Power loss in a 52v 24ah triangle

[bosn]

After a year of trouble free riding (yeahh!) my 52v 24ah battery has started to act up. I could use some advice. I use a BBSHD and generally run it on level one assist when I ride, and the battery is hung in a triangle bag inside the frame (btw, if you use Lunacycles triangle bag I highly recommend you find a upholstery/sail/canvas shop with a long arm sewing machine and have them change how the velcro is sewn on the bag. The 52v 24ah battery at twenty pounds is a lot of weight for the bag as sewn and any movement of the bag will pop the stitches on the velcro. It was a pretty easy fix). The battery/motor/bike has performed flawlessly over the last year and thousands of miles. I only dumped the bike once with a few broken bones, but I did't see any external damage to the battery bag or pack and it ran great so I could gimp home the last few miles to the house. No problems when I was able to get back to riding in two or three months. The only problem I noticed recently on inspection was that the battery meter on the battery pack isn't working when I push the button.

I charge to 80% and haven't been balancing the battery. When the first power loss occurred I was at the end of a two hour ride and the charge bar on the DLC10 showed all the bars, but the motor shut down and the computer followed a few seconds later. I charged it to 80%, went out the next day for test drive and I was able to quickly recreate the same symptoms within ten miles using lever 9 on the PAS. I charged up the battery to 100% for the first time in a "long" while to see if it is a problem with balancing the cells. Did that for three days straight without draining a significant portion of the electricity from the cells, just get the enough drain to get the charger to start and charge to 100% and I saw the green light. The charger would do its thing and the battery charger showed a charge of 58.8ish volts.

I ran the bike for 16km with zero pedal assist, then turned it up to level one PAS for the next 30ish km. Had the same problem with the computer showing all the bars, I felt the motor kick off with no error codes displayed on the computer, quickly followed by the computer shutdown. After this ride, the battery charger showed zero charge on the battery pack, and charged it up. That was when I noticed the battery pack meter didn't work any longer. I didn't feel any hot spots on the battery, or see any signs of deformation of the battery case due to damage. Any ideas?

[ykick]

My experience and opinion differs with many “mojo bones” which are supposed to make battery packs last longer.

The 80% thing is sorta fool’s Gold. 1st problem is that you’re short-charging the battery pack so what happens if you need 90-100% capacity for a trip?

2nd thing, many BMS simply never balance until cells go a bit over 100% SOC (state of charge).

When you exclusively “short charge” what happens is that a low SOC cell group may spend much, if not all of it’s discharge curve close to ODDV (over discharge detection voltage) Due to the extra heating this pattern of use actually damages and kills the cell chemistry even further.

In practical daily use, full 100% charging is the best way to cycle Lithium based battery packs. Now, the main downside about that is to just never, ever, leave fully charged packs sit around for more than a couple days, at most.

I believe the best way to use 80-90% charge settings is for those situation where you may not be certain you’ll ride the bike again in a day or two? In that situation, charge to 80-90% and then when you know for certain you’re going to ride, top it off to 100%.

I believe the worst thing someone can do is to short charge a pack and wind up needing more energy than it contains. That’s much much more damaging than simply charging to 100% and burning that charge off within a day or two. "Penny wise and pound foolish" is the saying which comes to mind....

I’m not saying you gotta store at 3.85V/cell. Merely, 4.0-4.1V/cell is a HUGE improvement for sitting around unused even weeks at a time compared to 4.2V/cell top charge.

In other words, just don’t let ‘em sit around fully charged for more than a day or two and whatever you do, don’t short charge packs and run the risk of damaging them from OD (over discharge) condition.

[bosn]

Thanks ykick, good info. I don't remember riding the pack to exhaustion until the problems started last week. From your info, I figure I would have been better served with the way I have ridden by charging to 100% instead of 80%. If I understand what you are saying, I created the environment with the long term 80% charging, for some of the cells to have a drastically different power curve than the whole pack, and when they drop off line after discharging quicker than the other cells, the BMS shuts down the fun due to low voltage. Any ideas on a way to remedy this?

[calfee20]

My experience and opinion differs with many “mojo bones” which are supposed to make battery packs last longer.

The 80% thing is sorta fool’s Gold. 1st problem is that you’re short-charging the battery pack so what happens if you need 90-100% capacity for a trip?

2nd thing, many BMS simply never balance until cells go a bit over 100% SOC (state of charge).

When you exclusively “short charge” what happens is that a low SOC cell group may spend much, if not all of it’s discharge curve close to ODDV (over discharge detection voltage) Due to the extra heating this pattern of use actually damages and kills the cell chemistry even further.

In practical daily use, full 100% charging is the best way to cycle Lithium based battery packs. Now, the main downside about that is to just never, ever, leave fully charged packs sit around for more than a couple days, at most.

