# EV sizing issues- Help!



## kasi124 (Jun 30, 2008)

Hello everyone,

I am new to EV's and have no training in automobiles or electronics. I have been reading up on EV conversions on this site and I am looking into the option of building a electric motorcycle. 

Some of the basic specs I have gathered this far:

1. Total weight of existing bike (including engine and parts) - max 300 lbs (~ 135 kgs)
2. Speed is not my concern, hoping to reach max speeds of about 40 mph (~ 64 kmph)
3. Range is very important, hoping to get at least 60 miles/charge (~ 100 kms)
4. The peak power should be in the range of 10 hp


Having set my goals I started looking for similar projects.
I looked for projects using a 2 hp (continuous) motor and found one on evalbum - http://www.evalbum.com/1415

Having no background in this field I am a little stumped by the ratings and calculations, hope somebody can clarify my doubts:

1. That project uses an Advanced DC 140-07-4001 motor (http://www.evparts.com/prod-MT2110.htm). How do I read/understand motor rating information?
The motor specifications are:

Voltage: 24 to 36 VDC

Current Ratings: 45 amps continuous, 60 amps for one hour, 275 amps intermittent

Horsepower Ratings: 2 HP continuous, 3 HP for one hour, 10 HP peak

2. Assuming I was using that motor, I moved to sizing the battery. I plan on using 3 x 12 V batteries. That takes care of the voltage.
Then used the formulas on the forum to calculate the energy required. 


```
Assuming efficiency to be 75 Wh/mile (may be low for bike of this size)
Energy Required = 75 x 60 = 4500 watts
Ah rating = 4500/36 = 125 Ah
Allowance = 125 x 1.25 x 1.8 = [B][COLOR=Red]281 Ah[/COLOR][/B]
```
Is something wrong with the calculation? 281 Ah seems pretty high. 

Hope somebody can clarify these issues relating to sizing the motor and battery pack.

Thanks


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## ngrimm (Oct 19, 2007)

Welcome to the club! You didn't mention what type of batteries you plan to use and the weight is drastically different between them. For instance three 12 volt 85ah lead acid batteries will weigh at least 150 lbs and the motor will be 50lbs or more so that only leaves 100 lbs for the bike in order to end up with 300 lbs total. I think lithium etc. weight about a fourth of that. Hoplefully someone else will chime in here with their experience. Norm


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