Planning on putting 2 or more 18650 in parrallel but having my doubts if its alright to do. Charging 4 18650s in series need the use of bms with multiple ground connection for bllancing, now my dilemma is if it's fine to wire 4 18650s in parrallel all iwth the same name brand and voltage but different charged voltage. Would they all balance their charge eventually?

 

Never connect batteries with different terminal voltages together in parallel. Particularly LiIon, they could explode.

 

Planning on putting 2 or more 18650 in parrallel but having my doubts if its alright to do. Charging 4 18650s in series need the use of bms with multiple ground connection for bllancing, now my dilemma is if it's fine to wire 4 18650s in parrallel all iwth the same name brand and voltage but different charged voltage. Would they all balance their charge eventually?

The problem isn't whether they will eventually balance, it's whether they will balance so fast that one or more of them catches fire or explodes.

If you must connect them in parallel, do so first through a resistor bridge that limits the current to a tolerable level. Let them equalize. Then connect them with suitably low resistance straps.

 

The problem isn't whether they will eventually balance, it's whether they will balance so fast that one or more of them catches fire or explodes.

If you must connect them in parallel, do so first through a resistor bridge that limits the current to a tolerable level. Let them equalize. Then connect them with suitably low resistance straps.

Ohh never thought of this, thank a lot

 

Hi,

What I would do I think is first try to build 4 chargers to do each one separately.

If not that, then maybe place a current limit resistor in series with each cell. You can then monitor the voltage of each cell individually.
As you are pumping current into the cells, it is possible that one charges before the others, so if you are using a current source to charge you have to make sure it only puts out around 1/4 of the current that all four cells can handle. So if each cell can take 1 amp max, then the current should be 1 amp max.
If charging from a voltage source through the current limit resistors, then you can rest a little easier. You would have to then make sure the current is limited enough when the cells are not charged very much to start with. This means it will take longer to charge all four.

If you MUST connect them all in direct parallel, then you should ensure that the terminal voltages are very close to each other before they are connected.
To charge, you should make sure the current is only as much as a single cell can take so that if there happens to be only one cell charging it will only get the max current for a single cell.

I do not like connecting these cells in parallel, but one very high power flashlight I have does this automatically because of the internal wiring scheme. I only need this light sometimes but it's great for outdoors at night because it puts out about 70 watts of white LED light. Lights up the whole driveway and it's a long driveway. Looks like daytime out there.