I believe the best way to use 80-90% charge settings is for those situation where you may not be certain you’ll ride the bike again in a day or two? In that situation, charge to 80-90% and then when you know for certain you’re going to ride, top it off to 100%.

I believe the worst thing someone can do is to short charge a pack and wind up needing more energy than it contains. That’s much much more damaging than simply charging to 100% and burning that charge off within a day or two. "Penny wise and pound foolish" is the saying which comes to mind....

I’m not saying you gotta store at 3.85V/cell. Merely, 4.0-4.1V/cell is a HUGE improvement for sitting around unused even weeks at a time compared to 4.2V/cell top charge.

In other words, just don’t let ‘em sit around fully charged for more than a day or two and whatever you do, don’t short charge packs and run the risk of damaging them from OD (over discharge) condition.

MMmm..............I like this. I to do not agree with everything I have been told either. This flies in the face of the "fact" that these new batteries won't develop a memory. It also explains why laptops have such a bad battery reputation. Most people plug them in and leave them plugged in and use them like a desktop. Then very soon they only work plugged in.

[funwithbikes]

The 80% charge for longevity vs. pack will only balance at 4.2 Volts certainly throws a wrench in the works. I am not 100% sure about this, but a quick look at some schmetics indicates that the leakage current will be higher at or above the leveling voltage. That might be why most BMS's are set for 4.2V.

There does not seem to be a cost difference in the chips used in the BMS if the leveling voltage is set for 4.1V or 4.2V

[Green Werks]

The 80% thing is sorta fool’s Gold.
I like that I have always wondered about that my battery is new and I am still charging it to 100% to balance it out
It will charge to 58.9 then unplug the charger and it will over time drop and stabilize at 58.6

[funwithbikes]

Almost all of the references about batteries lasting longer when charged to 80% refer back to a study done on single cell lithium coin type batteries. If anyone has access or links to original research material I would love to see it.

[ykick]

I wanna be clear I do find the 80-90% short-charge useful but just not how majority of people use it. My mission in regard to battery longevity is to prevent cells from sitting for more than a few days fully charged. I'm so convinced of it that if I fully charge any lithium pack and realize I'm not gonna be using it in the next couple days, I ride around the block a few times or drag the resistive load out and burn off that top charge.

And yes, 52V (14S) - it's reassuring when they settle down to around 58.5V give or take 0.1-.2V after 100% charge/balance. With a healthy pack that usually indicates a decent balance.

[osmaster]

Hey BOSN:

Your battery pack is getting old. Nothing lasts forever. Your pack is 70% of its former full pack capacity, perhaps reduced to a measly 52V 17AH pack.
Do you have over 400 charges? Over 10,000 miles?

Here's what to do.
Drain the battery until the BMS shuts off.
Borrow / buy a Grin Cycle Satiator and charge to 58.8V
Record the final charge totals - I'm guessing your pack is old, and doesn't hold 24AH of power anymore.

Conclusion:
Buy smaller packs, because one big pack dying sucks.
Sell the pack you have
Use the pack for a second ebike project
Buy a new pack and use the pack you have for shorter trips.
Start charging your battery to 100% from now on.

$834 and your problem will be solved (It's in stock and available)
https://lunacycle.com/triangle-52v-p...er-long-range/

[Green Werks]

Dudes Iam going to have to go along with ykick cause I want to have a balanced pack
every body knows that a unbalanced pack can lead to some one getting bit
ANd if we are wrong what the hell we are only out $835.00
besides any one who would possibly have owned a fender twin cant be too far off
I my self was a super six man 1971 vintage same head as the twin but with 6 tens instead of 2 twelve's
cheers

[bosn]

Osmaster: Yeah, I am coming to that conclusion. I figure my charging regime has screwed up the chemistry in the some of the cells, or as I go, most of them as the problem has continued to worsen over the last week. I have some hrs/km's on the pack; I don't have anywhere close to 16K, more likely under 10K. I don't have 400 full up charges. My understanding of battery charging (please correct me if I am mistaken) is that 400-1000 charge number is referring to full 100% charges, so five charges of 20% count as a full charge, not five charges. If that is the case, my pack should have power for a while unless the battery chemistry has been impacted by human error. Pretty expensive lesson. Long story short, I ordered a new pack hoping that solves the problem. I really dislike black boxing w/o a source - gets really expensive and doesn't necessarily fix the problem.

A concern for me is that I have a problem in the motor that is drawing more amps that it should, and that I don't have a battery problem. But I am not getting any error codes on the display and the SOC on the display is not moving. I'll have to dig into the computer to see if it has any other error codes, if I can remember how. The motor isn't getting hot to the touch, etc. Oh well, more research.

