Abnormal heat when charging phone from powerbank

Arklight

Hi,

I do this pretty rarely, but the last few times I have used my rechargeable powerbank to charge my smartphone it has generated a large amount of heat in the phone.

The circumstances are generally:

1) Phone battery is very very low
2) Usually travelling on a long train journey with patchy signal
3) Sometimes the powerbank can't charge the phone as fast as the phone is draining, so despite drawing current the phone's battery continues to deplete
4) The heat is far in excess of normal, almost too hot to touch

I should stress the heat buildup is in the phone not the powerbank. Even after unplugging it right away the heat continued for some minutes

The last time it happened I think it damaged the battery on my phone, as after that, and then forgetting about it and leaving it on the dashboard of my car on a summers day, the battery was never the same again.

I haven't used a powerbank since and was wondering if this is normal for these battery packs, and if they are safe to use in general.

I have a new phone now and don't want to damage its battery while playing Pokemon Go!

kwikbreaks

The power bank is just a source of energy and it's up to the phone's charging circuit to limit the current drawn. With a poor signal the phones radio transmitter is working at its highest power if you then add in the charging current that probably accounts for the high temperature.

It's possible that the phone designers assumed that you'd be using the supplied charger with a lower available maximum current. If so that was a poor design decision.

My question here though is why you continued to let the thing charge if you thought is was getting dangerously hot. Li-ion batteries have a track record of catching fire if subjected to abuse. Or even when not in the case of cheap ones such as those in the now banned hoverboards and there is at least one youtube video of an e-cigarette catching fire in a trouser pocket.

Fightsback

Good article here explaining what happens with Li-ion batters regarding heat:

http://electronicdesign.com/boards/keep-eye-temperature-trends-during-li-ion-battery-charge-and-discharge-cycles

The phone with remain hot due to latent heat, i.e. the components within the phone have heated and release that energy gradually.

How is the phone when charging from a 2A (not 500mA) wall charger, is it getting very hot ? This could be a sign that your battery is failing, increased internal resistance of the battery but for the same current gives a higher heat dissipation. What model phone, what model powerbank and how old is the battery in your mobile ?

Arklight

It was a Sony Z1 Compact, never had any issues with wall charging.

The Powerbank is a Pebble, now pretty old. I am wondering if the fact that the phone was discharging while being charged was the cause of the heat?

I wont use the Pebble again anyway.

Fightsback

Arklight wrote: »

I am wondering if the fact that the phone was discharging while being charged was the cause of the heat?

Quite possibly as that phone has a Snapdragon 800 and if you are gaming (or some other high power activity) and high current charging at the same time then perhaps a lot of heat will be generated. It's not an experiment I've conducted myself to confirm the idea.

kacie

try changing the cable, I had one that would get hot when charging my phone and didn't work well, changing the cable reduced the heat and made it charge better.

forgotmyname

Get a little USB volt/amps tester. Only a couple of £ and it shows the voltage charge rate.

Strider590

By their nature, power banks can supply a greater charging current than OEM chargers.

Firstly they usually have short charging leads, this reduces the voltage drop between the power bank and the phone.

The other thing they have is what's known as a boost converter circuit, to take the 3.6V battery and boost it to 5v. Boost converters are very good at maintaining a stable output voltage, so where the charger might drop to 4.8v at say 900mA (causing the phone to reduce the charge rate), a powerbank would probably maintain a higher voltage, causing the phone to charge at it's maximum rate until full.