Sanyo NCR20650A Battery Rank D (?!)

Sachs

10 µW
Joined
Sep 27, 2022
Messages
5
Hello everyone,

I recently ordered 100 new NCR20650A cells for the 36V conversion of my Sachs Classic ebike, they didn't cost the world and i am hoping for a nice increase in range and power with a 10S10P battery pack. They aren't fakes but i'm kinda questioning the condition of these cells.

The date code on the cells is 7203 which means "3 Februari 2017" if i'm correct, which was 5,5 years ago. :roll: The box states they're rank D, no idea what that means but D doesn't sound as a good rank. A would give me more confidence. :lol: They came charged to 3.50V so that's nice. Are these cells still usable or are they degraded? And do any of you guys know what this Rank thing means?

EDIT: Added some pictures, they are clickable.

 
You'd have to ask the specific seller how they rank their cells and what each classification level means. They may be honest about it, or just make something up, but at least you'll know what they say.

If the box markings are from the manufacturer, you'd have to check with their testing info to see how they sort them, and what the classifcation means. Their system will probably be consistent between every cell they make, and every testing they do.


There are a lot of cell testing and pack building threads here, many in this subforum, with useful and even critical info for a first-time pack builder. I recommend reading as many as possible--even the not-so-good ones, to know what "not" to do. ;)
 
amberwolf said:
You'd have to ask the specific seller how they rank their cells and what each classification level means. They may be honest about it, or just make something up, but at least you'll know what they say.

I contacted the supplier and they state that Panasonic/Sanyo uses a ranking system that ranges from A to H. What the actual ranks mean is unknown at the moment. They also stated that they had tested a few different models of cells and that they lost ~3% of capacity after ~5 years of storage. It's also unknown how they will age from now but i guess i'll find out. The price was reasonable so i'll take a chance on that one. :mrgreen:

There are a lot of cell testing and pack building threads here, many in this subforum, with useful and even critical info for a first-time pack builder. I recommend reading as many as possible--even the not-so-good ones, to know what "not" to do. ;)

Thx for the advice. There is a lot of useful information around here, although the little storage-life info there is of rechargable lithium batteries can be quite contradictory. I have read many threads on what to do, what not to do and how to keep the cells alive for respectable time. I'm also finishing my study for Electrical Engineering currently so at least i have a slight idea of what i'm doing. 8)

The cells aren't going to be loaded hard anyway, they are ~2900mAh and have a max discharge current of 30A. The 36V 10S10P pack will power a 24V ~250W brushed ebike. The higher voltage is needed for a higher top speed (~20mph) but the original torque was already enough for me so i'll probably limit the motor to~10A max. The low voltage protection of the controller is 31V and charging happens at 41V/5A so that's on the safe side as well. The range will be long enough anyway so a little loss of usable capacity isn't a problem. I'm using a programmable BMS as well that can do some mild passive balancing at 200mA.

I'll try to match the IR of the cells, or would capacity matching be more important in this relatively low-current use case?
 
Sachs said:
I recently ordered 100 new NCR20650A cells for the 36V conversion of my Sachs Classic ebike, They aren't fakes but i'm kinda questioning the condition of these cells.

The date code on the cells is 7203 which means "3 Februari 2017" if i'm correct, which was 5,5 years ago. :roll: The box states they're rank D, no idea what that means but D doesn't sound as a good rank.
They aren't new (old unused stock) at 2-3$ ($250 for 100 + shipping). Do you plan on using a 'smart' BMS or manually balancing your 10S10P DIY build?
Sachs said:
I'll try to match the IR of the cells, or would capacity matching be more important in this relatively low-current use case?
Have you already tested both the capacity and IR of the cells? What's the variance?

Sachs ELO Classic [currently converting to 36V conversion and new control system :flame:]
What's up with reason for inserting the flame :flame: ... is this your 1st DIY spot-weld build ??
 
eMark said:
They aren't new (old unused stock) at 2-3$ ($250 for 100 + shipping). Do you plan on using a 'smart' BMS or manually balancing your 10S10P DIY build?

