<1 second brownouts and electronics - Page 1
Forum section: electronics / general

author: grifftech
author_rank: Frequent Contributor
timestamp: April 20, 2017, 02:52:49 pm
content: Can a brownout that lasts for less than one second cause damage to electronics?The brownouts are caused by an AC compressor starting.

author: brucehoult
author_rank: Super Contributor
timestamp: April 20, 2017, 05:24:27 pm
content: If it's purely a voltage drop then I don't see how it could physically hurt them. A motor starting (or stopping) could well result in some high voltage spikes, in a general voltage droop.Of course a brownout could result in some things temporarily not having enough voltage to operate, and then resuming with settings in a corrupted state. That depends on the quality of the equipment and its power supply. I think it's been a common experience over the years to have a very short power outage or brownout in an office or classroom or home and all the Windows PCs reboit while all the Macs carry on as if nothing happened. At some point in the 80s I liked to demonstrate to people that I could move a Mac power plug from one wall socket to the adjacent one without the machine missing a beat. Of course in those days CPUs used so little power they didn't even have heatsinks. And they already had switch-mode power supplies that worked on 80 - 280 (?) volts, and so if you started on 240V you could lose 67% of the voltage in a massive brownout indefinitely with no worries at all.

author: james_s
author_rank: Super Contributor
timestamp: April 20, 2017, 07:10:36 pm
content: Properly designed electronics should account for this and not be harmed. That doesn't mean that everything is properly designed though. Some switchmode power supplies have been known to blow up when they experience brownouts, computers may reboot, microprocessor and microcontroller based devices may wind up in unpredictable states but probably won't be damaged. If a specific piece of equipment acts up you may try putting it on a UPS.

author: Red Squirrel
author_rank: Super Contributor
timestamp: April 20, 2017, 09:41:59 pm
content: The danger is when it repeatedly lowers the voltage on/off very fast and the UPS can't kick on fast enough or keeps kicking on/off fast too. Then the device at the other end ends up getting the brunt of it anyway. I'd say this is poor UPS design but I've seen it a lot even with APC. Though I never seen an A/C compressor cause it, but I have seen laserjet printers cause it. The computer will reboot or freeze and you can hear the relays in the UPS going crazy like it can't make up it's mind if it should be on battery or not. I had to tell my parents to turn the power bar to the UPS OFF before they print, so that the UPS can get a clean power cut and switch to battery, then they can print. (printer is not on UPS of course). It's always been an issue in their house for some reason but never experienced it here. My server UPS at home is probably less prone as it has a delay before it switches back to AC power, which is smart.

author: David Hess
author_rank: Super Contributor
timestamp: April 22, 2017, 03:43:31 am
content: In off-line switching power supplies, poorly designed soft start circuits can cause damage if they do not operate properly with an unstable line input. Another possibility in some circuits is latching into a inoperable state but this should not cause damage.Any UPS should be able to handle this and protect its load but as Red Squirrel mentions, some are better than others. A sure fire solution is an online UPS unless its own power supply fails and some online power conditioners that are effectively online UPSes without batteries have enough hold time to handle short brown outs. At one place I worked, I added capacitance to the input capacitors of the power supplies to increase the holdup time.I always thought it would be neat to rebuild an old online UPS to use super-capacitors for this type of application but the cost effectiveness is questionable compared to replacing the batteries.

author: Unknown
author_rank: Unknown
timestamp: April 22, 2017, 03:52:25 am
content: Quote from: David Hess on April 22, 2017, 03:43:31 amReminds me of flywheel UPSes, which are generally just used to hold the load until the generators start.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 22, 2017, 04:07:03 am
content: a.Check your wiring.One second brownout (V < Vmin) is too much, too long. You may have a fire hazard in the works!b. Or, your equipment isn't rated for sufficient "dips", and it is not staying on through an otherwise tolerable dip. Buy better equipment.Quote from: james_s on April 20, 2017, 07:10:36 pmNote that "proper design" includes IEC 61000-4-11 (for CE market) which should ride through such an eventwithout operational change. Let alone damage!I don't see why a dip should cause damage. Maybe a very frequently fluctuating line could cause overheating or fatigue of the fuse, causing it to open?Tim

