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Roger Lee

resolution to common CT grounding issues

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I have been testing and looking into radio and instrument read out issues which are usually a grounding related. FD has the ground wire start at the water pump, down to the center engine mount bolt, up to the starter solenoid and battery, over to the reg/rec, and up to a bolt on the firewall and into the instrument panel and connected to either a bolt with all the ground wires stacked or a grounding block attached to this bolt. This bolt loosening and sometimes the other grounding points loosening cause radio and instrument issues. Simple things like low oil pressure or the oil temp bouncing 20F and other anomalies are related to the ground.

 

I have experimented and think I have come up with a good solid solution. I have tried this on 3-4 CT's and seems to have corrected owner complaints.

 

I take a #8 thin strand wire cable and solder brass ends on and then cover the connection with heat shrink. Make this 14" long. Then run that from the battery negative to the #3 cylinder drip tray screw which is located on top of the #3 cylinder to the rear. If you have an LS this is just an empty screw hole as your drip tray mount is different.

I make another #8 wire that will go from this point on the #3 cyl. and routes into and through the plastic tubing or fire sleeve which ever you might have into the instrument panel. Make this wire 18" long. This end connects directly to the ground screw or on the ground buss. I leave all the standard CT ground wires in place and this is just an addition. After testing this on a few CT's it has worked very well as the resistance loss is less and there is no loss from loose connections or corrosion. It's about as solid a connection as we may see on the CT. My bouncing oil temps quit. They do fluctuate 3-4 degrees, but this is because of the sensor type and high temp for it which makes the reading a little less stable (per Dynon tech). Another had a 30 psi oil pressure, adding this ground wire setup increased it to 48-50 psi and nice and steady. Another issue was some radio interference and that went away. The ammeter fluctuation is reduced. It won't totally go away, but is is certainly reduced. I think this addition will help many, but it may not fix everyone, but it's a good start.

 

When I go out to the field tomorrow I will take a few pictures and get wire length and post them here, but I wanted the testing out of the way first.

 

p.s.

Don't buy the normal #8 wire as the strands are thicker which make the wire stiff. The thin strand is very flexible. Make sure you buy the electrical solder connectors with the right size hole for the smaller screws. You can buy all this for a few dollars at most any Hardware store or my favorite Ace Aviation (a.k.a. Ace Hardware).

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Hi Roger. Hate to add more wires but this seems to be logical. Where does one get the thin stranded #6 wire you mention? I'm going in for my conditional inspection and will ask my mechanic to help me take a look at this.

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Does FD not use some kind of locking fasteners (nylock, castle nut/cotter pin, etc) on the bolts at these locations? Seems that would be an easy fix for this kind of problem.

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There is really nothing wrong with FD's, but this is just a little better.

FD does have fasteners. The issue is they can loosen and do, they can get corroded, but most of all they go from one point to another so many times it's easy to have resistance. The way I mentioned is a short straight solid connection that seems so far supirior to the multi point connect setup. I seems to have cured some ills and it is always right in front of you to check and more solid a connection.

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Hi Roger. Hate to add more wires but this seems to be logical. Where does one get the thin stranded #6 wire you mention? I'm going in for my conditional inspection and will ask my mechanic to help me take a look at this.

 

Use real aviation hookup wire, not 6 gauge THHN that is sold in hardware stores. Aircraft Spruce 11-14506 at $2.55/ft should work good.

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Not to be too nit-picking as I think the bypass ground wiring is a great idea, but #6 wire is rated for 55Amps and weighs ~1lb/ft. There's really no way to pull more than 200W, and only 100W if you use a nice LED landing light. That's just 8Amps which can be easily handled with even 18AWG wire (6.4mohm per foot). Use 14AWG if you want overkill but I am doubtful you will be able to sense any improvement with lower AWG

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Hi Kurt,

 

 

I agree it could be smaller, but after the results I have seen it works well.

This #6 thin strand wire I found is super flexible and lighter than the thicker stranded #6 wire. You only use about 25 inches. Both wires plus the end fittings can't weigh more than a few ounces. It is over rated, but that helped me make sure it wasn't a marginal issue.

 

p.s.

8-2-12

I bought some new supplies today for this ground and picked up some #8 thin strand wire. The wire was $1.99 ft. and the 4 solder connectors were $0.79 each so the total was around $8.15 for a single installation.

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Not to be too nit-picking as I think the bypass ground wiring is a great idea, but #6 wire is rated for 55Amps and weighs ~1lb/ft. There's really no way to pull more than 200W, and only 100W if you use a nice LED landing light. That's just 8Amps which can be easily handled with even 18AWG wire (6.4mohm per foot). Use 14AWG if you want overkill but I am doubtful you will be able to sense any improvement with lower AWG

 

In this type of grounding, the general rule of thumb is "larger gauge size is better" and "more conductors in a wire is better". (Practicality does play into this of course). Currents are carried at the surface of a conductor. The more surface area of the conductor the better it is at transferring from point A to point B. There is a difference between having an adequate conductor size to handle the calculated current flow and bonding the multiple surfaces in order for ground to be at the same potential everywhere for the purposes of eliminating noise and ground loops.

