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« on: January 22, 2010, 11:32:45 PM »
Anjan
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Hi guys.
Again bugging u all with my stupid questiöns.
Wanted to know how the lipo
cells in a pack r charged independently ?
Is each cell getting the current
separately ?
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« Reply #1 on: January 23, 2010, 04:42:20 AM »
Rao
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I think the main load current carrier wires are used for main charging and at some point in the charge cycle the balancing connector wires which are used to monitor each cell voltage are used to bring all the cells to the correct voltage level by discharging or charging the individual cells through the balance tap wires only to balanced state. My opinion only.
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« Reply #2 on: January 23, 2010, 09:15:48 AM »
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This is the simplest yet probably the best information link on this :

http://sites.google.com/site/tjinguytech/charging-how-tos/how-lipo-chargers-work

Quote
Lipo charging in basic terms
The goal of a lipo charger is to charge a lipo to a specified voltage. That voltage is based on the number of cells multiplied by 4.2V. The charger goes about this by adjusting the output voltage in order to make current flow to the lipo. Initially the charger raises the voltage enough to match the amount of current flowing to what the user has selected. This stage is referred to as the Constant Current stage. Current flows because of the difference in voltage between the charger and the pack. The greater the difference, the greater the charge current. During the charge process the resting voltage of the pack rises. Once the charge voltage reaches the maximum voltage of the pack, the charger holds it there. This stage is referred to as the Constant Voltage stage. The charging voltage is now held at the max pack voltage but current continues to flow because there is still a difference between the charge and pack resting voltages. As the pack resting voltage rises, the difference will become less and less until they are very close. During this stage the charge current will drop off more and more until it is very small. Once the charge current and voltage reach predetermined values, the charge cycle is complete.

Lipo balancing in basic terms
Almost all new lipo chargers come with built-in cell balancers. Some older chargers have them but not many and so the use of an external balancer is required for balance charging. Like the name implies, this device is designed to balance lipos. But what does balance really mean? It simply means that it makes all the cells in a pack the same voltage. How does it do this? Well that too is fairly simple. The balancer uses the lipo balance connector to access each cell. Once connected it can do 2 things, monitor the voltage of each cell and if need be, discharge high cells in order to make all the cells the same voltage. That's it, it really is that simple.

Chargers that work at the individual cell level are very rare.  It is said that the FMS CellPro 4s line has 4 individual single cell chargers inside, and they work on charging each cell independently. All the others charge using the leads on the ends (one positive the other negative) across all cells, and balance by discharging the individual cells that go over 4.2v.
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