My relatively new battery is rated 48v and 17.5ah. That works out to 840wh. But when I charge the battery from cut-off voltage up to max voltage, the charger only consumes 550wh. Is it normal for battery manufacturing companies to use a bogus capacity rating like this, or do I have a battery problem?
Battery capacity issue or not
- Thread starter dcuste
- Start date
wturber
1 MW
Have you measured the discharge? What are you using to measure the charge amount?
There is a lot of fraud with batteries from China - especially individual cells.
I'd try to measure performance a couple of ways before coming to a conclusion.
There is a lot of fraud with batteries from China - especially individual cells.
I'd try to measure performance a couple of ways before coming to a conclusion.
Thanks for your input.
I haven't measured the discharge as I don't have the equipment needed. I plugged the charger into a kill-a-watt meter. I'm pretty confident that it is accurate. The total wh measured jive with the current rating and time it was charging. The battery is made with Panosonic cells.
How can I measure discharge? I have kt-lcd3 display. It displays watts but not watt hour info.
I haven't measured the discharge as I don't have the equipment needed. I plugged the charger into a kill-a-watt meter. I'm pretty confident that it is accurate. The total wh measured jive with the current rating and time it was charging. The battery is made with Panosonic cells.
How can I measure discharge? I have kt-lcd3 display. It displays watts but not watt hour info.
Measuring capacity accurately requires a CC load an ammeter DMM and a timer.
A coulomb counter is less accurate.
You should precisely measure peak capacity after the break-in period as a benchmark, to measure declining SoH against usage cycling.
Without that initial benchmark, no way to know how much missing capacity is due to the pack's health declining or the fact you got ripped off to start with.
Not all charging Ah make it into usable stored power, so that's not an accurate indicator.
A coulomb counter is less accurate.
You should precisely measure peak capacity after the break-in period as a benchmark, to measure declining SoH against usage cycling.
Without that initial benchmark, no way to know how much missing capacity is due to the pack's health declining or the fact you got ripped off to start with.
Not all charging Ah make it into usable stored power, so that's not an accurate indicator.
docw009
1 MW
The actual AH out of a battery is probably 80-90% of the rated value, mainly because the ebike controller is designed to shut off when that much energy is used.
Lithium cells are rated for their AH capacity by testing them between their minimum and maximum voltages. For a cell like the Panasonic GA, that is between 4.2 and 2.5 volts.
Your ebike controller will not use that full voltage range. A 48V controller shuts off around 40-41 volts. This works out to a minimum voltage of 3.1 volts per cell, leaving maybe 15-20% of the cell's AH unused. This is much better for cell longevity, and it also allows some margin if the cells in a pack get unbalanced. Also, the ebike maker doesn't know what the minimum voltage of the cells are in your battery. Some cells are only rated for 2.7 volts minimum.
However, 550 vs 840 is like 33%. Did you buy from a well respected vendor? Is it cold where you are? We dropped from 75F to 50F. My ebike lost some power.
Lithium cells are rated for their AH capacity by testing them between their minimum and maximum voltages. For a cell like the Panasonic GA, that is between 4.2 and 2.5 volts.
Your ebike controller will not use that full voltage range. A 48V controller shuts off around 40-41 volts. This works out to a minimum voltage of 3.1 volts per cell, leaving maybe 15-20% of the cell's AH unused. This is much better for cell longevity, and it also allows some margin if the cells in a pack get unbalanced. Also, the ebike maker doesn't know what the minimum voltage of the cells are in your battery. Some cells are only rated for 2.7 volts minimum.
However, 550 vs 840 is like 33%. Did you buy from a well respected vendor? Is it cold where you are? We dropped from 75F to 50F. My ebike lost some power.
docw009
1 MW
Well, you can't complain much if it's ebay and the price was right. You can get a RC wattmeter like this one. for 15 bucks. ( If you're willing to wait six weeks, 10 bucks from China.) Put it in the charger leads so you don't have to cut the battery leads. I've put these on the controller and on the charger, and found it's about the same going in and coming out. The AH numbers are pretty repeatable (I have several of these).
What type of battery is it? Does it look like it could hold 65 cells? When I see 17.5AH, that means 13S-5P with 3.5 Ah cells. Those would be quality cells, not cheap.
What type of battery is it? Does it look like it could hold 65 cells? When I see 17.5AH, that means 13S-5P with 3.5 Ah cells. Those would be quality cells, not cheap.
Good to know about the wattmeter. You're right about not complaining. I really enjoy riding it.
I opened the battery. There are probably 65 cells. I know for sure there are more than 60 and less than 70 cells. So it pretty much has to be 65. Not sure what the capacity of each cell is but they appeared to be labeled as INR18650-35E SAMSUNG SDI 3 JG3T.
From this spec sheet https://voltaplex.com/samsung-35e-18650-battery-inr18650-35e
Voltage, charge max. 4.20 V
Voltage, nominal 3.60 V
Voltage, discharge end 2.65 V
Watts (discharge, max.) 28.8 W
energy Energy, max. 12.60 Wh
It appears that the battery is 12.6 X 65 = 819Wh. If Docw009 is correct, and the voltage drop from 3.1v down to 2.65v represents 15-20% of the cell capacity, I'm missing at least about 819 X .8 = 655 - 550 = 105 Wh. Such is life.
