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I currently have a 50,000 mAH USB power bank powering my Arduino Uno and micro servomotor. Unfortunately, my power bank has an automatic shutoff and shuts off after 2 hrs of runtime (I need 16 hrs for my project). I can restart the power bank by hitting the on button and it will run just fine for another 1-2 hrs at which point it will shut off. In one instance, the power bank ran for the desired 16 hrs straight hours. I believe that my arduino/servo are very close to the current threshold of the bank which could explain some of the variability I am seeing in terms of turn-off time. Would hooking up a resistor in the circuit do the trick and if so where?

Not quite sure about the brand of power bank (just one I found off Ebay). I believe the arduino uno and servo consume about 60 mA for power.

  • This might be too vague to answer. Perhaps edit question to specify brand and model of power bank and tell how much current is drawn on average by Uno and servo. – James Waldby - jwpat7 Feb 20 '17 at 5:18
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    50,000 mAH for a USB power bank sounds extremely well specified. Some powerbanks shut off after detecting a period of low current consumption. There are tricks to periodically shunt a low value resistor across it, say with a timer, to create sufficient load to keep the powerbank 'alive'. A powerbank I have (much smaller than yours) requires a 47 Ohm resistor shunted across it every 2 seconds for 20 mS to suppress its auto shutoff. – 6v6gt Feb 20 '17 at 8:29
  • I have a "50000mAh" power bank. By my estimation, and looking at what could actually physically fit in (I haven't torn it down yet), you can expect 8 18650 batteries at no more than 3600mAh each, totalling 28800mAh - probably less, since cheaper batteries used in cheap power banks have less capacity than the top of the range expensive ones. – Majenko Feb 20 '17 at 9:52
  • once it shuts down automatically, how do you turn it back on? if it's by replugging, you can simulate that electronically with a relay or mosfet. – dandavis Feb 20 '17 at 13:34
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    @Majenko. Big Clive (youtube.com/user/bigclivedotcom/videos) is guy devoted to tear down and review all kind of cheap chinese products like power banks, LED's and chargers. After watching his videos, I will never buy another chinese "consumer" products like those. – user31481 Aug 7 '17 at 14:55
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You have a couple of options, depending on how much you want to dive into electronics.

  • Find/buy a new powerbank that does not auto-shutoff
  • Find the current-sense resistor on the internal circuitry of your existing powerbank and change it out so that the device always thinks there is current flowing, or is more sensitive to your low-draw attachment. I was able to find a few websites describing this for specific powerbanks by searching.
  • Add a dummy load in parallel with your circuit, which wastes power, but does trick the powerbank into staying on.

It's also worth noting on the side, that you very likely do not have 50,000 mAh capacity in this powerbank, as others have noted. However, you ought to be able to get 16h of runtime with even a lower-rated powerbank if your claim of 60mA current draw is true.

  • Thank you jose! Yes, I am very skeptical about the "50,000 mAh" but suffice it to say I have never completely drained the power bank so it is likely in the five digit range. – kingrumak Feb 20 '17 at 16:09
  • Generally the mAh number they quote is the internal battery capacity. They have to step that up from 3.7 V (nominal) to 5V and will be using the cheapest possible supply to do that because they can without impacting the numbers on the spec. Which means you'll be looking at about 60-65% of the headline number in terms of mAh delivered to the USB output. – Andrew Feb 20 '17 at 16:48
  • @Andrew: i would think a fixed-output boost converter would be more efficient than 60%; even adjustable ones (not optimized) are typically >80% worst-case. The fact that the case is not 35% as hot as the watts out says so too... – dandavis Feb 21 '17 at 14:29
  • @dandavis I was assuming about 85% for the power supply. The rest is the inherent current capacity loss when converting voltages. 1000 mAh at 3.7 V = 740 mAh at 5 V assuming 100% efficiency. – Andrew Feb 21 '17 at 14:41
  • @Andrew: true. you also can't get more than 80% or so out of the cell; buyer beware. – dandavis Feb 21 '17 at 17:29
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I can't see this helping.

It could only help if your power bank switched off its output when the current drawn dropped too low - but unless your circuit's current consumption drops after two hours, which you don't mention, that is unlikely to be the reason it's switching off.

  • Thanks Mark! I cannot say for certain whether or not my current consumption decreases with time. The powerbank sometimes will shut off 15 min after it has been turned. And in some lucky cases stays on for 16 hrs straight. I believe that whatever current threshold my powerbank has my servo/arduino are right at the tipping point. – kingrumak Feb 20 '17 at 15:39
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Expanding @jose can u c first suggestion I did a little research and found that Voltaic Systems sells power banks with an option to disable auto-shutoff mode. There may be others. I found two of their power banks offered on Amazon. The blurb in the Amazon listing explicitly mentions using it with Arduino and Raspberry Pi.

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As the company Voltaic has been mentioned I feel that it would be helpful if I warned you of that company. We are after all trying to offer solutions and if you follow the advice of the person who suggested Voltaic then I know from first hand experience that the thing turns itself off even when the auto shutdown mode is disabled. Though this may not be an end solution I know that by helping you to avoid useless information I can keep you on track and help you towards your solution. In detail : I'm a chauffeur and I bought a Voltaic for this specific reason and guess what? It switches off even when auto shutoff mode is disabled. I wanted my customers to be able to charge their devices as quick as poss and with as little complication as poss. I'm thinkin bout puttin a led fibre optic charging cable in so there is always a tiny power usage from the LED near the big USB jack. At least then also the cable wld be more 'look at me, look at me' I'm thinkin the problem comes either from an auto time out or from the completion of the charging of the power bank which is itself on a dribble charge from the car's electrics.

  • Look into the OmniCharge for that: omnicharge.co It won't let you down. You could even feed a SLA battery with this device if it's drained and can't start your car. – user2497 Aug 8 '17 at 16:48
  • Could you please clarify a bit more how this would solve asker's problem? – Avamander Aug 8 '17 at 21:59

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