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Electrical System Planning - Input requested

akarmy

akarmy

Well Known Member
Like I really needed to ask. I'm sure I'll get a full dose of the input I desire.

The basics first. I'm building a very simple VFR only RV-8. Single Dynon Skyview 10" with a GTR200 radio / intercom. LED lights, dual P-MAGS, manual trims. No autopilot initially, but wired for the servos with brackets installed. PC680 on the firewall, B&C starter, Plane power alternator "with OV"...

My last plane had a basic Aeroelectric Z-11 primary / ebus. I'm looking to go even simpler with this one. Don't think I really need the endurance bus concept as the Dynon has a backup battery so what else is really needed to continue going or to land? Lastly, I'm leaning towards the dreaded avionics switch as I have a few devices that don't have a power switch and while they can be on during start, I would rather be able to cut them off if needed.

Here's what I have thus far. What am I missing?

12093432533_f91b0c7232_o.jpg
 
What you have drawn is almost identical to my rv-4 system. All I would add is put in a couple of extra breaker/fuses on the main bus just in case. I would also upsize the wiring and breaker to the avionics buss I think 10 amps is a little low. Look at the worst case the auto pilot starts trimming just as you key the mike and start transmitting an the transponder responds all at the same time. You don't want to loose the avionics buss right then. Just size the breaker/fuse,wire, and buss bar for 15 amps or so and you will be just fine.

Bob burns
Rv-4
n82RB
 
Hi Andy-

If you use a Plane Power alternator with built in OV you can ditch the external OV protection.

Otherwise your plan is very simple and very similar to mine. Like you I went ahead and used a avionics bus. In particular, I used it so that I could put my Dynon on it and start up with the av buss off and the Dynon running on its internal battery. Though I know it's not necessary per Dynon, it does isolate it from start-up spikes and also provides confirmation that the internal back up battery is working.

Also, like you, I think the e-bus is entirely unnecessary for most of the aircraft we build, especially VFR a/c. If I lose electrical power it's easy enough just to flip a few switches for anything not immediately needed.

Ditto the above post regarding upsizing av bus breaker a bit.

Sounds like you are making progress!
 
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Any reason you need those items on the battery bus? You could eliminate the batt bus altogether and put those on the main bus. Also, why are there switches on those two items?

P-Mags should have a switch so you can test the on-board generator.

As mentioned, starter switch and upsize the avionics master circuit.

Do you want switches on the exterior lights?

Electric trim? What type of flap control?

The Plane Power alternator has OV built in - you don't need a separate module as indicated.

Why do you have a fusible link for the alt field? Why not a 5A breaker? Also, you have both 18 & 20 AWG wire for the field. Recommend 18 for all.
 
Couple Minor Points

Having the alternator B-lead attach to the main contactor rather than the starter contactor eliminates a failure point (the starter terminal). Also the avionics bus switch is a single point failure. If you have internal batts on your critical avionics this is less of an issue. Some people install two avionics bus switches in parallel, one to each end of the bus bar. But these are minor points, really.
 
Have you already installed the Advanced AOA? If so, then disregard. If not, a perfectly fine AOA indication can be had on Skyview, either using the Dynon pitot or making your own.
 
I don't see fuses for your landing, taxi, and position lights. Since your -8 will be a trail dragger, you want to switch your landing and taxi lights independently. That is because your landing light will be aimed parallel to your wings and the taxi light will be aimed down.

I don't see a fuse for your Dynon's engine module, which should be on the main buss.

Regarding your P-mags, you can always use pullable breakers, which will allow you to drop power to them, for your pre-flight. (That or look at how I wired mine.)

Placing the wire size on your schematic for each circuit would be helpful.
 
n82rb said:
All I would add is put in a couple of extra breaker/fuses on the main bus just in case. I would also upsize the wiring and breaker to the avionics buss I think 10 amps is a little low.
Click to expand...

Sounds good on both fronts. I'll add those in. Thanks!
 
Oh, and I didn't see anything for interior or panel lights.

