Follow-up: USB Power Bank Tested and Repacked (5000mAh, 30000mAh)

I did some quick teardowns of the 5000mAh and 30000mAh power banks previously, and I found that the 5000mAh power bank seemed to be genuine, but the 30000mAh power bank is a bit unknown. One reader reported disappointing performance from the power bank, and I would be inclined to agree after some more extensive use.

But it’s hard to find out exactly how good or bad they are, without testing them under controlled conditions. Thanks to the element14 RoadTest program, I was the lucky recipient of a Keithley 2110 5.5 digit USB and GPIB Digital Multimeter which was perfect to run this investigation.

Test Setup

I built a configurable 2.5 ohm and 5 ohm equivalent ceramic resistor pack as a dummy load, hooked to the end of a piece of scrap USB lead. Measurements of voltage and current were taken once a second (roughly) with the dual-measure facility of the Model 2110.

After many many hours of testing, I ended up with a >10Mb spreadsheet from which I performed calculations upon to get to the bottom of it.

Capacity Result

Power Bank Test Results

We can see that the error due to the meter itself is tiny, but there is error from the leads. There is also errors due to differences in operating temperature, USB connector resistance, etc – but their effect on the final figure is unlikely to be even 1%. Variation in separate runs is “normal” as most battery packs are only specified to 100mAh accuracy with variation due to self-discharge and charge termination points.

For now, you can ignore the yellow result – this was after I rebuilt the pack (later on in this posting). We can see that we ended up with about 3800mAh at 3.7v for the 5000mAh battery pack loaded at about 1A (the port rated output) – this is due to losses in power conversion as heat (poor design?) and losses in indicator LEDs etc.

But worst of all, the 30000mAh packs loaded at 1A measured about 4000mAh at 3.7v of effective capacity. This isn’t much more than the 5000mAh pack! It’s physically much larger for no good reason at all.

Loaded at the 2A rate, the capacity drops to about 3800mAh at 3.7v effective capacity! The cells in the 30000mAh pack are literally rubbish!

Also disappointing is the efficiency – it seems that the 5000mAh packs have sub-optimal conversion efficiency at 1A loading. Properly designed DC to DC converters should be able to achieve 88-94% (or thereabouts) efficiency.

Voltage Result

USB Power Bank Output vs Time

The voltage result shows even worse news. These power packs fail miserably when loaded to around their rated current. Over 2.5 ohms, you’d expect 2A to flow, but instead due to the voltage droop and tolerance, we see only about 1.6A. So this test is already a little generous. The voltage provided by the packs loaded at their rated current (5000mAh at 1A, 30000mAh at 2A) all show voltages below the 4.75v limit (5v – 5%). It’s a wonder that devices are so accommodating to even work with them at all.

The 30000mAh pack does provide much better voltage figures when loaded at the 1A load suggesting it was designed for that load. Chances are, the difference in capacity may have come about from the heat evolved from the converter circuit and difference in efficiency as the voltage droop suggests the converter itself is overloaded and possibly noisy.

The legend is coded as follows:

  • First letter – battery design. A is 5000mAh, B is 30000mAh.
  • Second letter – battery number – I have two packs of each type.
  • Load Current – 1A or 2A (approximately, really means load resistance 5 ohm or 2.5 ohm).
  • Run Number – Some runs repeated three times to gauge accuracy.

Unfortunately, it was also discovered that the 5000mAh pack has a design flaw. It has no MOSFET cutoff at end of dicharge, and so the voltage abruptly drops from 4.6v to 2.3v, suggesting possible over discharge from incorrectly set end-point. Leaving a USB device attached after the pack appears depleted could further deplete the cells and damage them irreversably!

The 30000mAh pack disconnects its outputs to 0v when reaching its termination point – although we do need to determine the actual termination point voltage-wise to ensure safety for our Li-Ion cells.

Rebuilding the Pack

It was suggested that it might be possible to rebuild the pack – now while, in principle, I agree, soldering directly to Lithium-Ion cells are not advisable. I happened to find that it was possible, if one was careful, to solder to tabbed Lithium-Ion cells, so I gave it a go.

