Switch ID

Muddymike wrote in news: snipped-for-privacy@brightview.co.uk:

It looks like a micro switch - I guess it is part of an assembly that has something that expands when hot that presses the plunger.

That's the sort of thing but the one I need is larger at 50mm long. I've already been right through the RS catalogue of micro switches.

Mike

Does it have to be the same size, or would a smaller one mounted on/in a suitable block of something do the trick if the button could be positioned in the right place?

Muddymike wrote in news:h5CdnW4gfq snipped-for-privacy@brightview.co.uk:

I wonder if someone can suggest an electronic version - sensor and electronic switch - or are you a restorer who likes things to be as original. What is the temperature that it needs to switch on at?

I cannot see why a kenlowe fan meeds a microswitch.

Where in the system does it go?

The dead one is adjustable.

Mike

Possibly, if lower rated It could feed the fan via a relay.

Mike

This is an older series of microswitch compared to the modern ones that will be in the catalogues such as RS.

Study the catalogues from makers like Burgess, Honeywell etc for the right case size (there is one at 49.x mm long BA or BZ series comes to mind from the depths!) and then the match plunger style and travel that you need to get a part number, then search for a stockist.

It might be cheaper to buy a smaller series one and being slimmer too which will give enough room for an adaptor mounting plate to put the plunger in the right place using the old mounting holes. Make sure the contact current rating is man enough for lots of amps at 12v DC

It goes under a plunger operated by a thermocouple. Water gets hot, thermocouple expands, presses adjustable plunger, depresses micro-switch, supplies power to fan, fan spins, cools water, thermocouple contracts...

Mike

Muddymike wrote in news: _Y2dnQWhZ snipped-for-privacy@brightview.co.uk:

I presume you have tested the switch and proven that it has failed as I would expect the most likely failute would be in the capiliary tube arrangement that pushes the plunger. (not a thermpcouple) Does the switch still click when you manually press it?

Thermocouples don't expand and contract with temperature - they simply provide a temperature dependent voltage output. More likely that what you have is a wax capsule or somesuch.

Bob Minchin formulated the question :

Typical current for a 12v cooling fan is 50amp, unlikely that would be powered directly from a microswitch. There will already be a relay in place.

I've always called this type of thing a Thermocouple no electricity involved. Change temperature of the probe at one end and the dohicky at the other end moves. What do you cal it?

Mike

Muddymike wrote in news:S snipped-for-privacy@brightview.co.uk:

The photo is indeed a Thermocouple. However that is not what you have to operate the switch - you will have a Capillary Tube that actuated a bellow that operates the swithch and is likely to be broken.

Muddymike wrote in news:S snipped-for-privacy@brightview.co.uk:

See the Bulb and Capillary sensor on this site:

Basically the fluid in the bulb expands and this pushes a piston at the other end which operates a microswitch.

Have you tested the switch yet?

I doubt its 50A, they don't usually have fuses that big.

Admittedly that photo is on many sites advertised as a "boiler thermocouple", but it isn't. "Couple" implies "Two" different metals. I call it a capillary-tube temperature sensor. You would be all right to call it a thermostat, because it keeps the temperature constant, but not a thermocouple.