Need help with AC voltage stabilizer

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Old 08-18-17, 07:19 AM
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Need help with AC voltage stabilizer

Hi,

I am from India and I have a very old 1.5 ton window AC connected to a 4KVA automatic voltage stabilizer. Both these things are like 15 years old.The stabilizer has two meters on the front, one for amperes and another for voltage with a button with which we can choose to see output or input voltage. We normally have around 230-240 volts on the wall socket in our area. When the stabilizer is turned on and the Ac is off, if i check the input voltage, it correctly has the needle pointing at 230-240, however the output always shows around 220 volts. When I turn on the AC, the input voltage drops down and reads 220 volts and the output further drops down and points to 200 volts. The amp meter reads 9 amps.

So far I have never worried about what the input and output reads because the AC has been working fine for about 15 years and cooling effectively. Just day before yesterday, We felt that the AC's airflow was not adequate and it was not able to cool effectively. I knew it was not a problem with the filters and cooling coil as I had recently cleaned them. I checked the stabilizer and saw that the voltage was little low by just 10 volts. What surprised me is the fact that without the AC running the input voltage was 220 volts and output was 200 volts. With the AC turned on, the input voltage read 200 volts and the output was pointing at somewhere near 180-190 volts and the current was at 10 amps.

Multiplying the previous output current and voltage readings and the new readings, everything seems fine as the AC's power consumption is near about 1800 Watts, but isn't the voltage stabilizer suppose to keep the output voltage in the nominal range? Why do I always see output voltage lower than the input voltage? Is it not working fine or are the meters just lying?
 
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Old 08-18-17, 07:56 AM
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What country are you in? .
 
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Old 08-18-17, 10:15 AM
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Originally Posted by ray2047 View Post
What country are you in? .
I am in India and the nominal voltage here is 240 volts
 
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Old 08-18-17, 12:42 PM
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What is the nominal rated voltage of the air conditioner? The reason I ask is that motors, particularly ones that run compressors such as in air conditioners, refrigerators, etc. don't like under voltage (voltage less than the rated voltage). When the voltage is low, the current draw goes up, which causes the motors to run hotter than normal. If the rated voltage of the air conditioner is 240VAC, unless you have wild voltage swings or power surges, you might be better off not using the voltage stabilizer and just plugging the unit directly into the outlet.

As for why the output voltage is always lower than the input voltage, it's impossible to say without knowing how the voltage stabilizer is designed. DC voltage regulators usually have a lower output voltage than the input voltage. A voltage regulator can't "create" voltage, only reduce it by whatever amount is needed to maintain a constant output voltage. As I mentioned, that is for DC voltage, AC voltage regulators aren't very common, at least not in the United States (I don't recall ever seeing one). AC voltage is normally stepped up or down using a transformer. However, short of using a Variac (variable transformer), usually the input/output voltage ratio is fixed, depending upon the ratio of the number of turns of wire on the input & output windings. It is possible to make an AC voltage regulator, however it uses PWM (Pulse Wave Modulation) technology to be able to raise or lower the output voltage as required. However, often these kind of AC voltage regulators don't output a nice sine wave, it's usually a modified square wave, which can bother some equipment.
 
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Old 08-20-17, 04:23 AM
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As long as the air conditioner starts at voltages down to 200 volts if the unit is still running there should be almost no effect on cooling performance.
The fan motor electronic components and compressor would run hot but it should still cool.

You likely have a problem with ac unit that doesn't involve low voltage.
 
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Old 08-27-17, 08:28 AM
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Thanks, for the replies. I can't really say what is the rated voltage for the air conditioner. Its quite old and I don't have any documentation that came with it. I don't even have a sticker on it anymore that can shed some light. However, regardless of what the voltage stabilizer is showing as input and output, I think it was a temporary problem with the power being supplied from the grid. The issue seems to have been fixed and the air conditioner is back to normal working.
 
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