An aspirated screen for the WH1080

[beteljuice]

You've not had the weather to check it yet repairman, probably have to wait until the next global warning scare

Having got a 'muffin' fan (40mm x 40mm) in the huge amount of debris on my table, I got to thinking sideways.

They seem to vary between 0.07A => 0.16A, start up 7.0V, prefered running 10.8 => 11.5V

It occured to me perhaps everyone is too keen on the DIY !

As long as the sensor is in a rain proof, solar proof, freely vented enclosure - then with a few extra holes, this small fan could be mounted directly onto the thermo-hygo unit and provide more than adequate airflow.

This unit (say one of the 0.08A) could be powered by one of the many cheap enclosed Solar Panels you see advertised for cars, caravans etc. but would give no spare capacity for charging batteries.

A larger / better quality panel (say 2W or even 5W) would allow for charging 8 x 1.2 batteries (say 1000 mAh) - but as you correctly point out it is unlikely to give 24/7 operation in winter months, but I don't see that being a problem.

Talking of problems, the height of your sensor - how much of an offset are you having to apply to imititate 1.5(ish) metres ?

[Repairman77]

Thanks for your comments; I suppose there are no end of configurations that could work in aspirating the sensor unit.
I guess I went for one of the common designs that was also cheap to build.

With regard to the solar panels for cars, caravans, etc. Mine arrived yesterday and I did some tests on it. It has some charging circuits inside (not a direct connection to the panel elements) and gives out a charging pulse rather than direct DC, so it won't run any kind of motor direct.You would have to run the motor (fan) from a battery and use the solar panel to charge it, unless you wanted to dismantle the panel and rewire it. However it only gives out a useful current in sunlight so it's unlikely to suffice in our poor climate; would perhaps work in a desert climate. My small muffin fan runs with no problems on 9V at 100ma and gives a good airflow at that.

I am supplying the motor from a transformer supply in future; when it stops raining and I can get onto the roof. The readings certainly show an improvement but to early to quote any figures yet.

I haven't gone into the subject of the correct height of sensors yet. That could be a bit of a problem as they all appear to want to be at different heights which is a bit impractical unless you want long extension leads trailing everywhere.

My main reason for a WX station was wind direction and speed so above the roof (around 10 metres) in the clear is obviously the best place for that sensor

Mike.

[beteljuice]

has some charging circuits inside (not a direct connection to the panel elements) and gives out a charging pulse rather than direct DC, so it won't run any kind of motor direct.

I hadn't realised that - one for people to watch outfor !!

I thought the kit came with a long cable so you could have your anemometer high and everything else low ?

[Repairman77]

has some charging circuits inside (not a direct connection to the panel elements) and gives out a charging pulse rather than direct DC, so it won't run any kind of motor direct.

I hadn't realised that - one for people to watch out for !!

I thought the kit came with a long cable so you could have your anemometer high and everything else low ?

No, mine came with the two cables, about 3ft long (from memory) to connect the rain and wind sensors to the transmitter unit.
I could get some long extension cables but I don't think it's worth it at the moment.
What is the problem with the temperature and humidity probes being at 10 metres? Can it make so much difference?

The solar panel gives out a pulse (as shown on the oscilloscope) every 500ms; the pulse dies away in a triangular form over the next 500ms and then there is a break of 500ms until the next pulse. The whole cycle taking 1 second.
It appears to be sealed so that it is water repellent so I don't want to break it apart.
I rather think the circuit is designed to charge a capacitor from the panel and then discharge it as a pulse in order to trickle charge a battery. This would mean that the solar panel itself would not have to produce a continuous 1.7W at 17.5V. Just conjecture, but a good guess I think.
Batteries actually like a pulse or a little AC on the charge as it seems to wake them up.

By the way the fan is being run from a transformer in the garage/workshop now; I managed to get a little break in the rain long enough to get on the roof.

Mike.

[Repairman77]

Update on the Car Battery Trickle Charge Solar Panel for anyone thinking of using one to power a fan...

I had a quick look to see if it would come apart and indeed it did, just some plastic bungs covering the screws.

There's no charging circuit inside, just a flashing LED connected to the output of the panel via a resistor.
The strange readings I was getting on the scope, as mentioned above, were apparently due to the LED grabbing most of the current in bright light rather than Sunlight. A slight improvement to the output could be achieved by disconnecting the LED.

I've measured the output open circuit voltage as around 22V DC in Winter Sun conditions, and the maximum current when charging a 12V battery of around 55mA; hardly enough to power a fan of the CPU Muffin type. My fan takes around 100ma with a 9V regulated supply (more at 12V direct obviously).

