June 4, 20223 yr Hey, I've been rebuilding an old Kudos Eiger with a new bafang mid drive. Id put it all together and when I eased on the throttle the screen went off like it reset, so I tried again and as soon as I put load on the motor the screen died. And now the screen is dead, no response, I checked all the connections , my 36v battery at full charge seems to be 40.6v - I do have the diagnostic cable so was going to see if the motor is still alive. I'm guessing it's either the control board, the display computer or the battery , all of which is brand new. I've had the screen on for a while testing settings and spinning the motor with the throttle and no chain ie load But I feel like I've now killed something or the battery is a lemon. Thoughts appreciated
June 4, 20223 yr 40.6v isn't very healthy, most likely an issue there somewhere. One suspects a low cells group that crashes or is near the lvc so can't take much load and and sags suddenly.
June 4, 20223 yr Author 40.6v isn't very healthy, most likely an issue there somewhere. One suspects a low cells group that crashes or is near the lvc so can't take much load and and sags suddenly. Ah right good to know thx for the quick reply , I'll stick it back on the charger, but sounds like that might be the culprit, might need to get a replacement or see if I can get it fixed
June 4, 20223 yr it is at least 1v low if 40.6 is the full charge, it could mean that whilst 9 cell groups may be sitting at 4.16v - 4.2v. The tenth one may only be at 3.2v or so, that lost 1v is highly critical. The battery will need opening and some cell voltgae readins taken to see if the issue lies witha low cell group.
June 4, 20223 yr Author Yeah my next step is to open it up and take some cell by cell readings and see if it's an easyish fix, I've got a bench power supply, so I can try to bypass the BMS and charge an individual cell if it's down on charge and see if it recovers as a whole , or maybe I can swap out some 18650 cells if it's not beyond my expertise.
June 5, 20223 yr Author The weird thing is even at 40.6 it used to turn the display on at least and now it doesn't do that, like something else is faulty, even plugging in the charger whilst the battery is on the so there's 42.6, and the display doesnt work , I'll try and dig into the battery this week.
June 5, 20223 yr Yeah my next step is to open it up and take some cell by cell readings and see if it's an easyish fix, I've got a bench power supply, so I can try to bypass the BMS and charge an individual cell if it's down on charge and see if it recovers as a whole , or maybe I can swap out some 18650 cells if it's not beyond my expertise. I really hate to be in anyway negative, but rely on the fact that battery problems are never an easy (ish) fix. Sorry to have to say that. But it might be an easy fix if it has nothing to do with the battery, for example, maybe the charger is defective, or a connector somewhere is corroded........ Best wishes for an easy fix. regards Andy
June 5, 20223 yr Author I really hate to be in anyway negative, but rely on the fact that battery problems are never an easy (ish) fix. Sorry to have to say that. But it might be an easy fix if it has nothing to do with the battery, for example, maybe the charger is defective, or a connector somewhere is corroded........ Best wishes for an easy fix. regards Andy It's my own fault, the mid motor and accessories is all brand new, the battery I bought as a factory second unit because it was scratched but supposedly brand new, and I've since discovered is a no return sold as seen, so maybe an expensive lesson in not going cheap when buying certain items
June 5, 20223 yr Author So I took the battery apart just now, all cell groups between 4.10 and 4.12 and a total + to - on the cells of 41.1 , there is a definite 0.5 to 0.7 loss coming through the BMS negative cable, I also wonder if the BMS is cutting out too soon given 4.1 seems low across each cell group £14 for a replacement BMS seems like a worthwhile test to see if they'll charge to 4.20 across each bank Edited June 5, 20223 yr by Mgbv8
June 5, 20223 yr It's my own fault, the mid motor and accessories is all brand new, the battery I bought as a factory second unit because it was scratched but supposedly brand new, and I've since discovered is a no return sold as seen, so maybe an expensive lesson in not going cheap when buying certain items Have you kept it at a mid voltage level charge, since you bought it? If its a Li-ion as I believe, they do not like to be ignored for very long periods..... They need to be checked and at least partially charged, say once a month or so.... Yours needed to be kept at say around 34-36 volts, partially charged, and only fully charged to a max of 42.00 volts before using. (Values may be different depending on the charger quality and the volt meter quality of course!) Meters need to be checked against a known good meter for check accuracy, but a reasonable one should show for a good 36v battery, to be around 42 volts, plus minus 0.3 volts or so. This ahould also be the output of the charger, with no battery connected. regards Andy
