I have build simple LM317 power supply.Input is 12v (I am using computer power supply), and the output is around 4v .I was wondering, can i use this to charge my 3.7v lithium batteries?
Here is schematic of my circuit
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1\$\begingroup\$ You need to be able to control the output current. If you can't do this then it's game over. \$\endgroup\$– Ignacio Vazquez-AbramsCommented Dec 4, 2014 at 16:53
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\$\begingroup\$ I already connected this to battery.It is charging, but very slowly, and i am checking heat every minut.What u think, could it be charged to maximum (4v) ? \$\endgroup\$– RickyCommented Dec 4, 2014 at 17:01
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2\$\begingroup\$ There are lithium battery charge controllers for a reason - I suggest you use one. \$\endgroup\$– MajenkoCommented Dec 4, 2014 at 17:46
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Be careful charging lithium batteries. There are lots of safety issues. You need a way to control the current, terminate charge, and monitor battery temperature to do it properly. If you don't do these things properly there's a real risk of fire or even explosion. Yes, most lithium batteries can charge with a voltage of 4V, but without carefully following the charging recommendations in the battery datasheet you run the risk of getting in trouble. So to answer your question, no, you should not use your LM317 circuit to charge your lithium batteries.
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1\$\begingroup\$ I just want to point out that if the maximum charge voltage is 4V, the battery will probably not be fully charged. I agree with others that you should use a dedicated lithium battery charger IC. It would be difficult to design a good, safe charger without using a dedicated charger IC, and a simple voltage regulator is not adequate. \$\endgroup\$ Commented Dec 4, 2014 at 18:28
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1\$\begingroup\$ @mkeith is correct, and 4.2V is the usual charging voltage for Li, but again if whatever you use to charge is not specifically designed for your battery chemistry you are risking fire or even explosion. It's not just about the charging voltage. \$\endgroup\$– John DCommented Dec 4, 2014 at 19:14
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1\$\begingroup\$ @Ricky, this is a complicated topic and there are a lot of details which matter. When you say "using a mobile charger" what do you mean? You mean connect your battery to a mobile phone in place of the OEM battery? That might work if the battery is the same basic type and capacity. It will probably not work if your battery is larger than the mobile battery (because the charger will time out and might not terminate correctly either due to capacity difference). If you think the so-called "charger" for a mobile phone is actually a charger, you are mistaken. It is just a DC supply. \$\endgroup\$ Commented Dec 4, 2014 at 19:19
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2\$\begingroup\$ Again, @mkeith is correct, the mobile phone "charger" that plugs in to the was is just a DC supply, the Li battery charger controller is in the phone itself. So if that's what you are talking about (and it's not entirely clear what you mean by mobile "charger") then it's a no-go as well. \$\endgroup\$– John DCommented Dec 4, 2014 at 19:59
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1\$\begingroup\$ You can buy chargers for Lithium chemistry batteries. I have several 18650 round cell lithium batteries (for flashlights), and I charge them with an off-the-shelf charger. Private message for make and model if you are interested. It is off-topic for this forum. Or go search the candlepower forums. \$\endgroup\$ Commented Dec 6, 2014 at 5:46