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Messages - petespaco

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1
Here is a walk-through of a 1930's 500,000 watt AM radio station in Ohio, USA:
/>Somewhat lengthy, but
I thought it was a pretty amazing feat for the time.

2
Electronic circuits / Re: CRT hacking ideas....
« on: June 19, 2019, 11:29:28 PM »
Wouldn't the horizontal oscillator be a good start for a tesla coil?

3
Thanks for clearing that up and thanks for the link.  Now I understand that there's a lot more going on than I thought.
That's quite a package!
When I multiply 65V X 45A, I get 2925 watts.  I wonder why they only rated it as a 2000 watt unit. 

4
Quote
Since the 200V are the minimum rating, it should be OK to 70V.
I respectfully disagree.  On the datsheet that I saw, "200" was the ONLY number.  There was no entry at all in the "max" column.

Where do all the "uC" points go?
It appears to me that they would all originate at the output of the opamp, but I guess I just don't understand that kind of a schematic diagram.


5
Thanks so much for putting up the schematic.
  I'm not too sure yet, exactly how the system "checks the Mosfets" before turning power on, though.

Re: your comment about max input voltage:
The datasheet for the IRFP260N says 200 volts max.  Somebody on this forum has said the you can expect to see pi X the input voltage across the Mosfet.
If that is true:
48                     55                       65  Volts In
3.14159            3.14159             3.14159
150.79632   172.78745   204.20335 Volts across Mosfet



This seems to imply that you might get away with 55 volts, but 65 volts would be over the top.


6
I thought I'd wait until someone else mentions the "shorting turns" thing.
When I did that, (unintentionally, early on)  I always liked to have a bunch of extra Mosfets and gate components around.  And even some heavy copper wire to use for replacing evaporated pcb traces.  For me, half a second is tooooooo  looonnnggg!  But maybe your heater's circuit is different.
See:
https://spaco.org/Blacksmithing/ZVSInductionHeater/1000Watt12to48VoltZVSInductionHeaterTroubleshootingGuide.htm
for how and WHY I used to have to repair them!
I have seen people do that "shorting" thing with other units, but you'd better be sure that your driver  board itself has a current limiting function.  Just because your power supply may have current limiting is NOT good enough.  It's the degradation of gate signals that kills the board.

7
Here's my final test of watching the surface of the molten copper with better camera filters:
/>
Pete Stanaitis
----------------

8
hightemp1:
Quote
But since we are limited to 50 amps on the 2500w unit we would have to gradually lower the crucible (instant variable amp/power regulator),  lowering it completely when metal is all melted, or when fully inserted and safely stays below 50 amps??
I think this is an excellent idea.


9
Badpeter-
  Maybe try casting the dagger vertically?  That way it would be certain to fill.  I think they do cannons that way.

10
Quote
links did not work, for me?  Any ideas for a "simple" -more power" controller board add-on for these heaters?

Hmmm--- I just tried both links and they did work for me.  Just a simple "click" on each one and there I was.

I don't have any idea for a "more power" controller board to add on.  However, maybe you want to bit the bullet and buy the $1000 unit that is 7 KW.
https://www.ebay.com/i/221663967797?chn=ps
(This is just one of the many sellers)
  That ought to do it.  You will, however, need a TIG  water cooler for it and they run at least $400 more.

I still feel that it's a "heat in vs heat out" equation.  You only get 3412 btu's of heat for each 1 KW of electricity.  So, if you are losing more than you are putting in, the temperature quits rising, right?   There is still the opportunity for any or all of us to conserve more heat.

