> Jerry Avins <jya@ieee.org> wrote:
>
> (snip)
>> The disconnect relay that you cite is called a reverse-current cutout. I
>> don't know why it could be expected to fuse, but as I wrote, it can make
>> a big loud spark. It has both a voltage coil in shunt with the generator
>> and a current coil in series with it. The way it works, the voltage on
>> the disconnected generator builds up enough to pull the relay in on the
>> voltage coil alone. When it pulls in, current flows to the battery
>> through the current coil, increasing the field that's pulling the relay
>> in. When the generator slows enough for the current to reverse, the
>> series and shunt fields buck instead of adding, and the relay drops out.
>
> According to the "everything is on the web" rule:
>
> http://www.gus-stories.org/november_1968.htm
>
>> So why did the Karmann-Ghia generator work after I pulsed the cutout by
>> hand? Hint: think residual field.
>
> For it to work in the first place, the genertor has to supply some
> voltage with no field current. There is enough "permanent magnet"
> magnetization in the generator to do that. The first time you power
> it up the other way, it will reverse that field.
Right so far. If you turn the generator the other way, it "builds down,
instead of building up. Connecting the battery willy-nilly by pushing
the current cutout reversed the residual magnetization -- polarizing the
field the other way -- so it will henceforth build up instead of
building down.
>> Those DC generators needed not only the reverse-current cutout,
>> but also voltage and current regulators. The three relays in
>> the box performed one function each. An alternator needs at
>> most a voltage regulator, and can get by without even that.
>
>> How come?
>
> The battery will keep the voltage pretty constant, until it
> dries up. Excess current electrolizes more water, making more
> hydrogen and oxygen, and less water. The chemistry of older
> batteries wasn't so good, and it was normal to add water every
> so often. Now, many are sealed with no water caps.
Yup! The same reason that the taillight bulb on my bicycle burns out if
the headlight is disconnected. My generator (no diodes) delivers about
half an amp whatever.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Jerry Avins●October 16, 20122012-10-16
On 10/15/2012 3:33 PM, glen herrmannsfeldt wrote:
> Jerry Avins <jya@ieee.org> wrote:
>
> (snip) (also, I probably should have changed the subject along the way)
>
>> An alternator with fixed field excitation has an equivalent circuit that
>> consists of an inductor in series with an AC source whose voltage and
>> frequency are both proportional to rpm. (The magnetic field due to the
>> armature current directly opposes the excitation field. the equivalent
>> circuit follows from that.) The result is that the current is constant
>> when the alternator looks into a short circuit, and nearly so at high
>> loads, such as your headlights or a storage battery. The diodes, of
>> course, prevent reverse current. I used to isolate the alternator and
>> fiddle the voltage regulator to run 110-volt power tools. With no
>> battery and no voltage regulator, the headlights would blow. As long as
>> a battery was in place, it set the system voltage.
>
> I remember ads for boxes that would let you run 110VDC power
> tools off the alternator. (I don't remember if the ad specified DC,
> though.)
DC it was. Power drills and such have AC/DC motors. Without the
rectifiers, the frequency would be too high to get significant current
through the tool inductances.
> At some point, I figured out that it wasn't quite as useful
> as could be, and wanted a real power inverter. (A favorite
> project for Popular Science and Popular Electronics over
> the years.)
More useful and more costly. What else is new? :-)
> First year college, my dad bought a boat. With the excuse of
> needing one to shave (electric, non-battery razor) I bought
> the Heathkit power inverter. I still have that one.
>
> It won't run most power tools, though, but still enough things
> to make it useful.
I have a few 75W units that work off the cigarette-lighter outlet, and a
600W unit with clip leads to the battery. Nice!
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by glen herrmannsfeldt●October 15, 20122012-10-15
Jerry Avins <jya@ieee.org> wrote:
(snip) (also, I probably should have changed the subject along the way)
> An alternator with fixed field excitation has an equivalent circuit that
> consists of an inductor in series with an AC source whose voltage and
> frequency are both proportional to rpm. (The magnetic field due to the
> armature current directly opposes the excitation field. the equivalent
> circuit follows from that.) The result is that the current is constant
> when the alternator looks into a short circuit, and nearly so at high
> loads, such as your headlights or a storage battery. The diodes, of
> course, prevent reverse current. I used to isolate the alternator and
> fiddle the voltage regulator to run 110-volt power tools. With no
> battery and no voltage regulator, the headlights would blow. As long as
> a battery was in place, it set the system voltage.
