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05-17-2018, 07:31 PM
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Join Date: Jul 2014
Location: West Covina, Ca
Posts: 52
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Responding to Ross's comment:
" I'll put the question out there though- what are the diodes really doing for you though with the isolation switches on each bus feed, assuming you have only one source at a time connected to the bus, current can only flow one way. I'm thinking they could be ditched too. I've seen diodes fail both shorted and open a number of times over the years."
Yeah, good point. I was initially thinking that in an emergency, I would possibly flip a "both" battery switch. But that does bring in the diode reliability thing. Is there more merit in having a single three position switch for "Battery 1-OFF-Battery 2"? That would now bring me down to two contactors and one switch. I could keep two separate SPST switches, maybe that would be more reliable? (although that allows someone to flip both ON and possibly backfeed some bad voltage).
And the high current switch possibilites look interesting, thanks Charlie and Carl.
Great comments, thanks!
__________________
Cliff Langlois
Meridian, Idaho
Cliffsrv10.blogspot.com
Project Sold 9/2018
RV-10
Empennage finished!
QB Fuselage and wings in hand
Taking a bite of the elephant every day.
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05-17-2018, 07:35 PM
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Join Date: Oct 2017
Location: bellingham, wa
Posts: 202
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I prefer relays to switches carrying power. I have changed lots of switches in my life. Maybe one normal relay I have changed, not counting a few starter relays. Different animal.
My engine bus will be powered through a relay, unless someone convinces me otherwise, which i am open to.
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05-18-2018, 06:05 AM
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Join Date: Nov 2006
Location: Savannah, GA
Posts: 1,029
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Quote:
Originally Posted by rv6ejguy
If we do a single schematic with every wire and pin shown it would be very hard to follow the basic concepts being discussed in this thread. We prefer to have separate drawings to more clearly illustrate each section. This is simply an overview of the basic power and ground connections, switches and breakers.
Lots of people's eyes glaze over when you have 150 connections shown on one frame.
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I don't think Dan's saying that we need the detailed wire-by-wire diagrams in this thread. For our purposes here, and for understanding the basics of the system, the simple block diagrams work well. But for installation, troubleshooting, etc. it would be really nice to have a full wire diagram with everything on it. Or even full separate diagrams for each harness. Just looking at the documentation as it stands right now, I don't really see enough to feel confident in installing and terminating the harnesses that would come with a kit.
Quote:
Originally Posted by rv6ejguy
I'll put the question out there though- what are the diodes really doing for you though with the isolation switches on each bus feed, assuming you have only one source at a time connected to the bus, current can only flow one way. I'm thinking they could be ditched too. I've seen diodes fail both shorted and open a number of times over the years.
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I think that's an invalid assumption with most of the people proposing systems here. At least, my intent with diodes is to have redundant power feeds going to the engine bus that are both on under normal operations.
__________________
RV-7ER - finishing kit and systems installation
There are two kinds of fool in the world. The first says "this is old, and therefore good"; the second says "this is new, and therefore better".
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05-18-2018, 06:15 AM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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Quote:
Originally Posted by rmartingt
I don't think Dan's saying that we need the detailed wire-by-wire diagrams in this thread. For our purposes here, and for understanding the basics of the system, the simple block diagrams work well. But for installation, troubleshooting, etc. it would be really nice to have a full wire diagram with everything on it. Or even full separate diagrams for each harness. Just looking at the documentation as it stands right now, I don't really see enough to feel confident in installing and terminating the harnesses that would come with a kit.
I think that's an invalid assumption with most of the people proposing systems here. At least, my intent with diodes is to have redundant power feeds going to the engine bus that are both on under normal operations.
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We have ECU pinout diagrams if you need them. When we leave the FWF cables unterminated, you get the connectors and pins in a bag for each sensor with the wire colors and terminal numbers/letters marked. Each cable is marked on the ends as well. Easy to match up and do. Each sensor has a multi conductor, sheathed cable to keep things clean for routing. I've never liked the all white wire thing they commonly do in the aircraft world so we use multi colored single conductor wires to make things easier to trace and hook up like in the automotive world. All Tefzel of course.
On the second point, just throwing the diode thought out there to make people think. If you'll have both batteries feeding your engine bus at the same time the diodes serve a purpose, otherwise not and are another possible failure point which could bring you down to only one power source.
Last edited by rv6ejguy : 05-18-2018 at 07:32 AM.
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05-18-2018, 07:46 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by rmartingt
But for installation, troubleshooting, etc. it would be really nice to have a full wire diagram with everything on it.
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Or merely assessing it before buying it.
Quote:
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I think that's an invalid assumption with most of the people proposing systems here. At least, my intent with diodes is to have redundant power feeds going to the engine bus that are both on under normal operations.
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Precisely.
Perfect = The failure of one feed requires no immediate pilot action to keep the fan turning.
Acceptable = The failure of one feed requires a single pilot action, preferably standard and familiar to all operators.
Unacceptable = The failure of one feed requires several pilot actions, in some specific order.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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05-18-2018, 08:34 AM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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Quote:
Originally Posted by DanH
Or merely assessing it before buying it.
Precisely.
Perfect = The failure of one feed requires no immediate pilot action to keep the fan turning.
Acceptable = The failure of one feed requires a single pilot action, preferably standard and familiar to all operators.
