I have some probably entirely insignificant questions about chargers that’ve been bothering me. I don’t think the answers will help my electricity bill, but it would be fun to know how these things works.
My phone’s instructions tells me to connect the charger to the outlet first, and then to the phone. Why does this matter, and even if it did, wouldn’t it be better the other way around, so the charger doesn’t run on empty for a few seconds?
Everyone knows leaving the phone in the charger is bad. However, I’ve also heard that computers use less electricity while connected, which seems to make a bit of sense. Wouldn’t the same be true of phones?
“running empty” has no meaning. if there’s no load on the output (i.e. no phone connected) the charger does nothing.
this is untrue. mobile phones (and pretty much anything with a lithium rechargeable cell) have intelligent charging circuits which will stop charging when the cell is full.
I’ve always been told they do, and I know my laptop’s charger lights up whether or not the computer is connected, so it must use some energy. Also, why would the people who make my phone, who certainly must know what the charger is doing, bother to tell me to disconnect the charger, which they say is to save energy, if it doesn’t matter?
Well, “seems” “a bit” to me like they do. No biggie.
The no-load power draw from your phone charger will probably be 2 or 3 digit mW.
The handset makers have a star rating system for the no-load power requirements of their chargers. A 5 star rating requires 30 mW or less:
My phone just says “unplug the charger”, with no rationale. The message should make it clear that they mean to unplug the charger from the wall, not just to unplug the phone from the charger.
Still, I fall into the camp that says we are getting way too bent out of shape about “vampire power”. Get a more efficient refrigerator, think twice about your need for outside lighting, and don’t worry about a few power dongles for your consumer electronic devices, beyond unplugging them if it’s convenient.
It sounds like the voltage regulation in their charger takes a couple of seconds to settle out when it is first powered on. Sounds like a bad (or cheap) charger design to me.
Most chargers these days can run without a load without anything bad happening. They do waste a tiny bit of power doing this. As yabob said though I think a lot of folks are getting way bent out of shape over this while wasting significantly more power on other things than they will ever save by unplugging wall warts. If you are anal about unplugging all of your chargers you might save a buck or two over the course of a year. There are a lot more effective things you can do to help out the environment and cut down on the world’s ridiculously high energy consumption.
For most chargers and most phones, leaving the phone in the charger isn’t bad at all. It’s a slight waste of energy (not enough to be worth worrying about IMHO) but it won’t cause any harm to your phone or the charger, especially if it is a lithium ion battery. Those types of batteries tend to do very bad things if they are overcharged (like explode) so out of necessity the chargers are designed to shut off before they cause damage.
And if you are that worried about such a small waste of energy, why are you using a mobile phone in the first place? You could save a lot more energy by ditching the mobile phone completely. Most folks don’t really need to be in constant contact. You are wasting energy for a convenience then complaining about wasting a tiny amount more of energy on the charger when the phone’s not attached. Just seems silly to me.
I don’t understand what you are trying to say about computers using less energy while connected.
Also, one thing that kills the life of lithium ion batteries is having them run hot. Running a laptop off of a charger with the battery in it can shorten the life of the battery considerably, if the battery is getting hot. Most laptops do tend to run a bit hot. It’s one of the sacrifices they make to keep things compact.
If it is really taking a few seconds to stabilize its output, most likely it is never stable at all (having designed switch-mode power supplies, an unstable power supply typically results in an oscillating output voltage).
There is a surge when the charger is first plugged in that stresses a few components. If it is loaded (connected to the device) when this occurs, the stress is increased a little. Also, there are often some circuits that monitor the output for excessive voltage, and short it out if it is too highe (crowbar circuits). These don’t act instantly, and the most likely time for something to go wrong that causes over voltage is when first connected, so plugging into the wall first offers a little more protection for the device.
Probably because the tech writers had to write something. They can’t just say “it doesn’t matter which you plug in first,” because eventually someone will call tech support and demand a concrete answer.
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I don’t understand what you are trying to say about computers using less energy while connected.
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Just something I heard. Seems it doesn’t make sense, then. I wouldn’t know - not my field, hence this post.
Thanks for all the answers. As hinted to at the outset, I expected any excess energy use to be insignificant, but I was curious as to how these things work, as information seemed inconsistent. I have better ways of reducing my own footprint
Having a load connected when plugged in won’t increase the magnitude of the inrush surge; many switch-mode power supplies also take a fraction of a second (up to a second or so) to start up since they use a resistor to charge a capacitor until it reaches a threshold voltage, then the controller starts to run (this done so that you can use a very low startup current, then run off the capacitor until the output, and power to the control circuit, comes up). As for overvoltage protection, crowbar circuits are pretty rare to find these days in SMPSs; the controller instead senses its supply voltage (which comes from the same transformer, so tracks the output pretty closely) and shuts down if it gets too high (naturally this is slower; true crowbar circuits can operate in a microsecond, far faster than necessary to avoid damage). This assuming that there is any OVP at all, as many of the simple supplies used in chargers and the like don’t have any (some don’t even have overcurrent/short protection), so a failure in the feedback circuit will destroy the power supply and possibly anything connected to it (unlike linear supplies, a SMPS (flyback topology) can generate output voltages staggeringly higher, as in up to dozens of times, than the design output).
I’ve developed the habit of doing this the other way around, in that I connect everything up before turning on the AC power. It’s true that a poorly designed wall wart could produce a brief overvoltage condition when the AC power is applied, but if it’s designed well and the control loop is stable then this shouldn’t happen. That said, there are plenty of bad designs out there, and I suspect some butt-covering from yelimS’ phone manufacturers in order to minimise warranty claims from a known design issue.
On the other hand, plugging a DC source into an electronic circuit that’s decoupled with modern ceramic capacitors can produce a vicious voltage spike that can do some damage. This is due to LC resonance between the inductance of the DC cable and the input capacitance of the circuit being powered; it didn’t use to be a problem as until relatively recently the input decoupling capacitors had a relatively high equivalent series resistance (ESR) that provided enough damping to prevent any such spike getting too large, but now that large capacitance, low-ESR ceramics are widely available it can be a real issue. For the curious, here’s a white paper on the topic: http://cds.linear.com/docs/Application%20Note/an88f.pdf
In summary: Damned if you do, damned if you don’t.
On one occasion I’ve used a spike deliberately generated in this fashion to unfreeze a hotel TV that crashed on me. Turning the AC off and on several times didn’t work, so I plugged in the DC plug while power up and it rebooted nicely. I wouldn’t do this to my own TV, of course…