 

Our little planes create a virtual cesspool of noise. There is RF noise from our transmitters (radio and transponder), there is impulse noise from our ignition systems & spark plugs, all further complicated by high vibration and extreme temperature variations. In RF applications ground wires are usually flat braided wire (looks like straps). Vibration over time causes electrical connections to become slightly loose. wires secured with crimps, push on connectors and screws can develop resistance since the connection is relying on physical point to point pressure in a vibrating environment to transfer the current or signal. Grounds that are all supposed to be at the same potential wind up not being so which allows for the creation of noise.

 

What Roger is doing is bonding multiple surfaces so that ground is at the same potential everywhere, thus limiting the potential to create noise. Noise is created when various paths to ground are at different potentials (ground loops). It is possible for noise to get worse (create noise where none exists) so each installation may act a little differently.

 

Here is a discussion of grounds, ground loops and noise.

 

http://en.wikipedia....8electricity%29

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I spent some time studying the ground wiring on my 2006 CTSW this morning. I have to say that it's pretty much a mess compared to good engineering practice. I don't doubt that Roger's jumper wire improves things. I'm installing a Dynon EMS in the next week or two and I'll see if I can come up with something a little better.

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Ground loops are a problem with RF noise. The CT problem is resistance in the ground path since they do such a quirky job with the wiring. Thus current pulses create large voltage pulses onto ground. The goal then is to wire out the loss such that the current pulses create negligable changes in voltage. With a 12V system and osmething like 10 amp pulses you want to be below 50mohm. Anything much less than that will show rapidly diminishing improvement. That's why 14AWG is probably a good compromise. BTW, DC current is carried evenly through the cross sectional area of a conductor. AC currents are carried with exponentially decreasing denstiy of depth into the conductor; the exponent being a function of frequency (called skin depth). At the kilohertz and below level, the skin depth is a few mm so essentially throughout the wire.

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Roger,

 

I wouldn't pretend to know how to tell you to handle a fire or other emergency. OTOH, I've been doing electronics since I was 8. I'd like to think that I've learned a little about that profession in the last 52 years. Now I'm sure that what you did worked and made everyone happy. I just think that if I'm going to start moving wires around, I'm going to understand the problem and the fix and make it the best I can. I've seen lots of ad hock fixes and even done a few. But in this case I have the resources and time to try to do it correctly from an engineering standpoint.

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Jim/Kurt,

 

My knowledge of electricity is rudimentary. For example, if you reach up to unscrew a light bulb, the electricity runs out, down your arm, and drips off your elbow.:unsure:

 

Seriously though, Rogers suggestion is simple, cheap, and apparently works. If there is a better, easier, more effective way of doing this I would be interested

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I have seen the ground issues on CT's for 6 years and tested this very solution now on a few planes. seems to work. I don't touch the FD grounds, this is only in addition to and the owners seem to be happy after a few years of small nagging issues, but usually not serious problems.

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I'm installing a Dynon EMS in the next week or two and I'll see if I can come up with something a little better.

 

I'm doing a major rewiring this winter and would very much like to hear anything you'd like to share. Grounding is a specific interest. I'll be putting in a SkyView, some new radios, new transponder, new AP, plus more.

 

 

 

 

 

 

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Roger, it would be nice to see some pics of your ground install. I'm willing to forgo the theoretical armchair quarterbacking and like Nike, "JUST DO IT".

 

Jim, Sounds like you have a great winter project planned, love to see some pics of that upgrade as you go through it. You'll sure like the Skyview. I am a huge fan of Dynon. Imagine a manufacturer that lets you download software upgrades for free and allows you updates for charts, obstacles so on and so forth all for free with no subscriptions! Add in ADSB for free weather and the only thing you have to pay for is XM if you so desire. No more Garmin over priced subscriptions!

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The REAL way to do this is with a milli-ohmeter which requires 4-lead kelvin probes to sniff out a 5mohm connection from a 50mohm across all the connection points. I am certain the main noise is from path loss turning current pulses into induced voltage noise. So I bet Roger's fix is on the right path, I just think it is overdone with 6AWG. An ordinary DMM is only accurate to 0.1ohm so is not much help here. I used a milliohmeter on the exhaust stacks, but have never teased out the whole ground path.

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Hi Kurt,

 

Red was the only color in the thin strand I had at the time for testing. It's just to show concept as this was first testing installs to make sure everything worked well. Black or white is available.

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Holy Smokes,

 

I'm unable to even formulate an intelligent question.....the expertise in these posts is simply amazing for the wiring/electrical system challenged....me. Here's what I think I've learned. I at least now know, that as these noise/grounding related issues pop up over time, its basically a hopeless situation unless one expends a lot of resources on experts to chase down a phenomial amount of highly technical symptoms.

 

Oh, my question: What is resistance? How is it measured? Why is it bad....Like in a Gas or Oil Pressure Sensor and if one can identifiy its physical location (resistance) like a terminal....can't one just change the terminal and recondition the connection...?

