intermittently cutting out

R

randomlight

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Nov 3, 2010
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The power on my ebike cuts out after about 10 mins of riding or when ever it is under a heavey load (going uphill).
The strange thing is that all I do is switch the key from on to off and on again and the current is back .However ,after that it cuts out every 15 seconds or so.I am thinking that it may be the controller but I don`t know where it is on my bike.Could the controller be in the battery pack or the motor hub? Any insight here would be greatly appreciated.
I will provide a of picture of my bike below. The specs are as follows:
High Torque 350W Geared Motor
36V li-mn Battery
b9bxh3.jpg
 
randomlight,

randomlight said:
The power on my ebike cuts out after about 10 mins of riding or when ever it is under a heavey load (going uphill).
The strange thing is that all I do is switch the key from on to off and on again and the current is back .However ,after that it cuts out every 15 seconds or so. Any insight here would be greatly appreciated.
Click to expand...

If it always performs as you have described, then it sure seems like your controller has gone wonky. As it heats up it's shutting down the current on its own. It's essentially a computer, so when you turn it off and the then back on the electronics are reset until the heat builds up again causing another failure. From your description it seems unlikely, but it could just be a funky connection somewhere, but that would likely mean a more intermittent failure. You might try bypassing the the on-off key switch and see if that makes a difference. If it still does the same thing, disconnect your batteries for 10 seconds to reset the controller. Of course if you have access to another appropriate controller, try that.
 
Thanks Uncle Ron, I will try cleaning the controller up. I think I have found the controller. There is a little box directly under where the battery sits. I will take it apart and see.If I needed a controller would any 36v controller work? If not could you or someone tell me How I determine what i need thanks Again
 
Thanks Icewench but I took a multimeter with me and tested the voltage after it cut out and I turnrd the switch off and on. I got 39 volts so I don`t think it`s the battery but thanks
 
Battery problem, or wiring and connector to the battery problem.
 
If it was a battery or low volt problem i wouldn`t have got 39 volts when I tested the battery would I ? ( I took a multimeter with me and tested the voltage after it cut out and I turned the switch off and on).
Does anyone have any suggestions on how I could systematicaly trouble shoot this problem? thanks for any replies
 
Low voltage cutoff is my guess.
Your battery could be sagging a bit too heavy under load due to a wonky cell.
And your LVC could be set conservatively.

Something like a cycle analyst or, GT power analyzer, or turnigy watt meter would be really useful here to see the sag in action.

li-mn runs on the same voltages that lipo runs on, so you can use all the fun stuff like cellmeters, balancing chargers etc on it.

Anyhow, a battery that is sagging badly will hit a low voltage, then slowly rise back up. This is probably why it happens every 15 minutes.
 
My first thought, from a similar experience, is that you have a weak battery.

Could you temporarily connect your DMM to pick-up battery voltage, and tape the display where you can see it easily?

I think it would be a lot more telling if you knew the voltage at the moment it cut-out, not after you cycled the switch and when the battery is at rest.
 
if this pack has cell level LVC then it could be that one cell is low and it drops below LVC under load. you need to know if that battery has a BMS and if there is one cell much lower than the others. that sounds like your problem.
 
randomlight said:
If it was a battery or low volt problem i wouldn`t have got 39 volts when I tested the battery would I ? ( I took a multimeter with me and tested the voltage after it cut out and I turned the switch off and on).
Does anyone have any suggestions on how I could systematicaly trouble shoot this problem? thanks for any replies
Click to expand...
randomlight:
You have battery problem. It is either:
- BMS is failing
- in-balance cell

Let's assume that you battery is construct in 10 cell, each cell had 4.2v to start, that makes 42v when you full charge the battery. When one of you cell are in balance that drop from 3.9v to 3.0, but the rest of the cell is still at 3.9v. The BMS detected one of the cell dropped below certain voltage, it will cut you off. Ever if you have total voltage of 39v. And most of BMS had timer, so it may shut down voltage for a moment (that you can't detect) like you were having intermittently losing power. After the timer is over, it reset back to total voltage at 39v. That is why you could mesaure 39v.

