# 48v battery pack



## Spence (Nov 18, 2011)

I need to make a 48V battery pack that can out put 300Amps for 30 seconds and can propel a 350Lb mass at 20Mph for 15 miles. This pack can be made from lead acid batteries or LiFePo batteries, but needs to be small enough to fit on a bicycle.


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## Rational (Nov 26, 2011)

Spence said:


> 20Mph for 15 miles


Do you have an estimate of the drag coefficient Cd and an approximate cross sectional area? For a bike the rolling resistance is possibly negligible.

This may help with Cd
http://www.google.com/imgres?q=drag...0&tbnw=156&start=0&ndsp=24&ved=1t:429,r:3,s:0


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## electrabishi (Mar 11, 2008)

Spence said:


> I need to make a 48V battery pack that can out put 300Amps for 30 seconds and can propel a 350Lb mass at 20Mph for 15 miles. This pack can be made from lead acid batteries or LiFePo batteries, but needs to be small enough to fit on a bicycle.


A 40 ampere-hour pack of either TS or CALB cells would exceed all your requirements so your pack need'nt be any larger than that. 16 buddy-paired Headway 8- or 10- AH cells would still get you the range and performance you are looking for.

Here is the 48V 40 AH pack I put together for my Honda CB-360 project. More than you'd need for a bicycle but if you could fit in onto your bicycle you'd get 50 to 60 miles of battery only operation, maybe more.










Mike


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## MN Driver (Sep 29, 2009)

That would make for one heavy bicycle unless that long of a distance could actually be used often. 50 miles on a bicycle in one day. I've done 80 using pedal power and I couldn't imagine doing half of that, even if it were powered at 30mph on anything more than maybe a monthly basis. My limit is an hour on a bicycle in a day myself if its a daily basis unless its very occassional that I go longer, then the comfort issues start and I'm not an old man either. That pack and whatever associated range on a motorcycle, no problem as those are designed to be comfortable.


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## Spence (Nov 18, 2011)

electrabishi said:


> A 40 ampere-hour pack of either TS or CALB cells would exceed all your requirements so your pack need'nt be any larger than that. 16 buddy-paired Headway 8- or 10- AH cells would still get you the range and performance you are looking for.
> 
> Here is the 48V 40 AH pack I put together for my Honda CB-360 project. More than you'd need for a bicycle but if you could fit in onto your bicycle you'd get 50 to 60 miles of battery only operation, maybe more.
> 
> ...


Thanks mike so if I used 16 38120S headways how do I calculate how much range I would get @ 20 mph?

Also would this BMS ( http://stores.headway-headquarters....-100a-bms,-16/Detail.bok?category=BMS/PCM/PCB ) work if I was discharging the pack @ 300 amps?


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## Spence (Nov 18, 2011)

Rational said:


> Do you have an estimate of the drag coefficient Cd and an approximate cross sectional area? For a bike the rolling resistance is possibly negligible.
> 
> This may help with Cd
> http://www.google.com/imgres?q=drag...0&tbnw=156&start=0&ndsp=24&ved=1t:429,r:3,s:0


I will calculate the RR.

With the Cd where do you measure the area?

And by the cross sectional area do you want the distance of the supportive material or the gaps between the support beams?


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## Sangesf (Apr 21, 2011)

What you're asking for is not so easily done... 
But you have to remember this...

It's the old EV motto of:

I can build it to be light
I can build it to be fast
I can build it to get distance
I can build it cheap
Choose any 3. 

However, if you're so inclined, you can go LiPo not lifepo4. 

You would need LiPo (RC) NanoTech packs. (45-90c)
Somewhere in the 48v 30Ah setup. 
You would get light, fast and distance, but not cheap. 

You can go lifepo4 in a 48v 50Ah..
You would get cheap, fast and distance, but heavy.


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## Spence (Nov 18, 2011)

when I wire up those 16 headways in series the total Ah of the pack will only be 10Ah right?

how do I calculate how many watts and amps my bike will take to give a continuous speed of 20 mph and if it only weighs 250 lbs max?


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## Sangesf (Apr 21, 2011)

Spence said:


> when I wire up those 16 headways in series the total Ah of the pack will only be 10Ah right?
> 
> how do I calculate how many watts and amps my bike will take to give a continuous speed of 20 mph and if it only weighs 250 lbs max?


Real world numbers work this way...

48v 10A will definitely get you 15 miles distance at 20mph..
But no way will it take a 300a discharge for any length of time (greater than 1 sec)...

