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Is there any problem on pluging/unplugging simple devices to my power source that only require power (no data cable) while the computer is on?

For example :

  • Fans.
  • LED lights.
  • Water pumps intended for computing.

As can be seen, these devices have no data interaction with the computer or motherboard.
I assume that a hard disk must not be plugged/unplugged while the computer is running, but a hard disk has a second connection cable for data. That is not the case for devices like the above referred in the examples.

Is this operation supposed to be safe?

NOTE 1:
This question is not asking about devices like:

  • Hard disk drives (IDE, SATA, SCSI... etc).
  • DVD/CD internal drives.
  • USB devices.

The devices this question refers are only power-requesting ones, not "intelligent" and complex devices capable to maintain an effective communication with the software: they will not be detected by the operating system.

WHY SHOULD YOU NEED THIS FOR?
Basically, just to avoid the need for additional power sources to turn on/off things like:

  • Fans cooling the computer case or the external radiators that many people (like me) likes to manage in a manual way (turn it on/off whenever I want).
  • LED lights that you want to turn on only some times to check the inner computer (i.e: if you use liquid cooling it is good to check there was no spilling).
  • Water pumps: when you have more than one (I have 3 on my main computer) pumping the same circuit, you manage the speed of the water with the simple method of turning them on or off (I always have 1 pump running, and sometimes I turn on the others).
  • Peltier plates: they are 12 Volts devices, but they take too much consumption (15 Amps is not unusual), so you sometimes will want to turn it off.

NOTE 2: We are talking about plugging/unplugging devices to the power supply, not to the motherboard (or Fans to the graphics card... etc).

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    You will be taking a risk that there may be an electrical surge or charge.
    – Xavierjazz
    Sep 11, 2015 at 16:35
  • Why would you want to do this? Whenever I work on the inside of my computer, I make sure it's turned off, the PSU switch is off, it's unplugged, and that there is no obvious static charge on me. While I have admittedly unplugged a fan before when the PC was running to no negative side effect, it is high-risk and it's definitely not worth jeopardizing your hardware when you can turn off the machine. Hard reboots can be troublesome enough, let alone running the chance to surge the computer.
    – Daedalus
    Sep 11, 2015 at 16:51
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    In general, no it's not safe, because most internal power connectors are not designed in a way where they can't make half-assed connections during plug-in, and can't accidentally fall back onto the same (or near-by) pins, causing intermittent connections, power surges, etc. I've fried more than one HDD in my life because the Molex power connector accidentally fell back against the drive's power pins, making a big ZAP followed by a drive that won't spin up anymore. Sep 11, 2015 at 16:51
  • On the other hand, SATA power connectors were designed with hot-swap in mind, and can't just fall back into place and accidentally make connections. Sep 11, 2015 at 16:53
  • @Daedalus: added details to show why could this be used for. Basically just to avoid the need for another power supply for such devices. Sep 11, 2015 at 20:14

2 Answers 2

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LEDs and Peltier plates are perfectly safe to hot plug. It will create a very small voltage drop on the 5v or the 12v but any respectable power supply should be able to handle it. Peripherals connected on the same rail will see that voltage drop but they should not be that sensitive to voltage input. Even hard drives can take it.

Fans and Pumps contain an electrical motor. Not only will the voltage drop go lower but it also often causes a power surge when they pull their initial current. It MIGHT be safe to hot plug directly to the power supply but NEVER hot plug a fan/motor directly on a motherboard fan header. The surge will almost certainly cause damage to it!

Unplugging is never an issue unless the device you want to unplug is pulling high current, it could spark and damage the connector. Also remember that a power failure could harm certain devices. Most wont have a problem but hard drives, for example, could be harmed by a power failure.

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  • Indeed, I am not refering to the motherboard. Thanks you for remembering. I have edited the original question to make sure of it. Sep 11, 2015 at 20:22
  • What do you think about unplugging? Might it too be safe? Sep 11, 2015 at 20:23
  • What could you tell about Peltier cells? I have some 12Volts-15Amps and 12Volts-5Amps and (as edited in my original question) if it is not safe to plug/unplug them to the power supply, I will probably use some other external power source. Sep 11, 2015 at 20:25
  • Peltier plates should not be a problem. No motor or coil inside, no surge.
    – Alex G.
    Sep 11, 2015 at 23:48
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Unless the device/unit/part is EXPRESSLY compatible with being "hot plugged" (in or out) you should refrain from anything else than using the power button.

It is unavoidable to create power surges and spikes with the power on.

It takes two or three tries to catch a spike with an oscilloscope, using a simple cable-end (e.g. AMP) connector onto powered pins.

Whether the device in question has data connection or not is really not relevant, it is more about the sensitivity to glitch, surge, discharge and similar - i.e. current or rather energy rush.

The higher required energy to run and/or start the device, the more reluctant you need be.

The bad effects may also cause damage not only to the device you are handling, but also other devices in electrical vicinity of the connection you make.

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  • Maybe I was not clear enough: this question is not about hot pluging computing devices, but rather about hot pluging devices on the power supply of computers. I have edited the original question to reflect. Sep 11, 2015 at 20:15
  • Maybe I wasn't clear enough, ;-) - hot plug is a special case of what you asked for, and the only situation where you can feel safe. - moved rest of comment into answer.
    – Hannu
    Sep 12, 2015 at 8:31

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