Today's Message Index:
----------------------
1. 04:22 AM - Re: Magnetos (racerjerry)
2. 06:19 AM - Re: Clearance Delivery Diode Leakage (user9253)
3. 06:22 AM - Re: Clearance Delivery Diode Leakage (user9253)
4. 07:54 AM - Re: Clearance Delivery Diode Leakage (Dick Tasker)
5. 12:03 PM - Re: Clearance Delivery Diode Leakage (MFleming)
6. 12:38 PM - Re: Firewall Penetration Redux (mike Pienaar)
7. 12:39 PM - Re: Clearance Delivery Diode Leakage (user9253)
8. 08:31 PM - Re: Clearance Delivery Diode Leakage (Robert L. Nuckolls, III)
9. 08:38 PM - Re: Re: Clearance Delivery Diode Leakage (Robert L. Nuckolls, III)
Message 1
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Efraim,
In order to simplify things, lets try to isolate the magnetos to see if they are
EVER actually producing a spark. First, pull all the top spark plugs to insure
there is NO COMPRESSION and no possibility of injury with the engine suddenly
coming to life. With all spark plugs removed, reconnect all ignition leads
and lay the plugs on top of each cylinder and insure that each plug is electrically
grounded to the engine. Try to aim the sparking end of the plugs outward
and to each side, so that a relatively weak spark can be easily observed.
View one side or one bank of cylinders at a time. That way you don't have to completely
remove and reroute the magneto ignition leads for the test.
At this point, since there is no compression in any cylinder, you can easily and
with complete safety turn the propeller by hand OR by the starter if you wish.
If you rotate the propeller TWO turns in the normal direction of rotation, a spark
should be observed at each sparkplug sometime during the two-turn rotation
at the instant you hear the loud click of the impulse coupling snapping free.
In other words, a spark should occur once every other propeller rotation at
the click.
Jerry King
--------
Jerry King
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=499903#499903
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| Subject: | Re: Clearance Delivery Diode Leakage |
A voltage drop across a diode is normal. A drop of o.4 volts is low. It will
be
2 or even 3 times that much under heavy load. Power (heat) equals volts
times current. Suppose that the load is 10 amps. 10 amps times 1 volt equal
10 watts. That is a lot of heat and the reason for the heat sink. If you want
to minimize the amount of power lost, a Schottky diode will waste about half
as much as a regular diode.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=499904#499904
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| Subject: | Re: Clearance Delivery Diode Leakage |
Use heat conductive paste between the diode and the heat sink.
Otherwise the diode could overheat and fail.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=499905#499905
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| Subject: | Re: Clearance Delivery Diode Leakage |
As far as I can see on your picture, you have no loads anywhere and have the positive
supply lead only connected to the CD bus. Under those conditions any voltages
you can measure are pretty much
meaningless. A good DVM has a very high input impedance so puts no load on whatever
it is measuring.
On the other hand, if there is any load on the main bus then you may have a defective
diode. To check, just put some sort of load on the main bus (resistor,
light bulb, relay coil, etc.). With a
load there I doubt you will see anything (unless the diode bridge is actually bad
- pretty unlikely).
Dick Tasker
MFleming wrote:
>
> The wiring has begun for my RV-7. I've decided to use fuse blocks for circuit
protection.
>
> The architecture will utilize a clearance delivery (CD) buss. The CD buss has
a diode installed per Z101B. When applying DC voltage to the CD bus and measuring
the voltage at the main buss, there is a 350 to 390 mv reading.
>
> Is that enough to worry about or do I have a bad diode? This is the B&C Essential
Bus Diode w/ 8 watt heatsink PN-221-200.
>
> Heres a photo of the fuse blocks while being tested for leakage. You may be able
to make out the 351.8 mv leakage.
>
> http://myplace.frontier.com/~tokosha/avionics/test_diode.jpg
>
> --------
> Michael Fleming
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=499896#499896
>
>
Message 5
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| Subject: | Re: Clearance Delivery Diode Leakage |
user9253 wrote:
> A voltage drop across a diode is normal. A drop of o.4 volts is low. It will
be
> 2 or even 3 times that much under heavy load. Power (heat) equals volts
> times current. Suppose that the load is 10 amps. 10 amps times 1 volt equal
> 10 watts. That is a lot of heat and the reason for the heat sink. If you want
> to minimize the amount of power lost, a Schottky diode will waste about half
> as much as a regular diode.
So the voltage feedback, leakage is the issue.
