safe
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- Mar 28, 2009
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Adding A Charge Pump?
I'm "firm" on the idea that a "toy" ebike should not require more than 48 volts for a battery. To expect a kid to be trusted with a 120 volt DC battery is to invite disaster.
But it might not be necessary to configure the battery as 120 VDC.
PWM controllers usually have a sort of "preload" stage where a row of capacitors temporarily store the battery energy before passing to the MOSFET's. Why not just add a second "preload" stage with a charge pump and step up the voltage to double?
So 48 VDC becomes 96 VDC...
More specifically the battery chemistry values would start at:
SLA - 13 * 4 = 52 volts * 2 = 104 VDC
NiCad - 1.3 * 40 = 52 volts * 2 = 104 VDC
At 104 VDC you are pretty close to the standard voltage that these little AC Induction motors are designed for, so the rewinding is not necessary or as important. It might be possible to find the exact motor you need "off the shelf" and not even need to fiddle with it.
So this inverter would need:
Three Phase AC power.
Variable Frequency Drive (VFD).
"Step Up" inverter that would double the voltage. (or more)
Be designed to be as efficient as possible. (90% or better)
Must have a strict 1000 watt input restriction.
What's radically different with the AC Induction motor verses the DC permanent magnet motors (brushed or brushless) is that voltage and motor rpm are UNRELATED. This is really cool because it means that the more voltage you use just increases the efficiency of the motor with no change in the motor speed. (efficiency improves up to a point... I was reading how you can actually go too high with voltage too)
The central mechanical problem that ebikes have dealt with is that all the permanent magnet motors require the motor rpm to be very HIGH before they gain their best efficiency. These motors also become limited in the width of their usable powerband, so you are forced to use gears if you want to cover all possible situations.
With the AC Induction motor the efficiency is best when a certain amount of "slip" is taking place. VFD's allow you to target the ideal "slip" and with the use of PWM it's possible to adjust the voltage at lower frequency to eliminate the excess current problem.
Will the AC Induction motor be the future of ebikes?
We will see...
I'm "firm" on the idea that a "toy" ebike should not require more than 48 volts for a battery. To expect a kid to be trusted with a 120 volt DC battery is to invite disaster.
But it might not be necessary to configure the battery as 120 VDC.
PWM controllers usually have a sort of "preload" stage where a row of capacitors temporarily store the battery energy before passing to the MOSFET's. Why not just add a second "preload" stage with a charge pump and step up the voltage to double?
So 48 VDC becomes 96 VDC...
More specifically the battery chemistry values would start at:
SLA - 13 * 4 = 52 volts * 2 = 104 VDC
NiCad - 1.3 * 40 = 52 volts * 2 = 104 VDC
At 104 VDC you are pretty close to the standard voltage that these little AC Induction motors are designed for, so the rewinding is not necessary or as important. It might be possible to find the exact motor you need "off the shelf" and not even need to fiddle with it.
So this inverter would need:
Three Phase AC power.
Variable Frequency Drive (VFD).
"Step Up" inverter that would double the voltage. (or more)
Be designed to be as efficient as possible. (90% or better)
Must have a strict 1000 watt input restriction.
What's radically different with the AC Induction motor verses the DC permanent magnet motors (brushed or brushless) is that voltage and motor rpm are UNRELATED. This is really cool because it means that the more voltage you use just increases the efficiency of the motor with no change in the motor speed. (efficiency improves up to a point... I was reading how you can actually go too high with voltage too)
The central mechanical problem that ebikes have dealt with is that all the permanent magnet motors require the motor rpm to be very HIGH before they gain their best efficiency. These motors also become limited in the width of their usable powerband, so you are forced to use gears if you want to cover all possible situations.
With the AC Induction motor the efficiency is best when a certain amount of "slip" is taking place. VFD's allow you to target the ideal "slip" and with the use of PWM it's possible to adjust the voltage at lower frequency to eliminate the excess current problem.
Will the AC Induction motor be the future of ebikes?
We will see...
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