I am planning to charge four 18650 Li ion batteries that are connected to four TP4056 in parallel making 4 amps in total to charge them in their usual rate. I was thinking of connecting two 2 amp phone chargers in parallel to charge the circuit but found this article that it won't work.

  1. Can I use a B0505 to isolate the connection in between these two chargers?

  2. I only managed to find 1-3 watts of B0505, I calculated a 10 watt B0505 to allow 2 amps to flow through, Can I also connect B0505's in parallel?


1, 2 No , it's pointless to use B0505 you will have the same issue connecting the outputs in parallel.

Better use two resistors 0.1 ohm in series with each phone charger ( I suppose you have two 5V USB wall adapters) that will balance the current. TP4056 can work down to 4.5V so the voltage drop on the resistors is insignificant.

Edit following the comment I will explain better why putting two identical 5V wall adapters in parallel is not such a bad idea at it seems.

This is not similar with two batteries in parallel, the adapters cannot sink current like a battery can. The battery with a lower voltage will sink current from the other battery maybe heating up and discharge the other battery.

The adapters have a diode that prevent them to sink current when the output voltage is higher than nominal. Even the ones without a diode are acting the same. What happens is that the internal regulator circuit shuts down slowly and do not transfer power to the output. For small amounts of overvoltage this is reversible and when the voltage is lowered the regulator will transfer power to the output again. For higher overvoltages the regulator might activate a protection and require unplug to work again but for small, in the accepted range, overvoltage this is not happening because small transitory overvoltage is normal when you plug or unplug a load.

Also if you force a higher load than the nominal the voltage will drop due the maximum power limitation of the adapter. Again, as long as the voltage drop is not to high this is also reversible. Actually this voltage drop is used by phones and tablets to detect the maximum current that can be sourced by the wall adapter by increasing the charge current until the voltage drops under the accepted limit (usually 5V).

So when you connect in parallel two identical adapters with slightly different output voltages if the load is requiring under half of the power the higher voltage adapter will source all the current, then form half to full power the other one will source the additional current needed. Adding the resistor will balance the current a bit, still the the highest voltage adapter sourcing most of the current needed.

If you're asking, I did that many times and in practice it works, never had any issues.

  • \$\begingroup\$ just to confirm, balancing the current would be the greatest issue right? \$\endgroup\$
    – kit
    Dec 6 '18 at 7:58
  • \$\begingroup\$ @kit It's not really an issue, because it's a longer explanation I will put-it in my answer. \$\endgroup\$
    – Dorian
    Dec 6 '18 at 8:40
  • \$\begingroup\$ Can I have a comment for the downvote? If somebody ever burned a wall charger in this way please share your wisdom with us. I did that ,it worked and I explained why. \$\endgroup\$
    – Dorian
    Dec 6 '18 at 16:19
  • \$\begingroup\$ thanks for the added explanation, your method seems reasonable. But the slightest doubt I have because of the uncertainty makes me think of another solution. My circuit requires a 4 amp supply, 3 solutions, 1. your method. 2. a DPST switch to split two TP4056 and have each pair connect to their own respective 2 amp supply(total of 4 amps) or to just 1 (2 amps only with half speed/slow charge). 3. find a 5v 4amp charger and have its output compatible to usb micro port. I'll try them all and report back if I have some results. \$\endgroup\$
    – kit
    Dec 6 '18 at 17:31
  • \$\begingroup\$ @kit Agree. Both 2 and 3 are safer. \$\endgroup\$
    – Dorian
    Dec 8 '18 at 8:09

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