For 300a for any length of time (10sec max), you'll need at least 30Ah in HEADWAYS...

For 300a for 30sec you'll need some 20Ah LiPo nano-techs..

Basically anything that will give you 300a for a decent amount of time, will also give you the distance (at normal amp usage) that you're looking for..

Why do you want to pull 300a for? 300a at 48v is 14.4Kw.. That's a BIG motor!


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## Spence (Nov 18, 2011)

Sangesf said:


> Real world numbers work this way...
> 
> 48v 10A will definitely get you 15 miles distance at 20mph..
> But no way will it take a 300a discharge for any length of time (greater than 1 sec)...
> ...


I'm pretty new to electrical engineering as I am only 17 and am still learning how everything works (no high school engineering classes  )and so far I now understand how battery discharge and wiring works thanks! 

I got the number of 14.4 kW (peak) from a calculation, but I am actually toning this down to more like 0-30 mph in 2.0 sec then I would only need around 5.5 kW (peak). 

Here is how I calculated it: first I find how much Kinetic energy it will take (1/2 *113.63*13.412)= 10216.93J then I decide my acceleration time (2 seconds) 10216.93J/2.0= 5.1kW then I divide it by the seconds to get how much power I will need, then I added .4kW to compensate for air friction and RR (I am not sure how much power air friction and RR will take though so 400W is just a guess). Is this the right way to calculate the power consumption?


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## hardym (Apr 2, 2008)

It sounds like you want an e-bike. A 48V 10Ah pack on a 500 or 750W motor should go 20mph for 15 miles. Not sure where the 300A requirement comes from. A good pack at 20 or 30A will accellerate very quickly to 20 mph. A 48v pack will go to 30 mph. 
This headways pack would probably work for ya: http://www.evassemble.com/index.php?main_page=product_info&cPath=1&products_id=59


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## Sangesf (Apr 21, 2011)

In a perfect situation, 5.1Kw would do it, however there is not only the (small amount of) coefficient of friction (per air resistance and RR) but also instantaneous power requirements of the motor and it's efficiency to deliver what's put into it..
You're also gonna need a fat rear tire capable of compensating for (lack of) resistance too!
Not to mention, you'll need a substantial amount of weight to keep the tire from just spinning in place.
In other words, at the low end of the motor's efficiency (first start) you're looking at about 70% or 7.2kw to get the instantaneous 5.1kw needed. 
At 48v that's 150a. 
Better to run 72v @ 100a... 72v 16Ah HEADWAYS would be much better, as they would allow the ability to pull ~6C with a smaller amount of voltage drop then the 48v setup at about 10C. (and even that's pushing them.. They're really only rated for 5C max.)
Also would give you about a 40 mile range at 20mph (given an average of 540w needed to maintain that speed.)

I know you asked for mathematical computations for everything involved, but real world (experience) is much better and easier to understand then trying to figure out the math...

To minimize voltage drop (sag), you're even better off with LiPo nano-techs rated at 30C and up. 
(In that case a 72v 10ah nanotech pack will EASILY give you the 10C discharge rate with minimal voltage drop and will still net you about 20 miles at 20-25mph speeds-with some room to spare!).


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## Spence (Nov 18, 2011)

I think I will go with A123 26650 cells, If I build a 16s4p 48V 11.5Ah pack that will give me 552Wh and if the bike consumes 540W a second @ 20 mph that is a 20 mile pack and if I want to do a 0-30mph in 2 seconds it will do so at 13C and around 7% sag (according to this graph:http://www.emissions-free.com/image...lx_new&title=A123 ANR26650M1 Cylindrical Cell I believe it is 7% sag)

how much power would the bike use at 30 mph?


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## Sangesf (Apr 21, 2011)

Again, you'd be better off with a 72v pack...
With the 48v at the required 150a discharge, you'll see more of a 17% sag in voltage on that pack.. 

With 72v 11.xAh at your disposal, you would achieve the required results...
(You also need a motor capable of the 7.xKw required for your 0-30 in 2 sec.)

To sustain 30mph, you would need probably around 1100w or so on a normal bicycle.. Wind resistance is a BlTCH over 20mph... On a low riding bike, like a tadpole trike, you're looking at about a 15% drop in required wattage or 950w or so..
(The above is a random guess as I've never used a low riding trike, but its about right.. Those with experience on those kinds of vehicles, could give you a better (more accurate) watt usage at above 20mph)


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## Spence (Nov 18, 2011)

If I need 1.1kW continuous and 8kW peak for 10 sec (I added in more power for wind resistance) what kind of motor would you recommend?

