Electronic Load Controller (ELC) Circuit

The post explains a simple electronic load controller or governor circuit which automatically regulates and controls the rotational speed of a hydro-electric generator system by adding or deducting an array of dummy loads. The procedure ensures a stabilized voltage and frequency output for the user. The idea was requested by Mr. Aponso

The Circuit Request:

Hi Swagatam

Thanks for reply and I was out of country for two weeks. Thanks for info and timer circuit is working very fine now.

Case II , I need electronic Load Controller(ELC)My hydro power plant is 5 kw single phase 220V and 50Hz and need to control excess power using ELC. Please give reliable circuit for my requirement



The Circuit Design

If you are one of those lucky people who have a free flowing creek, river stream or even an active small water fall near your backyard, you can very well think of converting it into free electricity simply by installing a mini hydro generator in path of the water flow, and access free electricity for lifetime.

However the main problem with such systems is the speed of the generator which directly affects its voltage and frequency specs.

Here, the rotational speed of the generator depends on two factors, the power of the water flow and the load connected with the generator. If any of these alter, the speed of the generator too alters causing an equivalent decrease or increase in its output voltage and frequency.

As we all know that for many appliances are such as refrigerators, ACs, motors, drill machines, etc voltage and frequency can be crucial and may be directly related to their efficiency, thus any change in these parameters cannot be taken lightly.

In order to tackle the above situation so that the voltage and the frequency both are maintained within tolerable limits, an ELC or electronic load controller is normally employed with all hydro power systems.

Since controlling water flow cannot be a feasible option, controlling load in a calculated manner becomes the only way out for the above discussed issue.

This is in fact rather straightforward, it's all about employing a circuit which monitors the voltage of the generator and switches ON or OFF a few dummy loads which in turn control and compensate for the increase or decrease in the speed of the generator.

Two simple electronic load controller (ELC) circuits are discussed below (designed by me) which can be easily built at home and used for the proposed regulation of any mini hydro power station. Let's learn their operations with the following points:

ELC Circuit using IC LM3915

The first circuit which uses a couple of cascaded LM3914 or LM3915 ICs are basically configured as a 20 step voltage detector driver circuit.

A varying 0 to 2.5V DC input at its pin#5 produces an equivalent sequential response across the 20 outputs of the two ICs, starting from LED#1 to LED#20, meaning at 0.125V, the first LED lights up. while as the input reaches 2.5V, the 20th LED lights up (all LEDs lit up).

Anything in between results in toggling of the corresponding intermediate LED outputs.

Let's assume the  generator to be with 220V/50Hz specs, means the lowering its speed would result in lowering of the specified voltage as well as the frequency, and vice versa.

In the proposed first ELC circuit, we reduce the 220V to the required low potential DC via a resistor divider network and feed pin#5 of the IC such that the first 10 LEDs (LED#1 and rest of the blue points) just illuminate.

Now these LED pinouts (from LED#2 to LED#20) are also attached with individual dummy loads via individual mosfet drivers, in addition to the domestic load.

The domestic useful loads are connected via a relay on LED#1 output.

In the above condition it assures that at 220V while all the domestic loads are in use, 9 additional dummy loads also illuminate, and compensate to produce the required 220V @50Hz.

Now suppose the speed of the generator tends to rise above the 220V mark, this would influence pin#5 of the IC which would correspondingly switch the LEDs marked with red dots (from LED#11 and upwards).

As these LEDs are switched ON, the corresponding dummy loads get added to the fray thereby squeezing the speed of the generator such that it gets restored to its normal specs, as this happens the dummy loads are again switched OFF in back sequence, this goes on self-adjusting such that the speed of the motor never exceeds the normal ratings.

Next, suppose the motor speed tends to decreases due to lower water flow power, LEDs marked with blue start shutting off sequentially (starting from LED#10 and downward), this reduces the dummy loads and in turn relieves the motor from excess load thereby restoring its speed toward the original point, in the process the loads tend to switch ON/OFF sequentially in order to maintain the exact recommended speed of the generator motor.

The dummy loads may be selected as per user preference, and conditional specs. An increment of 200 watts on each LED output would probably be most favorable.

The dummy loads must be resistive in nature, such as 200 watt incandescent lamps or heater coils.

Circuit Schematic




ELC Circuit using PWM

The second option is rather very interesting and even more simpler. As can be seen in the given diagram, a couple of 555 ICs are used as a PWM generator which alters its mark/space ration in response to the correspondingly varying voltage level fed at pin#5 of IC2.

A well calculated high wattage dummy load is attached with a sole mosfet controller stage at pin#3 of IC#2.

As discussed in the above section, here too a lower sample DC voltage corresponding to 220V is applied at pin#5 of IC2 such that the dummy loads illuminations adjust with the domestic loads to hold the generator output within the 220V range.

Now suppose the rotational speed of the generator drifts towards the higher side, would create an equivalent rise in potential at pin#5 of IC2 which in turn would give rise to higher mark ratio to the mosfet, allowing it to conduct more current to the load.

With increase in the load current, the motor would find it harder to rotate thus settling down back to its original speed.

Exactly the opposite happens when the speed tends to drift toward lower levels, when the dummy load is weakened in order to pull up the speed of the motor to its normal specs.

A constant "tug-of-war" continues so that the speed of the motor never shifts too much from its required specifications.




The above ELC circuits can be used with all types of microhydro systems, watermill systems and also wind mill systems.

60 thoughts on “Electronic Load Controller (ELC) Circuit

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Hi Swagatam,

    am doing project on automatic temperature control system that uses both K type thermocouple and operational amplifiers in a greenhouse . am an engineering student. The circuit has an indicator when the temperature has risen above 29℃ or fallen below 27℃. can you please help me with the circuit and all.please…

  3. Hi sir,
    I need a help in relation to my final year project.It is concerned with creating a micro model of a hydro power generation system.Is there any way to regulate the output voltage of an alternator according to a dip or fall in speed.is there any small alernator(12 v range) that i can use?