A cool trick Bret Smith did was to put very small white LED's under the wings, close to the tie-down rings and wired to the position lights. He did that to help when tying the plane down on a dark ramp.
 
MCA said:
Any reason you need those items on the battery bus? You could eliminate the batt bus altogether and put those on the main bus. Also, why are there switches on those two items?
Click to expand...

My thinking was to be able to switch them on without the master on so you could charge a cell phone or iPad while sitting parked (like when camping or traveling somewhere) for the USB ports, then the 12v one I use for trickle charging the battery so it's nice to switch on direct to the battery then switch off so it's not active all the time.

Thinking about it, I think you are right about the USB moving to the main bus, not really that much usage for that charge situation and the risk of leaving the device charging in the plane unattended is not the best.

Maybe move the 12V charge port to a single inline fuse and eliminate the battery bus.

MCA said:
P-Mags should have a switch so you can test the on-board generator.
Click to expand...

Yes I'll use a multi position switch for each PMAG allowing both p-lead and power to be cut to test them.

MCA said:
Do you want switches on the exterior lights?

Electric trim? What type of flap control?
Click to expand...

Yes lights will be switched, with double throw, off-taxi-landing + a separate wig-wag. Same for off-nav-strobe for the other switch.

no electric trims - all manual

A basic manual up / down flap control wired through a (down)-off-(up) switch.

MCA said:
Why do you have a fusible link for the alt field? Why not a 5A breaker? Also, you have both 18 & 20 AWG wire for the field. Recommend 18 for all.
Click to expand...

The fuse link is to protect the wire between the main bus lead and the switch all before the 5A breaker. Since there will be a bit of distance to go to the switch panel first.

Thanks for all the input!
 
Noah said:
Having the alternator B-lead attach to the main contactor rather than the starter contactor eliminates a failure point (the starter terminal).
Click to expand...

Good point.

Noah said:
Also the avionics bus switch is a single point failure.
Click to expand...

Yep, I'm ok with that, as my "avionics" is a single screen dynon with battery backup, really I'm only loosing the com radio / transponder.
 
krw5927 said:
Have you already installed the Advanced AOA? If so, then disregard. If not, a perfectly fine AOA indication can be had on Skyview, either using the Dynon pitot or making your own.
Click to expand...

I would be happy with the Dynon AOA if they would produce an external indicator. As they have not, I'm going with AFS so I can put the display on top of the glare shield. I had this setup in my 9A and just loved it. So easy to make landings having AOA in your field of vision while looking out at the runway. I will be using the AFS / Dynon probe that includes the AOA data so I could also feed it to both systems for redundancy, but not sure that's needed.
 
N941WR said:
I don't see fuses for your landing, taxi, and position lights. Since your -8 will be a trail dragger, you want to switch your landing and taxi lights independently. That is because your landing light will be aimed parallel to your wings and the taxi light will be aimed down.
Click to expand...

Yep, i'll have a progressive switch so off-taxi-landing positions to accommodate. The lights are a new design from AeroLED which should be pretty neat. Guess the question is, do I need to be able to have them both on at the same time?

N941WR said:
I don't see a fuse for your Dynon's engine module, which should be on the main buss.
Click to expand...

The Skyview EMS takes it's power from the SV-Net cable, not dedicated power (I think).

N941WR said:
Regarding your P-mags, you can always use pullable breakers, which will allow you to drop power to them, for your pre-flight. (That or look at how I wired mine.)
Click to expand...

Yes I'll do something like you did, or G-IKON's switch config. But basically yes switched power and p-lead to test everything.

N941WR said:
Placing the wire size on your schematic for each circuit would be helpful.
Click to expand...

Yep, will do.
 
good

I have very similar set up.

I'd up the Aux power port to 10A to cover anything you might want to plug in, just like in a car

Dynon EMS uses a fused input for voltage, I used 3A I believe

10A for LED nav/strobe seems high. I don't know what their landing lights need.

#22 awg on a 5A breaker? As posted already, recommend 18awg for alt field

My PP alt has OV internal so just field, bat, and indicator (failure light) wires to unit.

