Affects On Motors Running Directly From Solar Pnnels

Flubber
Flubber Registered Users Posts: 19
Hi all, I want to use some 12 or 24v automotive type radiator fans for moving some air around in a green house.
I have 12: 60w 12v panels that I am not using and would like to put some or all of these to work for this.

What I am wondering about is the affect on the motors due to the varying out put from the panels.
I want the fans to cool when the sun is out so I am ok if they slow down or stop when it gets darker.
But can the motors operate under the varying conditions.

Thanks

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Affects On Motors Running Directly From Solar Pnnels

    Should be fine... if you want, start with just one panel to power the fan... Then add more panels in parallel (probably somewhere between 2-4 will be ideal). You can monitor the noon time running of the fan and see what the voltage is... You probably don't want the fans running over 14-15 volts for best life... Or slower if you want longer life/quieter operation.

    There are Linear Current Boosters that are designed to run the fans (and pumps) when the sun is not high in the sky (they basically take the high voltage/low current of the array and down converter to low voltage/high current that is required to start/run the motors).

    LCB's though, are not cheap.

    This then gets into other issues... Typical DC Fan motors are "brushed". And the brushes will need replacing after some 1,000-3,000 hours of run time or so (guesstimate).

    There are DC fans intended for barns and such... And there are electronically commutated DC fans (computer fans are an example) that can last 10,000+ hours.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Flubber
    Flubber Registered Users Posts: 19
    Re: Affects On Motors Running Directly From Solar Pnnels

    Thanks for that quick reply!

    So as clouds come over, and or as the sun goes down, I don't have to worry about the fan motor experiencing the voltage and current reducing and eventually going down to zero? I can just let the motor run out of electric and "turn itself off" I don't need any switches or regulators in between the panels and fan


    I was wondering about this because I thought I read some where once about low voltage being bad for motors.

    Thanks
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Affects On Motors Running Directly From Solar Pnnels

    "Brown outs" are bad for motors that can stall (air pumps, refrigeration compressors, etc.) where you don't have enough voltage/current to start the motor turning, but still enough current to overheat the windings.

    Fans and other motors that do not have high torque loads should not be an issue. They will start turning as soon as there is a minimum level of current (rotating motors draw less current vs stalled motors).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Flubber
    Flubber Registered Users Posts: 19
    Re: Affects On Motors Running Directly From Solar Pnnels

    So essentially I can run one of these radiator fans directly form the panels at any voltage and current and it will do no harm to it, but it will run slower and have less torque?

    Thanks
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Affects On Motors Running Directly From Solar Pnnels

    Typically, DC motors will run higher RPM the more voltage (and current) you feed them.

    Solar panels will supply more current (up to rated voltage of approximately Vmp -- voltage maximum power).

    You have to look at the voltage rating of your panels to see how high they will go. Most likely, you will start with a couple panels in parallel, and add one at a time until you find the optimum RPM for your needs.

    It is possible to "over speed" your motors by feeding them too much voltage--So, you probably do not want 5 or more panels in parallel feeding 17-20 volts into the fans as they will run too fast and wear/burnout quicker.

    I don't know, but I would be surprised if radiator fans will last much more than 1,000 hours or so at full speed (say 5 hours per day, that is 200 days of operation).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Flubber
    Flubber Registered Users Posts: 19
    Re: Affects On Motors Running Directly From Solar Pnnels

    Thanks again Bill,

    Well I am thinking about some 24v 9amp fans as listed by manufacturer.

    And I just pulled some of the my 10 year old12v 60w Uni Solar panels off the shed roof today, so tomorrow I am going to hook them up to a meter and see what they do.

    But I am sure I would like to slow the fans down from their top speed, so I am hopeing that four panels per fan will be just about right (2 seriesed pairs paralleled).

    Does that sound correct?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Affects On Motors Running Directly From Solar Pnnels

    Sounds like a good place to start...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Flubber
    Flubber Registered Users Posts: 19
    Re: Affects On Motors Running Directly From Solar Pnnels

    Bill I was just wondering what would be the effect of running that fan at 12v, I think I want to run it at 24v for the thinner wiring size needed , but I am just curious what the effect would be?
  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Affects On Motors Running Directly From Solar Pnnels

    I have a 12 volt nominal ciruclator pump on my solar hot water system. It it hooked directly to a solar panel. It has been running fine for several years on variable voltage from the panel. When the sun is bright it really cranks which corresponds to the time when I want high flow. I expect that is a good match for a green house. I expect it will work well but if you use used fans from junkyard, ieven if you cook one, its not a big investment. If you want to get fancy, Arttel in maine(?) offers 12 volt DC solar controllers that mihgt be adapted so that the fan doesnt run when its cool out.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Affects On Motors Running Directly From Solar Pnnels

    Running the 24 volt fan motors on 12 volts (or less than 24 volts) should not be a problem.

    Lower voltage, motor spins slower, fans move less air, less power through motor--Should run cooler too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Flubber
    Flubber Registered Users Posts: 19
    Re: Affects On Motors Running Directly From Solar Pnnels

    What would be the difference between running the 24 fan with two 12v panels in series where you would have the 24v or paralleling them to have higher amps at 12v?

    So I hooked up the Unisolar Panels to a multi meter in full sun and I got 20V at about 4 to 5 amps, I know this is a no load reading.
    What do you think the readings would be with a 24v 9amp fan hooked up in the same sun conditions as above with average wiring resistance?

    Thanks
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Affects On Motors Running Directly From Solar Pnnels

    Solar panels "confuse" the answers because they are not "solar batteries" in the classic sense of what we understand a battery to be (i.e., 12 volts from 0-100 amps, above 100 amps the battery voltage collapses). Batteries are a "voltage source" and attempt to keep 12-14 volts regardless of load or charging currents.

