Temperature warning light

[sbwnik]

I've come up against the edge of my knowledge of things electrical, and know we have a couple of proper leccy people in here, so hope someone can help.

I want to make a cylinder head warning light. I don't want a numerical one, just a warning light that I can stick behind the screen to come on at around 175C. Any suggestions as to how to do this simply (I've seen a complex method using DIY circuit boards, but I think that will just get shaken to death) would be appreciated.

Thanks


I can almost grasp it - variable range thermocouple type thing and some way of triggering the light at the right temp, but 'how' whilst keeping everything compact?

[sime66]

I’m going to try to liven this thread up because I’d quite like to have the answer too.
I was following your post on Facebook, but it doesn't seem to be making progress.
I see the problem of replacing a gauge with a light triggered at the required temp, which I agree is a good idea. Unfortunately I don’t know how - the bimetal arm and variable resistor normally being in sensor/sender pocket together, which doesn’t work with a CHT plug ring, which needs the gadgetry inside the gauge to convert the resistance change into something useful.
You need something simple, but adjustable, (the variable resistor), but which isn’t part of the sender or the gauge, but I don’t know what or how, so I can’t add to the debate at present, but will continue to chew it over/investigate. If you make any progress, do share it. Or maybe now some proper leccy people might join in....?

How did you do it when you had your indicator idiot light borrowed to do the job before? (FB)

[joey]

This is an interesting one............

I would imagine it can be done. I was thinking about it yesterday while lokking at oven..... bear with me.......... the thermostat in your oven keeps the little light on until the oven reaches temp and then goes out, how hard would it be to reverse the trigger?

[sime66]

I think the crux of the problem is that using a CHT ring with a bulb needs something else, which needs to be kept simple. A normal sensor/sender and bulb would be something like these:

In an oven, the thermostat that switches the heating element and light is inside the oven, but that’s more difficult with an engine.
With just a CHT ring, which gives a signal and isn’t a switch, there is the need for something else to make that signal close a circuit to light a bulb, and also to make the switch adjustable for the right temp (when we settle on what that is).

[henri]

gaz beat me to it but reckon maplins would have the answer ,a thermo couple on a head stud reads 10-15deg less than under the plug so maybe get 1 that triggers at 160deg an as joey suggested run into a relay which supplys the warning light .
or a frankenscoot 1 ,ordinary car water temp sender wud need dc supply but hooked up to a gauge hidden inside glovebox with a hole an pin through glass so when needle gets to 175deg it touches completes the circuit an lights ya light, an if switched by ignition to be trigger for a petrol tank bomb/large spike to shoot up through seat base wud give instant justice to a scoot thief .H

[rab]

Ill have a word with the sparkys at work they do this type of thing and the company also have any parts required in stock so will be very cheep with top end electronics/electric parts in ac or dc

[henri]

weather was nice an "greens" traffic calming measures were workin so well it was nose to tail stationary traffic ,too good to miss so took scoot out car-baiting an dropped in at maplins , they dont seem to have any bi-metalic switches or thermo-couples in store ,closest thing was a digital thermometer ,which if you split you cud lengthen the wires an have readout on glovebox an senser on head , am thinkin of something similar to use when setting up jetting ,the circuitry you'd need to trigger a warning lamp from this is beyond my 30 year old electronics o-level ,will ask my old-man at weekend as he was in electronics durin his work-life ,H

[rab]

Asked the sparkys for the probe temp sensor and to convert from display to warning light over 130 quid thats before staff discount so still expensive i can get you the names of the parts you need .you will be able to find the parts you need cheaper elswere but i do know the sensor and probe are stego parts and the electric bits will probebly be omron

[kru251]

All you didn't want but it's cheap and I use same for testing on the Lammie when I was working out cylinder head shrouds. Could you adapt that?

Multi Meter and thermocouple

[rab]

think the deep fat fryer may need a little too mutch voltage unless you like your hair stood on end .hold that thought now giggle hehehehe

[sbwnik]

I've so far drawn up about a dozen ways of doing this, and the simplest method requires a bi-metal strip somehow fastened to the cylinder head (Can't see anyway of doing a bi-metal ring), which triggers a light as soon as it's closed.

The hard bits are the variable switch and the mounting.... Everything else is just simple feed and light circuit. £130 is well outside what I was thinking! About £100 more than it


Slaving the indicator? I used the wires from the buzzer and rerouted them back up to the screen. Crap idea though tbh