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A project log for SolarCharger SZBK07V2

A MPPT solar charger using a DC converter, MOSFET diode, Arduino Nano for control and an MPPT software library for simple integration.

keithhungerfordkeith.hungerford 07/16/2018 at 01:444 Comments

13 July 2018: I decided to try and submit an entry for the .energy harvesting competition. I have been working on this topic for some time but have not created an end product so far. My concept is to create a modular MPPT charger based on a  SZBK07 DC converter, a MOSFET diode and Op-amp current sensor using the 4 milli Ohm resistor in the SZBK01.

Software will be a library with an MPPT class. It will be configurable for battery set points and temperature input. It will have an interface to get logging data out, so that the system integrator can add a display, local data logging or remote logging by WiFi or other technology.

Working on the hardware schematic diagram.

Discussions

JP Gleyzes wrote 11/18/2018 at 09:55 point

Hi Keith,

I made a typing mistake, you are totally right the chip is indeed a LM25116.

Regarding the current sensing, I can confirm that it works right out of he box !

I sent you a PM/chat on this site with an attached picture.

Regards

JP

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keith.hungerford wrote 11/19/2018 at 06:17 point

Thanks JP. I have replied to the PM/chat.

Keith

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JP Gleyzes wrote 11/17/2018 at 18:37 point

I finally succeeded in writing a comment :-)

First of all thank you for sharing your schematics and code. It's very helpful.

I have bought a SZB07 module from aliexpress and got pretty much the same  but with reference LB07. Interesting is that the chip's name is readable and is a Ti LM25116 buck converter.

 On the board is a current limiter made with a simple OpAmp reading the voltage on the .04Ohm resistor and feeding the feeback pin of the chip via a diode with this (voltage - ref) coming from the pot.

f you remove this diode then you have the current sense resistor + OpAmp circuitery available for measuring your solar panel current with absolutly no outside components :-)

You can even adjust the output range of the OpAmp to fit your arduino ADC range with the pot (I use a 3.3V ESP32 MCU) !

Cheers

JP

[edit] the buck converter is LM25116 and not LM26116 (sorry !)

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keith.hungerford wrote 11/18/2018 at 04:10 point

Hi freedom2000, thanks very much for this. A couple of other readers have identified the controller chip on their modules as LM25116, which is an appropriate buck converter IC. Searching for LM26116 does not yield anything relevant, so I wonder if yours is also LM25116?

I think it is possible that different manufacturers of this converter are using LTC1625 and LM25116, which have very similar capabilities.

I will study the current measuring setup you suggest, which seems a good advance relative to the scheme I have been using.

Thank you again.

Keith

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