Hoover FM216LI cordless vacuum refuses to charge

[flat-earther]

Alright, I have an 0603 resistor kit on the way.

[flat-earther]

Finally got a new resistor soldered. It's very small so was difficult, I stopped trying to make it better aligned since it is practically attached.


I verified with multimeter that it's connected to the traces.

After that I plugged in the charger and the 3 LEDs turned on, I think it blinked slightly different than before the resistor, but immediately all 3 LEDs stayed solid which is as if charging is complete, just like before the resistor.
I was disappointed, I thought there still was a problem...
I replugged the charger many times and same thing.
I turned on the motor and it spun up and immediately had only 1 LED light and blinking as if battery is running out then motor stopped, although I previously manually charged it to 24V and before replacing the resistor the motor would stay on and with 3 LEDs showing full charge.

I repeated plugging charger in and out, and trying to spin the motor (it didn't try to spin again unless I plugged the charger in and out, it's probably related to a feature that once voltage cut off has been reached you can't turn the vacuum on unless charged has been plugged in and out first (but in this case the controller for some reason falsely thought battery was empty)), and then all of a sudden it started charging again!
Maybe the controller needed time or many tries until it cleared a fault and was happy again? IDK... Anyway now it charges so all good.
Thanks CapLeaker for advice.

[sam_sam_sam]

First of all you need to know if the battery pack cells are good or not please show a picture of the battery cells so I can see what type you have
But basically you need to know the exact voltage of each battery cell under a load

Use the same load ( incandescent light bulb preferably) on each battery cell if the battery cells are more than 0.250 volts ( run the test for at least five minutes at a minimum ) different then you might be having an issue with the BMS protection system circuit locking up and refusing to turn on properly

Now if your battery pack cells are unbalanced then you might have a bad case of end of life syndrome issues and there is no cure for it other than replacing the battery cells all of them reason being that the other battery cells might also be close to end of life syndrome but are not to the point of self discharging

There is a test that will verify if this is the case fully charge each battery cell to it's recommended voltage and then let the battery pack sit disconnected from the device for 30 days and recheck the battery voltage on each battery cells and the voltage should not have dropped more 0.500 from where you left it but let the battery pack sit for 3 hours before you take the voltage reading so the battery voltage becomes stable for accurate reading

How these BMS protection devices work is that if the voltage is different more than a certain amount it locks up the charging circuit if the voltage goes beyond 4.2 volts depending on the type of battery cell used it could be 3.8 volts or a little lower than that but in general if any battery cell reaches this voltage limit it turns off the charging current circuit or if a battery cell is below 3.volts or lower depending on BMS protection parameters to protect the battery cells from damage and from it self

[flat-earther]

Thanks sam_sam_sam,
The vac is already assembled, but I saw before that the cells are Samsung ICR18650-22P.
I already completed full charge after replacing the resistor and I monitored the battery voltage during the first charge and it stopped before 25.2V I think the last reading I got before it stopped charging was 25.16V then the voltage settled a bit lower, then I vacuumed for probably over 30mins and it was still going and had 1 out of 3 LED left when I turned it off, then I completed another full charge, so at the moment I think it's good.