Not Getting Claimed AH's on New Lithium Battery.

P

pediman

100 mW
Joined
Nov 30, 2010
Messages
36
I have two Lithium Ion Batteries for my pedicab running a Bafang 750 with the newer controller. The first battery is rated at 16ah. I ran a "What's Up" meter inline under and found that I get very close to 16ah if I run the battery to complete discharge.

I just purchased a second Lithium Ion Battery rated at 20ah using Panasonic PF cells. When I tested the 20ah battery with the "What's Up" meter inline I got only 17.13ah before battery fully discharged, and prior to full discharge the motor started cutting on and off at 16.3ah.

So I called the dealer on the second battery (20ah) and explained I was not getting the full 20ah out of the new battery. His response was that this is normal because the the BMS is designed this way to protect the longevity of the battery and to protect the cells from over discharge. Furthermore, he said that the fact that I am getting close to 16ah on my old 16ah battery is a bad thing and that the 16ah battery will be killed very quickly and never see the rated cycles.

Is the dealer right? Or did I just get a battery that doesn't perform to its rated AH's?

Thanks for any help in this matter.

Pediman
 
Sorta making an excuse but in some cases what they’re claiming could be legit. We don’t know what values are being used for ODDV (over discharge detection voltage) in each BMS so your comparison may also be an Apples/Oranges thing?

Another unknown thing here is what’s peak power demand for the system? High power drain/load will often “waste” more capacity than low power drain/load.

The only true way to know if your pack cells are operating at advertised capacity would be to work with the cells directly on an RC Charger. But honestly with the capacity you’re currently seeing probably not worth the trouble.

You might try cycling a few times and making sure the charger has plenty of time connected to balance the cells? That may improve practical capacity?

Are you using the same charger across each battery pack?
 
Thanks. I use different charges because the charging ports are different. I charge the 16ah battery with a 2amp charger and the 20ah battery with a 4amp charger although the dealer gave me an additional 2amp charger for the 20ah. In any event, both the 16ah and 20ah battery charge up to around 54.16 volts when fully charged. Are you saying that with different BMS systems that both batteries could be functioning normally? If so, then the 16ah seems a much better value because it's delivering the stated amp hours while the 20ah battery isn't.

As far as "peak power demand", not sure if I'm clear on what you mean, but the pedicab usually runs at between 8-12 amps per the What's Up Meter. When I give it full throttle it will hit the 25amp mark, but I only do this when empty and in a hurry. With customers we go pretty slow around 6-8 mph.
 
I have two 48v Lithium Ion Batteries for my pedicab running a Bafang 750 with the newer controller. The first battery is rated at 16ah. I ran a "What's Up" meter inline under and found that I get very close to 16ah if I run the battery to complete discharge. That looked good to me.

I just purchased a second Lithium Ion Battery rated at 20ah using Panasonic PF cells. When I tested the 20ah battery with the "What's Up" meter inline I got only 17.13ah before battery fully discharged, and prior to full discharge the motor started cutting on and off at 16.3ah. That didn't look so good.

So I called the dealer on the second battery (20ah) and explained I was not getting the full 20ah out of the new battery.

His response was that this is normal because the the BMS is designed this way to protect the longevity of the battery and to protect the cells from over discharge. Furthermore, he said that the fact that I am getting close to 16ah on my old 16ah battery is a bad thing and that the 16ah battery will be killed very quickly and never see the rated cycles.

Is the dealer right? Is it normal that his battery is delivering less than the stated amp hours and that getting the full stated amp hours on my 16ah battery is a bad thing? Or did I just get a battery that doesn't perform to its rated AH's?

Thanks for any help in this matter.

Pediman
 
AH ratings for battery packs are usually based on very low discharge rates at controlled temperature of 25C. If you discharged your 20ah battery at .2C, you'd probably see 20ah from it, assuming it was fully charged and ambient temperature was 25C.
 
Thanks. The temperature yesterday when battery was done was close to 25 C. Discharge rate varied from draws of 2amps to probably 18amps, depending on speed and terrain. What about the dealer's claim that the reason I'm only getting around 80% of the claimed amp hours is because the BMS is set that way to preserve battery life? He also said that the fact my other battery (rated 16ah) gets 16ah is not good and the BMS is either set wrong or not working. Does he have a point or is it not true?
 
Correct cell LVc varies greatly depending on the cells being used. The lower you run a cell, the more likely to do permanent damage to it. But he's just guessing. This has been discussed in depth many times.
https://endless-sphere.com/forums/search.php?keywords=longevity&fid%5B0%5D=14
 
Thanks. Both 48v batteries cut off at practically the identical voltage (43.5 volts). So wouldn't this contradict the dealer's claim that my 16ah battery is being damaged because its BMS delivers all 16ah's, while his 20ah battery only delivers a fraction of the stated amp hours (16-17ah) ?
 
