# Can anyone explain this method of dc motor control?

S

#### [email protected]

Jan 1, 1970
0
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

T

#### Tom Biasi

Jan 1, 1970
0
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

The article is talking about controlling the motor speed my adjusting the
duty cycle of the pulses being sent to it.
Look up DC motor speed controllers and this type will be discussed
somewhere.
It seems the person made his own version with some simple parts but as you
can see he goes into no detail.
Tom

C

#### Chris

Jan 1, 1970
0
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.

"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

S

#### [email protected]

Jan 1, 1970
0
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

F

#### Fritz Schlunder

Jan 1, 1970
0
Hey. Crosspost properly. Not only did you crosspost improperly, but you
also made subtle changes to the title. Grrr!

J

#### Jamie

Jan 1, 1970
0
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
Pulse Width Modulation?

J

#### Jamie

Jan 1, 1970
0
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
Hmm.
sounds like a backyard hack job to me.
lets see.
Generator is attached to the shaft so it generates
more power as the RPM's increase, this in turn drives
the Fan Motor or Helps in increasing the FAN motor
speed.
then the blades on the fan simply hit a mechanical weighted
switched that will pulse the contacts and at some point when
going fast enough stay closed..
sounds like hack to me.
or it could be using some kind of optical switch via the fan
who knows..
i guess the centrifugal would take over at some point and
keep the contacts closed.

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