Intermotor 50091 testing

[ThreeSheds]

Hi,

I am currently fitting twin electric fans to my RRC and have bought an Intermotor 50091 switch to control them (per standard advice on this forum).

I had a few minutes to fill last night and so I thought I would test it before fitting - and I have found that it does not do a clean switch from open to closed circuit like I expected, but a shows an unstable decreasing resistance with increasing temperature, like I would expect a (poor quality) sender to do.

I can't believe this is right, but just thought I would check before taking it back for a replacement...

Test Detail:

I am testing with a multimeter with one probe connected to the 'top' contact and alternately checking the side contacts with the other probe.

I first tried placing the unit in a cup of near boiling water, but both switched contacts stayed open circuit - even after refreshing the water from a boiling kettle.

Next I tried resting the unit in the spout of the boiling kettle - this is when first one and then the other contact started to show a resistance rather than infinity, whereupon continuing with the boiling brought one down to a few hundred ohms and the other to a couple of k-ohms. Both readings were very unstable.

Cheers,

Roger

[Quagmire]

I know they are supposed to work reliably- and i can't comment on how things should look when tested on a multimeter... but i dont think they are that accurate temp wise.

All I know is that mine switches on when using the upper range at around 86 degrees, and then off at 82. The lower range on mine is unusable as it basically runs the fan continuously. I might have got a monday morning/friday afternoon one though.

They use bi-metallic strips dont they? (Could be wrong though) I would have thought that would cause the lack of a clean switch point, as they contact slowly compared to a normal switch.

[ThreeSheds]

They use bi-metallic strips dont they? (Could be wrong though) I would have thought that would cause the lack of a clean switch point, as they contact slowly compared to a normal switch.

Thanks for the reply - not sure what's inside these, but bi-metallic strips switches I have seen in the past are over-centre types which go click...

I have decided that I'm going to get a new one this pm anyway so I will try that and report back.

[MECCANO]

I think its actually a spring with a contact on the end, same sort of principle though.

I played around with mine like you have, and found a similar thing with the triggering. Once installed to the vehicle though it worked perfectly.

[ThreeSheds]

Just got home with the replacement switch - did the same test in the kettle spout and this one went from open to closed circuit (less than one ohm) on both as soon as the steam hit it. On checking while it cooled there were two audible clicks about ten seconds apart as each contact opened again.

I'm happy now

[fozsug]

That must be what mines doing, as when i wired it up as per X engineering diagram with voltage in at top pin ,got only 1,2volts out of low pin and 1.6 volts out of high pin. must be a dogy one, as when connected directly fans work. Trip down the shops needed to get another one.