Advice needed - Double check my electrical system

Hey yall,

I'm hoping some of you smart folks will chime in here and help push me in the right direction with my electrical distribution system. First off, thanks to all the folks who have already been there done that and posted their results. It was really helpful for me starting from scratch with electrical design. If my design looks familiar, it's because I blatantly stole elements from posts on this site.

Let's just say the electrical portion was a lot harder for me than I thought it would be.

Design Overview:
Like many others on this site, I did not see a need to re-invent the wheel here. I pretty much followed Bob Nuckoll's architecture and what others had done. KISS, right? Well, maybe I went overboard but my goal is a simple to operate (and maintain) electrical system.

Paul Dye said something that stuck in my head : re-defining avionics to only the radios....not the PFD/MFD. I knew I wanted the G3x screen(s) to be on prior to and during engine start to monitor the engine. The thought of 2 alternators was a bit much (weight, complexity, and cost) for me, so I opted for 2 batteries instead. This "backup or brownout battery" would allow me to dual - feed an endurance buss and also power up and keep alive the G3x during cracking. Kudos to Garmin for integrating dual power inputs.

Design Goals:
Simple to use, reliable. Few parts as possible. Affordable.

Eventually, I would like to use the plane IFR, so reliability is important.

If I wasn't on a budget I would have gone with a VP-X, but frankly it's too expensive for me to consider replacing the fuse blocks and the cost-benefit analysis did not come out favorable for my conditions. Looks like a nice product, but too rich for my blood.

Equipment:

• Main Batt: PC680 (possibly antigravity LiFe0 in the future if compatible with alternator)
• Alternator: Plane Power 60A internally regulated
• Backup Batt: SLA-12V7-F2 7.6Ah
• Ebus solid state relay: Ztron Labs ZL-MB50
• Avionics relay: B&C 40A
• Backup Batt charger: Sterling Products Battery maintainer
• Boost pump: Airflow Performance 3090050
• Switches: B&C 1-3 and 2-10
• E-bus diodes: B&C D-25
• Wire: Tefzel 20 AWG to most, 14 AWG to pump, 16 AWG to lights/flaps, and copper bus bars from battery contactor to start contactor/anl fuse.

Right off the bat, you can see I've got some single failure points.

The avionics are dependent on the relay/switch. I've heard the arguments for removing them, but I could not figure out a way to keep them off during engine start but make sure they are running at all other times. Garmin tech support agrees, and while the components are capable of withstanding voltage spikes and all that, it is preferable to have them off during engine start. Plus, the ADS-B, ARINC, Audio panel, and Transponder do not have an "off switch" of their own. I see the risk as acceptable, because I don't think the relay would dropout/chatter/fail in-flight, but rather show symptoms on the ground. Losing the radios is not ideal, but I would still have the endurance and main buss. Of course, if someone has an idea how to isolate the avionics bus during startup but have it on all the rest of the time please show me (maybe a fancy 3 way switch?)

The aux charger was a cool find from Jack Maljaars. It liminates diodes, resistors, fuses that are needed to link the primary battery to backup for charging. Limited to 3A and only comes alive when primary voltage is above 13.3V. Plus it as UV/OV protection. Pretty cool and I think a nice alternative to an alternator, though not as powerful.

The ztron labs solid state relay was found in a box that I got when I purchased the project. Figured, why not?

I'll have 2 circuit breakers (pullable) - 1 for the Alternator Field and 1 for the servos.

Seat heaters will be re-wired for tefzel, and the relays replaced the same type as the avionics for spares.

You are better off using one of Bob Nuckolls' electrical diagrams or this one:http://www.vansairforce.com/community/showthread.php?t=109065
As for the avionics switch, it creates a safety of flight danger (loss of all avionics) to eliminate an imaginary monetary danger (voltage spikes during engine start).
The starter contactor coil is wired incorrectly with 2 positive wires and no negative wire.
The avionics relay contacts are wired incorrectly.
Depending on the leakage current of the solid state relay when off, it could drain the aux battery over time.
Joe Gores

When the alternator fails, the master contactor and alternator field are unnecessary loads that will reduce the energy stored in the main battery. If wired according to Bob Nuckolls' diagrams, these unnecessary loads can be shut off and the E-Bus switch turned on.
Joe Gores

Mich48041 said:

You are better off using one of Bob Nuckolls' electrical diagrams or this one:http://www.vansairforce.com/community/showthread.php?t=109065
As for the avionics switch, it creates a safety of flight danger (loss of all avionics) to eliminate an imaginary monetary danger (voltage spikes during engine start).
The starter contactor coil is wired incorrectly with 2 positive wires and no negative wire.
The avionics relay contacts are wired incorrectly.
Depending on the leakage current of the solid state relay when off, it could drain the aux battery over time.
Joe Gores

Click to expand...

