How does a generator an a fan motor 'pulser' control a dc motor?

[[email protected]]

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

 

[Fritz Schlunder]

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!"

It is hard to say for sure what he is talking about, however, maybe his car
generator has brushes and contacts inside of it. Maybe what he did was hook
the fan motor up to the car generator to make it spin. Then he somehow
wired up some of the brushes and contacts such that they make and break the
main power connection for his main motor as they spin around. In this way
he made a crude mechanical method of reducing the average voltage applied to
the main motor at startup. Seems like a primitive, heavy, and unreliable
method to me. Unless I was stranded on a remote desert island I would go
for the electronic PWM approach with some nice beefy MOSFETs.

 

[John Woodgate]

I read in sci.electronics.design that Fritz Schlunder <[email protected]>

Seems like a primitive, heavy, and unreliable method to me.

The fact that the inventor only found out about starting current when
the contactor melted suggests that such a method would be all he could
cope with.

 

[Fritz Schlunder]

I read in sci.electronics.design that Fritz Schlunder <[email protected]>


The fact that the inventor only found out about starting current when
the contactor melted suggests that such a method would be all he could
cope with.

Seems like a fair assessment. On the other hand I shouldn't be too critical
of him since he did use his grey matter to fashion something that evidently
does function, and in fairness his background probably isn't in electronics.
Kudos to the developer even if I wouldn't do the same thing myself.

 

[[email protected]]

Seems like a fair assessment. On the other hand I shouldn't be too critical
of him since he did use his grey matter to fashion something that evidently
does function, and in fairness his background probably isn't in electronics.
Kudos to the developer even if I wouldn't do the same thing myself.

The inventor was out $800 and was not willing to get 'burned' again.
For $25 he claims to get slightly more power that is possible with PWM.
Is that factual?


For a non-elctonicer, replacing brushes is much simpler than cracking
open a Curtis controller and trying to repair it.


BoyntonStu

 

[Fritz Schlunder]

The inventor was out $800 and was not willing to get 'burned' again.
For $25 he claims to get slightly more power that is possible with PWM.
Is that factual?

If he had say a relay in parallel with his "pulser" to make hard contact
after the motor was up to speed, and if the PWM controllers didn't allow for
full 100% duty cycle, then it is conceiveable his method could yield more
full power power. Alternatively if the PWM controller had a really large
semiconductor voltage drop for some reason, maybe this could explain why he
claims more power. But it is hard to say for sure without physically seeing
what he did and how the electronic counterpart it was designed to replace
functioned.

For a non-elctonicer, replacing brushes is much simpler than cracking
open a Curtis controller and trying to repair it.

Indeed.

 

[Fritz Schlunder]

The inventor was out $800 and was not willing to get 'burned' again.
For $25 he claims to get slightly more power that is possible with PWM.
Is that factual?


For a non-elctonicer, replacing brushes is much simpler than cracking
open a Curtis controller and trying to repair it.

It appears the complete article can be accessed here:

http://www.motherearthnews.com/library/1979_July_August/An_Amazing_75_MPG_Hybrid_Electic_Car

I see it is dated summer 1979. I don't know what an FCR controller is, but
power electronics have come a long way since 1979. This is probably why he
claims to get more power from his method, whatever an FCR controller is
probably wasn't very good by today's standards

As for the rest of the performance claims, I would say they are rather
fanciful. Five horsepower just isn't enough juice to push a normal car on
level terrain at 50mph. Four regular automotive batteries would not be able
to supply too tremendously much more power than 5hp, and they wouldn't last
very long at all. Additionally they would require replacement very quickly
since automotive batteries aren't intended for that kind of use. Expecting
a top speed of 90mph is also fanciful. The 1.0L Geo Metro has a rated
maximum output of something around 55hp if I recall correctly. That car,
which only weighs 1800 lbs and has very small tires for high efficiency has
a top speed of around 80ish miles per hour on level terrain.

I suspect the car described in the article would be lucky to sustain 25mph
on level terrain, with a total inability to go up even the smallest of hills
at any speed.

 

[R Adsett]

It appears the complete article can be accessed here:

http://www.motherearthnews.com/library/1979_July_August/An_Amazing_75_MPG_Hybrid_Electic_Car

I see it is dated summer 1979. I don't know what an FCR controller is, but
power electronics have come a long way since 1979. This is probably why he
claims to get more power from his method, whatever an FCR controller is
probably wasn't very good by today's standards

At a guess someone said S and he heard F. The two sounds are very close
and get confused all the time especially over a phone line.

Robert

 

[Eric R Snow]

The inventor was out $800 and was not willing to get 'burned' again.
For $25 he claims to get slightly more power that is possible with PWM.
Is that factual?


For a non-elctonicer, replacing brushes is much simpler than cracking
open a Curtis controller and trying to repair it.


