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Messages - T3sl4co1l

Pages: [1] 2 3 4
1
Good stuff, Pete.

Pro tip, literal: the way we did coils with interesting geometry, was to use square or rectangular tubing.  This can bend very sharply without kinking or tearing, and zero-radius corners can be mitered (cut out a wedge in three sides, leaving a thin web along the back; solder or preferably braze the seam closed).

The hard part is finding the stuff.  McMaster does sell it, in short lengths (and McMaster typical prices).  Never saw where we got the stuff from, but it was by 25'+ rolls, probably not cheap either way.

Swaged fittings, and using ~telescopic sizes for couplings and adapters, is an excellent method, of course.

I highly recommend brazed joints.  These are super easy in copper: you can use a self-fluxing (phosphorus-bearing) rod like Harris Dynaflow, no paste flux needed.  A plumbing torch will do for small tubing like this, or a somewhat bigger torch for bigger stuff of course.  The filler is considerably stronger than the base metal, no worries about strength; actually if anything, that's a liability as the joints are inflexible and break rather than bend -- plan your joints accordingly.

Tim

2
Electronic circuits / Re: I need a developed circuit for induction heater
« on: September 10, 2019, 04:54:35 PM »
I'm back in active development of one, as a matter of fact:

https://www.seventransistorlabs.com/Images/Induction1501.jpg

Let me know if you'd be interested in a kit or complete machine.  The control board should also be useful for TCs (though the maximum switching frequency is kind of low -- a TL494 at heart).

Tim

3
Dual Resonant Solid State Tesla coils / Re: UD2.7 Gate Signals
« on: September 07, 2019, 04:51:25 PM »
About the comparator, only thing that comes to mind is lack of supply bypass, or ground bounce, which also depends on layout.

Tim

4
Dual Resonant Solid State Tesla coils / Re: UD2.7 Gate Signals
« on: September 07, 2019, 01:15:01 PM »
I don't know what else to tell you... the answers are in the very thread you linked ???

Tim

5
Vacuum tube Tesla coils / Re: My 833A VTTC
« on: August 29, 2019, 09:01:01 AM »
Nice!

Tim

6
Electronic circuits / Re: Version 2 of power supply
« on: August 28, 2019, 03:18:49 AM »
Seems like a lot of diodes for not a lot of capacitors?

Tim

7
Yup, it's a polyester, so you're doing an acid/base catalyzed reaction, hydrolyzing it into its components (alcohols and acids).  Specifically, ethylene glycol (the major component of antifreeze) and terephthalic acid (which is much more fun to pronounce than it is to type, I must admit).

If done in a shortage of water -- say in concentrated sulfuric acid, a reasonably strong dehydrating agent and also a strong acid -- the reaction goes the other way, condensing alcohols and acids into esters (Fischer ester synthesis reaction).  An O-chem class staple being amyl alcohol + acetic acid ==> amyl acetate (a major component of banana scent). :)

As for storage, prefer nonreactive polymers like hydrocarbons -- polyethylene (HDPE) and polypropylene most common.

Glass is perfectly fine too, if less rugged; but very strong NaOH should not be stored in glass as it will be attacked (forming some water glass in solution).

NaOH also reacts with atmospheric CO2 (forming the much less aggressive, but still basic, sodium carbonate aka washing soda), so it needs to be stored tightly, preferably dry.

Tim

8
Capacitor banks / Re: Suitable capacitors and switches? 10kV
« on: August 16, 2019, 09:28:35 PM »
Does the spec give rise time and pulse width?  Does it conform to, or resemble, any existing standards e.g. IEC 61000-4-5?

Just dumping a capacitor, without any impedance controlling the waveform, is likely to give extremely destructive results!

You may also need a coupling network so as to apply it to active e.g. mains connections properly.

Calling it ESD sounds very peculiar; only surge has energy levels like this.  ESD as such is in the 10s mJ range (typically capacitors of 300 to 1500pF).

Tim

9
Electronic circuits / Re: ESAB Power TIG 200 Welder Teardown
« on: August 16, 2019, 09:14:36 PM »
Popping audio. :(

Surprised at the relatively small transistors, that's why there's so many I guess.