June 5, 20223 yr Author Have you kept it at a mid voltage level charge, since you bought it? If its a Li-ion as I believe, they do not like to be ignored for very long periods..... They need to be checked and at least partially charged, say once a month or so.... Yours needed to be kept at say around 34-36 volts, partially charged, and only fully charged to a max of 42.00 volts before using. (Values may be different depending on the charger quality and the volt meter quality of course!) Meters need to be checked against a known good meter for check accuracy, but a reasonable one should show for a good 36v battery, to be around 42 volts, plus minus 0.3 volts or so. This ahould also be the output of the charger, with no battery connected. regards Andy The charger is a modiary one from the old battery for this bike, I believe it puts out 42.1v supposedly at 2amps , which I've tested before. I've kept the battery charged up near to 100% , it was on 39.6v for a while , i.e a month while I was fitting the drive, but it showed that on the HUD when it worked. And since charged to the point at which the green light stays on the charger, I even left it on the green light for a further 6 hours to see if it altered the max charge but it didn't. The test I just did makes me think the BMS is bypassing the charger current when the BMS thinks the battery is full . Reason for this, is that with the charger plugged in, the battery pack +/- reads 41.1 but after the BMS it reads 42.1 , if that makes sense. My voltmeter is a mastech 8268 I've had for years, it's always been pretty accurate I think, but I will check with a second volt meter just to be sure. I appreciate all your suggestions, thanks for the continued help Edited June 5, 20223 yr by Mgbv8
June 5, 20223 yr The charger is a modiary one from the old battery for this bike, I believe it puts out 42.1v supposedly at 2amps , which I've tested before. I've kept the battery charged up near to 100% , it was on 39.6v for a while , i.e a month while I was fitting the drive, but it showed that on the HUD when it worked. And since charged to the point at which the green light stays on the charger, I even left it on the green light for a further 6 hours to see if it altered the max charge but it didn't. The test I just did makes me think the BMS is bypassing the charger current when the BMS thinks the battery is full . Reason for this, is that with the charger plugged in, the battery pack +/- reads 40.6 but after the BMS it reads 42.1 , if that makes sense. My voltmeter is a mastech 8268 I've had for years, it's always been pretty accurate I think, but I will check with a second volt meter just to be sure. I appreciate all your suggestions, thanks for the continued help Many believe that storing fully charged is not good for the battery. I myself "believe" this, but I haven't seen it to be bad for fully charging, but my batteries are used daily..... The LED on the charger, when showing green, has (at least!) two different meanings:- 1) Fully charged 2) Battery is so low, the BMS will not allow charging. The only way I know to fix that is with a so called "0 Volt Charger", provided that the battery has not gone siper low!) which I have used when my bike was delivered very late, and the new battery had slipped down to 26 volts if I remember correctly, and the Company lent me one, which recovered the battery fully and I have been using the battery ever since 2017. The bike company from which I bought my bike, are the only company that I know of that sell them:- https://starkdrive.bike/accessories/0v-recovery-charger/ Interestingly, once the battery is back to normal with its voltage, this charger charges at 2 amps, just like any other!!
June 8, 20223 yr Author Good news, fitted a new Daly BMS and it's charging past its original 41.1 and the BMS no longer restricting the thru put , both +/- of battery and +BMS to - read the same value . Cells up to 4.16 and still charging
June 8, 20223 yr Author It was the BMS, both input and output, , fully charged to 42.4v , I now know the BMS was stopping me taking charge off of the battery, I e using the motor. The thumb control works as expected and I get movement woop, time for a test ride tomorrow hopefully
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