On Sunday 31 July 2016 03:26:00 Erik Christiansen wrote: > On 30.07.16 12:43, Gene Heskett wrote: > > On Saturday 30 July 2016 08:10:20 Erik Christiansen wrote: > > > On 23.07.16 18:03, Erik Christiansen wrote: > > > Armed with that info, one unit might suffice, especially if the > > > junkbox includes reasonably equivalent spare MOSFETs. > > > > Such as those in the common atx power supply? > > They'll have pretty good voltage specs, e.g. 400 to 500v if for 220v > (>300Vp), but have an RDSon in the general vicinity of 100 - 200 mOhm > or so, rather than the <50 mOhm of a lower voltage device of current > manufacture, I figure. So they'll run hotter. > > Good results were achieved in one of the youtube clips, using the > Banggood unit, drawing 15 A. At 0.2 Ohm that's 15^2*.2 = 45W, shared > between two half-cycle-conducting MOSFETs. Add some for switching > losses, and bigger heatsinks or a gutsy little fan would definitely be > called for, unless the cooling water for the tube coil were first > routed through some an Al heatsink slab. > > Easier might be to parallel a couple of salvaged MOSFETs on modestly > larger heatsinks, for mounting space. I'm sure you're ahead of me > here, ready to point out that at half the current per device, the > dissipation will be reduced to a quarter. > > > Anyway, it seems they need a hard switched power supply, so turn it > > on first, then hard switch it to the unit. > > Yeah, a "Count to three" label on the switch could substitute for > timer and relay, but the auto-dropout of a latching relay would be > rather handy at power-off, so we're safe for the next turn-on. Might > as well add the timer, then. > > > My problem is sourceing a suitable supply. > > The RSP-1000-48 SMPS this guy uses: > https://www.youtube.com/watch?v=1wwlbN-9jsU > > answers to a quick google, with multiple suppliers. It just costs > around 9 times as much as the 1 kW coil driver. > > What some people do is retrieve an old microwave oven from the > recycling area at their local dump, extract the ~ 1 kW power > transformer, hoik out the high voltage secondary, and replace it with > a low voltage one. The rest you're likely to find close to hand. We > have a hard rubbish day twice per year, and there's always a few old > microwave ovens amongst the goodies left on the kerbside for a few > days, until the truck makes its way round. A cruise around the > neighbourhood late on the weekend before pickup day can be rewarding > for a dedicated repurposer. > > > I'd assume if I use A2, which is air hardening steel, that if I > > wanted full length hardening, I could simply pass a long piece thru > > it, paced to obtain the temp needed, that I would wind up with a > > full length hardened piece. But that generates a couple questions. > > I'm not sufficiently informed on the properties of A2 steel to answer > the questions which you've now answered anyway, but the ursine part of > my brain looks for bear traps, and I wondered if the zone-refining > effect of passing an incandescent zone down the bar would alter its > metallurgy, but I guess not. As you'd not be melting the zone, > alloying components couldn't migrate. (I.e. not in solution.) > > On 30.07.16 14:43, Gene Heskett wrote: > > On Saturday 30 July 2016 12:43:55 Gene Heskett wrote: > > > 1. Is the austenitic state hot enough for A2? > > > > Couple answers from the practical machinist blog. > > This on is no, the heat range for A2 is 1725 to 1750F. Thats a > > fairly tight spec that would need to be verified with a pyrometer, > > something thats not on my tool shelves. > > That's 940 to 954 °C, around bright cherry red or a bit more. Now, is > there a cheapo pyrometer with analogue output? > > > > 2. Does A2 need a faster cooling profile than I'd get by doing the > > > slow transport like this: > > > > Again no, A2 needs to "soak" at that temp for 20 to 30 minutes in > > order for the chemical changes to do their job. So it must be > > protected from the oxygen in the air, either by a controlled > > atmosphere, or by wrapping in SS foil, or possibly by dipping it in > > a flux powder once its hot enough to melt and make a coating of flux > > to block the air. > > OK, the pyrometer could measure the temperature of the flux layer, as > it'd be pretty close, I guess. It'd be possible to regulate the > temperature by gently oscillating the bar along its axis, increasing > the length of the heating zone as temperature rises. That'd increase > productivity rather than throttle the power supply back - something > that might be awkward with a fixed voltage SMPS. > > > That also demands a water cooling setup for the coil if its going to > > be excited for the several hours it might take to do a 6" long piece > > given the needed soaking time. > > For 6" I'd possibly make a smaller diameter coil with smaller Cu pipe, > and wind it 6.5" long. Spacing the turns a little bit more would stop > the inductance from increasing too much, and for a few dollars, might > do that job at one hit. See the length of this higher power job: > > https://www.youtube.com/watch?v=0vL-sArhmkI