I was thinking of using a brushed starter motor and changing the wire to the brushes to 1/0 gauge and putting in different power receiver terminals, would that be enough to handle a max of 115A for 10 seconds though?

Also, could I use 14 AWG wire to bus between cells as the max C would be 5 if I used a 23Ah pack? I figured that each cell in parallel and the main pack would give off a max of 11.5A (2.3Ah per cell in parallel) (14 AWG can take 20A continuous).

Is the amperage transferred to cell to cell? like cell one adds its output amps to cell two then the output amperage in the wire at cell two would be 23A?


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## charliehorse55 (Sep 23, 2011)

Spence said:


> I'm pretty new to electrical engineering as I am only 17 and am still learning how everything works (no high school engineering classes  )and so far I now understand how battery discharge and wiring works thanks!
> 
> I got the number of 14.4 kW (peak) from a calculation, but I am actually toning this down to more like 0-30 mph in 2.0 sec then I would only need around 5.5 kW (peak).
> 
> Here is how I calculated it: first I find how much Kinetic energy it will take (1/2 *113.63*13.412)= 10216.93J then I decide my acceleration time (2 seconds) 10216.93J/2.0= 5.1kW then I divide it by the seconds to get how much power I will need, then I added .4kW to compensate for air friction and RR (I am not sure how much power air friction and RR will take though so 400W is just a guess). Is this the right way to calculate the power consumption?


To accelerate to 13 m/s in 2 seconds means an acceleration of 6.5 m/s^2. Gravity is only 9.81 m/s^2, so you will be accelerating at 0.7g! You will almost certainly not be able to control this level of acceleration on a bicycle. 

Additionally, you can not calculate acceleration by simply dividing the amount of kinetic energy by the power of the motor. Power is equal to torque * velocity, so as you start the bike you would need infinite torque to provide 5kW of power. As you accelerate, the torque output from the motor will remain constant, while the velocity increase. Thus, the total power output of the motor will increase as you accelerate. This continues until you hit the peak power output of the motor, at which point torque will decrease linearly with speed to maintain a constant power output.


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## Spence (Nov 18, 2011)

charliehorse55 said:


> To accelerate to 13 m/s in 2 seconds means an acceleration of 6.5 m/s^2. Gravity is only 9.81 m/s^2, so you will be accelerating at 0.7g! You will almost certainly not be able to control this level of acceleration on a bicycle.
> 
> Additionally, you can not calculate acceleration by simply dividing the amount of kinetic energy by the power of the motor. Power is equal to torque * velocity, so as you start the bike you would need infinite torque to provide 5kW of power. As you accelerate, the torque output from the motor will remain constant, while the velocity increase. Thus, the total power output of the motor will increase as you accelerate. This continues until you hit the peak power output of the motor, at which point torque will decrease linearly with speed to maintain a constant power output.


If was to go about calculating the energy cost of acceleration, how would I do this?

Also, I can't find a dyno that I will be able to test what power my motor puts out at X watts and a torque vs rpm graph and such, were can I test the motor I will use to find out exact power consumption?


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## major (Apr 4, 2008)

Spence said:


> If was to go about calculating the energy cost of acceleration, how would I do this?


K.E. = ½mv² 

This would be added to the energy required to overcome road load (aero and friction) and any change in elevation during the acceleration period. This amount is "at the wheel", so the energy cost at the battery needs to include the propulsion system loss (efficiency consideration). And the real cost would include the charging system loss to get to the real energy figure which your utility company uses on the bill.


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## major (Apr 4, 2008)

Spence said:


> Also, I can't find a dyno that I will be able to test what power my motor puts out at X watts and a torque vs rpm graph and such, were can I test the motor I will use to find out exact power consumption?


Welcome to the boat the rest of us are in  Dynamometers are expensive. Companies which have them are not inclined to lend them to hobbyists. It may be possible to find a college or technical school having one. Enroll for a class and use it


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## electrabishi (Mar 11, 2008)

Back to the comment about needing 300 amps for 20 seconds. Here is a preliminary run I did on the Headway 38120-P cells before my computer blew up and I lost all my test data. This being the firs run it was rather conservative. You can see from the plot here they would do the 300 amps for about 20 seconds. Of course temperature has a big effect. They wouldn't quite make 20 seconds on the first run as you see here at 18 seconds. But after the first run and a quick charge the current at the 20 second time was almost 350 amps.

Going from memory, I'll have to find my journal, but I believe I was doing some 100 amp testing and was able to run over 2 minutes at a 100 amp draw.


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