Reduced Range

[adamsavage79]

I've noticed that lately the bike has been acting quite strange. I find despite the motor using 1/2 the power it was normally using, I'm not getting the same range as I was when I was pushing the motor harder. I do the exact same route to and from work, and I have only 2 - 3 stop and go at the most. Going to work I was typically pulling 1200-1300 watts, and coming back I was using 500-700 watts while riding.

I find the battery is going down 1 bar to 50v roughly 2km sooner than it was before hand, and I'm using about 500-700 watts now going to and coming back from work, going the same route. The only difference is the outside temp is cooler now. So I'm using less power, and yet I'm still getting less range.


My question is, would the cooler temps be playing a role in this ? I've always assumed you would need below freezing temps for any noticable change in range to happen. It has been any where from 4 degree's celsius to 15-16 celsius.

Here are the specs of the bike and the battery.

https://www.teslica.com/purity-mountain-ebike-m1h.html#proTabPanelSpecs

 

[calab]

Storing your battery at full voltage or near full is not good for the battery and is a fast way of reducing the range.
This is why you should always buy more battery then you need so your not at full voltage for 12hrs overnight to ride right away the next morning. Instead of a 48V 15Ah battery that does your distance requirements you could buy a 48V 20Ah battery, this helps in several ways, your not at full voltage overnight and your not emptying the battery every time you ride. It is actually better to use very little of the battery a million times over then using all of your battery for half that time.

Cold weather does have an impact, but -5 celcius to +25 celcius is fine, I don't have much experience with very high temperatures on a regular basis as the desert people have. The key is to not charge when the battery is cold because the battery could rise in voltage above the rated maximum. When you ride and use your battery the battery warms up from the inside, but that to depends on what you are using. If your using 13S 2P with 18650's that are rated for 5A 2P x 5A = 10A and your using most or all of that 10A then your really stressing the batteries, using 13S 20P at 5A is 100A and only using 50A your barely stressing the battery.

Many factors go into why a battery would have reduced range.
The most common is the battery management system draining and killing your battery when its been stored and forgotten about.
Storing the battery at full voltage will reduce range, how deeply a 12 hour storage overnight affects range is minimal compared to storage for days weeks and months.
Cold weather well below -5 celcius, when you start getting into the -10 or -15 celcius need to start looking at that.

 

[adamsavage79]

I still have plenty of battery left when I get home, and I never charge right away after a ride. I've always let the voltage settle and if it's cold out, I give the battery a few hours to warm up. I've only once gotten it down 46 volts, and I've been told the LVC is 44 Volts. I do plan to upgrade to a 15Ah battery as the 20Ah is nice, it's pretty big and makes the bike heavier to pick up. With both batteries combined, I would have the equivalent of 25Ah. This much more than I would likely ever need.

I've treated this battery with care, and I try to not let it sit on the charger overnight and generally I've been pretty good with this. I can't see that causing an issue with the battery range. That being said, I'm going to record the temp going to work, coming back and @ what landmark on the route home, does the bike dip to 50 Volts. I will even bring the battery inside where it would be little warmer.

 

[goatman]

yep, winter, at 15c and cooler i throw another 10ah on the bike to do the same trips id use 20ah for in the summer.

i was going to go to the trip simulator to see the difference in range between a hot phaserunner controller and a cold one to see if cold controllers get less range

 

[adamsavage79]

So even 10-15c Can effect the range ? I would of thought it wouldn't cold enough to have any sort of impact.

 

[calab]

I noticed today at +4C and -5C at night I got 10-15km less range then I normally do. The temp's have been the same the last week. I charged up before I rode at noon hoping it would warm up a bit more but it never did. I also needed to do a little work on my bike before I left. Riding was no different then any other time, as a matter of fact I was using the pedals more now then I ever did before with a nice new 21 speed drive train.

 

[adamsavage79]

The more I think about this, the more I'm convinced this is a battery problem. I first got the bike @ the end April and the temps where still 10-15 at the max, but likely 5-10 going to work. Had no problems. I find it hard to believe the battery being @ 21 degree, can drop down 6 degree's outside in the span of 15 minutes tops and while being used. Still, I'm going to try a battery cover, and see about a different battery. If the problem is still there, then it somehow it something to do with motor or controller.

