Battery question; or, "do I really need a battery capacity double my range consumption estimate?"

[bz16]

Hi Endless Sphere, first timer poster and first time builder here. I am planning to electrify my old bike to do long commutes with mostly Grin's parts, but seeing how busy their sales teams are and how (relatively) generic my questions are, I figured asking here would be a bit faster – I plan to get this conversion done in a month so I can use the bike to commute to college! I hope I wouldn't be inundating y'all with too many text at once.

I have a Nishiki Anasazi – they call it a "hybrid bike", which is basically mountain bike frames on road wheels; it came with a front shock and 700x40C tires, and I plan to keep that unchanged. I want to ride the bike up to my local speed limit (28mph, ~45kph, with pedal assist), my one-way commute will be 12mi/21km long with about half up-and-down hilly region and half gentle (~0.5%) and mostly consistent grade. I anticipate I'll have a way to charge my battery before going home, so the battery just needs to last ~15mi or ~25km. I'm about 100kg and I plan to fit the bike with a large cargo rack, so on Grin's trip simulator, I overestimated mass and underestimated human power at 150kg/70W respectively.

At this point I am already pretty much set on the motor and drivetrain: Grin's Rear All-Axle direct-drive hub motor, 52V system, Grin's CA3 and Baserunner with regen braking (more for extra braking force than for energy recapture / ease of maintenance); with this configuration, the Grin trip simulator gives me a maximum battery consumption of ~530Wh (when going home up that gentle slope) and a maximum sustained battery draw of about 1600W – these seems to occur on steeper uphill sections for several minutes at a time, so I imagine me dropping speed and increasing human power should be able to reduce those peaks by a fair amount.

Grin sells a 52V, 14.5Ah nominal battery pack with NCR21700A in 14S3P configuration for about USD$700; using 50.4V as the actual voltage, the pack gives me about 730Wh, which means my 530Wh commute cost is about 73% of the rated capacity; I imagine the 27%, 200Wh reserve would be enough. But Grin's sales just got back with me recommending me their 52V, 20Ah pack (Samsung 35E or Panasonic GA in 14S6P) at a whopping USD$1000. That's... a lot, and also would be double the 530Wh energy expenditure I'm expecting. Granted the total energy used for a round trip is around 900Wh, so with the 20Ah pack I don't need to wait for a full charge at school, but I really don't want to fork over another $300 on top of the already expensive $700 battery budget if I don't have to.

And then I discovered EM3EV: their downtube battery with 35E in 14S5P is rated at 17Ah for only about USD$500, and they have a 14S6P triangle battery rated at 20Ah for USD$570 – still much cheaper than Grin even with the approx. USD$100 shipping added on top. The downside? I would really prefer a downtube battery if it's possible (easier to lug around and charge and less likely to be seen as a home-made bomb), and EM3EV's battery cradle does not have a controller space for Grin's Baserunner. There's also the long shipping time from China.

So, I am just not really sure why the Grin Sales rep recommended a 20Ah battery? I guess it could be concerns over either energy capacity or current draw.
Looking at energy, if my calculation above is correct, then the 14.5Ah battery should be fine in ideal situations and gives me a 27% margin of error – which I think is enough? Or is battery energy calculation not as simple as "multiply voltage by amp-hours"?
Looking at current draw, that 1600W peak translates to just under 32A at 50.4V. There's not a lot of documentations on NCR21700A, but I found some sellers stating its current capability at 10A to 15A per cell; Grin also claims their 14.5Ah pack has a 40A BMS, so it should deliver 32A with no issues. On the other hand, EM3EV claims their 17Ah downtube battery could only do 25A continuous, which would clamp my continuous power below 1260W at 50.4V. Again, the high-power situation occurs for several minutes on uphill sections, so I should be able to mitigate it by dropping the speed and increasing human power, right?

If the 14.5Ah battery will do, I'm willing to get the more expensive Grin battery since mounting the controller under the battery is really the sleekest option – or if someone can point me to some legit US sellers, that would be sweet too; if it's really not adequate, I guess I'll have to go with EM3EV. what do you guys think? Is there more details needed?

Thank you so much for reading my rambling; I hope that wasn't too much! I appreciate any help you can provide.