DSC_0001

I consider myself an intermediate at soldering – soldering to the cells themselves would be impossible as the cells would sink the heat away and cause damage to the cells. It would be best to use spot-welding, but I don’t have such equipment. I took the risk and ordered almost $100AU in Lithium-Ion Cells.

DSC_0003

I opted for eight Panasonic NCR18650B’s. These are now the world’s highest capacity 18650′s, rated at 3350mAh each. Even with eight, the best I could expect was 26800mAh – still shy of the 30000mAh it was “rated”. Also, the pack would look ugly. Not that it really mattered to me.

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After some careful soldering, and lots of electrical taping – I ended up with this monstrosity. It was much heavier than the initial pack, and it takes a lot longer than 24 hours to charge. Luckily, the charger and converter are “voltage sensing” devices, so they don’t care about the change in capacity (or so it seems – it is yet to be conclusively determined).

Charging takes almost two days, and the LED indicator does sit on the first bar for almost a day, giving the impression that nothing is happening, but the PCB does get warm indicating the charging circuitry is working …

Rebuilt Pack

The improvement in run-time was phenomenal. The gauge now is inaccurate, displaying the single bar for a long time. As I soldered to the ends of the tabs, there was much less mechanical rigidity in the pack, so I used some Nitto electrical tape to bolster it. Since the solder is proud of the tab profile, I needed to bend the plastic slightly to shoehorn the whole thing in. But it works.

USB Power Bank Output vs Time with Rebuilt

The output is a bit lumpy, but it blows the competition away at the 2A load rate. It took almost ten hours at the 2A (1.6A) rate to finish it up. At the 1A rate, I could easily be waiting for a bit longer. I think it’s obvious why I couldn’t afford to make multiple runs – there has been much interest in this subject, so I wanted to get the word out as soon as possible.

I’m not quite sure why the output is lumpy – this could be sudden changes in contact resistance in the USB connector when heating/cooling, and or it could be discrete stepping of the duty cycle/frequency of the switching converter (although, I would expect much smoother steps in properly designed converters). Interestingly, both packs seem to eschew the use of more conventional dedicated IC drivers, and seem to utilize OTP microcontrollers to do the work – so this “mystery” may come down to the code and or limited PWM/output resolution.

If you head back to the capacity result table, you can see that I’ve used the nominal capacity of the Panasonic cells (I trust them) to derive a converter efficiency percentage for the 2A rate. Applying this to the existing eight cell pack gives me a reading of 632mAh per 18650 cell in the original pack. Waste of space!

Checking out the Original Cells

Since the original pack was so worthless, I decided to take it apart and grab a cell to pull the wrap off, hoping there’d be some clue as to who was behind the mess.

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But the cell is naked. I’m sure the manufacturer isn’t proud of what they’ve achieved.

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There is one difference to the cells – the ring that sits on the positive terminal is made of plastic rather than paper. Hmm.

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So there is such a thing as too good to be true. And it can be even worse than you were expecting, even if you were expecting a lie. Never underestimate the power of lies …

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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19 Responses to Follow-up: USB Power Bank Tested and Repacked (5000mAh, 30000mAh)

  1. Pingback: Review: Unbranded 30000mAh 2 Port USB Power Bank | Gough's Tech Zone

  2. k says:

    thanks for the review and update.

    just wanted to let you know that your work is being read and appreciated

  3. Chinoy says:

    So do you have any recommendations when buying a power bank? There are a ton out there!!

    • lui_gough says:

      Excellent Question!

      Unfortunately, as I don’t have an ‘infinite’ need for power banks, nor an infinite supply of money, I haven’t really tested enough power banks to find something of true quality. There are drawbacks in capacity and voltage stability.

      I suspect that one has to pay more and buy branded power banks if they want to ensure quality, capacity and longevity – but I can’t say for sure whether you get more if you pay more.

      - Gough

  4. Brad says:

    Thanks Gough. The tip about leaving the cord plugged in the bank and it depleting the battery explains why mine is loosing it to the point of being useless. Note to self: Unplug the device when charged and not in use. Cheers. Brad

  5. Nesar says:

    HAve some good ideas about those cheap skates. Thanks, really appreciated.

  6. Jaydog says:

    Thanks for the excellent review/breakdown Gough!

