Jan 062013

Voltage stabilizers are designed to feed constant voltage current to household appliances, incl. refrigerators, air-conditioners, etc. The stabilizer is constructed by means of a toroidal autotransformer, contact regulator – servomotor, actuator, control and protection circuit. When changing the input voltage, the motor sets in motion the movable arm of the contact regulator and provides stabilized output voltage. The regulator needs to be precise, to make fast corrections, to have small consumption and provide long-lasting service. The device can be equipped with different type of protection – delayed start after dropping of the voltage, protection from high or low input voltage, overload protection by automatic switches with C-curve, etc.

Main characteristics:

– Input voltage range – 165 ÷ 245VAC.
– Steady output voltage – 220VAC ± 4%.
– Rated frequency (Hz) – 50Hz/60Hz
– There may be simultaneously 220VAC steady voltage and 110VAC output voltage.
– Protection from lower than 165VAC and higher than 240VAC input voltage
– Delayed switch of output voltage – 1 or 5 minutes for sensitive
consumers such as refrigerators and air-conditioners – yellow switch.

– Indication of the value of the input and output voltage.
– Regulation speed ​​ (V / s) – <1s (when the input voltage has a change of 10%)
– Effectiveness, Efficiency -> 90%
– Power factor cos φ ≥ 0.9
– Operating temperature – 10 ° C ÷ +40 ° C
– Relative air humidity – <90% RH (non-condensing)
– Overload protection – two automatic switches with C-curves

The circuitry of precise AC voltage stabilizers with power range 0.5kVA to 10kVA is shown in Figure 1.
Load curve (Figure 2):
P-Output power
Pe-Rated Output Power
U- Input Supply Voltage
Ux-Lower limit of minimum input voltage
Us-Upper limit of maximum input voltage



Figure 3 – General view

1 – Box

2 – Operating mode switch

3 – Panel

4 – Distributor-box cover for cable connections

5 – Opening for the input and output cables

6 –Mounting bracket (hook )

7 – Voltmeter 8 – Input voltage indicator

9 – Delay Indicator when the stabilizer is switched on

10 – Low input voltage indicator

11 – High input voltage indicator

12 – Time delay switch when the stabilizer is switched on

13 – Switch for voltage measuring ( Input/ Output )

14 – Operating mode selection switch – stabilized / non-stabilized

15 – Switch for enabling protection from low input voltage.


Installation and use:

Choose a dry, well-ventilated location in proximity to the dashboard meter. Using conductors with proper size and color, connect „phase „, „zero“ and grounding to the input of the voltage stabilizer. Lead to the load „phase „, „zero“ and properly sized ground conductors, consistent with its power. Example connection scheme is shown in Figure 6.


When the load is active, the stabilizer can be loaded with its full rated power, but if the load is explicitly inductive or capacitive, the loading must not exceed 33 % of the rated output power of the stabilizer! If a load with inductive or capacitive nature and power close or equal to the rated power of the stabilizer is connected, it will damage it because this type of consumers have a large inrush current and reverse voltage when switched off!

If the consumers are refrigerators or air-conditioners, the delay switch for the output voltage has to be set in position „long delay – 5 minutes „.  Then the automatic fuse must be turned on in a stabilizer position and the device will start regulating. If voltage regulation is not required, you can switch the automatic fuse to position“ direct output voltage“ but before that you need to switch off the stabilizer. If turning off the stabilizer becomes necessary, first you need to turn off the consumers and then the stabilizer. If the input voltage exceeds 240 ± 4V or is less than 165 ± 4V, then the stabilizer will automatically turn off and when the input voltage gets back to normal, the stabilizer will automatically switch on and will continue regulating.

If the switch for high / low input voltage is set to „NO“ position , this protection will not be activated if the voltage is less than 165VAC, but this hides risks . When the arm of the contact system is actuated the stabilizer makes noise and releases heat, especially when fully loaded. The stabilizer must not be covered with cloths, clothes or blankets as this will impede its cooling down. After continuous operation time, ask a specialist to remove the dust and dirt on the toroidal transformer and on the brush holder. If you notice anything unusual, turn the stabilizer off and call a qualified technician or contact your supplier.

Symptom / Problem / Cause / Solution

No voltage stabilization.

1. There is a problem with the actuator of the servomotor.

If the motor cannot actuate the movable arm, although it spins and there is voltage, it must be replaced.

2 . The input voltage is beyond the limits of regulation. Check if any of the protections have been actuated. If so, please wait until this protection automatically resumes the work of the stabilizer. If this doesn’t happen, turn off the stabilizer, wait for 10 minutes and then turn it on again. If that doesn’t work either and the motor lacks voltage, check the setup and protection board. If the problem cannot be easily removed, please replace or repair the setup and protection board.

No output voltage.


  1. The main circuit-breaker.
    Turn on the main circuit-breaker. Check whether the cables are connected correctly and securely.
  2.  Error or burnt mini-fuse due to overload.
    Restart the stabilizer, replace the fuse and reduce the load.

The stabilizer operates but there is a deviation from the values of the steady voltage.

  1. The potentiometer for regulating the output voltage is not set up.
    Set the desired value of the output voltage by means of the potentiometer for setting-up.
  2. The indications of the voltmeter are not correct.
    Replace or repair the voltmeter.

The stabilizer coil has burnt.
1. The power of the fed load is too high, beyond the capacity of the stabilizer.
Take special care and check the installation location and the value of the output voltage when changing the coil or the transformer.

Sometimes the device makes noise while operating.


1. The frequent change of the supply voltage leads to constant setting of the output voltage towards the input voltage.
Only the output voltage is a steady nominal one. It is usual for the stabilizer to make noise, which is caused by the movement of the arm and the servomotor.

The voltmeter pointer constantly moves and sparks come out of the brushes.
1. The contact between the brushes and the surface of the coil is too weak and there is distance between them. Use very fine sandpaper to clean the surface of the coil and the brushes.
2. The brushes are worn. Replace the brushes.

You can find on the market the so called „Relay-operated voltage stabilizer“ at a surprisingly low price. We do not recommend the use of this type of stabilizers for the simple reason that they don’t have a servomotor and the regulation is done by switching relays. This process causes impulse interference in all appliances, connected after the stabilizer, after each switching of the relays, and this happens with every attempt to regulate the voltage. In addition the accuracy of these „stabilizers“ varies in the range of + / -8%, which means 17.6 volts deviation at 220 VAC. In short, this isn’t a real stabilizer and we don’t recommend the purchase of such a pseudodevice, regardless of the tempting low price.


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