Refresh of "Big Inductor, DIY Style" - Page 1
Forum section: electronics / projects

author: Purduephotog
author_rank: Regular Contributor
timestamp: January 07, 2017, 08:38:43 pm
content: Sung to... Gangnam StyleShort: Were I to buy a Torroid (aliexpress, micrometals if I can find a distributor), and wrap it with 4 gauge Aluminum wiring... what should I expect?https://www.eevblog.com/forum/projects/big-inductors-diy-style/I have an AC buzz box welder (HF, if you must), which runs around 100amps max. I've already added a rectifier and filtering caps, bleed resistor, better fan, and feed control. Why? Because it's a combination interesting and what I could afford at the time.Now I need to add an inductor to control the current surges. I made a few small ones using 10 gauge stranded wire, wrapped in parallel, around an old MOT- and it rattled and shook and otherwise made a ruckus.I would like to follow in the above mentioned link steps.http://www.micrometals.com/pcparts/torcore7.htmlfor really large inductors.I had intended on using Aluminum 3.5 gauge wire (0.220" diameter, conservative) and wrapping an old E core that I've been separating into sheets for the last few days. Heat it up with the garage turbo-heater to soften the shellac and then chisel apart the alternating direction E sections. However I'm thinking that I could purchase a T650-52 torroid and wrap that by hand a heck of a lot easier than finishing up the E core, gluing them back together, wrapping a bobbin and sliding it onto the new core.Frequency? 60hz mains. 100 Amps (ish). <50V DC.

author: dmills
author_rank: Super Contributor
timestamp: January 07, 2017, 10:35:08 pm
content: A 52 mix sounds like a ferrite of some kind, it will be deep into saturation with 100A of near DC in play, you would have better luck with a powdered iron composition.You need a gapped core, lower inductance but much less prone to saturation.Maybe try gapping the center post of that MOT with a slitting saw, it will ruin it as a transformer but might make it workable as a high current inductor?Regards, Dan.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 07, 2017, 10:50:53 pm
content: Go back to the MOT. Put in a gap, maybe 3mm worth (1/8") between the 'I' and 'E' parts. You'll probably get around ten turns on it, but the more the merrier.Powdered iron isn't big enough to be economical. Consider an MOT-sized stack of toroids...To have any hope of success, you need the filter choke to be about the same size as the power transformer itself. So that should give you some idea of just how big it has to be.Dmills: #52 is a powdered iron, as is everything else from Micrometals. Look up the properties on the same website. The highest permeability they offer is 100 or so. Saturation comes very gradually, typically reaching ~50% in the 2000At range (that's 20 turns at 100A!). Inductance vs. magnetization curves are given for all the 'power' type materials.Tim

author: dmills
author_rank: Super Contributor
timestamp: January 07, 2017, 10:57:53 pm
content: Thinko, you are of course correct, but the MOT with a gap is probably still the better approach.Regards, Dan.

author: Purduephotog
author_rank: Regular Contributor
timestamp: January 07, 2017, 11:20:54 pm
content: Well it was a small MOT. Now I've been separating a huge forklift charger transformer. It easily weighs more than the welder.Don't I want to be saturated for DC welding?

author: Ian.M
author_rank: Super Contributor
timestamp: January 07, 2017, 11:43:27 pm
content: How many identical MOTs (or at least, with identical cores) can you source? You can stack a pair of cores side by side to increase core area, and discard the 'I's and use a pair of E's to double the available winding area.As Aluminium only has 60% of the conductivity of pure copper, its a false economy for a one-off when you have a limited core aperture to work with. Probably the best option would be to wind the choke with heavy copper foil or sheet, with a single turn occupying the full width of the aperture, interleaved with Kapton tape stuck to its inner surface and wrapped over the strip edges. The inner end of the winding can be wrapped around and soldered to a heavy copper wire running parallel to and against the side of the center leg of the 'E' core. Winding in situ on an E core is a mug's game. For ease of winding, make a dismantleable mandrel to hold a home made flanged bobbin or with enough clearance to allow the wining to be taped to insulate it from the core, then insert the core after the winding is complete and fully taped to secure the outer end.If the completed assembly is varnish impregnated under vacuum and properly cured, and the core properly clamped with rubber pads, it wont buzz.

