Battery Pack Dimensions

[Clyde]

So I'm looking at a handful of (to me, anyway) very exciting and creative ideas for mounting batteries to an ebike, and one of the first things that strikes me is the weird variance in the dimensions of some 18650 cell lithium battery packs.

For example, (using DHGate not because I'd ever buy anything from there, but because lots of good examples):

Here's a 52v15ah triangle battery with dimensions 240x200x150x70x45x70mm(+/-5mm) : https://www.dhgate.com/product/51-8v-52v-15ah-triangle-electric-bike-battery/468430598.html

Here's another 52v15ah battery that's 310x140x200x160x58x70mm : https://www.dhgate.com/product/triangle-style-1500w-52v-15ah-lifepo4-battery/512104976.html?

This one's 265x250x180x75x70x45mm(+/- 5mm): https://www.dhgate.com/product/52v-750w-triangle-battery-51-8v-15ah-14s/483675115.html?

So.... what the... heck? 18650 is short for '18mmx65mm', yeah? And sure, there's hot glue and crap of varying thicknesses, but that doesn't explain the wide variance. Are they just different but similar shaped arrangements? Are the larger batteries using an extra set of 14 to reach capacity using lower power cells? If it purports to be built with quality Japanese cells can I ignore the fact that it's larger or smaller than other packs of the same capacity?

Appreciate any illumination you can shed.

TIA

 

[Clyde]

I found the answer to part of my question: 70 cells in the smaller pack vs 98 in the larger one. Still groping about in the darkness, though. How are they the same amp hours? Or are they?

 

[harryS]

Battery one is a 14S5P pack. It uses five 2.9AH cells on parallel. You get the AH for a pack by multiplying the parallell count (5) by the cell AH (2.9). In this case, you get 14.5 AH. and 14S x 5P is a 14x5 array of 70 cells.

Battery two uses LiFeP04 cells, which are 3.2V nominal, as opposed to the 3.6V nominal LiPo cans, You need 16 series groups to get 52V. LiFePO4 is less likely to go up in flames, because it has less energy density but it will be far heavier than a pack made out of more standard lithium cells because it needs more cells. If you picked the 16S-6P, so that's how you get 98 cells. I see they also have a 17S model.

Battery three is a real loser. It uses 2.2AH cells. Now that you know the formula for pack AH, you know that 15AH would need seven of those 2.2AH cells in parallel. And with 14 series groups, that is 14S-7P or 91 cells.

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[Clyde]

Thank you! I'm starting to like this place. May move in...

 

[Clyde]

Does that first pack seem okay? It's correctly sized for my application, and takes the Panasonic NCR18650PF 2900 mAh, 3.7v 3C cell.

Another option is very close in size, but uses Samsung cells at 2600 mAh.

Or am I barking up the wrong tree entirely trying to use a triangle battery pack that's that compact (Roughly 9x7)?

TIA

 

[Decrepidude]

So I'm looking at a handful of (to me, anyway) very exciting and creative ideas for mounting batteries to an ebike, and one of the first things that strikes me is the weird variance in the dimensions of some 18650 cell lithium battery packs.

For example, (using DHGate not because I'd ever buy anything from there, but because lots of good examples):

Here's a 52v15ah triangle battery with dimensions 240x200x150x70x45x70mm(+/-5mm) : https://www.dhgate.com/product/51-8v-52v-15ah-triangle-electric-bike-battery/468430598.html

Here's another 52v15ah battery that's 310x140x200x160x58x70mm : https://www.dhgate.com/product/triangle-style-1500w-52v-15ah-lifepo4-battery/512104976.html?

This one's 265x250x180x75x70x45mm(+/- 5mm): https://www.dhgate.com/product/52v-750w-triangle-battery-51-8v-15ah-14s/483675115.html?

So.... what the... heck? 18650 is short for '18mmx65mm', yeah? And sure, there's hot glue and crap of varying thicknesses, but that doesn't explain the wide variance. Are they just different but similar shaped arrangements? Are the larger batteries using an extra set of 14 to reach capacity using lower power cells? If it purports to be built with quality Japanese cells can I ignore the fact that it's larger or smaller than other packs of the same capacity?

Appreciate any illumination you can shed.

TIA

For one thing, your middle example is using lithium phosphate cells, which have lower nominal voltage for the 18650 size format, so would require more batteries to achieve the desired voltage, and the third example is only 14ah. which would use fewer cells to achieve that spec.

 

[tomjasz]

WOW!!!! My Q100 was shipped by DHL and was here ten days after ordering. DH gate shipping is worse than typical Aliexpress slowpokes!
"United States Via DHL
Estimated delivery time: Apr. 17 and Apr. 20, ships out within 35 business days"