Storing Cookies (See : http://ec.europa.eu/ipg/basics/legal/cookies/index_en.htm ) help us to bring you our services at overunity.com . If you use this website and our services you declare yourself okay with using cookies .More Infos here:
https://overunity.com/5553/privacy-policy/
If you do not agree with storing cookies, please LEAVE this website now. From the 25th of May 2018, every existing user has to accept the GDPR agreement at first login. If a user is unwilling to accept the GDPR, he should email us and request to erase his account. Many thanks for your understanding

User Menu

Custom Search

Author Topic: Testing the TK Tar Baby  (Read 1989363 times)

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Testing the TK Tar Baby
« on: March 25, 2012, 11:11:53 PM »
If permitted.....

The only claim I make about this Tar Baby of mine is that it performs just like the NERD device in all significant respects.

(RA has repeatedly denied that I am replicating her circuit. So fine... this Tar Baby is all mine, even though it is eerily similar to hers.)

Much discussion has proceeded elsewhere and I've made a few videos detailing my present work, and there will be more to come. This is the most recent:

http://www.youtube.com/watch?v=w60ycUsuPIY

I'll be happy to take constructive criticism and suggestions. Ranters and ad hominem abusers need not bother to post, because I am the master of BIPS.


TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Testing the TK Tar Baby
« Reply #1 on: March 25, 2012, 11:28:19 PM »
A proposal for consideration:

I don't know if this will work and I don't have the components on hand to try it out. But I'm thinking that an optoisolator might work to isolate the FG's current path from the system, with minimum extra additions to the main circuit.

Here's what I'm thinking of, and I'd appreciate advice on whether or not it would even work, and also what effect it might have on oscillations.... and of course, inadvertent battery charging by the function generator. Well, at least it seems clear that it would eliminate that latter possibility.



TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Testing the TK Tar Baby
« Reply #2 on: March 26, 2012, 01:10:33 AM »
Can anyone tell me the amp-hour capacity of a Raylite 669P 12 Volt silver-calcium battery? I can't figure it out in the units they are using on the manufacturer's web site -- such as it is -- , but the best outside source I've read so far puts it at 50 A-H. Other, less reliable information has it at 40 A-H. This is a significant difference, and I don't know which one, if any, is correct.

I'd really like to get the exact figure.

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Testing the TK Tar Baby
« Reply #3 on: March 26, 2012, 01:47:32 AM »
Mosfets.... how do _they_ work ? ?   ???

http://www.youtube.com/watch?v=_CXWWupl0MU

(Be patient towards the end... it takes me a minute to coax them, but the oscillations do come out to play....)

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Testing the TK Tar Baby
« Reply #4 on: March 26, 2012, 01:52:11 AM »
(snip) Ranters and ad hominem abusers need not bother to post, because I am the master of BIPS.

And nobody, out of over 100 page views already, deigns to comment at all? Are they _all_ ranters and abusers?

Ok... carrying on, then.

(Heh.. .just giving an example of an abusive rant. Pay no attention to the man... the very short man with the toothbrush moustaches---- behind the curtain. )

hoptoad

  • Hero Member
  • *****
  • Posts: 1009
Re: Testing the TK Tar Baby
« Reply #5 on: March 26, 2012, 03:35:09 AM »
A proposal for consideration:

I don't know if this will work and I don't have the components on hand to try it out. But I'm thinking that an optoisolator might work to isolate the FG's current path from the system, with minimum extra additions to the main circuit.

Here's what I'm thinking of, and I'd appreciate advice on whether or not it would even work, and also what effect it might have on oscillations.... and of course, inadvertent battery charging by the function generator. Well, at least it seems clear that it would eliminate that latter possibility.

 I can't see one good reason why the opto-couplers wouldn't work. The only thing that might be a negative issue is dependent on the signal frequency. The rise time response of the opto couplers may be a little slow and introduce slur if your input signal is in the megahertz range. Other than that, I don't see any great issues.
 
 If you want to retain the possibiltiy of parasitic oscillations arising, then the circuit as shown might still allow that to happen. If however you only want a faithful reproduction of the input signal to your mosfets, I'd be inclined to connect a resistor anywhere in the range value of 150 k to 1 meg between the gates of the Mosfets and ground. This will help to damp floating voltages, and help prevent stray capacitance from interfering with the operation of the Mosfets, and also from interfering with the true input signal.
 
 Cheers

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Testing the TK Tar Baby
« Reply #6 on: March 26, 2012, 03:50:16 AM »
Thanks, hoptoad. I think you are realizing what I want to do. I am trying to remove the FG's current path and power source from the switched power circuit in the TarBaby device. Whatever method I eventually use it must preserve the oscillations in the full 5-mosfet design. As soon as the stores open tomorrow I'll pick up a few optocouplers, plain and triac kind, to see what happens next. The required switch rate is absurdly slow.

