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  #1  
Old 05-06-2019, 01:05 PM
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majuro15 majuro15 is offline
 
Join Date: Feb 2013
Location: Charlotte, NC
Posts: 558
Default Check those diodes!

Funny story:

I'm ready to flip the master switch for the first time Friday night. I've poured over schematics for years, wires for months, and rechecked connections and pins for days.

My B&C contactor is ready to rock electrons through my $XX,XXX panel for the first time, so nothing more is holding me back.

I flip the switch holding my breath only to hear a pffffffsssssss and see a trail of smoke coming from the firewall. The wife says, well that's not what we wanted to see. Yeah, you're right babe.

A phone call to Parish and 40 minutes of troubleshooting later I realized that one of the contactors from B&C has the diode facing one way while the other contactor has the diode opposite. Which one is right?

Long story short, one contactor came from them with the diode installed backwards and caused a short to ground on the power lead to the coil. Fortunately the only damage was 2" of 20 AWG wire on the contactor itself.

I called B&C and expressed my displeasure knowing that it came that way since it was impossible to reinstall (I never took it off the studs) backwards due to the way the diode had the terminals crimped and heat shrunk.

So, fixed the damage, gathered up all the magic smoke, stuffed it back in the wires and then enjoyed the fruits of my labor watching all of my avionics come to life!

Check your diodes!
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  #2  
Old 05-06-2019, 01:06 PM
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bkervaski bkervaski is offline
 
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Congrats! Pics please
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  #3  
Old 05-06-2019, 01:11 PM
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rswalden rswalden is offline
 
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Same thing happened to our RV-12 when the battery was initially connected. Sparks at the battery lead and abrupt power-on of the airplane.

The Vans-provided diode for the battery contactor relay was backwards. It's supposed to be foolproof with large and small ring connectors at each end to prevent this.
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  #4  
Old 05-06-2019, 02:23 PM
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RV7A Flyer RV7A Flyer is offline
 
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Location: US
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Quote:
Originally Posted by majuro15 View Post
I'm ready to flip the master switch for the first time Friday night. ...
My B&C contactor is ready to rock electrons through my $XX,XXX panel for the first time, so nothing more is holding me back.
I applaud your gumption , but a good take-away might be to not do an all-up test right off the bat, but rather test incrementally, adding each component as you go.

My first power-up of the master was to a single lighting circuit.

I don't know if I'd have the b@lls to do what you did LOL! Glad you sorted it out...it's an exciting time when the ship starts to "come alive"!
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  #5  
Old 05-06-2019, 02:34 PM
Mich48041 Mich48041 is offline
 
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The banded end of arc suppression diodes always connects to the positive terminal.
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  #6  
Old 05-06-2019, 05:04 PM
RandyAB RandyAB is offline
 
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Location: St Albert, Alberta, Canada
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Thank God it was just that. I would have cried right there. Iím not lying.
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  #7  
Old 05-06-2019, 05:32 PM
Jimbot Jimbot is offline
 
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Location: FL & NC
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Hi Tim,

I'm glad this ended up only being a minor issue.

Truth be told, as I was starting to read your post, my first thought when I got to the smoke part was...

"OH, SNAP!!!"
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  #8  
Old 05-07-2019, 05:54 AM
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majuro15 majuro15 is offline
 
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I'll get some pictures posted on my build log soon. It's too much work and fun building!

Since I'm using the ACM from AFS, you can't really do one circuit at a time. I know their stuff was all wired correctly, so I wasn't worried about that part. It was a big pucker moment flipping that switch!
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  #9  
Old 05-17-2019, 11:13 AM
Paul 5r4 Paul 5r4 is offline
 
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I don't remember how I first applied power to mine but I suspect just like you did. I do LIKE RV7A Flyer's advice of one circuit at a time and start with something that's not important or expensive..... GREAT ADVICE!

Your experience was a good lesson. Glad your smoke was an easy fix.
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  #10  
Old 05-18-2019, 04:56 AM
bobnoffs bobnoffs is offline
 
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you are so lucky your $xx,xxx panel didn't fry if it had been a bigger problem. like said before, start with the cabin light circuit. boy, the builders with electric dependent engines would have the ecu to worry about too.
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