Hot inline fan

[m0t]

Our bathroom fan failed this morning and I purchased a replacement unit manufactured by Manrose on the way home.

I fitted the fan and came back about 20 minutes later to tidy up and noticed that the box the electronics are housed in was hot and smelt burnt.

I turned the power off and took the lid off expecting to see a loose wire but the heat is being generated by a resistor. I know resistors generate some heat but this was too hot to touch. It's this sort of thing normal for these fans?

 

[flyingsparks]

Sounds like a faulty 'box'. Is it by any chance an extra low voltage fan, with a separate timer and transformer which is causing the problem?

 

[m0t]

Its a standard 240v unit - this one http://www.amazon.co.uk/gp/product/B005F41YOM/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

 

[JohnW2]

Sounds like a faulty 'box'. Is it by any chance an extra low voltage fan, with a separate timer and transformer which is causing the problem?

It's apparently a 240V one. IME (on the basis of many fan timer autopsies!), the series resistor of the 'power supply' (usually a ~22kΩ resistor, diode, zener diode and electrolytic capacitor!) of the timer units of Manrose (and many other) fans is by fair the most common component to fail. They clearly run pretty hot at the best of times, but what the OP is describing sounds a bit OTT. I've never known one to fail very early (it usually takes a year or three), but nothing's impossible.

Kind Regards, John

 

[m0t]

Its the 22k resistor that is getting hot. Just checked it again after tightening everything up and I would now describe the box as warm rather than hot (the circuit board was not seated properly).

I find it a bit odd that it got so warm when off though (the fan does work properly though). Presumably its wasting electricity at the moment?

 

[JohnW2]

Its the 22k resistor that is getting hot. Just checked it again after tightening everything up and I would now describe the box as warm rather than hot (the circuit board was not seated properly).

They always get pretty warm, because they are dissipating something like 1W or so (current flows only during half cycles)

I find it a bit odd that it got so warm when off though (the fan does work properly though). Presumably its wasting electricity at the moment?

Since it's powered from the permanent live feed, there is always essentially the same current through that resistor, 24/7 - that's why they get and stay hot (and fail!). As you say, it is a 'waste', of around 1W.

Kind Regards, John

 

[m0t]

Sounds like it is fairly normal then, just not particularly desirable.

The other fan failed this morning causing all the lights to trip, when I disconnected it the electronics were all scorched. I am just a little nervous that something more serious could happen.