Joe,

Thanks for the input. As you can probably tell this is my first bite at the apple in electrical design. Sure is frustrating for a mechanical guy. I'm not sure if the link you posted is really applicable for a future IFR mission. You tell me... maybe I'm missing something. What I tried to re-create was a Z13/8 - but substituting a charger for a second alternator.

Avionics circuit:
I agree with the avionics switch being a "pain in the side" for single failure. In fact I point that out in the original post. However, I want to make clear that it is not a "loss of all avionics". It's a loss of the transponder, com and nav radios. The G3X system is wired to the E buss and Main buss. Sure, that would probably suck, but I'm curious how often switches and relays fail. Would you find it acceptable to replace the switch and relay (and maybe wiring?) at 5 year intervals? I don't know much about relay failure modes or switch failure modes, but the system you proposed in the link appears to have the same configuration. Taking Bob's own words, overall system reliability is key. If they fail because of service limits, I'll make it a conditional inspection item to replace them. Can anyone shed light on how/why these devices would fail? The reason I put in the switch is three-fold:

1. Ability to isolate avionics
2. Preserve battery power for engine start.
3. Follow manufacturer's recommedations

I sent G3xpert this email about that, and here is there response (I hope that's OK with Garmin).

Also note that the transponder, ads-b box, ARINC, and I believe the audio panel do not have off switches. In fact, with the exception of the audio panel none of them are accessible and will need some sort of switched power - to my knowledge. So, to keep those off I HAVE to have some sort of switch.

Leakage current of solid state relay: Should be zero. The marketing literature (linked in the first post) states that:
If anyone knows something I do not - I'm going to take this at face value and assume it's a very low consumption device when on, and practically zero when off.

Wiring Errors: Can you point out the specific error? Like I said I'm pretty new to this, so if the wire from x needs to be moved to y please let me know. I'm limited by the software symbols, the relays are all normally open. In the starter contactor it's hard to see but there is a diode connected to ground.

Here is how the contactors/ANL60 are wired up in "real life":

Alternator failure and E-buss The E-buss is active 100% of the time (unless there is a fault in the auxiliary battery.) So, if the alternator craps the bed, the crowbar OV protection should kick in, or the ANL60 should catch it, or the 5 amp circuit breaker for the alternator field should blow. If none of that occurs I can manually pull the alternator field circuit breaker or just flip the switch down one to battery only. As you point out, I can just kill the Master and the Ebuss will power everything I need anyway. Maybe I'm missing your point?

Thanks again for the advice! I'm eager to get the project moving so it's very helpful.

Hi Chris,
A charger is not a substitute for a backup alternator. I see no benefit of having that charger in the circuit. Read this thread: http://forums.matronics.com/viewtopic.php?p=316578
Relay coils can fail open at any time without warning. I would not replace switches or relays as part of a preventative maintenance program unless they are subject to thousands of operations. Switches and relays do not fail very often. But there needs to be a backup plan in case one does fail.
The email from Peter D. Cowles Sr does not recommend an avionics switch. He said it is common practice and gives two reasons why. But neither reason is valid. The starter contactor coil does not produce voltage spikes if a diode is installed across the coil. And even if it did, their "units are pretty well protected from spikes". Read Bob Nuckolls document about starter contactor coil spike suppression. http://www.aeroelectric.com/articles/spikecatcher.pdf
Switches need to be exercised to remove oxidation from the contacts. And so the second reason is not valid either. Garmin's switches should last thousands of on-off cycles. Ask them what the mean number of cycles is before failure of their avionics switches. And ask Garmin for a yes or no answer to this question, "Does Garmin recommend powering off their avionic products during engine start?" "If yes, why?"
Bob Nuckolls wrote a document about switches. http://www.aeroelectric.com/articles/Switch_Ratings.pdf And he has more interesting things to say about switches in this thread: http://www.matronics.com/archives/archive-get.cgi?AeroElectric-Archive.digest.vol-idSearch for the word "cycles".
I agree that the ability to shut off avionics is a good feature. But they do not all have to be controlled by one switch. If more than one switch is used, then the failure of one switch will not disable all avionics. It is also a bad idea to protect all avionics with just one fuse. (Not that you are doing that)
OK, you answered my question about the solid state relay leakage current. Very little is good.
Maybe you wired the plane correctly but the schematic has errors due to the limited symbols available in the software. There is nothing dangerous. The worst that can happen is the starter will not work and the avionics bus can not be shut off.
Joe Gores

