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