I remember ads for boxes that would let you run 110VDC power
tools off the alternator. (I don't remember if the ad specified DC,
though.)
At some point, I figured out that it wasn't quite as useful
as could be, and wanted a real power inverter. (A favorite
project for Popular Science and Popular Electronics over
the years.)
First year college, my dad bought a boat. With the excuse of
needing one to shave (electric, non-battery razor) I bought
the Heathkit power inverter. I still have that one.
It won't run most power tools, though, but still enough things
to make it useful.
-- glen
Reply by glen herrmannsfeldt●October 15, 20122012-10-15
Jerry Avins <jya@ieee.org> wrote:
(snip)
> The disconnect relay that you cite is called a reverse-current cutout. I
> don't know why it could be expected to fuse, but as I wrote, it can make
> a big loud spark. It has both a voltage coil in shunt with the generator
> and a current coil in series with it. The way it works, the voltage on
> the disconnected generator builds up enough to pull the relay in on the
> voltage coil alone. When it pulls in, current flows to the battery
> through the current coil, increasing the field that's pulling the relay
> in. When the generator slows enough for the current to reverse, the
> series and shunt fields buck instead of adding, and the relay drops out.
> So why did the Karmann-Ghia generator work after I pulsed the cutout by
> hand? Hint: think residual field.
For it to work in the first place, the genertor has to supply some
voltage with no field current. There is enough "permanent magnet"
magnetization in the generator to do that. The first time you power
it up the other way, it will reverse that field.
> Those DC generators needed not only the reverse-current cutout,
> but also voltage and current regulators. The three relays in
> the box performed one function each. An alternator needs at
> most a voltage regulator, and can get by without even that.
> How come?
The battery will keep the voltage pretty constant, until it
dries up. Excess current electrolizes more water, making more
hydrogen and oxygen, and less water. The chemistry of older
batteries wasn't so good, and it was normal to add water every
so often. Now, many are sealed with no water caps.
-- glen
Reply by Jerry Avins●October 15, 20122012-10-15
On 10/15/2012 12:42 PM, clay@claysturner.com wrote:
>> Those DC generators needed not only the reverse-current cutout, but
>> also voltage and current regulators. The three relays in the box
>> performed one function each. An alternator needs at most a voltage
>> regulator, and can get by without even that. How come?
>>
>>
> My motocycle's alternator would run in saturation. The main current
> draw was for the lights which were always on.
>
> Clay
An alternator with fixed field excitation has an equivalent circuit that
consists of an inductor in series with an AC source whose voltage and
frequency are both proportional to rpm. (The magnetic field due to the
armature current directly opposes the excitation field. the equivalent
circuit follows from that.) The result is that the current is constant
when the alternator looks into a short circuit, and nearly so at high
loads, such as your headlights or a storage battery. The diodes, of
course, prevent reverse current. I used to isolate the alternator and
fiddle the voltage regulator to run 110-volt power tools. With no
battery and no voltage regulator, the headlights would blow. As long as
a battery was in place, it set the system voltage.
Jerry
--
"The rights of the best of men are secured only as the
rights of the vilest and most abhorrent are protected."
- Chief Justice Charles Evans Hughes, 1927
���������������������������������������������������������������������
Reply by ●October 15, 20122012-10-15
>
> Those DC generators needed not only the reverse-current cutout, but also
>
> voltage and current regulators. The three relays in the box performed
>
> one function each. An alternator needs at most a voltage regulator, and
>
> can get by without even that. How come?
>
>
My motocycle's alternator would run in saturation. The main current draw was for the lights which were always on.
Clay
Reply by Jerry Avins●October 15, 20122012-10-15
On 10/15/2012 3:07 AM, glen herrmannsfeldt wrote:
> Jerry Avins <jya@ieee.org> wrote:
>
> (snip)
>>>>> Few basic questions on DFT:
>
>>>>> 1) what is the signifiance of -ve amplitude in frequency domain
>
>>>> If I tell you that my car battery reads -13 volts, what does that mean
>>>> to you?
>
>>> That you installed it backwards, at least on any car that I
>>> know about currently.
>
>> Do you know that the ted lead of my VOM isn't connected to ground?
