Today's Message Index:
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1. 10:17 AM - Re: Clearance Delivery Diode Leakage (MFleming)
2. 11:33 AM - Re: Re: Clearance Delivery Diode Leakage (Dick Tasker)
3. 04:24 PM - Re: Clearance Delivery Diode Leakage (user9253)
4. 05:16 PM - Re: Clearance Delivery Diode Leakage (MFleming)
Message 1
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| Subject: | Re: Clearance Delivery Diode Leakage |
[quote="nuckolls.bob(at)aeroelect"]At 09:48 AM 12/30/2020, you wrote:
>
> 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).
So this is correct, there are no loads during this test. BUT there is not supposed
to be a load or current on the main buss in this photo during the test.
The test was supposed to verify that the diode is doing its job of preventing flow
from the CD bus back to the main buss when the CD buss is energized and the
main buss is deenergized. The test simulate the CD buss being energized while
the master contactor is open, ergo - main bus should show no voltage.
Now if your saying I need a load on the CD buss during this test great...but a
load or any current on the main buss would negate the test as far as I can see.
On the other hand it sounds like Bob is saying what I'm seeing is normal...so I
think I'll move on to more wiring.
--------
Michael Fleming
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=499930#499930
Message 2
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| Subject: | Re: Clearance Delivery Diode Leakage |
In an attempt to clarify: In the situation where the master contactor is off there
will be no active avionics on the master buss because there will be no power
to the buss. However, all the avionics
that reside on the master buss will still be connected and will thereby provide
a load on the buss.
In that situation, the diode will be doing what it is supposed to be doing and
if you measure the voltage on the master buss you will see nothing.
A diode is not a "perfect" one-way valve. Darn close, but it you have no load except
the 10 Megohm impedance of the DVM you will still measure something as you
discovered and as Bob described. This
is due to the reverse leakage of the diode - a very small number but not zero.
MFleming wrote:
>
> [quote="nuckolls.bob(at)aeroelect"]At 09:48 AM 12/30/2020, you wrote:
>
>>
>> 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).
>
> So this is correct, there are no loads during this test. BUT there is not supposed
to be a load or current on the main buss in this photo during the test.
>
> The test was supposed to verify that the diode is doing its job of preventing
flow from the CD bus back to the main buss when the CD buss is energized and
the main buss is deenergized. The test simulate the CD buss being energized while
the master contactor is open, ergo - main bus should show no voltage.
>
> Now if your saying I need a load on the CD buss during this test great...but
a load or any current on the main buss would negate the test as far as I can see.
>
> On the other hand it sounds like Bob is saying what I'm seeing is normal...so
I think I'll move on to more wiring.
>
> --------
> Michael Fleming
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=499930#499930
>
>
Message 3
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| Subject: | Re: Clearance Delivery Diode Leakage |
Check for electricity on the main bus using a test light.
The light will not illuminate. That means there is no voltage on the main bus.
Leave the test light connected to the main bus, then measure the voltage with
the digital meter again. The main bus will have zero volts. The diode is OK.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=499932#499932
Message 4
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| Subject: | Re: Clearance Delivery Diode Leakage |
user9253 wrote:
> Check for electricity on the main bus using a test light.
> The light will not illuminate. That means there is no voltage on the main bus.
> Leave the test light connected to the main bus, then measure the voltage with
> the digital meter again. The main bus will now have zero volts. The diode is
OK.
I see....The test light (load) on the main buss drains the residual voltage and
kinda make the diode seal better like a check valve with differential pressure
would.
--------
Michael Fleming
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=499933#499933
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