solar battery charger

[rapr1ext]

hello, 

I am using the STEVAL-ISV012V1 demonstration board, which is based on the SPV1040 solar voltage boost converter and the L6924D single-cell Li-ion battery charger.

My solar panel consists of 4 parallel solar cells. 

The solar cell is: KXOB201K04TF-TR. 

From the datasheet of the solar cell: 

VOC open circuit voltage 2.76 V

ISC short circuit current 83.8 mA

Vmpp voltage at max. power point 2.23 V

Impp current at max. power point 78.7 mA

Pmpp maximum peak power 175.6 mW

with 4 solar cells in parallel:

Impp = 4 x 78.7 mA = 314.8 mA

Vmpp = 2.23 V

Pmpp = 702 mW

My battery is a Li-Ion battery, single cell, 3.7V 1100 mAh. (It is a GoPro Hero-3 battery). 

Here is my test setup: 

(4 solar cells in parallel)

Here is my measurement: 

During this measurement, I used only two solar cells in parallel.

Pink is the current, yellow is the solar voltage, and blue is the battery voltage: 

BUT in the application note: 

I noticed the current graph has a higher period of current flow. See the pink graph below: 

NOW, I would like to know how to increase the turn-on period. How to achieve the flow of current for a longer time, as shown in ST Application Note AN4050. 

Which parameters should I check and tune to increase the period of current flow? 

The development board operates in Quasi-Pulse Mode, which is suitable for the solar cell input. 

Thank you in advance. 

regards

[Peter BENSCH]

Welcome @rapr1ext, to the community!

The pulse duration in quasi-pulse mode is not directly programmable. It mainly depends on the available PV power, the MPPT operating point of the SPV1040, and the charge current demand of the L6924D.

To make the current flow last longer, you could:

• Reduce the L6924D charge current by tuning R14 (see AN4050)
• Check the SPV1040 MPPT setting and make sure the PV voltage stays close to the panel’s VMPP
• Verify the inductor and input/output capacitors, since they affect peak current and stability
• Verify that the saturation current of the coil is well above the actual peak current, with a good margin, and the DCR is as low as possible
• Test with a lower battery state of charge, because a higher battery voltage shortens the pulse time

To obtain longer current pulses, the best first action is to lower the requested charge current and ensure the MPPT point is correctly matched to the solar cells.

Regards
/Peter