Building an EV motorcycle. Batteries: Need opinions.

[P-hack]

do you know how much force your bike needs at various speeds? An interesting thing to consider is how fast it can go on 11.5kw as that is the continuous rating of the motor (regardless of the voltage applied). Can be determined by a bathroom scale weighing wheels and rider, and high and low speed coastdown tests.

This page lists 315lb/in at 2800rpm, 200 amps continuous (72v system). 72 volts can create about 26kwh @450 amps which is close to the peak rating anyway...

Mars ET-S Permenant Magnet Motor

before you buy more stuff, like %33 more batteries than you need...

So once you know your max continuous speed for 11.5kwh, you can choose appropriate gearing to hit 2800 motor rpm, and hope you have enough torque at max kwh to get you there satisfactorily (or do more maths, F=MA, or A=F/M plus resistance fudge).

[TurnNBurn]

Originally Posted by P-hack

do you know how much force your bike needs at various speeds? An interesting thing to consider is how fast it can go on 11.5kw as that is the continuous rating of the motor (regardless of the voltage applied). Can be determined by a bathroom scale weighing wheels and rider, and high and low speed coastdown tests.

This page lists 315lb/in at 2800rpm, 200 amps continuous (72v system). 72 volts can create about 26kwh @450 amps which is close to the peak rating anyway...

Mars ET-S Permenant Magnet Motor

before you buy more stuff, like %33 more batteries than you need...

So once you know your max continuous speed for 11.5kwh, you can choose appropriate gearing to hit 2800 motor rpm, and hope you have enough torque at max kwh to get you there satisfactorily (or do more maths, F=MA, or A=F/M plus resistance fudge).

Once the bike is together and working with the basics (batteries, motor, controller, etc...) I was going to try and refine it to get what I want out of it over the course of the next year. Gear ratios, reducing weight, etc... were all things I was going to do once I get it registered and drive it around for a while. To start I'm shooting for 35-45 MPH and then work my way up from there.

[P-hack]

k, are you starting at 72 volts? Or do I need to keep typing? It is more than enough for continuous use and is sufficient to burn out the motor in under a minute, plus it is a standard voltage for chargers, and your controller is designed for it.

Sprockets on the other hand are fairly cheap to experiment with, though still worth making an initial educated guess.

[TurnNBurn]

Originally Posted by P-hack

k, are you starting at 72 volts? Or do I need to keep typing? It is more than enough for continuous use and is sufficient to burn out the motor in under a minute, plus it is a standard voltage for chargers, and your controller is designed for it.

Sprockets on the other hand are fairly cheap to experiment with, though still worth making an initial educated guess.

I was going to start at 72v for everything, but I didn't plan on going full speed ahead at 72v until I sorted everything out at 36v. I don't want to kill myself on the first run.

[Daox]

Meh... go with 72V right off. Thats what a throttle is for!

[P-hack]

Just curious (I have not looked at controllers in much detail so this is educational for me too), have you experimented with the programming interface for your 7245? You might need to just to see what the under/over voltages are currently. You can also do things like customize throttle response and set the max current to %50 or whatev. But I would agree with daox if you can afford 72v off the bat, just don't wang the throttle open on your very first takeoff

http://www.youtube.com/watch?v=STdttpsmPrg

[TurnNBurn]

Originally Posted by P-hack

Just curious (I have not looked at controllers in much detail so this is educational for me too), have you experimented with the programming interface for your 7245? You might need to just to see what the under/over voltages are currently. You can also do things like customize throttle response and set the max current to %50 or whatev. But I would agree with daox if you can afford 72v off the bat, just don't wang the throttle open on your very first takeoff

I haven't personally used the programming interface yet (I need a serial to usb cable) but that's part of the reason I stuck with the alltrax 7245 is that I can re-program it and tinker with gear ratios and throttle responses. I've watched a few youtube videos of people programming the controller, so I know what features it offers.

[Ryland]

always go with as high of voltage as you can, you'll have less line loss and you'll pull fewer amps from the battery bank and you can always use less throttle to go slower.

[Wayne_bruce12]

You can opt for MotoBatt MB2.5U 12v maintenance free battery. I experienced, can vouch that this is descent kind of battery, got positive reviews from experts and users. I'd suggest exploring mrpositive.co.nz will be helpful.

[TurnNBurn]

Originally Posted by Wayne_bruce12

You can opt for MotoBatt MB2.5U 12v maintenance free battery. I experienced, can vouch that this is descent kind of battery, got positive reviews from experts and users. I'd suggest exploring mrpositive.co.nz will be helpful.

Not enough amps from those things.

Here's an update: I'm sending the motor back to the company for credit and exchanging it for the ME1003. I should be on track in the next week or two and next I'm buying the batteries. I've settled on Winston or similar batteries.