High power short pulse generator for LENR experiments

Quote from asdf506f

Please let me know (by liking this post) if you are interested in these efforts...

Experiments and experimenters are very welcome here.

These pulses require extreme care from experimenters. Have you designed UHF wideband front-ends? If not you probably are not aware of the techniques needed to make a sensitive analog circuit work reliably in the presence (same ground line, or physical proximity) of this stuff.

The waveform shown - if corresponding to a 30A pulse - would show 2500A/us slew rate. That will inject 2.5V across any 1nH inductance - a typical lead parasitic even using good high frequency layout.

Similarly any unshielded or poorly shielded wire carrying that pulse will inject voltage spikes into any random wire nearby, or the local ground connections.

The two edges of the pulse are asymmetric with an HF content 10X larger on leading than falling. That is typical, and means even in a symmetric amplifying circuit you will get asymmetric rectification due to slew-rate limits. In any case most amplifiers have asymmetric slew-rate limits. Think of what this means when you are amplifying TC signals and 1mV is seen as a significant power output change?

These effects are not so difficult to control, but only if you are familiar with UHF EMC layout precautions and techniques in challenging situations. I'm wondering how many of the experimenters using this stuff are aware of the issues here, and know the ways to diagnose and cure them?

Regards, THH

Quote from Alan Smith

I have been making 50V30A AC square waves using an adapted and very inexpensive H-Bridge circuit (as sold for control of brushless motors in models). It is driven by an astable vibrator, and seems to produce pretty damn clean square waves at anything from 1Hz to 2k Hertz. More might be possible, but not yet tested beyond 2kHz.

The nice thing about using the astable vibrator circuit (about $5 from China) is that not only can you control the frequency you can control the mark-space ratio. Sadly I didn't take any scope shots when it was on test. But I do have a photograph of the general layout of the 2 boards etc, and will post it here later. Not so much fun as building your own from scratch, but then again, I blew a few of my homebrew ones up before resorting to the China route.

On the topic of inductive pick-up in nearby leads, this didn't seem to happen. Being a former radio ham, I am pretty open to the idea of co-channel interference so looking for it was part of the testing. Worth pointing out that this circuit is used to drive heater coils in a reactor, and the stainless-steel sheathed K-Type TC's actually end up smack in the middle of those coils, a position where you would expect maximum induction of 'phantom signals' to occur. Happily, nothing seen.

The TC's are (as mentioned) sheathed in stainless steel and have fully screened and earthed leadouts to the data-logger - which probably helps a lot.. There is no direct connection between the data logger circuits which are grounded to earth, and the power supply that runs the H-bridge(s) which is not earthed but has a 'return to neutral. Since DC power input is measured before the H-Bridge circuit there is no tricky integration required either- the H-Bridge losses are considered 'trivial' and in any case are equal for both test and control parts of the reactor.

All good fun, and keeps me out of the pub.In fact, I have forgotten where it is.

Display More

I'm glad this does not happen in your circuits. What control test, as a matter of course, would you do to check it is not happening? My point is that it will happen in some setups... And if not controlled there, it will easily be confused with LENR.

THH

Quote from Alan Smith

Very simple. Take a reactor and run the heater coils off straight DC. Measure the temperatures. Do the same thing with the square wave system and compare. Or- run a reactor up to any temperature you like using square wave heat, then switch it off. Check the cooling curve- if there is a kink in it at shut-down point you know you have an interference problem. Simples. In fact, switching the heat on and off and watching for anomalous bumps (or dips) in the temperature gives you a very good indication of mischeif in the machine.

So - I would do this.

(1) Measure - somehow - the electrical time constant of the TC amplifier. For example by injecting a sq wave at 1Hz and measuring the rise and fall time etc.

(2) In the actual experiment (so that leads etc are in identical positions) have a control period where the stimulus wave form is switched on and off. Observe the synchronised change in the TC output. Measure rise and dfall times. If this has the electrical time constant - it will be RFI. If it has some longer time constant it might be some stimulus-induced chnage in termperature.

(3) For added validation do the same thing with a control experiment where no change in temperature with stimulus is expected.

If your stimulus adds significant power to the system, so is known to change temperature anyway, the electrical (RFI) and temperature components of this can be accurately differentiated as long as the time constants are significantly different which is likely due to the thermal inertia of the system.

These things generate high voltage pulses and they're very cheap. The discharge through air-gap + capacitor generates very short pulses (for example nitrogen laser requires sparks shorter than few nanosecond).

Quote from Alan Smith

The time constant of the TC amp is tiny - they are simple linear voltage amplifiers AFAIK. But it can be measured sure nuff.

So it should be possible to distinguish temperature chnage from stimulus with direct RFI effect of stimulus easily. This BTW is what I wanted SRI to do with the Brillouin stuff. Perhaps they will.

Quote from Eric Walker

Experiments and experimenters are very welcome here.

A number of years ago I had the opportunity to build a 1000V, 50A pulse generator using IGBTs. Pulse width was fixed at ~ 5.7 us with a rep rate from zero to 5000 pps. Proper gate drive voltage and current are key to making IGBTs turn on and off properly. Gate driver ICs are available from several manufacturers, as are pulse isolation transformers that permit stacking or bridging of IGBTs to obtain voltages higher than can be sustained by a single device. As was previously mentioned, it is important to maintain isolation between the input and output in order to avoid unwanted Ldi/dt voltages from appearing in the low voltage circuits. Separate grounds are essential, and here the isolation transformers are a help. I have used this pulse generator to heat a Celani type setup, but did not observe any excess heat.

Quote from Alan Smith

By George, I think you've got it!

Must be cleverer than SRI?

Just a quick question. The rise time is about 10ns while the fall time is approximately 60ns. The switching hardware is a half-bridge. Why the relatively large switching characteristic difference?

So you want to speak about high voltage pulse generators?

So you want to speak about hight voltage pulse generators?

The commercial “high voltage generators” of the link above are not “800 kilovolts” of course. It is induction coils for tasers. The actual voltage is only around 80 000 volts.

The law (spark lenght/voltage) in air at normal pressure is complex, but a simple approximation is 10 kV = 1 cm.