Battery cutting out

[Thomas]

So, two issues:

One is that the GM 36v 16a battery simply cut out once the indicator changed from red yellow and green to simply red and yellow.

Once the changed to yellow the battery motor shut down.

Is this a fault or simply a fairly useless battery indicator?

And, why is it like riding an exercise bike when the battery is off (either in the locked or unlocked position).

Two (or three) is that the bike was inside and the GM MP rear wheel off the floor because I had been checking the wheel alignment. I left the power on, but no throttle twist on at all. The motor was not spinning, then after 1/2 hour to 45 minutes - the wheel began to spin at a fairly slow clip. Ghost in the machine?

Thanks,

Tom C

[Bikemad]

Tom,

The battery indicator gauges were originally intended for use with lead acid batteries, so it may not be very accurate with the lithium packs.  With lithium batteries, the voltage tends to drop much less noticeably while being discharged than with lead acid batteries, and lithium packs are also protected from becoming discharged too low by the built in BMS.
If the cells are slightly out of balance, there's a good chance that one group of cells may reach their minimum voltage before the rest of the pack, causing the BMS to cut off the supply to protect the weakest cells.
A good long charge will usually ensure that the cells have chance to become equally balanced.
I would charge the pack for at least 10 hours before you use it again and see if there is any noticeable difference.
It should be fine to leave the battery on charge for much longer periods if necessary without causing a problem.

All permanent magnet motors will exhibit some level of magnetic resistance while being manually turned.  As the Magic Pie is much larger than most hub motors, it has many more magnets, which are also located further from the axle. This is basically why the Magic Pie develops so much torque, but unfortunately it also means there is considerably more magnetic resistance that has to be overcome while you are pedalling without motor assistance.
As well as the motor resistance, you also have to remember that the bike is now carrying a lot more weight in the form of the motor, wiring, controls and battery, which will also make the bike more difficult to pedal.

Regarding the motor starting to turn on its own, the only things I can think of would be a faulty throttle control or a poor connection on the ground wire somewhere between the throttle control and the main wiring harness on the motor.
Resistance in one of the ground wire connections would have the effect of slightly increasing the throttle signal being sent to the controller. If the resistance gradually increased over time, the motor could eventually start to turn.
With the battery turned off, if you disconnect and reconnect the throttle connector (and the 8 pin connector on the motor harness) a few times, this should help to clean the pins and sockets of the connectors, hopefully ensuring a good connection.
It only takes an increase of 0.5V on the throttle signal wire to go from no power to low power.

Alan
 

[Thomas]

Thanks Alan
I checked the voltage before putting it on the charge; it measured 33.6v. So, from your comments: if a couple of cells go low then the BMS balancing may need to adjust overall charge even if reading fairly high voltage? I rode the bike a lot yesterday and last night and was wanting to see what sort of range I would get, so I didn't charge it last night.

It sounds like the gauge simply didn't reflect the battery state. But I was surprised at the indicator switching basically from full charge to no more go.
 
Or, is it more likely bad connections? I stopped and checked the cabling, and the bike pulled a little and the motor shut down even though the LEDs had only begun showing no green and only red and yellow. I could tell a drop in power before the LEDs changed. An, I turned the battery on and off a couple of times.

I need to eliminate the wiring harness connectors - it is too easy to develop a bad connection. I thought about using a block, like dip switches. The harness connectors are a source of problems as is. 

I have the brakes connected and the regen set to 50%

The main reason I haven't rewired is that the bike is way too fun.
All of my problems have been connection issues so far (either the Throttle at the harness, or at the 8pin connector)
Also, the power cable ends (my crimps vibrated loose after one ride, so I soldered it), and the Magic to harness connections can be a problem.

thanks,

Tom

[Leslie]

Once you have found the spot for your wires, a little electrical tape snug around the plugs to secure them maybe a good thing.

[Bikemad]

Thanks Alan
I checked the voltage before putting it on the charge; it measured 33.6v. So, from your comments: if a couple of cells go low then the BMS balancing may need to adjust overall charge even if reading fairly high voltage? I rode the bike a lot yesterday and last night and was wanting to see what sort of range I would get, so I didn't charge it last night.

It sounds like the gauge simply didn't reflect the battery state. But I was surprised at the indicator switching basically from full charge to no more go.

Tom,

Your battery consists of 40 individual cells, each rated at 3.7V and 4Ah. To get the 16Ah output, 4 cells are wired in parallel to form a single group of 3.7V 16Ah. There are 10 sets of these grouped cells which are wired in series to provide 37V and 16Ah. Each group of cells is individually monitored by the BMS to ensure they do not become overcharged or overdischarged.
Maximum cell voltage will be around 4.2 Volts, but I'm not sure what the actual low cell voltage limit is, so for this example let's just assume it's 3.2Volts.
Any group of cells reaching 3.2 Volts will trigger the BMS into disconnecting the battery output to prevent discharging the cells below this minimum set voltage.
The other 9 groups of cells will probably be at a slightly higher voltage, which will vary according to how well matched the cells are and how well balanced they were in the first place.

Let's take a look at some possible cell readings:

Cell group 1      3.4V
Cell group 2      3.3V
Cell group 3      3.4V
Cell group 4      3.4V
Cell group 5      3.4V
Cell group 6      3.2V <<< First cell group to reach minimum voltage
Cell group 7      3.4V
Cell group 8      3.4V
Cell group 9      3.3V
Cell group 10    3.4V
Total voltage 33.6V

If the cells in this pack had been perfectly balanced and had all reached the minimum voltage at the same time, the pack voltage would be nearer to 32 Volts instead of 33.6 Volts.

Notice how the battery has cut out 1.6 Volts higher than if it had been a perfectly matched and correctly balanced pack.
This 1.6 Volts difference may explain why the yellow light was still on just before your battery cut out.

Hopefully you will now understand what I was trying to explain in my earlier post.

Here's a graph showing a typical discharge curve for a lithium cell, you will notice that it drops of pretty quickly as the cell becomes depleted. By the time your pack reaches 37 Volts it will have less than 5% of its capacity remaining, so a slight imbalance in the cells is unlikely to have much effect on your range, but a large imbalance may be more noticeable.



If you would like to try and fine tune your battery gauge so the lights starts to go out a little bit bit sooner, this can be done by putting a resistor in-line so it thinks the battery voltage is lower than it actually is.  
Check out this post for more details.

Alan
 

[dicko]

Hello 
Any luck with your battery? ive also had mine a short period and now having troubles.

I've had my E-Bike up and running for around 6 weeks now and it’s running well, until the last few times I've ridden it. The first 4 weeks I could ride to and from work on one charge, 9km to work, 9km return. Last week, I could only ride to work and halfway back, and the battery cuts out. A few days ago, I could only ride to work 9km before needing a recharge. Nothing has changed, I ride the same way each time, with hard tyres. I noticed on the site that a 48v12ah battery should do 50km on a full 48v charge, but im not getting anywhere close to this. I always use regen breaking where possible, and also peddle aswell. Is there a way to check if any lithium cells are faulty?

ive checked voltages as suggested by Goldenmotor, but now havent heard anything back regarding replacement under warrenty.
Have you had anyluck from GM?

regards

[Thomas]

I'm not sure the RMA process. I bought through a US dealer to have a contact. From posts it seems patience persistence works eventually. I haven't had power problems. The battery drop off is steep and a few bad cells can sink the ship by dropping the whole volatage below a low battery threshold.

If cells are bad the the battery needs replacing or reconditioning.

If they have simply fallen by the way they may be revived by a long 10hour charge. Or, so I hear

My impression is that LiPo batteries are best left charging between uses.

tom c