Curious warning printed on a power bank - Page 1
Forum section: electronics / beginners

author: atmfjstc
author_rank: Regular Contributor
timestamp: March 24, 2019, 03:23:30 pm
content: My 10,000mAh powerbank has a warning printed both on the case and in the manual:"Do not use with wall chargers that exceed 1A output"by which it is referring to when we need to recharge the powerbank itself via its USB-like input port.My question is, isn't the charging controller inside this thing supposed to limit the charging current? Surely they didn't wire up the lithium battery directly to the input port? Obeying the directive would be quite inconvenient, as pretty much all of my chargers have 2.1A max output ports.

author: jeroen79
author_rank: Frequent Contributor
timestamp: March 24, 2019, 04:38:33 pm
content: That sounds odd.Could the instruction be mistranslated?Usually powerbanks are made to be charged from USB where the supply provides a fixed 5V.The powerbank then should not draw more than 500mA unless the supply signals that it can provide more current.What is the brand and type of your powerbank?Does it have a USB input or it's own supply?What does the powerbank draw if you give it 5V?

author: edpalmer42
author_rank: Super Contributor
timestamp: March 24, 2019, 05:43:09 pm
content: I've seen one cheap speaker/media player that charges from USB and has a small Lithium internal battery. A label says (translated from Chinglish) to limit the charging time to 3 - 5 hours. When I looked inside, all they did was put a single diode from +5V to the battery. This gives about 4V3 which is close enough for them.If your unit is similar, a discharged battery will suck huge amounts of current and burn out the diode.Ed

author: janoc
author_rank: Super Contributor
timestamp: March 24, 2019, 06:02:38 pm
content: Quote from: edpalmer42 on March 24, 2019, 05:43:09 pmIn that case that 10Ah capacity is likely completely fake as well.

author: edpalmer42
author_rank: Super Contributor
timestamp: March 24, 2019, 06:29:24 pm
content: Quote from: janoc on March 24, 2019, 06:02:38 pmI thought that all battery capacity figures that come from China are to be considered fake until proven otherwise.I bought a battery bank kit where you provide your own batteries. I used 4 18650 cells in parallel. I tested each cell and confirmed that they were in the range of 2500 mah each. In the bank, it takes ~10Ah to charge them, but I only get ~6 Ah out of the bank. So part of the discrepency can be attributed to differences in charge and discharge limits while part is due to inefficiencies in the circuitry. Add in battery capacity ratings that are often wildly exaggerated and there's no way to know what you're going to get.Ed

author: amyk
author_rank: Super Contributor
timestamp: March 24, 2019, 06:52:10 pm
content: Quote from: atmfjstc on March 24, 2019, 03:23:30 pm...yes, yes they did.This was the case for a lot of mass-produced media players roughly 10-15 years ago, although they also had a current-limiting resistor in addition to the diode.https://www.eevblog.com/forum/projects/lithium-batter-for-3-3v-circuit/?action=dlattach;attach=163889;image

author: atmfjstc
author_rank: Regular Contributor
timestamp: March 25, 2019, 12:39:19 am
content: Model number is HYC-25770-BLK , the brand name is "Hype" (a most fitting name methinks). I found a link here:https://www.newegg.com/Product/Product.aspx?Item=0ZK-0203-00001. It didn't come with its own adapter so yeah, you're supposed to charge it either from a computer or a wall adapter.In retrospect, it does seem like the kind of no-name trash where they really might wire up the battery directly to the input for all we know. I vaguely remember picking this up in an airport duty free somewhere. I've used it a good number of times on the road and the capacity, at least, does seem to hold up to what's advertised.I'll have to test the actual charging current some other time. I still need it for this week so I've fully recharged it in the meantime. Maybe when I'm done with it I can take the time to open it up and definitively solve the mystery.

author: magic
author_rank: Super Contributor
timestamp: March 25, 2019, 08:17:30 am
content: Quote from: edpalmer42 on March 24, 2019, 05:43:09 pmNot even a zener?I suppose the 4.3V is regulated by some internal battery protection circuit then but still... that's just pathetic. And it overcharges the cell so lifetime may be reduced.

author: janoc
author_rank: Super Contributor
timestamp: March 25, 2019, 12:31:45 pm
content: Quote from: magic on March 25, 2019, 08:17:30 amI have seen this too. Who cares that the battery may overcharge and go POOF on the user, proper charger IC costs a few pennies more than that diode/resistor ...

author: kjr18
author_rank: Regular Contributor
timestamp: March 25, 2019, 01:20:04 pm
content: Quote from: edpalmer42 on March 24, 2019, 05:43:09 pmI've seen these. When those batteries have built-in protection, then it's barely acceptable, but when they don't, then you should call them portable flame generating devices.

author: tkamiya
author_rank: Super Contributor
timestamp: March 25, 2019, 02:18:13 pm
content: Poor performance or out of spec products are one thing but total disregard for safety is very maddening. This behavior does not seem to be limited to electronics. Today's battery has so much energy density, when they burst, they burst like explosives.All of my UPS uses sealed lead acid batteries. They are at least predictable in failure modes. (like come home and all unix servers are down....)

author: edpalmer42
author_rank: Super Contributor
timestamp: March 25, 2019, 06:51:54 pm
content: Quote from: magic on March 25, 2019, 08:17:30 amNo, there's no battery protection circuit. The 4V3 is close enough to the maximum Lithium charging voltage of 4V2 that, as long as you remember to limit the charge time to the specified 3 - 5 hours, the batteryprobablywon't explode - at least for a year or two! But don't worry, the battery is small so itprobablywon't shatter the case!Ed

author: macboy
author_rank: Super Contributor
timestamp: March 25, 2019, 10:14:02 pm
content: Quote from: magic on March 25, 2019, 08:17:30 am...Both its lifetime and yours, should the battery overcharge and catch fire.

author: amyk
author_rank: Super Contributor
timestamp: March 26, 2019, 12:37:34 am
content: Before you scream your head off about the lack of safety, consider how many of these products are in use, and how many lion cell fires you've heard of...4.2V was the safe maximum charge voltage for a long time, but in the past few years there have become more common cells with 4.35, 4.4, and now even some 4.5V maximum voltages.Also look at the typical safety tests which cells are subjected to, in particular overcharging tests:https://www.jameco.com/Jameco/Products/ProdDS/2144243.pdf"Then charge the cell until voltage is 10 V(!) ... No fire, no explosion."High-power RC lipos are another thing altogether. Those can be deadly even with all the protection.

author: magic
author_rank: Super Contributor
timestamp: March 26, 2019, 08:59:18 am
content: Quote from: macboy on March 25, 2019, 10:14:02 pmIt depends. I've heard li-ion charging voltage is specified a fair bit below their "catch fire" point because getting them close to the "catch fire" point would significantly reduce lifetime.People on RC forums (of course) experimented with it and found that some cells can take 50~100mV above their spec and still work reliably and deliver some % of extra juice.Of courseit's not recommendeddo on your own risk

author: janoc
author_rank: Super Contributor
timestamp: March 26, 2019, 02:20:19 pm
content: Quote from: amyk on March 26, 2019, 12:37:34 amAnd you believe that the cells that go into crappy products like this, where every single corner has been cut, have been actually tested to this standard? Seriously?They are likely the cheapest piece of crap/rejects that the manufacturer could get somewhere and are probably a risk even if they were charged using a proper charger. That we don't hear about more fires is more likely because the item in question is so poorly built that it dies and is discarded long before the battery will go bang, not because this is somehow OK to do.