# Project motorcycle, battery choice



## johnbridgedesign (Mar 22, 2010)

Hello, i am seekeing advice on batteries to power my electric motorcycle.

The project is near complete now all bar battery selection and charging pack. Its too much of a mine field for me at the minute and researching into it is very confusing.

Some facts about my motorcycle

Motor - LEM-200-D127 
( power 13KW - Revs 50 rpm/v )

Controller - Alltrax 4865 controller 
( 24-48 Voltage DC, 250 amps cont. 600 amps peak )

I have been told i need 48 volts for my chosen application;
-1-2 hours ride time
-top speed of 80 MPH
-the bike shall be used more so as a commuter and top speed will not need to be achieved constantly, it would just be nice.

Id would appreciate any advice and help. Motors and controllers are one thing but there are too many battery variations.

My only desire is they be lightweight and as small as possible.

Many thanks

John


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## Jan (Oct 5, 2009)

The only relevant information for calculating your battery capacity is the mass of your bike, its frontal area, CW value, and the efficiency of the controler, motor and drivetrain.


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## Frank (Dec 6, 2008)

Have you already purchased the motor/controller?

To get any kind of range you'll need lithium. Assuming 125 watt-hr/mile, to have an absolute range of 60 miles (that might give you 40-45 usable) you'll need 60*125 = 7.5kwh pack. At 48 volts that's about 16 cells. 7.5 kwh/16 ~468 w-hr/cell ~150 AH cells. They're pretty big and harder to package than smaller cells. Someone please check my math!

What kind of bike are you converting?


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## pgt400 (Jul 12, 2008)

80 mph top speed will require more power....more like 72v and likely 130 amps or more. If you limit yourself to 48v you will have to pull more current to get your power...your batteries C rating may limit this.


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## Frank (Dec 6, 2008)

I agree. As a point of reference, I'm converting my old Suzuki GT550 which broke a con rod a while back. I'm using a D&D SepEx 72 volt system with 24 T-Sky LSP100AH cells. I based gearing on 80 mph top speed and figure I'll be able to reliably (hopefully?) get 50 miles at 50 mph. My first motorcycle conversion was an old Aermacchi Sprint with a 36 volt series DC motor/275A controller. It was geared for 50 mph which it would hit on a slight downhill but pulled a lot of amps doing so. It liked to cruise at 35 -40 mph.


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## jorhyne (Aug 20, 2008)

Yes you really should have a higher voltage system if you want to be able to reach your performance goals, 72v at a minimum. I've yet to see a 48v motorcycle conversion that can go above 40 or 50mph.


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## frodus (Apr 12, 2008)

1-2 hours ride time is going to be hard to do, maybe 30min-1hr is more realistic, depending on speed. You won't get 80mph AND 1 hour ride time unless you have a very large pack.

Your motor is a little small for 80mph, and it will pull a ton of amps. 2400rpm is what 48V would drive that motor, and to get 80mph, you're looking at a 2.3:1 gear ratio. At low speed, its going to accelerate like a slug and draw a lot of current (hundreds of amps) and it'l draw that for a long time before going down. Normal ratios for this motor are usually between 5:1 to 6:1



Start over with the design.

Start with a bike in mind. Its got to have plenty of space, because you're going to need 5-6kwh of batteries onboard. You won't fit lead on there, so you're going to have to look into Lifepo4 (thundersky, sky energy, headway, etc). Now, you need to do some rough calculations on power needed for a bike of xx weight and yy frontal area.

Go here, download this spreadsheet:
http://lennonrodgers.googlepages.com/vehicle_calculations.xls

Fill in the info you know and calculate how much power you need to go 80mph. With my bike, I'd need about 175wh/mile to go 80mph. If I wanted to go 40 miles at that speed, I'd need 7kwh. If I reduced that to 50mph and 40 miles, I'd only need 3.7kwh. 

At 50mph, I'd need the motor to drive 5+hp continuously. If I wanted 80mph, I'd need more like 15+hp continuously. Most motors have a continuous and a peak rating. You can't run a motor continuously at its peak rating, it will overheat.

So from there, choose a motor based on your requirements for speed and power. Then choose a controller to match that. Now make sure the batteries you choose can fit in the bike and supply the power you need for the bike to meet your requirements.

Basically, get a bike and work backwards, not forwards. You need to know where you're going before you can start to walk along the design path.


My bike with Lifepo4 (headway), an AC motor/controller, 6.1kwh of batteries should give me about 50-60 miles range at 50mph. Again this is calculated, but the spreadsheet has been fairly accurate for most people. Its a starting point. I'm on the final stretch, getting my motor mount and battery frame built.


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## Kjnevin (Jan 20, 2021)

Hi, 
Not sure if anyone would be available to help. I am trying to plan to convert my Piaggio Vespa to electric. 
I am looking for help to select a suitable battery or batteries to power my motor(4000W). I am limited by space and will need the require power supply to fit into a space of 12 x 6.5 x 3.5(inch) or 300 x 165 x 90(mm). 

Thanks for your help, 
Keith


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## 67BGTEV (Nov 1, 2013)

Kjnevin said:


> Hi,
> Not sure if anyone would be available to help. I am trying to plan to convert my Piaggio Vespa to electric.
> I am looking for help to select a suitable battery or batteries to power my motor(4000W). I am limited by space and will need the require power supply to fit into a space of 12 x 6.5 x 3.5(inch) or 300 x 165 x 90(mm).
> 
> ...


I don'y think you can fit in anything to ride in reality. You can add some capacitors to prove it to yourself that it runs


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