16s9p or 17s8p?

[cloudy]

I'm running 9c 7x9 motor, 45A green time controller on a hardtail with 26" wheels. I do use regen and have been riding this setup for about 2 years. I want to go up to 50km/h and mostly ride streets with some hills. I'm interested in range and battery longevity over speed/torque.

My current battery is a 14s8p pack (salvaged, with no-brand BMS), in series with a smaller 2s10p pack with 2500mAh cells salvaged from a scooter and no bms. I bulk charge the 16s series string outdoors up to about 62.5V and hope for the best. I avoid going anywhere close to 4.2V/cell. I have bypassed BMS on on the larger pack for discharge, and only use the BMS for charging. None of this is best practice and I want to improve.

I'm generally happy with the performance, but have noticed its getting sluggish and range is lower than it used to be. The pack voltage measured at the controller is sagging from 62V down to about 54.5V when going up a steep hill. I'm not measuring battery current but assume its around 45A (no shunt mod). Is this bad for Sag?

I'm looking to build a pack with Queen Battery 18650 2500mAh "12A" cells and Smart BMS. Has anyone had direct experience with this cell? I am particularly interested in longevity/cycle life.

QB18650 2500mAh

I want to limit the weight of battery <150 Cells so I can still lift the bike over fences and into car. I cannot decide between 16s9p and 17s8p. My current 16s battery leaves me wanting more speed, but is sagging so badly I'm not sure if thats the issue. I think regen is quite stressful on the cells due to lower rated charge rate, would the 9p config have greater longevity when using regeneration? Will a new 8p battery perform so much better that 9p is overkill?

Smart BMS
The main reason for building a new battery is I feel my existing one is unsafe, particularly for charging. I want a smart BMS to improve safety.
Others have recommended Heltec, Tucc and JBD smart BMS. I am leaning toward JBD as they seem to allow up to 17s on their 80A models. Again, I'm interested to hear peoples experience with this BMS. I cannot tell from the advertisement if NTC temperature probe and balance wires are included, and the seller is unresponsive. Also unsure if I need to purchase any additional module to allow bluetooth connectivity to change basic BMS parameters (UART/CAN). I think the Ad says Bluetooth included, but UART/CAN is not. Does anyone know?
JBD BMS link

I have a MOT spot welder, and have plenty of dead cells to practice on. planning on using copper sandwich using 0.1mm copper strip and nickel plated steel strip on top. I'll use cell holders, and insulating washers.

 

[pwd]

I'm interested in range and battery longevity over speed/torque.

I cannot decide between 16s9p and 17s8p.

That is 144 cells vs 136 cells, I'd go for more if it fits. 9p will be less stressed during charge / discharge than 8p at the same current levels.

 

[docw009]

I know it must be tough to get ebike components in Australia, but I recommend against generic cells from China that are priced in the $2-3 USD range. Also, 2500 mah is pretty low by today's ebike standards. I would suggest increasing the battery budget for name brand cells. 17S vs 16S is only 8% more voltage, but I think 9P will give you better cell life and less sag, etc. If you can do the copper sandwich, you will have less issues with series current thru the strips. How about 21700 cells?

If you're sagging to 54.5V, that's 3.4V per cell on the average. Maybe some cells are lower. If you had a discharge BMS in place, I bet it would be very close to shutting off the big battery. I guess the cells are getting old, with the internal resistance getting higher. If you can still access the leads, do a static check on the group voltages before your next charge, so see where they stand.

I recently bought a Jabaida BMS from the same store to explore the blue tooth. It's a small 17S 30A, but did come with balance harness and the thermal sensor plugged in. Should have bought the UART dongle for $12 more. Won't have a chance to try it out for a long time. No battery builds planned. I hear they make good product. At least it is a "brand" name in the wild world of Chinese BMS. There is also Daly, which is considered poor, but I think half of the Daly's are counterfeit copies. Also ANT.

 

[amberwolf]

I'm interested in range and battery longevity over speed/torque.
<snip>
None of this is best practice and I want to improve.
<snip>
I'm looking to build a pack with Queen Battery 18650 2500mAh "12A" cells and Smart BMS. Has anyone had direct experience with this cell? I am particularly interested in longevity/cycle life.
<snip>
The main reason for building a new battery is I feel my existing one is unsafe, particularly for charging. I want a smart BMS to improve safety.

All the BMS can do is monitor and assuming things work as designed, shut off input or output when a limit is exceeded. By itself, it doesn't create a safe battery.

To do that, you should start with good, well-matched cells that are more than capable of handling the worst-case conditions you'll put them thru, even when they are old and degraded.

So, if you're set on 18650s or other small cylindrical cells, the first thing I would do for safety is pick a well-known cell vendor (like nkon, etc) that can supply those, and ask for well-matched cells.

