Electrical System Design

[whee]

I'm looking for a little feedback on my electric system. I've read Bob Nuckles book in its entirety😴 Lots of great information and he certainly provides a good/safe/reliable way of doing it. I can't help but let my own ideas influence the design though....probly for the worse.

For general info: My airplane will draw approximately 23A with everything on. Has an electrically dependent engine (SDS CPI ignition). Will be flown at night. Will have a GTR Sport usually displaying engine instruments and a tablet wirelessly connected to the sport to display flight instruments. Single alternator (B&C I hope) and dual battery (PC680).

First question is battery contractors. These are the standard but all use power to keep the contacts closed. Seems that most people use a standard contractor but have a Essential Buss with a relay that consumes less power to remain closed than a normal contractor. What about using a "perko" switch? I like the Blue Sea battery switches and could easily mount one in the pilot side kick panel. No waste electrical consumption and very reliable. Easily can switch from one battery or the other or both. Down side I see is that I'd have to bring bigger wires into the cabin. But these cables would only have to be AWG 10 though I'd probably go with 8 which really isn't that big.

Thoughts?

[PaulSA]

In my RV-10, I used a relay to get power to the ESS buss. With power on the main buss, the relay switched power from the main buss to the ESS. If power fails, the relay flips and takes power via a 20A fuse directly from the battery. I have a On/Off/Auto switch so that I can depower the ESS buss or bypass the relay and manually power it.

[whee]

Thanks Paul. I thought about doing something similar but decided to not do an essential buss and I'm trying to limit the number of components in my electrical system.

[marcusofcotton]

My plan is to not have an engine driven system so I plan on using mechanical switching instead of normal contactors. Details yet to be determined.

[jaredyates]

I'm reluctant to put myself into a position to direct discussion away from this venue, but being that your engine will stop running if your electrical system fails to perform, it might be advisable to start a thread on the AEC list also. There may be good reason to not use the mechanical switches, but being that it wasn't something I considered, I couldn't tell you if there is. There were some minor adjustments that I made to the Z-13/8, but only after (that) Bob agreed that they were superficial. The AEC list is the primary place to discuss any deviations from the original drawings. But do please keep us posted here too!

[Battson]

Mechanical switches will mean having all that power right behind the panel, flowing through the switch.
It seems the industry has deemed this more unsafe than using a relay or solenoid.

I would tend to imitate designs which are known to work, or be prepared to accept the risks in an open and transparent way. You want to be thoroughly aware of the consequences of failure.

In my system, I have a small secondary battery which is totally dedicated to keeping the engine (or half of it) running, in the unlikely event of total electrical failure of the battery and charging system. Everything else hangs off the other larger battery (PC680). The two can be switched together to charge, or to power "optional" devices during an emergency situation. My core avionics have their own independent batteries (very small).

[whee]

Thanks Jared. I'm not a fan of email groups and don't really want to join another list for one question. I tried to contact Bob directly and did get a reply that mechanical switches are fine but the leads from the battery "should be less than 12" long." I suspect this is because of high loads during starting. The design I'm considering wouldn't be carrying starter loads.

Battson, The architecture I'm considering mimics that found in a boat and is similar to that of an old Ford pickup. There wouldn't be any more power behind the panel than a conventional system; regular starting load wouldn't flow through the perko switch. The big difference is that the 'disconnect' is behind the panel rather than on the firewall. The leads from be would be protected with useable links.

Additionally, I know some builders have put their battery under the copilot seat. This battery placement means long battery cables and that all electrical power runs through the cabin.

[BTAZ]

Can you mount your disconnect switch to the firewall and extend the operating handle with a torque tube to the panel.

I had a Stinson 108 and that is how the fuel valve was set up. Valve was at the firewall and a torque tube with a lever stuck through the panel,

[schu]

I'm looking for a little feedback on my electric system. I've read Bob Nuckles book in its entirety😴 Lots of great information and he certainly provides a good/safe/reliable way of doing it. I can't help but let my own ideas influence the design though....probly for the worse.

It's your airplane, build what you want!

For general info: My airplane will draw approximately 23A with everything on. Has an electrically dependent engine (SDS CPI ignition). Will be flown at night. Will have a GTR Sport usually displaying engine instruments and a tablet wirelessly connected to the sport to display flight instruments. Single alternator (B&C I hope) and dual battery (PC680).

So by using a single alternator you are basically relying on battery power in the event of an alternator failure. In this case, you absolutely need a way to detect alternator failure. My alternator has a Alt Out Indicator lead (Plane Power internally regulated). You also need to make sure that you can turn off the alternator field.