Can anyone tell me what it looks/feels like when your BMS shuts down? Is there an error code on the display? When my bike system shuts down, the battery meter in the computer display is solid bars, showing no power drain and no error codes. I just have motor shutdown, couple of seconds later display shutdown; it is kinda like the battery just hit the wall and bang is dead. Does that sound like a BMS shutdown or a drained pack? My experience with the pack over the last year has been a steady meter showing full charge in the computer until I get in the 50-60km range and then it starts to drop as I keep riding. My experience of the pack has matched what I have read on the flat power curves of the cells; nice steady flat discharge until you start to get to the cells end then it starts to drop quickly. That was what I noted in the computers battery SOC meter. I am not seeing that curve any longer; just a shutdown out of the blue, which is occurring quicker each time. If the cells are losing power quicker and getting drained, wouldn't I see that on the computers charge state display? How am I hitting the LVC or draining the pack w/o seeing a corresponding drop in the computer SOC meter?

[osmaster]

Good to hear that you bought another pack!

Here is my strategy for when the BMS shuts down

It seems to take an hour for the BMS to wake up again. When your pack shuts down - observe what time it is. (lets say 5PM)
Get a bike that can carry two batteries and ride with a spare battery. Do you have a rack / panniers for your bike?
When the pack shuts down due to the BMS, switch packs
Choose a backup battery pack big enough that you can ride for one hour, then test out the one that had the BMS error (at 6PM)

I don't have a BBSHD, just a small hub motor. When the BMS shut down - the bike and power shuts down. I then pedal to a safe location off the street and then swap batteries.

[ykick]

Good info osmaster, thank you for contributing.

BMS cutoffs simply discos power from the system. Doesn't really matter the type of system, power simply cuts off as if you unplugged the battery pack.

[Kocho]

If the cells are losing power quicker and getting drained, wouldn't I see that on the computers charge state display? How am I hitting the LVC or draining the pack w/o seeing a corresponding drop in the computer SOC meter?

This seems to point to a group of cells that are either well out of balance or gone bad and lost a significant portion of their capacity. Perhaps due to over-discharge beyond the level of the rest of the groups. I am guessing the shut down is due to the BMS sensing that one group is at low voltage cutoff. Because you have 13 other groups that are at normal voltage when this one is near low voltage, the overall battery pack voltage you see on the display is still high enough. The low voltage of that one bad group is masked but the rest of the pack being well-charged.

If repeated balance charging does not seem to help, you might need to replace that one group of cells. Having access too the BMS leads would be very helpful in troubleshooting exactly these kinds of issues - you will see if a group of cells is losing charge quicker than the rest, dropping voltage lower than the rest of the groups..

Discharging fully is worse than charging fully, from what I gather. So better to do 100-20% SoC than 80-0% on each ride. You will actually get more distance covered too.

I wish the BMS had a configurable "100%" threshold where it would start balancing not at 4.2V but at 4.1V or whatever user-configurable value we want below true 100%. Of course, the charger would need to match that voutage and throttle-down as to not overpower the BMS at that voltage during the constant voltage stage. It would be tricky to match the charger voltage with the BMS balancing voltage at some value below 4.2V if they are made by unrelated manufacturers, so my guess is that's why with kits like ours it probably won't happen...

EDIT: the good news is that, maybe, you only have one group of cells unbalanced. Balance it qnd all will be bqck to normal. It might take many hours over several charge cycles. Kind of like conditioning a brand new pack per the instructions (I think they say half a dozen full charges and partial discharges, nowhere close to empty!) That's best case. Problem is, without access to the BMS taps, you don't know if this is the case or you got a bad cell, in which case you do not want to keep using the pack until fixed, and trying to repeatedly balance it for long hours just over stresses the healthy cells unnecessarily.

Or a cell or all cells in one group damaged enough to lose capacity permanently. Worse, but still can be repaired fairly easy by someone who is good with a soldering iron.

Or, worst case would be the entire pack is evenly aged, but I doubt it - if you don't observe gradual voltage drop before shut down.

Either way, you do not want to be stressing bad or unbalanced cells - you can cause overheating or even fire if the cells damaged. Or prevent/make it more difficult for other cells from charging properly. If they are not yet damaged, just unbalanced, draining them repeatedly to empty will damage them and shorten their life or kill them. So, find out what's wrong and don't over discharge this pack until you fix it. And charge it in a safe place ...

EDIT 2: would you see error codes if this he BMS senses LVC on one group only or if it senses excessive temperature? I'very had a single cell in a large battery pack with 102 cells in series - the overall pack voltage barely registered there was one cell dead, and that caused that one cell to short and overheat and physically blow-up because I kept using the bike. These were NiMh cells, luckily, so no fire, but there was some smoke and that one bad cell damaged the 2 adjacent cells. I replaced these 3 cells and the pack was back to it's previous capacity.

EDIT 3: or bad BMS thinking a LVC or high temp is there when it isn't. Could be as simple as some $0.05 resistor/sensor gone out of range. And again, without access to the BMS taps you just don't know...