Panel wiring, circuits, breakers, switches, etc.

After a bit more tweaking I think I'm close to the final draft. Today I got the radio stack situated to make sure there are no interference issues behind the panel, and was able to move the "six pack" a little left, and a little down. Balance and symmetry are important to me, and I think this looks pretty good given what I have to work with...

Looks like I'm not going to be able to avoid sticking the primer and starter on the lower right due to space limitations. I'll just have to do a little more stretching and learn not to kick the instrument panel when I climb into the airplane....after this panel is done, I'd be more careful around it anyways.

the main thing here is the big holes. I'll be relocating the switch and c/b rows a little higher to "center up" a little better...


Worked on the radio stack most of the day, making sure everything is square and no interference issues behind the panel...just need a few more nuts and bolts and this will be done. I know, I know...I shouldn't have the space between the com and Xpdr, but there is method to my madness and I'll just leave it at that...unless somebody really wants to know why I am doing it this way.




Here is the final(ish) draft on the "Paint Panel". It's not really to scale, so it looks like there is more room in certain places than there actually is. For this reason I'm not committing to the mixture, cabin air, and magnetos just yet...the big stuff will stay where pictured.

Make sure that you have enough room around the primer so that you do not mash your knuckles on the right side.

Steve Pierce said:

I just went through all of this myself. I used schematics from Piper, B&C, Electronics International, AC43.13 etc. I used the chart Daryl posted for CB sizes and it coincided mostly with what Piper did. I also got rid of redundancy by using circuit breaker switches where possible. Takes a lot of fore thought to figure out how to get everything in there with no interference. I use Clyde Smith's instrument panels with a 2024-T3 doubler behind. Piper used a doubler on their gyro panels. Piper did not use a master relay on this 1971 Super Cub and after some research and pondering I did not install one. They also changed from a single double throw switch to two single switches for the landing light. I debated on this and ended up using a single switch to turn both the landing and taxi light on simultaneously since I am using HID lights and the current draw is very little. I have way too much time in laying all this out so I will scan and post what I came up with to try and save someone else the time. Of course thy are all different but a lot of things are the same.

Click to expand...

Kind of how we did ours in the re-build. If I had to do it again, I would put my GPS higher in the panel. Down low like this, and your head is down in the cockpit looking at it and it's a bit hard to see.

You may want to consider putting in some sort of support bracket for back of the radios.

OK, here is the latest try for my wiring diagram. Theres still a couple areas that need fine tuning...one is the panel light dimmer, not sure how that wires into the system, I should know more today when I get to the hangar. Also realized I need a couple more C/B's on my panel layout too, one for the Master switch, and one for the Low Volt annunciator.

Let me know what you think...will I fry everything as soon as I connect the ground?!?!

If you are planning to fly at night you might want to think about placing the strobe light on the belly or wing tips. If you mount it on top of the rudder you will be getting flash back from the prop and the wing struts which can be very annoying.

Helmetfire said:

OK, here is the latest try for my wiring diagram. Theres still a couple areas that need fine tuning...one is the panel light dimmer, not sure how that wires into the system, I should know more today when I get to the hangar. Also realized I need a couple more C/B's on my panel layout too, one for the Master switch, and one for the Low Volt annunciator.

Let me know what you think...will I fry everything as soon as I connect the ground?!?!

View attachment 10269

Click to expand...

Looks better, but a few quick observations...

1. Your master relay doesn't seem to serve any purpose other than power the starter solenoid. It doesn't connect your batt. to your main bus.

2. A continuous-duty master relay rated high enough for a starter load would be big, heavy and expensive. Suggest you feed the starter solenoid from the batt. side of the master relay.

3. The ammeter shunt (and a +/- ammeter) is most useful between the batt. and the bus. If your mind is set on monitoring the alt. load too, maybe a 2nd shunt between the alt. and the bus (as on your diag.) with a selector switch is the answer.

