Charging lithium ion battery - Page 1
Forum section: electronics / beginners

author: GeorgeTsak
author_rank: Contributor
timestamp: December 25, 2016, 04:37:30 pm
content: Hi! I saw a video Dave posted about charging lithium ion batteries with a power supply and I was wondering if this procedure is safe for the power supply. I am asking this because I have seen a couple videos people posted about their supply got ruined. (I think that they applied less voltage than that of the battery resulting in current flowing from the battery to the power supply, eg they applied 2V in a 3.7V cell, I am not completely sure though)

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: December 25, 2016, 04:47:59 pm
content: Get a TP4056 module from eBay or Ali and don't worry about it. Sure if you're testing absolute capacity what Dave did will give better results but for the man on the street the aforementioned is perfectly fine. Or a dedicated charging station etc...

author: GeorgeTsak
author_rank: Contributor
timestamp: December 26, 2016, 09:13:47 am
content: Quote from: RGB255_0_0 on December 25, 2016, 04:47:59 pmYes I am aware of this module and I have bought some (Thank you for mentioning it though). However my question is; Is charging a battery with a power supply dangerous for the power supply? I just want to know that.

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: December 26, 2016, 09:42:33 am
content: https://www.eevblog.com/forum/blog/eevblog-919-how-to-charge-li-ionlipo-batteries-with-a-power-supply/Read that thread then.

author: Rerouter
author_rank: Super Contributor
timestamp: December 26, 2016, 09:59:43 am
content: it comes down to how the power supply is made internally, and how it holds up to an external power source on its output when its turned off or set to a lower voltage.Personally i have used this guy to charge all sorts of batterieshttp://www.ebay.com.au/itm/30V-5A-Portable-Switching-DC-Power-Supply-Test-Adjustable-Variable-LED-Digital-/142029184752?hash=item2111995ef0:g:HFYAAOSw-W5Uvf-AYou can generally find them a bit cheaper, and the 10A versions only come with a single turn current set pot, while the 5A comes with a 10 turnNow they will happily survive loosing input power, but i would say if you ever plan to walk away from it, use a diode inline, as it does have a load resistor on the output for regulation.For most battery types it will need to have a constant current mode, especially lithium. and for the lithium types, don't get impatient, charge at 1C (the amp hour rating of the battery) or lower.in general if it has balance leads, check the state of all the cells, to see that there pretty much even, if not you may need to charge cells in the pack to a matching voltage and monitor them carefully to see that 1 cells isnt chearging drastically different from the rest.If the battery doesnt have balance leads, then only charge on a non flammable surface, if the cells are rated to 4.2V, only charge him to 4.1 per cell (that way if your supply is off a little you have a safety margin, and you dont really loose much capacity)If you want something a little more plug and play and already have a power supply without a current limit, then i suggest something like this guyhttps://hobbyking.com/en_us/turnigy-accucel-6-80w-10a-balancer-charger-lihv-capable.html

author: Seekonk
author_rank: Super Contributor
timestamp: December 26, 2016, 05:43:46 pm
content: Love those TP4056 modules. I just hook them up with a cell phone wall wart. Note in the spec it says to use a .5 ohm resistor in series. You don't have to, but better to put the heat in a resistor than an IC. This is a linear regulator. I use up to a couple ohms to limit charging rate on iffy used cells. It lowers maximum charge current but not end current. These shut off charge in the end. A power supply won't do that. Under charged cells last longer and only a few percent of capacity is lost under charging.

author: Rick Law
author_rank: Super Contributor
timestamp: December 27, 2016, 05:24:40 am
content: If you want to limit (lower) the charge current, the TP4056 can adjust charge current from 130mA to 1A.Change Rprog(pin 2) to different values for different charge current.I = 1200/RprogSo, an Rprogof 1.2K give you exactly 1Amp charge current.Look up the specs and you can find all sorts of other goodies there.

author: GeorgeTsak
author_rank: Contributor
timestamp: December 27, 2016, 03:38:41 pm
content: Quote from: RGB255_0_0 on December 26, 2016, 09:42:33 amThanks for the info!Quote from: Rerouter on December 26, 2016, 09:59:43 amhmm... Yes I should have thought to use a diode in series and using a multimeter to increase the voltage to compromise the voltage drop. Also I agree the using 4.1 volts is the safest thing to do... (Unless you have an expensive power supply or an accurate multimeter)Quote from: Seekonk on December 26, 2016, 05:43:46 pmDoesn't the TP4056 module limit the current by itself? Owning this module I have never used a resistor in series... As far as I know the maximum current it can provide is 1A.Quote from: Rick Law on December 27, 2016, 05:24:40 amThanks for the info! 130ma? Is there a 18650 cell with such a low capacity? Unless you want to slowly charge a low capacity cell e.g. a 260ma at 0.5C

