Poll: What size LiFePO4 packs are best?

We are preparing to manufacture several LiFePO4 polymer packs and would like to poll the public on what configurations would be the most popular. We have the following cells available: 5AH, 10AH, 20AH, 30AH, 40AH. There are some specs in the For Sale section (I will move to here). The 40AH would probably be better suited to motorcycle use due to the size. But if you had the cash, what rating would you want? 36V 20AH ? 36V 30AH? 48V versions? What would be the maximum physical dimensions? A typical rack size? What about paniers? Do you think anything above 20AH is too big for ebikes? This is your chance to determine what packs will be available. Thanks for your input.

a lot depends on the cell design. foil packs are smaller and lighter than the hard cased prizmatics, and botyh are smaller and lighter than the round can cells.

36V 10 Ah suits My needs 50% of the time, but that means a cell that can handle 4c discharge without trouble.

if your cell can, than having 10Ah batteries that can be parralleled or run in seires would be helpfull. stack them together to place them were you want.


I'm finding that long thin rectangles work better than square bricks for most ebike mounting solutions.

48V 20Ah is the biggest practicle battery i've seen on an ebike. bigger would be better for Motorbike conversions, and if the C rating can handle it, some of the high amp high speed setups.

Personally I now use a 36V/6Ah LiMn pack with a Bafang motor which comfortably offers good assistance to 20 miles and with conservation to over 32 miles when ridden at normal bicycling speeds however I doubt a small pack has much broad appeal. Because of this a good starting pack appears to be either a 36V/10Ah or 48V/10Ah size. The problem is so many of the packs in this range use 1C or 2C cells at best. What would make this size have much more appeal is to offer packs made with 3-4C cells for people who need the current but not necessarily long range.

The physical dimensions of the basic battery packs should allow them to fit in most rear trunk bags or say a maximum of 6" wide and 4" tall and 8-12" long. Once you go outside these maximum dimensions on a bike you have to think about splitting the pack for use in panniers.

The trend recently is to have the battery pack in a metal box which can slide on to a bracket mounted to the rear rack. While this is nice in theory it leaves less places to store items we all bring with us on rides and commutes. I think it would be better to offer something like the Topeak MTX rack/trunk bag system as an option with batteries of less than about 20 pounds. Over 20 pounds it would be awesome to have a split pack in a custom rigid pannier system which would look something like the setup Ezip uses for SLA batteries on its Trailz series ebikes however that is probably beyond what a reseller could make happen.

A bit off-topic but controller mounting is also a problem that should be addressed. Offering a custom HIGH rear rack with space underneath (shielded against water from the tire) would be great. Another option you might want to consider is to offer a handlebar (where I have mine), downtube or seattube mounting system for your controller.

FWIW

-R

+1 for DrunkSkunk's comments

* 10Ah at 36V is marginal for my needs; 15Ah good tradeoff of capacity and size; 20Ah can limit my mounting options
* more than 48V and 20Ah and you're more in motorcycle territory than e-bike
* I like three different form factors depending on my bike setup:
(a) Long, skinny rectangle -- this is good for mounting batteries within
the frame triangle, and for mounting directly on top of a rear rack.
However, in this form factor, the battery pack is exposed to the
elements and needs to be in a sturdy, water resistant case. An
integrated power switch and charge port is also desirable.
(b) 10-15 Ah rectangular block that fits in typical rear trunk bag dimensions
(c) 20Ah split into two halves -- each half fits in typical rear pannier, or can be stacked to fit in
a large trunk bag on top of rear carrier
* Some of your packs are rated at 30A continuous but have a BMS cutoff at the same 30A current. In order to avoid
tripping the BMS, one is probably limited to using a controller rated at a maximum of 25A. I would prefer that the
BMS be set at least a few amps higher than the continuous rating of the pack so the full continuous rating can be
utilized without tripping the BMS.

Joey

Thank you very much for your excellent comments. I will take them into consideration. BTW, the cells are polymer (foil bags). It's looking like 20AH is the max for one pack for size reasons, unless I can make one with the same size but higher AH. Paralleling packs is easy, we do that now. Anybody else?

-Terry

Joey said:

+1 for DrunkSkunk's comments
* more than 48V and 20Ah and you're more in motorcycle territory than e-bike
Joey

Click to expand...

I agree with Joey. As I´m just now building my first rig and haven´t decided on batteries yet I can give only a more general perspective (full disclosure: just bought motor kit from Terry). Keep in mind that the average ES poster is more of an enthusiast/tinkerer/engineer and possibly not representative of your average kit buyer (I am somewhere between).
A figure you often hear bantered about regarding EV transport is how the average US commuter commutes 29 miles a day for 55 min (avg 32 mph). This applies directly to my situation (22m roundtrip) and many others on the board, and I think that 20+ miles each way at up to 30mph are practical sane limits for most folks. More than that is a Sunday tour for fun- I don´t want to battle traffic and the wind for 2hrs a day just to get to/from work. That´s where the train or car come in.