 

[bz16]

As I wrote this post I poked around the forum and Google and found some US batteries sellers.
It looks like UPP would be fine as the budget option if you overspec it a bit? They have a 19.2Ah downtube rated for 30A out that is somehow only USD$365, so low I'm not even sure if it's legit – that's just a smidge over $6.5 per cell for 21700's? There's two other downtubes rated for 40A out at $500.
I found a couple posts on the forum saying good words about Calibike. They have a 20Ah downtube with controller space (!!) at $565 before shipping.
FTHPower is in north LA and even has dealers very near me; however it appears they don't carry 52V systems, only 48V.
Bafang USA Direct has 17.5Ah batteries at around $750 and 20Ah batteries around $1000. I guess that's a bit too high for me too, plus they don't have the motor controller space.

 

[docw009]

When I load test my batteries, I usually get about 90% of the advertised AH, and that's a tester limited to 3 amps on a 48V battery running down to a cell voltage of 3V/cell. Pulling ebike operating currents. I do not believe I'd get more than 80-85%. Any applicatication predicting 73% usage is likely not far from running flat,

In addition, for steady daily use, I think you will get better battery life not going under 50% state of charge. Running cells down to 25% on a daily basis will probably lead to lead to unbalanced cells.

 

[bz16]

When I load test my batteries, I usually get about 90% of the advertised AH, and that's a tester limited to 3 amps on a 48V battery running down to a cell voltage of 3V/cell. Pulling ebike operating currents. I do not believe I'd get more than 80-85%. Any applicatication predicting 73% usage is likely not far from running flat.

I see. Do you think the loss come from heat with all the current in the nickel ribbons and cables, or is it more of a inherent loss in the battery itself? Grin's simulator does differentiate between "battery output" and "motor power" (there could be a 400W difference at the peak), but I don't really know how they model these loss at high current. Indeed it's more like a ballpark estimate until I actually try it out.

Running cells down to 25% on a daily basis will probably lead to lead to unbalanced cells.

Isn't it the job of the BMS to balance the cells though? I understand that some of the poorer quality batteries have BMS that does not balance-charge the cells, but surely that's not every battery... right? Or, is it impossible to balance with many cells in parallel, or letting the cells go unbalanced during use is harmful enough already?
I guess I could try to get a UPP battery with very high amperage, but I'm not the most comfortable carrying a lot more energy then I need between my legs or on my back. But yeah, if that really is just the case with ebike batteries then 20Ah it is.

 

[amberwolf]

For the EM3EV packs, they offer various cells, each of which has different capabilities (even though they come with a 40A BMS, not all the cells support this rate). So if they don't do this at the factory, you'd want to set the max current the BMS allows (if it's user-programmable; it says it's a "smart" bms and those typically are) to below the cells' capabilities max and continuous (if the BMS has both settings available).

If the BMS isn't settable (or preset) to these, then you should do that in the controller, so it doesn't draw more current than the pack can handle. (good idea to do that anyway, even if the BMS does correctly protect itself, just so the controller doesn't peak higher than it can handle and cause the BMS to power off the system from overcurrent, since all the BMS can do is turn on or off, it can't regulate current--that is what the controller is for).



For capacity, I'd recommend assuming say, 80% of rated capacity, for calculating range, just to be sure you still ahve enough capacity as it ages, and for adverse conditions (cold, etc) that reduce available capacity and/or increase voltage sag under load.

Also, as noted by others, regularly using most or all of a pack's available energy can be hard on it, and ages it faster. How much faster depends on the specific cell and conditions. Pajda has been doing some aging testing on some cells; there's at least one thread around here. Generally speaking, the higher the voltage you stop discharging at, and especially the lower the voltage you stop charging at, the longer the cells should last.

If it is more practical to replace a smaller and/or cheaper pack that doesn't do the job anymore than to carry a larger and/or more expensive pack, then that's probably a good decision. It depends on your particular usage, budget, etc.

For instance, if you have a lot of hill climbing, every pound you have to move up it is going to cost energy, so the less weight there is the less energy it takes. How much more energy depends on the speed too. (it also depends on wind, road surface conditions, etc, but those are things you don't have control over). The Grin simulator can help you see what energy savings, etc., that you might have one way vs another. (just keep in mind it *is* a simulation, and sometiems reality is different).

