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Discussion Starter · #1 ·
Taking the formula for battery pack building is their a minimum ?

for example a 500 pound vehicle
500 / 10 = 50 watt hours per mile needed

with a 144v motor in the 500 pound vehicle i would only need 250 watt hours to go 5 miles .

what would this battery pack look like ?

this is a serious question as i only care to have a 5 mile range but i would like to have a top speed of 70-80 mph

i have a feeling the battery pack will be bigger than i think because im not sure any battery type can safely discharge most of its charge in only 4 minutes (correct me if I'm wrong)
 

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At 70 mph the weight is not an issue as much as aerodynamics! - so forget about the 50 watt hours per mile!

A battery's ability to discharge is called the "C" rate
1C means that you can discharge it in 1 hour
10C means that you can discharge in 1/10th of an hour - 6 minutes

The batteries we use in EV's can usually survive 15C - but only for a short period

You can buy batteries for Radio Controlled aircraft that are rated at 40C - or even more - we don't use them in cars as they have a habit of exploding

I'm using a Chevy Volt battery pack (most of one) - 14 kwh - but on the drag strip I use up to about 400 kw - 28C - for a few seconds
 

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i have a feeling the battery pack will be bigger than i think because im not sure any battery type can safely discharge most of its charge in only 4 minutes (correct me if I'm wrong)
To discharge a battery in 4 minutes will be a 15C medium discharge. But in order to accelerate to speed you will need much more than that.

I have designed manny packs for applications like that, usually racing, here are some tips:
  • For racings from 5 to 30 minutes you can use RC high discharge Lipo batteries, they usually can handle it quite well (Do not expect a long battery life)
  • Over 30 minutes racing other chemistries can be used.
  • Under 5 minutes races we usually add super capacitors to the pack in order to handle accelerations better.
  • RC high discharge cells are heavier (around 150Wh/kg) that normal Li-Ion EV cells (around 180Wh/kg)
  • Other possibility is to use high discharge Life cells but they are heavier (around 120Wh/Kg) and weight is not something you want in a racing machine... (In this case battery life is longer than RC Lipos)
 

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Discussion Starter · #4 ·
2 great replies!
Why I have some knowledgeable people on the line let me give you more info .
What I am wanting to do .

Start with a full size sport bike and add a small cc motor. 50cc to 125cc gas ⛽

My goal is to build a commuter that has a top speed of maybe 60 mph on Ice alone .
But I want a 10- 20 mph electric booster when I get on the highway. Or anytime I push the boost button.
Aerodynamic drag is minimal due to it being a motorcycle and acceleration amps should be kept low because much of the work will be done along with the ICE motor. .
Small battery pack with a few caps should be perfect. But I’m trying to assess the different variables involved.

This is getting off subject but when boost is not activated I want the motor to be in regen mode . This will lower mpg and top speed of the ice motor some but that’s not the point 👍
When boost is on the ice motor will not be regenerating and will free up HP to go with the electric booster.

Think of the F1 race car system .
I could scale this up but I need proof of concept first
 

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2 great replies!
Why I have some knowledgeable people on the line let me give you more info .
What I am wanting to do .

Start with a full size sport bike and add a small cc motor. 50cc to 125cc gas ⛽

My goal is to build a commuter that has a top speed of maybe 60 mph on Ice alone .
But I want a 10- 20 mph electric booster when I get on the highway. Or anytime I push the boost button.
Aerodynamic drag is minimal due to it being a motorcycle and acceleration amps should be kept low because much of the work will be done along with the ICE motor. .
Small battery pack with a few caps should be perfect. But I’m trying to assess the different variables involved.

This is getting off subject but when boost is not activated I want the motor to be in regen mode . This will lower mpg and top speed of the ice motor some but that’s not the point 👍
When boost is on the ice motor will not be regenerating and will free up HP to go with the electric booster.

Think of the F1 race car system .
I could scale this up but I need proof of concept first
So a motorcycle with an electric "boost" system. Maybe a hub motor on one of the wheels would be the easiest way to do this.
 

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Interesting idea
Aerodynamic drag is minimal due to it being a motorcycle
Incorrect, a motorbike has more air drag than a full family car unless you have aerodynamic fairings/helmet/etc. and adopt a racing posture.
acceleration amps should be kept low because much of the work will be done along with the ICE motor.
Incorrect again sorry, acceleration of the bike and even of the IC motor will be done by the electric motor. An IC motor revs up very slowly in comparison with and electric motor and torque availability for the IC motor is very low in comparison with the electric motor.
This is getting off subject but when boost is not activated I want the motor to be in regen mode
Yes it is posible, you will need a controller that is able to do regeneration. You can do it by a switch that activates it, or in more advanced controllers like a Kellycontroller you can set it up automatically and define its parameters when you release the electric "throttle/switch"
 

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As it is not a racing machine and a bit of extra weight will not be very critical. I recommend you high power Lifepo cells. they are a bit heavier but they will last much longer that high discharge Lipo cells.
Note that there is normal Lifepo cells and high discharge rate ones, you need the high discharge ones.
Recommended K2 cells or A123 cells
 

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Discussion Starter · #8 ·
I just watched a video of an electric 48v golf cart parts motorcycle that has a top speed of 60mph . That doesn’t seem like very many volts. Hmmm
That may be a good cheapish prototype place to start.
 

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Volts doesn't really mean anything about power. Power is measured as a combination of volts and amps. Volts x Amps = Watts. So a 48v motor at 1000 amps is producing more power than a 300v motor at 50 amps.
 
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