View Full Version : Quick one on extending thermocouples

profqwerty - n/a
22-Jan-08, 05:00 PM

Have received the EGT guage today, the wires that came aren't quite long enough to comfortably reach to the console.

The probes' wires are steel braided, but with the dual guage comes a short section of 4-core mains cable with connectors crimped onto the ends.

I'm assuming I could just cut this and extend it a metre or so?


jon_curtis - n/a
22-Jan-08, 07:02 PM
you want a cable of minimum resistance/low impedance!

so dont try and use that bit of cat 5 network cable thats in the loft lol!

a multi stranded copper wire, like mains cable is best! but the longer the wire, the less effective the gauge will become!

team black - n/a
22-Jan-08, 07:09 PM
Chock block and twin core is fine

Jeremy - n/a
22-Jan-08, 09:41 PM
Whilst using ordinary wire works, it introduces errors, as you are adding more dissimilar metal junctions. To retain best accuracy you need thermocouple wire and connectors. Both are sold by suppliers like RS and Farnell. Here's a link to the RS stuff I use: http://uk.rs-online.com/web/search/searchBrowseAction.html?m (uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6118012) ethod=getProduct&R=6118012

CHT and EGT thermocouples are normally Type K, so ideally need wire with alloys in each conductor that match those of each side of the thermocouple to reduce errors. Similarly, thermocouple connectors are designed to have the same electrochemical characteristic as the wire, again to reduce errors.

Whether this is worth doing with a cheapo Chinese instrument is a moot point, but for use with a decent digital meter with a fairly accurate readout then it may well be worth the bother.


Iceman - n/a
22-Jan-08, 10:29 PM
When I was building microlights, the instruments always had the cables extended in order to reach the dashboard.

The display on instruments is fairly vague so you will not get pinpoint accurate readings. As long as your initial setup provides figures slightly below the maximum values you will be fine. After that you are only looking for variations to indicate running issues.

In my experience, instruments are only really useful for setting up, you might check them once in a while when operating but you will find a piston can melt and stop your engine in a matter of seconds, you might get a glimpse of which cylinder gave you the problem but not with enough warning to save your engine.

keith_b - n/a
23-Jan-08, 09:39 AM

I have EGTs on my standard 503 (with cooling tin).

I have used a couple of metres of European standard towing cable to get everything from the back to the front (rev, fuel guage, EGTs, Lanyards), I also have the guts of a 13pin connector covered in maplin self amalgamating tape so's the engine can be "unplugged" when I need to get it out.

This setup has been going now for two seasons, I use the EGTs to manage the carb setup - they have also saved the engine when one of the carb sockets came loose enough to lean the mixture. I am sure that the EGTs are not 100% as calibrated but it is "good enough" for what I need.

(European standard towing cable = 13 core - http://www.towsure.com/product/1831-Euro_13_Core_Cable_-_Per (www.towsure.com/product/1831-Euro_13_Core_Cable_-_Per_Metre) _Metre)


profqwerty - n/a
23-Jan-08, 09:49 AM
I believe I'm using the cheap chinese instrument http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif .

I'm going to set it up with the dials plugged straight into the probes as it's meant to be, note what it's showing, then put the extension in with normal wires and see what it says and use that as 'normal'.

I never thought about using towing wires. I've just been using lengths off of a roll of single core we had - all the same colour http://hovercraft.org.uk/images/icons/smiley_icons/icon_razz.gif

I have a din plug with tach and chts on, a 2 thicker plugs for kill switch.

The EGTs have their own plugs.

I'll wire it up tomorrow.