The voltage drop when the diode is supplying current to the CD buss from the main
buss is expected.
When the CD buss is being fed from the battery and the diode is supposed to prevent
the main buss from seeing current is when I'm seeing the 350+ millivolts.
I'm not sure if the feedback through the diode to the main buss is considered OK
or not.
user9253 wrote:
> Use heat conductive paste between the diode and the heat sink.
> Otherwise the diode could overheat and fail.
> Assuming that the heat sink will be mounted to an aluminum surface, also
> use heat conductive paste between the heat sink and mounting surface.
B&C provided the diode and heat sink as a unit so I'm hopping they assembled it
with the proper paste. Would dielectric grease be suitable as a heat sink paste?
--------
Michael Fleming
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=499916#499916
Message 6
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| Subject: | Re: Firewall Penetration Redux |
When I installed mine I put the pipe end of the fitting inside the cockpit
This is purely cosmetic, the firesleeve and sealer clamp are then out of sig
ht
=46rom the engine side you only see the wires bundle going into the fitting
Mike
Sent from my iPhone
> On Dec 29, 2020, at 2:28 PM, Robert L. Nuckolls, III <nuckolls.bob@aeroele
ctric.com> wrote:
>
> =EF=BB At 02:03 PM 12/29/2020, you wrote:
>> BobN,
>>
>> A couple of weeks ago you posted a picture of a Bonanza's firewall under c
onstruction. It shows a firewall pass-thru fitting with a 90 deg bend and s
ome sort of flange attached to firewall. What is that fitting made of?
>
> Beech fabricated their fittings from stainless
> steel.
>
>
> 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 7
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| Subject: | Re: Clearance Delivery Diode Leakage |
It is normal to see voltage like you are with no load. Put a load on the main
bus and that voltage will disappear. A 12 volt test light will make a good load.
Use a test light that does not have an internal battery. The test light should
operate off from the aircraft battery. Grease might melt. Home Depot and
Amazon sells part number 98003/202932736
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=499917#499917
Message 8
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| Subject: | Re: Clearance Delivery Diode Leakage |
At 09:48 AM 12/30/2020, you wrote:
>Tasker <dick@thetaskerfamily.com>
>
>As far as I can see on your picture, you have no
>loads anywhere and have the positive supply lead
>only connected to the CD bus.=C2 =C2 Under those
>conditions any voltages you can measure are
>pretty much meaningless.=C2 A good DVM has a very
>high input impedance so puts no load on whatever it is measuring.
>
>On the other hand, if there is any load on the
>main bus then you may have a defective
>diode.=C2 To check, just put some sort of load on
>the main bus (resistor, light bulb, relay coil,
>etc.).=C2 With a load there I doubt you will see
>anything (unless the diode bridge is actually bad - pretty unlikely).
Right on! I set up an experiment on
the bench with an exemplar bridge
rectifier. A multimeter set to read
leakage CURRENT indicated less than
0.1 microamps. Changing the meter to
read VOLTS gave an indication on the
order of 400mV.
What you're seeing is normal and expected.
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 9
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| Subject: | Re: Clearance Delivery Diode Leakage |
At 01:57 PM 12/30/2020, you wrote:
>
>
>user9253 wrote:
> > A voltage drop across a diode is normal. A drop of o.4 volts is
> low. It will be
> > 2 or even 3 times that much under heavy load. Power (heat) equals volts
> > times current. Suppose that the load is 10 amps. 10 amps times
> 1 volt equal
> > 10 watts. That is a lot of heat and the reason for the heat
> sink. If you want
> > to minimize the amount of power lost, a Schottky diode will waste
> about half
> > as much as a regular diode.
>
>
>So the voltage feedback, leakage is the issue.
>
>The voltage drop when the diode is supplying current to the CD buss
>from the main buss is expected.
>
>When the CD buss is being fed from the battery and the diode is
>supposed to prevent the main buss from seeing current is when I'm
>seeing the 350+ millivolts.
>
>I'm not sure if the feedback through the diode to the main buss is
>considered OK or not.
Doing the math on your observations:
Assuming a nominal 10,000,000 ohm input impedance
of your multimeter in the voltage mode . . .
E 0.400
I = --- = --------- = 4 NANOAMPS!
R 10,000,000
Some multimeters have as much as 20M Ohms input
impedance which would give you 2 NANOAMPS . . .
quite normal and insignificant.
If you put your multimeter into the current
measuring mode, the impressed current would
be too small to wiggle the display on the
most sensitive scale.
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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