It would be possible to power the fans from a Solar Panel if you wanted it to run only during the day, and only when the Sun was shining but you would probably need a bare minimum of a 8 watt panel, preferably a 10 watt plus one to be sure of reliable operation. I know some of the more expensive set ups use panels in this way.

Mike.

[akasonny]

Mike,
I run a 5 watt/12v panel just fine with a 10CFM 12v muffin fan and it works just fine. I keep a 12CFM an on-hand as a backup should failure occur but, thus far, everything has benn ok.

I picked the panel up on ebay new for around $30 and the fan for $12. I don't run a battery so it shuts off at night but I have a regulator and battery available should I decided to change my mind on that one. Frankly, at this point, I think my air-flow is good enough at night to negate the need for it. The time-plot of declining, post-sunset temperature seems quite normal to me and it follows closely with the NOAA station data 12 miles away.

Actually quite the fun project when I look back on it.

Update on the Car Battery Trickle Charge Solar Panel for anyone thinking of using one to power a fan...

I had a quick look to see if it would come apart and indeed it did, just some plastic bungs covering the screws.

There's no charging circuit inside, just a flashing LED connected to the output of the panel via a resistor.
The strange readings I was getting on the scope, as mentioned above, were apparently due to the LED grabbing most of the current in bright light rather than Sunlight. A slight improvement to the output could be achieved by disconnecting the LED.

I've measured the output open circuit voltage as around 22V DC in Winter Sun conditions, and the maximum current when charging a 12V battery of around 55mA; hardly enough to power a fan of the CPU Muffin type. My fan takes around 100ma with a 9V regulated supply (more at 12V direct obviously).

It would be possible to power the fans from a Solar Panel if you wanted it to run only during the day, and only when the Sun was shining but you would probably need a bare minimum of a 8 watt panel, preferably a 10 watt plus one to be sure of reliable operation. I know some of the more expensive set ups use panels in this way.

Mike.

[Repairman77]

Hi sonny,

The only difference is our locations; you get one hell of a lot more Sun than we do LOL.
It's pretty weak in the UK in Winter and I think we may have a job running a fan on a 5W Solar Panel here.

Mike.

[akasonny]

Mike,
Thats very true. I've learned alot about solar panels (Arizona is a big solar equipt. manufacturing state for obvious reasons). I'm sure those who reside in more northerly latitudes, more cloudy areas and/or those who reside near mountains or other obstacles that shorten the length of daily direct sunlight, are at a disadvantage.

I rather believe, tho, that the current consumption of the fan is more of a key to success or failure. Some 10CFM fans draw more current than others. On the few cloudy days we get in the winter, my 5-watt panel may struggle but does pretty well. I credit the fan on that.

And I couldn't locate, anywhere, just HOW MUCH aspiration is enough. It seems to depend on the design of the temp sensor, the manner in which its encased in plastic, natural ventilation and etc. Though there probably isn't' such a thing as TOO MUCH aspiration, we deal with TOO LITTLE.

For all I know, 5cfm my be adequate to keep the sensor in-line...depending on where one lives. In that case 250mw/3 watt panel may be adequate. I went with 10cfm and knowing that works in this climate, its conceivable that less is required in temperate climates.

Anybody out there with the test equipment and know-how to run this experiment for us?

So many variables.

Hi sonny,

The only difference is our locations; you get one hell of a lot more Sun than we do LOL.
It's pretty weak in the UK in Winter and I think we may have a job running a fan on a 5W Solar Panel here.

Mike.

[Repairman77]

Sonny,

I guess any amount of aspiration within reason will do as it's mainly to stop the sun warming up the sensors (especially the temperature sensor) and throwing them out of calibration. Of course it helps by giving the Humidity sensor a constant supply of air too.

I doubt it would make much different to the readings even if you had a hurricane passing the sensor box.

Mike.

[dc1500]

These problems have been documented in earlier threads as well with various solutions. Personally, I have found the internationally recognised standard solution of a Stevenson's screen to be the best. It can be made for a few pounds and can be solar aspirated. Seems to work well and if possible to site correctly will of course give a standard temperature measurement which includes an element of solar heating.
http://www.laindonweather.co.uk/images2/Thumbnails.html

[Repairman77]

These problems have been documented in earlier threads as well with various solutions. Personally, I have found the internationally recognised standard solution of a Stevenson's screen to be the best. It can be made for a few pounds and can be solar aspirated. Seems to work well and if possible to site correctly will of course give a standard temperature measurement which includes an element of solar heating.
http://www.laindonweather.co.uk/images2/Thumbnails.html

DC1500,
I've been using a standard home made Stevenson screen for a decade or two with my Thermo/hydrograph and thermometers but it wasn't aspirated. I was trying to make life a little easier with the automated system but I don't find it quite as accurate.
But with some mods I do feel that I'm getting there.
Mike.