The choke hanging off the transformer is the choke-input filter; the outermost choke is just for HF start, and whatever amount of filtering it adds of course. :)

Input power cable looks awfully dinky; but, I guess if that's 400V 3ph, it really only needs about 10 amps, huh?

Tim

10
Probably just that the impedance is so high, from the high inductance.  Same overall dimensions but fewer turns, should be back with normal power levels I would think.

Peter, try using it to boil corn or maybe a fish boil  ;)

Back when I was working at an induction company, there were at least several lunches I ran on the machine in the proto lab.  Seems that a can of Chef Boyardee can't take much more than a kilowatt, two even with stirring, and so the heat time is about two minutes.  Just as you'd do with a bowl of the stuff in a microwave oven, oddly enough. ;D

Tim

11
Solid state Tesla coils / Re: tesla coil varnish is dumb
« on: July 14, 2019, 09:59:40 PM »
Huh.  What's the point of varnishing the outside, if there's air between the wires, under the tape?

I have one experience with water-based urethane; I was thoroughly underwhelmed by its performance.  It cost much more, went on much thinner (it's mostly water, so the dried film is quite thin and many coats are needed), is softer (though still strong enough not to be peeled off by fingernails alone), and seems to turn a bit gooey/sticky with prolonged contact with oils.

There probably are better-performing mixes, and I happened to get the worst one out there.  Ironically, I feel like the stuff I had, wouldn't have given you trouble -- it doesn't seem brittle enough to crack.  But then again, vinyl tape is rich with plasticizers (basically, oils that turn the plastic gooey -- pure PVC is a brittle white solid -- see where this is going?), and maybe that's strained or weakened your coating, causing it to crack.

Varnish is kind of dumb anyway, since at the voltages we're talking here, you need whole cm's of thickness to effectively insulate something.  Modest layers can still provide some protection, such as corona suppression or protecting against smaller streamers; I don't have enough experience in this direction to know how significant this is, so I'll let others fill in.

Tim

12
If that's the traditional combination of materials, it probably won't be very conductive, and the coating is a flux/slag material that tends to bead up on the surface and drip off (presumably can be refreshed with the right goop).

SiC is a modest conductor when heated, making microwave heating possible, and maybe induction still (but maybe with higher voltages/frequencies than are available here).

SiC-graphite crucibles can practically be quenched in water; they're very tough, as ceramics go. :)

Tim

13
Yes, exactly.  There is a best-load matching condition.

Too low resistivity, and there's no voltage drop in the work, the magnetic field reflects nearly perfectly, and frequency simply rises, instead of DC current being drawn.

Too high resistivity, and there's no current flow, the magnetic field penetrates nearly perfectly, and little DC current is drawn.

We know that, somewhere inbetween, current consumption is higher.  We don't necessarily know if we're on the rising or falling slope of that curve, or optimally on the peak, but we know definitely that there must be a peak, somewhere between these extremes!

This has been today's shop application of calculus.  Cheers. ;)

Likely, it just so happens that a full heel of molten copper is below the peak, while a chunk of steel above curie temperature, is above the peak.  Graphite of this thickness is certainly above.

Different people have different setups, landing above or below as well.

The positioning of that peak, is driven by the number of turns of the work coil, how close it is to the work, the characteristics of the power supply, etc.  Frequency affects skin depth, which affects the equivalent load that a given chunk of material reflects.

If you're below the peak, I would suppose, try adding another turn or two; if below, remove a turn or two.

This type of supply also delivers the most power into the lowest Q factor, and the lowest impedances.  Q can be lowered by reducing the distance from coil to work.  (You need some space for insulation, and loads like copper won't give a terribly low Q anyway, even at point blank distance; there's only so much room to push in this direction.)  Impedance can be lowered by reducing inductance and increasing capacitance.

Tim

14
When the load resistance is low (e.g. cold copper), it tends to reflect rather than absorb magnetic field; this reduces power consumption compared to a better matched load.

Whether current draw increases or decreases with heel size and temperature, depends on which side of best match you're running at.  Which in this case I think depends on the crucible thickness, and porosity (overall conductivity), as far as how much magnetic field it absorbs before reaching the copper within.

Tim

15
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.

Startup is an issue at very low Q factors.  Transistor gain is quite high so it's not usually an issue at common Q factors.

