batteries

esuark

Finding my (electric) wheels
Jul 23, 2019
19
4
kent
can anyone enlighten me about 48v batteries that I see advertised as 5-parallels 13-series cell quantity 65 with different AH`s with Samsung 35E cells? and in general how the AH rating is calculated. just confused. o_O
 

sjpt

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Jun 8, 2018
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AH should be the Ah rating of each cell, times the number of parallels (5). Those cells claim 3500mAh, so you should get Ah 3.5*5 =17.4Ah.

voltage is cell voltage * #series, eg 3.6v*13=46.8v
current rating is cell current rating & #parallel. max is 8amp*5=40amp, I can't see the continuous rating for that cell.
 
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vfr400

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Jun 12, 2011
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All cells have the same voltage and run from 3.1v to 4.2v (average 3.6v), so to get a 48v battery, you put 13 in series, 10 for a 36v one. Each cell type has different other characteristics -mainly the amount of charge in them, expressed in Ah or Wh, and the rate at which they can give it, expressed as the continuous current.

When you buy a battery, it needs to be able to deliver the current that your controller allows continuously, with a bit of headroom, so if you have a 15A controller, you need a 20A continuous battery.

You need enough charge in the battery to do your rides. For a legal ebike, an average figure would be about 12 to 15wh/mile, so if you always want to ride 30 miles, you'd need over 450wh.

Watt-hours (wh)is a more accurate way of expressing battery capacity than amp-hours (Ah). A 10ah 48v battery is 10 x 48 = 480wh.

The cells normally have a designation that relates to capacity, like 18650 22P, where 22 means 2.2Ah. The P is the variant relating to other characteristics, like life and discharge rate. SAMSUNG 35E means 3.5ah (actually 3.45) and is capable of delivering 8A continuously, so 13S5p would be 13 x 3.6 = 48v (approx), 5 x 3.45 = 17Ah and 5 x 8 = 40A.

That's what the cell-pack can deliver, but the management board (BMS) has its own current limit. Only the battery supplier knows what that is. They normally write it in the listing. I'd fit a 30A or 35A BMS to a cell-pack like that.

Batteries degrade with use, so whatever characteristics you need, always try for 20% extra from the cell-pack to avoid problems in the future. The BMS won't degrade, so it will always allow the same current, but if you had a 20A cell-pack, a 20A BMS and a 20A controller, you'd start getting your first cut-outs pretty soon.
 
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Nealh

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Aug 7, 2014
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Parallel are the batteries connected to each other to form a string or group of cells, the amount of cells in parallel can be as many as you like.
Series is the amount of Parallel strings/groups also connected to gain the required voltage.
Each parallel string/group has a nominal voltage of 3.6/3.7v & max voltage which is 4.2v no matter how many cells in parallel. The voltage is always the same the capacity/mah & current isn't.
The mah & current are multiplied by however many cells there are.

For voltage one cobbles as many strings/groups together in + - + - + - + - +, ratio etc,etc as one likes.
So for 12v one has 3 groups in series.
24v = 6 groups in series.
36v = 10 groups .
44v = 12 groups.
48v = 13 groups.
52v = 14 groups.
60v = 16 groups.
and one can keep connecting more for more voltage.
 

esuark

Finding my (electric) wheels
Jul 23, 2019
19
4
kent
Parallel are the batteries connected to each other to form a string or group of cells, the amount of cells in parallel can be as many as you like.
Series is the amount of Parallel strings/groups also connected to gain the required voltage.
Each parallel string/group has a nominal voltage of 3.6/3.7v & max voltage which is 4.2v no matter how many cells in parallel. The voltage is always the same the capacity/mah & current isn't.
The mah & current are multiplied by however many cells there are.

For voltage one cobbles as many strings/groups together in + - + - + - + - +, ratio etc,etc as one likes.
So for 12v one has 3 groups in series.
24v = 6 groups in series.
36v = 10 groups .
44v = 12 groups.
48v = 13 groups.
52v = 14 groups.
60v = 16 groups.
and one can keep connecting more for more voltage.
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
9,822
3,922
Basildon
For voltage one cobbles as many strings/groups together in + - + - + - + - +, ratio etc,etc as one likes.
So for 12v one has 3 groups in series.
24v = 6 groups in series.
Slight correction: 24v is 7 cells. Probably just a typo, otherwise you should have had another cup of coffeee to clear your head before starting your work.
 
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Nealh

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Aug 7, 2014
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Yes quite right 24v is 7s.
 
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