The information that I have received, which might not be totally accurate, is that most of the testing is done in constant current mode operation. The supply current would be monitored and then plenty of negative feedback would come into play to ensure that the current remains fixed. This type of control can be made very stiff and not sensitive to the voltage appearing across the output terminals. A large capacitor connected across that set of terminals would offer an easy path for any transient currents generated by bursting bubbles or other short term changes that appear due to load variations.
I would not consider the capacitor as making the supply a constant voltage system. It is true that it allows any instantaneous load transient currents to have an easy escape and therefore to bypass the DC current from the supply itself. But, at the same time it allows the constant DC current to flow without having to compensate for large fast voltage swings that would normally appear across its output terminals. This is the best of both worlds. Steady DC current exiting the supply that can be assumed constant and in fact would be...slow voltage swings across the capacitor that can easily be followed to determine the true power being delivered into the load. The larger the capacitor the better provided that supply stability can be maintained. The instantaneous power being delivered by the source is equal to the product of the current and voltage. When the current is constant, only DC voltage loads can accept power and thus energy from the source. All of the AC voltages that appear across the source terminals integrate to zero during a full cycle and do not enter into the input power equation. This understanding seems to escape most people until they review the theories carefully. I had to prove roughly the same issue to several skeptics that thought that DC due to load rectification of the AC power source could be used to sneak extra power into the earlier ECAT. They thought this was possible since the input power meter did not monitor DC directly. The input power can be accurately determined in a system such as I am referring to by merely taking the slowly varying DC voltage that is residing across the large capacitor averaged over the entire time of the test. This average DC voltage can then be multiplied by the known DC current from the source to arrive at the average input power. Multiply this number by the time and you get the energy input into the cell. I believe that it is as simple as that. I read an article from a skeptic that made an attempt to confuse the issue by bringing up the small rapid AC currents generated by the collapsing bubbles. I suspect that he just did not understand the problem. Dr. McKubre has convinced me that he is a very savvy guy and I suspect that many of the skeptics underestimate his knowledge. These skeptics are looking for every possible avenue in their quest to discredit everyone associated with this subject. It is too bad that they are not up to the quality of the researchers that we have the privilege to know. Dave -----Original Message----- From: Bob Higgins <rj.bob.higg...@gmail.com> To: vortex-l <vortex-l@eskimo.com> Sent: Mon, Oct 27, 2014 1:02 pm Subject: Re: [Vo]:questions on McKubre cells and AC component I have no first hand knowledge one way or the other [this was not my assertion]. I believe Dr. McKubre to be an outstanding researcher and have no reason to believe this escaped his attention. Even if it did, it would only be a minor error and does not alter conclusions. It will make a difference whether in constant current mode or constant voltage mode. Given the nature of the chemical cell having a "cell voltage", constant voltage mode would likely be worse because I think the bubbles would cause larger swings in real instantaneous power than if the cell were run in constant current mode. The problem exists to some extent with almost any real DAQ. If the current remains perfectly fixed, the voltage will change and there will still be real instantaneous power variation, only I think less real instantaneous power variation than in constant voltage mode. The smaller the real instantaneous power variation, the smaller the error introduced by using average current and average voltage over a discrete interval. Keep in mind, we are talking about small changes in resistance - well within the regulation circuits of most power supplies. Adding a capacitor across the supply just insures constant voltage mode - which I believe would be worse than constant current mode. The most practical solution is to reduce the sampling period by spending more on the DAQ. The error can be reduced via shortening the sampling period until the error is no longer a concern - at additional cost of the DAQ. Just like anything else, you can usually buy more accuracy. Bob On Mon, Oct 27, 2014 at 10:21 AM, David Roberson <dlrober...@aol.com> wrote: If the internal current control feedback mechanism is slow to act, then the output current might indeed change significantly. I have never put a constant current supply under careful supervision before but assumed that the guys designing them would go to lengths to ensure that they in fact maintain the output DC current constant under varying loads. Have you performed this measurement on a high quality constant current supply? We also would need to assume that McKubre was not aware of the possible problems that have been pointed out. Perhaps we should get feedback from him to answer that question. If the current does not remain fixed and DC, then there are many possible errors to follow up on. On the other hand, if the source really does keep the current constant with adequate feedback control then the input power can be accurately determined by only taking into account the average DC voltage appearing across the supply terminals. AC signal voltages generated due to bubbles, etc. should not enter into the power input measurement unless they force the supply to go into operation outside of its normal range. Bob, I would be somewhat surprised to find that an expert of McKubre's caliber would not have a good handle upon the input power and energy levels after chasing that sort of problem for many years. Surely he would have seen the significant variation in current flowing through his test system at some time and attempted to rectify the situation with a better constant current system. Perhaps something as simple as a large capacitor across the supply output terminals would smooth out the current pulses. How confident are you that he missed this issue? Dave