Ken
 
You most likely cannot acess the wiring too easy on that battery to check things. You want to look for cell groups that are weak when fully charged, and again look for cell groups that are weak when it's discharged. That can give you clues to whether it's a balance problem. Another thing, you could have a wonky connection to the bms, from one of the cell groups. This could cause it to remain out of balance, and when disconnected intermittently, cause the bms to shut down.


At a minimum, you need a voltmeter. Idealy you have a voltmeter and a wattmeter. Hook up the battery to a slow drain device, like a car headlamp, and then monitor voltage on the cell groups as it slowly discharges. See which one drops under a load, and that's your stinker cell group. The stinker may have dead cells in the group, or bad ones that won't hold a charge. The wattmeter can tell you what load you are discharging at, and how many WH you get from the battery.

Best fix may well be to replace the battery with a better new one. How old is the bike? New? Or has some miles?
 
does anyone have specs on this bike? im not familiar with it. I was wondering if its pedal assist and hes just not pedaling?
 
First I would like to say that you guys are all great and that is what makes this site so good.Without you, someone like me would be totally lost and probably just give up the hobby.
I have decided that I should buy a new battery and charger. Currently I`m using a 36V li-mn (350W Geared Motor)
but I think this battery from Ping should do the trick .

36V 10AH V2.5 LiFePO4 Battery Pack
Light Weight: 3.70 kg / 8.2 lbs
Small Size: 150x105x150 mm / 5.9x4.1x5.9 inches
for use on up to 400W motors
Price: $289.00

I have read some good things about Ping batteries but sure would welcome any other suggestions. thanks again for all the great replies.
 
Shoud work fine with that motor. If you think you might want to upgrade to a more powerful motor in the next 2-3 years, you might consider the 15 ah one. That would work with a 20-25 amp controller common on 700-1000 watt kits.
 
Just prior to ordering a new battery I have one more question. I did another test run and as expected after going uphill for a few moments It cut out. This time I did a test without turning it off and back on (reseting it), I just pulled the power connector off and tested the battery prongs with my multimeter.I got a strong reading of 38 volts. Could this indicate that it might be the controller after all as Uncle Ron suggested earlier?
 
You would need to read the multimeter while under the load of going up the hill....do you have any way to connect it, and tape it to your handlebars or something? Then try to repeat the test run and watch your voltage as it does it again.
 
did you ever even measure the cell voltages? there is no way any decision can be made until you know what the cell voltages are. you may only need to replace one bad cell. all this other stuff is just guessing, we don't have any info yet.
 
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.
 
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. Which would be dumb because I really do enjoy ebikes.
I was wondering if someone could tell me how to measure individual cells on my battery .I managed to get the bms off the top of the battery pack but I don`t know where to touch my multimeter posts to
I uploaded a picture.Thanks for any help
16b0v12.jpg
 
those blue wires are the sense wires that connect the BMS to each cell. the BMS measures the voltage between adjacent cells by measuring the voltage between each of those blue wires. you should see where they connect to the BMS and you can measure at that point on the BMS or just put the voltmeter probes right on those connectors where the blue wires are soldered.

you won't damage anything. just don't short them out because that burns up stuff. once you have all twelve of the voltages recorded, if you post them up here we can guess if one of the cells is bad, and what to do next.

if they are all good, then there could be a problem with the connections or in the BMS. first we have to eliminate the likelihood you have one low cell shutting it down.

do you know if these are actually limno4 like you said originally? i have some lifepo4 that look identical except for the tabs they use on that one. i thought limno4 never failed to balance though.
 
thanks dnmun but I`m really dense with this stuff and am scared of a shorting something so I have to ask.If I put the red (positive probe on the blue weld where would I put the black probe ?. :oops:
As far as the type of cells ..I am only going by what they told me at the shop where it was originally purchased.
 
It would be best if you can get to both ends of the cells and then just measure the voltage of each cell.
If you can only easily get to the part in the picture you can just touch the metal straps where the blue wires are soldered on and that will give you the voltage on a pair of cells.
 
I have 10 cells and I measured each one by putting the multimeter probes on the pos and neg posts of each one.
I got 3.6 per cell and I did it 3 times with the same results. even reversed the multimeter probes and got -3.6 all the way. It appears that the cells are an even 3.6 accross the board.
Any ideas on how I can narrow this down.I think It has to be either bms or controller now but there is no visible sign of a problem with either.
 
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