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I've attached a TP4056 to each of my 8 cells (4 parallel Li-ions) to charge each group of 4 18650 cells as one cell.

However, currently I've got 8 5v USB chargers plugged in the wall and each one is connected to a TP4056 board.

My question is this, which I'm a little hazy about... If I wanted to use one power supply to charge each cell through their respective TP4056, what voltage and amperage power supply would I require?

Is it 40v 8A, or 5v 8A or something else? Can you feed these TP4056 boards with a higher voltage than 5v? Will they just take what they want or will a higher voltage blow it?

Thanks for all your help

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  • \$\begingroup\$ What is the arrangement of your cells? Is it 8 total, 2 parallel sets of 4 in series, (commonly known as 4s2p)? \$\endgroup\$ – circuitpatrol Jul 4 '17 at 16:27
  • \$\begingroup\$ No sorry, it's 8s4p @circuitpatrol \$\endgroup\$ – Kevin Dark Jul 4 '17 at 17:11
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The standard solution for charging/discharging series-connected batteries is balancing. The BMS (battery management system) monitors voltage on each battery cell and makes sure they are all equal. This can be achieved by:

  • discharging the highest voltage cell until it equals the lowest voltage cell (passive balancing)
  • transferring charge from highest to lowest voltage cell (active balancing)

Having this kind of system, you would charge the whole battery pack with your nominal current and voltage = cell voltage * N. That's just one charger for the whole pack.
My description of how balancing actually works is oversimplified here. For proper description, see TI paper on cell balancing.

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  • \$\begingroup\$ This isn't an answer to my question though. I'm asking, if I had 8 TP4056 boards, each one going to their respective parallel groups of cells (4 cells in parallel), what type/capacity/amp charger would I require? I've answered my own question any way. \$\endgroup\$ – Kevin Dark Jul 6 '17 at 10:01
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I've worked it out. Each module requires 5v at a maximum of 1A. So in order to feed all 8 modules I'd need a power supply that can deliver a minimum of 5v 8A.

However, you can't use the same power supply for all modules when you have cells in series because ultimately it creates a short if you try.

Each module needs it's own isolated power supply.

You can achieve this by using one 5v (min) 8A supply, and by then using one B0505S-1W DC-DC 5v converter for each of the 8 TP4056 boards. This creates a 5v power supply to each module on their own isolated circuit, therefore creating no shorts.

You could also use diode/rectifier such as 1N4001S connected to each of the negative input terminals of the TP4056 board and then just use one power supply negating the need for 8 B0505S-1W components. The B0505S-1W's also reduce the A down to 0.2A so not ideal, whereas the drop with a rectifier is negligible.

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