RV-10 Electrical System

[AviatorJ]

Was out of town for a week on business and used my flight and down time to read through Marc's book. Was initially put off with it only being 80 pages but once I got into it I found it had quite a bit of information. I made a series of notes and today I updated my Power Distribution drawing accordingly.

Want to ask about sizing an alternator. How do you speculate the pull on sporadic amperage outliers like Radio Transmitting, Strobes, ect? Was thinking a primary Plane power 70 amp with a 30 amp backup.. but wanted to run some numbers to make sure that was going to work.

[AviatorJ]

Resurrecting this thread vs starting a new. I'm diving back into the electrical planning this month and I plan to get everything worked with and ordered from Stein in January. I'm trying to simplify everything as much as possible but still have a capable IFR setup with redundancy for safety. The catch all on my setup is the Garmin G5-- If ALL else fails it has an independent battery that should keep it powered for 'up to 4 hours'. So here are the changes I'm thinking and wanted to get any feedback while I work through this.

- Start Button - I'm backing off my original setup of having the mag switches function as the engine start sequence. It's still a neat idea but adds some complication and also requires you to have your hand off the stick to start the plane. Now I'm going to put the start switch on the stick. The VPX will disengage the starter function once the planes running so I'm less concerned about accidentally hitting the button in flight. My question is do I put this on both sticks or just one?


- Dual Batteries - Technically a setup with IBBS could be considered two batteries I suppose. However the IBBS only powers a handful of devices in the case of an outage, but is somewhat independent of the VPX, so if that drops I can still get power to a G3X, GTN 650 and a few other things. Lately I've been thinking about instead doing two EarthX 900 batteries, but even with a drawing from Carl I can't tell if this is more complicated or not... to get away from the single point of failure of the VPX it seems I would have to have a separate essential bus. Am I missing something?


- Dual Alternators - If I can get an hour or so of extra power from the batteries and up to 4 hours on the G5, do I really need an extra alternator? I've had an alternator go out a few times while flying and it's always a bit of a non-issue. My gut is saying do it anyways because you're only talking a few extra wire runs and it should extend your backup endurance by quite a bit.


Any feedback will be appreciated. Thanks!

[tspear]

Originally Posted by AviatorJ

- Start Button - I'm backing off my original setup of having the mag switches function as the engine start sequence. It's still a neat idea but adds some complication and also requires you to have your hand off the stick to start the plane. Now I'm going to put the start switch on the stick. The VPX will disengage the starter function once the planes running so I'm less concerned about accidentally hitting the button in flight. My question is do I put this on both sticks or just one?

Why re-invent the wheel and deal with the trouble of extra wiring in the stick. Save that button for something you use more than once a flight.
You really need a handle on the throttle and the starter switch. That is all; so go sit in a dozen certified or existing RV planes and see which solution you like. Button position to the left of the stick, in the center high on the dashboard...

Originally Posted by AviatorJ

- Dual Batteries - Technically a setup with IBBS could be considered two batteries I suppose. However the IBBS only powers a handful of devices in the case of an outage, but is somewhat independent of the VPX, so if that drops I can still get power to a G3X, GTN 650 and a few other things. Lately I've been thinking about instead doing two EarthX 900 batteries, but even with a drawing from Carl I can't tell if this is more complicated or not... to get away from the single point of failure of the VPX it seems I would have to have a separate essential bus. Am I missing something?


- Dual Alternators - If I can get an hour or so of extra power from the batteries and up to 4 hours on the G5, do I really need an extra alternator? I've had an alternator go out a few times while flying and it's always a bit of a non-issue. My gut is saying do it anyways because you're only talking a few extra wire runs and it should extend your backup endurance by quite a bit.


Any feedback will be appreciated. Thanks!

Extra batteries and dual alternators should largely depend on the kind of flying you do. If a VMC flyer, keep it as simple as possible. If IMC of marine layers on the coast, you may need to fly hours to get to VMC conditions, in which case redundancy matters. Dual batteries and dual alternators is the "ultimate" expression of this.

Tim

[rleffler]

Start button - My preference is for it not to be on the stick, but if it was, I would only put it on one. I also have a button that interrupts the ground to all functions on the right stick, which effectively disables all functions. Great for flying Young Eagles and other youth in the front seat.

Batteries - I have two Odyssey 680s.

Alternators - I have two as well.

For the last three years, it's worked as designed. I did have to modify the schematic a bit from the VP/X manual to accommodate two batteries and alternators. I have one switch that enables one or the other alternators, so that I can never have both enabled at the same time. Another switch isolates or puts in parallel the 680 batteries.

