Power system architecture for EFI

[DanH]

Originally Posted by Mich48041

Yes. Normally open contacts are held tightly together by a strong
electromagnet. Normally closed contacts depend on a spring to hold them
together. The spring is not very strong compared to an electromagnet.
N.O. contacts might bounce less when closing.
Some automotive relays are rated 40/30 amps. 40 amps for N.O. & 30 for N.C.

Thanks Joe. I was aware of NC de-rating (like 30/50 and 15/20)....

https://www.delcity.net/images/lined...20170424182940

....but 3 amps NC with a 30 amp NO rating? I had no idea the NC rating could be that small a percentage. My "something-learned-today". The linked order page didn't offer a clue:

https://www.alliedelec.com/schneider...d-12/70185034/

[vlittle]

Originally Posted by 444TX

Ross and group

I work on cars from near new to very old age, just out of warranty to worn out. We have replaced relays with as little as 40,000 miles and I personally have cars with 400,000 miles that have everything original except the water pump, brakes, and maintenance. What happens while under manufacturers warranty is not usually experienced by me, but plenty does goes wrong. I hear the stories. Mileage and age are not the only factors.

1. We have replaced more than a few Bosch type alarm relays where the normally closed contacts are bad and the starter will not engage. As stated on a previous post, we have replaced hundreds of relays with problems with the normally open section. A relay is just another switch. Again, I feel they are becoming over used in circuit design.

2. Has anyone here ever had a Honeywell TL switch failure? I have seen several Carlin switches fail at the rivets (Can send pictures). Only Honeywell with screw terminals on my planes. Same for B&C alternators and starters.

3. I have seen strobe and fuel pump switch fast-on connections with heat damage, along with Bus brand fuse boxes with heat damaged fuses and melted plastic (can send pictures). All crimps and terminals appeared to be OK. Fast-On's are OK in general, but I feel EFI requires higher quality where possible. Redundancy can make up for the risks. Two EFI bus power sources, two independent fuel pump circuits, one independent backup ignition source, backup fuel system (see: Dave Anders install information, Cessna 185 missionary backup fuel system).

4. We have been running fuel injection on mechanical fuel pumps, with the electric pump only used for starting and TO/Landing. Now they will be necessary, not a backup. I have concerns and would want two independent pump circuits, not on one switch or relay, and carefully check electrical connections at every annual. Time will tell.

5. I see strange electrical failures with low mileage older aged vehicles. My RV8 is 16 years old. What will we do with old EFI computers, injectors, sensors. I have witnessed EI pickups, LS ignition modules, ignition coils fail and have witnessed intermittent problems. These planes will not be new forever. What are the plans here? Run until failure?

6. Terminal quality and crimps are important. A Daniels sub-D, environmental splice, Thomas Betts Sta-Kon WT145A style crimpers along with tefzel strippers are a good start, can be purchased on E-bay, and will provide high quality connections. Here is not the place to be cheap, there is a difference. Larger cable ends can be done with an inexpensive hydraulic crimper purchased on E-bay. They do a great job and are easy to use. An RV10 crashed with fatalities because of an improper crimp and Van's has a Service Letter for improper cable crimps.

7. Quality relays only. The ones on post #101 spec well and one can double up the contacts for load sharing. Same goes for switches.

8. Some of these diagrams have no redundancy and lack pilot control. I would have two battery power sources that could be used simultaneously or isolated, along with EFIS monitor/aural warning of both sources. I would want independent control of the fuel pumps allowing both for takeoff and landing. Both on the Battery EFI Bus, maybe one on a breaker or relay controlled by the ECU and the other on a stick grip controlled relay or panel switch by the throttle for takeoff, landing, emergency. I would run the coils and ECU from a dedicated EFI breaker panel, fewer switches and still maintain control.

I woke up this morning thinking I could find no good reason to install an EFI system on a Lycoming equipped airplane. Any benefits would be minimal at best and the complexity and chance of a dangerous fuel system failure is far greater. I like modern technology, but not for the sake of technology. Some will make the decision and install EFI, some will pursue (like alternate engines) and go back to the old tried and true Bendix style injection. Just go in, realizing the risk and responsibility, with eyes wide open. Sorry, but I will still continue to try and help to the best of my ability.

