# Current source

H

#### Hamidreza Shaiganfar

Jan 1, 1970
0
Dear friends,

I am trying to design an AC current source with power of 1kVA. Anyone
who has an idea I will be appreciated to know it.
Thanks

M

#### mike

Jan 1, 1970
0
Hamidreza said:
Dear friends,

I am trying to design an AC current source with power of 1kVA. Anyone
who has an idea I will be appreciated to know it.
Thanks

I have these little sockets in every wall that meet your specification,
not to be confused with your requirements which were not disclosed.
You probably have them too.

Or maybe, for those of us who don't have the psychic hotline on speed
dial, you could quantify some of those pesky little requirement
parameters like frequency, voltage, current, minimum source impedance
input power source parameters, and, and, and.
mike

--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
4in/400Wout ham linear amp.
Honda CB-125S
400cc Dirt Bike 2003 miles $550 Color LCD overhead projector Tek 2465$800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/

S

Jan 1, 1970
0
Hamidreza Shaiganfar said:
Dear friends,

I am trying to design an AC current source with power of 1kVA. Anyone
who has an idea I will be appreciated to know it.
Thanks

Generator, Inverter!

J

#### Jim Large

Jan 1, 1970
0
mike said:
Hamidreza said:
Dear friends,

I am trying to design an AC current source with power
of 1kVA. [...]

I have these little sockets in every wall that meet
your specification, not to be confused with your
requirements which were not disclosed. [...]
You probably have them too.

Strange, I have little sockets like that in my house too,
but mine are voltage sources, not current sources.

-- Jim L.

P

#### Peter Meyer

Jan 1, 1970
0
Hello,
Jim Large said:
mike said:
Hamidreza said:
Dear friends,

I am trying to design an AC current source with power
of 1kVA. [...]

I have these little sockets in every wall that meet
your specification, not to be confused with your
requirements which were not disclosed. [...]
You probably have them too.

Strange, I have little sockets like that in my house too,
but mine are voltage sources, not current sources.

-- Jim L.
No use being flippant...
Have you tried a short over those little "sockets"? V=0 and I=destructive!
Peter

S

#### Spehro Pefhany

Jan 1, 1970
0
mike said:
Hamidreza said:
Dear friends,

I am trying to design an AC current source with power
of 1kVA. [...]

I have these little sockets in every wall that meet
your specification, not to be confused with your
requirements which were not disclosed. [...]
You probably have them too.

Strange, I have little sockets like that in my house too,
but mine are voltage sources, not current sources.

Haven't you heard? The evil French Léon Charles Thévenin* has been
replaced with Mr. Norton.

*Althought some claim Helmholtz did it first anyhow.

Best regards,
Spehro Pefhany

A

#### Animesh Maurya

Jan 1, 1970
0
Thanks to all for that nice discussion.

I still remember those primary classes, where I studied that voltage
difference is necessary to make the current flow in the circuit.

Current source consists only current so how they are able to make the
current flow?

Or the voltage drop first occurs across parallel Thevenin Resistance
(in Norton Equivalent) which facilitates the current flow.

All seems to be silly & confusing!

Animesh Maurya

D

#### default

Jan 1, 1970
0
Dear friends,

I am trying to design an AC current source with power of 1kVA. Anyone
who has an idea I will be appreciated to know it.
Thanks
I take it you mean current limited AC source? Several ways to do it.

Fuse the circuit. Fuse the circuit with a resetable circuit breaker.

Connect a variable transformer (variac) in series with the load and
adjust the current manually. Or design a motor drive if speed of
response isn't a consideration, and it needs to be automatic.

Build an inverter, sense current, limit drive when current is
exceeded.

Wind a transformer with a magnetic shunt. Core is rectangular with
the primary on one side secondary on the other, in between is a gapped
magnetic shunt (laminations). Secondary tries to draw too much
current and the magnetic path finds it easier to get through the
shunt. Works well with a sharp "knee," good efficiency, high
reliability. Downside is big heavy expensive - unless you do it
yourself.

Use a DC current limiter and put it between the plus and minus of a
bridge rectifier. Wire the bridge in series with the load.

Design a phase control circuit and limit the firing angle as current
increases.

You would do better to post what you hope to accomplish as the end
goal in this endeavor. There may be a way to do it that doesn't
involve limiting AC current.

R

#### Reg Edwards

Jan 1, 1970
0
Insofar as low load resistances are concerned, a current source is a high
voltage in series with high resistance.

With an accuracy of 0.1 percent or better, a 1 megohm resistance in series
with 1000 volts behaves as a 1 milliamp constant current source to variable

It's such a simple idea some people can't believe it. But you are not one
of them are you?

Forget about Norton and Thevenin. Neither of them are of much use except to
make speakers sound clever to an ill-educated audience. Ohm is good enough
for most things. He allows you to invent your own theorems to fit your own
immediate applications.

J

#### John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Animesh Maurya
Current source consists only current so how they are able to make the
current flow?

A current source can be modelled as a generator in series with a very
high resistance. With no load on the output, the generator voltage
appears there.

B

#### Ban

Jan 1, 1970
0
Dear friends,

Reg said:
Insofar as low load resistances are concerned, a current source is a
high voltage in series with high resistance.

With an accuracy of 0.1 percent or better, a 1 megohm resistance in
series with 1000 volts behaves as a 1 milliamp constant current

It's such a simple idea some people can't believe it. But you are
not one of them are you?

somehow I have the feeling the OP doesn't even know what a current source
is, (he talks about 1kVA) sounds more like an Inverter 24V->120V~ or
something to me. At his level of knowledge it seems highly unprobable he
manages more than typing above question.
Or maybe it is a software guy?

ciao Ban

P

#### Paul Hovnanian P.E.

Jan 1, 1970
0
Animesh said:
Thanks to all for that nice discussion.

