Battery question

the 40A discharge will be likely because of the BMS they are using… if im not mistaken, the early SPACE cell that enertion sold had a 40A fuse on it as well.

I hate to burst your bubble - but if this pack works it will not work well.

As @Tuomalar has mentioned it will sag horribly and affect performance and range (and battery longevity).

Cells are rated with constant and peak (some specify max 10s discharge in amps): the most frequent are the 25R, 30Q, and other similar 20A continuous cells (some are now higher). Typically you can get higher capacity 3000mAh+ from cells with less continuous amps capability, or lower capacity 2500mAh and less that can sometimes output more than 20A.

The cells you linked on Alibaba are only 10A max discharge (peak to 20A for 10s):

You don’t want to use 100% of the discharge capacity or it will sag. They sag and heat - heat is bad for long life, and you’ll get significant performance and range decrease.

Here’s a great example of some great cells at their full 20A discharge: Especially note that right from fully charged they sag to 3.65/3.8 depending on cell! I have my voltage cuttoff warning set to 3.7 (and it’ll beep going up a hill as it sags under load - then not beep until i accelerate hard or another hill) (on lipos, but still applies).

Li-ion vs Lipo… I usually go Lipo because they have a higher discharge rating - especially when you get into the 30C+ batteries (5000mAh = 150A discharge capacity w/ peak to usually 40-45C), and i have some 65C lipos as well (smaller 3s 4500mAh A-Spec nanotech for 9/12s in series). at 65C *4.5Ah = 292A discharge! So when you only use 40-60A of almost 300A… no/minimal sag! better range and better performance.

I would not trust alibaba or aliexpress to sell legit cells, or to have honest ratings. I always figure even the lipo C ratings are more marketing than fact - but with so much more discharge capacity - more room for leeway IMO.

I charge and inspect my lipos, so i’m not as worried about them catching fire. Look for damage/puffed cells - and use a temp probe when charging - any bad batteries will have a heat issue before catastrophic failure. And charge in pyrex (cheap from goodwill/used).

my .02 - hope it helps.

I see 4 options:

  1. Make a battery out of 18650 cells. 10s4p / 12s3p. Samsung 25r, 30Q. Buy from https://eu.nkon.nl/samsung-inr-18650-30q-3000mah.html. Solder or tab weld, a few tutorials on the forums.

  2. Have someone build you an 18650 pack, there are a few builders on the forums. Maybe @chaka or @longhairedboy can make you one.

  3. Buy an 18650 pack that you know contain high quality cells (Samsung 25R/30Q etc) from @torqueboards at diyelectricskateboard or alien power systems

  4. Buy some lipo packs from Hobby King.

Edit: Highly recommend staying away from chinese no-name 18650 cells. They are not all created equal, and most 18650 cells will give poor performance, there are only a few good ones out there that have enough discharge ability to work on our skateboards.

Gare you trying to it all at once or just get going because doing an 18650 pack spot welded with a bms and switch is a lot. easier is just get some lipos from hobby king and a 10 dollar balance discharger and be done. the hobby king flightmax 2 or 3 cell packs will out do almost any li-ion pack’s power output so you won’t have to worry about that and you can just plug them in and same with the balance discharger. But I want a nice li-ion pack n button badly. Just has so many drawbacks. Not cheap

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Depending how big that bms is. You can try to remove it and set it next to battery if you deck is long enough to make it fit. But for example i dont’t have that much space so i ordered smaller one. I recommed to leave that bms and order better one for example from batterysupports.

http://www.etotheipiplusone.net/?p=4187

here’s the harbor freight chainsaw teardown i was talking about above with the large battery with no bms running by “the power of robot baby jesus” alone

I have another battery question. In this video he hooks up six of these HRB 7.4V 10000mAh 2S LiPo Battery 25C.

Why didn’t he route the balance cable harness through the deck for an external charger? When you charge these cells you need the balance cable connected to the BMS right?