Re: A three Phase question please

开云体育

John,
Your method relies on the vectorial sum of voltages and sum of currents in the branches being zero, which is the case in a delta or floating-Y connection.
But? when both the source and load are Y-connected and there's a neutral conductor with unbalanced phases, the ammeters in branch A & B have no way to know the current in C.
The latter being the most common case, I still think the triple meter method is the least prone to errors.

Le 24/12/2013 09:00, John Woodgate a écrit?:

Show quoted text

?

In message
, dated
Tue, 24 Dec 2013, jim.klessig@... writes:

>Won?t work properly for a wye connected system.
>You could have infinite power flow on the third phase [Ph C]
>with current return on the neutral, and you can?t tell the difference.
>?
Only if the other two phases are **open-circuit**, in which case, it's a
single-phase system.
--
OOO - Own Opinions Only. With best wishes. See
Nondum ex silvis sumus
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

power dependent resistor - thermodynamic model

#68835

Hello,

I'm trying to simulate (transient run) a power dependant resistor, the resistor is used to dump an high energy capacitive bank (like an RLC circuit). During the fast discharge, the resistor temperature rises due to Joule effect and it's value change.
I think to use behavioural source to model the resistor.
What I'm not able to do is to get the power variation (between 2 time steps ?) in order to calculate the temperature rise: delta RxI? = mass x heat capacity x delta Temperature. Then i will use the temperature to compute the resistance (Temperature don't need to be linked with the LTSpice Temp variable).

Any tips ? Even if it's not the appropriate method I'm sure that ltspice is able to do it !
This is a common for power electronics ...

Thanks for your help or comments !!

Micha

Re: A three Phase question please

John Woodgate

#68833

In message
<FDCC225ADA75E84DABFCD1B05EE2FC2B0140DD@...>, dated
Tue, 24 Dec 2013, jim.klessig@... writes:

Won?t work properly for a wye connected system.
You could have infinite power flow on the third phase [Ph C]
with current return on the neutral, and you can?t tell the difference.
?Only if the other two phases are **open-circuit**, in which case, it's a
single-phase system.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Nondum ex silvis sumus
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

Re: JFET Model

John Woodgate

#68832

In message <1932965163.4191125.1387841577938.JavaMail.root@...>,
dated Mon, 23 Dec 2013, Jim Wagner <wagnejam99@...> writes:

But, suffice it to say, the frequency change with supply voltage is
real. Further, the frequency change is due to changes in Miller
Capacitance. Finally, change in Miller Capacitance is due to gain
change AND due to changes in Cdg.?Agreed, but how big is the effect likely to be?
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Nondum ex silvis sumus
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

Re: Reference Information

#68831

Received my purchased copy today!!!

Re: UC1845A SPICE model?

#68830

I am sure LTC has the part. I used it. Even posted a SEPIC converter based on it. Jack

Sent from my BlackBerry? by Boost Mobile

From: <charles@...>

Sender: LTspice@...

Date: 23 Dec 2013 16:05:42 -0800

To: <LTspice@...>

ReplyTo: LTspice@...

Subject: [LTspice] RE: UC1845A SPICE model?

You can purchase the official model (original creators of the model) at?

Re: A three Phase question please

#68829

Jim,

If you implement the 2 wattmeter method correctly it works fine.? If one phase has a huge power, it doesn't matter.

Rick

Re: UC1845A SPICE model?

#68828

Same chip

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From: <helmutsennewald@...>

Sender: LTspice@...

Date: 23 Dec 2013 16:20:41 -0800

To: <LTspice@...>

ReplyTo: LTspice@...

Subject: [LTspice] RE: UC1845A SPICE model?

Hello Ken,

Some UC384x models can be found here.

http://groups.yahoo.com/neo/groups/LTspice/files/adventures_with_analog/my%20model%20files/

Maybe the UC3845 is similar to the UC1845.

Best regards,
Helmut

Re: UC1845A SPICE model?

#68825

Hello Ken,

Some UC384x models can be found here.

http://groups.yahoo.com/neo/groups/LTspice/files/adventures_with_analog/my%20model%20files/

Maybe the UC3845 is similar to the UC1845.

Best regards,
Helmut

Re: UC1845A SPICE model?

#68827

Charles,

The cost is ridiculous unless you work for a large company that really needs it and can afford it.? Someone familiar with LTspice who understands PWM ICs could build a useful model in a couple of hours.

