Replacement Manrose QF100T Bathroom Extractor Fan Wiring Query Ask questions and find answers to many subjects relating to electrics and electrical work

[londonhutch]

Hi. I hope you can help. It's my first post.

My existing bathroom extractor fan has broken. It was a timed fan which came on with the bathroom lights. When the lights are turned off, its runs for approximately 5 minutes. There is a manual fan cut-off outside the bathroom.

I have purchased a replacement Manrose QF100T "Quiet" Extractor Fan with Timer.

When I took the fan down, I found three wires - Blue, Brown and Yellow/Green. Only two were connected - Blue and Brown (see attached image).

My new fan requires three wires - Neutral, Switched Live and Permanent Live. Can you advise me which colour wire connects to which of these?

If the fan is not suitable (I can return it), can you suggest one that is?

Many thanks in advance.

[proptech]

Hi londonhutch

A fan with timer does require live, switch live, and neutral, plus an earth in some cases. The question is: how on earth did the old fan work ? on that wiring, it just isn't possible to have a timer, unless the green/yellow has been incorrectly used.
I do hope that whatever you do those connections are going to get tidied up!

[ericmark]

For the fan to run on for 5 minutes the timer will need at least 3 wires. So it would seem in your case the timer is not in the fan. Clearly you need to find the timer as it may be the timer not the fan at fault.

You could as a test fit something like a standard lamp and see if that works with run on.

With most fans bridging the switched line and permanent line will allow them to be used two wire without over run.

[londonhutch]

Thanks for the help so far.

I've just looked at the old fan, and this is what it was:

Micromark MM30090 4" Low Voltage Extractor Fan with Timer in White
Extraction rate: 80mÆ per hour
Integral adjustable timer (allows the fan to run up to 25 mins after being switched off)
IP57
Remote transformer supplied
IP44
Dimensions: (HWD) 165 x 165 x 34mm

Does the fact that it has a "Remote transformer" solve the question of the missing wires? Is there a like for like I could buy to replace the old fan, without having to root around in the ceiling?

[ericmark]

Well it may explain where the timer is but the description seems very odd.

Micromark MM30090 4" Low Voltage Extractor Fan with Timer in White
(Low voltage = 50 ~ 1000 volts AC so one would expect it was 230 volt)
Extraction rate: 80mÆ per hour
Integral adjustable timer (allows the fan to run up to 25 mins after being switched off)
(Integral means built in so everything together)
IP57
Remote transformer supplied
(Remote means not built in so in another location)
IP44
Dimensions: (HWD) 165 x 165 x 34mm

So reading between the lines it would seem you have a voltage dropper with some adjustment for run on time hidden some where. The question is of course which bit has failed and that's not easy to work out with a switched mode power supply.

Clearly the description is not accurate and rather than a simple transformer it is common to use a device with some regulation which turns AC to DC then back to high frequency AC then transforms down to required voltage then samples the output voltage to alter the mark/space ratio of the DC to AC electronics to correct the voltage. You can now forget what you have read the important thing is it has both a minimum and maximum output. When the output drops below the minimum the device shuts down so if the fan has failed any multi meter will likely read zero volts and if the voltage dropper has failed it will also likely read zero volts. This makes it hard to test to find out which has failed.

I would assume 12 volt as maximum voltage permitted in some areas of a bathroom but could be AC or DC. Either way likely extra low voltage not low voltage. (Extra low voltage = 0 - 50 volt AC)

Two things are likely to go wrong with the fan. One the bearing fail or brushes fail in fan often taking the winding with them. Or the capacitors fail in the power supply they have a limited life. So it is really 50/50 fan or power supply.

So sorry likely you will need to find it.