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Thread: How many panels needed

  1. #1
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    Default How many panels needed

    Hi,
    I am from India.
    I have 40 AH 48 V VRLA deep discharge battery. I like to charge it using solar panels.
    How many panels are needed. What is the charger specifications.

    Thanks,
    Jagadees
    India

  2. #2
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    you will need 2 72 cell panels is series, Total of about 40-60W and a 5A charge controller.
    That is a very small battery bank for a 48V bank. I assume it is 4 12 batteries in series?
    Rich
    WWW.solarsaves.net

    NABCEP certified Technical Sales Professional

    http://www.solarpaneltalk.com/showth...Battery-Design

    http://www.calculator.net/voltage-drop-calculator.html (Voltage drop Calculator among others)

    www.gaisma.com

  3. #3
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    Thanks for the reply.
    Yes its 4 12V batteries of 40 AH in series.
    You are saying, just a 60W panel is enogh?
    Why it should be 72 cell panels ?
    What should be the output voltage of the panels?

    thanks,
    Jagadees.

  4. #4
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    Depends on what type of charge controller you use being PWM or MPPT to deliver a 4 amps of charge current.

    If using PWM you need 270 watts of solar panels consisting of 4-12 volt battery panels of 65 watt panels, or 2 GTI 72 cell 135 watt panels with a 5 amp PWM controller.

    If using a MPPT controller you need 200 watt panel consistin of 4-12 volt battery panel os 50 watts, or 2 GTI 72 cell 50 watt panel panels with a 5 amp MPPT charge controller.
    MSEE, PE

  5. #5
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    Quote Originally Posted by Naptown View Post
    you will need 2 72 cell panels is series, Total of about 40-60W and a 5A charge controller.
    That is a very small battery bank for a 48V bank. I assume it is 4 12 batteries in series?
    Rich FWIW to get a C/10 charge current (4 Amps) using a MPPT CC = 48 volts x 4 amps = 200 watts. For PWM 4 amps x 68 volts = 270 watts
    MSEE, PE

  6. #6
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    Quote Originally Posted by Sunking View Post
    Rich FWIW to get a C/10 charge current (4 Amps) using a MPPT CC = 48 volts x 4 amps = 200 watts. For PWM 4 amps x 68 volts = 270 watts
    for some reason I was thinking 12V 40AH
    Rich
    WWW.solarsaves.net

    NABCEP certified Technical Sales Professional

    http://www.solarpaneltalk.com/showth...Battery-Design

    http://www.calculator.net/voltage-drop-calculator.html (Voltage drop Calculator among others)

    www.gaisma.com

  7. #7
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    Quote Originally Posted by jspchn View Post
    Why it should be 72 cell panels ?
    For every 12 volts of battery requires 36 cells with a Vmp of 17 to 18 volts. A 12 volt battery panel is 36 cells. It takes 68 to 72 volts to charge a 48 volt battery
    MSEE, PE

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    Quote Originally Posted by jspchn View Post
    Why it should be 72 cell panels ?
    thanks,
    Jagadees.
    It does not need to be 72-cell panels. Since you need about 144 cells total, it seems simpler and more economical to use two high voltage panels than 4 36-cell panels. But the choice is up to you.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

  9. #9
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    Quote Originally Posted by inetdog View Post
    It does not need to be 72-cell panels. Since you need about 144 cells total, it seems simpler and more economical to use two high voltage panels than 4 36-cell panels. But the choice is up to you.
    Assuming a MPPT controller is used; that would be 2 less expensive GTI panels with a minimum 72 cells each right? If a PWM controller is used; more expensive 36/72 cell battery panels must be used right?

    Sorry I am guilty of asking questions I know the answer too.
    MSEE, PE

  10. #10
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    Quote Originally Posted by Sunking View Post
    Assuming a MPPT controller is used; that would be 2 less expensive GTI panels with a minimum 72 cells each right? If a PWM controller is used; more expensive 36/72 cell battery panels must be used right?

    Sorry I am guilty of asking questions I know the answer too.
    Since this is a 48 volt battery, either an MPPT or a PWM controller will need a series string of panels totaling 144 cells minimum. If the OP wants to go beyond that, he can either add more panels in series into his MPPT controller up to its input voltage limit or add more 144+ cell strings in parallel.

    If using MPPT, it will be possible to add one panel or an odd number of panels at a time, while with PWM they would have to be added in 144 cell groups.

    I hope that is the answer you already know, or else I have screwed up again.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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