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Messages - petespaco

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1
Re:
Quote
What of a breaker to power the coil. Is that recommended?
I am pretty certain that most modern switched mode power supplies, such as the one there, are smart enough to only connect their output to the load after they are ready to deliver full power.
  So, a "breaker" or switch between the power supply outlet is not crucial for normal operation.
But I do like to have a way to shut off power to the while still allowing the water pump and fans to run while the induction heater board  cools off..
However, if the pump and fans ARE powered by the DC power supply, (through a small buck converter) you will need to make sure that their buck converter input is connected directly to the power supply's output, not to the induction heater board.
  I can't tell from the pictures whether there is a buck converter off of the 48 volt supply for the pump and fans or whether there is a small separate 220 volt to 12 volts (or whatever that pump takes) power supply that powers them.

Since I do not have one of these exact units in front of me, I have to do some guessing here.
---- I used to be part of a group that had to write completely unambiguous test questions.
You may have NO idea how hard it is to do that.
It can be just a hard to write completely  unambiguous answers to the questions of others sometimes.
So, if what I say does not make sense, feel free to question my answers or to ask for clarification.

I do not consider myself to be a "master" at anything.  Maybe just a page or two ahead of you in the textbook,
Pete Stanaitis
---------------

2
Answers, one at a time:
-Will 1100 watts be enough to melt metal?
    "Yes" to small amounts of copper, aluminum, brass,  silver and gold, etc. using an insulated graphite crucible in the work coil.
     Maybe up to about 200 grams or so.  You can see from my copper melting videos that I have melted as much as about 500 grams with the 2500 watt unit.
    "No" to steel or other ferrous metals.  Once they pass the "curie point" in temperature, (about 1500°F or 815°C) the heating rate drops substantially.

-Also needing a 12vac---
  Aren't the fans and pump built in to and powered by, the device?    For my own units, the fans and pumps are 12 volts DC not AC
Here is a unit that looks like the one you bought:
https://pt.banggood.com/220V-2100W-Mini-Induction-Heating-Machine-Heater-Air-Water-Double-Cooling-DIY-Device-Science-Model-Kit-p-1410359.html?rmmds=buy&cur_warehouse=CN
If it is like yours, I think I see a water pump and I see wires running from the fans to a circuit board below them.

-Can I plug it into the stove outlet with the appropriate plug?
   I assume that your (kitchen?) "stove outlet" is a 220 single phase outlet to answer this question.  If this is true, you could melt about twice as much copper.
   Depending on the stove and the age of the installation, it may have either a 3 wire or 4 wire plug/receptacle.  You will be handling a lot of power and ,
   of course, lethal voltages, so you need to know what you are doing from a safety and fire prevention standpoint. 
   So my answer is "Yes", but I suggest that you  get some help to get the wiring correct.  You don't get a second chance if you get it wrong.

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

3
This datasheet does show input voltage derating:
http://www.amppower.de/datas/APR48-3G.pdf
See right hand graph on page 2.

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

4
Sorry, but I don't know what wish.com is and I do not wish to register there.

I need a link to the advertisement for the place you bought it.

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

5
Post a link to the product that you bought.

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

6
Notes on the negative effects of increasing operating frequency of the ZVS induction heaters:
---------------------------------------------------------------------------------------------
Many of you are probably tired of hearing me talk about being careful to keep the Mosfets from spending much time in the linear mode.
But here I go again:
  We can easily see that the idle current varies when we change work coil designs.

From my own work coil data spreadsheet, I recently noticed that idle current and frequency seem to vary together.  When I plotted 9 pairs of idle current versus frequency observations,  I could see the relationship easily. I got a correlation of about 0.8.  Of course "correlation" does not necessarily equal "causation", but it seems reasonable to me.  It see this relationship as another indicator that higher frequencies create more lost power within the ZVS circuit components themselves.  This, in turn, leads to more stress on, particularly, the Mosfets and the tank capacitors.

But why do we care, as long as things seem to work okay?
 Well, here are a couple of reasons:

1. Assuming that you or your system has a maximum safe current limit, the higher the idle current, the less current there is available for heating the work.
In my case, the maximum sustained current that I will allow on my 1000 watt unit is about 22 amps TOTAL.  And, for my 2500 watt unit, it's 50 amps, TOTAL.
I hope that is clear to everyone.

