Rather than opening it, trying to figure out the circuitry, i want to make a little box i plug the power bank into so when the power is pulled, the box keeps the power flowing while the power bank switches from wall plug to battery, there’s a second to 3 second delay on most power banks commercially available
Problem is i can’t work out the best way to buffer that power, if i use supercapacitors, i might need up to 4 of them, if i use batteries, i have to sort out a bms…
Been down this ‘power bank’ / ‘power supply before’. A power bank is NOT a power supply. It is designed to charge other devices when there is no other power available. They mostly have a minimum current load so will switch off when the load is lower than about 100mA or so. This is how they detect a charge status on a connected device and will shut down. There is usually no special provision to suppress switching artefacts as in a “charging” situation they don’t matter much so the 5V might not be that clean.
Your description of EXACTLY what you are trying to achieve is a bit vague, a sketch might help here.
Opening what. In any case good luck with that. You would probably find a dedicated proprietary chip and a couple of other bits and not much else.
Been there, tried that.
You pretty much cant do what you want because the power banks were not designed in that way.
They pretty much all use a switching circuit to change between charge and discharge or use the same ports for charge / discharge.
Most power banks dont do pass through charging either.
I’ve tried a huge number of options to be able work out a system to have a battery powered system that can be powered externally and have the batteries charged while running my device, but when the power is removed then run from the batteries, with the capacity to then have the power plugged back in and the device running all the time.
There are a FEW powerbanks that can do this, but its impossible to know that without trying them and there really are not too many of them.
As I said, I’ve tried all sorts of add ons and alternatives and failed at every turn.
What I CAN tell you though, this one:
A power bank is a power supply, but it is configured for charging a battery-powered device, a different usage than the one you are talking about. A UPS is also a power supply, but it is configured for the sort of usage you need. A UPS typically monitors the source of the supply very closely, and triggers the changeover as soon as that source drops below a specific value. The alternate source needs to be able to start up before the reserve power in the UPS’s internal capacitance expires. Those two times must be matched. That is the reason that the UPS and the backup power are often combined in a single unit.
So the important part of the solution will be some way to measure the source of the power in order to get sufficient warning on the imminent drop in output voltage. If you are only able to monitor the power actually being delivered to the device, then there will not be enough time to cut in the alternate supply without some interruption. Of course in some case, such a driving a motor, the interruption may not matter, but usually it is important.
While this is all totally correct, you still need to be careful as I have tried a number of battery powered devices that are branded as a UPS but actually drop the power output momentarily when connecting or reconnecting the source power.
I think I know what you’re after, a cheap and effective UPS made by modifying off-the-shelf USB battery banks has been a bit of a search for the holy grail on this forum recently.
There was an extensive discussion on all the challenges involved in this thread very recently, which is likely why @AndrewBG@Robert93820 and @Jeff105671 are being so direct in their advice. The short version is that all the things that make battery banks cheap is also what makes them terrible UPS systems and filling that weakness is where all the expense and complexity of a UPS comes from.
I am not trying anything, just trying to help out.
Firstly definition. The “U” part of UPS means "Uninterruptible " That is “NO break”.
Now I have had contact with a few of these, some have battery banks which would cover the floor space the size of your house. Mostly these have a charging system, the battery bank drives a DC motor which in turn drives an AC alternator and the load runs exclusively off that alternator. Power fails, DC motor continues to run thus power is maintained.
Another had an AC motor driving an alternator which powered the load. This was also coupled to a very large flywheel of a few tonnes which was connected to a standby diesel via an electric clutch. When the power failed the clutch closed and the flywheel had enough inertia to keep everything going until the diesel started. That diesel really started spinning in a hurry.
Now that is what I call “uninterruptible”.What you are trying to do here is do much the same thing on a very much smaller scale. What I am saying is there will always be a delay if a switching method is used as Andrew and Jeff have pointed out. To be true “no break” your prime source needs to be battery float charged somehow so the “battery” will keep things operating alone until power is restored so recharging the battery. The charger then has to have enough Grunt to run your device(s) and recharge the battery.
That is the idea, Will leave most of the details to you.
The “U” stands for “Uninterruptible” and in my world that is exactly what it means. For instance you can’t have commercial aeroplanes flying around blindly while you wait for a diesel to start up somewhere. On the other hand a with TV station or similar a bit of a delay might not matter so much.
This is how im going to turn a power bank into a UPS…
All my banks have 5v usb pass through, none of them support QC or PD when 5v usb is connected
USB 5v >> power bank >> my circuit
Since there is no PD or QC support with pass through, it can only supply 5v…
My circuit will contain a low ohm value, around 2 ohms and say 3 or 5watts, that charges a capacitor and that powers your device, the capictor has to be around 100F so that when the power is pulled or dropped the power bank drops out and switches to battery…
While it swaps, your UPS (add on) will power it for 1 to 2 seconds …
My problems was decididing if i should use batteries or super capacitors, using batteries gets complicated vs capacitors but capacitors are much more expensive
I know how … just wasnt sure the best way to go…
Xiaomi, Romoss, Baseus all offer usb 5v pass through but none of them support higher voltage pass through, so in this instance it will be purely a 5v UPS system
The down side to using a capacitor is the discharge curve is the inverse of the charge curve, It will discharge to about 37% of its initial charge (5V) in one time constant that is the time in seconds when you multiply Microfarads by megohms. The megohms can be approximately calculated by dividing 5V by your load current (Current in A will result in Resistance in ohms). Now it is probable your load will not operate much below 5V so even with 100F your practical run time will not be 1 or 2 seconds required. If you Google around there is a formula to work out how long it would take to drop from 5V to say 4V but I can’t recall it off the top of my head. I think it involves natural logs.
It is true some equipment use a supercap instead of a back up battery but when this occurs the device is designed to operate way below 5V and the load is probably measured in picoAmps so the supercar is a good solution.