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Some Circuit Help Please

AndyRV7

Well Known Member
I'm trying to figure out how to power my ADSB equipment but I feel completely electronics illiterate. Maybe you guys can help me.

I have installed a Uavionics Echo and a GRT Safefly gps to be in/out compliant. My intention has been to pull power from one of the circuit breakers on my avionics bus. Here are some pictures of my panel and behind the panel. These were the best I could do in tight spaces.



This is a pic of the circuit breakers and switches I have in my panel. The Avionics Master switch powers the avionics bus.

49375981798_5d1be7f763_z.jpg




This is a picture from behind the circuit breakers/switch group above. I've outlined the avionics buss circuit breakers.

49375981783_fe9c68d530_c.jpg




Here I have zoomed in and circled portions of 3 circuit breakers I presume are "hot" wires and go to individual pieces of my avionics to power those avionics. I would like to run my ADSB red power wire back to one of these 3 terminals to result in switched power to my ADSB equipment.

49376638537_ac10b3cf33_c.jpg




Here is a picture of what I presume is a grounding block. I presume that only because it doesn't have a thick power lead coming in. I presume that means it IS actually a grounding block and not a power distribution block. I would like to run the black ground wire from my ADSB equipment back to this block and share a slot with whatever is already in that slot.

49375981068_09bf70b9d6_c.jpg




Is my assessment accurate, and is there any way to test the terminals in question to see if in fact they are power and ground as I've described? I haven't tried to follow any of these wires back to either end.



If this is all good, do I need a new, higher amp, circuit breaker after adding the ADSB to the circuit. Let's say that I tap into the EFIS breaker because it might be the easiest to access. If I add another 3 amps of current draw to power the ADSB equipment, won't I be overloading the 5 amp EFIS circuit now?? I know I can add a 3 amp in-line fuse to the ADSB equipment downstream of the installed circuit breaker, but I'll still be drawing approximately 8 amps through that breaker. I'm not sure how I should solve this problem.

Ill stop there for the moment. Sorry for the long and clueless post!

Thanks for any help you can offer?

Andy
 
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the second picture does not look like a grounding block. Looks more like a junction block. I used one just like that for my strobes and nav lights. Hard to tell where it is located. As far as taking power off the buss, you may be better off just using inline fuses and attaching them to the buss bar. Downside if you do there is no access to them in flight.

Jay
 
The simplest solution is to connect the new ADS-B equipment to the
transponder circuit breaker. Upsize the breaker to 5 amps if necessary.
 
the second picture does not look like a grounding block. Looks more like a junction block. I used one just like that for my strobes and nav lights. Hard to tell where it is located.
Jay
I agree. That does not look like a grounding block. Find the routing of the negative lead from the battery. It may go to a forest of tabs, something that looks like this.
FP20072010A00043.jpg

Thats where you will want to connect the grounds. You could also look for where the black wires are routed to as a start. With power down use a multimeter check for continuity (no resistance) between one of those wires and bare metal on the airframe to confirm that that is your ground.
 
The simplest solution is to connect the new ADS-B equipment to the
transponder circuit breaker. Upsize the breaker to 5 amps if necessary.
+1. I?d do this. While under the panel, trace out the transponder ground wire. Connect the adsb ground to the same location.
 
I agree with upsizing and using the transponder breaker as it makes sense but you will want to double check something. Understand that while the breaker must be sized big enough to handle the expected total current draw (transponder + ADSB) PLUS a buffer BUT it must not be too big either. While supplying current to the load, the primary function of the breaker is to protect the wires from too much current like when the insulation gets compromised and a short to ground causes a lot of current to flow in the wire. So, you should first determine the gauge of the existing wire going to the transponder. It will be printed on the wire. Then look up a chart to determine it can handle the value you’re planning to upsize the breaker to plus some more. ie, 18 AWG can handle the proposed 5amps. If this gets a pass, use the same (or larger) gauge wire for the ADSB circuit (even if the ADSB doesn’t draw much current).



