I do not follow how the set point can be the operating temperature. How is
this inputting to the comparator? Are you proposing some external heat source
which remains constant at that temperature? For a loop to function it must
have a reference that does not change with the controlled parameter. If this
is not the case, then the temperature will drift toward one of its limits.
The beauty of positive feedback is that this type of behavior is exactly what
you desire. As long as you can reverse the drift direction periodically you
are in control.
Dave
-----Original Message-----
From: Andrew <andrew...@att.net>
To: vortex-l <vortex-l@eskimo.com>
Sent: Mon, May 27, 2013 2:23 pm
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
Sure, the reference would be the set point, and that's simply the operating
temperature. Notionally you set this as high as possible, consistent with
materials integrity and the ability to regulate a strongly
intrinsically-positive feedback system (the device itself). The idea is that
you end up with Kp*Kn <= 1, where Kp is the intrinsic positive feedback gain
(>1, and becoming higher at higher temperature), and Kn is the negative
feedback gain (<1, representing the characteristics of the active cooling
system). Of course, it's more complex than that due to first (and higher) order
time differentials, and an integral term due to stored heat energy, but that's
the basic proportional rule.
Designing that would be fun. The most fun I had in my 40+ engineering career
was designing industrial robots. Right now, I'm looking for a new job.
Andrew
----- Original Message -----
From: David Roberson
To: vortex-l@eskimo.com
Sent: Monday, May 27, 2013 10:49 AM
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
Rossi keeps this information secret. It is unfortunate that he does this,
but that is his nature. I would love to see a number of measurements
associated with his material, but all questions of that sort are blocked due
to IP concerns.
It is frustrating to be kept at arms length from such important and history
making knowledge.
You mention active cooling in the context of negative feedback and I suppose
that might be somewhat applicable. Systems can be stabilized by adding an
overall negative feedback loop around the process but in this case I do not
see how any form of reference temperature can be used to generate an error
signal for correction. Do you detect a reference upon which this loop would
act?
Dave
-----Original Message-----
From: Andrew <andrew...@att.net>
To: vortex-l <vortex-l@eskimo.com>
Sent: Mon, May 27, 2013 1:30 pm
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
OK, thanks for the info - I had not seen those reports. Certainly it is in
general expected to happen if it's known that the reaction rate increases
with temperature. So the trick with active negative feedback (cooling) applied
at higher temperature is that this technique holds the promise for much higher
COP values. Indeed, an excellently engineered device promises to be very hot,
to be under complete temperature control, and to perhaps to generate double
digit COP values. Assuming that at some point Rossi licences this technology,
the thermal control and the temperature operating point look like they would
be key market differentiators.
Do we have data as to how low the temperature can go, and still maintain
over-unity COP?
Andrew
----- Original Message -----
From: David Roberson
To: vortex-l@eskimo.com
Sent: Monday, May 27, 2013 10:18 AM
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
The earlier posts by Rossi on his blog mention many cases where thermal run
away happened. Most of these were when he was developing the earlier
versions of his mechanism. The fact that thermal run away can occur has
been common knowledge for a very long time.
Anytime a positive temperature coefficient is present thermal runaway is
possible under certain conditions. Power transistors are a prime example
of this when they self destruct unless the heat sinking is adequate to
reduce the thermal resistance so that the positive feedback loop gain is
below unity. Rossi has a similar problem to deal with. In his case, he is
using what is normally a problem to his advantage to improve his COP.
Without this help he would have a far lower COP. You get a COP of 1 for
free, and much beyond that might result in unstable operation. Even
operating at a COP of 3 has risk of thermal run away.
Dave
-----Original Message-----
From: Andrew <andrew...@att.net>
To: vortex-l <vortex-l@eskimo.com>
Sent: Mon, May 27, 2013 1:03 pm
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
Glad we're back in sync. Although there's definite evidence for thermal
runaway 25 years ago with P&F, with Rossi's kit I'm not so certain. In
fact, I don't know of a single example. He only got the meltdown when he
applied continuous power at a level far above that which he uses now.
Andrew
----- Original Message -----
From: David Roberson
To: vortex-l@eskimo.com
Sent: Monday, May 27, 2013 7:00 AM
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
I suppose that it would be easier in person to discuss this issue, but
that is not available. Yes, we are on the same page regarding the
positive feedback threshold leading to self destruction.
I refer to what you mention as active cooling of the system. We have
discussed this in vortex on several occasions in the past. I think that
it is a winning idea, but so far I have not detected Rossi putting it
into his design. It appears to be a technique that would allow Rossi to
force the loop gain back to below unity at an elevated temperature that
would normally be beyond recovery with heat input modulation alone. This
should result in a downward retreat of his temperature excursion and
looks very promising for high power operation.
