Timeline for Multi-cell li-ion charger
Current License: CC BY-SA 3.0
10 events
| when toggle format | what | by | license | comment | |
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| Apr 10, 2020 at 5:54 | comment | added | Bruce Abbott | @KennSebesta for example, the top converter has an input voltage of ~24 - (4+4+4) = 12V. It steps the voltage down to 5V and the TP4056 draws 1A, so the input current to the converter is ~5W/12V = ~0.4A. This current must flow through the lower cells to get back to the power supply. Now imagine one of the other cells is approaching full charge. the charger on that cell winds its output current down to 0A, but there is still 0.4A coming in from above. The charger can't sink this current so the cell will get overcharged. | |
| Apr 10, 2020 at 5:38 | comment | added | Kenn Sebesta | @BruceAbbott, could you go into further detail why the original proposed circuit wouldn't work? I don't see why additional charge would make its way to the lower cells in the stack. | |
| Dec 6, 2016 at 15:48 | comment | added | Bruce Abbott | You should periodically check the cell voltages with a voltmeter, and charge at a low rate if there is significant imbalance (greater than +-0.05V at full charge). If you want the charge current to automatically taper off earlier then add a small amount of resistance (eg. 0.2 Ohm) in series. | |
| Dec 6, 2016 at 15:44 | comment | added | Bruce Abbott | Nominal full charge voltage is 16.8V. You could go to 17V if needed for precise balance, but charging current won't drop to zero because at that voltage the balancer will be continuously bypassing every cell (assuming the balance circuit is accurate!). Current automatically reduces when getting close to full charge due to resistances in the circuit, so the balancer should be able to correct small imbalances. If imbalance is too large then it won't be able to hold all the cell voltages down and the protection circuit will cut in, disconnecting the charger. | |
| Dec 6, 2016 at 9:58 | comment | added | frarugi87 | Sorry to bother you again. I have a couple more questions. What voltage and current should I set? If the balance voltage is 4.25V/cell, then for a 4S I should set 17V, right? Then the current can be 1A for instance (no need for a fast charge) but, then, the balancing current is 100mA, so should I lower the current when the balancing phase starts? And... What happens at the end of the charge? Should I manually disconnect the power supply or I can leave it attached? Thank you | |
| Nov 26, 2016 at 11:39 | vote | accept | frarugi87 | ||
| Nov 21, 2016 at 23:19 | history | edited | Bruce Abbott | CC BY-SA 3.0 |
added 10 characters in body
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| Nov 21, 2016 at 23:18 | comment | added | Bruce Abbott | Yes. Balancing is required to ensure that all cells have the same voltage so the charging voltage divides equally between them, and the protection circuit guards against incorrect charger settings or running the battery too low. The charger then just has to limit current and voltage (open-circuit charger voltage must be set to 16.8V or lower to avoid tripping the over-voltage protection circuit). | |
| Nov 21, 2016 at 21:15 | comment | added | frarugi87 | Thank you.. So I just have to add a balance circuit (not just a protection one, right?) then use any li-ion charger supporting 4s batteries or a voltage-current power supply forgetting about balancing and protection, right? | |
| Nov 21, 2016 at 19:41 | history | answered | Bruce Abbott | CC BY-SA 3.0 |