Bevan
 
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Or you could connect directly to your avionics power bar (top copper bar) and use an inline fuse. I see power feeds already tied in that way. Ground could be local or at a grounding block if you have one somewhere.

Edit; Sorry, Just reread your post and saw you wanted the power to be switched. Running from the buss bar would not give you separate switching. Transponder breaker is the way to go.

Get a multi meter from the local Harbor Freight if you don't have one to check for power vs. ground. About $7 for the cheap ones. They used to give them away for free with any purchase. There are a lot of Youtube videos on how to use them if you are not familiar
 
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The original post indicates that a good course of action would be to get 15min of hands on help to get started and identify a wiring plan.
 
The previous posts all have good ideas, so I won't go over them again.
BUT... every RV owner should own a decent DVM. They are cheap now days, compared to the Fluke meters of a few years ago. Some even have RS-232 output to record data from a voltage bus.
Get a meter.... go check both sides of those breakers. One side will be HOT when the breaker is pulled. Don't connect to that side or you bypass the breaker.
Current draw is minimal on modern transponders and ADS-B. You can even switch the meter over to measure amps. (ma. usually) of a device on your desk with a power supply. Using the transponder breaker will likely not even need upsizing. If it pops a time or two... then up size it by an amp or two.
You did mention switching the ADS-B. I won't get into the rules... since anyone can switch off their uAvionix by turning off position lights.
But... if you use the transponder breaker... and pull that to kill power, you have shut down both boxes. A separate toggle switch somewhere might be a better choice. Cheers,
 
Thanks everyone for the ideas.

The previous posts all have good ideas, so I won't go over them again.
BUT... every RV owner should own a decent DVM. Get a meter.... go check both sides of those breakers. One side will be HOT when the breaker is pulled. Don't connect to that side or you bypass the breaker.


You did mention switching the ADS-B. I won't get into the rules... since anyone can switch off their uAvionix by turning off position lights.
But... if you use the transponder breaker... and pull that to kill power, you have shut down both boxes. A separate toggle switch somewhere might be a better choice. Cheers,

I have a couple volt meters so I will check the breakers this weekend.

As far as switched ADSB, I just mean I don't want it drawing power from the system when the plane is shut down. So technically, I guess, the Master Switch would probably accomplish that too. But if I use the avionics bus, I can leave the ADSB off when starting the engine. I'll have too check the rules now but I can't see why that wouldn't be acceptable...avionics go on as soon as the engine is running.
 
Couple new questions

More of what you guys said makes some sense now. I was back at it today and accomplished some things.

I found the hot side of my breaker by pulling the breaker and checking for the powered side. The red wire side of the breaker happened to be the outbound power to the engine analyzer (also on the avionics bus).

I rigged a 12volt power supply using some type of plastic battery housing I had purchased sometime in my life. I cut the plug off and added alligator clips and 8 AA batteries. This allowed me to do two things. One, power up the ADSB for the first time, and two, check the amp draw. Here is my 1st question. I set the DVM to 10A DC and ran the meter in line from the battery pack to the ADSB and the ADSB ground back to the battery pack. My results were strange I think. I got a 0.30 reading. It is supposed to be 1.5A for each the transceiver and the GPS for a total of 3A. Is this odd, or am I reading the meter incorrectly? It was on the bench with no antennae attached.



I also checked the wiring gauge. I have 22 for the ADSB which is fine for a 3A draw. For the UBG engine temperature gauge, the wire is 20 gauge, which is fine for a 5 amp draw. 2nd question: if I upsize the 5A breaker to 7.5A or possibly 10A, I won't be protecting any of the wiring (old or new) with that breaker. So do I need to add inline fuses on All the wiring, downstream of the breaker??

3rd question
: what is the proper amperage for the new breaker?? Presuming 5A for the UBG and 3A for the ADSB, I would need a 10A fuse to leave a little headroom.

