DIY Battery Calc
- Thread starter Manc44
- Start date
cells in battery packs are organised in an array, in your case, 13S4P.
Each string has 13 cells in series, 4 strings are paralleled together to form the pack.
So for each string, you have 13 x 3.7V =48.1V, 3000mAH.
For the pack, you have 48.1V, 4x3000mAH = 12AH.
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4 cells in parallel (aka a string or group) is the capacity 4 x 3000 is 12000mah/12ah.
The max capacity one can get with 4 x 18650 cells is 13600/14000mah.
Each parallel string of cells in series connection make up the pack voltage required.
Each parallel string can only be the voltage of the max charge rate of one cell, so each string voltage added is accumulative.
In parallel only the capacity/mah rating and the current rating is accumulative, in series only the voltage is accumulative.
The max capacity one can get with 4 x 18650 cells is 13600/14000mah.
Each parallel string of cells in series connection make up the pack voltage required.
Each parallel string can only be the voltage of the max charge rate of one cell, so each string voltage added is accumulative.
In parallel only the capacity/mah rating and the current rating is accumulative, in series only the voltage is accumulative.
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Cheers Woosh & Nealh.
Calc fixed
www.dropbox.com
Woosh, do you not sell battery packs on their own?
I am thinking about something like a shrink wrapped 21700 based pack @ 48V/25Ah.
I know someone on eBay sells exactly that thing... but you're Woosh, he's not
Something like Samsung 21700 (50E) with a claimed 4900 mAh per cell, about £6 per cell at nkon.
Such a pack would only measure 28cm x 11cm x 7.5cm which is a big reduction in volume compared to the usual Hailong with 18650 cells.
It doesn't help that they are called all different things: "shrink wrapped", "PVC", "soft pack" etc.
I was looking at what goes into building them and sort of lost interest when it got to the BMS part lol, I'd just mess up somewhere and short it.
There's "Jimmy" with the high quality copper strip packs but those are out of my price range.
Calc fixed
Dropbox - File Deleted - Simplify your life
www.dropbox.com
Woosh, do you not sell battery packs on their own?
I am thinking about something like a shrink wrapped 21700 based pack @ 48V/25Ah.
I know someone on eBay sells exactly that thing... but you're Woosh, he's not
Something like Samsung 21700 (50E) with a claimed 4900 mAh per cell, about £6 per cell at nkon.
Such a pack would only measure 28cm x 11cm x 7.5cm which is a big reduction in volume compared to the usual Hailong with 18650 cells.
It doesn't help that they are called all different things: "shrink wrapped", "PVC", "soft pack" etc.
I was looking at what goes into building them and sort of lost interest when it got to the BMS part lol, I'd just mess up somewhere and short it.
There's "Jimmy" with the high quality copper strip packs but those are out of my price range.
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Not at the moment unless it's for fixing our bikes or kits.
There is a worldwide shortage of Samsung and Panasonic cells which we use for our batteries.
I have terrible problems with sourcing batteries for the last 6 months.
One can do a lot of damage before the BMS stage if t]parallel/series connections errors are made.
A 25ah pack will be quite heavy at about 6 - 6.5kg.
A 25ah pack will be quite heavy at about 6 - 6.5kg.
Updated the calc... added cost per cell and weight per cell to calculate totals for both. It's setup based on Samsung 21700 (50E) cells.
Let me know if anything's wrong with it and I'll remove the link.
It could have BMS, nickel strips and case weight added, but then it's becoming a bit much lol
EDIT: Urgh I forgot to add Wh to it!
Let me know if anything's wrong with it and I'll remove the link.
It could have BMS, nickel strips and case weight added, but then it's becoming a bit much lol
EDIT: Urgh I forgot to add Wh to it!
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you need to factor in about 15%-20% additional weight for the case, connecting strips, BMS, wires and insulation.
Just in case you didn't realise it, amp-hours don't have a constant value. An amp hour when the battery is flat is only worth 75% of one when the battery is full. The 3.7v is only thenominal cell voltage. They're 4.2v when full and 3.1v when empty, so at a constant current, power is only 75% when empty.
If the Dropbox link won't work, here's the calc on Sendspace: