Fan circuitry

[Yonner]

Is there anyone on here who is keen on electronics who wouldn't mind offering advice?
I'd like to set up a circuit to run a fan in a vent pipe, powered by a pv panel and a leisure battery, with the pv panel running it in the day and the battery taking over at night. I can't figure out the calculations around pv size from the info I can find on line, and would like to know how the pv panel runs the fan, rather than just charging the battery - or is that too simplistic a view?

Anyway, and help appreciated.

[RobertArthur]

@Yonner :
1/ 230 V ac fan or 12 V dc?
2/ Large/small bathroom or kitchen?
3/ 24/7?

[Yonner]

Thx for the reply RA.

Its a 12v dc fan,
its to fit inside a 80mm fosse vent pipe ( fan is approx 60mm square, computer style)
24/7.

[RobertArthur]

@ Yonner, keep it simple, stupid and low cost. One solar panel ----->DC voltage/current regulator----->12 Volt battery---->load. In front of me an old regulator as used 30 years ago in a shed in the garden. They look quite simple, but are clever: as soon as there is no sunshine they have to prevent discharging of the battery through the panels. About batteries: the normal car lead/acid batteries don't like to be discharged below 50% of their capacity, so this can be a problem in wintertime. The special solar batteries however are not cheap. So it might be an idea to begin with an old (starter) battery of a car. Capacity: let's take an old diesel battery of 90 amps. With the help of Mr. Ohm and the power consumption in milliamps figuring somewhere on a sticker of your computer style fan it's easy to calculate the max of the autonomy during long nights and dark days.

[L Austin France]

If it's to help vent off gasses from a septic tank have you considered the effect these corrrosive (& possibly explosive) gasses could have on the fan?

[Yonner]

Thx again RA. I have considered the gases issue, and am happy with the risk under these circumstances. Is it ok if I pm you?

[RobertArthur]

@ Yonner, it's a friendly forum here, so I do prefer to share information with all possible interested readers. Of course you can pm me, but my experience is that these technical matters never touch the private personal psychological depths where we need Mr. Freud, 19 Berggasse, Vienna.

Back to the wiring: the magical words here in France are < site isolé > and < camping > when searching for off-grid solutions. The prices of the solar panels came tumbling down the last thirty years, inside the regulators now very intelligent chips and we witnessed innovative battery solutions. For the DIY and the flow of electrons however not too many changes, the French side of the internet to illustrate how things work.

[Yonner]

I don't mind posting here, just conscious of shoving what may be a boring thread to many, back to the top of the active topics list.

I suppose my two main questions are:-
How do I calculate how big a panel I need,( does it need a regulator too) what info do I need to know about the fan and the battery to do that. And secondly,
the one I mentioned in my first post- how do I prevent the panel from just charging the battery rather than running the fan? Or can that just not happen.


I'm going to gather my thoughts, read your links and return

Thx again

[RobertArthur]

@ Yonner, step-by-step, start where the chain ends: the power consumption of your dc fan. And yes, you'll need a battery and regulator not only for autonomy, but also to prolong life expectancy of the fan. The maximun open-voltage of a solar panel is about 20 to 25 volts, so you'll have to bring it down to 12 V. A simple linear voltage regulator of the Fairchild 7800/7900-series ( handbook, 1978) or Linear Technology LM-series is not enough. Other factors: how much sunshine in your region, orientation of the solar panel etc. Last but not least, changing subject a little bit: this is the regular fosse ventilation, should do the job if secondary pipe is high enough.

[RobertArthur]

@ Yonner, a little computer style DC fan, 80mm square on the test table. Input voltage about 13 V from a still very reliable HP laboratory power supply. Power consumption measured: 104.4 mA. Your fan a little bit smaller probably about 100 mA (0.1A). A car battery rated at 60 amps would last - in theory - 10 hours with a 6 amp load. A load of 1 amp would push this to 60 hours and your little dc fan even further.....The widely available 12 Volt panels of 50 Wp (only one needed) would be enough in my opinion, recharging your battery with a maximum current of approximately 2 amps.

One extra cable for your house: blackout, not for you, emergency lighting with LEDS and a possibility to recharge smartphones and laptops if necessary....