TC splices ?

[Larry DeCamp]

I need to terminate my CHT and EGT wires inside the firewall. Do you have any suggestions how to do this ? Soldering will be a pain if you remove the engine. Terminal strips could bring conductivity &corrosion errors etc into the equation. Your thoughts ??? Larry

[Pat Hatch]

Larry, I use these guys, a 3M product; you have to order both the male and the female disconnects. I alternate the sex on the cylinders on each side of the engine so you can't mix the cylinders up. A lot of the CHT/EGT sensors come with these. I have also seen the ones that look like small ring terminals that screw together.

http://www.mouser.com/ProductDetail/...#37;2f5KvKLcBM

and

http://www.mouser.com/ProductDetail/...YcrwZjBszi0%3d

I double over the end of the thermocouple wire to get a good solid crimp in the disconnects--they are made of hard plastic so it takes a good squeeze. Good idea to cover them with shrink tube, too.

[N941WR]

Originally Posted by Pat Hatch

Larry, I use these guys, a 3M product; you have to order both the male and the female disconnects. I alternate the sex on the cylinders on each side of the engine so you can't mix the cylinders up. A lot of the CHT/EGT sensors come with these. I have also seen the ones that look like small ring terminals that screw together.

http://www.mouser.com/ProductDetail/...Wih%2f5KvKLcBM

and

http://www.mouser.com/ProductDetail/...YcrwZjBszi0%3d

I double over the end of the thermocouple wire to get a good solid crimp in the disconnects--they are made of hard plastic so it takes a good squeeze. Good idea to cover them with shrink tube, too.

Ditto for me. 500+ hours and no issues.

[Walt]

Don't forget, nothing lasts forever, so unless you got the best probes available (EI) many of the "economical" versions will need replacement after just 3-500 hundred hrs. so keep easy replacement/access in mind.

[gear1]

I used two 8-connector terminal strips mounted on the engine side of firewall, one on each side about level with the brake fluid reservoir. The stock CHT and EGT bayonet connectors need to be replaced with ring terminals, and the EFIS sense wires need also to be fitted with ring terminals. This makes the replacement of probes much easier. If you are using a digital engine management system (such as a Dynon FD180), you can cut off the excess wire from the management system. These systems measure voltage directly with no current flow, so wire length is not critical. (Unlike analog Gages that require current to move the needle, making wire length - and total resistance - critical.)

I installed the terminal strips about 18 months and 300 hours ago. No problems have shown up.

[BobTurner]

No one has mentioned this, maybe it's obvious: these are thermocouple wires. If you connect them to anything else (like copper) you will introduce an error into the system, unless you treat both wires identically, in which case the errors cancel. This includes keeping the splices on both wires at the same temperature.

[Doug Rohrer]

Bob Turner is right. You should not splice any copper wire into the TC circuit, as it will induce measurement errors. The right way to connect is using these plugs- http://www.omega.com/googlebase/prod...FcsRMwod_nAAGQ. They are made of the same material as the wire (alumel and constantan).

[SMO]

I used a d-sub terminal mounted through the firewall. Not flying yet so not sure how well this will work, however easy to disconnect and reasonably simple to change out the engine side when required.

[deek]

Originally Posted by Doug Rohrer

The right way to connect is using these plugs- http://www.omega.com/googlebase/prod...FcsRMwod_nAAGQ. They are made of the same material as the wire (alumel and constantan).

^^^^ Exactly right. This is the proper way to place a disconnect in the TC wire. These are available for all the TC types; ie, K, J, T. You need to specify what type of TC you have (EGT and CHT are usually different), as in chromel/alumel, iron/constantan, etc. Also, any extension leads you make-up must be of the same material as the TC's.

[Larry DeCamp]

Thanks for your helpful input everyone. Here is what I concluded:

1- My brother recommended Omega miniature connectors based years of experience at GE Aircraft and Cummins engine. You can even buy online from Omega. That's not saying the other ideas won't work equally well as you have referenced.

2- I must extend all 4 CHT and 1 EGT to reach the COPPER leads from my MGL TC instrument. Based on Rainer's input (MGL CEO), I will use copper Tefzel and silicone glass sleeving from B&C. The expectation is ; IF all dissimilar junctions are kept at the same temperature, error is insignificant in this application..Thanks again..Larry