Bigfillly said:
The motor is Indeed a motenergy, its capable of:-
2000-4000w
You might have to add external cooling to it so it doesn't overheat, especially if you're running it at higher speeds a lot, and/or doing a lot of repeated accelerations. I think another member is using the more efficient (less waste heat) brushless version of this motor on his kart here on ES, and still working out sufficient cooling for it.
The wattage on that motor is actually a lot higher than that, according to their page here:
http://www.motenergy.com/me0909.html
Capable of 4.8 KW continuous and 12 KW for 30 seconds.
though a google search shows that different sellers make up their own numbers for it rather than using the actual manufacturer specs.
(something you should keep in mind when looking up specs for parts you're going to use--sellers can lie and/or have no idea what they're talking about, so go to the manufacturer for specs).
Looks like the controller is easily capable of burning up the motor if you don't either be careful with the throttle or program in a lower motor current limit to match the motor you have.
The laptop batteries are 18650's and various makes,
You should note down which kinds you have, and find their spec sheets, then make a list of their important characteristics (capacity, C-rate (continuous amps), nominal voltage, internal resistance) so you can set aside all the types that don't meet your needs.
You'll need to know their factory specs anyway in order to do the testing, because you have to know if the cell still comes close to those specs--if it doesn't, you probably dont' want it in your pack.
If you just use all the random cells you have that test ok (compared to an arbitrary limit, rather than factory spec) for capacity/etc, you'll wind up having to build a bigger, heavier pack than necessary, which will affect acceleration (more mass is bad for quick acceleration, and also bad for good braking).
Let's assume you've got just one type of cell (to save time/confusion in discussion), and that they are 2Ah capacity, and a 1C/2C cell (2A continuous / 4A burst), 3.7v nominal voltage. And assume that all the cells you actually use still meet their factory specs.
13s x 3.7v is a common 48v pack voltage, so that's ok.
8p x 2Ah means 16Ah pack capacity.
8p x 2A means 16A pack current capability continuous.
8p x 4A means 32A pack current capability burst.
Let's assume you'd need a continous battery current (different from motor current, usually higher) of 100A to meet your speed needs.
100A / 16A (per pack capability) = 7 packs (have to round up
) in parallel.
If you need no more than 200A peak battery current, then that also meets the peak demand, but you might need more than that. You'll know best once you actually test the kart on the track, with a wattmeter between the battery and the controller (if you don't have one, you'll want one by that stage, if not before).
Keep in mind that these would be *minimum* requirements, and if you can get more parallel packs than that it'd decrease the load on each cell, making them last longer and they'd have less voltage sag, so you get more watts out of the pack, and so higher performance out of the system.
Now, for endurance, or Ah, you have to figure out how many watts are continously used. Until you determine that, let's just go with 4000W figure, since it's near the max the motor can do anyway.
4000W for an hour is 4000wh, (4kwh). if you need 3 hours of runtime, that's 12kwh.
At an average of 48v, 12kwh (12000 / 48) is 250Ah.
If each pack is 16Ah, then 250 / 16 = 16 packs.
If each pack is made of 13 * 8 cells, then 16 of those is 1664 cells total you'd need.
That's all assuming 2Ah 1C cells, and 4kW continuous power usage, none of which might be the case.
If the cells you're using are better than that, you'll need less cells.
If they're worse, you'll need more.
If the power usage is less, you'll need less cells.
If it's more, you'll need more (and a bigger motor, or two of the ones you have).
I'm using the 4x5 plastic cell holders to make the packs,
I'm not sure what holders you mean, as there are a lot of kinds. Pictures or links would be useful.
If you mean the spring-loaded ones like the type that hold AA or AAA cells (but for 18650), those may just melt (or at least deform) from the high-resistance connections they make, and you won't get the performance you need from the pack. There's other types of solderless/weldless holders out there but I don't know how well any of them perform at high currents. There's discussion about them in various no-weld pack threads around ES.
I'd recommend spotwelding the pack for best performance. There's other alternatives, but it's possible to damage the cells with some of them (like soldering) if you're not careful and work out your technique on dud cells beforehand. Lots of discussion on those in the various 18650 threads, some of which are in the lists below.
https://endless-sphere.com/forums/search.php?keywords=18650&terms=all&author=&sc=1&sf=titleonly&sk=t&sd=d&sr=topics&st=0&ch=300&t=0&submit=Search
https://endless-sphere.com/forums/search.php?keywords=spot+weld*&terms=all&author=&sc=1&sf=titleonly&sk=t&sd=d&sr=topics&st=0&ch=300&t=0&submit=Search