Dear peeps..I am a newbie here and thank you for having me 
I built a couple of Elec bikes 10 years ago now for myself and wife and use them constantly..I love them, they are both the same 500w motors in the front wheels running on 52V LI Batteries,
The first batteries we had were 10amp/Hr ones that had the little flat batteries like the mobile phone batts, my one soon chose to cut out so quickly, so I contacted a chap I know who sold me all the parts to do the build and he said it sounded like the BMS was playing up and cutting out too early and it would be safe to by-pass it because it had a LV cut-out in the controller, I think from memory they cut-out at 48v(I could be wrong, but that it what I have always had in my head), I I by-passed the BMS leaving it in situ but just connecting/Bridging the thick Neg wire that goes in and out of the BMS and leaving all the other wires in the BMS as is, it made my bike go so far before cutting out I was amazed at the distance I got.
I then done the same to my wifes battery at the time and we used them for the next 5 years or so and they were great, in the end my battery cut out and wouldn't charge after all that use and so I purchased another new one that was the same but 15amp/hour. I immediately done the same with the BMS bypassing the BMS in the same way, my wifes battery that I replaced a few months after I did the same to that too, so now we both had new batts with same BMS bypass and they have been great, I did notice that these new ones were 18650's as opposed to the last flat type batts, but now only a couple of years on one of the batts has lost its long range like the other one has still got, I did notice that when they were left for a couple of months between uses that one of the batts would always take a charge where as the other never seemed to need charging, it always seemed to have retained its charge after being left, now its the batt that used to not hold its charge so much that now has lost it's range, it still works well from off of the charger but after a few hills and use the bike will cut out when given full power, I can get it to cut back in again by un-plugging and plugging back in and the controller will re-set and I can use it again to get home, but if I give it full throttle/power on an incline it will cut out like LV cut-out again. Sorry for all the blurb but I wanted to set the picture of the situation, now my question/query is this..I have read some stuff on here and I know there are different ways of by-passing BMS's but that is where I have some confusion, because people talk about using the BMS for drain/balancing etc and so I wanted to ask and have a look inside the battery and see what I can find wrong, but I don't know if I should completely remove the BMS with all the wires to it or if maybe I have a dodgy cell pack that I can replace, but I also didn't want to do anything wrong and cause damage to anything if I shouldn't remove the BMS due to battery balance etc :|
Many thanks to anyone that be able to shed some light or thoughts on this for me Chaps/Chapesses ..
...... With my kind regards..Grant
PS..god we love these elec bikes, we have them on the island of Ibiza and use them constantly and love them, they speed along very quickly as we have them connected up for off road use!! ..Grant
I built a couple of Elec bikes 10 years ago now for myself and wife and use them constantly..I love them, they are both the same 500w motors in the front wheels running on 52V LI Batteries,
The first batteries we had were 10amp/Hr ones that had the little flat batteries like the mobile phone batts, my one soon chose to cut out so quickly, so I contacted a chap I know who sold me all the parts to do the build and he said it sounded like the BMS was playing up and cutting out too early and it would be safe to by-pass it because it had a LV cut-out in the controller, I think from memory they cut-out at 48v(I could be wrong, but that it what I have always had in my head), I I by-passed the BMS leaving it in situ but just connecting/Bridging the thick Neg wire that goes in and out of the BMS and leaving all the other wires in the BMS as is, it made my bike go so far before cutting out I was amazed at the distance I got.
I then done the same to my wifes battery at the time and we used them for the next 5 years or so and they were great, in the end my battery cut out and wouldn't charge after all that use and so I purchased another new one that was the same but 15amp/hour. I immediately done the same with the BMS bypassing the BMS in the same way, my wifes battery that I replaced a few months after I did the same to that too, so now we both had new batts with same BMS bypass and they have been great, I did notice that these new ones were 18650's as opposed to the last flat type batts, but now only a couple of years on one of the batts has lost its long range like the other one has still got, I did notice that when they were left for a couple of months between uses that one of the batts would always take a charge where as the other never seemed to need charging, it always seemed to have retained its charge after being left, now its the batt that used to not hold its charge so much that now has lost it's range, it still works well from off of the charger but after a few hills and use the bike will cut out when given full power, I can get it to cut back in again by un-plugging and plugging back in and the controller will re-set and I can use it again to get home, but if I give it full throttle/power on an incline it will cut out like LV cut-out again. Sorry for all the blurb but I wanted to set the picture of the situation, now my question/query is this..I have read some stuff on here and I know there are different ways of by-passing BMS's but that is where I have some confusion, because people talk about using the BMS for drain/balancing etc and so I wanted to ask and have a look inside the battery and see what I can find wrong, but I don't know if I should completely remove the BMS with all the wires to it or if maybe I have a dodgy cell pack that I can replace, but I also didn't want to do anything wrong and cause damage to anything if I shouldn't remove the BMS due to battery balance etc :|
Many thanks to anyone that be able to shed some light or thoughts on this for me Chaps/Chapesses
........ With my kind regards..Grant
PS..god we love these elec bikes, we have them on the island of Ibiza and use them constantly and love them, they speed along very quickly as we have them connected up for off road use!!
..Grant 