Rick

On Monday, December 23, 2013 6:05 PM, "charles@..." wrote:

You can purchase the official model (original creators of the model) at?

Re: A three Phase question please

[email protected]

#68826

开云体育

Some one said

“In real life, use two wattmeters. Call the phases A, B and C. One meter
has its current coil in phase A and its voltage coil between A and C.
The other meter has its current coil in phase B and its voltage coil
between B and C. The power is the sum of the two meter readings.

This works for a balanced or unbalanced load, star/wye or delta
肠辞苍苍别肠迟别诲.”

Won’t work properly for a wye connected system.

You could have infinite power flow on the third phase [Ph C]

with current return on the neutral, and you can’t tell the difference.

?

For the OP, google two element, two and ? element, and 3 element watt meters for help.

?

?

Re: UC1845A SPICE model?

#68824

You can purchase the official model (original creators of the model) at?

Re: JFET Model

#68823

You need to be careful about equating a JFET and a vacuum tube directly. Yes, they are very similar, but there are some very important physical differences. Because the frequency changes for one reason with a tube, that does not mean that the change is caused by exactly the same thing in a JFET.

As far as the cause being "Miller Effect", it is likely that gain change may be the dominant effect in a tube. But, in a JFET, it is likely to be both. To call one more "Miller Effect" than the other is false. Both are. Because Miller Capacitance depends on BOTH gain and internal inter-electrode capacitance plus any circuit capacitance. Inter-electrode C WILL change significantly with a JFET (and even more in a MOSFET) with electrode voltage. In fact, it will change as the signal voltage swings up and down so that it is time varying at the signal frequency. This makes detailed analysis quite complex. But, suffice it to say, the frequency change with supply voltage is real. Further, the frequency change is due to changes in Miller Capacitance. Finally, change in Miller Capacitance is due to gain change AND due to changes in Cdg.?

Jim Wagner

Oregon Research Electronics

KA7EHK

Show quoted text

From: "Chris Maness"
To: LTspice@...
Sent: Monday, December 23, 2013 2:47:35 PM
Subject: Re: [LTspice] RE: JFET Model

So would the change in gain due the change in B+ be the most likely cause of f_o change for a Clapp oscillator with a valve state amplifier?? The reason for the inquiry is at this point mostly academic.? I love learning things as I work my way through fixing an old radio.? If indeed that is the case, then it would be the Miller effect indirectly.

Thanks,
Chris KQ6UP

Re: A three Phase question please

John Woodgate

#68822

In message <l9afub+10tlbe4@...>, dated Mon, 23 Dec 2013,
sawreyrw@... writes:

The 2 wattmeter method will work, but to avoid building a model of the
wattmeters, it?would easier?to simply use the LTspice power plotting
feature.? You can easily get a numerical display of the power.? To get
total power you need to add the power in each phase.The OP asked how to do it in real life, and that is what I posted.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Nondum ex silvis sumus
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

Re: JFET Model

John Woodgate

#68821

In message
<CANnsUMHruA-cbtCW3yswZaaKDayat7KKSm1wdPE3YZpvtmrAww@...>,
dated Mon, 23 Dec 2013, Chris Maness <chris@...> writes:

So would the change in gain due the change in B+ be the most likely
cause of f_o change for a Clapp oscillator with a valve state
amplifier?? The reason for the inquiry is at this point mostly
academic.? I love learning things as I work my way through fixing an
old radio.? If indeed that is the case, then it would be the Miller
effect indirectly.One way to tell is to analyse the circuit in detail, or you could try to
find Clapp's original paper:

J. K. Clapp, "An inductance-capacitance oscillator of unusual frequency
stability", Proc. IRE, vol. 367, pp. 356-358, Mar. 1948.

For analysis, look at the size of the a-g1 capacitance compared with the
tuning capacitor (the 'capacitance tap' capacitors should be so much larger that their effect is negligible). The consider what internal gain
would  be needed for a small change in the Cag to affect the frequency
by say 1 kHz. If that turns out to give a gain of 10 000, you can be
pretty sure that you don't have a Miller effect problem.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Nondum ex silvis sumus
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

Re: A three Phase question please

#68820

John,

The 2 wattmeter method will work, but to avoid building a model of the wattmeters, it?would easier?to simply use the LTspice power plotting feature.? You can easily get a numerical display of the power.? To get total power you need to add the power in each phase.