You might just see it with copper coils tightly fitted around steel pipe, or with lossy coils (say a stainless pipe coil used for process heating).

Frequency is a problem for this circuit for example,



which runs around 500kHz, but can lock into other modes in the 400-650kHz range depending on what load you have attached.  The problem is if there is extra capacitance at the load, in addition to what's on the oscillator board itself.  The connecting wires between oscillator and load form another resonant circuit, and the frequency response becomes much more complicated.  In this case, the transformer is a step-up and its secondary has a resonance near this frequency, even if I didn't put explicit capacitors on it.

As I said, you're less likely to have problems with this, at low frequencies where the capacitors are more likely to act together.

Tim

16
For a typical e.g. N87 material, at that frequency and size you will want Bmax ~ 70mT, maybe more or less.  Expect a core around 70mm o.d. (toroid) or ETD50 (E-E style, various cross sections).  This should be a good starting point; vary size larger or smaller depending on how much winding area is needed.

Flux density Bmax gives the volts per turn:
Vpk / N = 4*Bmax*Ae*Fsw
for a square wave with full duty cycle (if this is a full-wave forward converter or the like).  Ae is in the datasheet, and N is the number of turns.

What leakage inductance do you need?  Litz has the regrettable property that, because it's transparent to magnetic fields (that's how it works), all the space within as well as around the cable counts towards leakage inductance.

For example, if you're making a welder with DC output, you'll need leakage low enough that it doesn't burn out your diodes.  That would be, uh, well 0.5*LL*Ipk^2 is the energy in the leakage, so the power dissipation (as diode avalanche or burned in a snubber) is that times Fsw.

If you use about a meter of cable for the winding length, with no interleaving, just overlap typical of a toroidal transformer say, then expect around 0.6uH of leakage.  Which would give, at 80A and 200kHz, 384W of dissipation.  Indeed, 0.6uH would drop 60V at 80A and 200kHz -- this is actually so much leakage, compared to your load impedance (less than an ohm!), that such a transformer would actually be practical in a resonant topology!

If low leakage is a concern, consider using alternating layers of foil on a rectangular style core (EE?).  A planar transformer is also not unreasonable, but gets a bit challenging to design at this scale.

Tim

17
Do you think, there is an principal limitation to the ZVS Royer circuit, like efficency or maximum Power output, compared to more complex used circuits?
Except for the savety and that it's difficult to adjust your output power.

And stability, because it's just a dumb oscillator and doesn't always start up at all, or at the intended frequency (more a problem for high frequency oscillators).

So yes, that's all.  Like how a car is an engine on wheels, with steering.  It's not like you need a throttle, or brakes, or a windshield. ;)

So, that's why we design more complicated circuits.  They're not very complicated really.  Tesla coil drivers have been made worse than what's needed for this.  (My typical controller circuit is implemented in about 200 components, maybe not something you really want to build a kit of, but not at all impossible.)

Tim

18
Electronic circuits / Re: Induction Heater schematic modification
« on: June 06, 2019, 09:08:12 AM »
Hah, I forget that Uzzors used some of my bitmap schematic symbols from back in the day. :)

Yeah, that's about right, though again it doesn't have an enable, so it's always flat out and you don't have any way to stop it if something goes pear-shaped.  Like if the inverter draws destructive current or such.

Tim

19
You may find this of interest:
http://hamwaves.com/antennas/inductance.html

Of course it doesn't give loaded Q, but unloaded L and Q at least are nice.

From Q and applied voltage, you can calculate coil losses, and then idle current, and get an idea of what loaded current consumption will be.

Loaded Q is best guesstimated from ratio of enclosed areas, and typical values for materials.

Tim

20
Electronic circuits / Re: Induction Heater schematic modification
« on: May 27, 2019, 09:18:54 PM »
Depends on the load.  The most extreme possible case would probably be around a 2:1 change, for a steel (~half freq) or copper (~double freq) pipe fitting tightly inside a solenoid coil.  The change under operation would be due to, say, melting a slot in said pipe, breaking the circuit.

Which would also be a fairly sharp transition when it breaks.

Frequency is normally starting high, but this circuit has no enable or startup condition so it reduces to a power-on case, which is around zero since the filter capacitors are ground referenced.  Which is, I forget what the 4046 does, is that minimum frequency?

Tim

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