Solar powered fan

[AndyH]

Hi all,

Can anyone recommend a reasonably priced solar powered fan that I can buy in the UK which I can attach to me Stevensons screen?

Thank you!

[rich27gc]

I bought this one, seems OK

http://www.cpssolar.co.uk/epages/620630 ... LARVENT%22

Priced at £ 32.99. It depends what you call reasonable

[bruce45]

if your wanting cheap these have been used by others to vent there screens not sure how good but 2 for £16
http://www.amazon.co.uk/2-NEW-BASIC-EDU ... 25&sr=8-60

[AllyCat]

Hi Andy,

I believe that the person who tried that "educational" kit reported that the motor failed quite soon (I'm not surprised).

"Computer" fans are available in various sizes, very cheaply (a Pound or two) from ebay, etc.. Although usually rated for 12 volts they will normally run from below 5 volts and a "1 watt" panel may be sufficient to drive one. Panel prices are said to be falling fast, maybe a "target price" is now around £10.

Cheers, Alan.

[Charlie]

a "1 watt" panel may be sufficient to drive one.

Actually Alan, most computer fans require 2 Watts or more. Perhaps an older CPU fan or a video card fan might be lower. Fans also require quite a bit more power to start from a dead stop. Worse, the "1 Watt" panels are "up to 1 Watt". Like your internet speed, it will be rare to see one performing at the upper limit of it's spec. You need perfect weather conditions, the right mounting angle, and so on.

I actually tried this in a different application with 2 of those panels and could not make it work, even with a battery for storing charge, unless I limited fan use to a couple hours per day. In the end, something more like 5 Watts of solar was required, and batteries for storing energy, and sensors to time on / off to prevent damaging the battery. It was far more complicated than I had hoped, just to get the fan running when the sun was shining.

[AllyCat]

Hi Charlie,

Yes, I tend to agree, but my comments were in the context of the recommendations earlier in the thread. The "Educational" cell is rated at 400mA and I suspect that it delivers only just over a volt, and then probably only with peak Summer sunshine. The fan in the previous post appears to have a cell about 10 x 5 cms which is unlikely to produce more than a watt (there are a number of PV cells of various sizes with probably reasonable quality on the same site).

Certainly an 8 or 12 cm computer fan at rated voltage is likely to require several watts but in my experience the smaller "12 volt" ones will run below 5v at well under a watt. Again, I believe the context of this thread is just to reduce the heat build up in temperature sensors when the sun is beating down on them (and the fan is not expected to operate at other times).

I do have plans to experiment with solar aspiration at some time, but I suspect that the greatest improvement will be simply the shading produced by putting the PV cell between the sun and the sensor.

Cheers, Alan.

[AndyH]

Thank you for the input - appreciated.

The 'caravan' one looks quite expensive and by looking at it the solar panel and the fan are all one unit. I think I am really after a separate panel and fan so that I can mount the panel on the top of the stevensons screen and the fan inside.

Yes, I had read that the motor was failing on the educational ones so not sure I want to go down this road at the moment.

I will keep looking around to see what I can find but if anyone else has some experience then their knowledge would be great.

Thanks again.

Andy.

[Charlie]

in my experience the smaller "12 volt" ones will run below 5v at well under a watt.

I'm glad this worked for you, but were you using a solar panel or a bench supply? I'm simply reporting empirical data. My 12V computer fans won't even turn using 2 of my 12V 1W panels.

[mcrossley]

Are they the older 12V DC voltage controlled fans (2/3 pins: gnd, +12V, sense [optional]), or the newer 12V DC PWM controlled fans (4 pins: gnd, +12V, sense, PWM signal). The latter I think need a minimum voltage to power the internal electronics. Do yours spin if you give them a hand starting?

[AllyCat]

Hi,

These are the type of fan I've been playing with, two 40mm fans with just two wires and an electronic commutator for just over a Pound. However, the (generic) specification is rather pessimistic, they actually consume about 100mA each from 12 volts. There is little difference between the start and stop voltages (about 4 volts), probably because their inertia and friction are small compared with the detenting produced by the magnetic field. They seem to run comfortably from 5 volts, consuming 50mA (250mW) each, but obviously the air flow is not great at this power.

Personally, I don't plan to just connect the fan(s) directly to a solar panel. My (partly tested) system will charge a capacitor of about 10,000uF from the PV cell until a threshold of typically 10 volts is reached and then "fire" the fan with a circuit like a Schmitt Trigger. With reasonable illumination the fan should then keep running, but the driver electronics will cut the supply before the motor stops, to ensure that it doesn't drain all the available power without turning.

But I must add that I don't have any great confidence in the viability of simple solar aspiration. There may be a need for aspiration when there is no sun (or even daylight), and IMHO the amount of energy available from (small) solar panels is over-rated. Also, my (un-related) attempts to transfer low grade heat using (mains-powered) fans (e.g. from a hot conservatory to an adjacent room) have been disappointing. It seems necessary to move a large volume of air for effective heating/cooling when the temperature difference is relatively small.

Cheers, Alan.

[Solorize]

Andy,

I bought the same solar fan as per the link in Richards post and
have been very happy with how it performs. I decided to spend
the £30ish pounds on a fan that I knew would work rather than
buy something cheaper and have it fail or not do the job 100%.

If you visit the thread below you can see some images of how I
have attached the fan to the radiation shield.

https://cumulus.hosiene.co.uk/viewtopic.p ... 3&start=20


Hope this helps.

Mark

[darc]

I am going to build a S/screen I never thought of putting a fan into the build I don't want to sound silly but I am new to this
what is the idea with useing a fan

[Solorize]

Hi Darc ,

The use of a fan is to draw air through the screen so that hot air does not build up within the screen.
Doing this with a solar fan is good as when the sun is on the screen and fan it starts the fan to aspirate the air.

[darc]

Thanks for that piece off info would never of thought of that I have a solar panel here that should do the job with a pc fan as it throws out upto 3 volts so shoud work finger crossed.

Geoff