Determining capacity of an unknow LiPo cell. - Page 1
Forum section: electronics / general

author: ARESRACES
author_rank: Newbie
timestamp: November 29, 2014, 02:56:32 pm
content: Hi all, I'm a brand new member with some electronics experience. I own a IMax B6 LiPo balance charger and have some surplus LiPo prismatic cells that are only marked with, what I believe is a Mfg house # (9908182106), but no amp hr rating. The lowest current setting I have on the charger is .1 amp . If I set the charge current to this lowest rate, with the proper cell voltage setting, can I safely (and actually charge) the cell fully? The cell appears to be a higher than 1.5 ah capacity (my guess) and measures 1 7/8"L X 1 5/16W X 5/16' thick. Does anyone know how to make a jig to determine the actual capacity of the cell? Thanks for any and all input.Bill

author: IanB
author_rank: Super Contributor
timestamp: November 29, 2014, 03:05:45 pm
content: If the cell is really 1.5 Ah capacity, then charging it at 0.1 A will take forever. However, you can always monitor the charging progress and if it seems to be going too slowly you can increase the charging rate. It is often reasonable to use a charging current of 0.5 C with lithium cells.As for the cell capacity, can't you measure it by doing a discharge test with the B6?

author: Rasz
author_rank: Super Contributor
timestamp: November 29, 2014, 03:42:44 pm
content: Quote from: ARESRACES on November 29, 2014, 02:56:32 pmnounless you calibrate it properly, they arent calibrated at allhttp://www.martinmelchior.be/2013/09/recalibrating-imax-b6-ac-charger.html+just charge that cell while you are around so you dont burn down the house

author: saturation
author_rank: Super Contributor
timestamp: November 29, 2014, 03:51:52 pm
content: Given the cell is unlabeled and from an unknown source [ even if you purchased it from a known distributor] I'd worry about the quality of manufacture and its PCM control. Even if you characterize the battery and it works for a while, the quality matters to insure it does not burst into flames later on, even if it passes your test today. So if you decide to use it, caveat emptor.You need an electronic load or you can rig a load using power resistors. A single LiPo cell is about 3.7V fully charged, and the IEC specifies the standard charge currents and discharge current as in this data sheet for the labels on the cells.http://www.all-battery.com/datasheet/30656-0_spec%20sheet.pdfAs charge proceeds at CC say at 0.2C, terminal voltage rises as shown in the sample graph so you can estimate when you are at end of charge, i.e., 4.2V. Ignore the axis labels since you don't know the capacity of your cell but the shape of the curve is the same for that chemistry.

author: IanB
author_rank: Super Contributor
timestamp: November 29, 2014, 06:08:40 pm
content: Quote from: saturation on November 29, 2014, 03:51:52 pmIt's actually about 4.2 V, as you indicate in the remainder of your post.

author: ARESRACES
author_rank: Newbie
timestamp: November 30, 2014, 09:14:29 pm
content: Thanks, guys, for your replies. I'm just learning how to get around here so please bear with me. I am not computer literate down to the programming level so I doubt if I can do the mentioned recalibration procedure on the charger. I am not interested in "fast" charging the cell, s l o o o o w is fine with me. My only interest is in charging the cell safely. I have a couple of questions (yea, more like a couple of hundred). When the charger charges the cell in the "current" mode of the charge cycle, and the cell comes up to the 4.2 v level, is the cell basically charged at that point? How important is the "voltage" charge mode of the charging cycle? Is the "voltage" charging mode cycle basically a "topping" off of the charge? Recently I purchased (waiting for delivery) of a USB single cell charger. I am seriously giving consideratiojn to using it for charging my cell(s) but without knowing the a/h capacity I don't know how to set the charge current problem again.P.S. I have built a sort of charging cage out of ceramic tile where I place the charger and cell during charging, just in case.Bill

author: IanB
author_rank: Super Contributor
timestamp: November 30, 2014, 09:29:49 pm
content: After the cell reaches 4.2 V in the "CC" part of the cycle it is "mostly" charged at that point (maybe 2/3rds full, maybe more). So in a sense the CV part of the charge is a kind of "topping off" of the cell.There is no real advantage in charging lithium ion cells too slowly. As long as you don't exceed the manufacturer's recommended maximum charge current the CC value you choose doesn't really matter.However, do take note of the warnings from others here. If a cell is of poor quality, or damaged, or if you exceed its charging parameters, it could burst into flames in a very spectacular way. Always charge in a fire safe location, on concrete, under constant observation, where erupting flames can do no damage. You can buy fireproof "charging sacks" to put the cell in while charging, which will contain any unexpected conflagration. It is no exaggeration to say that people have burned their house down while charging lithium cells.

author: ARESRACES
author_rank: Newbie
timestamp: June 19, 2015, 09:45:00 pm
content: Haven't been here for a while so I'm sorry for not replying to you. Just wish to thank you for your answer. I have been successful in charging the cell without an problems. Again thanks.Bill