Making a solar powered ventilation fan

[Kelpie]

Last time I visited the boat I was a bit disappointed by how damp she is inside. Clearly need some more ventilation.
I looked up the price of the neat solar powered fans from swindleries... seems quite a bit of money for what it is, really. Especially given I already have a 10w panel on the coachroof, doing not a lot (well, it is currently trickle-charging the house battery, but I could just take that battery home and charge it properly). I also have, somewhere, a selection of 12v fans from defunct PCs.

Could the answer to my problem be as simple as to wire the solar panel directly to a fan, and position this underneath a vent? Or are there electrickery reasons which will stop this from working?

Assuming the electrical side of it is doable, how best to arrange the ventilation? I have a fairly big cowled vent in the washboard, so I'm thinking of having that be the air inlet, and something like the hole for the mast could be arranged as the outlet- so the fan would blow rather than suck. Obviously a cover would be needed to stop rain driving right onto the fan.

 

[Even Chance]

Good stuff. Im onto the same idea. I got some new brushless DC fans home from RS, and now need a small solar panel to feed one of them. I have a 40W panel on the coachroof that charges my battery cos I dont have an inboard of charge regulator for the outboard, but I want a smaller seperate one for the fan. I was going to mount the fan to the coachroof under a stock vent, and another stock vent in the forrard end somewhere. I now also need to know whether to suck in or blow out from the fan. Cant beat the Northerners for tightness eh?! lol

 

[lw395]

If you can lock the forehatch ajar, and fit a windscoop of some sort over it, that can work really well, giving through draught to the louvres in the washboards and the aft cabin vent.

 

[alahol2]

May be worth putting a small 12v battery in parallel to keep it going all night...

 

[tinkicker0]

I have a 40W solar panel connected to my house batteries and two 80mm ballbearing PC cooling fans behind a vent louvre with switches. Have left them on for weeks without any problems, the batteries are always at full charge.

PC fans use very little current yet shift vast amounts of air over 24 hours, seem to remember 40CFM per fan on the spec sheet.

 

[Kelpie]

If I put a battery in the loop, does that not mean I will need some way to cut off the fan so that the battery doesn't get killed by being flattened?
Really would prefer to keep this simple if possible. I presume a direct connection between the fan and the solar cell risks the fan being overloaded and blown... which, given I have a pile of them doing nothing, is an acceptable risk. So long as there is no chance of damage to the solar panel, or indeed causing a fire, etc.

 

[William_H]

Solar panel driving a fan

yes obviously a good idea. A battery risks being flattened if you have a lot of bad weather. Lead acid battery would die. You would need an under voltage disconnect relay which is not too complicated to make but adds to complexity.
Without a battery you need to match the solar panel carefully to the fan. So a 12 v fan drawing 250ma is 3 watts so roughly needs a 3 watt panel. Unfortunately a 3 watt panel only delivers 3watts under ideal conditions. But if you went for a 10w panel you would end up with 20volts on the fan drawing perhaps 400milliamps. (of course the 20v would come down at 400ma) but the point is you could cook the fan.
With a 3w panel at anything but full power (sun) the fan would lose eficiency as high (correct) speed is essential for lots of air movement.
If you had a solar panel regulator then that could allow you to run a smaller fan on bigger solar panel.
Another answer might be to use a regulator like 7812 to limit the solar panel out put voltage to 12v but hopefully would provide 12v at a wider range of sunlight conditions. Or you could just fit a series resistor of around 20 ohms might stop the fan overheating but allow some operation with low sun.

What you really need to do is to experiment before you fit and leave it on the boat. get a bigger panel then limit the pow3er to the fan or even fit 2 fans. good luck olewill

 

[Kelpie]

Well, the solar panel size is fixed- it's 10w. Mind you, it's mounted flat on the coachroof, so given that this is winter at 58*N, I don't think the power output is going to be particularly impressive!

If I was feeling clever, could I work out the angle of incidence and do a bit of trig to see what the panel will really produce? Or does it not work that way?

 

[Wunja]

I have had this set up for a couple of years.

An advantage of not having a battery is that the fan will only run when there is reasonable light. This will also be when the ambient humidity is low so you don't suck damp air into the boat.

In terms of location, I have the fan under the foredeck vent, the forecabin being particularly airless. There are plenty of places in the back of the boat where air can get in, so this gives a flow of air through the cabins.

It works well.

<edit> Fit a grill of some sort over the fan. It really makes a mess of your knuckles and is less efficient with the resulting loss of blades.

 

[lw395]

I have had this set up for a couple of years.

An advantage of not having a battery is that the fan will only run when there is reasonable light. This will also be when the ambient humidity is low so you don't suck damp air into the boat.

I.....

The relative humidity may be lowest when the sun is shining, but the absolute humidity may be higher....