Help me understand power banks.

[tim...]

I have (elsewhere) previous been recommended to buy a power bank to uses as an emergency back up for my portable devices.

Which, because I have a candy bar phone with a standby time of 3 weeks, means my tablet and camera.

I was in a shop today, saw one on sale with "for smartphones and tablets" at a reasonable price and bought it

but after I looked at the back it said output 5V 1A.

Oh!

ISTR that when I bought my in-car USB charger I got one for phones and had to take it back and get a higher rated one for Tablets. And even then, one of my tabs reports that it isn't powerful enough to "charge" the device, though experimentation shows that it does keep it operating for a bit longer. Plugging my camera in and it doesn't even notice that there's a charge there.

So I went into all the other shops in the high street to see what they had (lest I should want to take the purchase back whist I was still there) and all of them, with one single exception were output 5V 1A, that exception was fugging expensive and more importantly 3 times the dimensions and 10 times the weight of the one that I had bought. I particularly wanted a small, lightweight, fits in your pocket example.

Back home I looked at my plug in the wall USB chargers, which I (successfully) use interchangeably on all my devices and one says output 5V

2A and the other output 5V 1A.

What's going on here?

what rating do I need to charge my device(s)

I did a quick Google to see if I could find out and found "5 Key Things To Know When Buying A Power Bank" and one of them is "When you buy a portable power bank, make sure that it can charge the battery of a specific device" Yeah, I know that? But how do I find out what that requirement is - I came here expecting that you were going to tell me as the manufactures of these devices keep it as secret as the coca cola recipe (I have been online and downloaded the full specs).

So the item in question is still in its unopened box with all the seals intact (as it's from one of these shops that aren't the best for taking stuff back to). do I take it back and seek out a more powerful one, or open it and try it, and risk the shop refusing my returning it?

tim

[Bill Wright]

You can't miniaturise the Watt

Bill

[Dave Plowman (News)]

Do all those devices have a 'standard' USB 5v charger as supplied? None of my laptops etc do.

[Another Dave]

The key figure is the capacity, measured in milliamperehours (mAh), typically on the cheap power banks 1200mAh. It will be stated on the packaging somewhere.

The 5V is the standard voltage for USB and 1A is the maximum rate at which it can charge your phone. So at 2A the phone will be charged in half the time it will take at 1A (assuming the phone can take it which I doubt).

The cheap power banks seldom have the claimed capacity but, for emergency top ups, does it matter that the phone will only be charged to half its maximum?

Another Dave

[Another Dave]

The key figure is the capacity, measured in milliamperehours (mAh), typically on the cheap power banks 1200mAh. It will be stated on the packaging somewhere.

The 5V is the standard voltage for USB and 1A is the maximum rate at which it can charge your phone. So at 2A the phone will be charged in half the time it will take at 1A (assuming the phone can take it which I doubt).

The cheap power banks seldom have the claimed capacity but, for emergency top ups, does it matter that the phone will only be charged to less than its maximum?

Another Dave

[Tim Streater]

You need to look, for each device, at the charger you already own for that device. My iPhone charger is a plug with a USB connector plugged into it, giving 1A at 5V. This *should* mean that I can charge the iPhone from any *other* device that I can plug the USB cable into, such as my Mac or my Dell display or even a disk drive with a USB socket. In fact, SWMBO regularly charges up *her* iPhone from her Dell display.

AFAIK, such sockets are rated at 5V, 1A max - that's the spec. This should mean that my iPhone when charging won't draw more than 1A, but I don't know whether devices are clever enough to "try it on", try sucking out more than 1A and look for voltage sag, give up if so.

So if the devices you want to recharge on the go have a charger cable with a USB connector, it should work from any power bank with a USB socket. As you've already noted, the size/cost of the bank just indicates how many recharges you can get from the bank.

That it's rated at 5V 2A won't make your device charge any faster (unless see speculation above). It may allow two devices to be charged at once, instead of one.

[tim...]

The difference is prices/size is to do with the capacity of the battery, sure

But I'm not bothered by having a power store that will only re-charge my device once, rather than 5 times.

It's the possibility that a low power output doesn't charge it at all, that's the problem

[tim...]

the tabs do

The camera came with an external charge unit that you insert the battery into to recharge it, but also accepts a USB charge whilst in situ in the camera - Plugging in either of my tablet USB chargers recharges it so I have never ever taken the battery out of the camera, through trying to charge it from my car USB port resulted in a failure to charge

tim

[tim...]

I understand that, it is 2000, the expensive one was 10,000 - enough to recharge a device 4 or 5 times. But I don't need that.

I'm not concerned by the battery capacity, it's the output current that's the issue here.

The devices are tablets, some of them (apparently) wont charge at 1A.

Nope, not a problem, as long as it works I don't care how inefficient it is. I really am only going to use this as an emergency back up whilst out during the day, not as a strategy to avoid plugging my tablet in every evening at the hotel (or at a location where I'm not staying in a hotel).

I am only concerned that it may not work at all.

tim

[tabbypurr]

do you need an emergency power backup for them?

Sounds like a no.

[tabbypurr]

Meet the pmpo watt, a truly miniature watt.

NT

[tim...]

for the phone no

for may camera and tablet

yes

tim

[charles]

Certainly the case with my iPhone

[Bob Eager]

But still larger than the Sinclair watt.

[Brian-Gaff]

Well, you can have a higher current for a short time or a lower current for a longer time, and hence you won't get a good battery that is lightweight if you need it to charge or power something for a significantly long time. This is the one problem with batteries I suppose.Also not every bit of kit will charge faster than its allowed to, look What happened when Samsung made their phone charge faster on sub standard batteries. Personally I'd take it back and get a larger device, something that maybe you wear as a belt with more oomph behind it, as long as your devices can charge faster, otherwise its not really going to make a lot of difference. Brian

[RJH]

That would only matter if you wanted a faster charge - is that what you're after? If so, yes, you're right, higher current. But IME it doesn't always work that way - some devices seem to 'choke' the input.

I've not heard of that. My iPad charges fine (if slowly) from a 1A charger. I can't explain why you had issues with the car charger.

It should work. Could you try with a 1A mains charger?

[Harry Bloomfield]

Iphones can be a bit picky about the sources they are charged from, mine is and complains, but still recharges slowly.

[Harry Bloomfield]

RJH was thinking very hard :

Each part, the charger and the thing being charged, defines its own maximum current - it is the lower of the two figures which defines the charge level.

[newshound]

Very slowly. I think that is a standard Apple marketing ploy, IIRC our original iPad was similar.

*Apart* from Apple, I think devices will charge at 1A on a 1A charger, 2A on a 2A one (if they are rated for 2A). Just takes twice as long on the 1A version.

At least we are moving to a civilised world where a high proportion of devices will charge either off 5V from USB, or 12V. And we have the EU to thank for phone chargers.

[Dave Liquorice]

Apple make products that are "fussy" about what they will consider to be a suitable energy source for charging. Various combinations of resistors between the wires an/or ground IIRC.