A lot of this seems to me to defeat the purpose (or capabilities) of having a resettable circuit breaker in the panel.

Thanks Andy
 
A 12 volt AA battery pack does not make a very good power supply for
testing avionics. I suggest using a 12 volt lead-acid battery instead.
If the AA battery pack is heavily loaded, its voltage will drop and the
measured current will not be representative of normal operating conditions.
-
Consider installing a fuse block with spares.
-
It is not a good idea to power up a transmitter without an antenna connected.
-
I would use fuses for the new equipment, especially for something that is not essential to
flying the aircraft. Fly the plane and save troubleshooting for when safely on the ground.
-
A popped circuit breaker might have prevented a fire. Why reset it and give the fire a second chance?
 
This is from the GRT website and the installation manuals for the echo UAT and the SafeFly GPS. (Please verify for yourself to make sure I am looking a the same components you have)
https://uavionix.com/downloads/echo-uat/echoUAT-User-and-Installation-Guide.pdf
http://grtavionics.com//media/GPS-Safe-Fly-Install-Manual-Rev-P.pdf

For the Echo, Section 7.7 Wiring Considerations, recommends a 1 amp breaker or 3 amp ganged circuit breaker.

For the GPS, the power draw is minimal, at 0.2 amps, page 8 power and ground.

What is the power draw of the transponder you have? You need to check the transponder data sheet or installation manual. If the transponder power wire is 20 gauge you could increase the breaker to 5 amps and then connect the new devices to that breaker. But the new devices power wire should also use 20 gauge. The breaker needs to protect the wire.

Or like an earlier suggestion use a 1 amp inline fuse for each on the new devices and connect it directly to the avionics bus.
 
I guess I have been trying to do this the hard way.:eek:

Is it fair to say that I should leave my transponder circuit alone. Why mess with a circuit that is working just fine. And instead, just wire the ADSB power to the avionics bus bar (as at least one person has suggested!). I don't know why I couldn't see this until now (tree before the forest??). I presume the actual copper bar that connects all the avionics circuit breakers into a single bus, is only energized when the avionics switch is ON. Therefore I can wire the ADSB power to any breaker screw along that bar, and add an inline 3A fuse. Problem solved!?

This way, I have not messed with anything that was already working and I simply protected the new circuit from the power source with its own fuse instead.
 
Ground Question

I've mounted my ads-b equipment under my panel and run my power and ground wires toward the avionics bus. I've also added a wire from the harness to my GRT efis for "IN." I've also installed the GPS antenna. I'm very happy with the result so far but locating an appropriate ground is keeping me from powering the system.

I pulled the cowl and mapped out my electrical system as needed. I have no grounds returning to the firewall in groups or individually. My battery is grounded to the air frame at the upper, passenger side engine mount bolt. It does not project in any way by jumper or otherwise, to anywhere on the cockpit side of the firewall. So my individual ground wires seemingly have to be terminated at some location on the air frame (in groups or individually).

I am going to attempt to cut open some of the wire bundles this weekend so I can attempt to trace a ground from a single avionics device, from the unit to its termination point. This has been very difficult so far but I hope that opening some of the bundles of wire might help in that regard.

I have 2 different types of "junctions" for groups of wires. One is a metal unit that wires screw into at individual screws. If I check continuity from any single screw, wire, or the junction unit itself, to the firewall, they indicate ground. I presume I am not learning anything from this other than that that block of wires is grounded "locally" thought the metal block. The other type is a plastic looking unit with pairs of screws in two rows. Some of these screws indicate ground while others do not. So I am assuming these pairs of screws are merely isolated links in some part of a given circuit. Some ground and some power. These can probably be viewed in my original pics. Some have already commented on them.

My question is is this a normal and acceptable way to wire a plane's electrical system? And if so, what is the logic? If everything is grounded locally to the air frame, I would presume you would have a ton of noise in the system.

When I began trying to figure this ADS-B install out, I figured I would just have to trace one installed ground wire to locate a good ground for ADS-B. But it has proven to be much more difficult than I thought it would be.

