Novice batt builder question

D

detrailers

10 W
Joined
Jan 24, 2019
Messages
69
Ok so im about 3/4 thru Micahs book and know a lot more than I did before but still questions. Im at the point where I am starting to lay out my pack. I plan on using the 18650 cells rated at 3.5ah. I have a 60v Hyper Racing scooter that has a battery labeled at 13ah, battery range is 48-67.7v. Stock battery is rated for 35a continuous....I don't have it near but the batt is roughly 12 x 6 x 4.
When im doing my layout on paper it seems like the config of 16 cells in series and 20 in parallel is way smaller than the current pack and would still give me 70ah. What am I missing here, do the 18650s not give me the discharge rate I need? Just seems too good to be true and why is the stock batt so much bigger but so much less AH?
Stock batt label attached
 
How big is your battery compartment ? How about other type of cells with less connections. 18650 means 700 conections https://endless-sphere.com/forums/viewtopic.php?f=14&t=89680
 
I have 12x10x4 avail space and what do you mean by 700 connections?

I was doing the 18650 because of their availability and ill be using Vruzend or similar connections because I don't have a spot welder....yet
 
320 cells is 640 connections plus. The vruzend I think was having trouble with its connections. I would do more reading of there problems with a snap together pack. There are good diy spot welders . https://endless-sphere.com/forums/viewtopic.php?f=14&t=89039#p1298272
 
So both if us are having the problem getting our batteries from the same eBay builder☹️

And both of us have decided to build our own packs. I received my 4X5 mounts today. I’m running 16s12P and from my estimation, this pack will be slightly smaller than 12” X 16”. So if you are running 12S20P, your long dimension might be closer to 18 or 19”.

You might want to check your dimensions again 😲
 
999zip999 said:
320 cells is 640 connections plus. The vruzend I think was having trouble with its connections. I would do more reading of there problems with a snap together pack. There are good diy spot welders . https://endless-sphere.com/forums/viewtopic.php?f=14&t=89039#p1298272
Click to expand...
320 cells? Im using 36 18650 cells
 
ronncat said:
So both if us are having the problem getting our batteries from the same eBay builder☹️

And both of us have decided to build our own packs. I received my 4X5 mounts today. I’m running 16s12P and from my estimation, this pack will be slightly smaller than 12” X 16”. So if you are running 12S20P, your long dimension might be closer to 18 or 19”.

You might want to check your dimensions again 😲
Click to expand...
Im doing 16s20p and using the battery layout diagram in the book it looks small...maybe im not factoring the added dims from the Vruzend blocks?
 
This is the 36 cells colored in - I know they are going to be 65mm high but the footprint seems really small (i know I need one more negative in my series connections)
 
999zip999 said:
16s × 20p = 320 cells ? One neg one pos. Connection.
Click to expand...
Im lost, 16 cells in series, 20 in parallel, 36 cells total, 2 connections on each cell, 72 connections, what am I missing
 
I must be way outta whack here guys. Im under the impression I take (16) 18650 cells and wire them in series to get 67 max volts, then connect them to (20) 18650 cells in parallel to get 70ah based on 3.5 ah cells
 
999zip999 said:
String one of 20 parallel cells string two 20p string. Three 20p times 16 strings of 20.
Grasshopper.
Click to expand...
Ok im sorry but I don't understand your responses and they don't match what I'm reading it the book, what I'm seeing is the connections between the cells and similar packs they are showing have no where near those connections. thank you for trying to help though, I apprieciate it
 
OK, I'll try...

If you take 20 batteries, each with 3500 mAh and wire them in PARALLEL, you essentially get the equivalent of 1 giant battery with a capacity of 20 X 3500 mAh = 70000 mAh or 70 Ah. But it is still only 3.7 volts!!

You would need an additional 15 of these same giant batteries wired in SERIES to achieve your 60 volts.

So 16 Giant batteries, each composed of 20 individual cells gives you a pack of 60 volts AND 70Ah... therefore, this equates to 16 X 20 or 320 cells total ... 16S20P
 
Yes, just like with 6V GC batts, pairs in series makes 12V, need 8 to get to 48V.

Each of those is **one string**, same Ah capacity as the component single cell, say 200Ah.

Now to increase Ah capacity say you want 800Ah, you need 4x those strings.

So 2S4P means 8 total 6V units at 12V, or

8S4P is 32 of them for 48V.