author: Seekonk
author_rank: Super Contributor
timestamp: December 27, 2016, 06:41:47 pm
content: "Doesn't the TP4056 module limit the current by itself? Owning this module I have never used a resistor in series... As far as I know the maximum current it can provide is 1A."Yes it does and it turns that into heat. ! amp and 1V means you are dumping 1W into the IC. It can take that, but wouldn't you rather put that heat somewhere else. Check the spec sheet, they have the resistor there and it has a spot on the board that is just jumpered out. The boards are shipped 1A and then taper to 0.1A till they shut off at 4.2V. I grab a lot of recycled laptop power packs and they can be risky if left unattended. I prefer not to charge an old cell at the maximum. I use phone wall warts. Many are self limiting as far as current, others are rated at just about a half amp. The resistor easily limits maximum current, but not the end current which is fixed at 1/10 the max charge rate determined by that little snot of a resistor. I wish you luck changing that. The foil is so thin on these boards, think they just rubbed a penny on them, it is likely to lift off changing that resistor. If you are that experienced with surface mount I would hardly guess you need to come on a forum and ask questions. You can go to MUCH lower currents than the 130ma specified in the chart. Some use this board to charge coin cells (the rechargeable ones that is).

author: GeorgeTsak
author_rank: Contributor
timestamp: December 27, 2016, 07:01:32 pm
content: Quote from: Seekonk on December 27, 2016, 06:41:47 pmI see your point and you are right. Thanks again for getting into the trouble to explain all this to meHave a nice day!

author: IanB
author_rank: Super Contributor
timestamp: December 27, 2016, 07:06:47 pm
content: Quote from: GeorgeTsak on December 25, 2016, 04:37:30 pmIf you can find detailed operating specifications for the power supply (good power supplies will have this information), it will tell you what the power supply can safely handle in terms of reverse voltage on the output terminals.There is no general answer to the question of "is it safe?". It depends on the specific supply you are using-- although most good adjustable laboratory power supplies will be able to charge lithium ion batteries without harm.

author: Rick Law
author_rank: Super Contributor
timestamp: December 27, 2016, 09:10:04 pm
content: Quote from: Seekonk on December 27, 2016, 06:41:47 pmFor current limiting, the TP4056 does not dump that much into heat. It lowers the charge voltage to keep the CC (constant current) selected byRprog.So the waste heat doesnotequal toVsupplied*(1A-Idesired), rather,the waste heat is theIdesired*Vdrop.If theIdesiredis lowered, your waste heat is also lowered.[ see EDIT below ]You can see that for yourself and connect an Amp-meter before the TP4056 and after the TP4056. The current coming out of it is the same as the current going in.Vdropis the difference in voltage going into TP4056 and the voltage coming out of it.Personally, I think letting TP4056 manage the current is just fine as long as your power supply is around 5V. I am however more concern about the (per-spec) 4.2V +/- 1.5% in charge voltage. On the real thing, 4.263V output is a bit more than I would like. If you get a fake-TP4056, it may be worst.I have a cut-tape of 20xTP4056es. I actually paid more from what I thought would be a reputable dealer. I tested two of them and they were in the 4.4V to 4.5V range. Since it was to repair a board,it could be other thingson my board that caused the 4.5V out, but I now adopt the "Trust but verify before use" mantra before I "deploy" the darn thing.Once tested, they do work like a charm. Love it.[EDIT: forgot to mention:]If theIdesiredis lowered, it is done by increasing Vdrop. So it may seem to be just a wash withIdesired*Vdrop. Experience with charging shows you don't need to drop the voltage by 1/2 just to drop the current by 1/2. So, Vdroprequires a small increase to cause a much bigger decrease in Idesired. End result is,Idesired*Vdropgot smaller.

author: Seekonk
author_rank: Super Contributor
timestamp: December 27, 2016, 11:01:20 pm
content: "For current limiting, the TP4056 does not dump that much into heat. It lowers the charge voltage to keep the CC (constant current) selected by Rprog.So the waste heat does not equal to Vsupplied*(1A-Idesired), rather,the waste heat is the Idesired*Vdrop.If the Idesired is lowered, your waste heat is also lowered."It's the internet. If I say it is a nice day, someone will come along and say there is a little cloud over there. That isn't at all what I said. Typical supply voltage is about 5v so you very easily can get 1W of dissipation with about 1V of drop. I still think that is a lot of dissipation in a chip that you don't know exactly who made it on a board with no dissipating copper. Don't think the OP was confused about that power loss at all.

author: Rick Law
author_rank: Super Contributor
timestamp: December 28, 2016, 02:21:13 am
content: Quote from: Seekonk on December 27, 2016, 11:01:20 pmI do get too argumentative. If that offended you, sorry! Didn't mean to be offensive...