Author Topic: Li-ion batteries.. How to charge them?  (Read 619 times)

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Offline extreme.alyTopic starter

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Li-ion batteries.. How to charge them?
« on: June 04, 2013, 08:54:00 AM »
Hello,
I bought some Li-ion cells (3.6V each) and joined them together in series to give me around 11V. However, I don't know how do I charge them! I heard that Li-ion batteries are very dangerous and must be handled with care or they'll explode!

So I guess charging them with a simple 12V adapter is not a good idea. Any suggestions how do I charge these batteries?

Offline johnwarfin

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Re: Li-ion batteries.. How to charge them?
« Reply #1 on: June 04, 2013, 09:57:25 AM »
you heard right. they can be much trickier to charge than nixx. cc/cv, constant-current/constant voltage. for one cell i use a usb cable with diode in series. toy plane and heli chargers ok for 1s too. but for multi-cell you need a proper charger. they can get very expensive but i have good luck with my multi-chemistry  cheapo detrum dc6 (bc6 clone).  you can get pretty good units from aliexpress and ebay for around $10-$20 shipped.

Offline jwatte

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Re: Li-ion batteries.. How to charge them?
« Reply #2 on: June 04, 2013, 10:31:22 AM »
If you have a benchtop power supply, you can set it to current limit at about 1C -- if your cells are rated 1000 mAh, set it to current limit at 1A.
Set the voltage to 4.2V*num-cells, so 12.6V.
Now, plug in the benchtop power supply to the cells, and it will CC charge until it gets to 4.2V, at which point it will CV charge. You have to check up on this, though, because when the charge current drops to about 1/10th (100 mA) it's time to disconnect the batteries. Do not keep them on extended trickle charge!

You *can* charge them with a 12V power supply, although they will not reach full charge. Use a multimeter to monitor the voltage. When the voltage has been at 12V for 10 minutes, disconnect the batteries.

Note that LiPo packs generally need balancing now and then, though -- this is why LiPo chargers have "balance" plugs; typically of JST type. To charge battery packs well, you want a specific LiPo charger, which can be had for about $20 online. You also need to properly solder the JST balance plug to your battery pack.

Offline extreme.alyTopic starter

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Re: Li-ion batteries.. How to charge them?
« Reply #3 on: June 04, 2013, 05:25:32 PM »
You *can* charge them with a 12V power supply, although they will not reach full charge. Use a multimeter to monitor the voltage. When the voltage has been at 12V for 10 minutes, disconnect the batteries.

OK, a noob question :P, Is it fine to check the voltage across the batteries while connected to the 12V supply?

One more question.. What if I supply more OR less current (A) to the battery than battery's current-hour (Ah)? Is it gonna burn? :P or just the time to charge is gonna alter?

Offline jwatte

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Re: Li-ion batteries.. How to charge them?
« Reply #4 on: June 04, 2013, 06:19:49 PM »
Quote
Is it fine to check the voltage across the batteries while connected to the 12V supply?

Yes it is, as long as you don't short it out :-) The multimeter is a very light load, and won't affect the charging.

If the batteries are deep discharged, then the 12V power supply will do one of three things:

1) Deliver its maximum current at a lower voltage. If the maximum current is 5A and the batteries are rated at 1000 mAh, you'd be charging at 5C rate. This may not be good for the batteries -- they could overheat and either go bad, or, worst case, catch fire! Make sure to match the capacity of the supply to the charge rate of the batteries.

2) Go into "hiccup" mode where it tries to deliver charge, notices the overload, disconnects, then repeats the cycle. (Sometimes, it won't repeat the cycle, in which case you can't use that supply.) This will slowly put a charge into the battery, without overheating it, but it's not very efficient.

3) Attempt to over-deliver on current, and burn out itself (rather than the batteries.) This will ruin the wall adapter.

So, hopefully you have wall adapter of type 1, and it's reasonable matched to the batteries. LiPos can often be charged at more than 1C, but how well that works depends on the specific battery. Monitor the heat of the battery!

I'd just get a B6 charger knock-off for $20 and solder in the appropriate JST balancing connector. That way, you know it'll be done right, and have less risk of burning the house down.

Offline extreme.alyTopic starter

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Re: Li-ion batteries.. How to charge them?
« Reply #5 on: June 05, 2013, 06:49:55 AM »
Okay thanks, but how do I check that how much current-hour (Ah) my each cell is?
I see nothing written on the cells.

Offline jwatte

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Re: Li-ion batteries.. How to charge them?
« Reply #6 on: June 05, 2013, 10:07:39 AM »
When you bought the cells, that should have been part of the specifications.
If you don't know, you'll have to estimate. Look at 1S battery packs on places like hobbypartz.com, and compare to the size of your cells. Whatever cells are of similar size are probably similar capacity.

Offline extreme.alyTopic starter

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Re: Li-ion batteries.. How to charge them?
« Reply #7 on: June 06, 2013, 06:30:47 PM »
http://www.batteryonestop.com/baotongusa/products/datasheets/li-ion/Samsung-SDI-ICR18650-26A.pdf

We have these batteries. What wall adapter must we use for charging these type of batteries? 2.6 A, considering that we have 3 cells in series. What voltage should we supply? Datasheet suggests charging voltage as 4.2 V for a cell

Offline jwatte

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Re: Li-ion batteries.. How to charge them?
« Reply #8 on: June 06, 2013, 06:59:29 PM »

 


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