Peter-
In general, most electronic devices are fairly tolerant of undervoltage, as many of them use switching power supplies. The power supplies will continue to operate happily until some low voltage, at which point many will simply refuse to start up. High voltage can be a problem, causing things like rectifier diodes, bulk capacitors, and switching transistors to (typically) short. Here in the United States, we sometimes have electronic devices with "universal" power supplies that can tolerate 90 to 250 volts. For these devices, overvoltage on our 120 volt power systems would be no problem. AC motors driven directly off the line are probably the most susceptible. At overvoltage, they will get hot and may fail due to insulation breakdown or a thermal fuse going open. At low voltage, they may also fail if not thermally protected in certain cases. Personal case in point: I have a 1976 vintage heat pump that heats and cools my house. About 20 years ago, there was a fire in the local power substation which caused the power line voltage to drop from 240 V to about 150V. The heat pump was running at the time. The voltage was high enough that the power relays stayed closed, but low enough that the compressor stalled. In this stalled condition, there was no cooling for the compressor (via refrigerant flow), the compressor overheated (no thermal protection) and it had to be replaced. I assume modern heat pumps have low voltage shutdown. On the other hand, an AC motor device like a fan would probably not have a problem. Many multispeed AC fans use motors with multiple windings. The low speed winding has more turns, effectively running the fan on what amounts to reduced voltage, thus reduced voltage is not a problem. The key difference is the nature of the mechanical load on the motor. The compressor works against a fairly contstant system pressure. The load on a fan motor decreases quickly with reduced speed. Also the motors are different - the compressor motor is designed (for efficiency) to operate with low slip from synchronous speed. The fan motor is designed to operate with high slip when necessary to achieve the lower operating speed. Incandescent light bulbs are perfectly happy running on low voltage. But at high voltage, their life goes down quickly, as life is inversely proportional to the 12th power of the applied voltage! Don Borowski Schweitzer Engineering Labs Pullman, WA Peter Merguerian <[email protected]>@majordomo.ieee.org on 12/05/2002 01:06:28 AM Please respond to Peter Merguerian <[email protected]> Sent by: [email protected] To: "\"EMC-PSTC (E-mail)\" <"<[email protected]> cc: Subject: Undervoltage/Overvoltage Effect on Household Appliances Dear All, I am interested the damaging effects on components of electrical household appliances as a result of overvoltages and/or undervoltages. As an example, what are the types of components that would be damaged in a TV or personal computer from an undervoltage or overvoltage in the electric power line? Every household appliance may have different components and I am intersted the effects on as many appliances as possible (refrigerator, vacuum cleaner, TV, lawn mower, jaccuzi, electric shaver, lighting power supplies, fans, etc. etc.). Thanks as Always, PETER S. MERGUERIAN Technical Director I.T.L. (Product Testing) Ltd. 26 Hacharoshet St., POB 211 Or Yehuda 60251, Israel Tel: + 972-(0)3-5339022 Fax: + 972-(0)3-5339019 Mobile: + 972-(0)54-838175 http://www.itl.co.il http://www.i-spec.com ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