But--- I think this item is even more important:
2.  The Basic ZVS power circuit that most of these Chinese ZVS induction heaters use works most reliably at a frequency below about 100 kHz.   And, the lower, the better, in my view!!!

So, when you design a new work coil, you need to know whether it will overstress the system or not.
You can quickly check it out by  powering the system up and noting the idle current. That current is primarily heating up the Mosfets and the Capacitors.  Of course it also heats the work coil, but as long as we are water cooling it, we won't worry about that.
   If the idle current is higher than about 8 amps, I think you will be stressing the system more than it was designed to be stressed.
See Chart:



7
I am using some of my  at-home time to clean up my two ZVS induction heater breadboard setups.

For the 1000 watt unit, I still had been getting 12 VDC for the water pump and the pcboard cooling fan from an automobile battery. Other than that, the whole system runs from the (USA) 120 volt mains.  And I had to plug in 3 other things to get it going:
-Radiator cooling fan
-48 volt power supply
-5 volt wallwart for the frequency meter

  So I am in the process of adding a walwart to replace  that 12 volts DC and a dedicated power strip for the rest.  This way, all I have to do is to plug in that one power strip to bring the whole thing to life.
   This whole system is mounted on 1 inch thick board that is about a foot wide.  That board is sitting upon a cart that is about 2 feet square.  It takes up a lot of valuable shop space. So, once I am done, I can put the whole system up on a shelf until it is next needed.   The cart can be stored someplace else until I get another wild idea.

2500 Watt ZVS induction heater:
  The big issue here is that, since the power supply requires 240 VAC, I have to locate the machine close to an outlet that puts it IN THE WAY between my engine lathe and my power hammer.
So, I am adding a new 240 volt outlet on the other side of that shop wall, so I can move the heater into another, slightly less cluttered room.  This has turned into a big deal since I have to work inside the wall, struggling with 10 gauge wire to add the new outlet.  Also, since it's not a good idea to go hardware store shopping these days, I am getting parts online.
This system is on its own wheels, so it will continue to take up floor space, but at least it won't be in the way of the lathe, powerhammer and grinder. But I will also add a wallwart to this one to remove the need to take water pump power from the pcboard, giving me a couple of extra amps for output power.

I think I may do a couple of aluminum melting experiments, just to see if my hypothesis that aluminum acts a lot like copper is true or not.

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

8
A "Corona Virus"?

9
Electronic Circuits / Re: TVS diode selection for 400v transistor
« on: April 09, 2020, 05:38:35 PM »
Quote
I was OK with MOSFETs - I bought 10 IRFP450s from Maplin for £3 each in the 90's and never had a problem in LOPT or ignition coil flyback circuits (with RC snubbers). As soon as I substituted IGBTs, they started popping. I gave up on them until fairly recently.

Could the problem with the IGBT's be rise time?
I read someplace that IGBT's normally aren't used at frequencies over about 20 kHz.   I assume that means that they don't/can't turn on as fast as a Mosfet in a given application.  And, if 20 kHz is the upper limit, approaching the speed might lead to  poorer performance.  And, come to think of it. you didn't discuss heat sinking or cooling.
   
I also read that Mosfets are good to about 200 kHz.
With the ZVS induction heaters that I play with, it is easy to see that turn on times start stretching out  significantly at about 120 kHz.  And, when they do. heat starts building up pretty fast, as you would expect.

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

10
Electronic Circuits / Re: TVS diode selection for 400v transistor
« on: April 07, 2020, 12:13:11 AM »
I wonder if electron microscopes might use/still use a flyback transformer.
I googled:
flyback transformer for electron microscope
and got several hits for companies that appear to make and/or sell them.

We used to have a machine that worked sorta like an electron microscope, at 20,750 volts (supposedly, just below the level where x-rays would become a problem).  Instead of scanning, it wrote characters about 120 microns high onto our special dry processed microfilm  (3M).  At the time, one of my jobs was to make sure that the flyback transformers were up to spec.   We had them made by Setchell-Carlson in St.Paul, Mn., in small quantities, of course.
I visited their lab a couple of times to work out specific issues.  They really knew what they were doing.

FYI, in case you are interested, here's a webpage that describes that machine:
https://spaco.org/History/3M-Graphic-Systems-Hardware-History/115EBR.htm

Pete Stanaitis
---------------
 

11
Electronic Circuits / Re: Smoking power resistor wattage overhead
« on: March 28, 2020, 03:10:04 PM »
Just a comment about what's hot (to the touch, etc..)and what's not:
   At work many years ago, we used a UL standard for making sure that hot surfaces were not too hot for users to touch.  Like the cabinet of a business machine.     IIRC,  the upper limit for being able hold your fingers on a surface for any amount of time was 137°F, or about 58°C.