 

Gosh, so much to learn, amazing...In the words of Jim Durante, "I'm Emortified"

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Resistance is the opposition to electrical current flow. It can be calculated by Resistance = Voltage / Current (R=V/I) per Ohms law. It is expressed in terms of Ohms. Often, we see resistance expressed as heat (light bulb, battery cable, etc.).

 

We see resistance in a couple of ways in our airplanes:

 

1. Resistance in a ground circuit is generally bad. We want the electrons to flow unimpeded from the positive side to the negative side. Any bad connection in the ground circuit can cause resistance to the flow of electrons, and this means that current doesn't flow as we expected or desired. That may mean a meter or appliance doesn't work as designed. Therefore, we clean connectors, choose good connector materials (copper instead of wood, for example), try to avoid dissimilar metals that promote corrosion, use short runs of big wires, etc. There is resistance in everything. The way to keep resistance down in a given material is to keep it short and have it be of sufficient size, as a larger conductor generally has less resistance than a smaller.

 

2. Some of the sensors are thermistors. That is, as they heat up, they change resistance. This causes a change in voltage and current and this information can be measured. It can then be displayed. So, your CHT reading has nothing to do with heat, it has to do with the different electrical properties of the sensor at different heat. It is a referred indicator. What this means is that your "heat" gauge may be off because of a bad ground (nothing to do with how good a thermometer it is).

 

Many of our circuits are DC, direct current, like a flashlight as opposed to alternating current as seen in a wall outlet. We have alternating current produced by the alternator. This is changed to direct current by a rectifier. If you get alternating current on a dc circuit, is shows up and acts like noise. We use filters to get rid of that. There is a big capacitor to help and the battery itself is a big capacitor that helps reduce AM noise. The noise can be one cause of twitchy needles.

 

Hopefully I have not made too many gross errors.

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Resistance is the opposition to electrical current flow. It can be calculated by Resistance = Voltage / Current (R=V/I) per Ohms law. It is expressed in terms of Ohms. Often, we see resistance expressed as heat (light bulb, battery cable, etc.).

 

We see resistance in a couple of ways in our airplanes:

 

1. Resistance in a ground circuit is generally bad. We want the electrons to flow unimpeded from the positive side to the negative side. Any bad connection in the ground circuit can cause resistance to the flow of electrons, and this means that current doesn't flow as we expected or desired. That may mean a meter or appliance doesn't work as designed. Therefore, we clean connectors, choose good connector materials (copper instead of wood, for example), try to avoid dissimilar metals that promote corrosion, use short runs of big wires, etc. There is resistance in everything. The way to keep resistance down in a given material is to keep it short and have it be of sufficient size, as a larger conductor generally has less resistance than a smaller.

 

2. Some of the sensors are thermistors. That is, as they heat up, they change resistance. This causes a change in voltage and current and this information can be measured. It can then be displayed. So, your CHT reading has nothing to do with heat, it has to do with the different electrical properties of the sensor at different heat. It is a referred indicator. What this means is that your "heat" gauge may be off because of a bad ground (nothing to do with how good a thermometer it is).

 

Many of our circuits are DC, direct current, like a flashlight as opposed to alternating current as seen in a wall outlet. We have alternating current produced by the alternator. This is changed to direct current by a rectifier. If you get alternating current on a dc circuit, is shows up and acts like noise. We use filters to get rid of that. There is a big capacitor to help and the battery itself is a big capacitor that helps reduce AM noise. The noise can be one cause of twitchy needles.

 

Hopefully I have not made too many gross errors.

Thank you for the education Jim...How do the oil and fuel sensors go bad..I'm guessing there is a Ohm range standard to help tell. I guess overtime something causes resistance to increase inside them, other than their electrical terminals and external wiring connections...???

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Vibration kills them because of the mechanism inside. The oil and fuel pressure senders are the same design internally. The pointer that you see in the picks moves along the horizontal rail and copper wire. This pointer is spring mounted and moves from pressure coming in. Because of this design with the pointer just hanging out there and the very small movement it takes to make a pressure change reading in the cockpit is is highly susceptible to vibration over time.

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Thank you for the education Jim...How do the oil and fuel sensors go bad..I'm guessing there is a Ohm range standard to help tell. I guess overtime something causes resistance to increase inside them, other than their electrical terminals and external wiring connections...???

 

Doug, think about a special wire that has a known resistance per inch or foot. This wire gets wrapped around a non-conductive center support. For each wrap the resistance goes up a known amount. Only one end of this wire is connected to a ground source. The wire from the instrument is connected to a pointer that moves up and down the wraps of wire. For each wrap that it moves away from the ground connection the resistance increases and the input voltage drops. The instrument actually measures voltage and displays it in what ever unit you want displayed. For oil pressure the instrument is supplied 12 volts. It then sends the 12 volts to the sending unit. As the oil pressure increases the pointer moves on the wire increasing the resistance. The resitance causes the voltage to drop. The instument measures the voltage drop and displays the increase in pressure on the instrument.

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