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Forum Index : Other Stuff : Lithium-ion trouble shoot
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| Schrockie71 Newbie  Joined: 11/11/2017 Location: United StatesPosts: 3 |
I have a 48v 1000w lithium-ion battery pack for an electric bike kit I bought about a year ago. I have recharged it roughly 300+ times. The problem is that it used to take 3 to 4 hours to charge and hold a 54.6v charge on my multi-meter. Now it's charging in under an hour and reading 50.3v(a week ago it was at 51.4). The battery pack consist of 13 rows of 18650 lithium-ion batteries, with 9 batteries in each row for a total of 117 batteries. Does anyone know how I can troubleshoot this, ie: battery, internal BMS(battery management system), charger, controller, electric wheel itself, or recommend a website of forum that can help. Also, while riding bike the power will just cut off and I have to turn the battery off then back on so it resets itself. Tends to happen more often when I'm on an incline. Thanks, Schrockie71 |
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Revlac Guru  Joined: 31/12/2016 Location: AustraliaPosts: 1024 |
HI Schrockie71 Check each set of 9 batteries with your multimeter and see if any are a different voltage than the rest, after it is charged and then when in use. could be a few bad batteries amongst it or the BMS might not be working properly. Hope that helps.  Cheers Aaron Cheers Aaron Off The Grid |
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Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
this sounds like one cell has gone reverse voltage so it will pay to put the battery on charge then check each cell to find the culprit then replace or risk it catching fire. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
I have pulled a lot of cordless battery packs to pieces and the biggest surprise I had was that very few of them have balance circuits in them. They rely on the cells being matched and evenly charged when they are assembled to stay at an even voltage for the rest of their life. it is quite common to see packs that stop charging when one cell is high and stop discharging when another cell is low and are left with a very narrow operating window in between. it is also possible to have a crappy connection in the pack somewhere and there is a bit of high resistance making a portion of the pack show a low voltage under load. in the case of the low cells I have used an old car battery charger or dc power supply with some screwdrivers on the clips for probes and while watching the voltage of that cell on a multimeter just bring it up to the level of the others. I have a fancy gadget for manually balancing high cells but I have never used it. If there is a soldered joint that needs repair, that could be a problem, depending on exactly where it is, working on a live 50v pack is not for the faint hearted, usually the joints that cause a problem are the hardest ones to solder the first time around, there are little tricks to make it easier and safer... but  mmmh yeah.I'm confused, no wait... maybe I'm not... |
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| Schrockie71 Newbie Joined: 11/11/2017 Location: United StatesPosts: 3 |
How can I check each individual battery when they are all spot welded together in series and parallels ? Schrockie 2017-11-12_221744_VPowerinside.pdf |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
The parallel groups of 9 will all be at the same voltage, if a cell has blown an internal fuse the pack will still function with a dead cell. Sometimes the spot welding can damage the o ring on the other end of the cell and gas all the electrolyte out. its not likely. rule of thumb with repairing stuff is, check the simplest cheapest and most likely solutions first Why do a $20,000 gearbox repair if changing the $5 filter fixes the problem? I would be looking at the wiring and or a fault with the battery management system first. See if you can get it out of the box and check the voltage of each series, The fact that you have 50.3 volts (4.2v less than it should be) says that you have possibly one dead sub pack. it is likely that a faulty bms has flattened that series of cells and damaged them. If the series are not even there is a problem with the balancing (if it is balancing) or it might be reading the voltages incorrectly, maybe a wire has rubbed and bared or the board has a fault. Then you could charge and discharge it on the bench and see if anything gets hot. the cutout on an incline is what I would expect, the voltage of the pack slumps low under heavy load and reaches the cutout voltage, as soon as you stop the voltage recovers and it can be reset. I'm confused, no wait... maybe I'm not... |
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| Schrockie71 Newbie Joined: 11/11/2017 Location: United StatesPosts: 3 |
Checked each parallel row of nine: Rows 1,3.95/ 2,-3.85/ 3, 3.72/ 4, -3.75/ 5,3.70/ 6, -3.75/ 7,3.81/ 8,-3.68/ 9,3.52/ 10,-3.72/ 11,3.82/ 12,-3.79/ 13,3.68 these stats are from some usage on the battery. These stats are fully charged according to charger: 1,4.1/ 2,-4/ 3,3.9/ 4,-3.9/ 5,3.9/ 6,-3.9/ 7,4/ 8,-3.8/ 9,3.7/ 10,-3.8/ 11,4/ 12,-3.9/ 13,3.9. Still at 50.3v fully charged. I had noticed that all the + and - were on the same side respectively, not like what you would see in toys or remotes +-+-+- etc. I pulled these numbers/letters of the battery: 18650S22 DHP- 1605 003741 if someone could decipher it for me. Ran it thru google got hits on the 18650 but none of the other number matched anything. Does the S22 mean 2200 mah? Dark pink/ Light purple shrink wrap covering. Schrockie |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
well that looks good, you haven't got a toasted subpack, just a few sets of cells that are out of whack.  8, 9 and 10 are all low, I would have to charge one of my own cells to work out how low but it is going to be a lot. The balance circuit has to bleed energy from every other subpack to stop them overcharging while these three come up. Several days worth of trickle charging. looks suspiciously like the charger is not functioning correctly and not getting up to the correct voltage or the bms is triggering for some reason and stopping the charge early. Would be nice if you could borrow a slow charger or one with some fancy advanced charging features to try. I'm confused, no wait... maybe I'm not... |
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