1
\$\begingroup\$

I live in Cambodia and power outages here are not uncommon.

One of the things I have noticed today that devices like kettle or induction heater would switch off after working for 10-20 seconds. I am assuming this is due to low current (or maybe lack of potential) in the power line. Does low current damage equipment? If yes which household supplies should I switch off not to cause permanent damage (fridge, tv, PC, etc), or should I just keep switching kettle on and make some coffee?

Does low power in the mains cause damage to household supplies? If it does should I disconnect any of them?

\$\endgroup\$
  • \$\begingroup\$ No, "low amperage" does not destroy your devices. That's nonsense. btw. I assume you meant low voltage. \$\endgroup\$ – Al Kepp Dec 8 '17 at 1:37
  • \$\begingroup\$ @AlKepp Hi Al, could be I am not very good with electrical stuff. I know you get watts by timing amps and vats. So I guessed there was not enough supply, but it could be something else... \$\endgroup\$ – Matas Vaitkevicius Dec 8 '17 at 1:41
  • \$\begingroup\$ @NateEldredge Hi Nate, would it make difference to damage caused to devices if it would be lack of potential instead of lack of current? I have no equipment to check... \$\endgroup\$ – Matas Vaitkevicius Dec 8 '17 at 1:55
4
\$\begingroup\$

Low voltage can definitively damage electronic equipment, such an induction heating equipment controls. The low voltage may very likely cause the equipment internal power supply to try to draw more current, which could result in overheating and possible equipment damage. Anything that contains electronics should not be supplied with voltages lower than the rated input voltage stated on the nameplate.

Resistive equipment such at resistance heaters will not be an issue.

It is not nonsense.

\$\endgroup\$
3
\$\begingroup\$

Low voltage can cause a lot of different kinds of electrical equipment to fail.

We had problems with low voltage in a house I lived in long ago.

We had to replace the motor for the water pump several times, and the heating elements in the oven and stove burned out.

That last sounds stupid. How does something that is supposed to get hot burn out because the voltage is too low? It wasn't the elements themselves, but rather the connectors. The heating elements draw less current when hot, but due to the low voltage didn't get hot fast enough. The connectors were therefore carrying higher current for longer than intended, and they got hot and burned out.

\$\endgroup\$
2
\$\begingroup\$

Devices such as AC LEDs have a wide input voltage rating, but if they drop below this then more input current must be drawn to regulate the output. This extra current can raise temperature and damage inexpensive designs.

Any devices that need a certain voltage to function properly will cut-out safely . Any designs that self-heat like AC motors stalling with 60% line voltage might be possible in a severe brownout when started in this condition, but you might know it. The biggest risk as I recall my brother's experience in Uganda is the re-closure of poorly balanced 3 phase lines can cause some farms to get excessive voltage that are lightly loaded. He said all his appliances got smoked. circa'80's

I had the same thing happen to my staff, when inside the factory after a power failure, our loads were unbalanced and power supply on the lighest load phase got 30% surge voltage on startup and broke the CA Marathon ATE tester... after repairs, we told maintenance to rebalance the drop cables off each phase.

\$\endgroup\$
  • \$\begingroup\$ Unbalance or missing neutral opens an entire new can of problems. I recommend an phase/voltage monitoring relay with breaker trip for such occasions. \$\endgroup\$ – Jeroen3 Dec 8 '17 at 8:23
  • \$\begingroup\$ Normally residential failures are before the Dist Transformer so surge is a greater risk from other neighbourhoods using the other 2 phases drawing more start up current. Thus the missing neutral is a low risk but an overvoltage peak hold DMM is a great idea. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Dec 8 '17 at 8:31
1
\$\begingroup\$

It's possible to design pathological equipment that fails under low voltage conditions, as an exercise in 'what not to do', but generally any design that has started life like this will have been caught by testing, and modified before it gets to customers, so that it 'fails safe' under low voltage.

A good way would be to have a heat generating mechanism that works at all voltages, and a cooling mechanism that fails. For instance, a motor cooled by a fan on its own shaft, that fails to turn at low voltage.

A kettle is such a simple device, that my first thought was 'yes, you can make coffee at any any voltage'. However, if you leave it unattended, the automatic switch-off might require a certain minimum rate of steam flow to send enough steam down to the thermal switch (mine does), so it could boil dry. But then all kettles (should) have an overheat cutout as well, that will switch off if boiled dry.

There's an interesting class of motor that will overheat if run at too low a load! Think about that one for a moment. It's a particular type of induction motor, and at low load the speed rises to near synchronous, so the slip frequency drops so low that the armature saturates and draws excessive current. Not all induction motors behave like this.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.