Dave
-----Original Message-----
From: Andrew <andrew...@att.net>
To: vortex-l <vortex-l@eskimo.com>
Sent: Mon, May 27, 2013 1:35 am
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
We are totally at cross-purposes here; if we were in the same room, this
crap wouldn't happen. So here's the deal. I'm considering the scenario
whereby we operate the heating system to bring the device just past the
stable temperature; further heating results in thermal runaway (at least,
that's what's claimed for Rossi's device - it actually melted down due to
the application of constant heating, but whatever).
To keep the thing stable when it wants to apply positive feedback to
itself, we need to apply negative feedback. And hence I began to discuss
and describe characteristics desirable of an active cooling system.
You dig?
----- Original Message -----
From: David Roberson
To: vortex-l@eskimo.com
Sent: Sunday, May 26, 2013 5:22 PM
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
But, we are talking about the ECAT. It operates by using positive
feedback to get high gain. You are the one that mentioned a negative
feedback system that achieves the same thing. That is not comparable.
Stable operation of negative feedback systems is trivial.
Think of taking a tunnel diode and keeping it within the negative
resistance region without heavy resistive loading. The problem is
similar to that which Rossi faces.
Dave
-----Original Message-----
From: Andrew <andrew...@att.net>
To: vortex-l <vortex-l@eskimo.com>
Sent: Sun, May 26, 2013 8:14 pm
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
Of course I'm talking exclusively about a negative feedback system!!
The positive feedback purportedly occurs internally to the device
itself.
Andrew
----- Original Message -----
From: David Roberson
To: vortex-l@eskimo.com
Sent: Sunday, May 26, 2013 5:09 PM
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
No, there is a large difference between a negative feedback system
and a positive feedback system. Tell us how to make your temperature
controller hold a constant temperature with positive feedback and a
loop gain of greater than 1. If you do, you might find that it
matches my model.
Dave
-----Original Message-----
From: Andrew <andrew...@att.net>
To: vortex-l <vortex-l@eskimo.com>
Sent: Sun, May 26, 2013 8:05 pm
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
See my follow-up on this. There's always going to be a tracking
error, no matter how sophisticated the regulation algorithm. I think
the prime objective here is not to have absolutely constant
temperature per se; rather, it's to guarantee that thermal runaway
cannot occur.
Andrew
----- Original Message -----
From: David Roberson
To: vortex-l@eskimo.com
Sent: Sunday, May 26, 2013 5:00 PM
Subject: Re: [Vo]:Re: Constant temperature Operation of ECAT?
How many of these controllers use positve thermal feedback to keep
the sink at a constant temperature?
Dave
-----Original Message-----
From: Andrew <andrew...@att.net>
To: vortex-l <vortex-l@eskimo.com>
Sent: Sun, May 26, 2013 7:52 pm
Subject: [Vo]:Re: Constant temperature Operation of ECAT?
Seems to me that if active cooling control is used as the only
control input, thus satisfying the "unplug it!" sceptics (and I'm
one of them), then it only has a chance of working if there is good
thermal contact and good thermal conductivity and substantial enough
heat capacity in the active cooling implementation. I don't know why
this is supposed to be hard. Gaming PC's of the high-end variety use
this all the time. Prompt temperature feedback to the cooling pump
is all that's needed, plus a simple PID controller. This is very
well-known technology.
Andrew
----- Original Message -----
From: David Roberson
To: vortex-l@eskimo.com
Sent: Sunday, May 26, 2013 4:44 PM
Subject: [Vo]: Constant temperature Operation of ECAT?
My model demonstrates that constant temperature operation of the
ECAT is not going to work under normal conditions. The
relatively high value of COP when temperature control is used
depends upon operation in a positive feedback region. This can
be thought of as related to the question that always arises about
why the device does not supply its own drive and therefore run
continuously in SSM.
Once the loop gain becomes greater than 1, the device will tend
to move in the direction that it is currently heading. This
allows it to heat up to a relatively larger temperature than that
due to the drive alone. When rising in temperature, the device
begins to put out additional heat, more with time. The trick is
to turn the process around at a good point before it goes too
far. The best turn around temperature is well defined and shows
up as a tendency for the device to continue putting out power at
a constant rate with time. Unfortunately, this exact point would
be impossible to achieve while maintaining control. It is a
balance between how long you want the temperature to remain
nearly constant and the risk of loosing control.
Rossi chose a relatively safe turn around temperature for the
last test which caused the COP to drop below his desired value of
6. I suspect he chose this because a COP of 3 well demonstrates
that the process is real and also has enough margin to keep the
device safe from melt down. I think I would have done the same
under the same constraints.
Dave
