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Discussion in 'General Electronics Discussion' started by Karthik rajagopal, Jun 5, 2017.

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  1. Karthik rajagopal

    Karthik rajagopal

    232
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    May 9, 2016
    Hi all,
    I recently bought a solar panel which is rated at 7.5 v max. But I get a voltage more than 10 v (approximately 12v) when it is exposed to sunlight (the temperature is around 43.4°C). Does that mean these solar panels can deliver a voltage higher than it's rated voltage? Can it even go higher that 12v when it is exposed to higher temperatures? Please explain

    Thanks.
     
  2. Gryd3

    Gryd3

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    Jun 25, 2014
    Do a quick google search for a solar panel IV curve.
    I'm not sure how you are measuring, but an open circuit voltage measurement will be higher than when the panel is under load. If you are noticing this voltage difference while the panel is under load, can you please provide us with detail on what kind of load you have connected?
     
    davenn likes this.
  3. Tha fios agaibh

    Tha fios agaibh

    2,128
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    Aug 11, 2014
    Yes, they deliver higher voltages during peak sunlight at noon. 12v does sound high though. I wouldn't expect it over 10v.

    I don't know about the role temperature plays but I'd guess the voltage would be higher at lower temps since conduction is better.
     
  4. Karthik rajagopal

    Karthik rajagopal

    232
    7
    May 9, 2016
    Thanks for the reply. I measured it using my multimeter. Even if i connect it to my circuit I don't see any difference in the voltage. I have even used it for my motor (DC 9v motor) without any change in the voltage. I usually use my solar panel to power my circuits through my voltage regulator. Can this be a manufacturing defect (as it supplies voltage more than the voltage rated)?
     
  5. Karthik rajagopal

    Karthik rajagopal

    232
    7
    May 9, 2016
    I got that voltage by around 12:30 pm. I think that might be due to peak sunlight here in our city. But I USUALLY get around 9.7 v max. This was the first time I got this voltage.
     
  6. davenn

    davenn Moderator

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    Sep 5, 2009
    probably because the circuits/motor you connected to were not drawing enough current to drop the voltage significantly
     
  7. Karthik rajagopal

    Karthik rajagopal

    232
    7
    May 9, 2016
    But this solar panel can supply only 180 mA. When I connect my motor to this it struggles to start and spins at a low speed without having any change in the voltage. So there must be a significant current draw when my motor is connected to it but even in this situation I don't know why there is no change in the voltage?
     
  8. duke37

    duke37

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    Jan 9, 2011
    If the motor struggles to start, then it is not getting high voltage.
    I have a digital meter which shows high readings when the meter battery voltage is low.
    I often use an analogue meter (without battery) for such conditions. Digital meters can be affected by AC fields.
     
  9. Gryd3

    Gryd3

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    Jun 25, 2014
    It sounds incorrect...
    We can't say it is, but it sounds that way.

    What kind of meter are you using, and is the meter connected while you connect the motor?
    It should most definitely cause a voltage drop from the open-circuit voltage, by how much I'm not familiar enough to say but it will be noticeable.

    How large of a motor are you using?
    Is it a digital meter? (With good batteries)
     
  10. Audioguru

    Audioguru

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    Sep 24, 2016
    A DC motor that starts running is stalled. Look at its spec's, its stalled current is much higher than its current when running with no load. Maybe your meter is too slow to show its stalled current then shows its current when it is running up to speed.

    My solar panel is 12V with its rated load. It measures 17V with no load.
     
  11. Karthik rajagopal

    Karthik rajagopal

    232
    7
    May 9, 2016
    I have a digital meter with new batteries.
     
  12. Karthik rajagopal

    Karthik rajagopal

    232
    7
    May 9, 2016
    I am using a digital meter (batteries are good). I measured my 11.5 v from my solar panel without load. But even though it is connected to a load (DC 9v motor, needs a minimum current of 400mA spin at a moderate rate) ,I don't see a significant drop in the voltage.... I see a drop of 0.5v to a maximum of 1v.
     
  13. Karthik rajagopal

    Karthik rajagopal

    232
    7
    May 9, 2016
    Can the ratings written on my solar panel be wrong? But I got this 11.5 v only on that day or else I will be getting a max voltage of 9.8v from my solar panel. My multimeter is good and works fine.
     
  14. Karthik rajagopal

    Karthik rajagopal

    232
    7
    May 9, 2016
    There cannot be any chances of my meter reading an incorrect voltage. But even if there was an error it must have got corrected once I switched it off and on again during my test because I also had the same doubt whether it would be able to supply 12v. But it stayed constant with a slight fluctuation between 11.7v -12v.
     
  15. Gryd3

    Gryd3

    4,098
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    Jun 25, 2014
    One other key item to address
    Yes,
    It's possible for an incorrect rating on the panel.
    Looking at other panels and various voltage curves for panels, you should see an additional 40-50% at open-circuit compared to a loaded circuit... and an overloaded circuit will be much less than the rated voltage.
     
  16. Karthik rajagopal

    Karthik rajagopal

    232
    7
    May 9, 2016
    Yes, think that might be the correct reason for this problem. Thanks for the reply
     
  17. Audioguru

    Audioguru

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    Sep 24, 2016
    "Incorrect rating"! That happens when you buy cheap Chinese junk from ebay.
     
  18. Karthik rajagopal

    Karthik rajagopal

    232
    7
    May 9, 2016
    Not always. I don't have the habit of buying online and we don't buy Chinese product. I bought this solar panel from BPL electronic company. They manufacture only high quality goods. May be it can be an old stock or an error which happens very rarely.
     
  19. Audioguru

    Audioguru

    3,085
    692
    Sep 24, 2016
    My high quality solar panel is made by Coleman. It is 12V, 2.5W and is on sale today in a local store for $7.00US.
    It comes with many connectors.
     
  20. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Not just eBay... I have a 1300mAh LiPo rated for 110C that I purchased from an unrelated web location.
    I can't say for sure if this panel is labelled incorrectly... but I can most certainly state that the observations don't match what a panel *should* do regardless of rating.
    Voltage should most certainly drop when a load is connected... unless the meter is enough of a load, but meters typically have a very high impedance to avoid noticeably loading the circuit when measuring.
     
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