While doing a discharge test on a small USB power bank, I discovered that even though the booster circuit cuts out when the lithium cell's voltage drops to about 3V, the load can still draw current through the boost inductor and diode. As such, if you leave a load connected to a USB power bank that has run low, it may still drain the lithium cell down below it's safe discharge level and damage the cell.
So the moral of the story is to avoid leaving loads connected to USB power banks for long periods of time.
So the moral of the story is to avoid leaving loads connected to USB power banks for long periods of time.
If you haven’t revisited this issue recently, I’m wondering if it’s still a problem… might be worth a revisit
Li-Ion and Li-Po batteries are SO easy to buy and cheap from recyclers and the little control boards are also real cheap that you can build your own battery systems and know what you really have, we have a recycler here that guarantees his batteries to at least 90% as the batteries he gets are from places that replace the packs every few months and you end up with better than Chinese and know what your getting
And this was the video where I first found Clive . 7,700 subscribers at the time 😉.
For power bank battery should be connected parallely or series???
I think the most elegant solution might be to replace the diode with another mosfet. PMOS where you draw the shotky or a more efficient NMOS on the opposite side. PMOS instead of the diode would have the advantage that it could be connected with its gate directly to the gate/base of the existing transistor.
Edit: Oh, no it could not be connected with the gate/base of the existing transistor, because then you would have the same problem as before. It would need its own connection, but still…
that is a major major design flaw, of course the protection is there but it will ruin the cell if you continue pulling current out. Designing for economy is one thing but leaving that extra transistor out really hurts the functionality.
This kind of power bank also happens to blow up if you attempt to charge a modern phone with it.
Hypothetically, can I just put in my own boost converter, so that I can still get 5 volt output from when the cell is less than 3.2 volts?
sir can you give a list on these parts?
it would appear that the circuit is incomplete, the NPN is shorting the Vcc to ground, a series FET or transistor between the coil and the diode anode would turn off the power, a reference voltage from the chip or a comparator to control the FET/PNP
I don't think this is going to apply to many, really if any USB devices on the market. I guess it looks as though your meter is still trying to work a little at that voltage. I'll have to take a look at my bank and see if I can get anything out of it below the the protection circuit voltage. If you leave the battery alone long enough it's going to drop down on its own anyway, it's just life, you get a new cell. 🙂
There could (should) be MOSFET at the output that turns off the load when the converter turns off.
A power bank without any protection circuitry? Eeek!