Disable auto-power-off of powerbank?  - Page 1
Forum section: electronics / beginners

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 14, 2023, 06:04:12 pm
content: Powerbank: Tronsmart PBT10 (https://www.tronsmart.com/products/tronsmart-presto-10000mah-quick-charge-3-0-power-bank).Attached are some images of the reverse-engineering that I've done so far. I cannot find a datasheet for the MCU. The images identify the names of the IC's (if known) and what they do and where they connect to (some FET's are driven directly by the MCU, others have a resistor before the MCU).The power bank can be turned on via the switch (bottom-right corner of image 1), as well as when a USB device is plugged in. The power bank stays on as long as it detects a load.I was thinking that attaching a resistor (I tried both 100k and 10k) between B+ and the shunt resistor (identified by the lightning bolts - connects from USB negative to ground, through FET's controlled by the MCU) would "fake" the charger and mimic a load but that failed (maybe a voltage divider would work instead?).Essentially, how can I disable the auto-power-off feature of this powerbank? I know that using a resistor on the output of like 100mah would work, but I'd like to avoid that route as that's a lot of wasted energy. Thanks.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 14, 2023, 06:05:23 pm
content: Image 2Edit:"RA7901A C X0727" as well as "FT4SJK" both don't have datasheets available, but as they connect directly to the USB D+/D- pins, I think they're simply USB protocol IC's that control Qualcomm Quick Charge and whatever other protocols this powerbank supports."H2 VUC 0T1103" both appear to be simple FET's controlled by the DW01A to prevent over-charge/discharge, so they can also both be disregarded.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 14, 2023, 07:04:51 pm
content: Quote from: LooseJunkHater on August 14, 2023, 06:04:12 pmHow long does it take for it to auto-power-off? If it is like 5 minutes, you could pulse a 100mA load on for a few seconds every 4 minutes. This way the average current draw would be quite low.Even if it turns off after 10 seconds or so, you may be able to pulse it quickly enough (100mS on & 8 seconds off) so the duty cycle, and thus the average current draw, is low enough.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 14, 2023, 08:46:19 pm
content: Quote from: Kim Christensen on August 14, 2023, 07:04:51 pmNot sure how long it takes to auto-power off, I think it's 30sec-1min.I'd personally rather NOT use an additional MCU for simply timing a load. At that point, I may as well just purchase a dedicated power bank which doesn't auto-shutoff.If I can use simple resistors/capacitors/FETs to prevent shut down, that would be preferred.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 14, 2023, 09:34:07 pm
content: You could do it with something as simple as a 555 timer... But I agree that it's a bit of a cheesy hack.If there is some sort of RC filter (Or just R1) between the shunt and the MCU or OpAmp current sense input, you could bridge a resistor to fake the 100mA:(My circuit assumes the shunt is in the negative output lead)

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 14, 2023, 10:45:00 pm
content: Quote from: Kim Christensen on August 14, 2023, 09:34:07 pmThe shunt is indeed on the USB negative side.There is actually a "power" button on the power bank. Holding the power button doesn't cause the output to stay enabled, but I wonder if alternating between pressed-and-unpressed (ex. using an NE555 to trigger a FET) would cause the power bank to stay permanently awake?I'm also not sure what you mean by "you could bridge a resistor to fake the 100mA" and don't understand your diagram.

author: thm_w
author_rank: Super Contributor
timestamp: August 14, 2023, 11:11:55 pm
content: If you just added one resistor to the shunt (R13 in Kim schematic), that won't do anything. You have to add the series resistor as they show to allow the rail to be pulled up.We don't know the schematic of the board itself as you have not drawn one.I assume it would have to be pulled up to a specific voltage and not too high to trigger overcurrent protection, hence the divider (Rx -> R1 + R13).

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 14, 2023, 11:45:08 pm
content: What is "Rx" suppose to be? Also what sort of values should I use for C1 and R1?

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 15, 2023, 02:52:40 am
content: Something like C1 & R1 on my diagram probably exists on your board (With different labels). We know that R13 does since you pointed it out with a "lightning bolt"...Current drawn by the load creates a voltage across R13 (0.025Ω) so 100mA through it would generate 2.5mV across it...So lets just pretend for a moment that you've identified a resistor like R1 in my diagram on your PCB and that it's 100Ω... To generate 2.5mV across 100Ω, we'd need to pass 25uA through it. So add Rx and make it 200K which when it has 5V across it would pass 25uA. This current would develop the 2.5mV across R1 (100Ω) and inject that into the current sense circuitry. Thus fooling it and keeping it turned on. Normally, there's near zero DC voltage across R1 because it and C1 are just for filtering.EDIT: If something like "R1" doesn't exist on your PCB, then you'd have to cut a trace and insert it as well as add Rx... Finding an existing R1 equivalent already on the PCB would make the mod easier to do.

author: Gyro
author_rank: Super Contributor
timestamp: August 15, 2023, 08:34:22 am
content: This question comes up from time to time. If fooling the current sense doesn't work then there are a few previous threads (I linked most of the others in reply #1)...https://www.eevblog.com/forum/beginners/defeat-powerbank-auto-shutdown/

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 28, 2023, 03:08:40 am
content: Quote from: Gyro on August 15, 2023, 08:34:22 amIt seems like the simplest way to go about it is simply following My Carlson's Lab Load Pulser. I know practically nil about the NE555 and I'm wondering if someone can explain what the other components inimage 1are doing? I obviously know what the SOT-23 LED and 330ohm resistor, 51ohm power resistor, and BC817, and 4.7k resistor are doing.What exactly is the 10uf tantalum and 220k resistor and D1 doing?What happens if I modify the value (or even use an electrolytic) for the 10uf capacitor and 220k resistor?

