Simple USB DIY Li-ion battery charger circuit update

in project logs by DP | 8 comments

Arup posted an update on his USB DIY Li-ion battery charger circuit in the project log forum.

Check out the video after the break.

This entry was posted in project logs.

Comments

  1. Conundrum says:

    This is handy as I’m in the middle of an e-bike project.
    Reckon that this could be used to charge FePO4 (Vmax 3.65V) ?

  2. r4k says:

    Charging a completely drained Li-ion is only a feature if you enjoy setting things on fire.

  3. sorin says:

    please, dont post this shit

  4. For those who can’t tell, this is a *terrible* battery charger design. Battery chargers can be built using discrete components, but the number of things done wrong here is significant.

    Using a green LED as a voltage reference is questionable, but then simply doubling it without a trimmer for fine adjustment is worse. For current limiting, the best I can tell is that it depends on the host USB port’s protection, which won’t work out if this happens to be plugged into a 2A+ wall wart USB charger. The lack of protection for the case where there is a battery plugged in but no power source is abuse to your pass transistor that you generally want to avoid, since it is the only thing keeping the battery from being dead short connected to 5V.

    This kind of battery topology is almost acceptable for more robust cells, such as flooded lead acid, but for any kind of sealed cell, and particularly li-ion, is terrifying. Please never build this charger.

  5. KH says:

    I second that. Li-ion charger ICs are really cheap these days (<USD1 per piece) and there's a reason why they specify end-of-charge voltage to less than 1%. I too would be terrified to use this circuit.

  6. Conundrum says:

    Thanks for the heads up, would avoid this circuit for Li-Ion now I see how it works.
    It might be OK for charging FePO4 cells for low current (ie solar) applications where they are happy with 3.65V to 10% capacity in mAh then shut down.

  7. Streetboy says:

    I was wondering to know how do you design these resistor value ? pls tell me why , thanks a lot

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