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: [email protected] 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 <[email protected]> To: vortex-l <[email protected]> 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: [email protected] 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 <[email protected]> To: vortex-l <[email protected]> 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: [email protected] 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 <[email protected]> To: vortex-l <[email protected]> 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: [email protected] 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 <[email protected]> To: vortex-l <[email protected]> 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: [email protected] 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