If you are going to use an avionics switch/relay combination (which isn't a bad idea at all) use 2 relays/switches as some certified aircraft do in their design. Either switch/relay can run all the avionics and you don't have a single point of failure.



Each avionics switch powers a 40A Relay similar to this one (available at any car parts store) in parallel with each other. This way not only do you have redundancy you can also test each switch/relay combination at any time. Here you can see how it looks on my switch panel.

Just an idea.

Also, doesn't your EFIS (PFD, MFD, EIS) have an internal battery capability? Mine does.

Chris

Shouldn't your aux charger connect directly to the aux battery? Otherwise if the E-bus switch is off then it won't be being charged.

Cheers

Peter

I think there may be some confusion because of the way you built your contactor symbols. Normally there is the coil side shown as two contacts to the coil which activates the switch when energized and the switch side. These are usually shown independently. Your starter contactor looks like you don't have a ground as mentioned before, but then you are showing the diode there which is hooked up wrong. I think I would start with changing those symbols to a more standard configuration then everyone can tell what you mean. The symbol for the avionics relay is closer but again you have hooked it up incorrectly since the input is tied directly to the output in the diagram. Remember the point of the relay or contactor is to use a switch that can handle relatively low currents in comparison to the relay or contactor. Those two paths should be separate.

Mich48041 said:

Hi Chris,
A charger is not a substitute for a backup alternator. I see no benefit of having that charger in the circuit. Read this thread: http://forums.matronics.com/viewtopic.php?p=316578

Click to expand...

Joe,

I read through the links you provided and came across this statement from Bob: The aux battery charger does exactly what Bob describes. It is a self-contained relay/diode package that only charges the battery when the main battery is "ready", and since the aux battery should not be discharging much if at all, it will not need more than this trickle charge. If I'm way off here with this assumption let me know.

Chris

Shouldn't your aux charger connect directly to the aux battery? Otherwise if the E-bus switch is off then it won't be being charged.

Cheers

Peter

Click to expand...

Peter, Good catch - I originally had it going directly to the aux battery, but realized if I put it there it would mitigate against an E-Buss or E-Buss wiring failure. Looking at it, I could probably move it over to the aux battery terminal.

If you are going to use an avionics switch/relay combination (which isn't a bad idea at all) use 2 relays/switches as some certified aircraft do in their design. Either switch/relay can run all the avionics and you don't have a single point of failure.

the ability to shut off avionics is a good feature. But they do not all have to be controlled by one switch

Click to expand...

I think everyone is in agreement that it is desirable to switch off the avionics during engine start. Can anyone think of a way to isolate the avionics buss during startup? Maybe put in an NC relay that opens when cranking? That way if the relay fails the worse thing that happens is you have the avionics on during engine start? Or maybe some sort of 3 way switch that has off-start-on positions? I've literally spent hours trying to devise this but frankly am not smart enough to figure it out. Any input (diagrams) here would be awesome!

Thanks for pointing out the wiring errors, when I get back home I will load up the program (http://www.expresspcb.com/) and see if I can get it sorted out.

Also, doesn't your EFIS (PFD, MFD, EIS) have an internal battery capability? Mine does.

Click to expand...

I plan on using the G3x system, which allows for two power inputs, but I don't think it has an internal battery. Speaking of which, does anyone know how the two discrete power inputs work? I'm assuming it auctioneers the higher voltage, or I wonder if there is an internal diode that only allows one flowpath.


