I just get my new iMAX B6 charger, and started to read the user manual first until the end, to be sure that I will be carefull with all settings and warnings if any shows up when charging the batteries.
One of the batteries I have is a 11,1V and 1500mAh, one of its cells goes to 2,18V, so it is far from the minimun voltage, but the two others was about 3,35V. I used this battery some months ago and I didn't check it until now. So when I tried to charge it, the charger detected a 2 cells battery instead of 3 cells.
Can a battery with a cell under the minimum limit works again?
YES! and the following method can be used only if the battery is not damaged!
What I did to bring it back to the minum voltage is using a voltage divider, and the following schematic shows how. It takes many hours to do it, but its safe and it works!
You can change the value of 220 ohm with smaller one to make the charging time shorter if you want, but smaller the resistance, more power, more heat and the risk is greater. The resistors here are 1/4W and no heat!
I did not test the charger if it can bring the cell back to the min accepted voltage, but this method is usefull if the charger decide that you throw away the battery.
I charged the battery for hours and when it goes over 3V, I tested it again, but still the charger detected only two cells. In the chargers manual it is said: ["R" shows the number of cells detected by the charger and "S" is the number of cells set by you at the previous screen. If both numbers are identical you can start charging by press START/ENTER button. If not, press BATT TYPE/STOP button to go back to previous screen to carefully check the number of cells of the battery pack before going ahead.]
I hesitated to press START charging, I contacted the seller, but it was weekend so finally I choosed balancing mode and even only 2 cells detected,
I pressed the START button.
The charger displays 11,..V and when I pressed "Inc" button, it shows the voltage of the 3 cells as I measured them. I waited that the cell that was too low goes over 35%, I stopped the charge and started again, and this time the charger detects the 3 cells. After some minutes under a 0,5A, the battery was balanced and about 4V each cell.
Other issue was the temperature sensor, by pressing the "Dec" button you can see different settings, and one of them is the battery temperature,
it displays the real time temperature of the battery if there is a temperature sensor attached to the charger and in contact with the battery's surface.
It is 0C if no sensor.
In my case without sensor all goes fine, and when I pluged the sensor and started charging, the charger started beeping. I checked the temperature and it displays "Ext. Temp 99C"
I opened the sensors little box, I find out that the wires was connected wrong, the Vcc was in GND and vice versa. After inverting the wires, all goes fine when I test it. Also the sensors protecting box is made curved, and I think it is not good for flat surface batteries, so I made a hole in the other flat side to let the sensor touch the battery.
Please, be careful with this kind of batteries, you have to read about Lipos before you use them!
This is my experiences I share it here, so be responsible for any damage if you do the same experiments!
The pictures here, I made them only to show my experiments, it is not safe to charge Lipos like this over a wooden table! And check the temperature of the battery everytime that it is not hot, in this schematic no heat must be noticed. I have a small thermometer attached to the battery so I can visually check the temperature.
I hope this can help someone, but as I said for your own risks!
This is a simple two resistors in serie with a 5V power supply, the voltage is divided so we obtain a 3V with a max current of 22,7mA.
It is safe to charge in a very low current, the cell didn't even get warm, but the charging time is long.
In this example the Cell C2 is connected, so as showen, check the polarity before connecting the cell, other wise if connected wrong it will be discharged not charged!
The charger did not detect the right number of cells, but you can accept to start charging. After that, and if the charger is the same version as mine, press "Inc" button and there you can see the real count of batteries, if not so you have to stop charging!
This is another battery with the same issue, only 2 cells detected but when charging it, it is balanced as you can see in the picture.
I use a sensor made for iMax B6, so the charger will stop if the temperature goes over a user defined value,
but an extra thermometer that I don't need to switch everytime between voltage and temperature.
The black one attached with a rubber band is the sensor for the iMAX, you can see that I turned the curved side up, and made a hole to the other side down, so the sensor senses well the batteries temperature.