How can a battery bank at 10% charge a phone at 90%
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Electric charge in lithium ion batteries is often compared to pressure, as such, how can it flow from a low pressure cell to a “higher pressure” one? This might sound dumb, but this thought just popped into my mind.
I know there is battery management boards, with controllers to ensure battery health, but principally, how can it flow from a lower voltage cell to a higher voltage battery?
You have a 100 liters fixed tank with only 10 liters left inside, you have to bring the liquid in to you house so you use a portable tank that hold 11 liter.
That’s all
The battery bank has a switching converter to bump up the voltage from the internal batteries to 5V to charge your phone. That way the power flow is only one direction from the battery bank to the phone.
It’s not directly hooking up the possibly lower voltage battery.
Well, because its a percentage…
It doesn’t specify what is the battery capacity of the bank nor the phone. If you could charge the phone for quite some time even with 10% of the bank’s battery just means that the bank have more capacity than your phone.
Lets say that the phone has 2500mAh of capacity and the bank twice that, at 5000mAh :
10% of 5000mAh is 500mAh
90% of 2500mAh is 2250mAh
To charge up the phone to 100% in this specific case only consumes 250mAh or 2500 – 2250. That corresponds to only 5% of the bank’s capacity, hence it can charge even with a low amount left
The charge % you see is more about how much energy is in the cell, not how much voltage is in the cell.
So it’s like a super soaker filling a bucket on top of the house. The bucket of water may have more potential energy in it than the super soaker, but if you increase the voltage (pump up the soaker) you can shoot the water from a lower energy place (you on the ground) to a higher energy place on top of the house.
Charge voltage has to be higher than what is being charged. The battery bank has an amount of power in it (usually expressed in watts or milliwatts, or amp hours). The bank will create a voltage higher than what it is charging, and move the power from charger to drained battery. So even if it is low on power, it can take that power, increase the voltage high enough that it will charge a battery. Even if the battery has more power than the battery bank.
If you have a tiny battery, but it is higher voltage than a bigger battery, you can charge the bigger battery with the smaller one. (note to add, it won’t increase the power by much, but it will increase).
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