The subject matter of the previous video, mosfet switching, seems so basic to you and me that we don't even think about it. However some other people working with similar circuits...you know who I mean, probably.... missed out on so many basics that they _can't_ even think about it. Believe me, years ago I spent weeks trying to convince...err... on..... somebody else that mosfets switched like this.

And now it's deja vu all over again.

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Testing the TK Tar Baby
« Reply #7 on: March 26, 2012, 03:59:12 AM »
So.... as demonstrated, the oscillations in the mosfet switch demo circuit come out to 9 cycles in 9 major divisions of the scope's screen. The timebase is set to 0.2 microseconds PER major division. How do we determine the frequency from this data?

ANSWER: since frequency is measured in Cycles PER second, or Hertz.... and we have counted 9 Cycles PER 1.8 microseconds, what is the frequency?

We perform the operation 9 cycles DIVIDED BY 1.8 microseconds. Notice the units: the answer, whatever it is numerically, will have the "dimensions" or "units" of.... CYCLES PER SECOND. So let us calculate: 9 / 0.0000018 == 5 000 000 Cycles PER second, or 5 MegaHertz, to within rough reading accuracy. Actually it's a bit higher since there were a bit over 9 cycles in the 9 major divisions.



TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Testing the TK Tar Baby
« Reply #8 on: March 26, 2012, 04:51:19 AM »
The version of the Tar Baby that I'm working with here uses IRF830a mosfets in all 5 positions. The circuit that the Tar Baby is modeled after, the NERD device, uses the IRFPG50 mosfet, and it seems to be the claim of the NERD RATS that this part is critical to the "effect" they are talking and talking and talking about demonstrating. So I thought it might be interesting to compare some electrical parameters of the two power Hexfet, avalanche-rated mosfets.

The first thing one notices is that the PG50 is in the TO-247 package, an awe-inspiring slab of black plastic with beefy leads. The 830a is in the standard TO-220 case which looks tiny by comparison, and its leads are smaller and have the standard 0.100 inch spacing, so they fit nicely into breadboards and dip sockets and headers.

The most critical parameters for most uses are listed at the top of the first page of the data sheets.

Further parameters of interest are the various capacitances and avalanche energies, transconductances, and so on.

I've attached the data sheets. To my eye, if one does not absolutely need the 1000 volt standoff capacity of the PG50, one might be better off simply using the 830a, since they are somewhat cheaper, smaller, and seem to perform similarly at low power settings. In fact the 830 has lower Rds and better transconductance and will dissipate less power at the mosfet itself at power levels within its range.
In other words, it should run cooler than the NERD mosfets at similar power.

MileHigh

  • Hero Member
  • *****
  • Posts: 7600
Re: Testing the TK Tar Baby
« Reply #9 on: March 26, 2012, 06:04:59 AM »
Hi TK:

You had a question about the capacitor test with respect to the capacitor size.

When I originally crunched the numbers I think the power dissipation in the other circuit was quoted as being about 30 watts.  I am now suspecting that was quite high.  I played with the number crunching and quickly realized with a single 25,000 uF capacitor it would drain very quickly assuming 30 watts being dissipated in the load resistor.  I also now realize that I wasn't even factoring in the fact that the total power dissipation would include the MOSFETs themselves and the 50-ohm resistor inside the function generator.

The bottom line is that I quadrupled the capacitance to 100,000 uF and crunched the numbers again and realized that they would still drain very quickly.   This is a real concern because if you let the caps drain to zero volts then they will continue past that and start to reverse-voltage.  Using polarized electrolytics this would be very very bad as you well know.

The simple crunching I did was to estimate the power dissipation.  Then calculate the energy loss in the 100,000 uF cap from 12 volts to about 6 volts (I think).  So then I could make an estimate how long that voltage drop would take based on the energy burn rate.   You have to keep in mind that the energy burn rate is not going to slow down because you are really talking about a voltage drop from 60 volts to 54 volts.   I had to base it on a 6-volt drop so the circuit could run for about 10 seconds.  I would have preferred something like a one-volt drop only but then the time got too short.  Again, assuming 30 watts power dissipation, you have to work around that if you only have a 100,000 uF cap.

So I would recommend that you make your biggest cap possible, and scope the voltage across the cap array when you switch on the circuit.  If it drops like a stone then disconnect right away so that you don't reverse-voltage the cap array.