[Carl Froehlich]

Recommend you not put the starter button on the stick. I did this in my first RV and quickly found how easy is was to bump it while the engine was running. It got disconnected and the other two RVs never had it on the stick.

As I have posted in the past, two PC-625 batteries are easy to mount in the stock RV-10 battery position (some minor modifications to the mount needed) and if wired with some thought both are available for start but either can power the panel if you have a fault someplace. No other backup batteries required or desired.

On the RV-10 I did later add a standby alternator that feeds Avionics #1 and Avionics #2 via isolation diodes. I did this as I found the full glass panel and especially the GTN-650 to be power hungry - so the batteries gave me about 2 hours of reserve capacity. I wanted 3, so the standby alternator was added. I?m still on the fence on adding this for the new RV-8 project.

Carl

[AviatorJ]

Okay no start button on the stick.

I'll have to do some more thinking about the dual standard batteries vs a standard battery and the IBBS setup. I'll push forward with the 2nd alternator, seems like relatively uncomplex to add.

Here's an add on question I just thought of while staring at my panel mock up. Is it common to have a power switch for your Autopilot Servos? I had planned to do one but in looking at other people's set ups it seems hit or miss.

[az_gila]

Originally Posted by tspear

...

Extra batteries and dual alternators should largely depend on the kind of flying you do. If a VMC flyer, keep it as simple as possible. If IMC of marine layers on the coast, you may need to fly hours to get to VMC conditions, in which case redundancy matters. Dual batteries and dual alternators is the "ultimate" expression of this.

Tim

Interesting point.

EFIS redundancy is usually provided by dedicated back-up batteries anyway, so your scenario really applies to the rest of the electrical stuff on the plane.

If you must fly IFR to get to VMC conditions then it implies your engine is running... and a second alternator would do the job of keeping the avionics going.

If the engine isn't running then the extra capacity of a second battery is probably not useful.

Does the above really say that a second alternator is more useful than a second battery if the EFIS systems take care of themselves in a "electrics out" situation?

[Bill Boyd]

I've always felt a second alternator/dynamo is of more value than a second battery for the exact line of reasoning above. How long do you need backup electrics to last in what has become a glider?

This assumes you have a way to know at the start of the flight that both alternators are functional, and that either or both could perform their function absent a battery to serve as a load/filter. Much has been written about this, but I remember little of it. I believe the dynamos like SD-8 employ a large electrolytic capacitor to mitigate the effects of taking the battery load off line.

[leok]

Originally Posted by AviatorJ

Here's an add on question I just thought of while staring at my panel mock up. Is it common to have a power switch for your Autopilot Servos? I had planned to do one but in looking at other people's set ups it seems hit or miss.

No separate switches. I'm not sure why I would want them.

I have power to the Autopilot servos group powered through the VPX with an "Avionics Switch". I can still access the individual output for each individual servo through the VPX page to override the Avionics switch on single outputs.

[tspear]

Originally Posted by az_gila

Interesting point.

EFIS redundancy is usually provided by dedicated back-up batteries anyway, so your scenario really applies to the rest of the electrical stuff on the plane.

If you must fly IFR to get to VMC conditions then it implies your engine is running... and a second alternator would do the job of keeping the avionics going.

If the engine isn't running then the extra capacity of a second battery is probably not useful.

Does the above really say that a second alternator is more useful than a second battery if the EFIS systems take care of themselves in a "electrics out" situation?

Most EFIS backup batteries for the primary EFIS is 45 minutes or so.
In a congested area like LA, Boston, DC... I would not only want to keep the PFD running in the common situations, but also NAV/COM and transponder. I do not enjoy the idea the a F16 joining me on a downwind flight

If I was a mid-west, VMC, daytime flyer; I would go with a single lead acid battery and a single alternator. This will handle almost any emergency, lead acid is bullet proof simple to monitor and be proactive on replacement when losing charge.
If night flying, I would add a backup alternator and setup the start procedures to run the system off the backup alternator for most of the taxi to test the system before starting the primary alternator.
If either coast, or flying over IMC, or dual electronic ignition; I would go with what I consider the ultimate solution. Dual batteries and dual alternators. One lead acid battery hooked on the main bus and is the ship primary source of power. A Li polymer battery connected via diodes for charging and when armed to provide the bus with power. Primary alternator set to slightly higher voltage than backup for automatic take over.
Reason I like the lead acid battery in the system; they handle transient current, voltage and spikes and drops much better than Li polymer batteries; and if a supper high spike do not go off line or blow up very easily. This offers the best "buffer" to protect the much more expensive electronics in the cockpit and helps ensure they are still working when the second battery and/or alternator comes online.


Tim