Small solar fan - basics

Options
athan01
athan01 Registered Users Posts: 2
in Solar Beginners Corner #1
I am a newbie in electronics and solar and I have a question for a simple problem requiring a simple solution:

I have used some cheap toy solar cells (2x1 inch size) to start a small fan in order to circulate air out of a cabinet at home (i have a pipe from inside the cabinet leading to the roof).

My issue is that even if there is a lot of sun out, my fan will not start automatically but needs me to give it a little push to start rotating (and then rotates at full speed until the sun goes down).

Right now, my fan is directly connected to my small photovoltaic (around 3v max output). Is there a simple circuit that I need to put in between, or even simpler solution like connect a capacitor between the two or something?

Many thanks
Andreas
· Share on Twitter

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #2
    Options
    Re: Small solar fan - basics

    If the fan does not start in full sun, you probably do not have enough solar panels in parallel (not enough current).

    Welcome to the forum Athan.

    Solar panels are "Current Sources" and they output a (roughly) fixed current for a given level of illumination.

    Remember that Power = Voltage * Current.

    When a motor is getting started, it has very low resistance (technically low impedance from low inductance) when stopped, which keeps voltage near zero volts--And P=V*I, very low V means very little power

    Once the motor is spinning, the impedance is higher, and therefore voltage is higher, and everything spins OK.

    Assuming the fan will start with sufficient current (say a couple of AA or D cell batteries at motor's operating voltage), then you simply need more current.

    For small motors, that is more solar panels.

    For larger motors, there is a functional device called a linear current booster. This can take the Vpanel*Ipanel and "convert" it to Vmotor*Imotor -- Where Voltage is low, and therefore current is much higher.

    These are frequently used on water pumps (for example), LCB's help the motor start earlier in the morning and run later in the evening to help increase overall water pumped.

    http://www.solar-electric.com/7amplincurbo.html
    http://www.solar-electric.com/dankoff-solar-pumps-controller-dsp200.html

    But an LCB (even a smaller one like above) is way more expensive at ~$150 vs just buying some more small solar panels for your usage.

    If you want to build one--I am not sure--But I would guess it is a Buck Mode switching power supply with an "interesting" control loop/feed back/control circuit. They can be designed and built with a cook book approach--But they are probably not an ideal "beginner project".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • athan01
    athan01 Registered Users Posts: 2
    #3
    Options
    Re: Small solar fan - basics

    Hi Bill,

    Thanks for the thorough answer.. I guess things are not as simple as I thought they were..

    Interestingly enough I have received a tender for installing a swimming pool solar pump, which is directly connected to the solar panels. I will review your links and perhaps talk to the vendor to ensure that this wont happen with the pump.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #4
    Options
    Re: Small solar fan - basics

    There is a lot related to pumping...

    First, an efficient pump is usually a Permanent Magnet type--And 3 (or poly) phase motor. Uses an external controller--VFD (variable frequency drive) (or may be internal to the pump controller).

    There are also (much simpler and cheaper) 2 speed motors/pumps too. Run on low most of the time, run on high to run the cleaning equipment.

    In times past, people have tried to use "universal motors" (brushed motors like in a standard electric drill) as DC pumps--But the brushes pretty much would not last more than 6 months to a year in continuous duty. Don't get one of these (brushed) motors

    Many pool pumps were much larger than needed--So changing to a smaller pump could save a lot of power/money. So could adding a VFD to an AC pump to allow it to run at low speed unless there was a suction/cleaning attachment being used.

    Also, pumps can be more efficient if they are below the water level of the pool (in a pit, or similar). Pumps that can lift water are usually less efficient (of course, a pump in a pit adds issues of leaks/flooding).

    Some pool pump discussions:

    Swimming pool pump
    powering up my swimming pool
    Lorentz PS600 Photovoltaic Pool Pump System
    Pool pump
    Pool pumps suck...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter

Categories