intermittently cutting out

[jonathanm]

Actually I got thinking and reasoned that if I`m going to get a new battery anyway I may as well experiment a little on this one and it also occured to me that if I`m too chicken to try I`ll never get to know this stuff.

Haha, that's the spirit! Glad I could help...don't know how much more helpful I can be as I'm a noob myself...

Do you have any way to put a load on the pack or individual cells while it's opened up? Then you can make individual measurements and see what the cells are doing. I wouldn't rule out the cells yet just because the resting voltages are ok....the pack voltage was ok as well when resting, but not under load.

 

[dnmun]

i saw a thermal switch laying on the top of the cells too, and that is connected to the BMS so it will shut down the BMS when the cells overheat. it is stamped 55C, i assume it is normally closed, with the charging fet gate current running through it. to stop the charge if it is overheating during charging?

it may also be connected to an output fet array, which would be on the BMS. i am on dialup now so try to reset the camera on VGA to 50-80k for the images of the BMS. thanks, dm

both sides.

 

[dnmun]

Thanks jonathanm that was a great suggestion, I spliced into the wires and using my multimeter I was able to watch the voltage under load. I started with 37 volts, It cut out 3 times, and I reset it each time . It dropped to 27v the first time it cut out after 5 mins, the second time after just 10 seconds it hit 16 volts and the third time just 5 volts. I think from what I`ve read here that implies that I have bad cells and not a controller problem.

dnmun, thanks for the suggestion that I measure the cell voltages but like dogman mentioned it is a bitch to get near the terminals because the bms seems to be attatched firmly on top of them and I can`t even see how it is attached. I`m scared I will break the bms just trying to get at the cells to measure them. Also when I looked at the controller it had 2005/11 stamped on it. I bought this bike used and it still has the original li-mn battery which may just be worn out.

I hate to spend the money but at the same time I am kinda looking forward to seeing how the bike performs with a new lipo battery on it. Thanks for the help again, you guys are great.

sorry i just saw this. i did not realize you had pulled the pack voltage so low. i guess i assumed it was always reading 39V after it cut out. but the voltage was way down around 5 volts on the last one which means they were really discharged.

 

[randomlight]

I hooked up my battery to my bike with the back wheel off the ground.
I couldn`t really put it under load this way but I ran it for an hour and a half before it cut out
I turned it on again and measured my cells, eight of them were 33-34 volts, one was 32 volts and one was 27 volts.
I don`t know what the cut off point is for a 36 volt li-mn battery .Do you guys figure that the cell with just 27 volts is the culprit? If so, any suggestions on where I can order just one cell from ?
thanks again for all the help.

 

[Icewrench]

The 2.7 cell looks to be a runt.
Not sure what kind of cells they are.
Maybe a better pic of the cells will look familiar to someone.
Have you tried to contact the folks that sell those bikes?

 

[randomlight]

The store where the bike originated from told me it was a li-mn.

 

[neptronix]

li-mn from what i have read, runs at about ~3.0v - ~4.15v.. similar to lipo/lico.

 

[USAEBIKECO]

Sounds like a battery issue. Mass produced ebikes from large corporations have a tendency for batteries to cut out.

I get calls from people in the same situation where they bought an ebike online only to have battery problems 3 months later and have no idea where to get a new one.

 

[randomlight]

Oh yea it`s wonderfull to buy here so that you can count on being gouged to death by your North American dealer if something goes wrong. One of the reasons I didn`t just take my bike back to the original dealer is because I am scaired to death about what they would charge me. I needed a charger a while back and they charged me 25.00 to check out my battery and 120.00 for a charger .I got home and realized it wasn`t even a new charger just a used one they had laying around. Came to 163.00 with tax...Now they want almost 800.00 for a new Li-po4 36 volt 10ah battery.I can get the same thing from ping for under 400 including shipping. Sure glad this bike isn`t from ebay lol.

lester12483 are you by chance the proprietor of Chicago Electric Bicycles.
If so what do you charge for the same battery?

 

[dnmun]

that's kinda what this place is about. helping you learn how to deal with the ebike yourself. kinda turning you from a green newbie to ebike mechanic. almost everybody here is in the same boat, gotta fix it yourself or there is no money left for rent.

there are some other US sources for lifepo4 too. joe has one of their packs. i lost the link.

it is a good excuse to learn a little electronics too. nothing very tough, but useful.

 

[randomlight]

So true dnmun and I really appreciate all the help I recieve here from you and the others. I have quite enjoyed learning the bit I know and look forward to learning more.
I don`t know if you have read my post about the volt readings on my idividual cells but I have a cell that shuts the battery down at 27.5 volts while the others are still up around 33-34 volts.
From what I have learned here that is the probable cause of my cutting out problem.
Could anyone recommend where I could go online to order a cell to replace the bad one ? Thanks again

 

[jonathanm]

Someone might know if you can get a pic of the cells or can see if there's any writing on them to ID with....can you get them out?

 

[dogman dan]

If those cells are limn, and supposed to charge to about 4v or more, then 3.3-3.4 v per cell is waaaaay undercharged. Pretty light charge even for lifepo4 too.

I wonder if the pack would perk up a LOT if you got the right charger. I'd be real tempted to go to ebay, get the cheapest possible 36v scooter charger and see what happens if you charge the pack to 41-42 volts or so. If your charger is stopping at 39 v, then it's just plain undercharging the hell out of it for one thing. Pretty nice, given the way you got overcharged for it.

Another thing, how long do you charge? Do you leave it on the charger after the light turns green so the bms can balance it? Overnight is fine.

One option for a charger. http://www.batteryspace.com/smartcharger10afor37vli-ionpolymerrechargeablebatterypack.aspx I'd want to know the voltage output spec though before buying it. A regular sla charger would be about 42-44v.

 

[randomlight]

Sorry dogman I didn`t make myself clear.when fully charged the cells are 41 all accross.After I ride the bike for ten minutes it cuts out, When I turn the switch off and back on it starts again but only lasts about 15 seconds before cutting out again.
Whe I went to test the individual cells I had no way to test them under a heavy load so I just picked up the back wheel and ran the battery till it cut out.
At the point of cut out 9 of the battries were down to 33-34 volts with one that hit 27.5 .
I figure before spending 400.00 with ping for a new battery I will try to replace this low cell and see what happens.
To anyone following this thread I just want to update by saying I think I may have gotten lucky here.I took the shrink wrap off the bad cell and found the company in china who makes it and a part number stamped on it. I found them online and will phone during business hours.

I do have one question though, The specs on my battery from the original dealer is a 36v 10ah li-mn battery .
When I go online (the manufacturers website) the part number I have on my cell refers to 2 different cells .They are the 36v li-mn like I need but rather than 10ah they are listed as 8ah and 9ah.
If I bought a 9ah cell instead of a 10ah cell for a replacement would this create problems for me... Thanks for any insight.

 

[wesnewell]

Before I did anything, I'd charge the battery full, then bypass the bms using a volt meter to monitor the battery voltage during a ride and see if it still cuts out at the same time. It may just be a bad bms.

 

[randomlight]

I`m real new to this but If I bypass the bms what would cause the battery to cut out at all ?
Doesn`t the bms control the lvc level ? meaning No bms = no lvc = no cutting out ?
Please tell me what I am missing here. thanks