If they don't know what this means, they are probably not the right place to buy from. If they have specs for matching like ">xxxxmAh capacity" or "<xxxmohm resistance" or "all same voltage shipped", they don't have a clue and I'd skip them. (most wont' even have that)

Cells from the same manufacturing batch are more likely to be close in characteristics (capacity, internal resistance, etc), so places that can guarantee the same batch, shipping them to you in their original boxes from the manufacturer, are at least better than those that can't or won't. But even within a batch there can be significant variation, so if you can get cells that are tested and matched to be identical, your battery will have more usable capacity for a longer lifespan. This will probably cost more, because it takes labor to do this. (if you were to do it yourself, you might have to get a few thousand cells to sort out a couple hundred that are actually "identical").


Many people will go for a battery that has a shorter usable lifespan and just replace it more often, rather than invest in one that *should* last longer, especially because needs change frequently for some people, and they might need a different battery in a year or two anyway. If you think that's possible for you, then don't worry as much about true matching, and just go for same-manufacturing-batch, which ought to be close enough.


Regarding how many parallel cells, the more in parallel, the lower the load on each one, so the less stressed they are, and the less voltage sag you have, so the more of the total power and capacity you actually get to use, and the less that's wasted as heat.

Like pack life vs cost, there's a compromise here, too--the point at which the pack is too large or heavy or costs too much, vs the benefit you get from it.

 

[99t4]

I want to limit the weight of battery <150 Cells so I can still lift the bike over fences...

That is an impressive feat-- what do you estimate the total bike weight to be?

 

[cloudy]

I know it must be tough to get ebike components in Australia, but I recommend against generic cells from China that are priced in the $2-3 USD range. Also, 2500 mah is pretty low by today's ebike standards. I would suggest increasing the battery budget for name brand cells. 17S vs 16S is only 8% more voltage, but I think 9P will give you better cell life and less sag, etc. If you can do the copper sandwich, you will have less issues with series current thru the strips. How about 21700 cells?

If you're sagging to 54.5V, that's 3.4V per cell on the average. Maybe some cells are lower. If you had a discharge BMS in place, I bet it would be very close to shutting off the big battery. I guess the cells are getting old, with the internal resistance getting higher. If you can still access the leads, do a static check on the group voltages before your next charge, so see where they stand.

I recently bought a Jabaida BMS from the same store to explore the blue tooth. It's a small 17S 30A, but did come with balance harness and the thermal sensor plugged in. Should have bought the UART dongle for $12 more. Won't have a chance to try it out for a long time. No battery builds planned. I hear they make good product. At least it is a "brand" name in the wild world of Chinese BMS. There is also Daly, which is considered poor, but I think half of the Daly's are counterfeit copies. Also ANT.

Yes it's difficult to buy things from here and postage is expensive. Where would you buy cells? I will check out NKON, but the website is not forthcoming with shipping quote to Australia.

Last time I opened up the battery, the cells in the 14s pack were perfectly balanced, and I did a Top Balance with the 2s pack at around 4V/cell. The 2s pack lasts longer as it's 10P, rather than 8p.

With the Jabaida BMS, why do you wish you ordered the UART? Can you change settings with just bluetooth, or do you need UART? What is UART? anyway? I only have USB ports on my PC, no serial port.

 

[docw009]

UART is a serial data port, same as what your ebike display uses. I am somewhat reluctant to put a chinese app on my phone, but I'm happy to plug my laptop into a BMS, as long as it's my beater laptop with bo stored passwords, etc on it,

 

[cloudy]

That is an impressive feat-- what do you estimate the total bike weight to be?

Current bike weight is 27.5kg. When I say fences, they are only waist height. We have areas were motorbikes ar prohibited but ebikes allowed, and there is usually some low gate or barrier to discourage motorbikes.

 

[cloudy]

All the BMS can do is monitor and assuming things work as designed, shut off input or output when a limit is exceeded. By itself, it doesn't create a safe battery.

To do that, you should start with good, well-matched cells that are more than capable of handling the worst-case conditions you'll put them thru, even when they are old and degraded.

So, if you're set on 18650s or other small cylindrical cells, the first thing I would do for safety is pick a well-known cell vendor (like nkon, etc) that can supply those, and ask for well-matched cells.

If they don't know what this means, they are probably not the right place to buy from. If they have specs for matching like ">xxxxmAh capacity" or "<xxxmohm resistance" or "all same voltage shipped", they don't have a clue and I'd skip them. (most wont' even have that)

Cells from the same manufacturing batch are more likely to be close in characteristics (capacity, internal resistance, etc), so places that can guarantee the same batch, shipping them to you in their original boxes from the manufacturer, are at least better than those that can't or won't. But even within a batch there can be significant variation, so if you can get cells that are tested and matched to be identical, your battery will have more usable capacity for a longer lifespan. This will probably cost more, because it takes labor to do this. (if you were to do it yourself, you might have to get a few thousand cells to sort out a couple hundred that are actually "identical").


Many people will go for a battery that has a shorter usable lifespan and just replace it more often, rather than invest in one that *should* last longer, especially because needs change frequently for some people, and they might need a different battery in a year or two anyway. If you think that's possible for you, then don't worry as much about true matching, and just go for same-manufacturing-batch, which ought to be close enough.


Regarding how many parallel cells, the more in parallel, the lower the load on each one, so the less stressed they are, and the less voltage sag you have, so the more of the total power and capacity you actually get to use, and the less that's wasted as heat.