    The only one on the web (that I could find) that actually gets to the heart of the matter – most cheap battery packs are no where near their stated output and have little protection

    It would be interesting to see if a branded battery pack has a better build quality and outputs at the rated amount??

    Cheers Jay

    • lui_gough says:

      Dear Jay,

      Thanks for the comment – much appreciated. I would assume many of the branded ones will be somewhat better just because the brands would probably value their brand image enough to put it through its paces before slapping their name on it (or in some rarer cases, they would design it in-house entirely).

      That being said, as I’m not exactly in the market for another power bank – I’m not likely going to have any hard answers just yet. If someone or company would like to donate their products for testing, I’d be happy to oblige!

      - Gough

  7. magnip says:

    Hello thanks for a interesting read i have the 30000 model you reviewed only differance mine is black. Do you know how to stop or bypass the auto shut off because when my camera goes into standby mode it dosnt pull enough current to keep the power bank from going into sleep mode thus shutting my cam down. Also i know this post is old but if your still about could you confirm the lenth of the pack because im sure mine is even more of a con a 20000 model with a 30000 sticker on, i did rip it apart just as you did thats why i enjoyed your post but i have put it back together with a role of e tape like yours and dont want to tare it apart again unless someone can instruct me on how to keep the power block constantly on. thanks and sorry for long post just hope its relervant and in the right place

  8. Magnip says:

    Ok look like I was done mine has three cells a side never mind I thank you for a very swift response.

  9. Adam Gill says:

    I bought the same 30,000 power bank .. testing it out now …. will also change over to the 3,400mah or higher 18650 cells …. I’m not sure if all the 30,000 power banks will be rated as low as you tested ..

    • lui_gough says:

      Dear Adam,

      Of course, there will be variations in the stuff the manufacturers put into the power bank. One indicator of the quality is weight, another is the charge time and finally the obvious one is runtime. If it was 30,000mAh, you should be able to charge a Retina iPad (massive battery) about 3 times from dead-flat. The original cells I had couldn’t even do it just once.

      The 3400/3500mAh cells I used are the largest 18650 cells which are legitimate at this time (to my knowledge). Most of the other cells rated above, especially UltraFire, TrustFire, etc are all fake.

      Good luck with yours :).

      - Gough

      • Adam Gill says:

        Gough,
        I successfully did the transplant – it’s charging now …. will take a while – I’m using 3,100 mah made in Japan. Will add pictures when the testing is done – how to add pictures here? The charge is on no. 3 flashing position – it started on no 2 as there as some juice in the batteries when i bought them. As i am living in HK/China – I can source batteries if anyone interested.

        • lui_gough says:

          Dear Adam,

          Unfortunately, it doesn’t seem WordPress will allow you to embed images into your post, so I suggest you upload them to a web service like imgur and then post the links to the images in your comments.

          With such large cells, if you’re using eight, and you fully deplete them, you can expect charging to take almost 2 days to complete in my experience. While it may be possible to increase the charge rate with a resistor tweak, I’m not too sure of the actual make of the charge controller chip and whether the PCB might not have enough heatsinking for it. As a result, it can be a little annoying if you don’t have a dedicated Li-Ion charger.

          Aside from that, having eight cells parallel in two groups of four with no protection isn’t exactly the “best” thing to do to a bunch of cells anyway – but it certainly makes the pack perform more like you would expect.

          Glad to hear it went well!

          - Gough

  10. Zee says:

    Hi,

    Just a quick question. Can this device be charged and charge a mobile phone at the same time?

    Thanks

    • lui_gough says:

      No, not for the 30000mAh pack. By plugging in the power adapter while the pack is charging an appliance, the output is switched off.

      The 5000mAh pack is inconclusive. While the output remains on, the LEDs look similar for charging and discharging. I think it may be charging the pack, but as it charges slowly, if the output is used to charge a tablet and a phone, the pack may still be depleted to some extent. I will have to observe its operation further to determine whether it is capable of doing both charging and discharging at the same time, however, do note that this can contribute to “micro-cycles” which can also wear out Lithium-Ion packs.

      - Gough

  11. Bobby says:

    Great review.. it has amazing content and really clears up any misconceptions about this Bargain “Wonder product”.

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