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I want to ask about wall adapter (switching) with 2.5mm jack let's assumed its label as 9V 2A. I saw many tutorial even some product use normal adapter (2.5mm jack) with BMS module to charge Li-ion cells. (for this function BMS just over voltage protect and balance for each cell) So BMS module it's self don't have function to control charging current.

Q1: What happen when load draw current more than 2A? (Will it perform constant current mode?)

Q2: Is it safe to use wall adapter to charge battery? (Can we consider current on label as charge current?)

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    \$\begingroup\$ It's fundamental design could but it was not made to do that so cannot. The current on the label is how much it CAN output, not how much it WILL output. The voltage is how much it will output. \$\endgroup\$
    – DKNguyen
    Commented May 23, 2020 at 20:07

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Q1: What happen when load draw current more than 2A? (Will it preform constant current mode?)

It could go into current limit. It might not and depending on the (lack of quality) could overheat and go on fire.

Q2: Is it safe to use wall adapter to charge battery? (Can we consider current on label as charge current?)

No. A charging circuit to suit the battery chemistry and capacity must be used to do this safely. It may be possible to find one that uses your 5 V power-supply as the mains to 5 V DC converter.

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  • \$\begingroup\$ It literally wall adapter with 2.5mm jack \$\endgroup\$
    – M lab
    Commented May 23, 2020 at 21:35
  • \$\begingroup\$ OK. Not USB then. I've edited the answer. \$\endgroup\$
    – Transistor
    Commented May 23, 2020 at 21:38
  • \$\begingroup\$ I change voltage to 9V for less confusing. \$\endgroup\$
    – M lab
    Commented May 23, 2020 at 21:46
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the current on the label is not an automatic limit, attempting to exceed it may cause a temporary voltage reduction, or cause the adaptor to shut-down, or even cause it to break.

The 2A limit will not prevent yout battery from being over chanrged, that is why a battery mamangemnt systrem is needed,

If you can set the BMS to limit the charge current to 2A or lower the adaptor will be safe and battery will not be damaged by a lower than normal charging current, just charging will take longer than usual.

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  • \$\begingroup\$ what if bms module can't limit charging current? \$\endgroup\$
    – M lab
    Commented May 24, 2020 at 10:49

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