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 28, 2023, 03:24:07 am
content: The 10uF, combined with the 220K, diode, & the 3.3M resistor define the ON and OFF times of the 555 timer output (pin 3)The ON time is determined by how fast the 10uF charges via D1 and the 220K resistor when pin7 (open collector) goes "open".The OFF time is determined by how fast the 10uF discharges via the 3.3M when pin7 goes low.Pins 3 & 7 go low when pins 2&6 rise above 2/3 Vcc.Pin 3 goes high & pin 7 goes "open" when pins 2&6 drop below 1/3 Vcc.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 28, 2023, 03:41:26 am
content: Quote from: Kim Christensen on August 28, 2023, 03:24:07 amHmm okay, so essentially if I want the circuit to be on for longer than 2.5sec, I need to increase the 220k resistor, correct?Do I strictly have to use a tantalum capacitor, or can I use an electrolytic? Why would Mr Carlson recommend a tantalum instead?

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 28, 2023, 04:17:42 am
content: QuoteYes!QuoteTantalums are more stable with temperature (capacitance value) and have lower leakage currents than electrolytic. So the OFF time might be a bit shorter, and vary more with temperature, if you use an electrolytic.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 28, 2023, 04:03:00 pm
content: Quote from: Kim Christensen on August 28, 2023, 04:17:42 amI had no idea! I always heard bad things about Tantalum capacitors from Lewis Rossmann and how they often died on certain Macbook models! Thanks!

author: radiolistener
author_rank: Super Contributor
timestamp: August 28, 2023, 11:06:09 pm
content: Quote from: LooseJunkHater on August 28, 2023, 04:03:00 pmThis is very strange, because tantalum capacitors is very widely used in military grade electronics due to it's very high reliability and stability. The least reliable capacitors are electrolytics.Some cheaters remove tantalum capacitors to sell it and replace it with cheap electrolytic. It allows to make a lot of money because tantalum capacitors are expensive. But such replacement leads to a short lifetime of equipment and also may lead to malfunction.But note that tantalum capacitors have some specific properties. For example when voltage is not applied their capacitance may decrease in time, but applying voltage leads to restore original capacitance.

author: radiolistener
author_rank: Super Contributor
timestamp: August 28, 2023, 11:18:23 pm
content: Quote from: LooseJunkHater on August 28, 2023, 04:03:00 pmProbably you're confuse tantalum capacitors with electrolytic. I never seen failed tantalum capactiors, they works very good even at 50 years age even if they used all that time in very bad conditions (high temperature)... This is why they are always used in military grade electronics, where reliability and long lifetime is critical

author: 807
author_rank: Frequent Contributor
timestamp: August 29, 2023, 10:43:30 am
content: Quote from: radiolistener on August 28, 2023, 11:18:23 pmWow. I've seen many over the years.I bought a failed piece of equipment many years ago. I can't remember if it was a frequency counter or DMM. It was full of tantalum decoupling capacitors. There was a short on one of the power supplies. A tantalum was to blame. Great. I thought it was an easy fix. But it still didn't work. Another shorted tantalum. Then another & another etc. There was around 8 shorted tantalums all together.Also, I used to work for a company making military equipment. The components we used were of course top grade & traceable. Even then we had trouble with tantalums. It got to the point where the test sets where we tested the individual boards had to be fitted with hinged perspex covers because tantalums were exploding at switch on, even though they were connected correctly & within voltage. I was there when one exploded & burned a hole in the operators shirt!Perhaps they are more reliable now than they were in the 80's/90's 🤷‍♂️

author: bitwelder
author_rank: Super Contributor
timestamp: August 29, 2023, 11:17:47 am
content: Granted, in cases like this one where the microcontroller is not known, there is no other way than trick it via some external circuitery.But in general, are these powerbank uC built to work with the auto-poweroff, or is it possible to expect the auto-poweroff is a feature selectable by e.g. tying a certain pin to GND/Vcc ?

author: radiolistener
author_rank: Super Contributor
timestamp: August 30, 2023, 04:33:13 am
content: Quote from: 807 on August 29, 2023, 10:43:30 amI mean military grade tantalum capacitors from Soviet Union, they were often used in a usual equipment. You can recognize them by diamond symbol on it's marking, and they still works ok. I don't remember the case when they failed. I'm not sure about modern tantalum capacitors for consumer electronics, but I think they also should be much more reliable than electrolytic. At least I don't remember the case when they failed. For comparison, almost all failed capacitors are electrolytic.Probably you're applied high overvoltage to capacitor if it was exploding, there is no component that can survive from high overvoltage. For example I was damage nixie tube with high voltage, it's electrodes within tube was melted and bended. But it doesn't means that it can happens when you use component within specification voltage.