Pros and Cons of leaving a multi-port USB wall charger plugged in?
September 5, 2013 6:43 AM   Subscribe

We use a multi-port USB wall charger to charge our various devices. I'm looking for information evaluating the pros and cons of leaving said charger plugged in with associated USB cables, versus unplugging the unit from the wall when not in use. Specifically I'm looking for info on the following:
  • any known power drain of leaving it plugged in but not charging any devices (significant? insignificant?)
  • risks (or conversely no risk) of fire from leaving them plugged in when not charging devices
We're trying to find the safest and most convenient configuration, and we're looking for some objective knowledge - please, no unsupported opinions "well, it should be fine" or "I wouldn't do it." We're really looking for known facts to help us make the decision.
posted by canine epigram to Technology (9 answers total)
My library offers "kill-a-watt" devices for checkout, which measure power usage of things plugged in. Might want to check that out for your first bullet point.
posted by unixrat at 6:48 AM on September 5, 2013 [2 favorites]

Without any more information (eg, model number) it's not really possible to answer your questions. I will say that virtually all modern USB wall chargers use switching power supplies which are ludicrously efficient and consume very, very little power when not in use. One possible rule-of-thumb is that if it says somewhere that it can be plugged into 110 or 220V outlets, it's probably a switching supply. Or you can grab a kill-a-watt and find out exactly what's going on.

Assuming this charger was made by a commercial company (and not, for example, by my electronics students), I wouldn't waste two seconds worrying about the fire risk, any more than I'd worry about leaving a toaster plugged in when I'm not using it.
posted by range at 6:55 AM on September 5, 2013

Some devices will trickle-charge if left plugged in, ensuring they're always at full capacity.

As range noted, there should be no fire risk, as such devices are designed and reviewed to ensure they operate safely. When fire risks are found for publicly available products, recalls are issued.
posted by filthy light thief at 6:59 AM on September 5, 2013

These things are basic AC to DC transformers, outputting 5 volts DC for power. They are the same as those transformers you find on all kinds of power cables, in terms of safety. If you're okay with regular transformers, you should be okay with this.

Transformers are century-old technology, and the main risk of fire occurs when they're drawing power and it's a vanishingly small risk. They could be damaged by surges as well, but most likely your power is conditioned to avoid this, and if you are prone to surges, you probably already know it from all the appliances breaking down or burning up.
posted by Sunburnt at 7:02 AM on September 5, 2013

I have my chargers plugged in all the time. If it were a fire risk, the units would not be certified for use (assuming you're not using some Chinese knock-off).

One thing I do use is a Belkin outlet timer--it sits between your plug and the wall, and can be set to pass current for a certain amount of time (I think, 30, 60, 90 minutes?) and then shut off.

I think the intended use is for your chargers, so if you wanted to charge your devices when you go to bed, it would then cut the power after the amount of time you select.

Personally, I use the Belkin thing in my kitchen to power off my espresso machine in case I forget. I do not use it for my chargers, which, again, have never (and I expect will never) burst into flames. There is some power drain, but I don't view it as material.
posted by Admiral Haddock at 7:05 AM on September 5, 2013

For a lot of information about USB charging, here's a detailed article titled "The Basics of USB Battery Charging: A Survival Guide."
posted by filthy light thief at 7:05 AM on September 5, 2013

For the question of idle power draw: This article is a good survey of power draw for a wide variety of chargers. The worst out of the 12 in terms of idle (no device plugged in) power draw uses less than half of a watt when idle. I'd be comfortable calling that "insignificant." Your charger might cost you as much as one dollar per year if its more than twice as bad (uses a whole watt) and if you leave it plugged in constantly. 1 watt * 0.001 kW/W * 365 days * 24 hr/day * $0.11 per kWH = $0.96. (It does add up to something significant if you have enough devices like this, though.)

As pointed out in that article as well, there are some very cheaply-made chargers out there, and they can be dangerous. Does the charger have an UL mark on it, though? If so, that indicates it meets a set of safety standards for electric devices. (Or, to be honest, it can just mean that the manufacturer is lying, but that is unlikely for any sort of recognizable brand open to lawsuits.) With anything plugged in, there is always some risk of fire or electrocution, but heck, there's some risk of electrical fire even if nothing is plugged in anywhere in the house. If the device is UL certified, then there's little to worry about, and even if it is not, the risks are minimal.
posted by whatnotever at 12:21 PM on September 5, 2013

[In my experience, that Belkin outlet timer mentioned by Admiral Haddock upthread is more likely to be a problem than a solution. I was awoken one night by the smell of burning plastic, and when I went to unplug the thing, it was so hot it almost burned me. I shudder to think what would have happened if I had been sleeping a little more soundly.]
posted by Corvid at 3:17 PM on September 5, 2013

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