4. You need a c/b to protect your radio master circuit.

5. Your total load might exceed the alt. capacity. Can't tell without equipment ratings.

For your '6-pack' you might consider cutting a large hole in the panel and covering it with a sub-panel from Seth Hancock:

http://www.bearhawkaircraft.com/vendors/preferredvendors.html

He is about the fourth vendor down the list. His panels are cut from .125 2024, and primed. Workmanship is excellent.

Aviator said:

Looks better, but a few quick observations...

1. Your master relay doesn't seem to serve any purpose other than power the starter solenoid. It doesn't connect your batt. to your main bus.

2. A continuous-duty master relay rated high enough for a starter load would be big, heavy and expensive. Suggest you feed the starter solenoid from the batt. side of the master relay.

Click to expand...

Okay...I'm confused about what terminals do what on my solenoids. Part of my brain keeps going back to the way it was wired before, but maybe it was wrong?? Here's a pic of how it was setup...Does this make sense?? The big red wire went to battery positive, and the big cable going towards the top right was the starter cable. The only ground I'm seeing here is the (painted) metal strip that the solenoids are attached to, but the only ground attachment from there is the bolt on the far right of that bar that attaches to the support bracket under the battery box shelf. This couldn't have been a good ground?!??!! Is the starter solenoid grounded through the case?? Everything seemed to function properly, although now that I think about it, the (skytec) starter never did seem to be that strong, even with a new oddyssey battery.


I'm going to try a different way to visualize where the wires need to go, to help with my wiring diagram. Can somebody tell me where each terminal on my solenoids should go? I'm a little confused about C,D and G....This would help a bunch...Thanks

There's a thread on this here.
http://www.supercub.org/forum/showthread.php?44218-Master-Solenoid-connection
Have a look at the links in post #6 to identify what you have, and go from there.

While on the subject, I noticed, a lot of wiring diagrams (and installations) show a c/b only at one end of batt-to-bus and gen(alt)-to-bus wires. Ideally, you'd want a c/b at both ends of every by-directional - or potentially bi-directional - power feed, especially if exposed live contacts such as a shunt are incorporated. (A ground-reset c/b somewhere ahead of the firewall for the gen(alt) if it doesn't have one built-in... not all of then do.) Any views on this???

Helmet fire if I understand your question correctly you don't exactly understand how the solenoid works? Assuming that I'll explain and maybe it will help you to visualize what you want it to do:
A solenoid is what I call a relay or magnetic switch. A small current passed through a coil makes a magnetic field that pulls on a metal rod which mechanically pulls a big switch, that can handle a large current, "on". Think of a little guy throwing a big knife switch in a power plant. So the little stud terminals run the magnetic coil while the big terminals do the real work. NORMALLY the big terminals are not connected to the little terminals in any way. The little terminals are connected to the electromagnet coil. The two small terminals on your relay on the left (master) have no polarity and will do their job the same no matter which way they are hooked up. If their is an external protection diode across the little coil terminals it does have polarity and must be hooked up correctly or it will make the magic smoke! Your master relay above is a two terminal type which only means YOU have to hook one of the terminals to ground where as your starter relay is a single terminal (coil control, small stud) which means the factory has already PROBABLY grounded one end of the coil to the case and so to energize it you just supply +12 vdc to that terminal and it will turn "on".
Now I said "normally" and "probably" because the fact that you labeled the small terminal on the starter relay "G" makes me nervous about my blanket statement. Was that arbitrary by you or is it actually labeled "G"? There is a third way the factory can wire up a relay coil internally and though it's rare it's possible and I have seen it in non aviation special applications. They could have wired one lead of the coil to one of the "big" terminals (in this case the one on the starter relay left side) and then you would supply "ground" from the dash starter switch. This would make the "big" terminals polarity sensitive since the the one with the internal coil connection would have to be labeled "hot" or "bat." etc. or the relay would not function.

When I say "knife switch" below I'm just trying to illustrate what a big current switch would look like. A solenoid actually has a couple of big copper contacts and a bar that connects them together when "on".

