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Topics - petespaco

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1
Electronic circuits / What happens when L and C are not matched?
« on: May 08, 2019, 04:42:35 PM »
Mads-
 The formula for  resonant frequency is: "Freq. = 1/(2pi X sqrt(L X C)).
This formula would imply, to me, anyway that ANY values of L and C will produce some resonant frequency.

But, I can find many references that say:
"Resonance occurs when capacitive and inductive reactances are equal to each other."
Well, that's fine, but we know that circuits DO oscillate when L and C are NOT equal.
Is this just a "play on words"?  The resonant frequency formula that I quote above doesn't seem to deal with that issue at all.

   I studied resonant circuits back in the early 1950's.  I vaguely remember that there is some negative "cost" to having L and C too far away from eachother, but I don't know why.

In my hobbyist work with the small ZVS induction heaters, I see that I can at least double capacitance or double inductance and still get the thing to oscillate.
My question:
   So what is the "cost" of "unbalanced" L and C in an oscillating circuit?

In my experiments so far, the main problem I see is reducing L and/or C so far that the oscillation frequency is  so high that the Mosfet gates can't turn on fast enough.  (This, of course, leads to overheating and failure.)
  But that still does not address that issue of "unbalanced" L and C.

2
I have been experimenting the the popular "12-48 Volt 1000 Watt ZVS Induction heaters" for a year or two and have many videos and web pages describing that work, as many of you may know.
   More recently, an improved version has become available and is being sold by well over a dozen vendors.  Instead of one pair of IRFP260N's driving the coil, they doubled up on them and added 2 fans on top.  The also added 50% more capacitance to the  tank circuit and increased the number of turns of the output coil from 7 to 10.  These tank changes should lower the oscillation frequency which is good for many things that people would want to heat.

  Just recently, I ordered one of them, a complete kit, called "Combo 2" by seller Aliexpress.
I had to wait quite a while for an analog ammeter and it’s here now.  I still haven’t connected it all up yet, but I have spent a lot of time unraveling the various  descriptions and pseudo instructions that I see on the vendor offerings.  These units are seldom soldi n as complete a kit form as the one the I got from Aliexpress.
Some vendors call them 1800 watt, some even call them 2500 watt, but I’m pretty sure they are all the same.
  Yesterday I put up a new web page to help new buyers understand what they just bought and how to set it up with a minimum of disappointment.
I tell you all this, because I’d like to get this link to others, since I am already getting inquiries anyway.
There are two web pages referenced here on this cover page:
 https://spaco.org/Blacksmithing/ZVSInductionHeater/ZVS1800Watt/1800-2500WattZVSInductionHeaterNotes.htm

Both pages are pretty messy, but, due to the apparent popularity of these devices, I wanted to get something out there.
Time will tell.

I will add to that page and to my youtube channel once I get my system up and running.

Pete Stanaitis
---------------

3
Electronic circuits / induction heating/Blacksmithing
« on: December 11, 2017, 04:30:06 PM »
Mads mentioned using an induction heater for blacksmithing; making knives.
  I do a fair amount of blacksmithing myself but am not a knife maker:
https://spaco.org/bk.htm

Anyway, I am very tempted to get one of the 7KW (sold as 15KW)  induction heaters from China.
Here's a guy in the USA who does a great job of explaining how they work and how to get one:
/>If you are at all interested in what he has to say, be sure to watch all of his videos on the subject.

Pete Stanaitis
---------------


4
Electronic circuits / What kind of oscilloscope to buy?
« on: December 08, 2017, 04:39:48 PM »
Hello Mads.
    I just saw your latest article on hacking the Induction Stove.
The amount of information displayed on the scope screen is pretty impressive.
Would you consider reviewing your Rigol DS 1504 'scope for us (me).
  My ancient Tektronix 422 is starting to fail and I guess I'm going to have to replace it one of these days.

I have spent a fair amount of time looking at specs for scopes within my price range (under $500 USD) and it is hard to tell if one scope or one set of features is better than others. 
Mind you, I bought about 50 of those Tek 422's in the late 60's, and they were a great field service tool for our needs back then.  But these days, I see all the digital scopes for sale, with lots of storage, etc..  I just can't separate all those features!!!

I won't need frequency response much over 50 MegaHz.
Two channels will probably do most of what I need, but the 4 channel idea sounds good, too.
One of the things that is really interesting is the idea of storing traces and being able to scroll through them after the fact.
I did buy a "knock-off" logic analyzer a couple of years ago (USD$8.00) and it does a surprisingly good job of the data storage, but it is only a 5 volt, digital signal only device. Works well with my many arduino projects, but not at all for this higher voltage analog stuff.
  A year ago I even bought one of those USD$50.00 DSO112 pocket sized 'scopes.  It works okay, but has only one channel and poor battery life.   And, since you have to switch screens all the time to access menus, it is a bit of a pain to use.  Triggering isn't the greatest.  Maybe it's just me.

Back to your  Rigol DS 1504:
Anyway, how do you like it?
Would you buy it again?
What issues does it have, if any?

Pete Stanaitis
---------------

5
Electronic circuits / 1000 Watt ZVS induction heater experiments
« on: April 16, 2017, 06:04:26 PM »
Several months ago I got one of the cheap 5-12 volt ZVS induction heaters from  China.  I tried it out and it worked okay, so I bought one of the 1000 watt versions.  Then I started a lengthy process of experimenting with that kind of unit to see how much power transfer to a load it could produce reliably.
Mads asked me to join this forum because I had been asking questions on his Royer Oscillator page and interacting with others on it.

So now I have a rather detailed a webpage that covers my experiments to date pretty well and several youtube videos on this specific subject.

4/17/2017: I am modifying this post because I didn't give readers the direct link to my ZVS 1000 watt induction heater page.
Mads discovered this omission and did insert it in a following reply, but I thought I'd add it here, in case a reader didn't notice it there:
https://spaco.org/Blacksmithing/ZVSInductionHeater/1000WattZVSInductionHeaterNotes.htm


Youtube Playlist :
https://www.youtube.com/playlist?list=PLVxWen9M87dBhvInCQ-3pELWdxCM3XH4I

Pete Stanaitis
--------------

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