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MPP Bq24650

simone frasanni
Intellectual 285 points
Other Parts Discussed in Thread: BQ24650

Hi to all !

I'm using bq24650 to charge a 6V/10Ah lead acid battery from panel solar or from an external source of 12V+-10%.

The panel solar is 18V at MPP, so I set MPPSET  to 17,8V (like demoboard).

When i connect the external source of 12V, I don't have charge current in the battery. If I increase Vin up to 17,8V, the bq24650 works correctly. I think the problem is the voltage in the pin MPPSET : the Bq24650 reduces the charge current until the input voltage increases....but input voltage remains 12V !.

There is a trick to disable MPPSET when bq24650 is supplied from external source, that isn't PV ? 

I can accept a dip-switch configuration, to set depending on source of supply

Thanks in advice

Simone

  • 0
    TI__Genius 11480 points

    Simone,

    The purpose of MPPSET is to prevent your solar panels from crashing. If your input voltage drops to VMPPSET, the bq24650 will reduce the charge current to maintain the panel voltage. If the input is below VMPPSET, the bq24650 will disable charging. 

    The maximum power point (MPP) of the panel is different for each panel. Usually it is given in the datasheet, but a good rule of thumb is 80% of the open circuit voltage.

    In your case, the 12 V supply is much less than VMPPSET, so it thinks that the "solar panels" are unable to source charging current - so it disables charge.

    If you need to switch between the two, you could definitely use dip switches to change your configuration. Some people use some sort of logic and an NMOS to switch between 1 resister and having two in parallel. Unfortunately, there is no way to disable it.

  • 0 in reply to David Wiest Jr
    Intellectual 285 points
    Hi David, thank you !!
    Ok, I have mounted a dip-switch to set the correct power supply like you suggest me !!
    Best regards
    Simone
  • 0 in reply to David Wiest Jr
    Intellectual 285 points

    If I set the MPPSET more than 1,2V when Vin >10V, can Bq24650 runs in both conditions? Is it so important tohvePVthatworksinMPP?

  • 0 in reply to simone frasanni
    TI__Genius 11480 points
    Simone,

    That is definitely one way you can do it. The bq24650 will work that way. If you set your MPPSET below your 12V supply it will run on both. If you do this, you just run the risk of "crashing" your solar panels.