If the total dissipation is more like a few watts as opposed to 30 watts then you should see a gentle voltage decrease across the cap and still see the 'magic' oscillations.  Then you can crunch the numbers and calculate the power dissipation in the circuit.   If you can time say 20 seconds and then do 10 runs like that and average your measurements, you will have a very decent number for the total power dissipation in the circuit.  You know the voltage so you know the average current flow.  That means you can calculate the power dissipation in the 50-ohm resistor inside the fucntion generator, and the power dissipation in in inductive resistor.  Look, you now get a very nice bonus, you can derive the power dissipation in the MOSFET array:  The power dissipated in the MOSFET array is the total power dissipation minus the 50-ohm resistor dissipation minus the inductive resistor dissipation.

Now, if you had a means to control the magic oscillation frequency, perhaps with an opto-isolator arrangement or something else, you could expect to see a trend.  The lower the oscillation frequency the less time the MOSFETs are in the linear region and dissipating power.  So if you lowered the oscillation frequency and ran the capacitor test again, you should be able to derive less power proportionally dissipated in the MOSFET array.

Finally, I tried to keep in simple for Rosie and I didn't want to mention the potential for the capacitors to reverse-voltage right away.  If anybody was going to go forward I was going to mention it.

MileHigh

MileHigh

  • Hero Member
  • *****
  • Posts: 7600
Re: Testing the TK Tar Baby
« Reply #10 on: March 26, 2012, 06:21:28 AM »
A little side comment about the whole capacitor test was that I wanted to emulate only a single battery with a large cap in the middle of the array of batteries to "keep it battery-like" if that makes sense.  This was to keep Rosemary happy, she would see exactly the same oscillations on her scope and the power source was still predominantly batteries so any imagined "battery effects" could still take place.

Anyway, I think that the test is an interesting and worthwhile exercise.  One of the important concepts is that if you have five batteries in series, each battery will contribute 20% of the power required to run the circuit.  Alternatively, if the bank is being recharged, each battery will take 20% of the recharging power.

So by "slipping a capacitor" into the battery array and replacing one of the batteries, whatever the capacitor is indicating will also be happening within each of the individual batteries.

And certainly the capacitor will go down in voltage as the circuit runs, even if your DSO is spitting out garbage data that says that the battery bank is being recharged.  That's because the capacitor is more accurate than the DSO and can't be fooled.

Just one little tweak:  Assuming 100,000 uF and 25-volt rated electrolytics, and assuming the batteries are actually 12.6 volts, then why not time how long it takes to go from 15.6 volts to 9.6 volts for high power dissipation.   For low power dissipation, time how long it takes to go from 13.1 volts to 12.1 volts.  That way you are quasi-centered around the true battery voltage and you get a slightly more accurate average power dissipation measurement for the circuit.

I also have a caveat:  In thinking about the process in my head I am quite certain that as the cap discharges the rate of voltage drop will actually start to accelerate, not slow down.  We are so conditioned to expect that the rate of the voltage drop on a cap will slow down as the cap voltage decreases.  So it may seem counter-intuitive but indeed, as the voltage on the cap decreases, the rate of the voltage drop will increase.  Kind of a fun brain twister. (** WRONG ** - I failed my own brain teaser.  The rate of voltage drop will NOT increase, it will decrease but very slowly.  Typically it will be so slow so that it will almost look like the voltage is dropping linearly.  That was my Doh! moment.)

MileHigh
« Last Edit: March 26, 2012, 07:23:46 AM by MileHigh »

MileHigh

  • Hero Member
  • *****
  • Posts: 7600
Re: Testing the TK Tar Baby
« Reply #11 on: March 26, 2012, 07:07:57 AM »
TK:

I went back and reread your posting.  You have only 40,000 uF to work with.  So I recommend that you scope the cap voltage like I said and watch very carefully.  Do not use a digital multimeter with a 1/2 second display update.  You might get squirted in the eye with some primordial ooze if you are not careful.

The fact that you are typically running with 30 volts instead of 60 volts may save you here because that's 1/4 the power dissipation rate as compared to 60 volts.

I have this gut feel that those 25,000 uF 25-volt "Coke can" electrolytic capacitors are relatively cheap.  Waaaay back I used to go to these 'electronics depot' type places that had recycled and Grey market and who-knows-what parts.  You may find some big caps in a place like that on the cheap.