The way your picture shows the "Big" current flows from the + battery terminal into the left side big terminal of the master, through the master "knife switch" and out on the right "big" terminal. From there it goes two places. First to the left side "big" terminal of the starter relay, through the starter "knife switch" and then out through the right side "big" terminal to the starter motor (when the starter relay coil is energized). The other place the right "big" terminal of the master goes is to that big white or gray wire that goes up into the loom and I assume that goes to the 12 volt bus.

I agree with the other posters that the left end "big" terminal of the starter relay should go directly to the battery and not to the master relay output (master right side big terminal) BUT Both relays should be wired as close to the battery as possible always remembering the battery wires going to the relays are unprotected and always hot. The way your stacking two switches in a row, each one will drop the voltage a little plus your prematurely wearing out the master switch. YOUR way is the best if you are going to put the starter relay away from the battery for some reason, say in the engine compartment. You don"t want a "big" always hot wire going through the aircraft and you can just buy extra master relays to have on hand .

Some of the other posters and I disagree on one safety issue and that is how the master relay is energized. This falls into the "choose your poison" category for experimental. I believe the relay should be energized by "+12 vdc" and not "ground". When you turn those switches off you want them to stay off in a crash and it seems to me it is easier for a wire to find ground in a crash than to find +12 volts. JMHO and you have to decide for yourself. This is the way I would wire it:




Hope this helps.

I am not sure where you are getting this. The standard Super Cub wiring diagram switches the ground side of the master relay, and the starter relay "Big" power to use your term is wired through the master relay, such that the master relay will shut off all power when turned off. In other words the starter relay power does not come directly from the battery. Admittedly most of my experience is with experimentals, but I have found that it is pretty typical to switch the ground side of the master relay with the master switch. This is especially useful when you have a remote battery installation in that is saves you from running a hot wire from the battery to the master switch, which in my opinion is much safer. Along those lines I typically use a master relay that has only one small post to which the switched ground wire goes. The positive side of the solenoid is then internally wired to the positive Big terminal coming from the battery.

I am not saying that my way is the only way you can do it, but from my experience it is the more common way and it is the way shown on the Piper Super Cub wiring diagram.

Lamar's 12VDC continuous-duty (master) relay, X61-0028, found on a lot of GA aircraft, is rated at 600A inrush, 200A max breaking and 100A continuous current. Their intermittent-duty starter solenoid, X61-0030 on the other hand is rated at 900A and 300A (zero continuous). The contacts use different materials too + other differences. I don't have numbers for White Rodgers' relays, but I suspect they're much the same. It means that if the starter draws more than 200A, the contacts of your master relay will weld together if it's installed between the batt. and the starter. With the old Prestolite starters that drew just under 200A on a good day (good battery), this configuration was already borderline. But with the newer B&C and SkyTec starters that draw up to around 300A it's a recipe for welded contacts.

Dave Prizio said:

I am not sure where you are getting this. The standard Super Cub wiring diagram switches the ground side of the master relay, and the starter relay "Big" power to use your term is wired through the master relay, such that the master relay will shut off all power when turned off. In other words the starter relay power does not come directly from the battery. Admittedly most of my experience is with experimentals, but I have found that it is pretty typical to switch the ground side of the master relay with the master switch. This is especially useful when you have a remote battery installation in that is saves you from running a hot wire from the battery to the master switch, which in my opinion is much safer. Along those lines I typically use a master relay that has only one small post to which the switched ground wire goes. The positive side of the solenoid is then internally wired to the positive Big terminal coming from the battery.

I am not saying that my way is the only way you can do it, but from my experience it is the more common way and it is the way shown on the Piper Super Cub wiring diagram.

Click to expand...

Well we are talking experimental here and I did say choose your poison. I installed many systems in emergency vehicles in my time and when things start melting down or getting crushed wires find ground a lot more often than they find +12volts. Cleaned up after a few vehicle fires and I'm just saying you don't want the power coming back on after you have shut it off? Right? Did Piper do everything right? Cross brace in the overhead, door post ot bottom of the engine mount? I admit they may have had a valid reason for doing it the way they did it but if so what was it? IF I put an electrical system in there will be a special two compartment battery/electrical box under the seat ( My seat will have to be crushed before the battery gets crushed and I won't care about fire at that point probably). The battery will be in one side (vented and the master switch and relays in the other sealed side.