Rick

Re: JFET Model

#68819

Jim,

The standard LTspice JFET model includes 2 nonlinear caps.

Rick

Re: JFET Model

#68818

So would the change in gain due the change in B+ be the most likely cause of f_o change for a Clapp oscillator with a valve state amplifier?? The reason for the inquiry is at this point mostly academic.? I love learning things as I work my way through fixing an old radio.? If indeed that is the case, then it would be the Miller effect indirectly.

Thanks,
Chris KQ6UP

On Dec 23, 2013 2:29 PM, "John Woodgate" <jmw@...> wrote:

Show quoted text

In message
<CANnsUMFiEqEOs9Si0pke8F-9R34KDT+DGL8kOgkA3oN15_WQ-g@...>,
dated Mon, 23 Dec 2013, Chris Maness <chris@...> writes:

>A friend of mind sites the miller effect as being the reason for f_o
>shift. ?I will have to read up to see if this is indeed the case.

Miller effect is feedback via the anode-to-control grid capacitance. It
can depend on B+ voltage if the stage gain changes with B+ voltage. I
doubt that it does very much in a JFET, operating in 'FET saturation'
(pentode region), which is not the same as bipolar 'saturation'
(bottomed). And the drain-gate capacitance is much smaller anyway than
in some tubes (you need to take external strays into account because of
the physical size difference).
--
OOO - Own Opinions Only. With best wishes. See
Nondum ex silvis sumus
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: JFET Model

John Woodgate

#68817

In message <CANnsUMFiEqEOs9Si0pke8F-9R34KDT+DGL8kOgkA3oN15_WQ-g@...>, dated Mon, 23 Dec 2013, Chris Maness <chris@...> writes:

A friend of mind sites the miller effect as being the reason for f_o shift.  I will have to read up to see if this is indeed the case.Miller effect is feedback via the anode-to-control grid capacitance. It can depend on B+ voltage if the stage gain changes with B+ voltage. I doubt that it does very much in a JFET, operating in 'FET saturation' (pentode region), which is not the same as bipolar 'saturation' (bottomed). And the drain-gate capacitance is much smaller anyway than in some tubes (you need to take external strays into account because of the physical size difference).
-- 
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Nondum ex silvis sumus
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

Re: JFET Model

#68816

In this case, "Miller Effect" capacitance is just the gate-drain capacitance multiplied by the stage gain. Miller capacitance won't change unless one or the other (gain, or Cdg) changes. Cdg WILL change with drain voltage. I am not sure, but it is pretty likely that the JFET spice model does not include the voltage dependency of Cdg. If so, this is NOT unique failing of LTspice because all of the spice simulators tend to share model definitions.

Jim Wagner

Oregon Research Electronics

Show quoted text

From: "Chris Maness"
To: LTspice@...
Sent: Monday, December 23, 2013 1:25:54 PM
Subject: Re: [LTspice] RE: JFET Model

The frequency does change in real life. I am working with the design
limits of late 1950's technology. The radio in question uses an OA2
for a shunt regulator. I thought of replacing it with a high voltage
zener, but they can't handle 15mA of shunt current. They also
probably have even worse regulating properties than the venerable OA2
Argon discharge tube. A friend of mind sites the miller effect as
being the reason for f_o shift. I will have to read up to see if this
is indeed the case.

Regards,
Chris KQ6UP

On Mon, Dec 23, 2013 at 1:08 PM, John Woodgate wrote:
> In message
> > dated Mon, 23 Dec 2013, Chris Maness writes:
>
>>. I was trying to see how changing voltage changes the resonant
>>frequency.
>
> It ought not to in real life, of course. If it does, it's due to some
> second or third order effect in the tube, such as a change in effective
> inter-electrode capacitance. Your tube had 4 or 5 electrodes, too,
> whereas the JFET has only 3 (or you could say just 2, because drain and
> source are interchangeable).
>
>>I guess spice doesn't model that though. Changing B+ has no effect on
>>freq in spice
>
> The same sort of effect on capacitances might occur in a JFET, and the
> model might or might not include that. If it includes it, then LTspice
> will, of course, take it into account. BUT the effect would probably be
> much smaller that for a tube, so the frequency shift would be
> correspondingly smaller.
> --
> OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
> Nondum ex silvis sumus
> John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
>
>
> ------------------------------------
>
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