>
> Yes, I wasn't so sure what you meant, but the usual way of
> measuring car voltage is relative to the frame ground.
>
>>> When I was younger, in the 1960's, my dad had a collection
>>> of Popular Science (1962 to about 1974) that I would sometimes
>>> read. One of my favorite to read was about Gus the auto mechanic.
>
>> One story, "Gus and the Backward Battery" I still remember.
>
> (snip)
>
>>> Sometime later, Gus figures out what happens and goes out to
>>> chase him down to tell him not to turn off the ignition.
>>> Among the things reported when he came by the shop was that
>>> the car radio didn't work anymore.
>
>> I am reminded of the night I helped a buddy replace his VW's generator
>> with one from a Karmann-Ghia. With only a little fudging, it fit.
>> Everything looked good when I showed up, but it wouldn't charge. I went
>> over the wiring twice and everything was in place, So I removed the
>> cover of the voltage regulator and pushed in the reverse-current by
>> hand. Even though I knew what was coning, the sparks made me jump. My
>> buddy looked like he wanted to clobber me. I said to try it now, and he
>> did, and it charged. He wanted to know what the fix was, but I was
>> annoyed enough to tell him only that the generator turned the other way
>> in its previous home. He eventually figured out why the fix worked.
>
> Trying to remember the Gus story "why" from about 40 years ago,
> the battery was so far discharged, that when jump started
> in the wrong polarity (I suppose it was a positive ground car)
> that the battery just recharged the other way around.
> (Lead-acid can do that, most others can't.) The field current also
> changed sign, so that the battery was now being charged in the
> new polarity. (Cars with alternators wouldn't do that.)
>
> But there has to be a relay to disconect the battery from the
> generator when it isn't running. (No diodes, like on an alternator.)
> As I remember it, that relay fused closed when charged backwards,
> so if the car stopped without disconnecting something the battery
> would discharge very quickly through the generator, likely with
> something melting. As I remember it, there were three relays in
> the voltage regulator, but I don't remember what they do.
>
> Besides the Popular Science, the story goes that one of the
> first books I read was the service manual for the 1960 Dodge
> that my dad bought (in 1960) when I was two years old.
> Well, maybe I mostly looked at the pictures.
By 1960, Dodge lightened the sheet metal considerably. My 1947 Dodge
(bought in 1951) was built like a tank. I broadsided a police car that
had run a stop sign, smashing the left rear door, removing the rear
fender and leaving the rear bumper dangling. My grille remained intact.
The disconnect relay that you cite is called a reverse-current cutout. I
don't know why it could be expected to fuse, but as I wrote, it can make
a big loud spark. It has both a voltage coil in shunt with the generator
and a current coil in series with it. The way it works, the voltage on
the disconnected generator builds up enough to pull the relay in on the
voltage coil alone. When it pulls in, current flows to the battery
through the current coil, increasing the field that's pulling the relay
in. When the generator slows enough for the current to reverse, the
series and shunt fields buck instead of adding, and the relay drops out.
So why did the Karmann-Ghia generator work after I pulsed the cutout by
hand? Hint: think residual field.
Those DC generators needed not only the reverse-current cutout, but also
voltage and current regulators. The three relays in the box performed
one function each. An alternator needs at most a voltage regulator, and
can get by without even that. How come?
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by glen herrmannsfeldt●October 15, 20122012-10-15
Jerry Avins <jya@ieee.org> wrote:
(snip)
> >>> Few basic questions on DFT:
> >>> 1) what is the signifiance of -ve amplitude in frequency domain
> >> If I tell you that my car battery reads -13 volts, what does that mean
> >> to you?
> > That you installed it backwards, at least on any car that I
> > know about currently.
> Do you know that the ted lead of my VOM isn't connected to ground?
Yes, I wasn't so sure what you meant, but the usual way of
measuring car voltage is relative to the frame ground.
> > When I was younger, in the 1960's, my dad had a collection
> > of Popular Science (1962 to about 1974) that I would sometimes
> > read. One of my favorite to read was about Gus the auto mechanic.
> One story, "Gus and the Backward Battery" I still remember.
(snip)
> > Sometime later, Gus figures out what happens and goes out to
> > chase him down to tell him not to turn off the ignition.
> > Among the things reported when he came by the shop was that
> > the car radio didn't work anymore.