Don't seal the battery in. I once had a remote repeater site with a bunch of lead acid batteries in it. The building was an old shipping container. After a few years some of the batteries started gassing a lot of hydrogen. Out in the field some deputy pushed his mic button to call dispatch and a relay pulled in at the remote site and a few days later I showed up to find one wall and the top collapsed inward. Apparently when you make water from hydrogen and oxygen it doesn't take up as much room!

Dave I know and understand your concern about running a hot lead to the dash. Why not place the switch next to the battery (assuming it's under the seat as most are)? Even if you run the hot lead to the dash let's consider what happens to either in an accident. First scenario: "Hot lead to the dash with power returned to relay": Ok you have the master off but some thing crushes the hot lead to the frame during the crash. The lead touches the frame, there is a small brief spark and the hot lead fuse at the battery blows. All power is dead. Scenario 2: "ground lead to dash" (Piper way): Before crash you shut switch off leaving "ground lead with 12V through relay on it (that's what happens). Power is off. Crash crushes the ground lead wire against frame. There is a brief spark AS RELAY REINGAGES and stays engaged! ALL power comes back on everywhere! If strobes are on wires going out to wing tips re-energize. Electric fuel tank gauge wires get hot, 12volt bus comes alive and radios turn back on etc. Your watching the dash light up and saying "what the f---"

I would add to aviators good post about relay specs: You must run the starter wire through the master if you are placing the starter relay/solenoid away from the battery. You will just be replacing master relays more often. Just put it along with the master relay right next to the battery and then you don't need to run it through the master.

Aviator & gsmx440,
I am one of those who thinks he knows just enough about electricity to get by, but really has difficulty understanding it, even though it does resemble hydraulics. ;-) I am under the impression that a relay's limitations are based on the amount of current that it can handle while the contacts are in the process of being closed and opened. Once the contacts are closed they are then able to carry a much larger load. That said, is it not so that if the master and starter relays are wired in series, the master will be closed before the starter is engaged. So the master will be able to carry a very high load without arcing? The main difference between the two relays is their ability to close and open with a high or low current flow without burning of the contacts?

Also, I was under the impression that one of the advantages of the new B&C and SkyTec starters is that they draw less current than the old Prestolite starters. This is one of the reasons that tired batteries are able turn them over more easily.

skywagon8a said:

Aviator & gsmx440,
I am one of those who thinks he knows just enough about electricity to get by, but really has difficulty understanding it, even though it does resemble hydraulics. ;-) I am under the impression that a relay's limitations are based on the amount of current that it can handle while the contacts are in the process of being closed and opened. Once the contacts are closed they are then able to carry a much larger load. That said, is it not so that if the master and starter relays are wired in series, the master will be closed before the starter is engaged. So the master will be able to carry a very high load without arcing? The main difference between the two relays is their ability to close and open with a high or low current flow without burning of the contacts?

Also, I was under the impression that one of the advantages of the new B&C and SkyTec starters is that they draw less current than the old Prestolite starters. This is one of the reasons that tired batteries are able turn them over more easily.

Click to expand...

I ain't no electrical engineer either + I've been known to err, so you could be right: True, opening and closing the contacts is what really sucks life out of a relay - and limits it to something like 50,000 cycles. But here, the problem is the current flowing from one piece of metal to another across a contact point. When you pump amps into a piece of metal, it heats up because of resistance. Since the resistance is highest at point of contact between two pieces, that's where it heats up most. And if high enough, melts the copper contacts.

As for starter loads... Starters - as I understand it - draw as much juice as they need to overcome the resistance, much like an electric drill. Since resistance varies widely - compression, friction, oil viscosity, etc. - it's hard to predict the amps a starter will draw. Add to that the voltage drop during a start that drives up the amp count (volts go down = amps go up), and the amp guess is out the window. The best one can do is measure the current flow during a series of starts of a given engine type using different starters, and come up with an amp draw for each. That's what Sky-Tec did. Below are their peak results for Lyc. 12V starters. Hope this helps.