George Meketa
ASE master tech, A&P mechanic

I had Carling switch failures in my RV-9A leading to burnt wiring and terminals in 2006. I published a forensic analysis on VAF and Aeroelectric but it is now obscured in the depths of the interweb. Conclusion: Never use Carling switches. The Honeywell TL switches are better. In my Rocket, I eliminated all load carrying switches and went to an array of relays controlled by low current switches.

As George mentioned, the rivets on the Carlings allow vibration, stress and current to degrade the connection. This can lead to thermal runaway with certain loads and smoke in the cockpit.

FMI http://www.aeroelectric.com/articles...h_Failure.html

[444TX]

In the past cube type relays often had NC de-ratings printed on the body. Not much anymore, but I do have a Potter Brumfield (T9AP5D52-12) panel mounted relay in front of me with a 10 amp NC / 20 amp NO spec printed on it.

The linked relay has no NC section? That is one reason, along with the silver contacts, that I like it. Specs are good, but quality materials and construction go a long way in the decision process. Some of the diagrams and posts here make much use of the NC section. Bad idea. Never for something like a fuel pump.

https://www.alliedelec.com/schneider...d-12/70185034/

Like I have been saying, relays are not the miracle devise many here believe them to be. Cut one open and look at the small contact areas. Use them sparingly and for function. Stick grips, dynamic braking / ground function for flap motors, sensor / warning lights, remote contactor functions, avionics annunciation, etc. I recommend a switch for important items: ECU power, at least one backup Bus power, at least one fuel pump on an EFI system, etc.

The electrical failure examples given here are clues to where we will see problems. I often tell my guys when they encounter some small subtle clue that "the car is talking to you", "are you listening?".

George Meketa

[rv6ejguy]

Rusty is using these Schottky diodes in his aircraft and he's been using these for years in other electronics he designs:

http://www.smc-diodes.com/propdf/122...17%20REV.A.pdf

[johnbright]

Originally Posted by Mich48041

George wrote, I took a Busman fuse block apart with the intent of modifying it so that it could be fed power at both ends for redundancy. While it was apart, I noticed that the fuse clips do not have much gripping strength. I decided not to use the fuse box in my plane because it was a poor design; weak fuse clips, cheap plastic could melt or burn, wires exited to the sides, not being compact takes up too much panel space. So I made my own fuse panel using
THESE fuse clips. They are board mounted fast-on connectors.

This is what a Buss 15600-08-10 ATC Fuseholder looks like inside https://photos.app.goo.gl/ZKjbqnU3DfkUKNex2

I'm not making an argument to use it or not; just showing the insides.

It's easy to add a 2nd power feed stud as shown in the photos.

[rv7charlie]

Two potential issues occur to me about using a fuse position as power input to a bus. One is a caution that a single blade position will have a current limit lower than the stud input location. The other would be the care needed in clearly labeling the unconventional input. Maintenance at a later date, particularly by a subsequent owner, could be somewhat hazardous if they weren't aware of the 2nd power input.

[rv6ejguy]

One of our clients sent along this photo today of his ECU install with ATO fuses feeding the circuits.

[rv6ejguy]

For those folks concerned about relay life, you can use these Tyco/ Potter Brumfield 70A relays VF-7-41F11.

http://www.sourceresearch.com/potter...ge=vf7_dsw.pdf

These won't have an issue switching any of the typical, under-10 amp loads associated with most EFI components. Not cheap but I've used them for many years, switching much higher loads. Zero failures.

[rv6ejguy]

I've used these Cole Hersee ATO/ ATC fuse blocks for many years with no issues in race cars and my aircraft. With the proper terminals used (below), you pretty much need pliers to pull the terminals off the blades.



These are the terminals I use for wiring. After crimping and pull test, I use double wall, glue infused, shrink tubing over the barrel and at least 3/4 inches back over the wire for strain relief and additional retention properties.

[johnbright]

Originally Posted by rv7charlie

Two potential issues occur to me about using a fuse position as power input to a bus. One is a caution that a single blade position will have a current limit lower than the stud input location. The other would be the care needed in clearly labeling the unconventional input. Maintenance at a later date, particularly by a subsequent owner, could be somewhat hazardous if they weren't aware of the 2nd power input.

Thanks Charlie... your comments inspired me to add a second 10-32 stud.

More photos at https://photos.app.goo.gl/ZKjbqnU3DfkUKNex2