Difference between revisions of "Charge controller project"

From Organic Design wiki
(See also: FreeChargeController.org)
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*[[Our power project]]
 
*[[Our power project]]
 
*[http://www.timnolan.com/index.php?page=arduino-ppt-solar-charger DIY Arduino-based MPPT charge controller]
 
*[http://www.timnolan.com/index.php?page=arduino-ppt-solar-charger DIY Arduino-based MPPT charge controller]
*[http://www.freechargecontroller.org FreeChargeController.org]
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*[https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2170337_-1 The Arduino-based version available as a kit]
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*[http://www.freechargecontroller.org FreeChargeController.org] ''- wiki dedicated to developing and evolving the Arduino-based controller''
 
[[Category:Projects]]
 
[[Category:Projects]]

Revision as of 02:36, 26 June 2013

I'm building a solar MPPT charge controller using a Raspberry Pi based on this Arduino-based project. The system consists of the following main parts.

Voltage and current measurement

We need to have real-time voltage and current sensing of the solar array to determine the optimal voltage and current to draw from it that delivers the maximum power (the maximum power point tracking, MPPT). And we need to also measure the voltage of the battery to know what kind of charging requirements it has, and finally the current on the load needs to be monitored so that we can graph our power usage over time.

The voltage measurement simply involves a very low current potential divider to ground set such that the maximum voltage the divided point can have is not higher than the maximum input of the system's ADC's.

Current measurement is a little more complicated and involves a shunt resistor (very low value with high precision) placed in the circuit segment requiring measurement, then taking the voltage measurement across this shunt resister and using ohms law to calculate the current. Since the shunt resistor's value is so low (to ensure minimal voltage drop) the voltage across it needs to be amplified using a current-sense amplifier chip which is basically an op-amp designed for single ended configuration rather than requiring a feedback system. See this current-sensing tutorial for more detail.

One issue with this is that there isn't any analogue inputs on the Pi, but that can be done with a single chip solution such as the MCP3008 which gives eight analogue channels and connects directly into the SPI port. See Analogue Inputs for Raspberry Pi Using the MCP3008 for more details.

MPPT algorithm

There's just one thing I don't quite understand yet which is how the circuit is adjusting the voltage of the panels, the only adjustment I see going on is the pulse-width to the MOSFET driver input, but that's adjusting the input to output voltage of the DC-DC converter and should not affect the input voltage/current I don't think.

PWM DC-DC converter

Three-stage battery charger

Web-based interface

See also