In this article we discuss an easy to build a 7 stage high wattage in the order of 5000 to 1000 watts stabilizer circuit which can be used  for controlling our mains AC line fluctuations and for producing very accurate stabilized voltage outputs for our domestic electrical appliances.

Simulation and Working

The proposed Accurate 7 relay OpAmp Controlled Mains Voltage Stabilizer  Circuit concept is rather very simple. It uses discrete op amps wired up as comparators to sense the voltage levels.

As can be seen in the diagram, each opamp's inverting inputs are provided with sequentially incrementing voltage reference levels through a series of presets which drops a certain amount of voltage across itself.

Each op amp compares this voltage with the common sample mains AC voltage level supplied to the opamps non inverting inputs.

As long as this sample voltage is below the reference level the respective op amps keep their outputs low and the subsequent transistor relay stages remain inactive, however in case the voltage levels tends to shift from its normal range, the relevant relays trigger and toggle the transformer taps so that the output is appropriately equalized and corrected.

For example if the input AC voltage tends to fall, the upper relays may get triggered connecting the relevant higher voltage taps with the output and vice versa in case the voltage shoots upwards.

Here the opamp output inter-connections makes sure that only one optocoupler and therefore only one relay gets activated at a time.

Parts List

P1---P8 = 10 K Preset,

A1---A8 = IC 324 (2 Nos)

R1---R8 = 1 K,

All diodes = 1N4007,

All relays = 12 volts, 400 Ohms, SPDT,

Opto Couplers are all = MCT2E or equivalent,

Transformer = Pink Tap is normal voltage tap, the upper taps are in the decrementing order of 25 Volts, while the lower taps are in the incremental order of 25 volts.

Full circuit diagram of the proposed Accurate 7-Stage OpAmp Controlled Mains Voltage Stabilizer.

IC LM324 Pinout Details

LM324 pinout details

Circuit Diagram


220V 7 relay 5kva voltage stabilizer circuit

Upgrading into a Solid State Version using SSR


The diagram below shows a rather simple voltage stabilizer design which can hold huge output power in the range of 5 to 10KVA. The use of SSR or solid state relays makes the output stage easy to configure and very accurate - thanks to the modern SSRs which are designed to trigger massive power in response to smaller input DC potentials.

Circuit Description


The proposed circuit of a simple high capacity automatic voltage stabilizer circuit is easy to understand. All the opamps are arranged in standard voltage comparator modes.

The presets P1 to P7 can be adjusted as per the required tripping points, which will correspond to the output SSR switching and the subsequent transformer tap selections.

The central green TAP is the normal voltage output, the lower TAPs gradually produce higher voltages while the upper TAPs are set for lower voltages.

These TAPs are chosen by the appropriate SSRs in response to the varying AC voltages, thus adjusting the output voltage to the appliances close to normal levels.

This circuit was asked by Mr. Alexandar and the SSR data was provided by him.

Parts List


R1 to R9 = 1K, 1/4 watt,

P1 to P7 = 10K preset,

C1 = 1000uF/25V

VR1 = 1K Preset,

opamps = IC 324,

Transformer = Input 230volts or 120volts, Taps - incrementing/decrementing voltage levels (TAPs) as per individual specs.

SSR = 10KVA/230volts = output, 5 to 32 volts DC = input

Full circuit diagram of the proposed A Simple 5 KVA to 10 KVA Automatic Voltage Stabilizer Circuit @220 Volts, 120 Volts

Solid State SSR Voltage Stabilizer Circuit Diagram

10kva voltage stabilizer circuit using SSR

SSR Image


solid state relay SSR image



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