The cells are actually from NKON and were 1.65$ a piece, so i can't complain for the money i guess. I measured some cells and it looks like they came pre balanced at 3.50V. I'm using a 60A 10-17S "smart" BMS from QUCC with 160~200mA passive balancing capability. The cells will be tested by charging them fully and then measuring the IR/Capacity with my programmable electric load that also has battery testing capabilities. After that i will have to balance them of course with my programmable load to be able to connect them up in parallel. I saw that a maximum difference of 10mV was adviced before connecting the cells together.

Have you already tested both the capacity and IR of the cells? What's the variance?

I've not yet received the devices needed to test the cells but when i do i will probably test all 100 cells because of the age.

What's up with reason for inserting the flame :flame: ... is this your 1st DIY spot-weld build ??

It is my first spot-weld build, but the flame is targeted at the bike upgrade itself. :lol: I definately don't want any battery fires especially when it's in the garage, so safety is a real priority here. That's why i went for branded cells from a reputable store in combination with an overspecced smart BMS.
 
Alright... A small update from my side. I have received the equipment needed to measure the capacity of the cells and get a rough estimate of the internal resistance.

I have currently tested 82 of the 100 cells with a DL24 configurable electronic load and a set of Nitecore Q4 chargers to top up the batteries. A quick summary of my measurements:

- Cell capacity ranges between 2740 to 2780 mAh, charged to 4.2v and discharged to 2.95v at a discharge current of 8A.
- Internal Resistance varies about ~4 milliohms between the cells, but this is a rough estimate.

The cell capacity seems to correspond with the measured cell capacity in the reviews of this cell back when it was new.

Measuring the internal resistance was kind of a problem since the battery holder has got a resistance of about 40 milliohms. I was able to measure the variation between the cells but not the absolute number, although i did a rough estimate and got to around 20 milli ohms for the cells themselves. This week i am going to redo the IR resistance in a bit more sophisticated manner. I included the additional voltage drop of the battery holder to the cut-off voltage for the capacity test such that the actual cell cutoff voltage is 2.95v.

At least i can conclude that the cells are still in a fairly good condition and have aged quite evenly. I currently see no problems in using them in a 10S10P pack for my ~500w ebike. Each cell will at most see a strain of 2A which isn't that shocking for this type of cell, having the internal resistance matched withing 10 milliohms at the 2A current rating will probably be good enough for my use i think.
 
Not too difficult to imagine there are thousands of Pedelec users (e.g. 24V,10Ah) that want to upgrade to 36V and 500W BLDC (even though it may not be legal). With your 250W ebike motor pulling briefly at most 20A (hills) ... why a BMS rated at 60A ??

Seems like improved capacity range (10p) using at most a 25A controller upgrade would provide enuf buffer if you don't plan on feeding more than 20amps. Afterall isn't Pedelec power suppose to be the primary propulsion (with motor assist), and not the other way around :wink:
Sachs said:
The 36V 10S10P pack will power a 24V ~250W brushed ebike. The higher voltage is needed for a higher top speed (~20mph) but the original torque was already enough for me so i'll probably limit the motor to~10A max.
Why the need for a BMS rated at 60A ?
Is 25mph the legal speed limit in your country (allowing room for some grace) ?
 
eMark said:
Not too difficult to imagine there are thousands of Pedelec users (e.g. 24V,10Ah) that want to upgrade to 36V and 500W BLDC (even though it may not be legal). With your 250W ebike motor pulling briefly at most 20A (hills) ... why a BMS rated at 60A ??