I know you know this stuff, but since you must have electricity, I'm going to be redundant.....

First question is battery contractors. These are the standard but all use power to keep the contacts closed. Seems that most people use a standard contractor but have a Essential Buss with a relay that consumes less power to remain closed than a normal contractor. What about using a "perko" switch? I like the Blue Sea battery switches and could easily mount one in the pilot side kick panel. No waste electrical consumption and very reliable. Easily can switch from one battery or the other or both. Down side I see is that I'd have to bring bigger wires into the cabin. But these cables would only have to be AWG 10 though I'd probably go with 8 which really isn't that big.

I think this is a very good idea for a dual battery system, simply tying them together doesn't give you the ability to use or charge or test them separately which would be as easy as starting on batt 1, and then alternating to batt 2 to see if they give similar starting performance. The only cons I see are additional weight, and the master switch would be a big knob on the kick panel instead of on the panel.

When designing my electical system, I went the other direction. Instead of dual batteries, I bought the 8 amp B&C alt that mounts on the back of the engine and made it so that I can flip the Aux Alt switch to on and it brings the alternator onto the back side of the master contactor. I also have an E-Bus Alt Feed switch that powers the E-Buss also on the back side of the battery contactor. The idea is that I can loose the master contactor, or the alternator, or the master switch (or all three) and still have another way to power my E-Buss. The only relay is a S704-1 which I would guess has around a 400ohm coil (around 30ma to power it).

Usability is good, if the Alt out light lights up (or EFIS says low voltage) then turn on Aux Alt. If that doesn't fix it, then turn off master and turn on E-buss alt feed.

I have attached my drawing for reference.

electrical.pdf

[whee]

Can you mount your disconnect switch to the firewall and extend the operating handle with a torque tube to the panel.

I had a Stinson 108 and that is how the fuel valve was set up. Valve was at the firewall and a torque tube with a lever stuck through the panel,

That is a possibility I have considered. I'd likely use a mechanical contractor that uses a push/pull rod instead.

[whee]

Schu, Thanks for your feedback and sharing your drawing. It looks similar to one Bob N developed and published in his book. It's a solid design.

I wanted dual batteries and with dual 680s I'll run out of fuel before I run out of battery. I'll use B&Cs install kit which includes a alternator light and I plan to have a audible alarm through my headset.

[schu]

It's very similar to Bob's design, except it has a dedicated avionics master which he doesn't like. I used an aero electric visio stencil to make my drawing look like the book. I have another drawing for the avionics wiring that was reviewed by Steinair. I hope to have very good documentation for my airplane so that if I ever sell it, it's got BETTER documentation than a certified, at least in regards to wiring and panel.

schu

[AKKen07]

Hey folks, just thought I’d get some smarter folks to see if this plan will work. It is a AEC design with one change - then expanded to include both panel switches and relays in the second diagram just to see if I understand how it all works. I am currently assuming a 2 battery, one alternator design with an essential bus. The setup is designed so that either battery can function as primary and the other as a brownout battery for engine start. In other words they can be isolated, one for the main load and one only for the E bus and it can be done either way. I’m a long ways from wiring, just thinking ahead.

[AKKen07]

Trying again...

[svyolo]

Mine is similar but my 2nd battery is a pure backup battery, only for the E-buss. It is only charged from ships power if it is manually switch on to power the E-bus.
My reasoning for this is if I leave the master on and kill the main battery, I might also kill the 2nd battery if it automatically switches itself on. The 2nd battery can start the engine, but only with jumper cables, or a second dedicated switch. I haven't decided on that last part yet.

[svyolo]

I have gone "off the ranch" in my wiring compared to normal certified aircraft wiring. I did use aircraft logic, 1 alt, 2 batteries, from Bob Knuckoles. Plus another voltage regulator wired in. But I wired it all like a car built the last 30 years. I didn't get the idea from Bob, but he did confirm my decision either in his book, or his forum. I can't find it. Modern car electrical systems are the best.

Basically, the wiring becomes permanently installed in the aircraft, it is part of the airframe. A "body" harness. It can be worked on, but difficult to completely removed. But it absolutely minimizes connections, and connectors. There are more splices than AC43 likes, but they are in non-stressed locations. Cars do the same. You have connector pin-outs, but no need for wiring labels.

My second choice, or maybe my first, would be what a couple of manufacturers are doing like Dynon. They have central wiring distribution and power panel that does most of the work for you. It has double the number of connectors, which I don't like, but they will do the connections for you (which I like). The best connections are made by those who do it for a living.