 
999zip999 said:
70ah is a huge bike battery.. Somebody chime in.
Click to expand...

16S20P is what people use for 35mph scooters with 4kW motors.
it will weigh ~20kg at least.

put that on a bike and you need a dual 2kW motor setup with 300A+ controllers. i expect a quarter mile in under 15 seconds with a bike like that. :mrgreen:
 
My scooter does do 35mph now, just want note range range...I ynderstand 70ah it out of the questions, just trying to figure out how much ah I can get into 12x10x4 and am totally lost on the connections issue
 
ronncat said:
OK, I'll try...

If you take 20 batteries, each with 3500 mAh and wire them in PARALLEL, you essentially get the equivalent of 1 giant battery with a capacity of 20 X 3500 mAh = 70000 mAh or 70 Ah. But it is still only 3.7 volts!!

You would need an additional 15 of these same giant batteries wired in SERIES to achieve your 60 volts.

So 16 Giant batteries, each composed of 20 individual cells gives you a pack of 60 volts AND 70Ah... therefore, this equates to 16 X 20 or 320 cells total ... 16S20P
Click to expand...

Thank you ron, since you explained it for me better, I get it. So if I have 12x10x4 to work with, need 48-67 volts, and want at least 30 ah is that possible with 18650 cells
 
Thanks everyone for your help, I got it now.. .so basically based on my space, it looks like I can do 16s8p And get 28ah in the space I have to work with. In looking back now at what I was thinking and feel like a dumbass sorry ..
And yes, I think the Vruzend are out and going to get a spot welder
 
ronncat said:
So both if us are having the problem getting our batteries from the same eBay builder☹️

And both of us have decided to build our own packs. I received my 4X5 mounts today. I’m running 16s12P and from my estimation, this pack will be slightly smaller than 12” X 16”. So if you are running 12S20P, your long dimension might be closer to 18 or 19”.

You might want to check your dimensions again 😲
Click to expand...
What cells are you using and where are you getting them from because now that I am no longer an airhead thanks to the peeps on this forum I realize I need 140 cells and the batt is - ahem - a bit more expensive that the 36 cells I figured before lol
 
Would it be better to build the eight 16s packs and connect them in par or build sixteen 8p packs and wire them in series. Prob a lame question just trying to get my head around all of this and coffee hasnt kicked in yet
 
My preference is parallel first at the lowest level.

They self-balance at rest there at the per-cell level.

Once you have strings (serialized, higher voltage) I would not parallel more than 3-4 of those, balancing becomes more of an issue long term.

But you should periodically check per-cell health in any case.

Not an EV guy myself, so there may be other considerations, just my 2¢
 
detrailers said:
ronncat said:
So both if us are having the problem getting our batteries from the same eBay builder☹️

And both of us have decided to build our own packs. I received my 4X5 mounts today. I’m running 16s12P and from my estimation, this pack will be slightly smaller than 12” X 16”. So if you are running 12S20P, your long dimension might be closer to 18 or 19”.

You might want to check your dimensions again 😲
Click to expand...
What cells are you using and where are you getting them from because now that I am no longer an airhead thanks to the peeps on this forum I realize I need 140 cells and the batt is - ahem - a bit more expensive that the 36 cells I figured before lol
Click to expand...

Glad you got it. Don't know where you are located, but I purchased 200 Panasonic NCR 1865PF from a seller in the New For sale section. These are 2900 mAh, so a bit less than you are looking for. The seller has a large variety of new cells and new with welds removed. Great pricing as far as I'm concerned and the shipping was only $43 to California all the way from the EU. I understand it may take quite a while to get here though. Seller has a very good reputation from the 30 pages in his thread that I scanned. I am going to build the pack as 16S12P, so 192 of my 200 cells will be used. I actually measured the cell layout using the standard plastic "inline" cell mounts and my battery should come in at a bit less than 13 X 10 inches sans BMS. I also measured a how many cells you could fit using these same cell mounts and it came out to 15 cells by 7 cells. So you could fit 105 cells in your available space. Probably more if you hot glue them in a staggered orientation.

Anyhow using 3500 mAh cells that gives you the possiblility of going 16s6P (using 96 cells) for 60 volts and 21Ah. If you could somehow shoehorn in 7 more cells for a total of 112 (maybe the staggered configuration???) Then you get 16S7P good for 60 volts and 24.5mAH.

Good luck with your build. My spotwelder came in just 2 days!!! A K-Weld...
 
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