I myself am going for a lighter rig to not feel too bogged down without assist and allow for cargo. Yesterday I met fifthmass and tried his rig (48v Clyte 408 with Clyte 40A controller 48v 20aH Ping lifepo4) which was VERY sweet but heavier than what I´m shooting for at ~90 lbs. He says his range is 60-70m with a tailwind and 40-50m with hills and front winds. What more could you need?
More than 20ah LiFEPO4 would be cumbersome on the rack, complicate cargo storage, and be above the average practical needs of a commuter.
My problem is figuring out if I will regret going for LESS than 20ah at a sacrifice of range for little weight difference. Since many outfits offer 10ah LiFEPO4 kits I would think these are workable for the avg user. The new 3C cells from Ping and others are giving an exciting range of choices now, so short bursts of power don´t require a heavy duty rig.
I´ll be sure to post my bat decision and first experiences. Till then i am open to suggestions :wink: .
Carl

I'm looking at a rear wheel drive kit, and I am trying to avoid a rear rack battery mount if at all possible. Rack mounts are great for front hubs, but with a rear hub, it shifts the weight too far to the rear.

I want to do this on a standard bike, so the triangle is about the only logical position. That limits the battery box to about 4 inches wide maximum, perhapse 5x7x3 inches. I'll probably get a 36V10Ah LiMn, but Li-poly would be a lot lighter.

I think it is very important that the battery box be secure and removable, which basically means it must have an integrated locking mechanism.

Since it is Li-poly and very light, I could probably live with a rack mount 36V10Ah, but it is not what I was hoping for. I would rather see a downtube waterbottle mount.

If money is no object, I'd probably get a 48V20Ah, if it weighs 10 lbs. or so, but I would rarely use that much energy. I'd probably be better off with a 48V10Ah.

for me, I'm more worried about the C-discharge rates....

if I get a 40Ah cell, I want it to be able to do 5C at the least. Will these do that?

Frodus, that would be 200 amps. Were you thinking of a motorcycle? You could draw 80-120 amps out of the 40AH cells. At 200A, you would be cutting into the lifetime. We are considering offering the 30AH and 40AH cells for use in motorcycles. It's possible they could replace SLAs in several bikes. The weight savings would be huge, plus free up some storage space.

It's looking like the 48V 20AH is the maximum practical size for an ebike. Even that is pushing it. A 36V 20AH or 48V 15AH is a better size for the rear rack. If you need more capacity, you can wire two 15AH or 20AH packs in parallel. This would double your current or your range. The two 10AH packs could go on the rear rack, anything bigger should go in panier bags.

There are three sizes that make sense to me for a "serious" ebike pack that could handle a 40 amp load

24V 20Ah
36V 20Ah
If you want 48V 20 Ah, throw two of the 24V together. There are those Currie folks out there that need a 24V pack so they can be covered and the 48V guys can use two in series. If you are requiring 48V and 40 amps of power, something tells me your bike won't be the lightest thing on the planet in the first place.

Another concept that would work very well is a 12.8V 20Ah LiFePO4 battery. It can be charged with an automotive charger, ganged together for 24/36/48/60/72V battery packs. This modular approach would work great for folks that use Chrystalite hub motors that run at 36 to 72 volts. For a starter pack, three "12V" packs to start and you can go up from there if you need more power without ditching what you started with. The battery can also be used for motorcycles, riding lawnmowers etc so the market would be larger. Just make a really stout 5C capable 12V battery with a BMS that won't freak if it sees a series connection.

Hi

I'm using 32 cell 96 volts 110 hot off the charger @ 40AH for my motorcycle builds and agree C rating is very important. I do 5C peaks for 10 seconds max and 2 to 3 C continuous. How do your cells compare to Thundersky cells in cost and specs?

Mark

I will check with the cell manufacturer regarding the 5C rating, specifically how that would affect the lifetime. I will do some calculating and come up with some projected prices for say a 48V 40A, 60V 40A, 72V 40A, and 96V 40A packs. I need to find a good high power BMS. If you have a recommendation for a supplier, perhaps one commonly used with theThundersky cells, let me know.

Best physical size is about 3" wide, less than 6" high and 10" long,... like the pack i custom ordered from Andy. They fit a rear pannier perfectly and a rear trunk also.

As for range, 10 amp/hr is the perfect cost, to weight, to distance balance, but 12 amp/hr is better . This is from owning three different ebikes in 8 years.

Interesting, perhaps a poll on this is in need. I was expecting to see a poll but where'd it go?