I opened the battery. There are probably 65 cells. I know for sure there are more than 60 and less than 70 cells. So it pretty much has to be 65. Not sure what the capacity of each cell is but they appeared to be labeled as INR18650-35E SAMSUNG SDI 3 JG3T.
From this spec sheet https://voltaplex.com/samsung-35e-18650-battery-inr18650-35e
Voltage, charge max. 4.20 V
Voltage, nominal 3.60 V
Voltage, discharge end 2.65 V
Watts (discharge, max.) 28.8 W
energy Energy, max. 12.60 Wh
It appears that the battery is 12.6 X 65 = 819Wh. If Docw009 is correct, and the voltage drop from 3.1v down to 2.65v represents 15-20% of the cell capacity, I'm missing at least about 819 X .8 = 655 - 550 = 105 Wh. Such is life.
docw009
1 MW
Samsung 35E are good cells. Maybe the new battery isn't balanced yet. SInce you have it opened up, measure the voltages on the 13 series groups. If it's fully charged, they will all be at 4.2 volts. If not fully charged they should still all be the same. If not the same within .1 volt, it's not in balance.
If unbalanced, the battery indicates charged when any group reaches 4.2 volts.Then you have to leave it on the charger to allow the other groups to eventually catch up.
If unbalanced, the battery indicates charged when any group reaches 4.2 volts.Then you have to leave it on the charger to allow the other groups to eventually catch up.
AZeBikeGuy
100 W
dcuste said:
Measuring at the input to the charger is going to be way off by the charger efficiency and most get pretty hot so it will give a much higher number than what gets to the battery...
AZeBikeGuy said:
Agreed. Hard to be conclusive without the proper measurements. So far, one conclusion is that the seller sold the pack as Panasonic cells and the OP received Samsung, drops the level of trust down a notch with respect to the vendor’s specs.
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dcuste said:
As other folks have mentioned, while your kill-a-watt meter may be accurate it's measuring something different than what you think it is.
You really won't know what's happening until you use a meter like docw009 linked to. Put it in series when you use the bike and again when you charge it. (But it only measures current in one direction, from source to load, which is annoying from a wiring perspective. Either get two--one for charging, one for discharging--or be prepared to figure out your males and females, unless you're using something like Anderson connectors.)
How much current are you drawing from the battery (average and peak)? And what current are you charging at? How hot are the cells when you're attempting to charge them? (That is, are you trying to charge them right after use when they're warm?) Without knowing all these things can't be accurately analyzed.
Batteries really aren't like a gas tank, where a full tank represented a fixed amount of energy that you can use. When they're "full" it just means that a certain amount of voltage is preventing more current from flowing in, and when they're "empty" there's insufficient voltage to push current back out.
Going back to the old analogy of water being like electricity, voltage is the height of water above a waterwheel (the "head") and current is the width of a stream. When only let the water flow over the waterwheel as a small current then that's the rated capacity. But when you use a lot of water all at once it effectively lowers the height of the stream bed from where it had been. This is referred to as voltage sag.
Also, you haven't stated what the cutoff voltage is that you're discharging to. Are you taking them all the way down to 2.65V? The maximum amount of energy can only be drawn out by taking them from 4.2 down to 2.65, but this is very hard on the cells and will quickly degrade their capacity to hold charge.
Instead of thinking of batteries as something like a gas tank that you can be emptied out without consequence, think of them more like a person digging ditches. Sure, they might be able to spend 24 hours in a day digging, but they're only going to be able to do that a few times before you kill the dude. If a person takes speed (charging to maximum voltage), they can dig more ditches, but that has a ill-effect, too (high voltage fatigue).
Some good sources are geared towards non-EE:
https://batteryuniversity.com/learn/article/bu_503_how_to_calculate_battery_runtime
https://batteryuniversity.com/index.php/learn/article/discharge_characteristics_li
https://batteryuniversity.com/learn/article/what_causes_lithium_ion_to_die
In order to get a very long life from my battery, I charge to 3.95V/cell and then only utilize about 20-25% of the overall capacity. This might seem like overkill to you, but I need to get about 450 cycles out of the battery per year (twice a day for every day I commute), and I want to use it for multiple years.
Take a look at this page for data on your specific cells:
https://lygte-info.dk/review/batteries2012/Samsung%20INR18650-35E%203500mAh%20(Pink)%20UK.html
The 35E's have awesome capacity, but in doing so they're not able to discharge current as fast as some others with lower capacity.
https://lygte-info.dk/review/batteries2012/Samsung%20INR18650-35E%203500mAh%20(Pink)%20UK.html
The 35E's have awesome capacity, but in doing so they're not able to discharge current as fast as some others with lower capacity.
For future reference, which vendor did you buy your battery from and what cells did you order originally for your pack?
If they were the lower rated Panasonics, then you got a deal. If they were the GA cells, then less so if you wanted the extra discharge current (almost 500 more watts continuous from the pack). In any case, you could have done way worse as far as the cells that could have been in the pack.
If they were the lower rated Panasonics, then you got a deal. If they were the GA cells, then less so if you wanted the extra discharge current (almost 500 more watts continuous from the pack). In any case, you could have done way worse as far as the cells that could have been in the pack.
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