Thanks everyone!

NTex said:

Can anyone think of a way to isolate the avionics buss during startup?

Click to expand...

Yes.

What I did is to power the items I consider essential -----radios and EFIS-----directly from the aux battery. The main battery is powering everything else.

There is a high capacity Schottky Diode that allows current to flow from the main battery buss to the aux battery buss, but prevents the current to flow from the aux battery to the main during engine start.

Quote from Sterling Power

What not to expect. This is a simple product which transfers up to 1 -2 amps from your primary charging source to your secondary . . . Do not use it to charge battery banks which are using more than about 0.5 amps continuous as they will simply not keep up with the discharge.

Click to expand...

Since the output of the charger is connected directly to the E-Bus, will the charger be overloaded by the E-Bus loads? It all depends on the output voltage of the charger compared to the output voltage of the E-Bus diode. The E-Bus will draw current from whichever source has the higher voltage.
The charger is not utilized in your circuit in the manner suggested by Bob Nuckolls that you quoted. He said that the module should operate a relay, nothing else. The module should not carry battery charging current or operate a load other than a relay coil. The relay contacts will carry the battery charging current or other loads. Nowhere in the Sterling Power literature does it say that their product contains a relay.
Jeff Luckey recently posted a schematic on the Matronics AeroElectric List. http://forums.matronics.com/download.php?id=38059 His final version, when available, may be worth considering.
Joe Gores

NTex said:

I think everyone is in agreement that it is desirable to switch off the avionics during engine start. Can anyone think of a way to isolate the avionics buss during startup? Maybe put in an NC relay that opens when cranking? That way if the relay fails the worse thing that happens is you have the avionics on during engine start? Or maybe some sort of 3 way switch that has off-start-on positions?

Click to expand...

No, not everyone is in agreement...count me in the group that says they're just fine leaving them on. In fact, the EFIS *must* stay on to give engine information in my aircraft, and the rest are sufficiently robust to handle whatever the system throws at them during start (mostly just a drop in voltage sufficient to cause a reboot).

Much, much simpler...no relays which close when cranking or 3 way switches or even just another switch for the avionics master.

Everything goes on (master, alternator, mags, etc.) and stays on until the flight is done. Simple.

I agree with RV7A Flyer. I routinely leave my avionics on during engine start.
When I said that the ability to shut off avionics is a good feature, I was thinking about sitting on the ground playing with one of the avionics and wanting others off to save battery energy.
Joe Gores

Mich48041 said:

I agree with RV7A Flyer. I routinely leave my avionics on during engine start.
When I said that the ability to shut off avionics is a good feature, I was thinking about sitting on the ground playing with one of the avionics and wanting others off to save battery energy.
Joe Gores

Click to expand...

I just use the Off button on each box Fortunately, the heads on all of mine have one. (I can pull fuses on anything else if I really needed to...but most of the time, I just plug in a battery tender if I'm going to work on things for any length of time or if doing a longish firmware upload, etc.).

Ok gents, thanks for the responses and help. I'm looking to order this stuff and slap it in the plane next week.

I've revised the drawing:



Sounds like the whole avionics switch is old school. That's fine by me, just want to verify with Garmin it's OK to subject the black boxes in the G3X system (which are remotely mounted and have no control head) are OK during startup. Makes it simple if so!

Mich48041 said:

Quote from Sterling Power

Since the output of the charger is connected directly to the E-Bus, will the charger be overloaded by the E-Bus loads? It all depends on the output voltage of the charger compared to the output voltage of the E-Bus diode. The E-Bus will draw current from whichever source has the higher voltage.
The charger is not utilized in your circuit in the manner suggested by Bob Nuckolls that you quoted. He said that the module should operate a relay, nothing else. The module should not carry battery charging current or operate a load other than a relay coil. The relay contacts will carry the battery charging current or other loads. Nowhere in the Sterling Power literature does it say that their product contains a relay.
Jeff Luckey recently posted a schematic on the Matronics AeroElectric List. http://forums.matronics.com/download.php?id=38059 His final version, when available, may be worth considering.
Joe Gores

Click to expand...

Joe,
Back to the charger - thanks for pointing out the charger will be competing with the regular e-bus loads and will turn itself off.