View attachment wire.pdf

Rough draft from a few years ago so disregard the wire sizes. Unsed # 8 for the alt and pretty much # 18 for everything else. # 4 for the battery and starter. Also used 7.5 CB for lights and 50 amp breaker for alt.

See Aviator, I told you that I didn't understand electricity. I would never have guessed that the current draws would have been higher on the Skytec and B&C. That just does not make sense to me.

skywagon8a said:

See Aviator, I told you that I didn't understand electricity. I would never have guessed that the current draws would have been higher on the Skytec and B&C. That just does not make sense to me.

Click to expand...

Try to plot the energy consumption over a timeline to compare total energy used to start an engine using different starters. (The numbers used here as examples are arbitrary.) A direct drive starter like Prestolite struggles to climb the compression humps. Hence it spends a lot of time, say 40% of the time doing that, and drawing 200A. The rest of the time it draws 100A. Geared starters like inertial starters use inertia stored in fast spinning rotors to help climb the compression humps. So, along with the additional torque they deliver, spend less time, say 10% of the time doing that, but draw 300A when they do. The rest of the time they too draw 100A.

So for a complete rotation (4 cyl. engine):
Direct drive starter: (2 x 200 x .4) + (2 x 100 x .6) = 280A
Geared starter: (2 x 300 x .1) + (2 x 100 x .9) = 240A

Add to that a faster spin and engine start, and the geared starter makers' claim (less amps drawn than direct drive starters) is true in so far as the total drain on your battery is concerned. But the peak current flow, the issue at hand, is higher. That's how I read it (but I won't quit my day job).

Skywagon8a very astute questions and I must confess I don't know the whole answer as I was a technician in the RF field and not an electrical engineer BUT here is what I think I know. Switch contacts corrode based on the type of load. If the load is say an incandescent light bulb the characteristic of a light bulb are that it has a low resistance for a few milliseconds until it heats up so a switch has to handle high "inrush" current for a few milliseconds causing a spark as the contacts "make" and then things settle down and I suspect turning it off is a non event with a much smaller spark. Now an inductive load (relay coil, spark coil, starter motor) is different. When the switch is closed little current flows while a magnetic field is built up around the coil. As soon as the field is established then normal current flows. Now comes the strange part about coils. Unlike a capacitor which can hold a charge when disconnected from a circuit, the coil cannot hold the magnetic field charge and the way it was explained to me eons ago, almost like magic, as the switch opens the circuit, the field collapses and WILL discharge across the contacts as they open. The reason I capitalized "will" is that the voltage will rise across the contacts to whatever level it takes to bridge the air gap as the contacts open. This is called inductive kick and if you would like to prove it just put one hand on the hot horn lead of you car and the other to ground and have a fried push the horn button (works on older cars anyway with buzzer type horns) Remember air has resistance and the farther apart two conductors are the higher the voltage has to be to spark across the gap. If I remember a 3/8" gap requires 50,000 volts? So depending on the size of the coil (and corresponding magnetic field built up around it) and the speed at which the contacts in the switch open, as they open there can be a very large voltage developed maybe approaching 500-1000 volts. The spark created by this discharge as the switch opens corrodes the contacts. If the contacts could be opened quick enough and far enough the voltage could rise to 50,000, 100,000, or whatever it takes and all that from a coil originally energized by 12 vdc. hope I have all that right.
Over time the build up of carbon on the switch contacts raises the resistance of the contacts and they start acting like a load in series with the actual load and the voltage divides accordingly such that if you start with 12 volts perhaps you lose 2 volts across the switch leaving 10 volts to run you starter.
I hope that is the correct theory behind why switches wear out.
So as to your original observation about "if a contact is already closed"etc. I agree it is a lot less damaging to the contacts but you will still drop some voltage and as the master switch ages there will be more voltage drop across two relays than just one.
I totally agree with you idea that all master switch control switches should be at the battery box with maybe one of those aluminum protectors around it.
Aviator answered the skytech question.
I thought a little more on the idea of should you provide power or ground to actuate the master. If the activating wires are in a wire harness and you have an inflight electrical fire I believe as a harness melts into a gooey mess the activating wire would more likely find a ground as the wires melt together. For instance lets pretend the landing light power switch is off when the wires melt together. The wire that would normally have 12 volts on it is dead since it's switch is off. BUT as far as the relay ground wire is concerned as it melts into the "off" power lead going out to the light that wire looks like ground (Path: relay ground actuating lead ----> melts to wire going from dash out to light -----> through light bulb filament -----> to lightbulb ground in wing). Relay turns back on after you have turned it off. There is no switch you can turn off to kill the master at this point! If you wired the master with power to activate well if the light is on turn it off-- relay stays off.

