Can anyone explain this method of dc motor control?

These paragraphs are from an article about a homebuilt hybrid car in
Mother Earth News.

"Any project fresh off the drawing board has its share of problems, and
the Opel hybrid was no exception. When David pressed the accelerator
for the first time, he got a 300-amp surge which melted his relays. So
he searched his graduate texts for the answer ... and finally found it
in-of all places-an old high school physics book: A pulser was
necessary to "chop" the current flow and prevent a heavy initial draw
to the drive motor.

As Dave explains it, "The motor will always have full voltage and full
current, but the pulser makes it 'think' the voltage and amperage are
cut down to about 1/4 of what's actually available. With this
gadget-which is simply a combination of a reworked car generator and an
old fan motor-I can keep the draw within limits and effectively control
the car's acceleration . . . without sacrificing the maximum current or
voltage that's necessary for high-speed driving. I could have achieved
the same results with a commercially available FCR control ... but one
of those units would have cut my power slightly, and cost in the
neighborhood of $800! I can build my own device for about $25, and I
can fix it myself if it breaks!"


Boyntonstu

 

[Chris]

stu@aaronj.com wrote:

These paragraphs are from an article about a homebuilt hybrid car in
Mother Earth News.

"Any project fresh off the drawing board has its share of problems,
and
the Opel hybrid was no exception. When David pressed the accelerator
for the first time, he got a 300-amp surge which melted his relays.
So
he searched his graduate texts for the answer ... and finally found
it
in-of all places-an old high school physics book: A pulser was
necessary to "chop" the current flow and prevent a heavy initial draw
to the drive motor.

As Dave explains it, "The motor will always have full voltage and
full
current, but the pulser makes it 'think' the voltage and amperage are
cut down to about 1/4 of what's actually available. With this
gadget-which is simply a combination of a reworked car generator and
an
old fan motor-I can keep the draw within limits and effectively
control
the car's acceleration . . . without sacrificing the maximum current
or
voltage that's necessary for high-speed driving. I could have
achieved
the same results with a commercially available FCR control ... but
one
of those units would have cut my power slightly, and cost in the
neighborhood of $800! I can build my own device for about $25, and I
can fix it myself if it breaks!"


Boyntonstu

Hi, Boyntonstu. You're talking about "pulse width modulation", or PWM.
It's a method to ramp up motor speed by rapidly (hundreds to thousands
of times a second) switching the motor voltage on and off. The motor
reacts to the percentage of time the switch is on. It has a lot of
advantages over many other kinds of motor control, particularly for
bringing high torque DC motors up to speed slowly.

Google this exact phrase:

"Pulse Width Modulation" +"motor control"

to get some information. I found the third hit helpful

http://mechatronics.mech.northwestern.edu/design_ref/actuators/motor_PWM.html

Good luck
Chris

 

Hey guys, you don't get the question.

I know all about electronic PWM controllers like Curtis and Alltrax.
The article is a PULSER speed controller that is made up of electrical
and not electronic components; namely a generator and a fan motor.

Let me rephrase the question:

How can you control the speed of a dc motor using a generator and a fan
motor?


Boyntonstu