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Sam
Joined: 18 May 2008
Posts: 135
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 Posted: Tue May 26, 2020 10:03 am Post subject: Schottky diode voltage drop. |
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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
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Sam Hoskins
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nuckolls.bob(at)aeroelect
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| Posted: Tue May 26, 2020 1:10 pm Post subject: Schottky diode voltage drop. |
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At 01:00 PM 5/26/2020, you wrote:
| Quote: | 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? |
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 . . .
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user9253
Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan
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| Posted: Tue May 26, 2020 3:44 pm Post subject: Re: Schottky diode voltage drop. |
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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.
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Joe Gores |
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Sam
Joined: 18 May 2008
Posts: 135
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| Posted: Wed May 27, 2020 4:42 am Post subject: Schottky diode voltage drop. |
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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(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 01:00 PM 5/26/2020, you wrote:
| Quote: | 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? |
 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 . . .
|
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Sam Hoskins
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user9253
Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan
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| Posted: Wed May 27, 2020 8:59 am Post subject: Re: Schottky diode voltage drop. |
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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.
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Joe Gores |
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Colyn Case
Joined: 12 Oct 2009
Posts: 13
Location: Thetford Center
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| Posted: Thu May 28, 2020 2:40 pm Post subject: Re: Schottky diode voltage drop. |
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if you are interested in minimizing Vf it's worthwhile looking at the Vf curves on the device you want to use. Here's one from the IXYS DSS2x81-0045B. A few trends: Lower Vf is associated with lower current and with higher operating temp. This particular device has two diodes in the package so you can cut your current in half by using the two diodes in parallel.
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Colyn Case
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