Good LI Ion battery packs  - Page 1
Forum section: electronics / projects

author: ianscott
author_rank: Contributor
timestamp: April 22, 2014, 08:59:37 am
content: HiIm doing a project and i need a proper Li Ion Battery, a LiPo battery would be good but are too dangerous. But all i can find are cheap Chinese ones like theseeBay auction: #http://www.ebay.com.au/itm/4KDQ7-DC-12V-6800MAH-SUPER-RECHARGEABLE-LITHIUM-ION-BATTERY-SCA-0650-/221252577867. The battery I'm looking for is a 12v 3000mah to 4000mah Li Ion.Thanks!

author: amyk
author_rank: Super Contributor
timestamp: April 22, 2014, 11:13:01 am
content: You won't get exactly 12V from lion batteries, since each cell ranges from 3~4.2V empty and full. A 3S pack will be 9~12.6V, a 4S is 12~16.8V. You can try looking at laptop batteries.

author: ConKbot
author_rank: Super Contributor
timestamp: April 22, 2014, 11:41:39 am
content: Ive used batteryspace.com for a source of battery packs with an integrated management/protection circuit for work projects a few times. For small projects they are pretty good imo.

author: techydude
author_rank: Unknown
timestamp: April 22, 2014, 02:30:45 pm
content: all-battery.com (aka Tenergy)e.g.:http://www.all-battery.com/li-ion18650148v4400mahpcbpreotectedrechargeablebatterywithbareleads.aspxas Amyk said, Li-Ion cell terminal voltage varies from ~3.0 flat to 4.2 full, so the industry often refers them by the middle value of this range, e.g. 3.6 or 3.7V per cell.also, i don't know what the quality is like, but the price is usually right, have you looked at HobbyKing.com ?

author: akis
author_rank: Frequent Contributor
timestamp: April 22, 2014, 05:22:36 pm
content: I have bought 4 Li-Ion/Po packs from ebay. All listed as 12V and something silly like 9600mAh.I have opened one up and noticed that it contains 3 cells in series. The cells are thin and flat measuring about 3" by 1.5". Each "cell" has a tiny circuit which is to protect from various conditions, not sure if it has a temperature sensor either (probably not).These ebay batteries are NOT 9600mAh or whatever they claim to be. Each cell is 3200mAh and the makers (with whom I have exchanged some funny emails), presume that 3 of 3.6V /3200mAh in SERIES equates to 12V / 9600mAh. My Chinese is crap and could not explain to them the error here.Secondly some of these batteries do discharge overtime on the shelf, and from the two I initially bought, one seemed to discharge much more readily than the other, so much so that it then would not charge. I opened it and removed the tiny circuits which you can see on the photo, and now it works much better. But I have built my own battery charger to avoid overcharging etc.Suffice to say that the chargers they come with are rubbish.

author: sacherjj
author_rank: Frequent Contributor
timestamp: April 22, 2014, 06:22:26 pm
content: If power density is not an issue, I would go with an LiFePO4 cell. This is about 30% larger for the same power than a cobalt style LiPo. However, it is made for longer service life and higher cycle count. It is also considerably safer chemistry. The cells are 3.0-3.7V and there are common versions to replace 12V NiMh or Gel-Cells, such as these:http://www.batteryspace.com/128vlifepo4batterypacks.aspxThis looks like 4x cells in series. So voltage would be 12.0V - 14.8V.

author: mark03
author_rank: Frequent Contributor
timestamp: April 22, 2014, 08:29:33 pm
content: I don't know about you, but most of my projects do not have safety risks, except for the battery. So that's the one place I would absolutely insist on a known/reputable vendor. Batteryspace.com is one.From what I can tell, the majority of the direct-to-consumer market for generic Li-ion cells is the RC hobby market. I would avoid these because they generally don't have a protection module built in, and who wants to futz with installing one themselves? Also, they are optimized for extreme discharge currents, which is probably not what you want (although I suppose it depends on the project).Finally, keep in mind that charging a Li-ion battery with cells connected in series requires extra care and hassle. You have make sure the cells stay balanced. For portable instruments and generic digital/embedded type projects I try to use a single cell (or multiple cells in parallel only) and design for a 3.7V power rail. If I need a higher rail I use a boost converter.

author: Yago
author_rank: Frequent Contributor
timestamp: April 22, 2014, 10:02:56 pm
content: Is it not dodgy to remove the protection circuit?It is not only for charge, but also overcurrent and under voltage protection.I also thought that as a rule of thumb, the cells with protection ccts, have them as they are one of the more volatile chemistries.

author: Psi
author_rank: Super Contributor
timestamp: April 22, 2014, 11:04:54 pm
content: +1 for LiFehobbyking sell them for RC transmitters.There voltage is damn stable until flat where it instantly falls like a rock. (Detecting battery charge can be an issue)

author: akis
author_rank: Frequent Contributor
timestamp: April 27, 2014, 05:50:47 pm
content: I have run some tests on these Chinese batteries. We know already that they are not 9800mAh as they claim to be, because they have added three of "3200mAh" in series, that does not give 3 times the capacity, only 3 times the voltage.I charged one to 12.5V which is very close to max and discharged on an average load of 380mA - the battery lasted 4:45h down to 11V and 6 hours to 10.8V. From that and using Peukert's law backwards I estimate the pack to be around 3000mAh.One pack weighs 337 grams. If we remove the packaging the 3 cells weigh 170 grams.We could theoretically take 4 of these packs to make a 4 * 3000mAh = 12,000mAh pack at 12V nominal.If we took the packaging off each battery and repackaged it in one, this pack would weigh 525 + 200 grams and would cost about £80 on ebay. That would give a price (pounds) to Ah ratio of 6.7 pounds/Ah and a weight to Ah ratio of 60 grams/Ah. Comparing with the Tracer batteries : the Tracer 12V/14Ah comes in at a price of 12.8 UK pounds/Ah and 68 grams/Ah in weight. So on the weight front we would not gain anything, but we'd be at half the price!And it gets better.An mportant factor is to know how the capacity is specified on the commercial batteries, eg on the 12V 14Ah Tracer, is it 14Ah down to which exact voltage? The cutoff is something silly like 8.5V so surely we do not care about that. If it is indeed so, then we can only assume that the "14Ah" battery would be more like 8Ah if we only go down to 10.8V - which would make the commercial Tracer all the more expensive, overpriced etc.