If you have to slow down to go up the slope and maintain a certain energy level, but have to keep too high a current to the motor, it can cause excess heating in the motor. Since you're using the Grin AA motor, it's in the simulator with thermal modelling, so you can see if this will be a problem or not there.



Less specific-fact-based opinions below.

EM3EV has been generally regarded as good. UPP doesn't have the greatest reputation (because some of the packs they sell are really not very good; some of them are not the best cells and probably not well-matched, and then provided with a non-balancing BMS, so they get worse every usage. Some of their packs might be better but I haven't seen any detailed testing / disassembly of any of those.)

Of the two, I only have experience with EM3EV, and only with pretty old stuff; I bought a well-used "48v" pack of 20Ah A123 cells from another ES member (about a decade ago) and it worked well for the time I needed it, and I pushed it a bit (not terribly hard, but harder than I would have other packs). I haven't used it myself in quite a while (gave it to my brother with a trike I built him, but he hasn't used it in years and hasn't maintained it so it might not be functional anymore. )

 

[bz16]

For the EM3EV packs, they offer various cells... you'd want to set the max current the BMS allows...

If the BMS isn't settable (or preset) to these, then you should do that in the controller...

Yep, I did notice EM3EV's wide cell selections, though I did not know if it's possible to program their BMS. I was planning on relying on the Grin controller settings (consider I now have some dumber batteries on my radar it's probably for the best).

For capacity, I'd recommend assuming say, 80% of rated capacity, for calculating range, just to be sure you still have enough capacity as it ages...

Right, I somehow totally forgot about cell aging. Taking that into consideration, 73% is indeed cutting it way too close.

For instance, if you have a lot of hill climbing, every pound you have to move up it is going to cost energy, so the less weight there is the less energy it takes.

Since I'm already starting with a 4-5kg battery and my commute isn't all hills, adding a kilo probably isn't really noticeable considering most of the mass would be yours truly. Indeed another argument for a bigger pack if I can afford it.

At this point I think I'll just get everything except the batteries from Grin, and ask EM3EV about their shipping time – I heard it can take upwards of months, so if that's the case I might as well get a 20Ah from UPP or Calibike and see if it will last me a year or two. My main goal is to reduce my car use and get a good excuse to pedal my bike everyday, so a year of reliable use would already be a huge win.

I wonder if I can squeeze batteries past their prime for some other application that does not require as much capacity... but that's for the future.

Thank you so much for your help, docw009 and amberwolf! I would let y'all know where I get to in a month hopefully.

Now I just need to find that front light I bought last year...

 

[amberwolf]

Do you think the loss come from heat with all the current in the nickel ribbons and cables, or is it more of a inherent loss in the battery itself?

Inside the battery pack there is loss everywhere in the circuit (also true outside the battery pack). Assuming it is built properly, most of the loss is inside the cells themselves, from their internal resistance (which varies with state of charge and age).

Some packs are not built as well as others, so resistance in interconnects, wiring, connectors, etc., may be higher (and in some cases has been high enough to cause noticeable losses and heating, and sometimes pack failures).

Grin's simulator does differentiate between "battery output" and "motor power" (there could be a 400W difference at the peak), but I don't really know how they model these loss at high current. Indeed it's more like a ballpark estimate until I actually try it out.

It's always an estimate, since simulations by nature are not exactly like reality.

If you hover over the various numeric fields below the graph, you get tooltips that explain the basics of that field. Some of these are also stated in the instructions below the simulator (quoted below), but not all of them are:

1. ElectricalThis shows some of the electrical characteristics of the system at the cursor speed:
   • Mtr Amps:is the phase current flowing through the windings of the hub motor. This is not the same as the current that you measure from the battery pack with a Cycle Analyst or other watt meter. At low speeds when controller is PWM current limited, it is possible for the motor current to be several times greater than the current drawn from the pack.
   • Batt Power:This is the power that is being taken out of the battery pack (battery amps * battery volts), and is what you would see on the Cycle Analyst watts display. It is not the same as the actual mechanical output power of the motor, don’t confuse the two.
   • Batt Amps: This is the current flowing out of the battery pack, again as would be seen by a Cycle Analyst or inline ammeter. You will notice that at low speeds the battery amps stays fixed at the controller current limit. At lower speeds still it may be fixed at the controller phase current limit. That is what a controller current limiting does.
   • Batt Volts: This is the terminal battery voltage as you would see by a Cycle Analyst or Voltmeter. As you move the cursor to lower speeds where more current is drawn from the battery, you'll the voltage on the battery pack sag due to internal resistance.