author: Purduephotog
author_rank: Regular Contributor
timestamp: January 08, 2017, 12:47:30 am
content: https://imgur.com/gallery/C9og1My slowly separating core.

author: orolo
author_rank: Frequent Contributor
timestamp: January 08, 2017, 01:38:52 am
content: I've been very interested in iron powder toroids recently, but I don't really have much experience. I'd like to try to predict what is achievable taking a core to the limit, just to see if I got the main ideas right. In the very probable case I didn't, please correct me.So, for a T650-52 inductor. The core has l=39.9cm of magnetic lenght, A=18.4 cm^2 of magnetic area and 734cm^3 of volume. For this material A_L = 405 nH/N^2.Theapplication notestell us that, for this material, a magnetizing force of 90 Oersted will reduce its relative permeability to 40%. Let's take that as a limit, and use the suggested formula:\$ H = \frac{0.4 \pi N I}{\mathcal{l}} \quad \rightarrow \quad N = \frac{H\mathcal{l}}{0.4\pi I} \$So N = (90*39.9)/(0.4*pi*100) = 28.57 turns maximum. Let us take N=28 turns and compute the inductance achievable:L = A_N*N^2 = 405*28^2 = 317520 nH = 317 uH aprox. That's the maximum inductance you can squeeze from this core at 100A.For 100A max current at 60Hz, the voltage across the inductance is V = 2·pi·f·I·L = 6.2832*60*100*317e-6 = 12 volts peak, 8.5V RMS.The peak flux for the toroid shall be:\$ B_{peak} = \frac{10^8\cdot E}{4.4 A N f} \$So B = 8.5e8 / (4.4 * 18.4 * 28 * 60) = 6249 Gauss. As expected, this is quite high, but not complete saturation.We have afitting formula for core losswhich suggest that, for the 52 material,CL = (60.0/(1e9/(6249.4**3) + 1.1e8/(6249.4**2.3) + 2.1e6/(6249.4**1.65)) + 6.9e-14*6249.4**2*60.0**2) = 44.3 mW/cm^3. Looking at the tables around, that would amount to about 15C of temperature rise, at least. The core loss dissipation will amount to P = CL·V = 44.3*734 = 32516 mW = 32 Watt.To that, copper losses should be added. If the magnetic area is 18.4 cm^2, the radius is 2.42cm. For a 0.220'' diameter wire, the radius of a turn is 2.42 + 0.28 = 2.7 cm. If we forget about winding pitch, 28 turns measure 28*2.7*6.2832 = 475cm. For aluminium wire, that length and diameter have a resistance of 0.0051199 Ohm. At 100 amps, the dissipated power is P = I^2R/2 = 25.6 Watt more.So a total power dissipation of 57.6 W should be expected, for and inductance of 317uH and the toroid going into 60% of saturation. It would also get rather hot, which is not good for its life expectancy.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 08, 2017, 10:30:31 am
content: Quote from: Purduephotog on January 08, 2017, 12:47:30 amThat'll be this geometry, by the way:Tim

author: Purduephotog
author_rank: Regular Contributor
timestamp: January 08, 2017, 04:20:09 pm
content: Quote from: T3sl4co1l on January 08, 2017, 10:30:31 amYep! And the first time I picked it up to move it I about threw my back out of whack. I was a bit surprised at the weight.If I halve the thickness of the final winding and double the number of turns (Make it a Double E with half the lamination facing each other) and ignoring the I portions, would I get any advantage?The math was fascinating- I wish I'd continued on with my EE work before going into ChemEng. Probably more useful nowadays.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 08, 2017, 04:50:05 pm
content: Rearranging the same core mass (less the I segments, but they're only 25%, not a huuuge fraction of the total), for opposing-E shapes, gives you a magnetic path length of 18A vs. 12A (more, but not double!), cross sectional area of 2A * (Z/2) vs. 2A * Z (where Z is the core stack height), and winding area of 6A^2 vs. 3A^2.For transformer duty, the half cross section exactly cancels the double winding area, so it's a wash.The increase in path length and decrease in cross sectional area causes the magnetizing current to triple, which isn't very convenient for transformer duty. (For inductor duty, it doesn't matter as you're adding your own gap, anyway.)Overall weight will be slightly less, which is neat. Which means core volume is less, too. I'll have to remember that.Tim

