Re: Proper Speed Controller Circuit for 24 VDC motor : electric bycycle
- From: John Popelish <jpopelish@xxxxxxxx>
- Date: Sat, 24 Sep 2005 22:44:28 -0400
greenwanderer108 wrote:
Hi, I'm an American living in Bangkok, Thailand. I'm new to this forum and an absolute novice with basic electronics, I was hoping someone here can assist me with a few basic questions.
I'm planning to convert my bycycle electric in the near future (after some electrical enlightenment of course). I've basically narrowed the motor down to a 24 VDC 250 watt motor. (Though 350 and 500 watt are also options)
Using Ohm's law (I think), I calculated that such a motor's current draw would be aprox. 10.416 amps (250 watts / 24 volt = 10.416 amps), which I assume from reading other threads here, is what the motor would draw an one hour under load. (Please don't hesitate to correct me--elaborate)
That calculation has nothing to do with time. If the motor is rated at 250 watts and 24 volts then the only way it can consume 250 watts is if it passes 10.4 amperes. How long it does that depends on how large the battery is (ampere hour rating). You will also probably not ask the motor to produce that power continuously, but may run it at lower current (torque) much of the time.
As for power supply, I've decided that I want to rig six 12 volt 10 amp/hour batteries in series-paralell for a total of 24 volts, 30 amp/hour power supply. This I figure should give me roughly two hours of motor work between charges...
I think you have this right.
Assuming my calculations are correct, my next task is to figure out the
necesarry (speed) controller. I've browsed the many schematics/theories
for DC motor controllers and am lost. I'm assuming a Pulse Width Modulator
circuit is what I'm looking for (rigged with a handle grip motorcycle
throttle set-up for precise control). So, then, I would like to know is
how to decide which particular circuit will suffice for the amp and volt
consumption required for my particular project.
Most every PWM circuit/schematics I've come across on the web are for low
amp consuming loads. As I mentioned, the motor will be drawing atleast 10
amps. What is the theory and/or calculations for amp consumption in DC
motor controllers?
I think the best drivability may come from an adjustable torque control (current control). This is because you feel the torque as acceleration, regardless of what speed you are traveling. So I would look for a PWM controller that included current feedback, and that used the throttle as a torque (current) set point.
Current control also protects the motor from overload in the event that you come to a slope too steep for it to handle. If the setpoint can reach only the rated motor current (or slightly above), stalling the motor will not overheat it.
Ideally, a universal controller that would work for 250, 350, and 500 watt 24 VDC motor with minimal power loss would be best.
That is just a matter of the current rating of the PWM controller.
Of course, I would like to know what determines/controls the current load/consumption in a control circuit. There is so much to decipher among---MOSFET, other capacitors, diodes, that I have still yet to learn their functions, purposes.
While we're at it, how does adding more amp/hours (placing more cells in paralell) to the power supply (battery pack) affect the control circuit?
No. it just provides power for a longer time. The supply voltage affects the top speed.
In other words, how must the control circuit be modified to accomadate the extra current without overloading/overheating the circuit, load, etc.?
.
- References:
- Proper Speed Controller Circuit for 24 VDC motor : electric bycycle
- From: greenwanderer108
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