Getting less range, while using less power doesn't make sense to me. If I was using the same amount of power, and got less range. Then I would agree 100% that the outside temp was playing a role. It's almost like the bike has a fixed distance it can go, before going to down below 50v. The amount of power being used doesn't seem to matter.

 

[adamsavage79]

I wonder if the BMS is reporting the wrong voltate ? It would explain how in temps well above zero, I'm still getting reduced range. I would open the battery up and check the cells one by one, but that would quickly Void my warranty.

 

[amberwolf]

If you never let it sit on the charger overnight, then it probably doesn't get any chance to balance the cells. With a good battery that doesn't matter because it won't go out of balance, but with a problematic one it can certainly happen, and the more out of balance it is the worse it gets during each use.

This takes away capacity because the unbalanced groups have less in them (and don't get fully recharged each time while others do).

You might want to let it balance overnight for several nights in a row, riding normaly in between, and seeing if there is any improvement.


A battery that easily gets unbalanced may also have problems with cell internal resistance that make lower temperatures affect them (in both capacity and current-delivery) even more than usual, as well.

 

[adamsavage79]

This is where things get strange. They swear up and down I overcharge the cells by doing so, and I still can't figure out how. I did have it charge overnight a couple times, but by mistake.

I was told the cells they use are "generix lithium ion 18650 cells"

EDIT: It seems if you have a protected cell and a proper BMS, you simply cannot overcharge the cells. I would love to know where he got this info from.

 

[goatman]

whats your range, 20km?

 

[adamsavage79]

I'm not sure. I've never triggred the Low Voltage Cutoff. I get about 5km per bar, and I have 4 bars in total. I would say 15-20km. With the 20ah. I have no idea. Typically I can go about 10km without going down a bar, but it's also below zero outside right now and even with the pack only being in the cold for about 15 minutes, I believe it gets cold enough to effect the range.

This could be something as simple as pack that is not balanced. I will see if I can convince the bike shop to open it, and have them check the cells one by one. Easiest way to know. I would do it myself, but I don't want to void the warranty.

 

[E-HP]

I would do it myself, but I don't want to void the warranty.

Seems like a warranty isn't worth anything unless you use it. Why not just tell the shop that you think the battery is defective? I don't think you need to diagnose the problem for them.

 

[adamsavage79]

I have and while I did have a loaner battery, I did only use it a few times and I may have not broken it in yet. I found I was getting a little bit more range with the loaner.

 

[amberwolf]

This is where things get strange. They swear up and down I overcharge the cells by doing so, and I still can't figure out how. I did have it charge overnight a couple times, but by mistake.

I was told the cells they use are "generix lithium ion 18650 cells"

EDIT: It seems if you have a protected cell and a proper BMS, you simply cannot overcharge the cells. I would love to know where he got this info from.

You can't overcharge them if the charger is correctly set for voltage, and the BMS does it's job (and is the correct one for the cells).

IF the charger is the wrong one and is set too high for the total pack voltage, then you can overcharge the cells if the BMS does not shut off the charge input when it detects cells have reached their HVC point. (or if it is the wrong BMS and/or has a too-high HVC point set).

If the charging is done thru the discharge port, and there is a separate charge port for the BMS rather than just a single port, then the BMS can't shut off charging when HVC is reached.

If the BMS does not have any balancing circuitry, then it wont' be able to drain down high cells, so the pack will become more and more unbalanced, with some cells becoming overcharged, and some becoming very undercharged, as time goes on.

(the same thing happens if it does have the circuitry but it isn't left on the charger long enough to perform this balancing. Typically a regular overnight charge will do this job for a minor imbalance, but it can take days or even weeks for a really bad imbalance.)




Otherwise, the charger and the BMS together will protect the cells from overcharging.



Regarding the "cell type" they told you, that generally seems to mean they are using whatever cheap cells they could get hold of to build the packs with. They could be new or recycled, they could all be the same or they could be a bunch of different kinds, etc. If they weren't all new and matched cells of the same brand/model/batch, then they can easily drift out of balance without performing regular balancing, which means in most cases leaving the pack on the charger long enough for this to happen.

