Kitchen Extractor Fan

[StuartO]

My Hymer has an extractor fan which works quite well but gets coated in cooking grease from time to time and is awkward to get at to clean and recently (after 15 years of service) showed signs of terminal decline. The motor/fan unit is a 12v thing which looks for all the world like a 90mm computer cooling fan but it isn’t, so my first attempts to replace it turned out to be far too feeble. Ordinary computer cooling fans appear to be identical but the thing to look for on their label is the current they draw or the power rating; computer fans draw only 0.1-0.5 amps whereas my original extractor fan unit was labelled as “2.8W” or about 4 amps, which is much more powerful.

 

I was however able to identify a source on EBay by searching on the maker and part number so. I now have a replacement ordered and on its way, albeit from China, arriving goodness knows when. It was priced at £17 (compared to £5 for a computer cooling fan) but I dare say it would have been far more expensive to buy as a Hymer part from Germany.

[John52]

StuartO - 2021-08-14 8:46 AM

 

“2.8W” or about 4 amps, which is much more powerful.

 

Watts (W) = Volts x Amps so 4 amps would be 12x4 = 48 Watts (W)

But where its positioned seems just as important

My roof fan is about 120 Watts, and only about half a metre away from being directly over the gas ring, but I can still smell the gas ring when its on (propane so its smellier than butane), so don't like using the gas ring without the side door open.

[Keithl]

I agree with John, you have divided your Volts and Watts the wrong way round!

 

2.8 Watts at 12 Volts will be a current draw of 0.23 Amps so mid range of your computer fans.

 

Keith.

[StuartO]

My Ohm’s Law calculations were clearly a bit wide of the mark but the idea of a clear distinction between low power (and low noise) computer cooling fans and more powerful extraction fans should still help others from making the mistakes I made buying the wrong ones if their wears out.

 

I got the current rating of EBay computer cooling fans wrong too; they are all 0.15 amps or less so extractor fans are twice or more as powerful - and twice as noisy too of course.

[John52]

StuartO - 2021-08-14 9:33 AM

 

My Ohm’s Law calculations were clearly a bit wide of the mark but the idea of a clear distinction between low power (and low noise) computer cooling fans and more powerful extraction fans should still help others from making the mistakes I made buying the wrong ones if their wears out.

 

I got the current rating of EBay computer cooling fans wrong too; they are all 0.15 amps or less so extractor fans are twice or more as powerful - and twice as noisy too of course.

Thats not Ohms Law, and the size of the fan blades probably affects the noise more than the power. So it could be twice the power with less noise.

[StuartO]

Sorry again; it’s a long time since I did Physics at school!

 

From what I’ve read (and not necessarily correctly understood) it seems to be primarily fan speed (of a fan of given diameter, in this case 90mm) which determines the volume of air moved by a fan, although the number of blades (i.e. blade area) will also have a role.

 

So for purposes of replacing a 12v extractor fan (and avoiding selecting a computer cooling fan by mistake) it will be the power rating on the label which matters, in my case 2.8w, rather than a fan labelled as 0.1 or so amps.