Defeat PowerBank auto-shutdown - Page 1
Forum section: electronics / beginners

author: PinheadBE
author_rank: Regular Contributor
timestamp: December 19, 2021, 06:14:40 pm
content: Hi,I would like to use a powerbank to power some XMas LED's on the dinner table.Those LED's are low consumption (20 mA for a string), and therefore, the powerbank keeps shutting down.Is there a trick to prevent that ?I am able to safely open the powerbank if tinckering with some components value could help.Does any of you a reference for a powerbank chip that has this function so that I can consult the datasheet to learn more about disabling this feature ?Any help is welcome and appreciated !(For what's it's worth, the model number of the powerbank is a PNY model C5200)

author: Gyro
author_rank: Super Contributor
timestamp: December 19, 2021, 06:32:56 pm
content: A couple of recent powerbank keep alive circuit threads...https://www.eevblog.com/forum/beginners/ne555-vs-icm7555-timer-power-usage/https://www.eevblog.com/forum/projects/(yet-another)-power-bank-stay-on/https://www.eevblog.com/forum/projects/power-bank-issues/

author: wizard69
author_rank: Super Contributor
timestamp: December 19, 2021, 07:41:49 pm
content: Quote from: PinheadBE on December 19, 2021, 06:14:40 pmAs already pointed out there are many keep alive circuits out there. However if you know what the minimal current is for this bank a load resistor might work fine. Or you could add a second string of LEDs. If this is a temporary Christmas project that might be good enough.

author: PinheadBE
author_rank: Regular Contributor
timestamp: December 19, 2021, 07:48:20 pm
content: Great ideas !The 555 idea,...I would add a trimmer to fine-tune the delay (to suit different powerbank models)Thanks for your help, Gyro !

author: PinheadBE
author_rank: Regular Contributor
timestamp: December 19, 2021, 07:49:52 pm
content: @Wizard69:Yes, indeed, but a continous dummy load seems a bit inefficient...I am really happy with the 555 solution

author: PinheadBE
author_rank: Regular Contributor
timestamp: January 05, 2022, 05:51:15 pm
content: Hi again,I am going for the 555 solution.For the specific set of Powerbanks I use, they turn off if there has not been a current draw of 200 mA in 70 secondsSo I would like to generate an impulse of roughly 1 second long every 60 seconds, to be on the safe side, so with a very low duty cyce (the astable mode with a diode on Rb to quickly discharge the cap)Timing precision is not critical.I was wondering what was the maximal recommended value for the timing capacitor, using an ILC or TLC555.I have not find any info on that in the datasheets.I was considering a 330 µF, but that seems huge compared to the values I've seen in other circuits....Any suggestions ?

author: Zero999
author_rank: Super Contributor
timestamp: January 05, 2022, 07:16:57 pm
content: Christmas was nearly two weeks ago. I suppose it's for next Christmas. lolWhy not use a higher value resistor?The maximum output current is 100mA sinking and only 10mA sourcing so a transistor is required to drive the load. I would skip the diode, design the circuit for 1s off, every 60s and use a PNP transistor to switch the resistor.

author: PinheadBE
author_rank: Regular Contributor
timestamp: January 05, 2022, 07:27:38 pm
content: That's exactly what I'm doing for the load.I would just like to know which max capacitance is recommended for the timing capacitor.Even by using a PNP (which I am currently lacking of), the question of the max cap would remain

author: Zero999
author_rank: Super Contributor
timestamp: January 07, 2022, 09:03:12 am
content: Quote from: PinheadBE on January 05, 2022, 07:27:38 pmI've had a look into this and I've not seen anything which gives a definitive answer. This application note, for the NE555, says thousands of µF have been used in real applications, without any problems. The main issue is the power dissipation, as energy is stored in the capacitor, which is dissipated in the IC. See figure 7.http://www.sophphx.caltech.edu/Physics_5/Data_sheets/555appnote.pdfOne of the advantages of the using the CMOS 555 is the input impedance is higher, meaning larger resistors and smaller capacitors can be used. The problem then becomes capacitor leakage current, so it's a good idea to use low leakage capacitors, such as tantalum and polypropylene.

