solar charger help

Discussion in 'General Electronics Chat' started by phil35581, May 11, 2014.

  1. phil35581

    Thread Starter New Member

    May 11, 2014
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    I am wanting to make use of a large solar panel I have. My goal is to make a simple circuit using an LM317 to charge my truck battery. I would also like to have an additional circuit with a usb port to charge mobile devices while camping.

    Question 1..... will a 4001 diode work to prevent reverse flow and protect the solar panel?

    Question 2.....how do I get it to stop charging when truck battery is full?
     
  2. #12

    Expert

    Nov 30, 2010
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    Lots to say here. If you set the charging voltage correctly, the battery voltage will stop the charger as the battery gets full. www.batteryuniversity.com
    You don't have to get it perfect, charging to 100.0%. Besides, the temperature of the battery changes every day. Just set the charging voltage low enough that it won't boil all the water out of the battery.

    Meanwhile, you can get 5 volts out of a second LM317 but a lot of devices won't just accept 5 volts and charge up. So glad modern technology wants to, "talk" with the charger half the time (not).

    Anyway, a 1N4001 should handle up to an amp on this stuff, but the whole 1N4000 series up to 1N4007 cost the same, and every number larger than 4001 is a better voltage rating. Pick one, any one.
     
  3. phil35581

    Thread Starter New Member

    May 11, 2014
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    Thanks for the Help. What should I set the voltage at? 13.5 volts?
     
  4. #12

    Expert

    Nov 30, 2010
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    I see it at 13.4 to 13.9 volts. Considering the heat where you are, 13.5 should work just right.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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  6. ian field

    Distinguished Member

    Oct 27, 2012
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    That voltage is more akin to the maintaining charge - commercial "intelligent" chargers usually put out between 13.8 - 14.2V for the bulk charging phase.

    Remembering that many of the PV regulators I've seen were shunt regulators, reminded me that the Lucas electrics on 60's British motorcycles used a dirty great 100W 15V zener to regulate battery charging - at maximum alternator output the dynamic resistance probably allowed more than 15V getting through - although short battery life may have been one of the criticisms of the Lucas "prince of darkness" electrical system.
     
  7. William L.

    New Member

    Oct 2, 2013
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    Don't expect to get the full open circuit voltage out of your solar module. Look on the back of the module for the VMP or maximum power voltage rating.
     
  8. #12

    Expert

    Nov 30, 2010
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    Phil isn't giving me a lot to work with, like whether the truck battery is in a truck and will get charged up good and proper on Monday. I'm just estimating for a way to avoid boiling it dry in a month.
     
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