So I just found this:
"Typical maximum temperatures for carbon composition resistors would be around 100 to 120°C and for metal and oxide film types, about 150°C. Wirewound resistors can operate at higher temperatures up to around 300°C."

My point is----- just because it's too hot to touch doesn't mean its over its maximum operating temp.

I suppose one could actually measure the temperature of the device, but don't use one of those non contact IR meters unless you understand how their field averaging works.  Many of them measure the AVERAGE temperature at an 8:1 ratio.  This means that, if the meter is 8 inches away from the surface to be measured, it will average the temps within a one inch circle, not just your resistor!

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

12
Melting Aluminum with the ZVS induction heaters:
   I guy recently asked if he could melt a half  Kg. of aluminum.   I haven't tried melting aluminum at all. 
I had assumed the aluminum would soak up energy about as well as does copper; that  is almost none.
There are a few videos out there but I saw only one where the guy was measuring current.  And, indeed, I saw no appreciable change in current when he added strips of aluminum to a graphite crucible.    The only caveat is that he was using a Litz wire coil on a Chinese 1000 watt unit and was only getting about 8 amps at about 40 volts .  I'd assume that Litz wire probably gave him a much higher frequency.  And, his crucible was quite a way from the inside of the coil.
  Maybe I need to try it out just to verify/determine the relationship between the two metals. 
Any interest in that?

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

13
Electronic Circuits / Re: Simple trickle charger idea
« on: March 04, 2020, 01:01:41 AM »
Interesting thought.
 But I don't know if it's good enough to properly recharge that type of cells.
I looked at one site that discusses the charging profile for this type of cell and here it is:
1. Conventional charging
During the conventional lithium ion charging process, a conventional Li-ion Battery containing lithium iron phosphate (LiFePO4) needs two steps to be fully charged: step 1 uses constant current (CC) to reach about 60% State of Charge (SOC); step 2 takes place when charge voltage reaches 3.65V per cell, which is the upper limit of effective charging voltage. Turning from constant current (CC) to constant voltage (CV) means that the charge current is limited by what the battery will accept at that voltage, so the charging current tapers down asymptotically, just as a capacitor charged through a resistor will reach the final voltage asymptotically.

To put a clock to the process, step 1 (60% SOC) needs about one hour and the step 2 (40% SOC) needs another two hours.
----------------------------------------------------------------------------------------------------------------------------------------------------

I do mess around with Li ion cells to some degree and I use the TP4056 (or TP4056A) charge controllers.  They cost less than USd$1 each and do handle the profile for THAT kind of cell.
I also have recharged many of those Li ion cells with a simple linear charger, but I watch the voltage carefully and switch to constant voltage when its time.

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

14
Water Cooling Notes.  Here is the reply I gave to a guy recently relating to water cooling the work coil:
----------------------
I have a couple of questions if you don't mind.
where did you get your radiator from? I am using a 12x 5 cpu cooling radiator and it can't keep up with the required cooling.
----------------------------------------------------------------------------------------------------------------------------
I bought several radiators like the ones you see in my videos at a local online  auction house several years ago. They were all used ones. That style of radiator has one continuous tube that runs from input to output.  There’s no “tank” at the top, so it doesn’t really matter which end is the input. Although I have not tried this myself, I think the heater core from an automobile passenger heater would work well, using the fan/blower that comes with it.  The radiator on my 2500 watt unit holds a bit over 2 quarts of water, by the way.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------

There are several air pockets in the lines that may be the issue. Any suggestions on how to bleed the air out of the lines?
-----------------------------------------------------------------------------------------------------------------------
   Re: air pockets-  It may not be apparent on my setups but:
  Note that I have an expansion  chamber (later on, I used a plastic pop bottle, upside down with the bottom cut out) on both heaters.  I either take water from the outlet just below the expansion port or from the other end of the radiator.  Makes no difference, as long as the water level is higher than my piping to the workcoil , and as long as any bubbles that form are allowed out the expansion vent so they are  not trapped within the system. This expansion opening is also very important since the water expands significantly  when heated, and its also a sort of safety feature in case the water were to boil.
  One other REALLY important point: The pump MUST feed water into the BOTTOM of the coil.  This is the only way to be certain that the work coil is FILLED with water.  I once made the mistake of doing that backwards and produced many bubbles of steam before I realized what I had done.
------------------------------------------------------------------------------------------------------------------------------------------------------------

