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Charging an AGM Battery with BQ24650 EVM

Keith Walls
Prodigy 60 points

I'm trying to use a 200W solar panel to charge an AGM battery. Attached are the datasheets for each.

I currently have the EVM set up with Vout=15.4V (the max charging voltage of the battery is 15.4V) by changing R15 to a78.7K resistor. I also have the MPP set to 24.4V (MPP of the panel is 24.5V) by changing R17 to 608K. By changing R6 to a 4mΩ , I set the max xharge current to 10A. This required a high current inductor, which I could only get a 1 µH with max current of 11A, so I had to add nine 10µF caps to keep the LC frequency in the acceptable range.

The problem I'm having is, when the input voltage is above the MPP voltage and charging begins, I'm only getting a small charge current of about 1/2A into the battery. When using a constant voltage load set to close to 15.4V(14.5 - 15.3V), I get a much better current of around 7A, but this doesn't happen on the battery. Am I missing something here?  It was my understanding that Vout was supposed to be the max voltage at which the battery could be charge... Should Vout instead be set to the batteries fully charged open circuit voltage of 13.1V?

Thanks in advance for any input you can provide!

8231.BP SX 3200 Solar Panel.pdf

4666.Optima D51 Battery.pdf

  • 0
    Prodigy 60 points

    So I have a theory, but I haven't gotten to test it yet... I think its because on the bench, my power supply has a max current of 5A, and when I use the battery and the voltage goes to 15.4V, it draws too much current form the supply , so the supply goes into some sort of protect mode.

    The reason I didn't get to test this yet is I fried mosfet Q1 when I stupidly swapped the positive and negative cables on the battery... I've ordered a new mosfet, but should I be worried about other bad components too?

  • 0 in reply to Keith Walls
    TI__Mastermind 36110 points

    I'm sure you are on the right track.  Carefully measuring the voltages and currents going into and out of the IC and calculating efficiency will show if it is converting power properly.