Help Required???

[thegavo]

Hi everyone im new to ebike scene and to this forum so hello and i hope you can help, i live in uk (newcastle upon tyne) and bought a 1000w 48v hub motor with a 20ah 48v lifepo4 battery from conhis motor, all was well untill 2 weeks ago my battery broke from its mount (strap snapped) while riding, it moved backwards over the metal plate it was secured into and the edge cut thru the outside wires on both the white ribbons that exit the battery, resulting in total power loss, i opened battery bag to see a small amount of smoke from bms so i disconnected everything and rode home gutted!!

I repaired the two cut wires by soldering them back together, taped it back up reassembled and put battery on charge, it charged up ok so i connected it to controller and went for a ride , worked great, have done a few ten mile rides since no problems at all, untill a few days ago !!! i had ridden to work (2 miles) but then drove home and left bike as was really bad weather, nothing unusual here as this has happenned a few times, next day i went to ride back home and after about 4 seconds of use it cut out, all lights off and no power at all, i unplugged battery and reinserted, lights came back on but same thing happenned as soon as i tried to pull off it chucked it again, i put it on charge thinking it may need charging but as it had only done 2 miles the day before and can achieve around 30 miles on a charge, i had a feeling something was wrong..
it charged up within 5 minutes, normally takes 3hrs from empty, i tried it up the street and back and it was fine, it rode about half a mile full throttle all ok, i left it an hour then went for a ride and it cut out as soon as i turned the twist grip, all lights back out, i put on charge, 5 mins fully charged and rode up street again no problem, but left it one hr and its got no power again!!
The bms has little black square things with 100 in white written on them, these had turned black and smelled so my friend removed 6 black ones and replaced, i have tried the bike again and same problem!!
i have plugged his lifep04 48v 15ah battery into my bms and bike seems fine, can leave all day and then ride it up street no cutting out, so as i have little understanding of whats the matter could my battery be broken, how can i know for sure, who can repair it, does it have to be sent back to china ?? would cost fortune, is there anything i can do to it, or is bms at fault, would 15ah battery ive lent trick the bms into working, or is anyone in uk able to test/fix these as im devastated and need a working bike, any help would be really apreciated cheers Gavin ps sorry for long post but wanted to relay the symptomsthegavo

 

[flecc]

Thanks for the full symptoms, very helpful.

It seems certain it's your battery that's the problem, since the capacity change from 20 Ah to 15 Ah wont affect anything.

Some of the characteristics you describe are like a poor battery connection somewhere, so it's worth checking all through connections both inside and from your battery. It may have been the shock that damaged a connection somewhere, or physically damaged one or more cells.
.

 

[Fecn]

It does sound like either the BMS is misbehaving. The thin white wires are the connections from the BMS to each of the individual cells in the pack. If the BMS detects that any of the cells fall below a pre-determined voltage (on my LiFePO4 pack, the cutout is at 2.2v) then the BMS will disconnect the pack to prevent damage to the cell.

As it sounds like the bike performs normally after a 5 minute charge, I suspect that either the BMS is cutting off a too-high a voltage for one of the cells, or that one of the cells itself has become damaged somehow, and no longer holds a charge properly.

BTW.. the little black square things which said 100 on the top will be 10 ohm resistors - When the BMS is balancing the cell voltages, it will 'burn off some watts' through the resistors, which will become warm. The fact one has turned black suggests that something went rather badly wrong for the BMS.

You can order BMSes seperately without a battery pack - I know that pingbattery will sell you one if you want (they sold one to me anyway) - Whoever swapped the little black square things for you sounds like they'd have the right skills and knowledge be able to fit a replacement BMS.

What you really need to do to work out what's going wrong is to wait until the battery is in not-working mode, and then measure all of the cell voltages to determine whether it's the cells themselves, or the BMS which is the real cause of the problem - However.. don't attempt this unless you know what you're doing already - Getting technical advice from internet forums is always a risky business.

Just thinking about this more... when you leave it for an hour, does the BMS get hot at the resitors? Perhaps the BMS is burning-off-watts from one cell all the time.. hence the blackened resistor.

