1 Purpose and Functions
The ACTii AC7391 PWM regulator with Maximum Power Point Tracking (MPPT) algorithm is an advanced device designed to optimize the power supply of standard domestic hot water electric heater elements directly from photovoltaic panels. The device solves a key problem of PV installations: voltage drop under excessive load. By using the regulator, panels operate at the optimal voltage point, allowing for efficient water heating even in low sunlight conditions or on cloudy days.
The system is equipped with a buffer module (capacitors, choke, diodes), which increases circuit efficiency by approximately 30% and minimizes interference generated by PWM regulation. Additionally, a built-in temperature sensor allows for precise management of the water heating process, stopping operation once the set temperature is reached.
Main features:
- ✔ MPPT algorithm for maximizing power point tracking from photovoltaic panels.
- ✔ Capability to power standard DHW electric heaters (230V or 110V AC).
- ✔ Integrated temperature sensor with thermostat function and adjustable cut-off threshold.
- ✔ Readable parameter display: Voltage (V), Power (W), and Water Temperature (°C).
- ✔ Manual switching on/off using plus/minus buttons.
- ✔ OUT signaling diode indicating power delivery to the heater.
- ✔ Potential-free relay output for notifications of heating completion or failure.
- ✔ Standard DIN TH35 rail mounting.
- ✔ Advanced thermal protection and active temperature-controlled cooling.
- ✔ Full galvanic isolation between high-voltage and power sections.
- ✔ Two operating modes: fully automatic and with manually set voltage thresholds.
- ✔ Compliance with CE and RoHS standards, manufactured in the EU.
Set contents:
- Main controller ACTii AC7391
- Load buffer module
- Temperature sensor (cable approx. 100cm)
- Cable connectors (depending on batch)
- User manual and packaging
2 Technical Specifications
| Controller supply voltage | 11V to 14.4V DC |
| Input voltage from PV panels | 10V to 400V DC |
| Maximum PV panel current | 11A (electronic limitation to 11A for stronger panels) |
| Maximum heater power | 2000W (2kW) |
| Maximum PV panel power | 2000W (2kW) |
| Power consumption (no cooling) | 0.08 A |
| Power consumption (with cooling) | 0.23 A |
| Temperature measurement accuracy | 0.1°C |
| Regulator dimensions | 90 x 54 x 64 mm |
| Buffer dimensions | 90 x 36 x 64 mm |
| Product weight | 330 g |
| Mounting | DIN rail TH35 |
| Certificates | CE, RoHS |
3 Controller Operating Modes
The regulator offers two main operating modes that allow for flexible adjustment to the specifics of the photovoltaic installation:
Mode One: Automatic (MPPT)
This is the default mode, which activates immediately after connecting power. When the input voltage from the panels exceeds the defined minimum threshold (set via the MINUS button), the controller automatically starts transferring energy to the heater using the MPPT algorithm. If the voltage falls below this threshold, the process is interrupted. This mode is ideal if you want to simultaneously heat water and, for example, charge batteries from the same set of panels.
Mode Two: Adjustable Voltage Thresholds
Allows for manual definition of two key parameters:
- Switch-on voltage: the point from which the controller starts increasing PWM duty cycle.
- Maximum voltage: the point at which the duty cycle is 100% (full energy from the panels goes directly to the heater).
This method allows for very precise maintenance of panels at the maximum power point (MPPT) by rigidly defining the voltage operating range.
4 Heater Selection and Calculations
The key to the proper functioning of the system is matching the heater resistance to the parameters of the photovoltaic panels. You can use both AC (230V/110V) and DC heaters, because their primary operating parameter is resistance.
Matching Principle (Ohm's Law):
If the panels nominally generate 140V DC at 7.14A (1000W), the ideal heater should have a resistance of: 140V / 7.14A = 19.61 Ohm.
Selection examples for standard 230V AC heaters:
Set 4x 400W (Operating voltage ~36V/panel):
Recommended 220V AC heater power: 3.0kW - 3.5kW
Set 4x 450W (Operating voltage ~38V/panel):
Recommended 220V AC heater power: 3.8kW - 4.5kW
Set 4x 500W (Operating voltage ~40V/panel):
Recommended 220V AC heater power: 3.5kW - 4.0kW
Tip: The safest solution is to use heaters with a single spiral. In the case of dual-spiral heaters, one can be powered from the 230V grid, and the other from the PV controller, but this requires special attention during installation.
5 Safety and Installation Manual
The device operates with high DC voltages (up to 400V), which are extremely life-threatening. Installation should be performed by a person with appropriate electrical qualifications.
Ensure adequate ventilation around the device. The regulator has active cooling, however, do not cover the enclosure ventilation openings.
Before performing any maintenance work, you must absolutely disconnect the power supply from the photovoltaic panels and the auxiliary DC power supply.
The temperature sensor should be mounted in a place that ensures reliable measurement of water temperature in the boiler (e.g., in a measurement sleeve). Do not allow direct contact of the sensor with water if it is not in a protective sheath.
The relay output is potential-free. Do not exceed the permissible contact load currents of the relay specified in the technical documentation.