    Solar panels are "current sources" (for the most part). If you have full noon time sun on a solar panel (1,000 watts per m2). The panel will output Imp (current maximum power) from zero volts to Vmp (voltage maximum power). If the solar panel voltage rises to Voc (open circuit voltage), then there will be zero current flow.

    Also, the output current of a solar panel is fairly proportional to the amount of sun light hitting the panel... Roughly 100% of Imp at noon, and at 9am or 3pm around 50% of Imp (tapering to zero current at dawn/dusk/dark).

    So, your motor when supplied with X amount of current will probably find an "operating point" somewhere between zero volts and Imp.

    Taking to panels in series--The fan might run faster at noon, but hardly run at 9a or 3pm.

    Conversely, run the two 12 volt panels in parallel, the fans may start earlier/stop later, and move more air at 9am and 3pm, but less air at noon when compared to the two panels in series. (note the Linear Current Booster is providing the "extra" current in morning/evening times--Sort of like connecting two 12 volt panels in parallel at 9am and in series at noon--using some sort of, probably, buck mode switching power supply).

    In the end, you will run very little chance of damaging anything. Connect 1-5 panels in parallel at 9 amp and noon, measure voltage and current for each configuration, and again at noon (sunny and clear days of course).

    Then try the same thing with two to three panels in series, and 1-3 panel strings in parallel.

    As long as Vmotor is not much more than 28-29 volts DC, you are not hurting it electrically.

    And with fan blades, reducing current/voltage is not damaging it either (and may prolong the life as the motor turns slower and runs cooler at lower power levels).

    Sorry--I really don't have any special insight to your DC fans and the ideal panel/array configuration--So I would be doing the same experimenting I suggested above.

    The only thing to be careful of--If you use batteries and solar panels. Connecting solar panels "backwards" to lead acid batteries will create a dead short through the solar panels and fry the cells/wiring (solar cells are just big old diodes and if you connect a diode wrong, it will pass maximum current from the battery bank too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Flubber
    Flubber Registered Users Posts: 19
    Re: Affects On Motors Running Directly From Solar Pnnels

    Thanks again Bill,

    Yes I will experiment and see what the 24v fans do under different configurations of volts and amps, now that I have an idea that it is ok for the motors.

    "Solar panels are "current sources" (for the most part). If you have full noon time sun on a solar panel (1,000 watts per m2). The panel will output Imp (current maximum power) from zero volts to Vmp (voltage maximum power). If the solar panel voltage rises to Voc (open circuit voltage), then there will be zero current flow."

    Are you saying here that the voltage output will drop as a device(load) consumes current?

    A couple of final things I am wondering about:

    I am planning on using 4 fans, is the best thing to do to wire each fan to its own set of panels, or could they be wired in parallel, whats best?

    Also when I tested my panels with the multi meter hooked up directly and saw 20v and 5 amps which is close to the ratings on the back tag. Is that an accurate indicator of the health of the panel?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Affects On Motors Running Directly From Solar Pnnels

    Three home methods to test solar panels:
    1. Measure Voc (open circuit voltage). Hot panels may read a bit low, cold panels a bit high (~77F is STC).
    2. Measure Isc (short circuit current). Isc=100% in full noon time sun. Isc is proportional to among of sunlight.
    3. Connect panel to load that is near Vmp and measure current. (Current should be ~proportional to amount of sunlight)

    #1 and #2 will weed out 80% of the failures.

    Voc OK--you can still have very poor/high resistance failures.

    Isc OK--You can still have shorted cells/open strings--In theory, you only need one or two good cells to move Isc at zero volts

    #3 should weed out the last 10-20% failures

    Running panel under load--That is what you need in real life. Using a car battery is usually "good enough" load (measure current with meter).

    Of course, be careful connecting panel to battery... If connected backwards, battery will be short circuited with all current going though cells/array and frying them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Flubber
    Flubber Registered Users Posts: 19
    Re: Affects On Motors Running Directly From Solar Pnnels

    Any advice on the wiring of four fans ?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Affects On Motors Running Directly From Solar Pnnels

    Lots of ways at looking at the problem...

    A few panels connected to one fan. If anything goes wrong, nothing much will happen (limited current from solar array, won't fry wiring or motor wiring because of limited current).

    Connect all panels together, you may need a fuse/breaker per fan connection to prevent a shorted wire/fan from getting too much current from the "large array".

    Connecting all fans to one array--Fan motors should provide "negative feedback" on current usage... I.e., if one fan runs a bit slow, it will draw less current.

    What you don't want is one motor stalled (say a refrigeration compressor with lots of back pressure) drawing all of the current and the other motors don't even try to start (while the stalled motor is pulling all current and possibly overheating or overheating the wiring).

    In the end, which ever is easiest to mount (panels, motors, wiring). Although, if I could do two (or X) panels per fan, I would just wire them up that way (separate array per fan).

    A problem with solar panels and DC current--They tend to sustain arcs very nicely (DC arc welders are known for their stable arcs, and DC rated switches are much heavier than similar AC rated switches).

    So, a "large array" has higher available current and (possibly) more wire runs where damage can occur (why I suggest fuse/breaker per fan in this configuration)--So I would "error" towards multiple small arrays with less available power in the circuit (I have on occasion loaded barns with hay in my youth, so always worried about fire with unattended electrical applications).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Flubber
    Flubber Registered Users Posts: 19
    Re: Affects On Motors Running Directly From Solar Pnnels

    Thanks, I,ll post on how it works out for any one interested in the future.

    Flubber
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Affects On Motors Running Directly From Solar Pnnels

    Yes, please let us know--We get quite a few requests on solar powered automotive radiator fans... Have not heard much how well they worked in the long term.

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