I have the same pump as you, but I am using 3/8 "clear tubing. I also can't get the pump to really circulate the water like it should be in my opinion.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Try to keep the pump and the radiator at about the same level.   Some guys put their water supply (usually a pail of some sort) on the floor, while the induction heater and pump are up on a bench.  The pressure output drops rapidly as the height increases, leading, of course, to lower flow.  Them if your radiator is very restrictive at all, flow gets even worse.

Link that will take you to most of my videos and webpages on the subject:
https://spaco.org/Blacksmithing/ZVSInductionHeater/1000WattZVSInductionHeaterNotes.htm

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


15
Electronic Circuits / Re: Induction heater
« on: February 07, 2020, 11:20:26 PM »
You might begin by setting some goals:

-What do you want to heat?
-How much power  will you need?

Basic assembled ckt boards  (without power supply, coolant pump, etc.):
150 watts? USD$10.00
1000 watts? USD$30.00
2500 watts? USD$50.00
7500 watts? USD$1000
and up, to many megaWatts.

The work coil is about the least complex component of the whole project.  Also, I wouldn't  a solid coil.  You need one that can be water cooled.

IGBT's?   I just read that they work best below about 20 kiloHertz.  If that is true, you may not find them a good choice for induction heating in the lower ranges above.  I hope others will comment on this point.

Start by googling "induction heating" or something like that and spend some time learning.

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

16
Electronic Circuits / Re: Prototyp construction techniques
« on: February 06, 2020, 10:43:36 PM »
@Da_Stier:

I don't think there ARE any links in that Word document.  Did you actually get 404's someplace?
I did notice that one time it took a while for the images to load, though.
If you did find an actual link, I'd appreciate it if you would reply here with the info.
I did notice that some of my spelling errors  and poor grammar (shame on me) have red or blue underlines, but they are NOT links.

Has anybody else had an issue?

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

17
Electronic Circuits / Re: Prototyp construction techniques
« on: February 06, 2020, 09:02:34 PM »
Wow!, Mads, you do some really nice looking complex stuff.

Since we are on the subject of prototyping, here's the link to document I put together 5 or 6 years ago about various methods of assembling electronic stuff:
https://spaco.org/Computing/Wiring up electronic components DetailWPix2.doc

Is there anybody on this forum old enough to know what a "Fahnestock Clip" is?

Pete Stanaitis

18
Lately some Russian hobby size induction heating videos have been coming up on my Youtube recommended list.  I don't understand the language, but I can get a pretty good idea of what is going on from almost all of them.
  Anyway, here's one where the guy simply couples the output from an induction HOB (British for "Hotplate Or Burner) to some copper coils and then parallels the output part of the coil structure to some capacitors.  So, as far as I can tell, without modifying the HOB in any way, he has a high frequency driver.  Maybe not great at power transfer, but I thought it was an interesting Hack:
/>
Pete Stanaitis
---------------

19
Thank you for your kind words, Mads.
   Nice demo of the little 150 watt unit.
Several members of our blacksmith club enjoy making things from horseshoe nails. This unit is just right for that.
If you power it from a 12 volt car battery (or appropriate rechargeable battery pack), you have a very portable heat source.

Salt spoons and finger rings are but two examples.
Works well for making tiny swords from double headed (duplex) nails, too.

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

20
Electronic Circuits / Re: 10 kVA Kjellberg Plasma Cutter CUTi 31 Teardown
« on: January 05, 2020, 01:10:11 AM »
I agree that many of our shop tools (as well as their owners) suck in a lot of bad dust.  We should all probably have  good exhaust systems, but yet, I don't.  I have much better dust collection in my wood shop than I do in my metal shop.
Not so worried about the old stick welder and big mig welder because they don't have any electronics to speak of.  But I think there's a big opportunity for the makers of newer inverter based equipment to do a better job of filtering.
I have blown up enough Mosfets over the last few years with my induction heaters to understand how some conductivity between gate and drain/source could lead to disaster.
  Several months ago, when we were holding a blacksmith meeting at a local chain Welding supply company, I noticed a large pile of trade-in welding power  supplies that was being scrapped.  Maybe for those same (conductive dirt) reasons?

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

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