Total novice solar circuit question

Thread Starter

nuttam

Joined May 27, 2017
6
Hello all

Looking through other posts on here I think my query is insultingly basic and I'm perhaps on a more specialist website than entirely necessary!

I'm looking to provide mechanical ventilation to my shed. It's only a shed, and so cost is very much an issue.

Given its position, my best bet is to solar power a small fan.

I'm looking at a small panel (Maximum power voltage: 17.9V, Maximum power current: 0.28A, Open circuit voltage: 22.4V, Short circuit current: 0.3A, Power allowance range: +/-3%) and something like a PC case fan (12v, approx. 4w - open to suggestions).

From my limited understanding, if I wire the panel straight to the fan it'll burn out (or the shed will take off like a helicopter).

Any help on how to make this work would be really appreciated.

Many thanks, Mark
 

wayneh

Joined Sep 9, 2010
16,399
I think there's a good chance it'll work fine. The panel cannot deliver the max current and max voltage at the same time. Once loaded down by the fan, it may match up fairly well.

A bigger problem might be getting the fan to start spinning. That takes more current than it uses while running.

If the panel turns out to be too much for the fan, you can add an inexpensive DC-DC converter to provide a regulated 12V to the fan. This would also allow you to add additional panel power.
 

Thread Starter

nuttam

Joined May 27, 2017
6
Thank you all for your replies, it's much appreciated. I've ordered the panel and the fan now, and will try just connecting them directly. I don't need it to run at high speed or all the time, so hopefully I'll get enough juice out of the panel to get the fan turning without getting too much!

I'll report back once I've (hopefully) got it up and running.

One more stupid question - is there any risk to dry wood near a 12v source? I'm assuming not, but better safe than sorry!

Thanks again, Mark
 

Bernard

Joined Aug 7, 2008
5,653
I see no problem with dry wood near a 12V source. Small fans seem to readily start from solar panels, maybe just a slight delay but with some motors , like pump motor, benefit from a start circuit that uses a capacitor to
store a charge from an unloaded solar panel to apply a large start current. Circuit is available if needed.
 

Thread Starter

nuttam

Joined May 27, 2017
6
Thanks Bernard. I understand what you mean about the start circuit but not what I'd need to do - I'll try setting up without first, but may well come back for some help to add that in if the fan won't start up.

Thanks once again, everybody on here has been very helpful!

Kind regards, Mark
 

Thread Starter

nuttam

Joined May 27, 2017
6
Hello again. I've got the panel and fan now. I've wired them up directly to each other, but have the problem that Bernard anticipated; if I spin the fan by hand then the panel provides enough power to keep the fan spinning, but it doesn't provide enough power to get it to start up initially.

Is there something I could add to the circuit to overcome this?

Many thanks, Mark
 

Thread Starter

nuttam

Joined May 27, 2017
6
Thanks Colin - I saw the dollar pricing and assumed it was US only!

I've ordered that now. Hopefully I'll be able to set it up when it arrives!

Thanks, Mark
 

ErnieM

Joined Apr 24, 2011
8,055
The basic problem with solar powered motors is getting them to start in the morning. The voltage out of a solar panel will drop to near zero if an excess of current is demanded by the load. What happens in the morning is the panel starts supplying a small amount of power, not enough to run the motor. So the voltage drops and the small amount of current is running thru the motor. As the sun comes up this current increases but the voltage does not, just heating up the stalled motor.

Even if you wait till full sun and connect a motor you may need a larger surge of current to kick start the motor. If the panel can't supply this it may go back into the shut down low voltage mode again.

I would suggest doing the following: wait till the sun is well up then disconnect, pause, and reconnect the motor. If it starts then your panel can supply the start up current. (If not, there are still things to do).

If so, it simplifies a controller. What I would suggest is something that senses the panel voltage, and if high enough will enable the motor. If not, keeps it off. Now during the start of daylight this may mean multiple attempts to start the motor are made over and over, but once the sun has risen enough the motor should catch and run till dark.

Do what you are doing, but if you still have trouble try the above experiment and holla back.
 

Bernard

Joined Aug 7, 2008
5,653
Might try connecting a cap. across panel & after it charges up to about 17 V, then connect fan. If it starts , C is about right. Start with about 1000 uF @ 35 V. Solar gleaner #2 was used to start some cranky motors.Solar Gleaner # 2 00000.png
Just about any P ch FET will do. 32k pot can be almost any thing, 10k to 250k.
ZD1 could be a white or blue LED, boost current up to 10 mA. 22,000 uF can be reduced to fit fan .
 
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