Isn't it the job of the BMS to balance the cells though? I understand that some of the poorer quality batteries have BMS that does not balance-charge the cells, but surely that's not every battery... right? Or, is it impossible to balance with many cells in parallel, or letting the cells go unbalanced during use is harmful enough already?

The thing about unbalanced cells...they have unmatched characteristics, and do not all behave the same under load or charge...which is why they end up at different voltages, because they are then at different states of charge (SoC). A pack with unmatched cells will always *get* unbalanced, and the harder it is used, the greater that will be (vs using it more gently). All packs will eventually have unmatched cells as they age, but the closer they are at the start, and the more gently they are used, the longer this will take.

The job of the BMS is to prevent the cells from being damaged in a way that could lead to a fire.

That means for a well-designed BMS (they are not all) if there is overcurrent, or overvoltage (HVC), or undervoltage (LVC), overtemperature, undertemperature, or if there is a difference between cell voltages (imbalance) greater than some given amount (often 0.1v) the BMS will disconnect the cells from the outside world at either charge, discharge, or both ports, depending on the specific problem.

So...a balancing BMS just has an added feature that at some SoC (sometimes user-programmable) begins to try to rebalance the cells (either by pumping charge from high cells to low ones, or by simply wasting the charge of high cells as heat in resistors). All this balancing does (can do) is make them all the same voltage. It doens't fix the differences between cells--that requires cell replacement.

Another thing about the balance--cells that go higher than others during charge are usually lower capacity and/or higher resistance, as are cells that go lower than others during discharge.

 

[bz16]

I see. So when we talk about unbalanced cells, it's about them wearing differently as they age; that makes sense. Thank you for the detailed answers and explanations again, Amberwolf!

 

[Slowchris11]

A simple, working, balancing industial BMS is so cheap it doesn't make sense to skip it. I have a simple rule picking battery pack's, if the number and exact type of cells is not advertised, don't buy it. These cheap batteries die because they are Chinese junk, recycled, rejected or stolen. I prefer Samsung and LG, even as there are other good brands, even Chinese ones. Just "China Cell" can be anything. Don't expect more than one trouble free year of service.
Concerning your energy consumption, this is so high because if you drive at average car speed. Not the best case for any e-bike. You have maybe 6 lbs of battery storage moving one person, a Tesla's majority of its metric 1.5 tons wheight is energy storage.
Limited to 15mph you can drive 30 miles with 12.5 AH. At 28mph you tripple the consumption. Recuperation only saves you 5%, even if you are very optimistic.
Prices for e-bike batteries are, I try to say it friendly, a little elevated. I usually buy at here PSWPOWER.com - Professional Electric Bicycle Parts They list prices in US$, you may compare and see what I want to say.
Since the 21700 are common, prices have droped. Some still sell for last years price.

 

[richj8990]

As I wrote this post I poked around the forum and Google and found some US batteries sellers.
It looks like UPP would be fine as the budget option if you overspec it a bit? They have a 19.2Ah downtube rated for 30A out that is somehow only USD$365, so low I'm not even sure if it's legit – that's just a smidge over $6.5 per cell for 21700's? There's two other downtubes rated for 40A out at $500.
I found a couple posts on the forum saying good words about Calibike. They have a 20Ah downtube with controller space (!!) at $565 before shipping.
FTHPower is in north LA and even has dealers very near me; however it appears they don't carry 52V systems, only 48V.
Bafang USA Direct has 17.5Ah batteries at around $750 and 20Ah batteries around $1000. I guess that's a bit too high for me too, plus they don't have the motor controller space.

