how to power fan directly from solar panel?

System
System Posts: 2,511 admin
in General Solar Power Topics #1
I want to power 12 volt fans in my greenhouse directly from a 75 watt solar panel without having to use a charge controller and battery. I am worried that without some sort of diode, I may fry the motors as the panel produces more than 12 volts. Exactly how might this be accomplished?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: how to power fan directly from solar panel?

    knowing the specs of both the panels, and the fans would be helpful.

    the little 12V computer type muffin fans would need to be tested, as some models do not like to start from a slow voltage rise, others have a little timer circuit that repeats the start cycle and that style will start.

    Frankly, 75 watts will not move much air, unless it's a small greenhouse.

    The fans may also shut down while the sun is still heating the greenhouse, and while that's OK in the morning, late afternoons may cook plants.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: how to power fan directly from solar panel?

    I actually plan to use 2 -75 watt panels that have an output of about 4.5 amps each. Not sure about the fans- they are not muffin-type but 12volt motors that I will affix blades to that I bought from Kansas wind power and seem much more substantial than muffin fans. I tested one on a panel and it really spun. Like I said, i am concerned that the 17 or so volts from the panel may burn it out eventually and wonder how I can regulate it to output only 12 volts. thanks
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: how to power fan directly from solar panel?

    "wonder how I can regulate it to output only 12 volts."

    controllers are regulators, but are more specific in their application and quality. it will be difficult to have anybody comment more specifically because we don't know the current draw from the fan motor. if it is low enough it may be possible to incorporate the use of a small regulator ic, but we don't know this. a diode will not regulate the current, but will drop a small fractional portion of the voltage across the board (meaning even if the pv voltage is low a diode will still drop at least 1/2 of a volt).
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  • System2
    System2 Posts: 6,290 admin
    #5
    Re: how to power fan directly from solar panel?

    I don't have the fan info now, but how bout this idea- connect any old 12 car or marine battery (without charge controller) between panel and fan and use that to regulate 12 volts to fan. Just let the fan run every day until the battery dies....any thoughts on that?
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #6
    Re: how to power fan directly from solar panel?

    Just connect the panel to the fan, no diode, no batterys, you probably have attic exhaust fans if you bought from a solar dealer

    Motors are not sensitive to the voltage, if its higher, its just spins a bit faster.

    I installed in a commerical shed a pair of exhaust fans, used 20 watts for each fans ( stuff was 60% off at home depot last year ), its does a good job and I'm sure a 75 watt panel will move lots of air.
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  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
    #7
    Re: how to power fan directly from solar panel?

    If you have spent money on 150 watts of PV and two fan motors it seems that little expense is required additionally to do a proper job. You have already mentioned adding a 2nd user reclaimed car battery as a buffer. A very small inexpensive charge controller $30-40 and a timer switch for the fan would allow you to keep the green house cool and still have the facility for a simple light as well with out cycling you battery to death.

    Theres a probverb some where about failing to spend a little extra to complete a proper job that I just cant put my finger on ;)
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #8
    Re: how to power fan directly from solar panel?

    A charge controller and battery add no value if the fans use all the juice during the day. Also Green houses probably don't need the fans at night

    If the fan doesn't need all the PV, yes a battery and low-voltage disconnect might get some more run time, but having actual installed something like this I still say wire direct and forget it.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #9
    Re: how to power fan directly from solar panel?
    scotty-b wrote: »
    I don't have the fan info now, but how bout this idea- connect any old 12 car or marine battery (without charge controller) between panel and fan and use that to regulate 12 volts to fan. Just let the fan run every day until the battery dies....any thoughts on that?


    BAD IDEA This will work for about 2 days, then the battery will be so low, the fan won't run, and your small panel won't be able to charge it up to 12V. There are only 5 good charging hours in a day, and the other 19 hours the fan will drain the battery. A deeply drained battery will soon sulphate and die too.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • System2
    System2 Posts: 6,290 admin
    #10
    Re: how to power fan directly from solar panel?

    Just to clarify for you, discharging a battery beyond the half way point will greatly reduce it's life. Letting it go dead each night is considered to be murder in the first degree. Whatever you chose to call it, the batteries rapid transition to death is still the end result. And yes, this applies to "deep cycle" batteries. Regular car batteries are all the more sensitive to abuse.
    Cheers
    Wayne
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  • lamplight
    lamplight Solar Expert Posts: 368 ✭✭✭✭✭✭
    #11
    Re: how to power fan directly from solar panel?

    I would just go direct without batts/controller too, but as someone said, with a little more investment wouldnt it be nice to have switches/timers/possible additional lighting? i would think if you could put some voltage regulation on there (I know exactly what youre asking about) you may even find it might be helpful to turn the fan speed DOWN sometimes. on new england solar electric website he has some wallmount switches that can adjust output voltage. i forget what ranges. i have a car 12v radiator fan as the gable vent in our house, its on a 12 hour wind up timer switch off our batteries. its been 2 years runs great and moves a lot of air for only about 20-30 watts i think it uses. with a custom built fan, hard to say wahat kind of cfm you'll be able to move.

    edit: heres the voltage switches:
    http://www.newenglandsolar.com/catalog_pages/catalog56.htm
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