Thanks. I believe both are Lithium Manganese and the 20ah uses Panasonic PF cells. I don't have the spec sheets on the 16ah battery. It makes sense what you say about the effect of different currents and both tests were run on different days with different conditions and therefore the amp draw was not the same. Probably need to test more than one day under different conditions to see if he usable amp hours are really all that different between the two batteries. It was windy and rainy when I tested the 20ah so perhaps I was drawing higher amps that day which affected the amp hours delivered.
 
They were purchased through two different Bafang Dealers based on recommendations of driver's in the pedicab trade. I haven't seen mention or reviews here on either of them. I feel it unfair to name names based on my supposition that one battery is better than the other because I may be wrong and at least in once case a small company is involved. However, what I can do is try and find out who manufactured each battery which would probably be more to the point anyway. I am starting to learn that amp draw can be a factor in total amp hours delivered so probably more testing will see if one battery consistently seems to outperform the other or if it was just two different kinds of days in different conditions. For example, the day I tested the 20ah battery was windy an rainy with the canopy up causing more drag then on a less windy day with canopy down.
 
So it looks like they are both 13S packs. What is the end voltage of each pack once it hits the BMS cutout? The 20ah pack may well have a more conservative LVC and as such the lower perceived capacity. However, missing 3ahr is is fair bit on a new battery even with a conservative LVC.

You should also consider measuring your WattsUp meter accuracy with a good quality inline amp meter if you can.
 
pediman said:
Thanks. Both 48v batteries cut off at practically the identical voltage (43.5 volts). So wouldn't this contradict the dealer's claim that my 16ah battery is being damaged because its BMS delivers all 16ah's, while his 20ah battery only delivers a fraction of the stated amp hours (16-17ah) ?
Click to expand...
A lot of possibilities here.
Do you use the same charger for both, or different chargers ?
Are the both at the same voltage when fully charged ?
Do you know the construction of the packs ? 18650, pouches, lifepo4, ?...12S, 13S, ??
Are they the same cells and chemistry ?
 
Thanks gentlemen, some answers:

1. Voltage at BMS cutout is practically identical for both chargers -- 43.5v

2. I use different chargers because the charge ports are different as supplied by dealer, however both charged to approx the same voltage -- 54.16v for the 16ah and 54.5 for the 20ah, however the charge on the 20ah was measured several hours after taking off charger while the charge on the 16ah was measured right after taking off charger. The 20ah charger is 4amps. The 16ah charger is 2amps. I was also supplied with an additional 2amp charger for the 20ah battery that I will use next time.

3. I believe both are Lithium Manganese, not LIPO4. According to the dealer, the 20ah uses high drain Panasonic PF cells, 2900 mah, 91 cells, just shy of 10amps continuous per cell. It comes in an aluminum case. I will try and get similar information on the 16ah. (See below for link to pictures of both batteries and charges)

4. As to accuracy of Watt'sUp Meter, I used the same meter, with the same Anderson PowerPole connectors, ie I plug both batteries into the same connectors on the Pedicab. Meter is between controller and battery. Good point on accuracy but I'm still getting a comparative difference and the meter does show a full 16ah for the 16ah battery. Also, anecdotally, the 20ah seemed to discharge faster although riding conditions were different (rain, higher winds and canopy up --more drag) on the day I tested the 20ah which probably meant more amp draw while riding. I will test again with canopy down in more normal conditions.

5. LINK TO PHOTOS OF BATTERIES AND CHARGERS: https://www.smugmug.com/gallery/n-2dRKcZ/
 
A cutout of 43.5V on a 13S pack seems very conservative. If the cells we able to run down to 3.0V per cell (39V), I would say you would probably get close to 20 Ah out of the pack.

If the 16 Ah pack is cutting out at 43.5V also, it sounds like its BMS is doing a conservative job also.

Are sure it is the BMS's cutting though? The BBS drive may have its LVC set to 43V and is what is cutting the power. Normally when a battery cutouts on its BMS, you need to unplug the battery and plug back in to re set it. If it cutting out on the BBS LVC, If you coast for a bit, the voltage recovers, and you get a minute or two more out of the pack.

Anything like that happening?
 
The 20ah pack uses Panasonic PF cells, not Samsung. I will try and get more info on the 16ah pack when I go the garage in a couple of days. I have a link to pictures of the packs in a previous post if that helps.
 
When you say "the BBS drive may have its LVC set to 43V" are you talking about the "low battery protect (V)" on one of the three tabs of the controller's software? That is set to 41V. I never tried unplugging and plugging the battery back in when it cuts out. I just switch batteries at that point. So if I unplug and then plug it back in after it cuts out, you say BMS resets. But I assume it would reset back to 43.5V, not helping me any?
 
pediman said:
3. I believe both are Lithium Manganese
Click to expand...
Kepler said:
A cutout of 43.5V on a 13S pack seems very conservative. If the cells we able to run down to 3.0V per cell (39V), I would say you would probably get close to 20 Ah out of the pack.
Click to expand...
I believe that for LiMn, a BMS cutout voltage of 3.35V/cell is okay. The curves are not that far off LiPo and other Li-ion chemistries.