11
Sorta OT, but---
Quote
I would have like to have seen the old-time pig iron smelt - make America great again! :(

This smelter hasn't actually been in operation since about the year 1900.  We just checked it out for historical curiosity sake.
See:
https://www.youtube.com/edit?o=U&video_id=0zTf4WdYXc0

If you want to see us MAKE "Wrought Iron" from iron ore, go here:
https://www.youtube.com/edit?o=U&video_id=493AsqZ4P54


12
There is very little increase in current, if ANY as the copper heats up (but before it melts).  The decrease in current that I report occurs at exactly the moment when the copper melts.  That has been my direct observation EVERY time I have melted copper.  And, the deeper the pool of molten copper, the more the current decreases.
  I don't see the "cold copper" phenomenon mentioned recently.
Also, since the addition of solid copper to the crucible does not seem to increase the current, I don't think the copper itself is participating to any significant extent in speeding up the melt.    It's radiation, convection and conduction that is transferring the heat from the glowing crucible walls, to the copper, in my opinion.
  ---So I will go "out on a limb" and say that I don't think the copper alloys that you want to use will present any worse of a melting problem than does the copper that I am using. 

Now for my hypothesis as to why the current drops just when the copper melts:  I think the molten copper actually "shorts out" the graphite as the copper makes intimate contact with the whole wall of the crucible.   

Lastly, for today, about stirring:
As you know, I am trying to be able to show exactly what is going on in the bottom of the crucible.
  I almost got to performing  my improved camera color-shift filtering test today, but--
A friend and I had a chance to inspect a pig iron smelter from the 1880's and we did do it.
Well worth the 20 mile trip.

  I hope we will all see that there isn't much "violence" going on in the crucible, after all.
I did get some graphite covers and additional insulations pieces cut and did a dry run to test for a 2 camera shoot, though.

13
This isn't really a "reply" to previous posts, but just a tiny bit of additional information  about the molten copper----

I just uploaded this youtube video about the looks of the surface of the molten copper:
/>
It's not my best work, but just another step toward better photography.
I also measure the temperature of the molten copper a couple of times.
I'm in the process of making several improvements that I hope will benefit those of you who haven't yet actually peered into a ZVS induction heater's graphite crucible with molten copper in it.

14
T3s---:
I don't have any recent experience with "the more complicated circuits", but, regarding the "ZVS Royer circuit", please tell me more about:
Quote
---doesn't always start up at all, or at the intended frequency (more a problem for high frequency oscillators).

I ask because I don't think I have had either of these problems.


15
badpeter:
  I just watched your earlier dagger casting video again.
If I hadn't said it earlier, I really appreciate your willingness to share.
From it I can understand your concern about being able to use your induction heater for melting that much material. 
If you have no particular attachment to "art" of induction heating, then going with an electric kiln, as you suggest in your recent post,  sounds like an appropriate solution.

However----  (isn't there always a "however"?):
I noticed that quite a bit of heat was coming out through the insulation in that video.  Whereas, the hard ceramic insulating cups that I am using NEVER show ANY signs of glowing at all on the outside.  I wonder if conditions would change significantly if you were to obtain such a crucible of the size you want.

Also--- about the depletion of the graphite:  the carbon can't really oxidize if there's no oxygen, right?   I 'm sure we have all read about commercial melters using inert gases, but that would be hard to do for us, I think.
But, what if we used a tight fitting cover?  The existing oxygen would be used up pretty quickly and then oxidation would be minimized.  We would only open the crucible to add material.   I have seen crucibles that have such a cover.
  For my own system, I will make some covers.  A guy gave me a 2" X 4" X 24"bar of graphite several years ago, so I have plenty of material  to experiment with.

For one source of graphite, the farm machinery companies around here used to sell quart size containers of powdered graphite for lubricating corn planters.  It wasn't too expensive.  Might be one approach to your inner and outer steel shell idea.  Just pour in more graphite powder as (and if) it still depletes.

16
Electronic circuits / Re: Induction Heater schematic modification
« on: June 05, 2019, 07:11:35 PM »
Sorry to be bothering you guys again----
    I don't get very large changes in tank frequency as the metal heats up with the ZVS heaters that I have.  For example, starting out at about 40kHz, the frequency may increase by 2kHz or even less when a significant chunk of iron bearing metal is inserted into the coil, cold.  Then I see only a frequency increase of a few hundred Hz or so as the metal gets toward the curie point.
  Okay--- 
So it seems that you guys are saying that the circuit under discussion "listens" to see what the frequency of the tank WANTS to be and then changes the driving oscillator to match?  If that is what is desired, why bother, if all you are doing is to match what the present  frequency already is?

