PWM regulator for heaters with the algorithm for finding the maximum MPPT power point from photovoltaic panels.
The regulator enables the supply of standard CWU electric boiler from solar panels

Sample installation – Film

The solar panel operates at maximum power only at the optimum voltage. Connecting the heater directly to the solar panel causes too much load and consequently voltage drop. With reduced voltage, the panel produces up to several times less power than at the optimum voltage. The use of a charge controller eliminates this problem. Even on cloudy days it will be possible to heat the water in the boiler.

The device has been equipped with an additional relay output (without potentials) enabling to notify external devices that the water heating has been completed (reaching the set temperature) or that the device has failed. This output allows you to connect additional devices.

The controller is equipped with a buffer module containing capacitors, a throttle and a diode, which enables to achieve higher efficiency (up to 30%) and reduce interference caused by PWM regulation.

The regulator has been equipped with a temperature sensor, which allows you to stop heating the boiler above the set temperature.


Answers to questions

Way to calculate what heater will match the PW panels.

Here is the Simple Calculator to calculate the heater power:
For 12 x PW Panels (100W 17V DC each) = 1200W, 204V (Series Circuit)
You can use 1500W 230V Heater.

I(A) = P(W) / V(V)
R=U / I
P = I2 · R
WP Panels I(A) 5,88A
PW Panels R(Ω): 34,68Ω
Optimal Heater Power P(W): 1525W ,230V

Remember that if you use a stronger heater or a weaker one, it will not be correct and may overload the PWM controller, and after it lead to its damage after several months of such work.

Have AC7391 PWM also DC DC voltage converters from 360 Panel Voltage to 24 output Voltage ?

The device does not change the voltage received from the PV panels. If the PV panels give 360V DC, the device will send 360V DC to the heater.

The max 2000 Wat heater can be operated by your AC7391  by PWM and Buffer charge continuously adjustable between 0 Watt and 2000 Watt. ( different solar radiation => different Power) ? ( if there are additional devices necessary please send me the specification )

Yes, power will be supplied to the heater continuously in the range of 0 -> 2000W. Even if the PV panels will only produce 10W, the 10W will be sent to the heater. There is no need to purchase additional devices

Does this controller smoothly regulate power from 0 to 2 KW? (depending on the sunlight?)

Yes, depending on the power it receives from the PV modules

Is there a temp sensor part of the set ?

Yes, the temperature sensor is supplied with the device

What heater should I use AC or DC and what power?

You should match the heater to the PV panels.
If your PV panels give a nominal 140V DC 7.14A 1000W, the most appropriate will be to use a 140V DC heater with a power of 1000W.
If in the boiler there are no two places to mount the heater and you need, for example, on cloudy days to heat the water using 230V from the mains, you can use the heater on 230V AC matching its power to the PV panels.

How to adjust it:
Because the only parameter of the heater is its resistance, and also current strength , it is possible to match the 230V heater to work with PV panels of a different voltage using Ohm’s law. From the right Ohm 140V / 7.14A = 19.61 Ohm. Our heater is to have 19.61Ohm. For heater 230V P = U * U / R. P = 230 * 230 / 19.61 = 2697W. We can therefore use a 230V AC heater with a capacity of approximately 2700W for PV 140V 7.14A panels.

Exceeding the power of 2000W and exceeding the power of the heater

Temporarily exceeding the power of 2000W does not cause problems but if it lasts longer the controller should turn off and display the error or something will break down with too much power increase.

If you connect the 340V 3A to the heater (230V 2KW), the heater will emit too much heat and it will not end well for it.

The heaters have a resistance characteristic.
Increasing the voltage applied to the heater causes an increase in the power allocated to the square.

If the heater with a single spiral is too weak, you can use a heater with two spirals and connect both spirals in parallel.

Two heaters connected in parallel -> the voltage on the heaters will be the same, so the value of resistance is important.

With a parallel connection of heaters, the total power will be twice as large with a parallel connection and the water will boil faster

Is it possible to use a heater with less power than the power obtained from PV panels?
It is important to fit. If the heater has 1kW and it connects to the regulator with PV 2kW panels, this set will not reach full power.

list of errors

Er.0 is too low supply voltage
Er.2 is an unstable power supply voltage or a power supply for a very “junk” or disturbance introduces. In the case of Er.2, the power source must be changed / checked.
Er.1 is damage to the transistors.

Is it possible to use a heater on 230V with voltage from PV 400V panels?

This is not a good idea.
When the heater has 1kW and is designed for 230V and will give 400V DC with a capacity of 2kW, it will wear quickly (perhaps they will soon be burned) because more power is released on it than the producer predicted.

The heaters have a resistance characteristic.
Increasing the voltage applied to the heater causes an increase in the power allocated to the square.

Do you think that it is reasonable to provide a cooling fan it case of often reaching the 2000 watt power (100%)

The controller has a fan. There is no need for additional cooling. (please do not close the controllers in very small electrical cabinets… the warm air must be carried away somewhere)
Many of these drivers are successfully operating in Australia and warm regions of the USA.

Is it possible to use a stronger heater than the nominal power of PV panels ?

Small differences in the power of the heater and PV panels are not a problem , but If the PV panels reach 140V DC 7.14A 1000W, and you will use a 140V DC 2000W heater, the load buffer at this load may ignite. Capacitance of the capacitors is too high, which can overheat and then overflow, which led to the ignition of the electric arc.

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