The 'lowest' place I'd look for batteries would be Amazon. They have 20Ah batteries now for under $400 and the reviews are pretty good. Others on here can certainly chip in their knowledge on this, but I think that the lithium battery market has made big strides lately, possibly a trickle-down effect from the major auto manufacturers getting verrrrrrry serious about battery range. As in spending billions on research and opening up entire battery plants for their EV auto testing. Lithium battery technology is making huge leaps, and the costs keep coming down. It's like the computer market of the 90's. Back then, 5 MB of memory cost $2000 for the whole laptop. Now you can get 2TB for under $1000, or an external drive for much less. A similar thing will happen with lithium batteries.

So IMO $1000 for a battery is ridiculous. As long as the battery is compatible, as in you plug it in and whatever controller recognizes it and it's the right voltage, you buy it. Don't buy on Ali Express. Not sure about E-Bay, for batteries I personally would be a bit wary. Amazon is fine as long as you read the bad complaints and make sure there is not a pattern. Remember that some people do what I did with my 1st battery and recharged it too early --- that made it only last 225 cycles. Wait for the charge to go under 15% (but not completely dead) and it should last 400+ cycles. That's many, many thousands of miles for what is now a $369 battery on Amazon.

 

[portals]

You will mostly get what you pay for.

Do not skimp on the battery, for Class A branded cells 52V 17.5Ah you will be looking at £400-500 GBP, pay substantially less at your peril...

 

[E-HP]

At this point I think I'll just get everything except the batteries from Grin, and ask EM3EV about their shipping time – I heard it can take upwards of months, so if that's the case I might as well get a 20Ah from UPP or Calibike and see if it will last me a year or two.

I'd go with the EM3EV if the timing works. Otherwise, If you need it fast, I'd go for the UPP pack on Amazon that uses the LG 21700 cells (4800mAh). https://www.amazon.com/Ebike-Batter...91189106&sprefix=upp+20ah,aps,168&sr=8-7&th=1

 

[bz16]

That's a variety of advices! Thank y'all for the help again.

Concerning your energy consumption, this is so high because if you drive at average car speed.

You're right, 28mph for an unareodynamic bike is quite a lot. I just really would like to not spend an hour on commute, and I am OK with battery cost under/around $500 provided they last, let's say, 300 cycles.

It's like the computer market of the 90's. Back then, 5 MB of memory cost $2000 for the whole laptop. Now you can get 2TB for under $1000, or an external drive for much less.

Did you know that quality 2TB solid state storage can be had for close to $100 now? And to think just five years ago I paid close to $100 for 512G... But I digress.
Yeah, looking at EM3EV's pricing it's very obvious that $1000 for 20Ah is way overpriced. It looks like on Amazon, downtube 20Ah batteries with some customer rating hover around $450 to $550, but then again that's still half-price.

Do not skimp on the battery, for Class A branded cells 52V 17.5Ah you will be looking at £400-500 GBP, pay substantially less at your peril...

Which is ~$USD510 to $640 now. Yeah, I see your point; I saw this one guy called JohnnyNerdOut on Youtube talking in October 2022 about how quality 18650's should cost at least USD$4 per cell, and adding on the labor a pack like the one I'm looking for should starts at $400 at the very bare minimum; maybe things with 21700's could be cheaper as suggested by Slowchris11. I will probably take a closer look at a FTHPower – the simulator shows that 48V systems would serve my need just fine too, so if they have something that suits me, a local seller should always be better.

I'd go with the EM3EV if the timing works. Otherwise, If you need it fast, I'd go for the UPP pack on Amazon that uses the LG 21700 cells (4800mAh). https://www.amazon.com/Ebike-Batter...91189106&sprefix=upp+20ah,aps,168&sr=8-7&th=1

Yep, something like that pretty much... I'm just waiting for EM3EV to return my email. Though, again, I doubt they can ship a whole 1kWh battery from china in under two weeks.

 

[bz16]

Oh EM3EV did get back to me! They estimates a 3 week period but (since they do not control shipping) cannot make a 100% guarantee. I'll just take a look at how long it takes Grin to ship me the bulk of the stuff – if they need 2-3 weeks too then I might as well get the good stuff.

 

[tomjasz]

I'll just take a look at how long it takes Grin to ship me the bulk of the stuff – if they need 2-3 weeks too then I might as well get the good stuff.