 

[thegavo]

thankyou for the replies guys, i dont think bms is getting warm when left but i will check, in fact it plugged in still so il check now, not be long.

 

[thegavo]

No its clay cold !!!

 

[onmebike]

First check your repair of the affected wire's, you may have an intermittent problem there. Then check all connector pins are clean and not burn't from the short. Check circuit board for burn't or damaged tracks and components. Try if you can to support the bike with the wheel off the floor and run the motor, while running see if you can recreate the fault by moving the connection's about. Also if you have a switch of any kind in line try switching on and off several times or better try bypassing, switches are notorious for burning contacts in the event of a short, so are relay's.
If you can, post some photo's. Good hunting. Tony.

 

[thegavo]

Hi guys cheers for all the replies and help its greatly apreciated, i was contacted by someone who is far more handy than me with these things and he went thru all the cell packs on the battery and they were all exactly the same 3.3v , he checked for continuity too, all seemed ok, but the areas where the resistors had been repaired on the bms were reading .97 .87 .79 and all the others, and there are loads of the bu@@ers, were around .31. and although the battery was in its problem mode, ie not even enough power to light the 3 leds for battery meter up, there was 52 v exiting the battery and 1.3 exiting the bms, so its pointing towards a duff bms !!!! perhaps i fried it !!!!
Could i plug battery directly into controller to use for short rides as clearly the bms is charging it nicely, but then cutting power too early, just till a new one arrives??? still doesnt explain how it was fine with mates battery on tho ??!!

 

[Fecn]

If you bypass the BMS for discharging, then you will loose the low-voltage-cutoff feature, and if you drain the battery too far, you might damage the cells.
The other feature you'll loose is the current limit, so if you do decide the bypass the BMS, then stick an automotive fuse in-circuit.

However... as long as you don't totally flatten the battery.. or exceed the currnet rating for your battery and cables... you should be OK.

 

[onmebike]

The fact your friends battery worked faultlessly through your bms points to your battery or it's connections to the bms being at fault. Did you check the bms output voltage with your friends battery connected as well?
Generally I've found that where shorts occur as in your cut wire's, the resulting damage will come before the point of the short although with many cells supplying the bms damage beyond this point isn't impossible.
The fact the fault is intermittant with your battery and non existent with your friends is puzzling and I'd opt for a bad connection in your battery or between battery and bms. Checking the continuity with a multimeter isn't quite the same as under load conditions, you can get false readings.Your battery may well show 50+ volts on a meter but try drawing some amps from it and the result may be entirely different.
The fault your experiencing sounds like your battery or connections are breaking down under load.
Try monitoring the battery voltage before the bms while powering the bike, try with your friends battery first then with your's.
Have you traced the cut wire's to their source within the battery and have you got a link to the battery and bms, somewhere where I can go see the setup?

 

[Dynamic Position]

The bms has little black square things with 100 in white written on them, these had turned black and smelled so my friend removed 6 black ones and replaced, i have tried the bike again and same problem!!

Does your Battery and BMS roughly look like this?

LiFePo4 battery 48v 20ah with BMS for e-scooter (Li-ion battery)-Large Photo & Picture

 

[thegavo]

Hi guys no my batt and bms are nothing like that, they are seperate and bms is like a six inch long 3 inch wide double level sandwich....

just an update, about the progress, after the guy i was put in touch with, malcolm, kindly went thru all the tests it appeared to be bms at fault so i ordered a new one the same day, on others advice i have connected battey directly to controller to use bike and it has been fine, it can normally handle around 30 miles on one charge so ive made sure its only done short trips 5 to 6 miles max with pedalling, then charged back up thru bms, (charging side works fine).
My new bms arrived today so i will solder the wires on and give it a go, huge thanks for the replies and help and especially to malcolm my new ebike pal for the very kind help he gave me, i will update after i have done a few runs on the bike Gav

 

[flecc]

Thanks for the feedback Gav, glad it's sorted and likely to be ok now.
.