Since a power bank holds energy and has both input and output ports, it doesn’t take long for people to get creative ideas and ask themselves what would happen if they’d plug the power bank into itself.
Granted, it’s a genuine question that sparks curiosity, so I thought it was worth entertaining.
First of all, here’s what will NOT happen: You will not discover the secret of generating free energy. For this, you’ll likely have more success by strapping a piece of buttered toast on the back of a cat.
Actually, it’s pretty difficult to predict exactly what would happen without analyzing each particular portable charger circuit first. Depending on the way the power bank is actually built (the circuitry, the build quality, etc.), there are a few possible scenarios.
To start things off, it’s very likely that the unit will discharge power from the output, and transfer it to the input. In this case, the outcome is highly dependent on the design and quality of the portable charger.
If the power bank is manufactured by a generic brand, you can expect it to have a poor battery build and low-quality circuitry. So, if you were to plug such a portable charger into itself, these two factors would cause the battery to short and start leaking, then the battery will constantly overheat until it either sets itself on fire or explodes. This a real hazard possibility that you should take into consideration before attempting to plug your power bank into itself!
Otherwise, if the unit isn’t completely destroyed, it will just overheat, suffer from exhaustion, and result in a shortened lifespan. The time it takes to completely discharge itself will take longer than it would charge a phone, maybe even 2.5 times longer. This is mostly due to the efficiencies of the converters in the unit.
To understand how it happens, you’ll need to know that both the input and output jacks located on a power bank aren’t actually connected to the internal battery. The battery has a charging and discharging range of 3.0 – 4.2V. While charging, the 5V input must be regulated in order to restrict the voltage to 4.2V and keep current in a safe charging range, which will keep the battery safe. While discharging, the output voltage of the battery must be raised to 5V to charge up the outputs with the current restricted to keep the charger safe.
Using this configuration would cause a certain amount of power to flow through the cable, which would be limited by the input/output circuits. The circuits aren’t 100% efficient, either, but can be 90% efficient for example. Let’s say that the output provides 10W of power, then the output circuit will need to harness 11W of power somewhere. The input circuitry will convert the 10W into 9W at the battery voltage and will attempt to power the battery. What actually happens is, the 9W of power goes to the output circuit along with 2W, which will be taken from the battery itself in order to supply the 11W needed by the output circuitry. In the end, energy will be lost to heat. This will cause the battery to die in a few hours, without actually charging anything.
On the other hand, portable chargers manufactured by well-known brands tend to be built with high-quality parts and circuitry. For example, Apple has resistors inside its smartphones to detect if the device is plugged into the proper charger. If it’s not, then the devices will show that an unsupported charger has been plugged in. This results in restricting the current draw to safer levels. This method is quite similar to what more popular brands use in their power banks to keep it safe.
The smart circuitry protects the device from short circuits, electric surges, and overheating. Power banks with these circuits that have a controller chip will detect when/if the device is plugged into itself. As it’s detected, the LED indicators on the power bank will start to blink in a specific pattern, which indicates a short circuit warning. If/when that happens; the power bank and circuits’ controller chip will have already closed off the connection completely.
As a result, the battery itself remains stable and safe because nothing actually happened to it. All you would need to do next is disconnect the cable from the power bank.
Do not attempt to plug your power bank into itself. The best-case scenario is that nothing actually happens. In the worst-case scenario, you destroy the power bank and render it unusable. It might even explode or catch on fire if the build quality is really bad. The consequences of this situation can be highly unpredictable, so it’s definitely not worth the risk!