Interesting. Both an insulated coil which I assume is water cooled, but it looks like he is tuning the frequency to maintain resonance. The BangGood device, since its self-exciting, would appear to do that automaticly. > Now you need to be able to drop the input voltage though, for > temperature regulation. Simpler might be to actively drive the > MOSFETs, and either shut them both down at the top temperature, or try > duty cycle regulation, as it does alter the energy pumped into the > tuned circuit. I might raise the price of scrap 1950's tech, out of service now for 8 years, old tv transmitters, but in both the RCA and GE transmitters in the 25 to 35 kw peak output range, there is a 3 phase powerstat rated at at least 2.5kw/phase, with a slowsin motor driving it up and down to regulate all the rest of the low voltage filament supplies. In the GE TF-3A, its controlled manually with a switch on the front panel, in the RCA TT25DL (new in 1962) a balance relay with platinum contacts watches its output and runs the motor. That "runs the motor" could be interfaced to a pyrometer to serve as the temp regulator. And it's big enough to run a 3 phase, 5 to 10Kw load. How many are sitting around in old analog tx's on mountaintops that have not yet been sold for scrap, I haven't a clue. Because it would when the part is cold, run itself to the up limit switch, I believe I'd have a PID controller watching the rate of temp rise so that it didn't overshoot the temp while the motor is running toward a lower voltage. That's Dgain I think. > Finicky isn't as easy as all the other firehose applications. Agreed Erik. And that auto-transformer by itself stands 30-32" high with the motor top, and occupies over a square foot on the floor, 2 if 2 or 3 inches of cooling space is allowed around it. SWAG at 200 lbs & change. I haven't a clue where I'd put it, my shop and garage both runneth over. I point that out as I have never heard of one of them failing and at one point 50 years ago, there were probably 500 or more of them in use here in the US. Here is one of that general appearance, without the motor on the top. <http://www.ebay.com/itm/3-PHASE-POWERSTAT-VARIAC-15-AMPS-7-3KVA-240-VOLTS-IN-0-280-VOLTS-OUT-/122032051715?hash=item1c69ad5603:g:W1oAAOSwkl5XdaiB> The motors are also in the never fail category, but since its custom hardware, I would save a lot of time by making an offer for one WITH the motor. It would be a forgotten resource now that hi-def is the law since June 30th, 2008, forceing the shutdown of all those old dinosaurs. For someone interested in doing this sort of heat treatment on a commercial basis, that could save you several thousand dollars in the hardware to do it, and give you + or - 5 degree control with the PID in good tune. Something else to watch for on fleabay if you are interested and have the real estate under a roof available. I don't, darn it. I saw 2 with motors, unlike the worm gear drive of the ones I am familiar with where the motor lays horizontally, but watch the input voltage, theres a batch that needs 520V 3 phase input. I've never heard of that voltage, so the sellers may be ignorant about how they work. They are more likely to be 480 volt input stuff. OTOH, those are older designs, and the std line voltage out of your duplexes has risen from 112 volts in 1947, to 127 today. So if these were made for 117 volt, then the multipier says they would be 480 volts when it was 117, and 520 now that 127 is the std. If it actually says 520, then its much newer than what I've many years experience with. But the old ones have tolerated that level of overvoltage for several decades, so its a never mind to me. Most are made with 3 taps the input can be fed to, but I never changed them, too hard to access w/o an engine hoist to pick them up out of their surroundings for access to the taps. Clearly, I have too many hobbies. ;-) Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
