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Name: Steven
Status: Student
Grade: 9-12
Location: TX
Country: United States
Date: Winter 2009-2010

For any home appliance or electronics, let us say a television or refrigerator, what would be the effect if we provide under-voltage? What would be the effect if we provide over-voltage?

Hi Steven,

An overvoltage condition can result in damage to appliances and especially to electronic devices. An undervoltage condition usually causes no damage to most electrical or electronic devices; they just stop functioning correctly. Sometimes the device or appliance just quits working when the voltage gets too low, or sometimes (especially with electronic devices like computers) they start operating strangely. It all depends on the appliance or device in question.

Appliances with motors such as refrigerators or freezers act differently with an undervoltage. The motors in these appliances generally start to overheat, since motors tend to draw increasing current as voltage falls.


Bob Wilson

The answer is: it depends on the type of appliance, and occasionally the effort that the manufacturer put into protection against those conditions. Modern electronic devices such as PC's or TV's have switching regulators in them that compensate for variable supply voltage. Interestingly, if the supply voltage drops, those devices draw *more* current in order to automatically keep the device's power level constant, unlike non-regulated appliances like incandescent lamps. In extreme conditions, though, these regulated devices also often have over and undervoltage lockouts to turn themselves off.

Some older refrigerators could also overheat if the voltage were too high or low, but modern ones usually will turn off if the voltage is out of range. Electric heaters will produce more or less heat with supply variations during a heating cycle, but their thermostat controls will compensate and make this largely unnoticed.

Lastly, incandescent light bulbs are exponentially sensitive to over voltage and just a few percent of overvoltage condition can reduce lifetime by one half. However, undervoltage does not shorten their life, except for halogens, which do not last as long if the voltage is below a certain amount (they operate best at a fixed hot temperature). In contrast, most modern fluorescents, especially compact fluorescents, have electronic power controllers which regulate and protect them against minor variations in supply voltage (another exception: some fluorescents are meant to be dimmable and thus do not regulate, and they will get dimmer with lower voltage).

Paul Bridges

Steven -

For electronics, it is generally not recommended to vary the voltage up or down. The supply regulators in side will compensate for small variations, but if large enough, the equipment will start to misbehave and/or some parts could be overstressed. In modern stuff there is rarely any glaring inefficiency that would be improved by changing the voltage.

For motorized appliances, there is some interest in this variation. At home my refrigerator is plugged into a small box, which in turn is plugged into the wall socket, whose expressed function is to reduce the voltage a bit so long as the voltage and current remain in phase with each other. The inventor of this box studied AC motors and noticed that such motors, when driving a lighter mechanical load than their maximum, were basically holding off an un-needed portion of the AC voltage by means of the inductance in their coils or a subtle change in rotor phase. Reducing the voltage at lightly-loaded moments reduces the voltage drop across that inductance, which might save some energy. I have not proved that this box saves energy in my house, but it does not seem to have killed my refrigerator either.

Notice that this box is adaptive: if the motor gets a heavy load for a moment, such as when starting up, the box senses this somehow and does not reduce the voltage during that time.

Motors without electronics in control are probably going to get progressively rarer. In the meantime, there may be another couple of helpful electronic voltage-changing inventions to help them do their job better. If you know enough electronics to try some, try to set up to fast temperature monitoring, to sense sudden overheating quickly, to discontinue the experiment. There can be thresholds at which the power wasted as heat increases drastically.

Jim Swenson


Let us first assume the Over/Under Voltage is significant enough to have an effect. Not all Voltage excursions are large enough to effect performance of equipment.

A significant over-voltage would burn out the equipment and possibly start a fire.

A significant under-voltage would be sensed in the equipment shutting off. There is just not enough juice to keep the stuff running.

Lightning that hits the electrical power grid results in intermitted over/under voltage events And as you have probably already seen, the equipment flashes on and off which is probably most damaging.

Surge protectors in homes are important to protect televisions, home computers, microwave ovens from over-voltage surges, Uninterruptable Power Supplies (UPS) are important to protect from Over and Under Voltage excursions and provide protection for facilities that have large installations of computer and communications equipment, such as computer data centers.

Sincere regards,
Mike Stewart

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