Good luck
 
Bob Nuckolls article on avionics master switches can be read here:http://www.aeroelectric.com/articles/avmaster.pdf
After reading that, it seems that installing an avionics master switch trades an imagined monetary
danger (damage to avionics) for a real safety of flight danger (loss of all avionics).
There is a way to address both dangers, perceived and real. Install some more switches.
Miniature toggle switches take up very little panel space.
If space is limited, two loads could share one switch.
One bus can supply current to all loads, no need for a separate bus.
Joe Gores
 
I have found starter solenoids to be redundant and an extra failure point. At 350A a small amount of resistance in the circuit will degrade starter performance. The starter already has a solenoid built-in. I don't wire them in. As long as the starter cable is properly supported and maintained it will never be a problem.
 
Double pole SW

If your worried about an avionics switch failure you can use a DPDT 3 position switch. Wired properly you have a backup set of contacts standing by if needed.
Agree on dumping the E bus, I have a small brown out/Aux battery on my plane and an E bus. After flying now I realize I have a belt, suspenders and duct tape holding my pants up. It's a bit silly for most missions.
I'm not saying the E bus isn't a good idea on some planes/missions.
Tim
 
rocketbob said:
I have found starter solenoids to be redundant and an extra failure point. At 350A a small amount of resistance in the circuit will degrade starter performance. The starter already has a solenoid built-in. I don't wire them in. As long as the starter cable is properly supported and maintained it will never be a problem.
Click to expand...

Hi Bob,

I pulled the archives on the topic and am convinced, one question, is there a similar solution for the B&C starter, I have not seen any mention if it can be wired in a similar fashion?

Looking at my Aerosport quote, it lists a skytec inline starter??? Is that the NL series? hum.
 
AF_Alan said:
I have very similar set up.

.......
Dynon EMS uses a fused input for voltage, I used 3A I believe
.....
Good luck
Click to expand...

I thought that too... but if you read the Skyview manual and wire list carefully that 'fused input' is the voltage measuring point, not the power input.

Pin 1 (red) is "Voltmeter 1 (0 to 30 volts DC)"

Pin 15 (red) is "Auxiliary 12 volt DC Output" for the fuel flow sensor.
 
Boost Pump

Not sure what boost pump you are using but mine (new airflow performance pump) states "The pump should be protected by a 10 amp.
circuit breaker. Electrical wiring to the pump should be a minimum of 16 gauge-stranded wire. The pump is supplied with 14-gauge wire." I used 14 ga for the short run to the pump.
 
Version 2

Ok, I've been taking in the input and making changes. The plan has taken a turn towards even simpler? Still thinking about removing the starter contactor depending on which starter I end of using. Here's the latest version.

12146659083_91d409acc1_o.jpg
 
akarmy said:
Ok, I've been taking in the input and making changes. The plan has taken a turn towards even simpler? Still thinking about removing the starter contactor depending on which starter I end of using. Here's the latest version.

12146659083_91d409acc1_o.jpg
Click to expand...

Which software are you using to draw your diagram? This looks really nice. Thanks!
 
KISS is better

Your latest is close to what I have in my RV-6, 650 hrs with no problems and no complaints. My plane is a basic VFR/Day and I followed the Aero Electric bible. My only differences from what you have are as follows. Instead of a double throw, double pole master switch/Alternator switch I used a single throw, double pole that insured you had the alternator on when you turn on the master. I then used a W23 circuit breaker for the alternator field that you can manually pull off as a means to shut off the alt field if needed, a very rare possibility. I placed the CB next to the master. I have my 12v electric outlets off the main buss instead of always powered as you have. I did not want anything plugged into it to drain my battery when not flying. This works well with my Ifly 700 since it has no power switch and powers up by plugging it in. I keep it plugged in and it now power on or off with the master switch.
 
mikehoover said:
Which software are you using to draw your diagram? This looks really nice. Thanks!
Click to expand...

