# BQ24650 MPPT design.

Hi, i would like to get help on how to design BQ24650 to work as a MPPT charge controller for a solar power system.

Thanks.

### 10 Replies

• Hi , i am using BQ24650 IC to make a MPPT charge controller that can support up to 10A from the solar panel. My battery is 12V battery. Can anyone guide me how to design the circuit please?

Thanks.

• In reply to solar boy:

None of the designs in the Application Notes section for the bq24650 come close to your specs? If not, none can be modified?

• In reply to John M:

I wondered if I can use MPPSET pin to control in mppt algorithm. Can I connect MPPSET pin to a Microprocessor such as MSP, AVR, PIC and use it to control output voltage?

• Hi, can someone tell me if the VMPP is same as VIN?  VMPP is the maximum voltage by the solar panel right? Can i also assume VMPP as my VIN value? These two values are found in the Excel based BQ24650 design.

Thanks

Solar boy.

• In reply to solar boy:

MPP - Maximum Power point........VPPM voltage at MPP.

Typically solar panels have a MPP at 80% of the open circuit voltage; check with the manufacturer.

• In reply to Charles Mauney:

Hi, basically my solar panel is 12V. Should i assume 12V or the VMPPT value as my  VIN value? Please guide me. Thanks.

• In reply to solar boy:

• Hi, i face a problem in calculation of R9. I put in all the values into the equation 7 and 8( in main datasheet)  to match the calculated values in the Excel design calculator.

For R10, i got 30.10Kohm but for R9 i got 5.16 mohm. According to the sample circuit in the Excel design calculator for the BQ24650, both  R9 and R10 are in kilo ohm, should i expect my readings to be in kilo ohm for R9 instead of mohm?

Also, in the circuit of the Excel design calculator, for Q3, where is the (CE bar) point connected to?

Thanks.

• In reply to solar boy:

If one narrows the temp window (0-45 ti 0-45.5), R10 starts to increase in value toward a high resistance or open. if the window gets too small like 0 to 44C, R10 goes negative.

If one wanted a hot temp of 40C then one would have to adjust the cold temperature down to some negative value until the resistor values becomes positive, or find a different 10k thermistor with a different beta value.

It would be helpful to tell your temp range so I could see what the issue is.

• I have a 12V, 100W solar panel having maximum output current of 5.3A charging a 12V,100Ah battery using the BQ24650 IC. I was recommended to set the IC's charging current to 4A.

My questions:

(1) Is that means i can only charge the battery at max 4A and the current is being "locked" at 4A max? Cannot use higher current like 5A?

(2) What will happen to the voltage if the current is to be set constant?

(3) I am also using water cooling on the panel, would that help boost my charge current?

(4) How long will it take to charge the 12v, 100Ah battery with 4A charging current with battery's DoD of 0.7 and 4-5 hours of sunshine/day?

Thanks.