Great 1-cell Lithium Polymer Battery Charger..... - Page 1
Forum section: electronics / general

author: pullin-gs
author_rank: Regular Contributor
timestamp: May 18, 2012, 01:12:58 am
content: Most of you already own it!Set your lab power-supply to 4.1VDial in the PS current to the MAH rating of the battery.It will take about an hour to charge the cell.Done.This only works for single cells....DO NOT TRY TO CHARGE MULTIPLE CELLS: Bad things will happen if you do.

author: nukie
author_rank: Frequent Contributor
timestamp: May 18, 2012, 01:33:03 pm
content: You forgot where the leads go.If you don't already know this then you probably should not try it.

author: pullin-gs
author_rank: Regular Contributor
timestamp: May 18, 2012, 03:21:01 pm
content: Quote from: nukie on May 18, 2012, 01:33:03 pmI forgot to tell the reader to remember to breath and exhale also! What was I thinking!

author: SeanB
author_rank: Super Contributor
timestamp: May 18, 2012, 04:33:12 pm
content: Heart - pump.Heart - pumpGuts - contract in peristalsisHeart - pumpWhat was I saying??

author: free_electron
author_rank: Super Contributor
timestamp: May 18, 2012, 05:26:05 pm
content: uhhuh.. and that works fine .. untilk the regulation of the supply is off, or the meter is off by 100mV and then you have a smoking crater where your house used to be....When chargin any kind of lithium chemistry battery you need to check the temperature ...

author: pullin-gs
author_rank: Regular Contributor
timestamp: May 18, 2012, 05:51:18 pm
content: Quote from: free_electron on May 18, 2012, 05:26:05 pmEven chargers DESIGNED for lithium can fail due to the very reasons you just mentioned.Ehem....100mv? Dont you mean 200mv? Hehehe, if you knew your lithium battery technology, you would realize that the recommended peak charge is4.2 VOLTS.Note I recommended 4.1V.

author: BravoV
author_rank: Super Contributor
timestamp: May 18, 2012, 05:59:53 pm
content: Let sum up ....- Voltage & current, whats your psu accuracy especially the voltage regulation ? 5% ?- Temp & time limit .. noneSee the problem ? I wouldn't called it a "great" charger, its merely a hair close to poorman charger grade.

author: pullin-gs
author_rank: Regular Contributor
timestamp: May 18, 2012, 06:12:16 pm
content: Quote from: BravoV on May 18, 2012, 05:59:53 pm"Poorman"?Not quite, I have about twice the money in my PS as I do in my two 5S LIPO chargers.But in a pinch, it is great to know that I can charge my gadget's LIPO with my PS.PS: timers are a good thing....I use those even with my LIPO chargers.PSS: Heat? Most LIPO chargers do not utilize them.

author: free_electron
author_rank: Super Contributor
timestamp: May 18, 2012, 09:30:35 pm
content: Quote from: pullin-gs on May 18, 2012, 05:51:18 pmVolts is NOT 'charge'. Charge is coulombs.No need to explain me how liion charging works. i have made several charger chips... and blown up many a cell in the lab ...Not all lithium cells use 4.2 end termination. some are 4.1 some can be as high as 4.5 or as low as 3.6. it depends on the cell construction and the chemistry used. There are MANY types of cells with different chemistries.just slapping on a voltage is NOT done ! Besides if you have a 4.2 volt cell and you terminate charge at 4.1 volt it will only be about 70% full... the real 'charge' is stored during that last 100mV rise ... you need to look at the dv/dt to terminate charge. True LiIon chargers use constant current to get to within a few millivolt from termination. Then they switch to constant voltage mode to avoid overloading the cell. The DI/Dt is carefully monitored. Really advanced chargers do pulse charging .

author: pullin-gs
author_rank: Regular Contributor
timestamp: May 18, 2012, 09:53:33 pm
content: Quote from: free_electron on May 18, 2012, 09:30:35 pmFeel better now?Like I said, a lab power supply makes a great LIPO charger as described.Give me a valid argument as to why not?Feel free to post the rest of your resume' if you like and your little factoids also, I had fun reading it.PS: Lithium Polymer (The subject cell) IS 4.2 volts. But you knew that already.

author: muvideo
author_rank: Frequent Contributor
timestamp: May 18, 2012, 10:00:02 pm
content: Quote from: free_electron on May 18, 2012, 09:30:35 pmHello, I associate the dV/dt and pulse changing to Ni chemistries, could you explain better the differentials you aretalking about (dV/dT dI/dT) and pulse charging for lithium chemistries?As for "True LiIon chargers use constant current to get to within a few millivolt from termination. Then they switch to constant voltage mode to avoid overloading the cell. " is no problem for the bench power supply (not considering cablingresistance that should only have the effect of lenghtening the charge time).Thanks,Fabio.