Seems like improved capacity range (10p) using at most a 25A controller upgrade would provide enuf buffer if you don't plan on feeding more than 20amps. Afterall isn't Pedelec power suppose to be the primary propulsion (with motor assist), and not the other way around :wink:
Sachs said:
The 36V 10S10P pack will power a 24V ~250W brushed ebike. The higher voltage is needed for a higher top speed (~20mph) but the original torque was already enough for me so i'll probably limit the motor to~10A max.
Why the need for a BMS rated at 60A ?
Is 25mph the legal speed limit in your country (allowing room for some grace) ?

The ebike i'm using is a Sachs ELO Classic, which is one of the first generation ebikes from the 90's. It's got a brushed DC motor in the rear wheel hub with two internal belt drive reductions, quite different from the modern hub motors. One advantage is that they are very cheap, i got the bike for a whopping $25, and the DC motor is easy to control with aftermarket control units. The disadvantages are the lower efficiency (i estimate that the range will be about 10% lower than with a modern hub motor) and the lack of top speed. With 24V, the motor only reaches a top speed of about 18km/h (~11mph), at 36V this should increase to about 27km/h (17mph) which is close enough to the legal maximum speed of 25km/h here.

The estimated power of the motor at 36V is 500~600w but i will probably current limit it to about 350w since the torque at 24V was already quite good and i only need the extra voltage for the additional revs. Actual power at top speed is guessed to be around 200w which means a 10~15A current limit would be totally fine.

Regarding the BMS, this can be approached from two sides. One side is indeed to look at what the bike needs, a 30A BMS would be totally fine in this case. But when i approach it from the other side and look at the capabilities of these cells, a 60A BMS is still very under specced. With this BMS i can load each cell to a maximum of 6A which isn't really that much. A 100A or even a 150A BMS for bursty loads will still be a nice match for this pack of cells. The fact that a BMS can deliver 100A doesn't mean it will push 100A in the motor, it works the other way around. The motor pulls the amount of power it needs from the battery/BMS, and the most important thing here is that the battery/BMS is capable of delivering the amount of power that the engine pulls from it.

The real reason i bought this 60A BMS is that i was looking for a smart BMS with a (passive) balancing system that can actually balance the cells at an usable rate. And this one was the cheapest option, at $60 it wasn't that expensive and the 60A current rating is a nice to have. This also leaves room for upgrades in the future for something like a 1000~1500W hub motor.
 
Sachs said:
The motor pulls the amount of power it needs from the battery/BMS, and the most important thing here is that the battery/BMS is capable of delivering the amount of power that the engine pulls from it.
What is the amp rating of your 36V Controller to limit the amperage pulled by the 250W brushed motor (250W nominal output, 350 cont. output, 600W max output)? That's assuming the true maximum output of your (older?) 250W brushed hub motor is 600W.

If you're figuring 600W maximum output did you decide to go with a 36V-15A Controller ... figuring 600W max divided by 41V = 14.6A
Sachs said:
I'm using a programmable BMS as well that can do some mild passive balancing at 200mA.
With your 60A "programmable" BMS and 10S10P 36V upgrade will you adjust your programmable 60A BMS to a 15A or 20A setting ?

If a 36V Controller is rated at 15A is it's amp rating even higher at 41V ?
 
eMark said:
With your 60A "programmable" BMS and 10S10P 36V upgrade will you adjust your programmable 60A BMS to a 15A or 20A setting ?

Unless there is a specific reason (cell protection, etc) to have the BMS cut power below the 60A, I wouldn't change it's current limit setting.

Since a BMS can't do current limiting in a useful way (just cut all current or allow all current up to the limit), then any current limiting settings are best done within the controller.

If there is a reason to have the BMS shutdown power to the entire system above 15A or 20A (or whatever limit), then I would change the BMS's current limit to whatever is required to meet that.


Controllers do useful current limiting by reducing voltage to the load to maintain current below the limit, rather than just shutting off current entirely when above the limit and passing all current below the limit, so as long as the controller is built or set to limit at a level that will protect the motor from overheating, and the rest of the system from overloading, then it's the best point at which to do any current limit setting.
 
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