Like pack life vs cost, there's a compromise here, too--the point at which the pack is too large or heavy or costs too much, vs the benefit you get from it.

Thanks everyone for your responses.

Regarding matching cells, is it normal to capacity test new cells prior to building packs to weed out bad ones? I was hoping not to have to do this. I thought having 8 or 9 in parallel would average out small irregularities.

My test setup is pretty basic, made of plastic/ spring cell holders. I charge up to 24 cells in a 1s24p configuration to match soc, then I put them I to a 24s1p string and attach a heater that draws about 4-5A. Then I measure voltage on each one and try to catch the first that goes below 3V under load. I put a known good cell in the mix as a reference point for capacity. Allows many cells to be tested simultaneously. Is this method crazy/am I wasting my time?

I think QB also manufacture the cells but not sure, I will try to find out. At least 2 other ES members use their cells with good results, but i think they are using 21700.

Comparing cost, capacity and weight, I couldn't really see the benefit of 21700 but might be missing something. Less welding and slightly better power to weight ratio?

 

[amberwolf]

Regarding matching cells, is it normal to capacity test new cells prior to building packs to weed out bad ones? I was hoping not to have to do this. I thought having 8 or 9 in parallel would average out small irregularities.

Not if you buy from a reputable seller that sells matched sets of cells, preferably as an advertised feature of their sales process.

As noted before, if they don't know what that means (and can't tell you what it means, or if you have to tell them), don't buy from them if you care about that (if reducing cost is your major goal, my guess is you won't find a seller you can use that does this).

There are multiple grades of cells, and the stuff that isn't the top grade is less likely to be closely-matched in characteristics, as that is usually part of what makes it a lesser grade.

Otherwise, you have to test for internal resistance and capacity, etc., so that you can build groups that are identical between each group. If you get cells from a typical generic cheap seller, expect to have to buy extra cells (possibly a lot of them depending on the quality and consistency of the seller) just so you can have enough that are good enough and close enough to do this with, and to have spares for when the less-capable ones begin to fail.

I don't know QB well enough to say anything about them, but I think Thunderheart or Pajda has a thread testing some of the cells they sell, that has more info there.

 

[amberwolf]

FWIW, if you are willing to build a pack from large-format EV cells, which usually come in modular blocks (that you'll probalby have to leave them in for mechanical support reasons), you can probably get ones sufficient for your purposes that will likely work better and last longer with much less trouble to make a pack out of, and possibly for cheaper than the 18650/21700/etc cell builds, from car scrappers / breakers, or various sites like batteryhookup, etc.

Because the QC and design process for large commercial EVs is generally going to be much better than that of the kind of stuff available in small cells or "ebike" stuff, so even as used packs they will probably be very well matched and have very good capacity, performance, etc., vs their original ratings.

The catch is these are likely to be larger and heavier and awkward to mount on a typical bicycle...so they aren't for everyone.

I've been using some ancient EIG EV cells for years (a decade?) (that were already well-used when I got them), and they are still good enough to run my SB Cruiser trike...in a stack-of-books type block inside one of the cargo areas, that for the 2kWh (52v 40Ah) pack weighs almost 40lbs (probably about 35 without the cabling and stuff).

 

[cloudy]

Oh yeah, I just found this thunderheart review. Somehow missed it in my earlier searches. Thanks for prompting me AW.

Queen Battery QB18650 2500mAh capacity test + comparison with QB18650 2600mAh

 

[offGridDownUnder]

Where would you buy cells?

This may not fit with your other requirements. I get batteries in Australia from Cap Rouge. They are subject to Aussie legal consumer laws:
Electric Bike Batteries, Conversion Kits, Motors and Accessories

 

[cloudy]

This may not fit with your other requirements. I get batteries in Australia from Cap Rouge. They are subject to Aussie legal consumer laws:
Electric Bike Batteries, Conversion Kits, Motors and Accessories

Yeah several friends have bought packs for their bafang mid drives at cap rouge. They offer some after sales support and the batteries I've seen are well built.

They don't stock what I'm looking for in a complete pack and individual cells are overpriced.

 

[cloudy]

Ended up building 16s9p and am stoked with the new battery. Thanks for your help.

 

[calab]

Its hard to lift even a non ebike over a regular height chain linked fence, its doable for adventurers like you and me, its doable.
I have to find a middle step of some sort, a log, a tree, a fence middle bar to step on but I always need that something else to even just get over the fence, let alone with a bike. A removable battery will help, just use the same method as if you were carrying a backpack (to put over the fence) as I do for tools, repair kits, u-lock, gloves, raingear, chargers. Take you a bit longer to hop the fence. I just did a few fences this past year, another good riding year. Mostly non-ebiking, but I plan to ebike the golf-cc's & ridges before it freezes and the rivers once they do freeze. Caught a couple brown trout today within 8 minutes, small ones. I still got the chops.

I;d go for more wh in a battery, but if you want that bit extra speed 17s good for extra speed and extra watthours means longer riding then 16s, but size and shapes of the battery design matter to properly fit.