  4. Do you have a circuit for the resistance dividor network that can be used for this design?
    For the first method doesnt the loads have to be in binary weights?
    How do you calculate the wattage rating for the dummy load to use in the pwm based design?


    • for feeding the input of the LM3915 you can calculate the required resistor deivider network with the help of any online "potential divider calculator" software.

      The load wattage selection will need to be done through trial and error and by experimentation.
      for the pwm circuit, apply 220V from the generator across the bridge and adjusted the 10K preset such that the dummy load adjusts to negotiate this voltage and doesn't drop this voltage any further.

    • the switch can be used for selecting bar mode or dot mode, in bar mode all leds in the relevant level will light up sequentially giving a rising bar like appearance, whereas in dot mode only one led will be lit at the the particular instantaneous level producing a dot like of indication.

  5. The second picture the one with the domestic load didnt catch that where does that fit in?

    and what is the part in the first circuit Where it is written 'bar' and 'dot'

    Thanks a lot for support

  6. Sir in the circuit associated with a bridge rectifier which diode are we using and the transformer rating for the circuit? (Fig is from the top 3rd one).

    • all the information is given in the diagram itself, please check it again.

      the LM3915 circuit will require a 12V supply which can supplied through a standard ac/dc 12V adapter using a 0-12V/500ma transformer

  7. Sir can u explain what is this "from ac hydrogen"? can we use a normal 220 50 hz ac supply instead of that? and what kind of domestic load should we use? and why is that connected "to hydro gen"? position of the measurement devices also to be connected where sir?


    • yes three different sections will need to be integrated together as per the given instruction….in fact each pin of the IC will include individual mosfet stages and the loads.

  8. Good day sir! sir may i ask a few questions about the ELC. sir why is that our ELC becomes load instead of dummy load?.when we connect the ELC to the micro hydro system, it consumes the power from the generator and only few power can reach the consumers…?thank you and God bless!!

  9. Sir',
    What is the type of load used in the MOSFET switching module? Is it ac or DC load? And what is the use of of the rectifier with the 6A4 diodes? What does the "bar" dot. Component do and signify.
    Thank you for your wonderful support

    • The load can be any resistive load, such as incandescent bulbs, heater coils etc.
      mosfets work with DC therefore supply is given through a bridge rectifier.
      bar mode produces the output sequence in the form of latched outputs, whereas the dot mode shuts the sequence as it proceeds along the output pin sequence

  10. Sir,

    The MOSFET IRF480 requires a gate voltage of 3.6V to trigger but the IC output is only 1.9V is there an alternative MOSFET that can be used? and also is there any alternative power diode that can replace 6A4 diodes. Thank you as always for your support.

    • Riyaz, in that case you can replace the mosfet with a PNP transistor and relay stage. The relay contact can be wired with the dummy loads.
      If you don't want to use a relay then simply join the collector of the PNP with the gate of a N-mosfet (IRF540)….also dont forget to terminate the junction with a 1k resistor to ground.
      6A4 can be replaced by any 6amp diode or more.

  11. Hi swagatam thanks for amazing circuits.
    i have a question. the dump load can be normal incandescent bulbs of specific wattage. the dump load switching will be in steps for example 40W , 100W and so on. so there is possibility that voltage might not be exact 220V. how to obtain continuous variation in the dump load for exact 220V?

    • Hi Ankit, the dump loads should be of equal wattage across all the outputs of the IC, the range of the system could be increased or decreased as per the specs either by equally increasing the lamp wattage and vice versa…for large hydro motors large bulbs could be used and for smaller motors smaller bulbs, and so on.

      this will ensure a constant voltage and frequency from the system.

    • thank u swatagam. could u please send a more clear image of the circuit using ic 555 ?? because the values of all the components cannot be read out or else could you please provide me with the values individually? thank you.

    • Ankit, please click on the diagram to get an enlarged view of it and the enclosed details….the BC547 for the PNP is wrongly printed, please use a BC557 instead.

    • Dear Chandana,

      for fewer dummy loads you can use a single LM3915 IC and configure it identically….you can refer to the datasheet of the IC for getting more info regarding its working principle…

  12. Would the second ELC design with the IC 555 timer work when the generator is equipped with an Automatic Voltage Regulator?
    I suspect it would not since the voltage is kept constant by the AVR while the ELC design is expecting changes in voltage.

    • if the 555 section is powered with a feed directly from the alternator, then it would work, and anyway the above circuits are intended to work with the supply from the alternator directly.

  13. Dear Sir thanks for this very nice circuit,The second option ELC
    I have some questions. How do you power the +12vdc side?
    The diode AC Mains Have earth on the left side is that correct?
    On the AC Mains input is that from the Hydro gen Line and Neutral?

    • Dear Johan, you can get the 12V by using 0-12V/220V transformer and connecting it with the hydro generator output. The 12V AC will need to be rectified using a separate bridge rectifier and capacitor.

      the indicated bridge rectifier is for the mosfet load and needs to be made using high power diodes, and yes its left side should be connected with the negative of the circuit, or the mosfet source pin.

      the AC input is from the hydro AC

  14. Hey SWAGATAM, if my frequency goes down from 60 to 55 Hz , will ELC help to make it 60 Hz or it will just disconnect the generator to the load?

    • sorry that cannot be possible, if the motor speed itself is below the intended limit, then there's no way it could be rectified, unless some smart circuit is employed

  15. Hi Swagatam,
    I am doing an the same Electronic Load Controller project but with 300KW load. Can you please suggest me changes to the above circuit or a new circuit?


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