MileHigh

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Testing the TK Tar Baby
« Reply #12 on: March 26, 2012, 11:40:48 AM »
Thanks, MH, I'm with you all the way. I've also got 16 x 4700 uF @ 40 v surge caps but that would be too much wiring for my liking. Unfortunately, I live in an intellectual "black hole" and there is only one electronic surplus place that will have big cap pulls from obsolete gear and they will be mixandmatch (but I'm going there today to take a look). The only decent "new" parts place is 100 miles away, the Fry's in Austin. Of course we have RS, if you need a battery or a common resistor or a cellphone... but for electronic components it's a weird wasteland. Not like TO where I could just walk down to the hardware store and browse thru their component section where they had _every_ Japanese 2sk transistor and _every_ 74 series logic chip IN STOCK to support the EE department at UofT, or go into one of three different surplus stores to get the "weird stuff". I even found a medical electroshock machine in Active Surplus there one time... nice bank of big caps in that one !!
But around here, electronics means car stereos and not much else, and the big caps they sell for those -- really impressive big caps -- are just too expensive for me to mess with. But sure, some of these car stereos around here will have FARADS of capacitance stuck into the trunk somewhere to pump that drumandbass into their blown speakers.



Meanwhile, I found this hour-long seminar on.... power measurements in AC circuits.

http://www.youtube.com/watch?feature=endscreen&NR=1&v=MHa18mC2ZLc

Your capacitor test will be a good easy one to do to test for battery charging vs. battery discharging by the circuit. But when I get down to actual power measurements, _assuming_ that the performance of the circuit can be derived from electrical parameters at all -- I'll be using the Clarke-Hess 2330 sampling V-A-W meter as a power analyzer. No scope traces to interpret, just digital readouts of nice red numbers. I'll measure the input for a while with the load at equilibrium temperature, then I'll swap leads quickly and measure the output for a while at the same equilibrium temperature, then re-charge lather rinse repeat.

Later on, I'll subject the Tar Baby to the fancy Tek scope with internal math and we'll see what kind of nice colored wiggly lines it will make. You don't want to skip ahead to the "money shot" already, do you ?
 8)

--TK

(Thanks for your help, I really appreciate it.)

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Testing the TK Tar Baby
« Reply #13 on: March 26, 2012, 12:22:25 PM »
There are still a few points about the open-source, help-to-replicate NERD RAT device I would like to understand.

First there's the value of the inductive-resistive load. I've seen inductances cited that are all over the map. I've seen 1.5 HENRY posted somewhere as the inductance of the load. This seems implausible to me based on the waveforms I've seen and what I know about the construction of common water heater elements. Also I have little confidence in instrumental measurements, especially difficult ones like inductance, that have been reported concerning that device.

Then there's the question of the battery capacity of the batteries that team used. I can't figure it out from the company's website catalog listing of the battery they used. The most reliable outside source I could find (humbugger) has it at 50 A-H, but the "official" reports of the NERD RAT device have it listed as 40 A-H. If battery draw-down tests are being considered, one would normally like to know the actual rated battery capacity, just in case someone cared enough to wonder if a 25 percent difference in actual capacity could affect such a test at all.
( 40 plus (25 PER cent of 40) = 50 ).



TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Testing the TK Tar Baby
« Reply #14 on: March 26, 2012, 12:23:35 PM »
How do we know the state of charge of a battery? It is not easily and directly related to the simple, no-load or lightlyloaded terminal voltage measurements that are so often cited as "evidence" for the battery's charge state. The battery's " discharge curve" must be considered, along with the load's demands. That's why drawdown tests or simple side-by-side tests like performance under a _heavy_ load are preferred to simple voltage measurements.
 
 What do we expect to see, as a measurement of the terminal voltage of such a battery?
 
 1) when it's being recharged by an automatic battery charger designed or approved for the battery type
 2) immediately after it's been fully charged by the charger, still no-load
 3) one hour after 2), unused, no load
 4) when first hooked up to the operating circuit, under load
 5) after running the circuit for long enough to "theoretically" (using conventional theory) to have transferred half of its stored capacity to the circuit and the load, tested both under load, and unloaded?
 
 For my 12-volt, 5 A-H, sealed lead-acid batteries, I can answer some of the questions.
 
 1) is about 14 volts. I am using an automotive "automatic" charger that charges at up to 2 amps and that goes into a "float" mode when it senses that the battery is full. How it knows, I dunno... but I am assuming it does and is consistent between batteries. (actually I do know, but it's not too important I hope)
 2) is about 13.8 volts
 3) is about 13.5 or 13.6 volts
 4) is about 13.0 volts (so I get about 39 volts from my stack when first running the TarBaby circuit)
 5) is still unknown

The most important point here is that simply citing "the battery is still over 12 volts" is NOT evidence that it is fully charged. In fact, if a large 12 volt silver-calcium-lead-acid battery IS fully charged, its terminal voltage should be something over THIRTEEN volts when measured under no or light load.