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Charging Li-Ion batteries

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Cobalt60

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So, I have a bunch of Lithium Ion batteries, but very few of them have a corresponding charger. I also have a Lab Power Supply (linear), 0-36V 0-5A. The batteries I need to charge are 3.7V and 7.4V

I have noticed that a fully charged (fresh off a real charger) 3.7V battery actually tests to about 4.2V, and a fully charged 7.4V to over 8.0V So, if I was charging a 3.7V Li-Ion battery, would I simply set the power supply to 4.2V? What about polarity, does the + of the power supply go to the - of the battery, or vice verse? Do I need to pay attention to the 3rd pin most of these batteries have?

Thanks for any info

-Chris P
 
Hello there,


One way to charge these cells from a power supply is to set the open circuit output voltage to 4.150v and the current limit to say 700ma or higher if the cell can take it. Some cells only take 300ma though so you'll have to check the specs.

You have to make sure the voltage setting is stable and it is accurate too. It's best to use a meter to double check, and make sure it can not change by itself for some reason like a temperature increase or decrease.

The higher voltage cell will be made up of two smaller cells in series and it's best to charge them separately if you can.

You have to be very very careful with these cells however as they can burn and catch fire. You should read up more on the precautions first before you start charging any cells.
 
Since you know nothing about your dangerous Lithium battery cells and do not know that they can catch on fire if you charge them wrong (you talked about connecting them backwards) then you should not touch them.
 
You must be very careful when charging Lithium cells as they can catch fire, as said before. Also when charging any battery you always connect them positive of the power supply to positive of the cell. A good site to tell you how to properly charge li ion and other batteries is The Battery University

Do not try to charge multiple cells of different charge levels in parallel at the same time as they will charge or discharge into each other at very high currents and get hot (risk of fire) even without the power supply connected.
 
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One way to charge these cells from a power supply is to set the open circuit output voltage to 4.150v and the current limit to say 700ma or higher if the cell can take it. Some cells only take 300ma though so you'll have to check the specs.

Ahh OK, the power supply is an old Power Design 3605, and the current limiter dial isnt working. I'll have to be fixing that first then.

You have to make sure the voltage setting is stable and it is accurate too. It's best to use a meter to double check, and make sure it can not change by itself for some reason like a temperature increase or decrease.

Yeah I frequently double check the PS w/ a meter. Good tip on checking it at different temperatures though.

Since you know nothing about your dangerous Lithium battery cells and do not know that they can catch on fire if you charge them wrong (you talked about connecting them backwards) then you should not touch them.

Sorry but that response isnt very helpful. Im well aware that charging a battery improperly can result in a fire, its pretty clearly written on just about every battery Ive ever seen.

Do not try to charge multiple cells of different charge levels in parallel at the same time as they will charge or discharge into each other at very high currents and get hot (risk of fire) even without the power supply connected.

OK. One at a time is all I intended. Thanks for all the advice.

-Chris
 
Hi again,


I've used a bench power supply to charge Lead Acid batteries but not sure if i would trust it with my Li-ion cells. I like to use circuits designed specifically for Li-ion cells that have well controlled current and voltage regulation. I guess it all depends on the quality of the power supply.
 
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