BoyntonStu

I read the article and it's full of mistakes. For one, it takes more
than 5 HP to move that Opel car at 50 mph. For another, it states that
the 5 HP lawnmower engine is efficient in it's use of gasoline. This
is not true. The lawnmower engine does not use much fuel, but compared
to the power output per gallon of gas by even the original engine in
that Opel it looks pretty bad. You can figure this out your self by
measuring how much gas your 3.5 HP rotary lawnmower uses when it is
run till empty and scale it to your car. You can get the HP figure for
your car at the library. Also, the wind drag goes up by the square, so
the HP required to push the car goes up the same amount. So it takes
3.24 times as much energy to push the car at 90 than it does at 50.
This comes out to 16.2 Hp required to drive at 90 if it only takes 5
HP to drive at 50. Even with the batteries it seems really unlikely
the thing could be accelerated to 90 mph.
ERS

 

[[email protected]]

myself.

I think so too. And I'd say his design works - though I think the
claims made are, if not factually/legally wrong, certainly blatantly
misleading.

OK no, I stand corrected, "AND IT'S REALLY PRACTICAL!" is clearly not
true.

"the little Opel' really has some get-up-and-go"

maybe be legally true claim, but plainly misleading. Ie only true for
the most miniscule values of 'some'. A vehicle like that takes minutes
to get upto a reasonable speed, is unable to accelerate away from
problem situations, and is forever limited to little more than the
slowest speed bits of a journey, ie corners.


Quite a good idea actually - this thread shows even tronic designers
cant choose the cheaper more reliable design.

Its very old tech, but thats no reason to reject it. It was 25 instead
of 800, an important consideration for any engineer, car alts are
reliable, ditto fan motors, and using a carbon copper switch means near
zero v drop - a good design really, and clearly a good choice in the
70s.

It appears the complete article can be accessed here:

http://www.motherearthnews.com/library/1979_July_August/An_Amazing_75_MPG_Hybrid_Electic_Car

As for the rest of the performance claims, I would say they are rather
fanciful. Five horsepower just isn't enough juice to push a normal car on
level terrain at 50mph.

Read again.

1. The gas motor puts out 5hp, and the batteries will put out a lot as
well.

2. The car is 50lbs heavier than it was with a gas engine and clutch,
so it has quite a bit of battery in it, not ordinary car batts.

3. The article sells plans and may mislead the unwary, ie 90 may be
only achieved on the steepest straight downhill stretch of road on the
planet, and 50 may only be achieved for short times under favourable
conditions.

Four regular automotive batteries would not be able
to supply too tremendously much more power than 5hp,

"the engineer installed four 12-volt, heavy-duty automobile
batteries-in series" not regular ones. I'm thinking very heavy duty,
like 100-200 Ah. The car gained 50lbs.

and they wouldn't last
very long at all.

yup, as is implied in the article.

Additionally they would require replacement very quickly
since automotive batteries aren't intended for that kind of use.

yes, a backyard tinkers design. I wonder if one could improve that to
some extent by refilling them with gel electrolyte. Still wont give
adequate lifetime though, or anywhere near.

Expecting
a top speed of 90mph is also fanciful. The 1.0L Geo Metro has a rated
maximum output of something around 55hp if I recall correctly. That car,
which only weighs 1800 lbs and has very small tires for high efficiency has
a top speed of around 80ish miles per hour on level terrain.

You dont need anything approaching 55hp to hit 90. A 30hp peak rating
engine, run at just over half speed, so roughly around 15-20hp, will
take a 1 tonne car to 85mph on the level, and more downhill. But... it
will take minutes to get there, as the excess power for acceleration
dwindles to zero at those speeds.

A smaller car doing 55 will need very much less.

I suspect the car described in the article would be lucky to sustain 25mph
on level terrain, with a total inability to go up even the smallest of hills
at any speed.

One human can push a small car like that at 10mph, on the level. Its
acceleration where more serious power becomes needed.

Having driven wildly underpowered vehicles, there are tricks. Hills:
take a run up, and most of the power you need comes from the inertia of
the vehicle.

This car shoudl meet its claims just about, but with many gotchas. The
prime reason for 75mpg is simply the dangerously low power output.
Hybrid tech helps too. But the driving experience would be dire. The
designer consider a clutch unnecessary for example. IOW if you stop the
car just once without going down thru the gears youve got your first
issue. And you have to get the gearwheel speeds dead right at every
single change. Fun.


Runnable, sure, but not workable on todays roads, ones with other cars
on them. Might have been fit for very occasional daring use out in the
middle of nowhere in the 70s, underpowered to the point of dangerous.


NT

 

[[email protected]]

Thanks for a well thought out and quite balanced response.

I wonder how such a device would allow the vehicle to stIn other words;
with the battery 'ON' how does the commutator come to rest with the
current 'OFF'?

Today, how does one build a really cheap/simple mosfet 'pulser'
(not PWM)?

What I mean by my question is this. Assuming a 150 Amp/100V mosfet is
available as a replacement for the carbon/copper switch, what is the
simplest way to modulate the mosfet switch?

BoyntonStu

 

[[email protected]]

Thanks for a well thought out and quite balanced response.

I wonder how such a device would allow the vehicle to stIn other words;
with the battery 'ON' how does the commutator come to rest with the
current 'OFF'?

My best guess is the fan motor + rewired alternator stay spinning as
long as the ignition switch is on. At least thats how I'd probably do
it. Taking foot off the gas pedal will mean no current to the main
motor during stopping.


NT