author: grifftech
author_rank: Frequent Contributor
timestamp: April 24, 2017, 03:06:12 pm
content: Quote from: T3sl4co1l on April 22, 2017, 04:07:03 ama. I might have used the wrong termthe voltage drop causes lights to dim for a fraction of a second

author: David Hess
author_rank: Super Contributor
timestamp: April 24, 2017, 04:27:49 pm
content: Quote from: T3sl4co1l on April 22, 2017, 04:07:03 amI have seen at least two ways damage can be caused by the power dropping for just long enough:1. An improperly designed soft start circuit may not reset so when the power rises, it produces a hard start condition. An under voltage circuit which resets the soft start circuit will prevent this. I have seen many old switching power supply designs which deliberately crowbarred the control circuit power under these conditions forcing an orderly restart as if the power switch had just been turned on. Some used an actual SCR crowbar so power had to be shut off and then turned on manually.2. If an NTC inrush current limiter is used, it will not have enough time to cool off and when power is restored, it will be in a low resistance state allowing a much higher surge current risking damage to an input rectifier. I have seen this result in damage when someone rapidly turned the power switch on and off repeatedly.Both conditions are made worse if recovery from the momentary power dip involves a voltage surge.I have also seen a third way but the damage is not caused in or by the power supply. If the power sag is bad enough to cause the power supply output to misbehave, whatever is being powered may end up latching into a damaging stage. Power on reset and power good circuits are suppose to prevent this but some are better than others. ATX power supplies for instance have a power good signal which is suppose to reset the computer if the output voltages go out of regulation. I remember a dot matrix printer which suffered from this; if the power switch was rapidly turned off and on or a power line sag was just right, the driver for the print head would latch on and catch the print head on fire.Power supplies with active power factor correction should be a lot more reliable because they can actively control their input impedance and protect themselves but I have seen a few of them mysteriously fail for no apparent reason.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 25, 2017, 03:10:11 am
content: If equipment fails due to a 1 second Mains dip, the designers of such equipment should give their Degrees back, & become street sweepers!That said, what Ihaveseen, is SMPS with a high value resistor connected to the Mains "Live" to give a momentary "flick" to start the supply.Being high value resistors, these often go "high" to the extent that the start circuit no longer works.If the gear is continuously running, nobody notices this until a short Mains fail happens, when they refuse to restart.This is not really a failure caused by the mains loss, but may end up being recorded as such.The obvious guard against this happening is to switch the equipment off then back on under controlled conditions.That way, you may have to fix one device from time to time, but it's a lot better than 4 at a time!(Been there, done that, got the "T"-shirt---no fun at all!)

author: Kelbit
author_rank: Regular Contributor
timestamp: April 26, 2017, 03:28:57 am
content: As T3sl4co1l said, voltage dips & immunity are specified in IEC 61000-4-11 which products should adhere to.This documentdescribes the appropriate test levels for generic equipment (the actual requirements can vary for specific circumstances like medical devices) - see the below table from that document.The "Performance Criteron" is defined as the following:Level A: Performance within specificationsLevel B: Temporary degradation which is self-recoverableLevel C: Temporary degradation which requires operator interventionLevel D: Loss of function which is not recoverable

author: Red Squirrel
author_rank: Super Contributor
timestamp: April 26, 2017, 04:14:31 am
content: When I worked at the local hospital the power there was very unstable, really not sure why, but we'd get brownouts at least once a week. It would have the desktop support guy running around for a couple days replacing power supplies in computers and troubleshooting weird issues. The MDG computers were notorious for failing. Diablotek power supplies.

author: David Hess
author_rank: Super Contributor
timestamp: April 26, 2017, 10:58:03 am
content: Quote from: vk6zgo on April 25, 2017, 03:10:11 amThere is often a high value resistor after the input rectifier which charges a capacitor to provide startup power to the switching regulator control circuits. After starting, power is provided from the switching transformer.Unfortunately a lot of designs do not properly derate the startup resistor making it likely to fail.