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Home Brew / Researching a conversion, have some questions
« on: May 19, 2011, 05:44:48 AM »
I recently discovered electric vehicles and I've started researching a conversion. I have a ton of questions though, most related to the engine and batteries. It's been too long since I took a physics class, I hope I've still got everything straight. I'd appreciate any help people could give me.
The minimum specs I'd consider to make a conversion worth it are:
~90mph top speed
30+ mile range
Basically I need to know how to calculate these (variables, formulas) so I can choose components that meet my needs.
Motor:
I've done some research into DC vs. AC motors and the consensus seemed to be "go with what fits your needs/budget" which is kinda vague. It looks like AC motors are more expensive (with more expensive controllers), but can have more hp and higher rpms. For the speed I want with decent acceleration I'm assuming I'd need at least 72V. Are there benefits to going higher? The way I understand it, horsepower is a function of wattage and torque is a function of current. Is this correct? How can you estimate the top speed of the bike? Is it strictly a function of max rpms of the motor, sprocket ratios, and tire size? Do other things like weight of the bike/rider and wind resistance come into play or are those negligible? Does this mean I should choose a motor primarily based on max sustained rpms?
What is the difference between these two motors?
http://www.electricmotorsport.com/store/ems_ev_parts_kits_emc-rt_7234.php
http://www.electricmotorsport.com/store/ems_ev_parts_kits_perm_7234.php
The cheaper one looks like it has better specs.
Assuming 17" rear wheel I calculate: 17" x 3.14 x 3700rpm x 60min/h / 12"/' / 5280'/mi = 187mph with even gearing
Is that right?
Without a torque curve (which they don't give) you can't calculate how long it would take you to reach that speed, but it should be reached eventually right?
Batteries:
It looks like Lithium Iron Phosphate is the way to go. The cheapest I've seen is ~$450/kWh vs. ~$220/kWh for SLA.
Is it safe to assume I should ignore "maximum" rates (current, discharge, torque, rpms, etc.) and base everything on maximum sustained rates?
Can someone explain battery discharging. Battery discharge rates are listed in coulombs and all seem to be ~3. How do I find out the maximum current output using this? I know C=As but I'm not sure how to use it to find what I want.
Is there a benefit to exceeding 72V? Would you need less current so it would run cooler and last longer?
Is the calculation for range: Range = battery AH / max sustained amps x top speed?
The minimum specs I'd consider to make a conversion worth it are:
~90mph top speed
30+ mile range
Basically I need to know how to calculate these (variables, formulas) so I can choose components that meet my needs.
Motor:
I've done some research into DC vs. AC motors and the consensus seemed to be "go with what fits your needs/budget" which is kinda vague. It looks like AC motors are more expensive (with more expensive controllers), but can have more hp and higher rpms. For the speed I want with decent acceleration I'm assuming I'd need at least 72V. Are there benefits to going higher? The way I understand it, horsepower is a function of wattage and torque is a function of current. Is this correct? How can you estimate the top speed of the bike? Is it strictly a function of max rpms of the motor, sprocket ratios, and tire size? Do other things like weight of the bike/rider and wind resistance come into play or are those negligible? Does this mean I should choose a motor primarily based on max sustained rpms?
What is the difference between these two motors?
http://www.electricmotorsport.com/store/ems_ev_parts_kits_emc-rt_7234.php
http://www.electricmotorsport.com/store/ems_ev_parts_kits_perm_7234.php
The cheaper one looks like it has better specs.
Assuming 17" rear wheel I calculate: 17" x 3.14 x 3700rpm x 60min/h / 12"/' / 5280'/mi = 187mph with even gearing
Is that right?
Without a torque curve (which they don't give) you can't calculate how long it would take you to reach that speed, but it should be reached eventually right?
Batteries:
It looks like Lithium Iron Phosphate is the way to go. The cheapest I've seen is ~$450/kWh vs. ~$220/kWh for SLA.
Is it safe to assume I should ignore "maximum" rates (current, discharge, torque, rpms, etc.) and base everything on maximum sustained rates?
Can someone explain battery discharging. Battery discharge rates are listed in coulombs and all seem to be ~3. How do I find out the maximum current output using this? I know C=As but I'm not sure how to use it to find what I want.
Is there a benefit to exceeding 72V? Would you need less current so it would run cooler and last longer?
Is the calculation for range: Range = battery AH / max sustained amps x top speed?