Another thought about the "inductive kick" high voltage described above. In the old days of the tube Lear radio the 100-200 volt spikes didn't really hurt anything. Today with many 5 volt circuits inside the avionics equipment and some of that stuff being destroyed above 10 volts wouldn't it be nice to be able to keep the starter spike off the 12v bus? Well if the starter does not go through the master you can. Just leave the master off until you are done starting.

Steve Pierce said:

...Piper did not use a master relay on this 1971 Super Cub and after some research and pondering I did not install one....

Click to expand...

Would this diagram be how you wired without the master relay? Also, what kind of master switch and wire size did you use for your setup?

Is it better to have the Ammeter/shunt downstream of the master switch?

Thanks to all for the time you're taking with this, I'm getting a little better with this wiring stuff :-?

Helmetfire,
I apologize for seemingly having hijacked your thread. My question about the relays has prompted some lengthy discussion for which I thank Aviator and gsmx440 for their informative responses. Hopefully our side discussion will be of some help to you.

Aviator & gsmx440,
My starter load observations have nothing to do with actually measuring current. It is totally an observation of how fast the prop turns when the starter button is pushed. When I first started pushing starter buttons on Lycoming engines, the starters were all direct drive with the only gear being the Bendix drive to the ring gear. It was common that after a little wear or rust on the gears, that the prop would turn slowly with great difficulty particularly with a battery that was not new. Later when Lycoming came out with the 0-360 and 0-540 series they used a starter with a reduction gear assembly which was a tremendous improvement. This prompted me to throw out the direct drive starters and remove them from my memory as they were poor at best, except when new when they were better than hand propping. Even these geared starters would have a hard time with low batteries and cold weather. Now, with the new smaller lightweight SkyTec and B&C starters, they spin the prop nearly fast enough to taxi. :lol: This observation tells me that since the prop is turning faster that it must be drawing less current from the battery. Using my logic, I just can not understand how the SkyTec chart can be correct. I do understand Aviator's explanation, thank you. Perhaps the chart depicts just a microsecond for the initial current flow and has no bearing on the total current usage for an engine start? Do they have an advertising advantage for making the claim that they draw a higher current? Not in my mind.

skywagon8a said:

I do understand Aviator's explanation, thank you. Perhaps the chart depicts just a microsecond for the initial current flow and has no bearing on the total current usage for an engine start? Do they have an advertising advantage for making the claim that they draw a higher current? Not in my mind.

Click to expand...

My pleasure.

Here's the word direct from the horse's mouth (Sky-Tec STC):

"...more output from the battery is required - about 45% more." And, (highlighted) "On runs from the battery to the starter of over 6 feet, AWG #2 wire (minimum) is suggested to provide sufficient current for good cranking performance." They also advertise a wire kit available from Bogert.

Since you mentioned Bogert: They'll make custom cables and P-leads as well. They're nice, and STC'ed.