I still remember those primary classes, where I studied that voltage
difference is necessary to make the current flow in the circuit.

Current source consists only current so how they are able to make the
current flow?

Current (and voltage) sources are theoretical devices.

A voltage source will produce its 'rated' voltage across either an open
circuit, which isn't a big deal. Or it will produce its rated voltage
across a zero ohm conductor, which is impossible in the practical world,
since that results in an infinite current.

Likewise, a current source will produce a current through an impedance,
including an open circuit. This will result in an infinite voltage.

In real life, each of these sources is incorporated into a circuit model
with the appropriate series (for a voltage source) or shunt (for a
current source) impedance, which gives the model a behavior that
approximates a real world circuit.

On the other hand, there are no real world circuits that behave exactly
as a pure current or voltage source.
Or the voltage drop first occurs across parallel Thevenin Resistance
(in Norton Equivalent) which facilitates the current flow.

The purpose of the Thevenin and Norton equivalent circuits is only to
analyze their behavior at the circuit terminals. You can calculate what
might be going on inside each circuit, but that isn't necessary and
doesn't correspond to anything that would occur in real hardware.
All seems to be silly & confusing!

Just wait until you whip out the old Simpson multimeter and try to
measure an imaginary voltage. ;-)

J

#### Jim Large

Jan 1, 1970
0
Peter said:
Hello,

No use being flippant...
Have you tried a short over those little "sockets"?
V=0 and I=destructive!

Tried? No I've never tried. I've DONE it plenty of times,
to measure the voltage. My gut feeling though, is that the
AC mains are a lot more like a voltage source than a current
source. The voltage is around 125 volts RMS when nothing's
plugged in, and it's around 125 volts RMS when I've got air
conditioners running and hair dryers running and etc. Heck,
I've even lived in places where we heated the apartment with
electricity -- fifty or sixty amps -- and the voltage was

-- Jim L.

W

#### Winfield Hill

Jan 1, 1970
0
Jim Large wrote...
I've even lived in places where we heated the apartment with
electricity -- fifty or sixty amps -- and the voltage was

Probably dropped about say 5V at 50A, implying a current of
over 1200A into a full short on the electric-heater lines.
For a few milliseconds that is.

Thanks,
- Win

whill_at_picovolt-dot-com

K

#### Ken Taylor

Jan 1, 1970
0
Jim Large said:
Tried? No I've never tried. I've DONE it plenty of times,
to measure the voltage. My gut feeling though, is that the
AC mains are a lot more like a voltage source than a current
source. The voltage is around 125 volts RMS when nothing's
plugged in, and it's around 125 volts RMS when I've got air
conditioners running and hair dryers running and etc. Heck,
I've even lived in places where we heated the apartment with
electricity -- fifty or sixty amps -- and the voltage was

-- Jim L.
Yep, them generators don't slow down much no matter how many people park
'emselves across the socket!

Ken

J

#### John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Jim Large <[email protected]>
My gut feeling though, is that the
AC mains are a lot more like a voltage source than a current
source. The voltage is around 125 volts RMS when nothing's
plugged in, and it's around 125 volts RMS when I've got air
conditioners running and hair dryers running and etc. Heck,
I've even lived in places where we heated the apartment with
electricity -- fifty or sixty amps -- and the voltage was

The source impedance at a US mains socket is around 0.3 ohms.

N

#### Norm Dresner

Jan 1, 1970
0
John Woodgate said:
I read in sci.electronics.design that Jim Large <[email protected]>

The source impedance at a US mains socket is around 0.3 ohms.
--

Not to be too argumentative, but where does this number come from?
There have to be so many variables entering into the impedance like the kind
of service, the wiring, and even concurrent loads, that I can't believe that
this is anything but a rough estimate.

Norm

M

#### Michael A. Terrell

Jan 1, 1970
0
John said:
I read in sci.electronics.design that Jim Large <[email protected]>

The source impedance at a US mains socket is around 0.3 ohms.
--

And DO NOT try to measure it with an ohm meter!

Hello John ;-)

B

Jan 1, 1970
0
In sci.electronics.design said:
mike said:
Hamidreza said:
Dear friends,

I am trying to design an AC current source with power
of 1kVA. [...]

I have these little sockets in every wall that meet
your specification, not to be confused with your
requirements which were not disclosed. [...]
You probably have them too.

Strange, I have little sockets like that in my house too,
but mine are voltage sources, not current sources.

Oh yeah, well the ones in MY house are sources of both AC voltage
AND AC current!
The Thevenin equivalent is about 120VAC with less than an ohm
resistance. The Norton equivalent is, well, a huge waste of electrical
power.

G

#### Glen Walpert

Jan 1, 1970
0
Not to be too argumentative, but where does this number come from?
There have to be so many variables entering into the impedance like the kind
of service, the wiring, and even concurrent loads, that I can't believe that
this is anything but a rough estimate.

The actual impedance at any "mains socket" varies widely, and could be
calculated fairly easily if you know the transformer rating and how
much of what size wire is between the transformer and receptacle; this
is routinely done in large industrial distribution systems but
essentially never for residential distribution because the available
fault current is limited to less than 10,000 amps, and you cannot buy
listed distribution components rated for a lower fault current. The
10 kA limit on 240 VAC implies a lower limit of .024 ohms at the
service entry, add to that the resistance of the wire between the
panel and the receptacle for the worst case impedance at a given
receptacle.

The nameplates on some "pole-pig" distribution transformers can be
read with binoculars from the ground, and the maximum fault current
from any distribution transformer with the worst case "infinite bus"
assumption (input voltage does not drop during fault) is the nameplate
rated current divided by the impedance factor, typically 0.05 or a bit
less (often expressed as percentage eg 5%).

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