CN3791 module changes MPPT voltage

dcexpert

CN3791 module changes MPPT voltage [Copy link]

The CN3791 charging module I bought is 12V by default, while the solar panel I have is around 6V, so the voltage needs to be changed before it can be used.

In the CN3791 data sheet, it can be seen that the MPPT voltage is set by R3 and R4.

The maximum power point is calculated as follows:

On the CN3791 module, the actual corresponding resistors are R1 and R2, one is 22K and the other is marked as 25D, the resistance value is 178K, so the corresponding Vmppt is 1.205 * (1 + 178/22) = 10.95V.

By changing the ratio of R1 and R2, the MPPT voltage can be changed. After calculation, it can be done by connecting a 200K resistor in parallel with R1 (the resistance after parallel connection is 94K), so the MPPT voltage is:

1.205 * (1 + 94/22) = 6.35V

I couldn't find a 200K resistor, so I used two 100K resistors in series.

The actual test result after modification is

tagetage

The voltage change is determined by the light output curve of the solar panel, right? ? ?

dcexpert

tagetage posted on 2022-3-27 20:54 The voltage change should be determined by the light output curve of the solar panel, right? ? ?

If you have data, you can refer to the curve. If you don’t have data, you can only estimate.

qwqwqw2088

Can you measure the current during constant current charging?

How big is the Rcs in the original poster's circuit?

This resistance value determines the constant current during the constant current period. The ending current is 0.16 of the constant current.

dcexpert

qwqwqw2088 posted on 2022-3-27 21:58 You can measure the current during constant current charging. How big is the Rcs in the OP's circuit? This resistance value determines the constant current size during constant current. The ending current is...

CN3791 can charge up to 4A. However, the power of this solar panel is too small to reach the constant current charging stage.

tagetage

dcexpert posted on 2022-3-27 21:37 If you have data, you can refer to the curve. For those who don’t have data, you can only estimate.

Well, yes, that's the only thing we can do.

se7ens

After reading the review of the modified version, read this post

It was found that the input and output of CN3791 were a bit abnormal

The input is the solar cell charging the 18650

But the output is to the power bank. Could it be that it can only realize the conversion of solar cell energy but not the conversion from 18650 to the output of the power bank board?

dcexpert

se7ens posted on 2022-3-31 19:41 After reading the comments of the modified and then looking at this post, I found that the input and output of CN3791 are a bit abnormal. The input is a solar cell charging 18650...

Yes, it mainly utilizes the MPPT function of CN3791 to maximize the solar charging efficiency, but it does not support discharge management.