They are both "good stuff".

 

[E-HP]

Oh EM3EV did get back to me! They estimates a 3 week period but (since they do not control shipping) cannot make a 100% guarantee. I'll just take a look at how long it takes Grin to ship me the bulk of the stuff – if they need 2-3 weeks too then I might as well get the good stuff.

Waiting a week for something that you'll use for years isn't really that long. Plus, I believe EM3EV uses a smart bluetooth BMS, so lots of peace of mind.

 

[richj8990]

Waiting a week for something that you'll use for years isn't really that long. Plus, I believe EM3EV uses a smart bluetooth BMS, so lots of peace of mind.

How many years will they really use that battery. Let's say the seller 'promises' 800-1000 cycles. How many average e-bike riders, especially ones just trying it out, actually use 800-1000 cycles in a few years. Not very many. I'm riding more or less every day now and I'm using 1 cycle every 5-7 days. Even if the battery had that many quality cycles, is it really going to stay quality lithium for 5+ years, if they only ride a few times a month and maybe not at all in the Winter.

 

[labrat]

"Grin sells a 52V, 14.5Ah nominal battery pack with NCR21700A in 14S3P configuration for about USD$700; using 50.4V as the actual voltage, the pack gives me about 730Wh, which means my 530Wh commute cost is about 73% of the rated capacity; I imagine the 27%, 200Wh reserve would be enough"

Lots of commuters here of course but here is my two cents. My setup is, Trek 950 (lugged), 150 kg all in, direct drive 9C, grinfineon 40 amp, 12s3p Samsung DYI pack with 6 k miles on it so far, which started out at about 8 ahr and is now down to 5 ahr. I have a 6 mile one way commute with nasty hills (up to 17% grade) averaging around 20 mph and use about 125 Whr from the pack each way. If the hills weren't there I would not have a motor. About half the whr are going into the steep hills, where much of that ends up as motor heating. The other half is to maintain a brisk +20 mph.

With the packs, you are definitely going to get what you pay for. You will be aiming for around 1000 cycles, or 500 two way commutes. If that pack costs 1k, that's 2$ per day. Much cheaper than running a car--just cheap overall in comparison to life's various expenses. So prioritize cell quality over cost, and you probably cannot do any better than letting Grin do the cell selection and curating.

530 whr one way sounds like a lot to me. 12 miles of mild terrain would be at most 300 whr for me, average speed around 20 mph. If you are doing a frequent commute, but currently not in great shape, you will grow some muscles, and that should cut down on whr consumption. Half the point of an ebike is to get regular cardio--and you do want to get your heart rate up some.

 

[sysrq]

The 'lowest' place I'd look for batteries would be Amazon. They have 20Ah batteries now for under $400 and the reviews are pretty good. Others on here can certainly chip in their knowledge on this, but I think that the lithium battery market has made big strides lately, possibly a trickle-down effect from the major auto manufacturers getting verrrrrrry serious about battery range. As in spending billions on research and opening up entire battery plants for their EV auto testing. Lithium battery technology is making huge leaps, and the costs keep coming down. It's like the computer market of the 90's. Back then, 5 MB of memory cost $2000 for the whole laptop. Now you can get 2TB for under $1000, or an external drive for much less. A similar thing will happen with lithium batteries.

So IMO $1000 for a battery is ridiculous. As long as the battery is compatible, as in you plug it in and whatever controller recognizes it and it's the right voltage, you buy it. Don't buy on Ali Express. Not sure about E-Bay, for batteries I personally would be a bit wary. Amazon is fine as long as you read the bad complaints and make sure there is not a pattern. Remember that some people do what I did with my 1st battery and recharged it too early --- that made it only last 225 cycles. Wait for the charge to go under 15% (but not completely dead) and it should last 400+ cycles. That's many, many thousands of miles for what is now a $369 battery on Amazon.

Never stumbled upon so far that new LiIon batteries would need to be discharged fully.
"This is an old myth that you need to fully.
discharge a battery and charge it full on first use. Today's modern electronics use Lithium-Ion batteries that don't have a memory which means they can be charged at any point in the discharge cycle".