I'm using a program called OmniGraffle which is a basic drawing app for the MAC platform.

http://www.omnigroup.com/omnigraffle/

I basically started drawing the components that I needed as templates to make adding them to the drawing easy. I'm basing the shapes on the drawings from aeroelectric.com which has lots of samples.

If you're using a PC, Visio is a very similar app.

http://office.microsoft.com/en-us/vi...103791871.aspx

You also can use any 2D cad program of which there are several free ones for both platforms.
 
akarmy said:
Hi Bob,

I pulled the archives on the topic and am convinced, one question, is there a similar solution for the B&C starter, I have not seen any mention if it can be wired in a similar fashion?

Looking at my Aerosport quote, it lists a skytec inline starter??? Is that the NL series? hum.
Click to expand...

Yes it can, I had a B&C starter for a period of time and had it wired without an external solenoid.

The switch must be able to handle high current.
 
Hey Andy. I don't know if your schematic is a physical representation of your system, but here's one suggestion:

Your ANL-60, like all fuses is there to protect your wiring. In this case, it should be as close to the battery (master) bus as possible-- not the alternator. It's there to protect against a short in the alternator, not protect the alternator from a short.


Cheers,
 
Version 1.5 update

Thanks for the catch Vern. I had just read about that in another thread.

Ok, here's version 1.5 after making more tweaks. It's slowing down a bit, so I think I'm almost done for now.

The main open decision is the elimination of the starter contactor. Looks like the SkyTec 149NL supports it, if I rewire it a bit. Need to find a good push button solution that will support the amp draw. I like the looks and function of the B&C red button with round bezel, but don't think it will support that amp draw.

Thanks for the help everyone! Really appreciated.

12194826924_b6e9681718_o.jpg
 
If you want to eliminate the starter contactor, I'd still recommend an automotive relay to control the solenoid. That way you can use a lower current pushbutton to control it.

I considered doing the same in my HR-II, but in the end I used a $10 contactor from ACS. No good reason, just my inherent conservatism.

Also, I highly recommend using 16AWG wiring in the alternator field circuit. The wiring harness from PP is 16AWG. This minimizes voltage drops in the field circuit which can cause noise and possible over voltage trips. In fact, if ever build again, I would use an externally regulated alternator and regulator with a separate sense circuit. In my opinion, internally regulated alternators are just too susceptible to resistance and voltage drops due to switch erosion or bad contacts in the field circuit to be reliable enough for aircraft use.
 
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Another thought?

What do you guys think about reducing the amount of different wire gauges and fuses in the design? For the very limited amount of wire we are using, how about eliminating all the 22gauge and 3A fuses and upsizing to 20gauge and 5A. Then move the 7.5A up to 10A and you could have the entire system a combination of 5A & 10A circuits. Seems like I could do 90% of the wiring with 20gauge and 16gauge wire outside of the large conductors FWF.
 
akarmy said:
Another thought?

What do you guys think about reducing the amount of different wire gauges and fuses in the design? For the very limited amount of wire we are using, how about eliminating all the 22gauge and 3A fuses and upsizing to 20gauge and 5A. Then move the 7.5A up to 10A and you could have the entire system a combination of 5A & 10A circuits. Seems like I could do 90% of the wiring with 20gauge and 16gauge wire outside of the large conductors FWF.
Click to expand...

This works, but a heads up... many avionics circuits use D-Sub connectors... the crimp terminals for these are for 22 or 20 AWG wires. I used 20 AWG for all of my avionics power circuits.
 
You will want to use a start solenoid

The inductive kick-back from the on-starter shift solenoid is huge. The arc induced across the contacts of a normal starter button will severely damage or destroy them in a few cycles. That's why it is common practice to use a "start-assist" contactor to control the big solenoid.

I am using one similar to http://www.bandc.biz/bandcstartercontactor12v.aspx.

These are nice because they have the coil spike-suppression diode built-in and they are more compact & lighter than the traditional "can" type solenoid.

With a little searching you can find a very similar device for about $20 less. These are derived from Ford start solenoids.

-Jeff
 
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