Thursday, August 6, 2015

Choosing the Motor and Battery for controller design

For designing the controller, we need the motor rating and battery voltage.

Requirements :
Speed : 40-50 mph.
Battery undervoltage Protection :
Current Limiting :
Method : PWM (Pulse Width Modulation)
Assumption : 30-35 Wh per Mile.
Motor : 48V 2000W
torque :  (still dont know how much i need, have to study)

For calculating rpm  (still have to analyse):
https://endless-sphere.com/forums/viewtopic.php?f=28&t=16114
http://www.algebra.com/algebra/homework/Rational-functions/Rational-functions.faq.question.501480.html


Motor rating : 48V 2000W , Sensored
From videos seen in youtube, 2000W or 3000W BLDC motors are doing good speed, but as this is my first project so i choosed 2000W, as our area have big slops/terrain.


Choosing Battery :
There are 2 choices in battery 'Li-ion cells' and  'Li-ion Polymer',
but Li-ion Polymer have lot of advantage over Li-ion batteries, like less weight, quick charge, high discharge current comparing to Li-ion cells battery,but in price point of view Li-ion cells are cheaper.

Li-ion cells :
Li-ion batteries are available in big block shape (we're using that in home UPS system) and Li-ion Cells
Tesla cars even use Li-ion cells.

Li-ion Polymer (LiPo) :
Lithium ion Polymer (LiPo) batteries are used for Ebikes mostly due to it's high peak current, Li-ion batteries are specified in 'C' and 'S' Value,

C means, Continuous, 
if battery show 40C means, we can grab maximum 40 A continuously.

S means, Series,
If battery shows 3S means, 3 cells are connected in series, that is 3.7 V  x 3 cell = 11.1 v .
 Li-ion Polymer battery is created by series joint of cells, each cell voltage is 3.7v

mAh  means, milli Ampere hour,
If battery shows, 4000 mAh means, its capacity is 4000 mAh or it can store 4000 mAh. 


Example :
Battery Specififcation :16 Ah 22.2V

For more detailed thing about battery (highly useful) :
 http://www.rchelicopterfun.com/rc-lipo-batteries.html
http://www.rchelicopterfun.com/rc-battery-chargers.html
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=6589&aff=143580

Battery Fuse :
http://infectedarmory.com/product/self-resetting-fuses/


Budget wise :
High budget (use LiPo), Low budget (use Li-ion cells)

 

Range Calculator :
Range is one of the important factor to consider in creating an ebike, if we use ebike for home to office, then back to home. we have to calculate the per day usage kilometer or Miles, and adding extra Kilometer, so we may use it for other works too.

Eg :
Home to Office distance = 10 Miles (16 Km) , to and fro distance is 20 Miles,  so we have to create ebike range greater than 20 Miles, say 25 or 30 miles will be better .



Range =  Number of batteries  x Capacity of single battery (in Ah) x Voltage of single battery (in V)
                 ___________________________________________________________________
                                                          Per Miles Watt usage



Per Miles Watt usage vary depends on speed, so we have to assume it as 35-50 Watt per Miles


Eg :
So assume Per watt Miles as 40 watt
i have 5 batteries of 26000 mAh , 22.2V ,
convert 26000 mAh to Ah, just divide by 1000, so 26 Ah.

Range  =  5 x 26 x 22.2    
              _____________
                        40

          =  72.15 miles

according to your need, you can increase or decrease the number of batteries.


Weight :
For Low weight (use LiPo), weight is not a matter (use Li-ion cells)

Example
 if we're going to use in bicycle/motorbike/car means, little extra weight is not going to affect a performance, so Li-ion cells is enough, still LiPo give less weight.

 but if you're going to use in helicopter/mini aeroplane/Drone, then weight matters, so LiPo is the only choice.


Example :
For Li-ion Polymer , 16000 mAh 6S1P 22.2V - Weight : 1932 gram.
 
think i am using 3 batteries,
3 battery total capacity in watt = 3  x 16 x 22.2 = 1065.6 W = 1.065 kilowatt

3 battery weight in gram = 3 x 1932 gram =  5796 gram = 5.796 kilogram.

 so  5.796 kg battery store 1.065 kw,

1 kg of LiPo batteries store    = 1.065/5.796   =  0.1834 kw
1 kw of Lipo batteries weight  = 5.796/1.065  =  5.442    kg


Now same calculation for Li-ion cells.
For Samsung ICR18650-26F cells , 2600 mAh, 3.7V - Weight : 48 gram.


think i am using 110 cells,
110 cells total capacity in watt = 110 x 2.6 x 3.7 = 1058.2 W
110 cells weight in gram = 110 x 48 = 5280 gram

so 5.280 kg of  cells store 1.0582  kw

1 kg of Li-ion cells store  = 1.0582/5.280   =  0.20 kw
1 kw of Li-ion cells store =  5.280/1.0582 = 4.989 kg


but thing is packing  of 110 cells need a special battery pack, have to weld, and connecting wires, charging of this 110 cell, these constraints increase the overall weight of the battery pack, resulting in LiPo the winner in weight range.


What i choosed :
16000 mAh 6S1P 22.2V
http://www.genstattu.com/ta-15-16000-6s1p.html



Range  =  1 x 16 x 22.2    
              _____________
                        40

          =  8.88 miles
 as i use very less, so choosed only single battery.


===========





Number of cells/power needed :


Li-ion cells  18650  2600 mAh 3.7V : 
Theoritical calcualtion :
10s 10p = 26.0A 37.0v,  0962.00W, 4800 gram, 100 cells.
11s 11p = 28.6A  40.7v, 1164.02W,  5808 gram, 121 cells
12s 12p = 31.2A 44.4V, 1385.28W, 6912 gram, 144 cells
 Practical values :



Li-ion cells 18650 6000 mAh, 3.7V :

10s 10p = 26.0A 37.0v,  0962.00W, 4800 gram, 100 cells.
11s 11p = 28.6A  40.7v, 1164.02W,  5808 gram, 121 cells
12s 12p = 31.2A 44.4V, 1385.28W, 6912 gram, 144 cells












In Progress, Will Update ...! 

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