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02-24-2019, 04:49 PM
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Join Date: Jul 2007
Location: Madison, Wisconsin
Posts: 778
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Quote:
Originally Posted by Jonathan Alvord
Voltage 12.9 amps 10 I believe all in the green on the EIS and displays. Half way back in VFR all the avionics turned off...
We were able to jump the power to the avionics and it still works , just not from the switch. When testing the panel for endurance fuses (fuel pump, manifold pressure, avionics, EIS, and inst lights) we could only get 2.7v, All of the Main fuses were working (nave lights, auto pilot, pitot, strobe, trim ignition, trim switch, landing, pwr source 1, interestingly Power source 2 had no fuse in it).
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Sure sounds like you have a problem between the main bus and the endurance bus - either a connection gone bad or the avionics/endurance bus switch itself.
The alternator could be a red herring. You say you believe voltage was 12.9 - any chance it was 13.9? "All in the green" implies that there was normal voltage (unless the alarm limit was set incorrectly).
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Alan Carroll
RV-8 N12AC
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02-26-2019, 07:47 PM
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Join Date: Feb 2018
Location: Prosser, WA
Posts: 107
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Update
Thanks everyone for you help and opinions, they are much appreciated. After some more testing and downloading a wiring diagram that closely resembles N122EF we determined that rectifier (diode) had 12.7v going in and only 2.7V out which also matched the E-Buss power in. Its also the only thing that could have gone bad that wasn't easily diagnosed/replaced. When bypassed everything works great. New rectifier is ordered, actually 2 have been so it will never happen again. Hopefully this will solve the problem of the charging system as well as I have checked all the lines for continuity, ground, etc. and all appear to be operative but we will chase that squirrel once the EFIS/EIS have power.
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N122EF RV7A
S40 Prosser Washington
=VAF Dues paid 2019=
Last edited by Jonathan Alvord : 02-26-2019 at 07:52 PM.
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02-26-2019, 09:26 PM
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Join Date: Mar 2013
Location: Houston,MS
Posts: 63
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Questions
Does your plane have a Ebuss switch? The picture looks as if it does not. Therefore no dedicated/alternate power for the Ebuss. Therefore no need in the diode. The diode prevents you alternate power from powering the main bus. Glad you tracked it down
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RV-4 flying
F1 Rocket
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02-27-2019, 02:20 AM
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Join Date: Feb 2018
Location: Prosser, WA
Posts: 107
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Quote:
Originally Posted by Mjuckes
Does your plane have a Ebuss switch? The picture looks as if it does not. Therefore no dedicated/alternate power for the Ebuss. Therefore no need in the diode. The diode prevents you alternate power from powering the main bus. Glad you tracked it down
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It does have an ebuss switch.
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N122EF RV7A
S40 Prosser Washington
=VAF Dues paid 2019=
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02-27-2019, 03:27 AM
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Join Date: Oct 2013
Location: Harare, Zimbabwe
Posts: 200
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Quote:
Originally Posted by Jonathan Alvord
Thanks everyone for you help and opinions, they are much appreciated. After some more testing and downloading a wiring diagram that closely resembles N122EF we determined that rectifier (diode) had 12.7v going in and only 2.7V out which also matched the E-Buss power in. Its also the only thing that could have gone bad that wasn't easily diagnosed/replaced. When bypassed everything works great. New rectifier is ordered, actually 2 have been so it will never happen again. Hopefully this will solve the problem of the charging system as well as I have checked all the lines for continuity, ground, etc. and all appear to be operative but we will chase that squirrel once the EFIS/EIS have power.
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Sounds like you have found your problem! However looking at how the rectifier is wired you may be able to make an improvement quite easily. As wired you are only using 1 diode in the rectifier, but there are of course 4 in there. You could solve your immediate problem by simply moving the white wire diagonally across to the bottom right contact, which should use a different diode in the rectifier. When you do get a new rectifier, I believe it is possible to run wires to both the top left and bottom right (as per your photo) thus using 2 of the diodes instead of just 1.
Perhaps someone more experienced could confirm I am correct?
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Ed Fleming
RV-7- Nearly there!
Harare, Zimbabwe
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02-27-2019, 06:56 AM
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Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
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Ed,
You're right about using a pair of the diodes in the block, but he does need to be sure that the diode block is sized properly for the load, and is properly heat sinked if it's operated at any significant percentage of its rated capacity. And rather than guess at terminals due to orientation in a pic, the pair of source wires should go to the two '~' terminals, and the load wire should go to the '+' terminal, with the '-' terminal having no connection.
Jon, hopefully, you'll create an accurate diagram of the system. You may well have found your problem, but I spent over 40 years working around that type of diode block, and while I've seen them fail shorted, and fail open, I don't recall ever seeing one fail to simply high resistance (which is what your description of symptoms implies).
Charlie
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02-27-2019, 01:09 PM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,596
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Some thoughts:
- The old block silicon bridge rectifiers where nice things to play with back a few decades ago, but for aircraft use I offer there are hundreds of better 20-30 amp dual package Schottky Diode to consider. I buy mine from Allied Electronics - they run $2-$6 a piece.
- I would not consider a vital buss being fed only via an isolation diode as acceptable. The only place I use isolation diodes is the output of the standby alternator going through a set of diodes to the left and right avionics buss. This prevents a fault on one buss taking down both. Each buss is normally powered via a dedicated power relay from separate batteries (two PC-625 batteries). The standby alternator provides power to each buss automatically if the primary alternator fails.
Carl
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02-27-2019, 01:16 PM
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Join Date: Jul 2013
Location: US
Posts: 2,251
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Quote:
Originally Posted by Carl Froehlich
- I would not consider a vital buss being fed only via an isolation diode as acceptable.
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Ummm....Why not?
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2019 Dues paid!
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02-27-2019, 01:37 PM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,596
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Quote:
Originally Posted by RV7A Flyer
Ummm....Why not?
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Because there are better options.
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02-27-2019, 02:32 PM
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Join Date: Jul 2013
Location: US
Posts: 2,251
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Quote:
Originally Posted by Carl Froehlich
Because there are better options.
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There are always "better" options. But what is unacceptable about the original solution?
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2019 Dues paid!
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