A Schottky diode drops about 0.5 volt less than a P-N Junction Diode. The
voltage dropped depends on the current. Diode manufacturers publish data
sheets that contain a graph that shows voltage drop at various currents. The
voltage drop across your diode can not be determined without knowing the
current and diode temperature and having the data sheet. I good guess is 0.6 volts.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=496528#496528
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