Testing the TK Tar Baby

[WilbyInebriated]

Wilby,

Wow, you guys really need to bury the hatchet... life is too short.

You do have to give TK credit for being one of the first, if not the first, to identify the inverted duty cycle issue in the COP=17 circuit.  And, oddly, how that inversion, if the calculations are also inverted, produced a similar COP result.

But yes, I would typically replicate first and then modify second.  I am asked to improve on designs all the time, and I always start with what the customer is currently using to make baseline measurements to improve upon.

PW

LOL yeah, there's really no hatchet for me. my righteous indignation at tk is more of me holding up a mirror to him... but he can't see it. or maybe he can and that's why he got so pissed off a year or so back and left 'till recently. i guess i can't blame him... i'm sure he realizes by now that it was even funnier that i made him do all the work to prove himself wrong after he and his sycophants tried so hard to get me to do it. harvey told him a long time ago that his type was easy to manipulate... i think it sailed right over tinselkoala/alsetalokin's head.

anyways, you're right, life is too short. i'm going fishing... you have fun here, you'll see soon enough.

[picowatt]

TK,

As for frying one of your quads, that is what happens when MOSFETS (or bipolars for that matter) are paralleled withour individual source (or emitter) degeneration resistors.  Likely the one that popped was the one that had the lowest turn on threshold and was doing most, if not all the work.  Source degerneration helps compensate for the variations in the threshold voltage of the paralleled devices.  It is very likely that in the RA circuit not all, or even only one, of the MOSFETS in the "quad array" is doing all the work, with the rest just providing capacitance for AC current.  If turned on hard enough, the rest will eventually carry some load, but the lowest threshold device will continue to carry the most current.

Seriously, off to work now...

Wish I was going fishing...

PW

[TinselKoala]

TK,

As for frying one of your quads, that is what happens when MOSFETS (or bipolars for that matter) are paralleled withour individual source (or emitter) degeneration resistors.  Likely the one that popped was the one that had the lowest turn on threshold and was doing most, if not all the work.  Source degerneration helps compensate for the variations in the threshold voltage of the paralleled devices.  It is very likely that in the RA circuit not all, or even only one, of the MOSFETS in the "quad array" is doing all the work, with the rest just providing capacitance for AC current.  If turned on hard enough, the rest will eventually carry some load, but the lowest threshold device will continue to carry the most current.

Seriously, off to work now...

Wish I was going fishing...

PW

I know, I know something about parallelling mosfets. You are now pitching a bit under my level, but that's OK because I know we have people of all levels reading here. Did you see the paper below? I think Fuzzy first found this one. Odd that that Morris didn't notice the massive overunity performance of his five parallelled IRFPG50 mosfets. Of course ... he followed your suggestion as to the proper way to parallel mosfets, and... he didn't get four of them in backwards, like the NERDs did.
I even told them what to expect when their "gang of four" had to carry 10 or 12 amps, much less the 4200 Amps like was implied by the famous "25.6 megaJoules" test that started my entire objection and involvement.

You might also be interested in my TinselKoil. It uses an H-bridge of 4 power mosfets to switch rectified line current at 170 vdc (roughly) through a 4-turn primary winding of a 300 kHz solid state Tesla coil resonator. The mosfet gates  are driven by phase transformer toroids that are in turn driven by a current amplifier H-bridge of silicon transistors, which in turn is driven by a PWM driver chip (TL494 IIRC). All developed by me, empirically and in public view, and all impossible to accomplish without protective circuitry and proper layout of the power stage to avoid stray inductances and achieve clean switching. Videos on my YT channel.


By the way... my Tar Baby oscillates just fine.... with the Q1 mosfet ENTIRELY REMOVED from the circuit. There is little difference in the scope trace and none in behavior except that it doesn't heat the load much that way. I'm pulling and testing all the mosfets now to see if there are any that are open... a shorted one shows up right away in-circuit but the opens are harder to detect.

[TinselKoala]

More on removal of Q1:

With Q1 in place, if one uses a bipolar drive signal instead of strictly negative going, one still sees oscillations on only one phase--- at least I do, but my Q1 is mounted with short leads -- but an interesting thing happens. Something that might not be noticed by someone who thinks oscilloscopes are for drawing pretty colored lines with.

The first shot below is using a bipolar gate drive signal of +/- 5 volts, about. This shot is with the lone mosfet Q1 _ENTIRELY REMOVED_ from the circuit by pulling it out of its socket and laying it down on the bench about six inches away. (Of course you can't see the invisible wires, silly.)

The second scope shot below is exactly the same except with the Q1 mosfet back in its socket. See any difference in the oscillations?

What about NOT in the oscillations?

Now, silly old fumblefingers me, barely tall enough to reach the controls.... I sometimes make mistakes in my knob settings or hookups or whatever. But I try to assume FIRST that I have made some error when I see something strange, so I go back and check my work and try to correct what I've done and interpret correctly what I see, by experimenting all around in the problem space, NOT simply "trying to replicate exactly" somebody else's claim of an a-priori impossibility.

Is it possible that other people, perhaps even more naive than I am, could make mistakes, and perhaps not notice them at all?

[picowatt]

TK,

Didn't mean to throw you a low ball, but, as you say, others may find that useful.

Yes, I have seen most of your HV videos, including your H-bridge driven coil.  It really is a thing of beauty and quite the accomplishment.  Fire up all those HV projects, turn off the lights... talk about mood enhancement...

Many (too many) years ago I built a VDG with a 3.5' foot upper terminal complete with cardioid shaped bottom section, 5" or 6"  belt, dry nitrogen filled column and active corona spray.  When it would discharge into its 24" discharge globe, well, let's just say you did not want to be around it.  Always enjoyed a good HV display, DC or AC.

With Q1 out of circuit, you probably lose around 20% of the AC current path.  If you monitor AC current at the CSR, that is likely where you will see the difference with/without Q1 in the circuit, i.e., a bit more AC current with Q1 in circuit.  Even the 830's have what, 600-800 pf of Ciss (I know you posted the data sheet, it was something like that if I recall).  I would think it would show up on a scope trace at the drain as a slight change in the osc amplitude (with Q1 in circuit). 

Break over,

PW