author: pullin-gs
author_rank: Regular Contributor
timestamp: May 18, 2012, 10:14:00 pm
content: Quote from: muvideo on May 18, 2012, 10:00:02 pmIndeed this is the case.Another error free's post is the voltage levels. This is a LIPO thread. Every single COTS Lipo battery charger I have ever owned has a hard voltage cutoff of 4.2V.

author: free_electron
author_rank: Super Contributor
timestamp: May 18, 2012, 11:13:58 pm
content: Quote from: muvideo on May 18, 2012, 10:00:02 pmInitially the cell is charged with a constant current. At a certain point we switch to constant voltage charge . From now on we need to look at the current. So we monitor now di/dt. If this falls under a certain level the remaining charge time required would become very long. For example : we take a specific cell. The charge specs claim that you can charge this particular cell to 90% capacity in let's say an hour. To get the remaining 10% in there you need to go on for another 4 to 5 hours ... At this point the system switches to pulse charging. ( they go back to CC mode but this time we pulse currents. after every pulse the cell voltage is analyzed. The cell voltage actually falls back in a few milliseconds. there is a technique where this dv/dt is monitored as well. i forgot who has the patent on that on. i believe Asahi Kasei. ) The handoff between CC and CV causes problems. it is posible that the step-up to CV actually causes current to increase beyond the allowed charge limit. This is where pulse charging can be employed as well. They modulate the on/off time until CV can be maintained.All the wile you need to monitor cell temperature.If all you are after is getting 80% charge in 5 hours .. be my guest : muck around with the lab supply , but quadruple check the output voltage !!! going 0.1 volt over can cause the cell to explode ...if you want to fill the cell to 80% in a reasonable time : you need an intelligent system. If you want to get 100% in a reasonable time .. pulse charging but this get s very complex very fast.As cells age the electrode changes. the solvents used create an isolation barrier ( this happens actually immediately after construction as well. this isolation barrior still allows for the exchange of ions. i'd have to go back to my notes for the finer details... last time i messed with this was 1997 .. ). these solvents can decompose under heat. -> kaboom ...smart lithium chargers ( doesnt matter if it is lipo or liion ) actually tack the curves over time. Benchmarq has really good chips for that. they maintain a record in eeprom of what has happened to the cell eand the charging system adapts itself depending on age. ( that is why in some laptop battery packs replacing the cells never gets you back to 'full' energy. simply because the eeprom data causes the charge controller to treat the cells as 'old'.Lithium chemistry batteries are NOT TOYS. Even the big boys like Sony , Dell and others mess it up big time ( look at all the battery recalls ). We had our cells in blastproof containers. ( a kind of plexiglass box. dont know if it was lexan or some other material ). and i have seen 4 or 5 go 'off'.. and these were the tiny cellphone cells. One time we had a kodak flexible battery. that thing bulged up like one of those drink puches you poke a straw in ... and then went kaboom.Whenever i see people 'muck about' with lithium cells i take a detour... these things are very dangerous if mistreated. oh, and never-ever throw water on a burst cell.. lithium is so agressive it can strip oxygen molecules from water ... giving hydrogen... combine that with oxygen in the atmosphere and the heat generated .... you know ... 1+1 is sometimes larger than 2 ...

author: pullin-gs
author_rank: Regular Contributor
timestamp: May 19, 2012, 01:12:57 am
content: Quote from: free_electron on May 18, 2012, 11:13:58 pmDitto.

author: nukie
author_rank: Frequent Contributor
timestamp: May 19, 2012, 01:45:36 am
content: In most commercial charger if not all, there is a charge termination at 4.20V? Why not let it float at 4.20V, and continue charging? Think about it.None of the battery datasheet recommend this type of charging. It works in a pinch yes but don't let lazyness turn you into a fool.There are many cheap charger in the market especially those for cylindrical cells some of these are are great for setting up houses on fire. Maybe even your neighbors house.

author: M. András
author_rank: Super Contributor
timestamp: May 19, 2012, 11:54:08 am
content: most of them cut the charge or the protection circuit cuts the charge at 4.2volts +/- 0.05volts. but most of them only charges them to 4.19volts or so they never reach the max limit

author: amyk
author_rank: Super Contributor
timestamp: May 19, 2012, 11:55:17 am
content: Quote from: nukie on May 19, 2012, 01:45:36 amIf you connect a full battery to a constant voltage source at 4.20v it will not charge beyond that, as by basic principles there is no current between two points of equal voltage. But it is a good idea to disconnect the charger when the voltage has reached the full point.Lithium batteries have the longest lifetimes when not charged fully. They should be stored around 40% charge.