Helmetfire: If you'll look on the original schematic I sent, you'll notice that I used a central ground buss for everything except the starter. This central grounding point can help prevent ground loops that would insert noise into your comm and nav electronics. I also used the big copper Bogert cables for both the starter and the ground connection from the battery to the bus bar, attached to the same point as the bus bar connects to the frame, if I recall correctly (I'm not at the hangar now). This helps avoid big, magnetizing currents running through the frame and noise and intermittent noise/faults caused by flexing loose bolts in the seat frame, etc. where a lot of folks ground the battery (assuming an underseat battery). It's probably not worth grounding the battery this way if the battery is still located behind the baggage compartment - the run would be too long.

I used twisted pair wiring (just twist it yourself) for all the lights in the wings - prevents mag dipoles from forming and avoids intermittent noise caused by the flexing the wing root bolts that has been shown to cause GPS problems when the wing structure is used as a ground.

Finally, I use a Odyssey RGLA battery and a SkyTec HT starter (use this one if the oil cooler has been moved to the engine baffles - this model has the anti-kickback clutch). The prop spins like a top during start.

All this extra wire weighs less than two pounds.

This is all probably overkill, but then, I don't have noise or ground loop problems.

Skywagon and anyone else. If you want to check the condition of your switches, relays, wires and loads for health do this: Assuming the load (starter,radio,light bulb etc. is in good shape (can be tested by substituting in another circuit or aircraft) and a known good battery (say load tested in another aircraft). First get an analog voltmeter if possible. Connect the negative or black lead to the battery minus terminal. Turn on the load (if it's the starter be careful of the prop or the engine starting. You just want it cranking). If the load has more than one state (with a radio test in both transmit and receive mode) test in all modes of operation. Now touch the plus (red) meter lead as close as possible to the power input at the load. I have a dental pick that I pierce the wire right at the input to a radio past any connector or fuses etc. Turn on your load (starter,light etc,), You should see close to battery voltage or else something is acting like a resistance burning up some of the power on the way to the load. If everything tests good there move the minus to right next to the load at ground again maybe piercing the ground wire if there is one at the load. Test UNDER LOAD again. If in the first tests you have close to battery voltage then you have determined the plus side of the system is good. If then the second test is good you have confirmed the ground side is OK. A for instance would be if your starter turns over slowly and the problem is a bad ground wire that jumpers around the engine mount, well the first test would show full 12v while cranking so you might deduce all was well with you wiring. But the second test would reveal the truth that you had a bad ground wire on the engine mount. The voltage on the second test would be low compared the first test and that would show you had a ground problem.
In the old days of commercial radio we used to do PM's. Preventative maintenance checks kind of like an annual for radios. This would not be a bad idea to do to your aircraft electrical system when it's working good. A benchmark of the readings at the starter and maybe the 12 volt bus (remember the reading only counts if you have most of the loads turned on) would help to know later if there is a problem with the wiring/switch part of your electrical system. A check at annual each year would show future problems before they become real problems. My guess is that most 12 volt bus's would read .3 0r .4 volts less than the battery with all the loads turned on. You can think of that .3 or .4 volts like unusable fuel in your gas tank.
I want to reiterate that without the loads turned on you are not stress testing the system and the volt readings are almost meaningless. This is what leaves a lot of non electronic folks scratching their heads and thinking voltage tests are useless. The circuit MUST be loaded for the readings to have any meaning.
I edited in the bold for the actual tests to remove all my explanations and show how simple this really is to do.

skywagon8a said:

Helmetfire,
I apologize for seemingly having hijacked your thread. My question about the relays has prompted some lengthy discussion for which I thank Aviator and gsmx440 for their informative responses. Hopefully our side discussion will be of some help to you.......

Click to expand...

Aviator said:

.....

Here's the word direct from the horse's mouth (Sky-Tec STC):.......

Click to expand...

qsmx440 said:

Skywagon and anyone else. If you want to check the condition of your switches, relays, wires and loads for health do this: ......

Click to expand...

