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Li-ion batteries and chargers — Parallax Forums

Li-ion batteries and chargers

Brian CarpenterBrian Carpenter Posts: 728
edited 2012-07-18 12:08 in General Discussion
Guys,
I have a bit of a problem in that a client of mine provided me with some parts to provide them with a solution. This solution is to be battery powered so they provided me with a li-ion 12v battery and charger that they sourced out of china. It is a 6 cel 4500 mah pack witch is not the troubling part but the "charger" that was provided with it is just a 12v dc wall wart and is to just be plugged into the battery pack. First, I thought that the pack may have charging circuit under the shrink wrap but this is not the case. Although I have not done much with li-ion batteries in the past, I have used Lipoly and know that they require a special charger. Inact I believe that parallax makes a charger and 2cell pack of li-ion. So.. What am I missing guys. The documentation clearly Bowes hat this pack is to plug into this wall "charger". What is going to go wrong?

Comments

  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2012-07-17 23:40
    Ahem ...... oy !

    when I was a young 16 lad I made a vain attempt to add a few Li-Ion cells to my old ham HT ( ICOM used poor 900mAH AAs ( I mean they had 1800s back then .. WTHeck Icom Jeez ) they were rated at 3 AH . twas a 14V max radio so I used used 3 cells .
    I used a 12V wart rated at 200 mA figure its Low amps I can shove the cells on it for a hour and be OK ....nope ...
    no sooner did I go to bed did I see a estes rocket flame apper from the end of a cell... 1 foot flame was roaring out theback.
    I used ducktape as as cell wrap. the tape melted and sputterd all over my forearm . I still have the scar from that day .

    As rude as it sounds........ the person whom sold it needs a good smaak over the head.

    besides C/30 charging a NiCd or SLA pack or perhaps I would never advocate a dumb charger out side of a lab .

    It's poor eng and uber unsafe .

    Peter
  • TorTor Posts: 2,010
    edited 2012-07-18 04:23
    Li-ion batteries need a charger which includes a regulating circuit. It must control the charging voltage so that
    a) the current doesn't exceed some specific limit, it can be around 1 ampere for packs around 1500mAh (so quite large compared to some other types of batteries actually).
    b) never let the voltage go above the maximum voltage spec'ed for the type of battery (for phone batteries (aka "3.76V") that limit is around 4.10V-4.20V, as their built-in protection circuit triggers at 4.30V. NB: Some battery packs, particularly those sold to the RC hobbyists, may come without a built-in protection circuit - they will go up in flames instead, as described by Peter. For those, you're supposed to provide the protection circuit yourself. They can be bought from certain companies, although I can't tell you which ones (all I know is that I own two batteries where the circuits were acquired from such a source, and the actual batteries from another).

    A good place to read up on this is: http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

    -Tor
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-07-18 07:04
    One of the artilcles I read at the link Tor just gave says that LiPo and Li-Ions are pretty much the same chemistry. Li-Ions need the same care when charging as LiPo batteries.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2012-07-18 10:33
    Parallax just started selling a very good $89USD battery charger that will charge Li-ion and just about all and everything sold (3 kinds of Lithium chemistry - up to 8 cells in series), NiCad, NiMh, and so on.

    What you were provided with is a typical problem with vendors out of China. The vendor is selling Li-ion batteries and chargers, but knows nothing about the product's safety requirements. The guy is just a vendor that was given something from a wholesaler. This kind of stuff usually never gets to the USA as isn't likely to meet UL approval, but gets exported throughout the 3rd world until everyone wises up.

    Lithium needs safety features in the charger; and lithium need discharge limiters to avoid sudden destruction of new cells.

    Lithium has 3 chemistries - LiFe, Li-ion, Li-Mn. I think they output 3.2V, 3.6V, and 3.7V respectively. Read the manual for Parallax's new charger to find out about the various charge requirements as they are indeed different. And be wary of schemes that don't have a limit to discharge, a limit to charge, and 3 modes of charging.

    What continues to puzzle me is how one gets a 6-cell, 12V battery pack out any Lithium batteries. The true voltage has to be something else.

    The MOST IMPORTANT thing is to stop charging if the pack swells like a pregnant guppy - you could be about to witness a nasty fireball. DO NOT use this charger in any place that cannot tolerate a dramatic rupture and fire hazard.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2012-07-18 11:32
    2X3 cells .. Its not true 12V but it will do for some uses ..



    I use a cinderbock as a charging pit for any batts besides my 12V PBA AGMs .. I have the batts the hole and I cover the top.. at least it will give me a sporting chance of escape ..
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2012-07-18 12:08
    Give it a try. I had an r/c airplane with a 7.4v Lithium pack that came with a wall wart and it charges nicely - but it has a green/red led that indicates some intelligence.

    I bought a spare 7.4v so I could fly more and that appeared to be exactly the same. But it failed about the second charge and swelled up to rather serious proportions. At the time it cost me $40USD or so.

    Lithium holds about 6 times the charge of other chemistries, but they are temperamental. One must do things right or they end up as trash.

    Recently, I have had two 14500 3.7v batteries ready to use on microcontrollers. I had to test a hobby motor and h-bridge, so I grabbed the two set up in series. Just rotating a hobby motor a few times in two directions was enough to completely short out one cell. It was brand new, fully charged - now it reads 0.7volts and seems shorted. I guess the rate of discharge was too fast.

    Do I dare to put it on a charger that can't recognize a defective Lithium battery? The battery may not explode, but a short is not good for the charger either. At the least, provide a fuse for a bit over the optimal rate of charge. It would be wise to have a thermal sensor and shut off if the battery got too hot, after all... all the cell phone batteries include a thermistor. I wonder why we have to add our own to other cells.

    Parallax is selling a system that properly manages the Lithium cells, but there are a lot of people that are not so diligent in what they are selling. Lithium requires a good management system, not just a good charger. Discharge needs control as well. Some 18650 cells are including this inside the battery itself, other 18650 cells do nothing.
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