Today's Message Index:
----------------------
1. 05:42 AM - Re: Schottky diode voltage drop. (Sam Hoskins)
2. 07:51 AM - Re: RX-7 Alternator mod - negative spike diode needed? (Robert L. Nuckolls, III)
3. 10:03 AM - Re: Schottky diode voltage drop. (user9253)
4. 10:28 AM - RX-7 Alternator mod - negative spike diode needed? (Finn Lassen)
5. 10:45 AM - Re: Aviation wire (Jan de Jong)
6. 12:24 PM - Re: DAS system (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Schottky diode voltage drop. |
Thanks Bob.
Recently, a fuse in my B&C generator blew (some wiring shorted to the
firewall) and my all-electric aircraft was staying in the air solely
courtesy of the batteries. For a variety of modifications, I need 14 amps
to stay in the air. That's why I want to see the actual main bus voltage.
My Dynon D-180 displays the actual voltage, I 'm not talking about
their programmable warning setting. I am using a Schottky MB2505 diode for
E-bus isolation.
This isn't a huge deal, and perhaps just using the E-bus switch is the
simple solution.
Thanks.
Sam
On Tue, May 26, 2020 at 4:47 PM Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> At 01:00 PM 5/26/2020, you wrote:
>
> Long story short, my Dynon display reads low voltage=C3=82 due to the iso
lation
> diode. Is there a better choice?
>
> I have had my Essential buss installed for 10? years now.=C3=82 My Dynon
takes
> it's power=C3=82 from the E buss and uses that to display the system volt
age. My
> Q-200 is all electric and I really want to see what the actual voltage is
> there.=C3=82 Unfortunately, the voltage drop across the Schottky=C3=82 d
iode seems
> to be almost a volt. So, when flying I mentally=C3=82 add a volt to the d
isplay,
> but I would really prefer not to, especially times when I might have othe
r
> 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 2
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| Subject: | Re: RX-7 Alternator mod - negative spike diode needed? |
>
>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.
Wouldn't hurt . . .
>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?
No positive spikes . . . not necessary.
>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.
Nice work!
Bob . . .
Message 3
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| Subject: | Re: Schottky diode voltage drop. |
The MB2505 bridge diode does not appear to be a Schottky type.
That is why it drops more than one volt. It also wastes energy as heat.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=496533#496533
Message 4
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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 5
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| Subject: | Re: Aviation wire |
For what it's worth, the supplier I bookmarked once (reasonable prices I
suppose):
https://prowireusa.com//c-32-m22759-16.aspx
Two thicknesses of insulation. Which to choose?
Cheers
Message 6
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>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.
They've become a LOT better and cheaper
since!
>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.)
You still have to break into the ground
path which involves terminations/splices
of some sort.
>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.
Which boards are you planning? I've got
an UNO DAS shield that was crafted to
mate with an Arduino R3. It's got one
dedicated LTS6NP sensor. The LTS6 has
three internal passes through the core
brought out on six pins. I've arranged
to exploit those internal passes with
terminals that place 1, 2 or all 3 in
series for 6, 3, and 2 amps full scale.
Of course, the drilled aperture is available
for customized passes on the monitored
conductor.
>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.
The device has
>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?
No
>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.)
Nothing magical about the 1 foot length.
The goal is to take 10% of total current through
the aperture while taking 90% around the aperture.
10AWG is 1 mohm/ft; 20AWG is 10 mohm/ft. What we're
looking for is a total paralleled resistance
of 1 mohm (10% of the 20AWG thru conductor).
If you want to parallel 10 mohm with something to
give you 1/10 the total you'll need about 1.1 mohms.
This would work out to about 13.2 inches of 10AWG.
My DAS systems just record raw, uncompensated
data. So 1 foot of 10AWG paralleled with 1 foot
of 20AWG gives me a total of 0.0091 ohms or
about 10% low for being a calibrated shunt.
You CAN calibrate the shunt-wires but it takes
careful cutting, splicing and verification.
My data analysis software allows me to apply
offset and scale factors to raw data to derive
calibrated data. Hence, my shunt wires need only
be in the ball park.
>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?
You need to strive for KNOWN, stable resistances . . .
unless you're using temperature stable resistance
materials, you'll want to use similar materials
for the two 'shunts'. Copper has a significant
positive temperature coefficient of resistance
and would normally make a 'rough' shunt. In
this instance, I don't care about the absolute
resistance, only the RATIO of the two resistances.
Being of similar material, the division ratio
is relatively independent of ambient
temp and temperature rise due to current
flow.
You haven't shared how many apples are already
in your 'cart' . . . don't what to toss off
too much effort but be aware of availability
of the DAS shield illustrated. The assembled
Arduino boards includes an SD memory card
socket. The software allows user selected
sample rates and writes data to comma delimited
ASCII files. If you'd like to explore this
hardware in more detail, I'll get you the
schematics. AEC-Lister Paul Fisher has put
considerable effort into the supporting
software. I'm pretty sure he'd be interested
in spooling this project up again.
Bob . . .
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