Also, I'd like to understand what the use of this circuit will be.  If I understand correctly, (and please correct me if I am wrong), this thing has a 15 volt power supply.   If so, it doesn't sound like it would be very powerful.  So, how much power are you expecting, and  what will this induction heater be used for?

17
Quote
If modding board is deemed necessary, do you think it would be safer to remove caps one at a time,  or make coils with lower inductance (there are two on board and just swap em)? 
My first choice would be to "make coils with lower inductance".  HOWEVER!!!!---  The two toroidal  chokes on the board are NOT the work coils.  They are there to decouple noise from the power supply.  It's the work coil that I would make with lower inductance.  That's what my work  coil data spreadsheet is all about.  I only list those two chokes  "FYI".
  I would NOT reduce the number of capacitors on the board.  All that tank circuit energy has to go somewhere and, with fewer of the same size capacitor, I'd thing they would heat up even more than they do now.  If you look at the way others build this kind of driver, you will see that they often attempt to spread that energy out by using many, many tank capacitors.  Of course in many commercial units, the capacitors are water cooled.  That's a whole different ball game.

18
The issue of changing frequency on the 2500 watt unit:
   Sure, it is easy to do.  Just remove some capacitors.  Just make coils that have lower inductance.  Do just one or do just the other, or do both.  You can see how all this relates if you watch my 1000 watt videos and visit my 1000 watt pages.
  A while back, I spent time determining how fast the Mosfet driver circuit can get the Mosfets into full conduction  SO THAT A USER CAN DEPEND ON ALMOST 100% DUTY CYCLE.
I have done that to my own satisfaction.  The oversimplified (but nonetheless useful) number for upper frequency is about 120kHz.  Higher than that and out go the Mosfets.
  But almost ALL of the work that I have been doing lately is the learn the minimum coil inductances that will produce the desired power transfers without exceeding my 120kHz upper limit.
  I think i am pretty close to having this one "in the bag" too, at least from the inductance standpoint.   I won't even connect up a work coil with an inductance less than 0.7 microhenry to the 1000 watt unit.  And, for now, I wouldn't go less than that on the 2500 watt unit either, since, as far as I can tell, they have identical Mosfet driver circuits.
  However, just to add to the still  UNknowns, I am NOT confident that we can 100% transfer gate drive concepts directly to the 2500 watt unit since we have 3 sets of  drivers in parallel. 
  Lastly, for today, I am not sold on the REAL value of going beyond 120kHz anyway. 
Sure, I have heard the more power gets transferred at high frequencies, but this offset by thinner skin depths.  Oh yeh? And by exactly how much?  And, is it worth the effort, when I see that a WIDE variety of small-end commercial units seem to be quite happy in the 30kHz to 80kHz range.
   Lately I have been spending a lot of time trying to improve my video capabilities so I can do two camera shoots better and be able to show the bubbling copper better.  I feel that you guys may be getting too focused on stirring, so I want you to see exactly what I see.  To that end, I am now into camera light filters and white balance issues.

19
Just in case everyone isn't "burned out" on this topic yet,  I just uploaded my work coil characteristics spreadsheet today.

It details my own observations about several work coils that I have gotten with various ZVS induction heaters or that I have made myself.
It, like most of my stuff, is a work in progress:
http://spaco.org/Blacksmithing/ZVSInductionHeater/Work%20Coil%20Data.xlsx

By the way, just yesterday, I noticed that the inside diameter of the graphite  crucible that I have been using for all my copper melts so far has eroded by about half, from its original thickness.

20
Electronic circuits / Re: Induction Heater schematic modification
« on: May 27, 2019, 04:27:10 PM »
Okay, please allow me to restate my question(s):

What is the actual  benefit that you see of changing the frequency as the metal heats up?

What is the  default frequency that is applied to the tank when the heating first begins?

Does the frequency increase or decrease as the metal heats up?
And, how much change is there?

As an example:   Let's assume that the frequency starts out at   50 kHz.
Does the frequency increase to just 70 kHz or so, or does it increase to 200 kHz or so?

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