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connecting different batteries to PV system

bjornderian

I have a PV system and a lead acid battery bank already attached with a solar charge controller. I want to charge a portable Lithium ion battery using excess energy during the day.

 

Is it possible to charge the portable battery without going through a dc to ac inverter and another ac to dc charger which would decrease efficiency? basically, charging directly from DC with another battery already attached to the charge controller.

 

If yes, how? and what do I need

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  • 0

    A lot will depend on your solar system specification and wiring.  Typically, the panels are connected in serial strings to get a high enough DC voltage that they do not need to add a voltage doubler on the front end of the power inverter.  Then extra panels are add in parallel circuits to add additional current.  Depending on the voltage range of you DC output of the solar array, you can get DC-to-DC convertors that will handle 150-400V inputs to provide 5V to 12V outputs. This would provide the correct range for many Li-Ion chargers.  What you will be missing in such an arrangement is the Peak Power tracking capability and protection circuitry that is built into the inverter.  If what you are dealing with is your excess capacity (beyond the lead acid battery bank), concerns of efficiency is sort of a moot point, as unless you are selling back your excess, the energy was not going to be captured anyway, so maybe an AC based charger would work fine.

     

    Gene

  • 0 in reply to genebren

      wrote:

     

    Depending on the voltage range of you DC output of the solar array, you can get DC-to-DC convertors that will handle 150-400V inputs to provide 5V to 12V outputs. This would provide the correct range for many Li-Ion chargers.  What you will be missing in such an arrangement is the Peak Power tracking capability and protection circuitry that is built into the inverter. 

     

    Thank you for your response in advance. I still have some questions left unanswered. How would the circuit be arranged, would it be okay to connect it directly to the DC bus after the MPPT charge controller. How would connecting it this way interfere with the Peak Power tracking capability of the charge controller?

     

    SInce I will be charging the li-ion only when the lead acid is full, what device would I need to shut off the connection to the lead acid and switch to the dc to dc controller-> li-ion charger automatically?

  • 0 in reply to bjornderian

    These are some great questions.  The answers to these questions would need very deep analysis of the actual equipment and the system interconnects.  This is not something that I could answer just by a rough description of your setup.  The simplest way to charge some Li-Ion batteries would be to connect a A/C powered charger to the output of the system.  This would allow all of the system's protections and features to operate as normal using excess energy to charge your extra batteries.  You could potentially be able to automate the charging by monitoring the charge status of the lead-acid batteries and switching on the Li-Ion charger when the storage batteries are full.

     

    If you wanted a more efficient and integrated approach your best approach would be to contact the manufacturer of the inverter system to see if they have any recommendations.

     

    Gene

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  • 0 in reply to bjornderian

    These are some great questions.  The answers to these questions would need very deep analysis of the actual equipment and the system interconnects.  This is not something that I could answer just by a rough description of your setup.  The simplest way to charge some Li-Ion batteries would be to connect a A/C powered charger to the output of the system.  This would allow all of the system's protections and features to operate as normal using excess energy to charge your extra batteries.  You could potentially be able to automate the charging by monitoring the charge status of the lead-acid batteries and switching on the Li-Ion charger when the storage batteries are full.

     

    If you wanted a more efficient and integrated approach your best approach would be to contact the manufacturer of the inverter system to see if they have any recommendations.

     

    Gene

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