Gumby22

I'm doing some work on my air cooled lawnmower engine (Briggs 26HP twin) this winter, and while I'm at it, I'd like to add a temp gauge (just because I like to keep an eye on it - no reason to suspect it's been running hot).

I've found CHT sensors that will mount around the spark plugs, but since it's a twin, I didn't know if I had to mount 2 separate gauges, or if I could wire them in parallel to one gauge. I realize that will only provide an average reading of the 2 and I'm fine with that, I just don't know enough about thermocouples to know for sure if this would work.

Is it possible to wire them in parallel? Or would a series connection be more ideal? Or will it not work at all?

It's a type K thermocouple, if that matters.

Thanks.

tech2

does a thermocouple work the same as a thermister? Using resistance or does it send/create it own voltage?

kevinkpk

Thermocouple generates electricity, albeit very small. He can wire them parrallel, but that will give the average for both cylinders, not individual, I don't think there would be an issue with that. K type are chromel, and alumel , make sure the gauge is for K type.

Gumby22

Thanks for the responses - I’ve been putting my search engine skills to the test on this because I don’t want to invest the time and money in setting it up unless I’m sure it’s going to work.

kevinpk is right - they can be wired in parallel, but it’s important that the individual thermocouples are of the same type, use the same wire, and have the same resistance to provide the most accurate measurement. It’s also recommended to add resistors to each branch of the parallel circuit in order to compensate for minor variations in circuit resistance due to different lengths of wire.

During my keyboard quest for knowledge, I found these websites to be the most useful and thought I’d share in case anyone else is curious. I emailed one of them today to ask for clarification regarding the set up I want to use but haven’t yet heard back.

Circuit details regarding thermocouples - https://www.allaboutcircuits.com/tex...thermocouples/

Thermocouple descriptions and temperature to voltage correlation charts - https://www.thermocoupleinfo.com/

kevinkpk

I don't think you need resistors in such a short circuit. I spent 30 years in industrial gas turbines as a service tech. The issue with them was concise supervisory monitoring of combustion temps. Your lawn tractor will be just fine. If you suspect one cylinder is running hot, check the gauge, disconnect one set of leads. The gauge will either go high or low, that will tell you which cylinder it is.

Gumby22

I don’t think I’ll need to add resistors either - I only mentioned it because I found it interesting that thermocouples can provide that level of accuracy. I’m an auto mechanic, so not surprisingly, my experience is with negative temp coefficient sensors; so other than knowing that my water heater uses a thermocouple, I had no working knowledge of their operation. This has proven to be a good learning opportunity for me.