This is very close to the 0% SOC voltage used by the CA V3 for that chemistry (3.32V/cell) -- very little charge left at that voltage.

I think the answer to the capacity issue lies elsewhere...
 
All I know is that if I have paid for 20 gallons of gas it better be 20. If I have $20 in change, then I expect 20.
Most earlier LiFePo4 packs were almost always short about 20%. Unless you got it from a fair dealing seller. Most were not and still many are not.
Dumb question is, are the battery cases the same size?
As said above, the BMS is to protect the battery from discharging too low. Yes it could be set high but then how do you get your moneys worth. When a car manufacturer over states it's mileage and people find out, they get some type of compensation. My bubby gets a debit card when he takes his car in for service. The amount of money on the card id based on mileage from the last service.
Others my not agree with me but you paid for a 20 gallon tank and it only holds 16. I would return it and get another 16ah one from the place you got the other. That is if the dealer doesn't make mends with you.
Just my feeling. If I can't draw 20AH from it then it's only what it can produce!!!!!

Dan
 
pediman said:
When you say "the BBS drive may have its LVC set to 43V" are you talking about the "low battery protect (V)" on one of the three tabs of the controller's software? That is set to 41V. I never tried unplugging and plugging the battery back in when it cuts out. I just switch batteries at that point. So if I unplug and then plug it back in after it cuts out, you say BMS resets. But I assume it would reset back to 43.5V, not helping me any?
Click to expand...

Yes the low battery protect V is what I am talking about. If set to 41V, then it is the BMS shutting the pack down. Depends on the BMS but most will reset if you uplug and re plug. The voltage will recover slightly and you should get a minute or 2 out of the pack. Might be worth trying a re set and just use very light throttle so you dont cause much Voltage drop on the pack. You may end up squeezing a bit more range out of the pack.
 
If you check out folks who have tested even well regarded brand 18650 cells you will see that even a somewhat moddest draw of current from the cells drops their rated capacity %20 lower then claimed..
Check out the Samsung 25R... thats 2500mah and its giving around 2100mah on its fist 100cycles.. on a 4amp discharge.. And using the same cells but just charging them faster gives a notable drop on top of that on their total discharge performance on top of that..
https://endless-sphere.com/forums/viewtopic.php?f=14&t=73883
file.php


Same with 29E cells..
https://endless-sphere.com/forums/viewtopic.php?f=14&t=76048
file.php


If your battery pack is 6P and you want to draw 1000watts from it then its drawing 3.3amps per cell (roughly/probably depending on its series size) then you should read %20 less total ah on your pack just like what is shown in individual 18650 cell testing.
If you draw a much more modest and boring amount of power so its 1amp per cell so its (1ax 6P) x 48v = 288watts then you should see your total rated capacity as when you draw just 1amp out of 18650 cells you get exactly its claimed rated capacity..
If you want to see exactly your theoretical rated capacity and draw 1000w-2000w continuously from your pack then your going to need a much bigger battery and probably one with no BMS.
If you want to argue that it doesn't apply because your 18650s are panasonic then my answer would be from most of the charts I have seen out there on panasonic 18650 cell tests the panasonics give crappier charts/performance numbers so just double what you see on the samsungs unless they are really super duper panasonic cells.
 
Thanks TheBeastie. Are you saying that the different amp hour results of the two packs could be that when I ran the 20ah pack and only got 80% of the listed amp hours -- it was because on that particular day I might have run the motor harder than on the day when I tested the 16ah pack that delivered 100% of the listed amp hours?

Most of the time we run pretty slow and the amp draw is usually between 5 and 12 amps even with passengers. Rarely goes near the 25amp capacity except when running empty with throttle wide open. That said, on the windy day I tested it, with canopy up and therefore more drag, the amp draw could have been significantly higher, but I wasn't paying enough attention to the What'sUp Meter to confirm that. Too bad it doesn't give a read out. I do plan to re-test the 20ah battery on a dry, windless day with canopy down to see if it makes a difference in ah delivered.

Also, you mentioned charge rates. I charged the 16ah pack with a 2amp charger, but used a 4 amp charger for the 20 ah battery. Could the 4amp charger cause a drop in amp hours? I plan to use a 2amp charger next time to see if it makes a difference.
 
The dealer is giving you lame excuses.

If he has intentionally set the bms to undercharge the pack by that much, then he should sell it as a 16 ah pack. If it was set to be undercharged one AH, that's one thing, but 4ah? Bullshit.

Far more likely, is that your 20 ah pack is either very out of balance, or has at least two crappy low capacity cells in it.
 
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