> I am reminded of the night I helped a buddy replace his VW's generator
> with one from a Karmann-Ghia. With only a little fudging, it fit.
> Everything looked good when I showed up, but it wouldn't charge. I went
> over the wiring twice and everything was in place, So I removed the
> cover of the voltage regulator and pushed in the reverse-current by
> hand. Even though I knew what was coning, the sparks made me jump. My
> buddy looked like he wanted to clobber me. I said to try it now, and he
> did, and it charged. He wanted to know what the fix was, but I was
> annoyed enough to tell him only that the generator turned the other way
> in its previous home. He eventually figured out why the fix worked.
Trying to remember the Gus story "why" from about 40 years ago,
the battery was so far discharged, that when jump started
in the wrong polarity (I suppose it was a positive ground car)
that the battery just recharged the other way around.
(Lead-acid can do that, most others can't.) The field current also
changed sign, so that the battery was now being charged in the
new polarity. (Cars with alternators wouldn't do that.)
But there has to be a relay to disconect the battery from the
generator when it isn't running. (No diodes, like on an alternator.)
As I remember it, that relay fused closed when charged backwards,
so if the car stopped without disconnecting something the battery
would discharge very quickly through the generator, likely with
something melting. As I remember it, there were three relays in
the voltage regulator, but I don't remember what they do.
Besides the Popular Science, the story goes that one of the
first books I read was the service manual for the 1960 Dodge
that my dad bought (in 1960) when I was two years old.
Well, maybe I mostly looked at the pictures.
-- glen
Reply by Jerry Avins●October 15, 20122012-10-15
On 10/14/2012 7:20 PM, glen herrmannsfeldt wrote:
> Jerry Avins <jya@ieee.org> wrote:
>> On 10/13/2012 10:47 PM, manishp wrote:
>
>>> Few basic questions on DFT:
>
>>> 1) what is the signifiance of -ve amplitude in frequency domain
>
>> If I tell you that my car battery reads -13 volts, what does that mean
>> to you?
>
> That you installed it backwards, at least on any car that I
> know about currently.
Do you know that the ted lead of my VOM isn't connected to ground?
> When I was younger, in the 1960's, my dad had a collection
> of Popular Science (1962 to about 1974) that I would sometimes
> read. One of my favorite to read was about Gus the auto mechanic.
>
> One story, "Gus and the Backward Battery" I still remember.
>
> You probably have to know some about cars in the 60's to
> understand (likely Jerry is one), but as the story goes one
> of Gus' regular customers comes by after jump starting his
> car that had an almost completely dead battery.
>
> Sometime later, Gus figures out what happens and goes out to
> chase him down to tell him not to turn off the ignition.
> Among the things reported when he came by the shop was that
> the car radio didn't work anymore.
I am reminded of the night I helped a buddy replace his VW's generator
with one from a Karmann-Ghia. With only a little fudging, it fit.
Everything looked good when I showed up, but it wouldn't charge. I went
over the wiring twice and everything was in place, So I removed the
cover of the voltage regulator and pushed in the reverse-current by
hand. Even though I knew what was coning, the sparks made me jump. My
buddy looked like he wanted to clobber me. I said to try it now, and he
did, and it charged. He wanted to know what the fix was, but I was
annoyed enough to tell him only that the generator turned the other way
in its previous home. He eventually figured out why the fix worked.
Jerry
P.S. Solution on request.
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by glen herrmannsfeldt●October 14, 20122012-10-14
Jerry Avins <jya@ieee.org> wrote:
> On 10/13/2012 10:47 PM, manishp wrote:
> > Few basic questions on DFT:
> > 1) what is the signifiance of -ve amplitude in frequency domain
> If I tell you that my car battery reads -13 volts, what does that mean
> to you?
That you installed it backwards, at least on any car that I
know about currently.
When I was younger, in the 1960's, my dad had a collection
of Popular Science (1962 to about 1974) that I would sometimes
read. One of my favorite to read was about Gus the auto mechanic.
One story, "Gus and the Backward Battery" I still remember.
You probably have to know some about cars in the 60's to
understand (likely Jerry is one), but as the story goes one
of Gus' regular customers comes by after jump starting his
car that had an almost completely dead battery.
Sometime later, Gus figures out what happens and goes out to
chase him down to tell him not to turn off the ignition.
Among the things reported when he came by the shop was that
the car radio didn't work anymore.
-- glen