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Applying higher voltage than rated

  1. Sep 23, 2012 #1
    I would like to power a 12 volt d.c. universal fan using a 50 watt 12 volt solar panel. Output voltage under load for the panel is 17.4 volts d.c. Open voltage is 19 volts. Would 17.4 volts be detrimental to the life of the fan or is it okay due to the low wattage output?
     
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  3. Sep 23, 2012 #2

    vk6kro

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    You would need to know, or measure, the current the fan uses at 12 volts.

    Measure this with a known 12 volt supply or it may be on the fan's label.

    If the fan has more than 12 volts on it when it is operating, this would mean it would draw more current than usual and probably run faster than normal, so this could damage the fan or destroy it.

    If the panel is portable, the easiest way to drop the voltage under load would be to point it away from the sun, but you would have to keep moving it as the sun moved. Maybe if you always pointed it to the East of the sun, at least the output voltage would tend to drop as the sun moved towards the West.
     
  4. Sep 23, 2012 #3

    davenn

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    Probably will be long term detrimental, would pretty much depend on the build quality of the fan and how much overvoltage it could handle. As you increase the voltage, the current is also going to increase and that will eventually to the burning of commutator contacts, increased heating of the windings etc

    cheers
    Dave
     
  5. Sep 23, 2012 #4
    The fan is an electric DC motor. Applying a voltage higher than the rated one will cause the fan to operate on speeds above the nominal and this could cause the fan to failure due to excessive vibration or incur in a bearing failure (both would take some time to happen). Electrically, the electric current becomes higher than the nominal and it may lead to excessive heating if the fan is on for long time and if there is no suficient ventilation. The winding can burn out. Moreover, if it is a brushed DC motor, brushes will wear out faster than usual due to both higher speed and current.

    Usually, all this things take many days or even months to happen. It all depends on the quality of your motor.
     
  6. Sep 24, 2012 #5
    Hello Pacodog - -- I am probably not as negative on this idea - the Open Circuit voltage for the solar panel - is just that - open circuit rating. By applying the motor to the panel full time - you will never see the 17V - if you wish to switch the fan on an off - you may want to experiment to see how high the voltage across the motor is - some simple filtering - like a capacitor may also be helpful.
    But the Solar panel may be able to put out more than 12V at nearly full power - 13 or 14 V - but the SP ratings are usually a little ummmm - embellished. So some experiments may be in order.
     
  7. Sep 24, 2012 #6

    uart

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    Actually he said the o/c voltage was 19V and 17 volts was measured under load. Presumably this is under a relatively light load, but his fan is likely to be a very light load for a 50W panel (most 12V computer fans are typically only in the range of about 1 to 5 Watts). So yeah, seeing 17 volts is quite feasible here.
     
  8. Sep 24, 2012 #7

    sophiecentaur

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    Cover the solar array with a sheet and take it outside. Connect it up and gradually remove the sheet until you get 12V with the motor load. You won't damage the fan motor that way. An alternative would be to use a 12V voltage regulator. That would maintain 12V across the fan over a range of lighting conditions.
     
  9. Sep 24, 2012 #8
    Thank you so much for all the helpful replies. I should have given a bit more info but I think it will be alright. The fan is a universal permanent magnet radiator fan, basically. It has a 12 volt 80 watt rating on it, so based on I =P/E, the current draw should be just under 7 amps. When I hook up the 50 watt panel, the motor only runs at about two thirds of the speed than when it is hooked up to a car battery. Voltage across pos. and neg. at the motor only reads about 7 volts and amps measured in line shows about 3 amps, so I am assuming because the panel has such a low wattage output, the motor should not be affected. It definitely is not heating up, even running all day which was also worrisome because I am sure these type of motors are not meant for continuous duty. I really do appreciate all of the help and thank you so much.
     
  10. Sep 24, 2012 #9

    sophiecentaur

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    If you're getting enough 'blow' then you're sorted. Good good. The question only remains- how bright is the sunlight to achieve this situation? Do you get more in full sunlight? It might be good if it could be operating a bit faster(?).
    Your fan is clearly a bit more beefy than the "computer fan" suggested earlier and, if it's an automotive fan, it will be plenty tough enough to run a bit warm continuously, I'm sure.
     
  11. Sep 24, 2012 #10
    Those readings were during direct sunlight. As a matter of fact, with any cloud cover at all, the motor drops in speed considerably but I think it may be because of the fact that the panel is polycrystaline and not monocrystaline. It seems to be affected even if the shadow of your hand crosses the panel.
     
  12. Sep 24, 2012 #11
    Get a voltage regulator to lower down to 12V. I am very conservative, I don't like to push things. 12 to 17V is 140% the rated voltage, you are going to shorten the life of any component.
     
  13. Sep 24, 2012 #12

    sophiecentaur

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    OK, so you now need to play at being a proper engineer and decide whether the cooling job requires more blow or whether it'll be good enough. Do you buy another PV panel or a more suitable fan? You can almost certainly get a much more suitable fan than the one you've got for not much money. Choose one that takes the right current and your panel will supply just the right voltage under load.
    Good luck.
     
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