Unacceptable = The failure of one feed requires several pilot actions, in some specific order.
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The docs are right there on our Aircraft Page under the bold type heading "Aircraft Manuals and Documentation". ECU pinouts for the 2 DB connectors here: http://www.sdsefi.com/em5aviationpinout3.pdf
The programmer ports use a molded data cable so you can't get that one wrong.
For the 16pin Molex connector, there are several different configurations depending on the system and type of injectors and options used. Happy to send anyone info on that aspect if you need it for troubleshooting your specific system. Color coded wiring here makes things pretty easy IMO.
A fair percentage of folks don't count wiring as their #1 forte. A simple, uncluttered layout for each aspect is far easier for them to grasp we've found after doing this stuff for 25 years.
Last edited by rv6ejguy : 05-18-2018 at 08:43 AM.
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05-18-2018, 09:13 AM
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Join Date: Jul 2014
Location: West Covina, Ca
Posts: 52
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Diodes in power design
I would LOVE to keep diodes in the design, and have both batteries supplying power as needed. However, I re-iterate what I was told by the automotive electrical designer: (and also reflected by Ross)
"I am suspicious of parallel operations. I have tried paralleling power supplies, coils, and transistors and due to imperfect matching things get hot due to oscillations: on and off and the switching causes heat. Getting the parallel devices to conduct equally is not easy. It also does not offer the same safety factor as having tested redundant components that can be switched out and in as needed. Some math analyses would be needed to verify this.
Another concern is that diodes can fail either open or short. I am not sure and will do some more thinking about the impact of a shorted diode. An open diode by itself would not be a problem, other than being able to detect and replace when back on the ground. What is not wanted is one battery draining into the other; one or both batteries might fail. To me a switching arrangement would be better. That is switching in and out either power system to either critical component set. The best would be on the ground checks, before air, of both power systems and both sets of critical components and then the capability of switching."
In light of the above statements, can anyone make a good rebuttal? Or offer a concept that avoids paralleling the batteries? Again, a redundant power source that does not need to be switched would be preferable, if it can be safely implemented. Trying to learn here....
__________________
Cliff Langlois
Meridian, Idaho
Cliffsrv10.blogspot.com
Project Sold 9/2018
RV-10
Empennage finished!
QB Fuselage and wings in hand
Taking a bite of the elephant every day.
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05-18-2018, 09:45 AM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,597
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Quote:
Originally Posted by Pukauma
I would LOVE to keep diodes in the design, and have both batteries supplying power as needed. However, I re-iterate what I was told by the automotive electrical designer: (and also reflected by Ross)
"I am suspicious of parallel operations. I have tried paralleling power supplies, coils, and transistors and due to imperfect matching things get hot due to oscillations: on and off and the switching causes heat. Getting the parallel devices to conduct equally is not easy. It also does not offer the same safety factor as having tested redundant components that can be switched out and in as needed. Some math analyses would be needed to verify this.
Another concern is that diodes can fail either open or short. I am not sure and will do some more thinking about the impact of a shorted diode. An open diode by itself would not be a problem, other than being able to detect and replace when back on the ground. What is not wanted is one battery draining into the other; one or both batteries might fail. To me a switching arrangement would be better. That is switching in and out either power system to either critical component set. The best would be on the ground checks, before air, of both power systems and both sets of critical components and then the capability of switching."
In light of the above statements, can anyone make a good rebuttal? Or offer a concept that avoids paralleling the batteries? Again, a redundant power source that does not need to be switched would be preferable, if it can be safely implemented. Trying to learn here....
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I?ve been running parallel batteries (normal operations mode) for 16 years in four, soon to be five RVs.
For one application I have the output of the standby alternator feeding the left and right Avionics busses via diodes. I do this so a fault on one buss would not take down the other buss. In short, I offer you concerns on diodes in not warranted assuming the components used are of appropriate ratings.
There in no magic in parallel machines or batteries. There is a lot of documentation out there to review.
Carl
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05-18-2018, 11:40 AM
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Join Date: Oct 2014
Location: Cedar Rapids, IA
Posts: 232
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Quote:
Originally Posted by Pukauma
In response to:
Unitink72:
"First of all, will you have regulators that you can adjust?"
Yes, BandC also.
"I don't think you need two switches to feed the engine bus."
I would defer to the post from Ross at SDS......."With any layout, we feel you must have a way to isolate the essential bus from each battery and alternator because if those go bad in some way you can take down the ECUs."
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Can we get specific about buses going "bad in some way"? These are the things I can think of off the top of my head, in reference to my design: - Overvoltage - Handled by the regulator
- Contactor Fail open - no biggie the main bus dies but Aux picks up the slack. Aux contactor no issue.
- Contactor fails closed - figure it out on the ground
- Main->ESS bus wire shorts - diode protects Aux backfeeding the short. Assumes diode is installed close to ESS bus so little chance of the short segment after the diode shorting.
- AUX->ESS bus wire shorts - Need to throw the ESS Aux Feed Switch if short is before the switch. If short is after switch, Main bus will short also
- Main->ESS diode fails open/closed - Ok assuming its the only failure.
This has been a good exercise, I've discovered the weak point is the wire between the diode/switch and ESS Bus. Did I miss any?

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