Laptop battery repair - Page 1
Forum section: electronics / general

author: akis
author_rank: Frequent Contributor
timestamp: December 14, 2015, 04:17:23 pm
content: This laptop's battery has died almost completely (charge lasts 10-15 mins) in 18 months since new. Although with a 3 year warranty, the battery is deemed "consumable" and thus excluded. I did tell the suppliers where to stick their attitude. Crooks.A new battery costs £60 + VAT + shipping, quite expensive. And of course it could break in 2 weeks and again they might say "consumable".I have looked in Alibaba and the best so far is a quite for $66 each including all taxes and shipping (around £43) - but am still looking for cheaper.The battery is 14.8V 5200mAh. At Hobbyking I can get a similar 4S (14.8V nominal) 5200mAh battery for £14. Also, if I know how to repair it / replace it, then I can do it again, when it breaks. I have bought many batteries from Hobbyking and when two arrived broken they refunded me.The only tricky bit would be to fit them physically inside the battery's enclosure so I would need to choose very carefully. Additionally I might find that only one cell is bust or some electronic monitoring board (they are known to trip for ever).I am about to try to open the casing, I will have to cut it open.

author: PeterG
author_rank: Frequent Contributor
timestamp: December 14, 2015, 09:57:51 pm
content: What model laptop is it?Regards

author: akis
author_rank: Frequent Contributor
timestamp: December 14, 2015, 10:34:49 pm
content: It is a Clevo P770 - something and the battery is model P150HMBAT-8.I have not yet opened it, I was working on another project. Probably tomorrow.

author: akis
author_rank: Frequent Contributor
timestamp: December 15, 2015, 10:41:33 pm
content: I have opened the battery just a little while ago. As can be seen from the husk it is not meant to be opened/repaired, a shame really, considering it contains 8 * 18650 Samsung batteries. I presume they are 2600mAh each - total of 8 , 4 parallel pairs in series. Each pair is charged as a unit and independently I presume, because they feed into the control/monitor/safety board which connects to the laptop via an 7 pin connector.I am not sure how to measure which unit is faulty, or if it is the monitor board that has gone bananas.The symptoms are that the charge does not last very long, maybe 15-20 mins.The units have been put in pairs and it is very hard or impossible to separate them to test them individually - it seems there are foil type connectors glued or welded somehow - not soldered. Even if I managed to pull them apart, I am not sure I'd be able to fit them back on.

author: sleemanj
author_rank: Super Contributor
timestamp: December 16, 2015, 12:04:02 am
content: No real sense in trying to rebuild it IMHO, you're not going to get a tidy result. Just salvage the good cells and use them in a project, probably there is only one or two cells gone bad and the rest are fine.Tabs are welded (spot) onto the cells, usually you can just rip them off with a pair of pliers, they are not so strongly bonded.When separating the cells, if you cut the negative bus strips first it is better because if you accidentally contact the metal shell of a cell with your nippers at the same time as the bus it won't matter, once the negatives are cut you can spread the cells apart to cut the positive straps easily.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 16, 2015, 07:24:19 am
content: I suggest not cutting away the tabs completely since it would be preferable to have a centimeter or two of tab left to solder to.

author: akis
author_rank: Frequent Contributor
timestamp: December 16, 2015, 11:05:33 am
content: The individual Samsung ICR 18650 -26 cells cost on ebay around $5.70 (£3.80) each. On Alibaba I think they are around $2.50 each (£1.70).One niggle is I am not sure how to do the "spot welding" - the brand new cells come with flat tops, nothing really to solder on, I do not think. Does anyone have experience with the 18650 cells?Second problem is I do not know how to tell if the electronic monitoring board is blown, and refuses to charge the battery properly - and there is no way I can find a replacement it is a Clevo own that they use in their own batteries, nothing that sells on the open market, I do not think.

author: krivx
author_rank: Frequent Contributor
timestamp: December 16, 2015, 11:07:50 am
content: Quote from: akis on December 16, 2015, 11:05:33 amYou have no way of knowing if you are purchasing genuine Samsung cells on ebay/Alibaba though. If you do buy new cells just get them with tabs, the hassle and danger of spot welding isn't worth it IMO.

author: amyk
author_rank: Super Contributor
timestamp: December 16, 2015, 11:43:11 am
content: You can test the cells individually (or in parallel pairs in this case, which just act like one bigger cell) by charging them with a current-limited power supply and discharging into a suitable load.Lots of good discussion on that here:https://www.eevblog.com/forum/projects/diagnosing-lithium-cells/The battery monitoring boards have fuses on them that you can check, and a little microcontroller that communicates with the laptop via I2C (Google "smart battery specification"). I doubt it's the problem though, as it's usually the cells which lose capacity/fall out of balance.

author: akis
author_rank: Frequent Contributor
timestamp: December 16, 2015, 01:35:24 pm
content: The individual cells (well, in pairs) appear to be OK. There is one pair that was at 4.050 V rather than 4.150-4.180 like the others (highly suspicious), but I have charged it separately at 500mA for 15 mins and it seems to be holding a charge - more or less.One bigger problem I have discovered is with the monitor board. There is no connection between the V+ of the battery (red wire) and the V+ on the connector.Is this a blown track, a blown component, or is there some sort of miniature relay/SSR that the onboard microcontroller switches on and off? Whatever it is I presume it must be quite hefty to pass the currents required without melting, so it should sit prominently on the board.One such item I have identified is shown on the attached photo, it appears to be a large metal fork meeting a single metal conductor, not quite "meeting" there is a minute gap, there is a 50 Ohm resistance between the two, and the assembly is doused in this hard, white paste they have applied randomly, so it is not a mechanical thing (or it would have been fouled already), I have no idea what it is.However the V+ of the battery pack (red wire) has a direct connection with the fork, and the other side, the single metal conductor, does *not* connect with the V+ of the battery pack connector.

author: tszaboo
author_rank: Super Contributor
timestamp: December 16, 2015, 01:48:06 pm
content: The positive will have one or two N channel MOSFET in "high side switching" configuration to the connector. It is not that hard to do it, its only like 10A. I suspect at least one of the SO-8 packages on the board will do that. Those unidentified components are fuses. I've counted at least 4 different type of fuse in one of the battery pack I've taken apart. Thermal, current, you name it. They will be OK, since it is a fuse.I would test the cells for internal resistance. probably you have 1 cell which is gone.

author: G7PSK
author_rank: Super Contributor
timestamp: December 16, 2015, 04:25:33 pm
content: Try charging each cell pair with a bench power supply, I have found that this often works. seems that for whatever reason the cells went below the protection device limit and that wont let the battery recharge after bypassing the protection for a short time every thing works again in some cases as good as new.

author: amyk
author_rank: Super Contributor
timestamp: December 17, 2015, 11:56:23 am
content: That 3-pronged device is a triggerable fuse:http://www.ti.com/ods/images/SLUSBS8A/FUSE_circuit_lau660.gifhttp://battery.newlist.ru/images2/Fuse.pdfIt is basically like a normal fuse, but with an additional heater that the microcontroller can drive to open it if it detects an overheating condition.

author: akis
author_rank: Frequent Contributor
timestamp: December 17, 2015, 01:12:13 pm
content: I read the docs thanks. Still a bit confused. Is this fuse "blown" ?The 3 prongs of this fork are made of very soft metal, as my small crocodile clips have left impressions as seen with the magnifying glass. Were they all three meant to have been connected and now they have melted off so we see the gaps?

author: amyk
author_rank: Super Contributor
timestamp: December 18, 2015, 04:10:09 am
content: Check continuity. The heater should measure a few ohms, and the fuse near 0R.