Are you guys done yet?!? Just kidding...all this info, although over my head, will surely help somebody's search in the future, which is what this site is all about :smile:

sjohnson said:

.....Helmetfire: If you'll look on the original schematic I sent, you'll notice that I used a central ground buss for everything except the starter. This central grounding point can help prevent ground loops that would insert noise into your comm and nav electronics. I also used the big copper Bogert cables for both the starter and the ground connection from the battery to the bus bar, attached to the same point as the bus bar connects to the frame, if I recall correctly (I'm not at the hangar now). This helps avoid big, magnetizing currents running through the frame and noise and intermittent noise/faults caused by flexing loose bolts in the seat frame, etc. where a lot of folks ground the battery (assuming an underseat battery). It's probably not worth grounding the battery this way if the battery is still located behind the baggage compartment - the run would be too long.

I used twisted pair wiring (just twist it yourself) for all the lights in the wings - prevents mag dipoles from forming and avoids intermittent noise caused by the flexing the wing root bolts that has been shown to cause GPS problems when the wing structure is used as a ground.

Finally, I use a Odyssey RGLA battery and a SkyTec HT starter (use this one if the oil cooler has been moved to the engine baffles - this model has the anti-kickback clutch). The prop spins like a top during start.

All this extra wire weighs less than two pounds.

This is all probably overkill, but then, I don't have noise or ground loop problems.

Click to expand...

Just to be clear, as far as the electrical components I will be incorporating an underseat Odyssey battery in a F. Atlee Dodge battery tray, and a B&C 40A alternator STC...The solenoids are mounted underseat as well. Steve, I plan to incorporate your methods for avoiding ground loops and such, your schematic is easy to follow in that regard.

Some interesting things I learned today whilst continuing with my project:
Upon closer inspection of the original starter cable, I cut into it thinking I would see the silver colored aluminum wire, only to find out that it was a blue #4 copper auto cable, sheathed in a white shrink tubing (12' worth)....still discovering sins of the past!! Doesn't really matter as I will be replacing with #2 cable from the underseat battery to the starter anyways.

The starter solenoid (seen in a previously posted pic), although looks different from the master solenoid, has the same part number and looks to be a continuous duty solenoid as opposed to the correct intermittent duty solenoid necessary for a starter solenoid...looks like another order to Spruce.:roll:

Attached is my latest version of the wiring diagram...I've simplified it a bit to show only the basic diagram, hopefully this will satisfy the Feds for my Field Approval, keeping it close to a stock (later model) super cub wiring diagram. I think I have it pretty close on this attempt...please correct me if I'm wrong.

Thanks a bunch guys!!

Helmetfire your schematic looks like it will work this time to me. One thing I assume you are going to use the B&C LR-3 controller. You didn't give the connection numbers to the controller. I assume the low volt light you have is going to pin 5. You don't show a bus "sense" line going to pin three. I think pin 3 is the line into the regulator that senses the voltage on the bus so that the field adjusts the alternator output so pin 3 is a mandatory connection.
http://www.bandc.biz/pdfs/001510VFRSingleALT.pdf
Maybe you have already taken that into account but thought I would mention it. The rest is personal choice and we all already discussed master activation schemes and the pros and cons of each and also about running the starter current through the master relay. Anyway I couldn't find any electrical problem with your schematic so it should work unless someone spots something I've missed. Good job!

qsmx440 said:

Helmetfire your schematic looks like it will work this time to me. One thing I assume you are going to use the B&C LR-3 controller. You didn't give the connection numbers to the controller. I assume the low volt light you have is going to pin 5. You don't show a bus "sense" line going to pin three. I think pin 3 is the line into the regulator that senses the voltage on the bus so that the field adjusts the alternator output so pin 3 is a mandatory connection.
http://www.bandc.biz/pdfs/001510VFRSingleALT.pdf
Maybe you have already taken that into account but thought I would mention it. The rest is personal choice and we all already discussed master activation schemes and the pros and cons of each and also about running the starter current through the master relay. Anyway I couldn't find any electrical problem with your schematic so it should work unless someone spots something I've missed. Good job!

Click to expand...

Thanks, couldn't have done it without you guys! That missing sense wire was an oversight on my part, updated and saved!