Looking for feedback on my project idea

[matthew6]

Hi,

I'm new to electronics and alternative energy, but am eager to cut my teeth on a project.  I'm wondering if my fledgling idea is doable and worth pursuing, and if anyone can give me any pointers on how I may go about it if it is feasable.

I opened up my bathroom fixture recently because the fan sounded really clunky and I found that if I wanted to I could run a wire up out of the vent and onto the roof, and perhaps make a solar powered nightlight out of an old garden light by simply extending the cord down into the light fixture.  Then I thought, I wonder if i could not only have a solar-charged-battery-powered led, but also a small fan to replace my clunky one.  My 85 cfm bathroom fan is from the 80s I think, so I'm wondering if I can find a modern fan (say from a pc or something) which will move a similar amount of air, but draw less power.  I don't know much about sla batteries, but I saw some pretty small ones online, which would fit in the space of the clunky old fan, while I put a smaller fan (I think a pc fan might be just the right size) right at the opening to the shaft.  

My options for the solar panel are currently a 10 watt panel and a 2.2 watt panel which I recently purchased on ebay.  The way I would like for it to work is for the pan to operate continuously during daylight (assuming I can find one that's relatively quiet) and then have the battery soak up the extra charge and come on at night for at least a few hours (don't want to bother with a switch, as it's too high up).  I could either do the led nightlight as part of that system or just extend the garden light and have it operate independently.

Does anyone have any thoughts as to whether this is doable for a newbie, and what else I need, what specifications might work or where I might look to get rolling?

Thanks for your time!

[nothing to lose]

Sure it's doable, if you can do it

Best place for fans I found is bestbyte.net many fans list dBa (noise levels) Watts, amps, RPM, CFM, etc...

They have cheap good fans, expensive fancy fans, Leds fans, etc... in lots of sizes.

I buy all my fans there and most cold cathode lights, been awhile since I bought anything though, I stock up extra's to save on shipping and have them when I need them not 2 days later.

You may need a charge controller of some type since sun will vary and you don't want to drain the battery too low or over charge it too much, doing either will shorten the batteries life.

You could get fancy and put a light senor on the LEDS to only turn on when room is dark, wire a sensor for fan outside near panels to only turn on fan durring day.

Turning on the fan at night for just a few hours without a switch might be trickey. I think you can get a 12V pull chain switch many places, using one you can just use a chain or string any length and turn fan on/off as needed when suns not out, and ceiling height is no problem then and lots of wireing not needed. Just wire switch on an extra wire parralel to the light sensor circuit to bypass the sensor at night when you want to.

How much sun you get for charging and how long the fan runs will make the differnce on how many watts of solar panel you need.

 A 92mm fan I took a quick look at for $1.30, DF129225SH  12v 0.37amp 4.44watts      2900rpm    51.78CFM 29.24dBa

A 120mm fan for $7 may be a better value though, since it's a cheap part of your system that should last for years.

LED 120mm fan, 12V 0.38amps 4.56watts 2,000RPM 78CFM 28dBa

More money for larger fan up front, but for only 0.01amps/0.12watts more power used you move 27CFM more air with slightly less noise. Also this particular fan has built in LEDS in your choice of colors.

So check fans out and see what you need and the best value. Then figure your hours to run fan, solar hrs available, and see what you need for a panel in watts, adjust as needed.

You could also get a fancy variable speed temp controlled fan, the warmer the room the faster it runs, the cooler the room the slower it runs.

[ghurd]

Sounds fairly simple to me.

Not sure why you want a similar CFM as the original fan running constantly during daylight.

If you are asking about this, you are going to need a switch, or a lot more money.

This is what came to mind, without thinking it through.

The 10W solar panel (PV), fan, a PB137ACV charge controller, maybe a 7AH battery, LED nightlight, 2 switches, and a fuse on the battery.

G-

[asheets]

Harbor Freight has a solar powered shed light that could be modified, and I saw several different kinds of solar powered attic ventalators at Home Depot last time I was there.  Perhaps that's something to look into?

[ghurd]

The HF solar shed light is nice for what it was intended (I was quite surprised).  But it is 6V, uses AA nicds, and can only turn on after dark. It doesn't look very modifiable because everything except the PV is built into the small light housing, but I didn't take one apart.

G-

[matthew6]

Wow, thanks for the great feedback!  I'll probably be back soon with more questions, in the meantime, feel free to chime in if you have anything to add.

[Bruce S]

matthew6;

   In addition to Ghurd's idea, if you wanted to make it a little more automatic. Grab one of those lawn lights that has the extra photocell in them. Take it a part, run the photocell to the nite-lite and let lighting trun it on/off, you could even use the entire light as a seperate setup. 3" - 4" won't atke up that much more room on the roof.

Have Fun!

Bruce S

[AbyssUnderground]

My charge controller (available to see on my website) has a "load" output which you can configure to turn on and off at set voltages to stop the battery running down too much.

It has:

Cut-off voltage: eg 12.0v

Cut-in voltage: eg 12.8v

So it will cut out at 12.0v but won't cut back in again until it hits 12.8v, and again, cut off at 12.0v in an endless cycle. My controller was £40 ($80) but it also has float charging with a changable voltage too which will help to stop overcharging.

Just my 2p.

[matthew6]

Hi,

Ghurd (or whoever can answer).  I have a couple of questions:

1.  About the PB137acv:  How is this little thing different from the larger, more expensive charge controllers you buy elsewhere (e.g. http://store.sundancesolar.com/suchco.html)?  
   
2. I'm still learning, so what sort of fuse would I use in this setup?
   
   

Thanks!

-Matt

[ghurd]

Oh yes, the SG-4 is very near and dear to my heart.

Dandy piece of plastic.

PWM, temp compensated, rated at 4.5A, no pointless LEDs to waste power, etc.

I DO tell people to use them on a regular basis.

But it costs like $35~$50 by the time you get one.

Shipping is a killer!

The PB137ACV, on the other hand, has no temp comp, PWM, etc.

But it works. And it works well...

For 12V solar systems under 1A.

And systems not likely to be overly discharged.

When the PVs add up to less than 2A, get a couple PB137ACVs when you order parts.

They now cost ~$1 each.

When the money has been spent on 3 or 4A at 12V of PVs, buy a SG-4.

If the system is planed to be expanded, buy an SS-10 or SS-20.

(same stuff, bigger amps)

Thank goodness I bought a bunch of PB137ACVs before the price went down. :-(

G-

[matthew6]

Great.  Thanks for the info.  Two more newbie questions though:  I have blown the fuse in my el cheapo multimeter twice trying to test things with more than .2 amps.  How do you test higher amp DC stuff?  Maybe this depends on the multimeter, and I'm sure I'll figure it out, but if you have an easy answer, that would be nice.  The manual that came with the multimeter is not exactly an electronics course.

Also, the PB137acv will act to stop discharge to panel at night as well, right?

Thanks again.

-M