if you have an issue with something powered by electricity, why do you need to count till 5/10 when you unplug/turn off power before restarting it?
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Because of capacitors that hold a charge like batteries. These can keep a low powered circuit charged for some time. To fully reset something (remove all power) the capacitors need to discharge.
Capacitors and transformers need to discharge the energy they’re holding.
Flyback transformers on old tube televisions could be unplugged for days and still hold enough charge to kill you.
The comments about the capacitors discharging are true, but it’s always been funny to me that your tech support would tell you the power stuff off for a full minute, sometimes 5 minutes – they just know most people don’t have a concept of what 20 seconds is or that they will just popped the plug out and right back in and tell them that they waited 5 to 10 seconds.
Say you’re trying to fill a cup of water from a garden hose. The water might overfill the cup, or might get stronger for a sec and knock the cup out of your hand, or someone inside the house may start the washing machine and make the hose water suddenly drop for a moment.
So instead, you poke a tiny hole in a bucket, aim the garden hose into the bucket, and fill the cup from the water coming out of the hole instead. No matter what the hose does, the trickle leaking out of the hole is steady and consistent as long as the hose stays on.
Then you shut the hose off – but water still keeps trickling out of the bucket for a few until it empties out. You need to give it a 5 or 10 count until the bucket is completely empty, even though the hose has already been shut off.
Electronics often have these things called “capacitors” that are sort of short-term batteries. They hold on to power for a short time and need a few seconds for the power to drain out of them. You’re counting to make sure that all of the parts of the machine have no power and reset to their unpowered state.
I’ve been told to wait a minute by customer service agents. Is that too long? Is ten seconds sufficient?
Most of the household items that you use that plug in don’t run off of Alternating Current directly, it has to go through what’s called a rectifier to turn it to direct current. This involves capacitors that take on a charge and hold it at a certain level…and will maintain that charge for some time even after being unplugged.
The thing is, 5 seconds isn’t often enough to discharge, so here’s a tip : If it has a power button, after unplugging, press and hold the power button for 10 seconds. That will drain the caps.
Every now and then, power will trip for milliseconds, but you normally will never notice this thanks to the invention of capacitors. They store electrical charge while the appliance is connected and turned on so when the power is interrupted for a very brief period of time and then returned to normal, the operation of a item such a PC is not interrupted as if the PC has been shut off and you have to fully go through the power on sequence again, because the capacitor then releases this stored charge to bridge the gap between this brief period of no power.
Well the only issue with this, is quickly turning a PC off and on again will unlikely have any effect because the capacitator will be doing its regular job and keeping the PC running, which is why it’s recommended to switch off and wait 5/10 seconds before starting back up, and is also why it’s recommended to switch off and wait 5+ seconds before working on electrical items to allow time for the capacitor to discharge all stored charge
To allow stored charges from various components including capacitors and memory and such to dissipate. Switch mode power supplies especially can take up to 15 seconds to completely dissipate the charge they hold. That’s why your monitor lights blink for a while even when you pull the plug.
You need to wait a period of time before turning it back on to allow any capacitors (circuitry that holds power) to fully discharge. This is important in devices that store temporary instructions in volatile flash memory because information is only stored in this memory when the memory has power. When the memory loses power, the memory clears and whatever instructions that were causing a problem will be gone.
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