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2022, 03:19:19 pm
content: Try this. The current is around 230mA, for just over a second, every 50s. I've set the on time for longer and frequency to a little higher, than specified, to account for component tolerances.C1 should ideally be polypropylene film, although you might be able to get away with tantalum. It's connected to +V, rather than 0V, to ensure the circuit starts with a pulse first. If the capacitor were connected to 0V, the circuit would take around 76s to output the first pulse, which might be too long. The first pulse is always slightly longer, because it takes time for the C1 to charge and it never fully discharges, whilst the circuit is running.In real life, there should be another 10µF capacitor across the power rails, which I've not shown, because it's just a simulation.R3 should be rated to 1W.

author: Peabody
author_rank: Super Contributor
timestamp: January 08, 2022, 03:44:51 pm
content: If this were to be done with a Pic or Atmel MCU, would it be possible to detect whether current is already flowing at greater than 200mA - so the current dump would be done only when needed? You wouldn't need an accurate current sensor, just an indicator whether it's below 200mA. Not a series resistor, but maybe a few turns of wire around a battery lead.

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2022, 05:48:01 pm
content: Quote from: Peabody on January 08, 2022, 03:44:51 pmThat will work, but it would be easier to build a current source, with load bypassesing the pass transistor, so it only turns on as much as necessary to ensure at least 200mA flows.

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 08, 2022, 05:56:28 pm
content: Why would they make the power bank shut down with 20mA current draw?

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2022, 06:12:38 pm
content: Quote from: BeBuLamar on January 08, 2022, 05:56:28 pmA powerbank has a built-in DC-DC converter, which gives a steady 5V power supply, from one or two lithium ion cells in series (3V to 4.2V, or 6V to 7.4V). This draws a fairly decent standby current, which would discharge the battery at an unacceptable rate, if left on continuously.

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 08, 2022, 06:29:02 pm
content: Thank you. In that case I would not use a power bank. It's so wasteful in my opinion.

author: Peabody
author_rank: Super Contributor
timestamp: January 08, 2022, 06:49:33 pm
content: Quote from: Zero999 on January 08, 2022, 05:48:01 pmI don't understand. What would the schematic look like?

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2022, 08:00:21 pm
content: Quote from: BeBuLamar on January 08, 2022, 06:29:02 pmThe main reason to use a powerbank is convenience. It can be charged from any USB socket and charge your phone, whilst you're away from mains power. The idea is, it automatically shuts down, when the phone is charged to save power.A power bank is not designed for the original poster's application, which is to power a low level load, for a long period, but they're cheap and have all the charging circuitry built-in.Quote from: Peabody on January 08, 2022, 06:49:33 pmHere are a couple examples.

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 08, 2022, 10:46:49 pm
content: I would buy a couple of Li-Ion batteries and assemble the battery pack. I wouldn't need precise voltage to power the LED. A DC-DC converter in the power bank seems wasteful of battery power.

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2022, 11:14:00 pm
content: Quote from: BeBuLamar on January 08, 2022, 10:46:49 pmYou're missing the point. Powerbanks are designed for use by ordinary consumers, who have no experience with electronics.By using a powerbank, the original poster can avoid having to design a battery charger and protection system

author: BrokenYugo
author_rank: Super Contributor
timestamp: January 09, 2022, 12:33:47 am
content: Quote from: BeBuLamar on January 08, 2022, 10:46:49 pmThe power bank is a convenient COTS solution that does most of the hard work (i.e. safely and properly packaging and managing lithium batteries) for you, this, for most people, greatly outweighs little things like the work required to make it drive a light load or the slight efficiency loss that comes with the internal boost converter.I'm somewhat surprised no one offers a nice canned solution for power bank keep alive yet (I.E. a little $1 board from china).