Switch ID

[Roger Mills]

That probably IS a thermocouple, and is part of the flame failure protection apparatus. There's a junction of two different metals inside the bulb, which generate a voltage when the bulb gets hot. The capillary tube contains two wires (or maybe only one if the tube itself is one of the conductors), and the remote end from the bulb is an electrical connector which connects to a coil with many hundreds of turns inside the gas valve. This holds the pilot valve open once it's opened manually via an over-ride button, and as long as the thermocouple is heated by the pilot flame. If the pilot goes out, it cuts off the gas.

This is not to be confused with a boiler thermostat - which has a bulb filled with a liquid which expands when it get hot - with a bellows-operated switch at the other end of the capillary tube.

Whatever it is that switches the OP's Kenlowe fan will be much more like a boiler thermostat than like a boiler thermocouple.

[The Other Mike]

The fan circuit could quite easily be fused at 50A with just a single fan of around 12" diameter but that fan will not have a current draw remotely close to that and in any case the fuses are there to protect the wiring not the fan. The actual current draw will in practice be much closer to 10A.

For instance two Kenlowe manufactured fans measuring around 17" diameter, shifting over 8000 cubic metres per hour draw only 48A combined.

[Harry Bloomfield]

dennis@home used his keyboard to write :

Sorry, but you are wrong....

The fuse supplying just my cooling fan is a 50amp. It is of a type with

6mm holes, drilled in it, and bolted to busbars in the main fusebox adjacent to the battery, one of several such fuses. The series resistor for the half speed function, is rated 100w. The original resistor was rated 70w and had a propensity to regularly burn out, so I replaced that with a 100w version when it did.

It needs to be rated 50amp, to survive the starting load. Any relay switching the load will be switching a similar high current, so needs to be suitably rated and rated for DC.

The run current will be very much less, but the fuse and relay need to accommodate the initial heavy starting load.

[Muddymike]

Enough!

The switch itself is dead, I have tested it, probably due to the amount of crap its had thrown at it over the past 15 years. Forget the terminology just tell me if you recognise the switch itself. If you don't stop wasting my time.

Once upon a time this newsgroup was populated with folk who would offer helpful or humorous comment. Now there are too many nit pickers who offer nothing helpful!

Mike

[Muddymike]

Thank you. Something helpful at last. Mike

[Muddymike]

I agree, maybe not 50a but it does need a 40a fuse. I believe the controller was designed for a lower amperage fan so I will certainly be incorporating a relay in the circuit of the replacement. I'm surprised it lasted as long as it has.

Rather than adapting an alternative switch if a direct replacement doesn't come to light I will be replacing the whole controller.

Mike

[The Natural Philosopher]

sounds about right to me

so you need a 50A microswitch

Unfortunately they seem to stop at 26A. Perhaps that why this one has burnt out?

I have to say these days Id probably look for a better way to do it than a wax capsule and a microswitch.

Some form of thermistor and a bit of electronics driving a fat power transistor or power FET would be my choice

[Graham.]

The picture is a thermocouple, and the linkage is not a capillary tube dispite its apperence.

It's a concentric electrical cable, like miniture Pyro.

[Roger Mills]

By its very nature, usenet often results in discussions which deviate from the original topic.

I admit that my contribution didn't help you to find your switch. But a considerable amount of discussion in this NG is about heating systems and boilers. Providing a bit of basic education about boiler thermocouples and boiler thermostats just might have been useful to someone - so I make no apology for it.

[Dave Plowman (News)]

How are the latest ones controlled? The actual fan motor is unlikely to change that much - but the control gear may well.

If I were doing it I'd use PWM control - so the fan isn't only ever off or on at maximum noise.

[Dave Plowman (News)]

50 amps at 12v is nearly one horsepower. 10 amps or so is more common. If you really need a powerful fan makes more sense to have a directly driven mechanical one, with a viscous coupling.

[Dave Plowman (News)]

Vehicle Wiring Products do a switch kit for theirs:-

[Muddymike]

Something like that is what I will have to buy if I cant replace the switch alone.

Mike

[Harry Bloomfield]

Dave Plowman (News) brought next idea :

As already pointed out, that is the starting current - the system needs to be able to to cope with the starting current. Once running, likely that demand will drop to 1/2 or even 1/3.

Mechanically driven fans, even with viscous couplings were a very inefficient means to provide cooling. My electric fan is much more efficient, much bigger and only consumes power when extra cooling is needed.

[Dave Plowman (News)]

Very odd then that so many modern cars still use them. What you have to remember is under most conditions, a powerful fan is only needed at very slow road speeds. On the move, the natural airflow takes over. And that also reduces any drag from a mechanical fan to near zero. After all, the drive belt still has to run the water pump and alternator, etc.

Many modern cars only have an electric fan to keep the AC condenser cool - again at very low speeds. And when running AC, any fan losses are a drop in the ocean.

[dennis]

You do know that there is no load on the fan when it is starting so you need little power to start it. You need a lot more power once it is getting up to speed.

[Harry Bloomfield]

I don't buy the economy cars, but even so I have not come across a mechanically driven fan in a car for decades.

You hit the nail on the head with most cooling is required when the engine / car is barely moving - which is where an electric fan scores.

[Harry Bloomfield]

dennis@home expressed precisely :

Yes, which is where the 'viscous' comes in to play. I have also had mechanical fans, which have a thermally triggered clutch, even one mechanical fan which rather oddly used an electric clutch.

So far as the mechanical fans not sapping engine power and fuel, they do take some energy, maybe 1/2 Kw. Which was why Kenlowe fan conversions were so popular in the 1960's and 70's.

[Harry Bloomfield]

It happens that Dave Plowman (News) formulated :

My engine ECU has a head temperature sensor, from that it determines whether the fan is needed at all, whether half speed is enough, or to put full speed on. There is a second input to the ECU from the a/c, for its cooling requirements.

Full speed is only rarely needed, luckily - because it sounds like a Vulcan cranking up for take-off.

[Harry Bloomfield]

Dave Plowman (News) explained on 11/04/2017 :

My climate systems fan uses a PWM system, for the heating/a/c. Rather cleverly it holds the fan off in winter, until the heater matrix has some heat to dispense as the engine warms up.