Quote:
Originally Posted by redpoint5
The Ego document says they are still using phase change material around the cells. They also design the pack with more surface area rather than packing the cells into the tightest block they can.
Don't really know how that plays out in longevity.
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2.5ah battery next to a 7.5ah, both from Ego packs:
You can see the convex shape to the cells 2.5ah; same cells inside, just with a layer of something (presumably thermally conductive) over it inside a second layer of heat shrink. The 5ah versions look the same as the 7.5ah.
My thinking was they decided that it wasn't necessary to add the extra material with the larger packs, seeing as they have more cells in parallel, therefore there is less current per cell, less heat each cell has to shed. And the inverse is true, meaning if any of them need the extra heat dissipation/large thermal mass, it's the smallest version...in case you decide to stick you 2.5ah pack in to your mower that came with 7.5ah.
Of course, they might have gone the same way with all of them, 2.5ah included, once they realized they could withstand the heat build up; the 2.5ah is probably a year or two older than the 7.5ah. I won't know without getting my hands on a newer 2.5ah. Or even a newer 5 or 7.5ah, to see if they're doing it to those now.
The 5 & 7.5 had "ARC" as part of their pack's name, and, indeed, were arc shaped. The 2.5's still had the same kind of shape, but with fewer cells it was certainly less pronounced. I assume the whole point of that is to give it more surface area, a thinner pack so that the cells are closer to the surface....rather than stacked like cordwood.
And while we're on the topic of cordwood, they are more generously spaced than most. ~20mm on center, so there's a good 2mm between them, except for the "phase change material" ones, where they actually come in contact with eachother -- both styles have the same spacing. That's pretty generous; most power tool batteries are made as compact as possible, where there might only be half a milimeter between each cell. Worse, some have rubber shaped to the cells between layers, meaning good luck with the air flow.
You'll find these same Samsung 2.5ah, 25-amp continuous cells in most brand-name power tools that have multiple of 2.5ah in their capacity rating. You'll find them in Dewalt, Ryobi, Milwaukee, Ridgid, and even Toro's 60v line...the Toro ones are amusing, as there's like 5mm between each cell. Probably to make the 2.5ah pack look bigger, as that's stupidly generous for cooling purposes.
Anywho, YMMV. Maybe the 5 and 7.5ah ones are only like that in Canada. Maybe the originals were straight imports from the US, and the later ones were made specifically for our market. Either way, they make a nice battery pack. 14s, 1, 2 or 3p. (they usually use 13s for 48v battery packs, having one more gives a nice bit of extra power/range to an e-bike without changing anything else)