We have been wanting to design, build and supply an open-design, relatively inexpensive but fully functioned charge regulator for solar PV, wind, pedal and small hydro systems for a while now.

The majority of off-grid renewable energy systems are based upon lead acid batteries. Lead-acid batteries need to be protected from over-charging by the renewable energy source and over-discharging from the loads. This can be one with a series regulator (in the case of solar PV) or a shunt regulator (for PV, hydro and wind).

The charge regulator pages here give the full design for a relatively simple but fully programmable and open-source charge regulator. Make one yourself or buy the kit.


A large proportion of the world (around 1.4 billion people) do not have access to reliable electricity systems.

These areas are typically remote, rural and difficult to access. Providing a grid-connection would be prohibitively expensive.

One way of providing a reliable electrical supply is to use renewable energy sources, such as solar photovoltaics, small wind turbines or micro hydro systems.

As renewable energy is variable there must be some form of energy storage to buffer the supply and demand. This is typically a lead-acid battery. Batteries need to be protected from over-charging by the renewable energy source and over-discharging from the loads. This can be done with a charge regulator, which monitors the voltage levels and ensures they are kept within safe limits by dumping excess power (in a shunt regulator), cutting the supply (in a series regulator) or cutting the load (in a low voltage disconnect).

The project here is to develop a robust and reliable charge regulator platform. This will provide a re-programmable controller, measurement of voltage (and also current), control of the output and some visual indicators for user feedback.

Here are the functions we would like to perform:


This design is open-source. We would love for people to build this design and give us feedback. Please get involved, either by posting comments or directly email us here.

Initial design

There are a number of parts to the system:

  • Microcontoller – the ‘brains’ of the device. This will make decisions based upon the voltage monitoring to control the power stage.
  • Voltage monitoring – monitors the voltage
  • Power stage – MOSFET and MOSFET driver – this will control the power from the input to the output.
  • Power supply – provides power to the circuit. Must be efficient.
  • Protection – Diode, fuse and over-voltage – Ensure that the device will not be damaged from incorrect installation
  • ISP: In series programming – The microcontroller can be reprogrammed easily without expensive equipment.
  • Current monitoring – for information and user interface (this is optional)
  • Display – LEDs will show the system status. This could also be an LCD display. (this is optional)
  • Data – output data as a serial data stream for use by other devices (this is optional)

An overview of the system is shown here:


The project pages here will give detail on the design and problems encountered.

Please visit the links below to find out more:

What is already available?

The initial starting point for all projects nowadays is to do a trawl of the web. Here is a brief list of the projects I found. I am mainly interested in open-source projects, but the ideas and costs of others is also useful.

  • Commercial manufactured units

Typical prices are in the range of £10 (eBay cheapest) to £200. Basic designs do not have a low voltage disconnect, nor V or I monitoring.

This looks like a really interesting project, with plans to build an open source maximum power point tracking charge controller for solar PV (and wind) systems.

12V and 24V versions. Cost is $14.50 + P&P, from USA. Based upon the ZM33064 voltage controlled switch, with a IRFZ44N mosfet to control the dump load. Hysteresis is controlled with a resistor value. No dump load is included (it must have this to function).

This is a PIC microcontroller based PWM solar charge regulator. UK designed and made. £17.99. Simple in-line series regulator for PV up to 100Wp, 12 or 24V. One LED to display function. Information about the design of the device is on the website, but I could not find the full design details.

(Edit 15/11/12: The circuit schematics have been made available: http://www.256.co.uk/?p=917)

A number of electronic circuits with a couple of solar regulator circuits (one and two). Relatively simple circuits. Full circuit diagrams.

Another reltively simple design (from an edition of ETI (Electronics Today International). Uses a 555 timer. For a 5W solar panel.

A simple PWM series regulator from an article in Elektor Electronic magazine, March 2000. This is for 12V panels up to 53Wp. I have made a number of these and they work well. They do not give enough information about the battery voltage.

Only for very small solar panels.

A load of solar circuits, mainly relating to solar tracking.

Based upon the LM2575T-ADJ switching regulator. Design is only OK for up to 1A, but is a switching regulator so should have very good efficiency.

  • Arduino-based solar charge regulators

timnolan – a hill-climbing maximum power point tracking solar PV regulator.

This uses realys to control the dump load and the supply.

Uses a relay to control a dump load

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