author: Purduephotog
author_rank: Regular Contributor
timestamp: January 13, 2017, 03:59:46 pm
content: Quote from: T3sl4co1l on January 08, 2017, 04:50:05 pmFinally got all of the stamped E and I separated.The I's weighed 8.6lb, the E's weight 26.6lb. Plus another lb or so of frame and bolts, bringing the total iron content to just under 40lbs. With the copper that was on it I'd have to guess it weighed at least double, which is good to know why my back hurt.Now to get them all flattened and into the 20 ton press to keep them that way... I'm guessing iso-cyanate ? Maybe I'll press them in 2 sections, so I can try winding the core two ways. Hey I like hearing myself think on the web

author: Purduephotog
author_rank: Regular Contributor
timestamp: February 10, 2017, 10:48:46 pm
content: I'm still doing the big E but I got a deal on these threeBig inductorshttps://imgur.com/gallery/Au3Gu

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 11, 2017, 12:45:38 am
content: Hmm, 0.23 uH/t^2...100A wire is at least 4.3mm dia wire, and... the curves go up to 3000 At, so let's use 30 turns at 100A. That should still fit comfortably (winding window is 2565 mm^2, copper area is 435 mm^2 = winding factor 17%), if a bit congested, and probably getting rather hot as I used a current density that's probably not suitable for very large coils.That'll give 207uH, per core, at zero bias, but it will drop to about 100uH under full bias.To use all three cores, you want to stack them, and wrap the stack with wire. That way you aren't wasting extra wire on the parts going around from inside to outside. It should also have a tunnel shape more conducive to fan cooling, which is nice?Lcrit is 265uH (assuming a load of 30V and 100A, which should be typical enough for stick welding, a little conservative for TIG, and a bit more so for MIG), which means you'll be right on the edge with three in series. Better than nothing, but that pile of iron will definitely give better control.Tim

author: Purduephotog
author_rank: Regular Contributor
timestamp: February 11, 2017, 08:19:49 pm
content: Ironically I just found a storage bin of 6 gauge copper wire. I mean, I've had it, it just kinda got 'lost' in the shuffle.So wrapping 3 pieces of 6 gauge gives me 1 gauge, but if I use 2 parallel strands I can easily hit 100A load. Well, just barely (3 gauge).It'll get hot, but I'm not too worried as I'm not going to be running at 100% duty cycle- I'm just not that good. (no jokes here please). And I already have a nice Muffin fan pushing about 100 CFM with high static pressure, so routing an air duct around it (aka, bent thin plastic) should be doable.The Iron core has flattened out nicely after 2 weeks in the 20 ton press. I've got to melt some milk jugs to make a bobbin, then I can get around to wrapping it. I think I'm going to have to hammer on the wire to keep it bent tightly though.

author: snarkysparky
author_rank: Frequent Contributor
timestamp: February 11, 2017, 09:15:17 pm
content: i made my welder inductor with 5 cores of amidon T400-26.The winding is 15 turns of a wire formed by 5 parallel 14 ga conductors.I have it calculated to be 146 uH.It's a switching regulator welder, gonna switch it at 50khz

author: Ian.M
author_rank: Super Contributor
timestamp: February 11, 2017, 09:17:44 pm
content: Don't melt milk jugs - too soft and too low temperature. Better to glue the bobbin up either with Epoxy and Paxolin sheet or bare FR4 (no copper), or PVA wood glue and heavy card stock then saturate the card with varnish.

author: Purduephotog
author_rank: Regular Contributor
timestamp: February 11, 2017, 10:23:04 pm
content: Quote from: Ian.M on February 11, 2017, 09:17:44 pmGood point.I was going to use it as a basic form and then wrap with fiberglass, but your way sounds a lot fewer steps.

author: Ian.M
author_rank: Super Contributor
timestamp: February 11, 2017, 10:37:24 pm
content: Just make sure you use a high temperature glue for a piece-build bobbin. Many epoxies have negligible strength at 100 deg C, and the inner layer of the winding can be expected to run pretty warm.