If you could open the pack to check cell group voltages, you'd know if this was happening, but if they void the warranty by you doing this then your only option to make sure it happens is to do regular balancing charging cycles.

When you do this, you'll typically see the charger turn on and off repeatedly over the several hours or more that this takes, as the BMS drains down the high cells so that the charging process can restart for the low cells. It may only run for a minute or two at a time, then a much longer time to drain the high cells, then run again, etc. When it sits for an hour or two without running again it may be balanced.

 

[E-HP]

I have and while I did have a loaner battery, I did only use it a few times and I may have not broken it in yet. I found I was getting a little bit more range with the loaner.

What's the current status? They have your battery and you have a loaner; or they returned your battery and said it was fine?

 

[adamsavage79]

I returned the loaner, as I didn't think there was any difference, as I forgot about the break in period with them. It does seem like these cells get cold quickly and are picky with the cold. I need to get my drivetrain fixed tomorrow, so I will either bring the small battery with me, or simply use it and see if I can convice them to open it up and check the cells. If they are balance, then the problem lies elsewhere, or these indeed lower end cells that are finicky with outside air temps. That being said, anything in the 50-60 degree range, should NOT have any effect on the battery, specially when it's in use.

 

[E-HP]

... as I forgot about the break in period with them.

Can you elaborate?

 

[adamsavage79]

I read somewhere that the packs BMS goes through a sort of learning process, and it takes a couple chargers for the BMS to "learn" This would explain why even with a 20Ah pack I lost a bar going only 8km. I was pushing the motor as hard as it would allow mind you. 1400-1450 watts.

https://www.rcgroups.com/forums/showthread.php?394914-Do-lithium-batteries-really-need-to-be-broken-in

 

[E-HP]

I read somewhere that the packs BMS goes through a sort of learning process, and it takes a couple chargers for the BMS to "learn" This would explain why even with a 20Ah pack I lost a bar going only 8km. I was pushing the motor as hard as it would allow mind you. 1400-1450 watts.

https://www.rcgroups.com/forums/showthread.php?394914-Do-lithium-batteries-really-need-to-be-broken-in

Maybe another reference. In the link they are talking about lipo pack, so there's not BMS involved.

A pack that's out of balance, or has wonky cells, will give you those symptoms.

 

[adamsavage79]

Hmm I didn't really notice a difference with the loaner battery. So if these cells are not out of balance, then it's something else. Perhaps the BMS or the controller consume more power in difference temps, but this doesn't make any sense. Nor does a pack using more power in 50-60 degree weather. This whole thing doesn't make sense, and it's bugging me. I want to get to the bottom of this and figure out the why!

 

[adamsavage79]

I keep circling back to the quality of the cells. I believe they are cheap China cells, and this would explain why they are able to sell me a 20ah pack for $589 USD or $750 CDN. The owner swears up and down that they are on par with the brand names, and I want to believe him. However, I've never heard of a battery being highly senstive to temps below 15 Degree's Celsius.

 

[99t4]

Just to clarify:

Above 15deg C ambient temps the battery performs as advertised (20Ah)?

Useable Ah plummeted when ambient temps dropped below 25deg C? How much? 50%? 70%?

How old is the battery?

Could it simply be a function of battery age-caused degradation? (Realize it might be several months until you can test at above 15deg C ambient temps. so might be hard to test that.)

 

[99t4]

The owner swears up and down that they are on par with the brand names, and I want to believe him.

So what cells are they?

 

[adamsavage79]

Above 15deg C Ambient temps, the packs in general perform as advertised. It's not a huge change in range. I would say on a good day 25-30% less. On a bad day, I get 40% less. As for the cells, I don't know.. They either refused to tell me, or actually don't know what is inside the packs. I find it odd that they don't know, and simply refer to them as Generic Cells. I know some of the packs are using Samsung cells, but I don't know which ones.

To clarify I have TWO packs now. The one that came with bike and a 20ah. With the 20ah I typicaly can go to work and back without loosing a bar, but I'm pretty close. I'm about a little over a km from going down to below 50v. So roughly 11km a bar I would guess.