[Elecraft] Solar Panels on sale !!

[Don Brown]

Hi

Solar panels are constant current sources. That is they will supply about the same current into a short or a battery as long as the battery voltage is somewhat lower than the open circuit voltage of the solar panel. The current they supply is determined by the size of the panel and the amount of light on the panel. The voltage is determined by the number of cells in series and to a small degree the amount of light also. Each cell will output about .5 volts, so enough cells are usually placed in series to give about 18 to 25 volts for a 12 volt system. If the panel is small and the battery is large the panel will trickle charge the battery and no controller is required. This is what the VW panels sold on ebay and Harbor freight will do if the battery is large like a car battery. Smaller batteries can be overcharged by these panels but it would take a long time to over charge a 7 amp hour battery with 170 ma. BTY don't expect the VW panels to supply 5 watts. the rating on these panels is 3.2 watts at 170 ma maximum and an open circuit voltage of 18.8 volts. You will almost never get the full rated power from any solar panel unless you can keep it aimed exactly perpendicular to the sun and it is a clear day. 170 ma is about 100 ma less then the required power for the K2 on receive so even though one of these panels would help you are still using more power from the battery than you are putting back in. You would need 3 of these panels to in parallel to get any gain and that is not including any power for transmitting.


Don Brown


  ----- Original Message ----- 
  From: Jim Brown<mailto:jimbrown.enteract at rcn.com> 
  To: elecraft at mailman.qth.net<mailto:elecraft at mailman.qth.net> 
  Sent: Wednesday, May 26, 2004 8:06 AM
  Subject: Re: [Elecraft] Solar Panels on sale !!


  I have no experience with solar panels, but would like to try some. It seems
  logical that more than one would be in order to get enough power to run some
  radios for a contest. My EE background suggests that each ought to be
  connected to the battery through a diode and current limiting resistor, and
  maybe even a regulator to prevent overcharging. Is there standard practice
  for this?

  Jim Brown  K9YC

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