MPPT Solar Charge Controllers

Solar charge controllers are used when solar panels are used to charge a battery bank. They regulate the high DC voltage generated by solar panels (PV generators) to a nominal value acceptable to a battery bank; eg 12V, 24V and 48V. Each controller will have a maximum current capability, so a controller is selected based on the maximum potential charge current that could be generated by the solar panels.

Important - if you use solar controllers to supply a battery bank, which then delivers power to an inverter or inverter charger - BEWARE - over voltage of the battery bank from a failed cheap solar controller could seriously damage the inverter! Only use good quality charge controllers like Studer VarioTrack and VarioString units.

To cope with larger installations Studer charge controllers can be paralleled. As the controller is now effectively acting as a battery charger, good solar regulators produce an output which is similar to a modern switchmode charger - the output is mutli-staged and varies according to the state of charge the batteries. There are different ways controllers do this and the most common for small regulators is a system using (PWM) Pulse Width Modulation technology. However, on anything larger than a small single or double panel installation, we want to extract the maximum energy from the solar installation.  Here, the better way is to use a technology called Maximum Power Point Tracking (MPPT). The Studer VarioString and VarioTack ranges of solar charge regulators are high efficiency MPPT controllers which can handle power outputs up to 105kW (multiple units used in parallel).


The VarioString...

The VarioString family consists of two models; one which will handle a max charge current of 70A and one which can handle 120A. The VarioString range is only available for 48V battery banks. With the VarioString MPPT solar charge controllers, solar installation costs can be reduced while at the same time still getting a better than average solar production and maintaining the battery bank in the best condition possible.

An exceptional device
The installation costs of a PV generator system are significantly reduced due to the higher acceptable PV input voltage range. This unique feature won the VarioString the internationally renowned "Solar Award" in the category "BOS", Balance Of System.

Despite converting a high voltage solar (600-900V) input to 48V battery voltage while maintaining galvanic isolation between the PV and battery, the VarioString achieves an amazing efficiency greater than 98%; the highest efficiency in the world in its category.

The VarioString shares all the features the VarioTrack offers regarding use with Studer Xtender units and the CANBUS communications system to efficiently control charge cycles and to independantly select the specific capacity of the individual PV and inverter/charger combination.  This lets you design the system you want.


  • Reduces Balance of System costs (eliminates expensive wiring for parallel strings, saving wires, connectors, junction boxes, fuses, space, time, etc.)

  • Safe, simple and trouble free connection with SUNCLIX™ (Phoenix Contact “tool free”) PV connector

  • Safety, guaranteed, thanks to the reinforced isolation between the PV generator and battery and between the two PV inputs of the VS-120. This allows for independent earthing of the battery and/or solar modules*.

  • World leading efficiency in isolated converter with >98 % conversion efficiency

  • 7kW per unit and up to 15 units in parallel; 105kW

  • 4 step charger fully programmable for longer battery life

  • 9 LEDs to monitor status and current

  • Full display, configuration and data acquisition with RCC-02/03 and/or via the internet with the Xcom LAN/Xcom-GSM or via SMS with Xcom-SMS

*Many manufacturers recommend that one of the poles of the solar generator be earthed to avoid PID (Potential Induced Degradation). It has been shown that this degradation can rapidly reach up to 60% of the initial power.


The VarioTrack...

The VarioTrack family consists of two models; one which will handle a max charge current of 65A and one which can handle 80A. With the MPPT solar charge controllers of the VarioTrack series, each installation is the best it can be with a maximized battery life due to an optimal charge.

A VarioTrack charge controller uses a sophisticated algorithm that ensures the maximum available power from the solar PV modules is delivered to the batteries.

The device meets the highest industry standards and with its IP54 rated rugged aluminium casing, it is well suited for harsh environments. In addition, it is fully protected against reverse polarity.

The VarioTrack is designed to be used with all types of solar systems and the combination of the VarioTrack and an Xtender results in a highly efficient system. The Studer CANBUS communication between the devices enables synchronisation of the battery charge cycle regardless of the technology (lead acid, lithium Ion, nickel, etc). Unlike other combined hybrid solutions, the VarioTrack with Xtender allows independent selection of the appropriate capacity of solar PV and inverter charger, resulting in a more accurately defined system.

Features and performances

  • Ensures optimal energy production

  • Tracking efficiency; > 99%

  • Conversion efficiency; > 99%

  • 4 step charging for longer battery life

  • 8 predefined battery charge curves as standard

  • Free programming of the battery's load curve with the RCC-02/-03

  • Low self-consumption; < 1W in night mode

  • Protection against incorrect wiring

  • Protection against reverse polarity

  • Fully configurable

  • IP54 enclosure

  • Comprehensive display, programming and data logging with the RCC-02/-03

  • Up to 15 VarioTrack in parallel on the same communication bus

  • Communication via Xcom-LAN, Xcom-GSM, Xcom-SMS; (optional)

  • Compatible with all PV systems

  • Optimal usage in an Xtender system with a synchronized battery management


Studer VarioTrack

Model Output (VDC) Max Charge (A) Parallel
VT-65 12, 24 & 48 65 Max 15
VT-80 12, 24 & 48 80 Max 15

Studer VarioString

Model Output (VDC) Max Charge (A) Parallel
VS-70 48V 70 Max 15
VS-120 48V 120 Max 15


Click on the links below - the document will open in a new window and can then be saved or printed.


VarioTrack Datasheet

VarioTrack User Manual


VarioString Datasheet

VarioString User Manual



Please contact us if you would like more information or would like to discuss your requirements further. You can call us on 01794 523900 or fill in the form below.

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