Lastly ;), it seems as though I am not going to discover a mythical central ground. If that's the case, Should I just ground the ADS-B next to the unit, or possibly all the way back to the firewall near the battery??

Sorry for the long and confused post. Thanks again. Andy
 
Using an engine mount bolt for grounding the aircraft electrical system is not a
good idea. Even though some aircraft are wired that way, doing so is not best
practice. It is better to use a dedicated brass ground bolt through the firewall.
Connect all grounds, both forward and aft of the firewall, to that common ground point.
 
When is a good ground not?

Hi Andy,
So lets get back to the fundamentals. I came across Bob Nuckolls material a while back and was so inspired by his articles I saved them for future reference. Read through this article; not sure how to attach it so I'll post a link to it as well. I copy/pasted the article however you really need to see the images as well so the link will be a better read. This is an excellent read on the fundamentals of grounding and should give you some clues as to what is going on. Here it is:

https://www.dropbox.com/s/dbb6d9raksbgj2j/When is a Good Ground Not.pdf?dl=0


https://www.dropbox.com/s/dbb6d9raksbgj2j/When%20is%20a%20Good%20Ground%20Not.pdf?dl=0
 
Blue mountain avionics gouge

Andy,
This is also an excellent read on the basics of avionics wiring. Greg Richter is a rock star when it comes to troubleshooting. Heres the link and the evil ground excerpt:

https://www.dropbox.com/s/7tk59earluhlb5s/Aircraft%20Wiring%20from%20BlueMountainAvionics.pdf?dl=0


---------------------
From Greg Richter, Blue Mountain Avionics

Power and Ground
First off, we?ve got to power the thing up, whatever it is, which brings me to Kirchoff?s
Law, which simply states that whatever electric current goes into something, has to come
back out and return to the battery. Which means anything you power up needs two wires
to make it go ? one for Power and one for Return. This brings us to:
The Evil Ground
In a car or metal airplane some wise soul thought it would be a good idea to just use the
chassis or fuselage as a common Return wire and save a few bucks. Great idea, if you
want to spin motors and make lights blink in a Model T, but not so good for delicate
electronics like EFIS, Radar, electronic engine monitors or FADEC. Both Electronics
International and blue mountain avionics specify ungrounded EGT probes because most
homebuilt airplanes have grounds all over the place and the stray currents that go with
them can cause odd EGT readings.

?Bad Grounds? cause more problems than just about anything else.
So -- I offer the Zen solution of not thinking about things in terms of ?grounds?. Ditch
the whole, outdated, tragically useless concept. If you stick to the two-wire rule, one for
power and one for return, you?ll never have a ground problem, and everything you
connect will work the first time. Remember, ?Ground?, in this context, is a convenient
shorthand for the return lead in a circuit. It doesn?t really exist as Earth Ground for us
aerospace-types. This brings us to our second rule:
All circuits are wired with a power lead and a return lead of the same size.
Power is color-coded yellow or red, return is color coded black.
 
Those links are pretty good! I've read some of Greg's stuff while I've been searching for answers here. I also have Nuckolls book and have spent a fair amount of time reading the chapters that pertain to my situation, several times!

I've actually learned some things since I began this thread. It may not sound like it, or maybe some things took a little while to make sense. When I began this small project I had no more understanding of an electrical system than that power leaves a battery through one wire, passes through a device that uses that power, and then the power returns to the battery through another wire. When you add switches and circuit breakers and multiple grounds and an alternator and solenoids and buses, things get a little more complicated.

Like most of the things I've learned to do to maintain my aircraft over the 5 years I've owned it, I've had to back up before I could go forward. I guess I only wanted to learn enough here to appropriately add ADS-B capabilities to my plane. I never suspected I would need to map the entire electrical system to accomplish that.

The search for knowledge will continue Saturday morning in my dark and NJ -cold hangar.:)

Thanks again for pitching in! Andy
 
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