Electronic Load Controller Using Triac

In this post we investigate how a triac dimmer switch can be effectively modified to work like an electronic load controller circuit or an ELC for controlling hydro motor speeds.

In the previous post we learned an effective electronic load controller circuit using a sequential multiple dummy load switcher concept, here we discuss a much simpler design of the same using a triac dimmer concept and with a single load.

What's a Dimmer Switch

A dimmer switch device is something we all are familiar with and can see them installed in our homes, offices, shops, malls etc.

A dimmer switch is a mains operated electronic device which can be used for controlling an attached load such as lights and fans simply by varying an associated variable resistance called a pot.

The control is basically done by a triac which is forced to switch with an induced time delay frequency such that it remains ON only during a fraction of the AC half cycles.

This switching delay is proportionate with the adjusted pot resistance and changes as the pot resistance is varied.

Thus if the pot resistance is made low, the triac is allowed to conduct for a longer time interval across the phase cycles which allows more current to pass through the load, and this in turn allows the load to activate with more power.

Conversely if the pot resistance is reduced, the triac is restricted to conduct proportionately for a much smaller section of the phase cycle, making the load weaker with its activation.

In the proposed electronic load controller circuit the same concept is applied, however here the pot is replaced with an opto coupler made by concealing an LED/LDR assembly inside a  light proof sealed enclosure.

Using Dimmer Switch as ELC

The concept is actually pretty simple:

The LED inside the opto is driven by a proportionately dropped voltage derived from the generator output, meaning the LED brightness now is dependent on the voltage variations of the generator.

The resistance which is responsible for influencing the triac conduction is substituted by the LDR inside the opto assembly, meaning the LED brightness levels now becomes responsible for adjusting the triac conduction levels.

Initially, the  ELC circuit is applied with a voltage from the generator running at 20% more speed than its correct specified rate.

A reasonably calculated dummy load is attached in series with the ELC, and P1 is adjusted such that the dummy load slightly illuminates and adjusts the generator speed and frequency to the correct level as per the required specs.

This is executed with all the external appliances in a switched ON position, that may be associated with the generator power.

The above implementation sets up the controller optimally for tackling any discrepancy created in the speed of the generator.

Now suppose, if a few of the appliances are switched OFF, this would create a low pressure on the generator forcing it to spin faster and generate more electricity.

However this would also force the LED inside the opto to grow proportionately brighter, which in turn would decrease the LDR resistance, thereby forcing the triac to conduct more and drain the excess voltage through the dummy load proportionately.

The dummy load which is obviously an incandescent lamp could be seen glowing relatively brighter in this situation, draining the extra power generated by the generator and restoring the generator speed to its original RPM.

Circuit Schematic


Parts List for the single dummy load, electronic load controller circuit

R1 = 15K,
R2 = 330K
R3 = 33K
R4 = 47K 2 WATT
R5 = 47 OHMS
C1 = 0.1uF/1KV
C2,c3 = 0.047uF/250V
TR1 = TRIAC BTA41/600

10 thoughts on “Electronic Load Controller Using Triac

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Please sir, i want to design a 300w stereo amplifier circuit using bridged TDA7294 IC(which means i will be using 4 x TDA7294 to produce 2 x 150w for the two 8 ohms speaker i am having). But my question is, what should be the current rating of the 25v-0v-25v CT transformer to use so that i can drive the 4 x TDA7294 in bridge so that they can produce 2 x 150w in the two speakers? The datasheet recommended 25v CT transformer without indicating the transformer's current rating. Please help!

  3. Need a 1/2 HP pump controller which is start and Off the pump for 5 minutes on every day at specially at day time if power cut it works after Electricity become regular. It possible Swagatam.
    Rajib waiting for Ur answer.

  4. Please sir, how can i test the output voltage and current of a transformer using DMM. Can it be done with a bridge rectifier and capacitor or without it during the test? Please sir explain to me in detail on how to test for the transformer's voltage and current

    • select the AC high volt range on the DMM….and check the output of the trafo by directly connecting the prode to the trafo sec terminals.
      do the same for checking amps, by selecting the 10amp AC range on the DMM

    • it can be removed, it's placed just for eliminating RF noise into the air, so not so crucial, you can make the circuit even without incorporating the inductor

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