As far as the design, it is a solid state relay system I believe... here's what they say:

The maintainer uses FETs instead of relays.
II. FETs use very little power compared to relays,
only 1.5 mA.
III. This makes FETs ideal to use with low power
charging equipment such as solar/wind.
IV. FETs have no mechanical parts rubbing together.
Therefore, they do not wear out, nor is there
any noise produced
1. The maintainer is activated when the primary battery reaches about 13.3 V and allows excess power to be
transferred to the auxiliary battery.
2. The auxiliary battery will then be charged at low current (1 or 3 amps, depending on model).
3. It then maintains the charge on the auxiliary battery.
4. If the primary battery?s voltage drops below 12.9 V the device switches to standby.
5. Ideal in boats where you may have a generator battery which topped up

So my plan is to keep the E-bus on during the startup up until climb. Then I can turn off the E-bus, and allow the charger to kick on. If I lose the main battery/alternator for some reason, I'll kick the E-bus back on.

I think this re-design simplifies the wiring and obviously corrects some problems. Again, I appreciate the input - electrical design is not in my wheelhouse.

You still have an error in the starter relay circuit. I corrected it here:

OK Chris, you convinced me that AUX Charger will work.
I believe the most important purpose of an E-Bus is to power essential loads from the main battery with the master switch shut off (after an alternator failure). Shutting off the master switch conserves energy by removing power to the master contactor coil and to the alternator field and to all loads on the main power bus. In your circuit, there is no way to utilize the stored energy in the main battery with the master switch shut off.
Joe Gores

GalinHdz said:

You still have an error in the starter relay circuit. I corrected it here:

Click to expand...

Thanks!

OK Chris, you convinced me that AUX Charger will work. In your circuit, there is no way to utilize the stored energy in the main battery with the master switch shut off.
Joe Gores

Click to expand...

I'm not committed to the charger, it just seemed like a poor man's way to add charging to the second battery. So, I'm not sold on it by any means, if there's reason to think it won't work then I'll go back to the drawing board.

So, what am I missing for the main battery? You lost me there... I'm trying my best to mimic Z 10/8, and as I see it our master switch works the same?

What he's saying is that with our Master switch off, your main battery is no longer connected to the E-buss, so it's useless. Take a closer look at Knuckolls' diagrams...especially this one:

http://www.aeroelectric.com/PPS/DCPwr/E-Bus/E-bus_Light.pdf

Mich48041 said:

OK Chris, you convinced me that AUX Charger will work.
I believe the most important purpose of an E-Bus is to power essential loads from the main battery with the master switch shut off (after an alternator failure). Shutting off the master switch conserves energy by removing power to the master contactor coil and to the alternator field and to all loads on the main power bus. In your circuit, there is no way to utilize the stored energy in the main battery with the master switch shut off.
Joe Gores

Click to expand...

Either use two separate switches, one for the alternator and one for the battery or a Cessna Split Master Switch. This is a simple setup that lets you isolate the alternator while still using the main battery as a power source.

Chris,
IMHO, that charger is not needed.
I will draw a schematic and post it showing how the E-bus should be connected to the main battery.
Joe

Guys,

Thanks for your patience with me. Obviously I overlooked some key areas. Good thing VAF has a pretty good QA department!

For the master switch, if I had an alternator failure I assumed one of the circuit protective devices attached to the alternator would blow, and I would get an annunciation on the G3X. My plan for this was to pull the 5A CB for the alternator field fuse.

It took 20 posts, but I'm starting to get it

Looks like it's back to the drawing board on how to power the E buss

Appreciate everyone's input.

Avioncs Electronic Switch

I used in my -8a my Avioncs Electronic Switch for controlling power supply to all the avionics instruments.
This Electronc Switch is, actually 7 seperated switches controlled by a single line (connected to the "Avioncs Master Switch").
Using this Electronic switch enabled me to use one circuit breaker to each equipment and in case of failure (which is very rare, since the usage of MOSFET transistors) all other avionc equipment are not affected.
This electronic circuit consumes as lo as several micro-Amps.

