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07-05-2012, 12:25 PM
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Join Date: Feb 2005
Location: Abilene, TX
Posts: 724
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Diode with a fuse upstream questions
This may be obvious, but:
If there is a 30amp fuse/breaker on the anode side of a 60 amp-rated diode, and you get an over-load on the cathode side that would normally cause the fuse to blow without a diode installed, will the fuse blow?
and...
If there was a direct short downstream of the diode, would the diode go TU?
Thanks for any clarification.
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Sam Evans
RV7-A O-360 C/S
VAF#812
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07-05-2012, 12:58 PM
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Join Date: Nov 2006
Location: Perham, MN
Posts: 350
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If the diode and fuse are in series, and the diode is rated for 60 amps and the fuse for 30 amps, the most current the diode will experience is 30 amps because that is the current at which the fuse will blow.
This a little over-simplified, but essentially, to answer your questions: Yes, the fuse should blow, and, No, the diode should not go TU.
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Paul Winkels
RV7 Standard Build - First flight 4/16/2016 - Now Flying!
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07-05-2012, 04:28 PM
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Join Date: Jun 2007
Location: Merritt Island, FL
Posts: 602
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A fast current spike exceeding 60 A might not result in a blown fuse, but it might result in a blown diode. However, most power diodes have significantly higher current ratings for transients - the faster the transient, the higher the current it can withstand.
Power also depends on how well the diode is heat sinked. A diode left hanging in the air will burn up at well under rated current. Any power diode should be thermally bonded to as much heat sinking metal as possible to keep it cool.
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Jeff Rosson
Repeat Offender
RV14 - Working on Empennage/Tail Cone
RV9A - Completed! First flight on July 18, 2012!
Based at Merritt Island, FL (KCOI)
VAF Number: 1170
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Star Trek Quote: "Logically, it could work. Also, logically, there are a hundred variables, any one of which could put us in a worse position than we're in now." Mr. Spock in Return to Tomorrow
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07-05-2012, 07:26 PM
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Join Date: Feb 2005
Location: Abilene, TX
Posts: 724
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Thanks, Paul & Jeff. (I like simple answers.  )
Yes, my setup is in series. (working on an e-buss)
Sam
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Sam Evans
RV7-A O-360 C/S
VAF#812
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07-05-2012, 07:59 PM
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Join Date: Jul 2009
Location: Longmont, CO
Posts: 236
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What kind of fuse are you using in series with the diode? A slow blow type of fuse might well not blow before the diode does, or - as often happens - the diode fails shorted, THEN the fuse blows, the worst outcome of all!
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Mark Olson
RV-7A First flight 2005 Sold 2019
F1-EVO Rocket First flight 2010
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07-05-2012, 09:56 PM
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Join Date: Feb 2005
Location: Abilene, TX
Posts: 724
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Quote:
Originally Posted by molson309
What kind of fuse are you using in series with the diode? A slow blow type of fuse might well not blow before the diode does, or - as often happens - the diode fails shorted, THEN the fuse blows, the worst outcome of all!
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ATO type fuse. I see that fast blow are available, so I'll be sure to use them.
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Sam Evans
RV7-A O-360 C/S
VAF#812
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