"The ARIEL's Electronic Avionic Switch is a self contained, avionics master electric switch package to protect expensive radio gear at an affordable price. The Electronic Avionic Switch is installed between the power bus and the protected radios and other avionic equipment. Not as a single circuit, the Electronic Avionic Switch controls up to 7 (seven) different circuits (max. 12.5 Amps each), means ? Each avionic instrument can be protected by its own individual circuit-breaker and wired individually, while all the different circuits are switched by only one toggle switch "Master Avionics", which might be located on a remote location. The avionics master switch then controls the Electronic Avionic Switch only and not the radios directly.
The Electronic Avionic Switch employs solid-state MOSFETs and no any mechanical moving parts, such as relays ? longer operational life and no electric arc which might ignite fuel fumes and cause fire in the cockpit.
If the Electronic Avionic Switch ever fails, the pilot just need to disconnect the two plugs connected to the Electronic Avionic Switch and to connect them to each other. The radios will just be controlled individually until the problem is resolved."

Chris,
This schematic has red lines showing the alternate current path from the main battery to the E-Bus. I am not necessarily recommending this circuit, just offering it as a possibility. Comments, criticism, and suggestions from others are welcome.
Download pdf version that is easier to read:
https://drive.google.com/file/d/0B7ZTG2VpCuDRVVFCaXJ6ME56YjA/edit?usp=sharing Click "FILE", "DOWNLOAD".
Joe Gores

if I had an alternator failure I assumed one of the circuit protective devices attached to the alternator would blow, and I would get an annunciation on the G3X.

Click to expand...

The fuse may or may not blow. But if the alternator fails, there should be a low voltage warning.

My plan for this was to pull the 5A CB for the alternator field fuse.

Click to expand...

Good plan.
Joe Gores

Wow

Mich48041 said:

Chris,
This schematic has red lines showing the alternate current path from the main battery to the E-Bus. I am not necessarily recommending this circuit, just offering it as a possibility. Comments, criticism, and suggestions from others are welcome.
Download pdf version that is easier to read:
https://drive.google.com/file/d/0B7ZTG2VpCuDRVVFCaXJ6ME56YjA/edit?usp=sharing Click "FILE", "DOWNLOAD".
Joe Gores

Click to expand...

Joe,

Beer is on me next time you're in Dallas. Really, this is above an beyond, thanks!

The only comments I have on the new schematic are:
1) cool, we eliminated a bunch of parts and removed failure points...ideal
2) the aux battery, should the output be a fused "load" on the main buss, or is it supposed to be hooked up to the positive lug on the left side of the e-buss lug in the diagram
3) would the aux battery need a relay on its output

thanks again everyone for their comments, hope to order my electrical components this week!

2) the aux battery, should the output be a fused "load" on the main buss, or is it supposed to be hooked up to the positive lug on the left side of the e-buss lug in the diagram

Click to expand...

The AUX Battery gets charged from the main bus through the diode when the aux battery switch is off. As for the fuse on the main bus being required, it all depends on how long the wires are and where the aux battery is located and what the chances are that something might short to ground. To play it safe, I put a fuse there. Fuses are cheap. I suppose the same can be said for the fuse on the E-Bus too. Maybe others can give their opinion.

3) would the aux battery need a relay on its output

Click to expand...

It depends on the load and battery location. If the load is 20 amps or more or if the battery is very far from the E-Bus (like on the other side of the firewall), then a relay should be used.
What is your main reason for having an aux battery? It will not help to crank the engine in my circuit. But it will prevent E-Bus brownout during cranking. And it will extend main battery life after an alternator failure.
I will be in Frisco TX for 5 days starting Feb 22 to visit my son.
Joe Gores

Chris,
I added a relay to my aux battery circuit.https://drive.google.com/file/d/0B7ZTG2VpCuDRVWYzM3JQYy1mNkk/edit?usp=sharing
Joe Gores

I posted my drawing on Bob Nuckolls' site for review and Bob pointed out that his Z-10/8 does the same thing with one less switch. http://www.aeroelectric.com/PPS/ACAD_Architecture_Dwgs/Z10-8A.dwg Like I said on Feb 1, "You are better off using one of Bob Nuckolls' electrical diagrams"
I have condensed Z-10/8 to make it easier to read: https://drive.google.com/file/d/0B7ZTG2VpCuDRdzlRS2YxQUtpc0k/edit?usp=sharing
Joe Gores