How to generate 25VAC at 500 amps? - Page 1
Forum section: electronics / projects

author: JohnnyP
author_rank: Regular Contributor
timestamp: May 22, 2015, 11:18:20 am
content: I was visiting my favorite anodizer today and he asked how he could get 25 VAC at 500 amps. He said he has 480VAC coming into the facility.I asked him what he was trying to do. He was a little coy, but I assume it has something to do with anodizing.So, I have no idea what waveshape would work.I googled and found a transformer rated at 50VA:http://www.grainger.com/product/SQUARE-D-Trans-Fused-1YUW1So that works out to 2 amps at 25v?Probably a bad idea to try running 250 of them in parallel.I gave him the address of eevblog, he wrote it in pen on the palm of his hand. Don't know if he will check in.I don't have the chops to do this, so ambitious electrical power wizards should contact Jeff at Dunham Metal Processing in Orange, CA.

author: langwadt
author_rank: Super Contributor
timestamp: May 22, 2015, 11:36:59 am
content: Quote from: JohnnyP on May 22, 2015, 11:18:20 am10 big of the shelf toroids ~1500VA, primaries in parallel, ignore the secondaries instead put a single turn* of a big fat wire through each?you can probably get transformers made with out the secondary.*Depending on the volts per turn you'll have to tweak the number of transformers/turn to get 25Vac

author: cs.dk
author_rank: Unknown
timestamp: May 22, 2015, 11:40:06 am
content: A couple of large old welding transformers should be able to deliver that amount.

author: JohnnyP
author_rank: Regular Contributor
timestamp: May 22, 2015, 11:44:48 am
content: ok, transformers, no triac arrays?"put a single turn* of a big fat wire through each"Would that be a separate wire for each toroid, or one wire, taking a turn around each toroid?Thanks for the ideas.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 22, 2015, 11:56:08 am
content: 25VAC will be in the ballpark of a welder of some sort, though welders are more oriented to current limiting than voltage regulation. probably worth a try as it's an off-the-shelf solution. Maybe rent one.

author: TerraHertz
author_rank: Super Contributor
timestamp: May 22, 2015, 12:20:51 pm
content: Photonicinduction has a couple of videos:youtube. com/watch?v=JhOzsFfG1rcBuilding A Monster High Current Transformeryoutube. com/watch?v=uXEPy6Za6cI50,000 Amp Transformer CompletedThough, I strongly question his numbers.Also, lugs not crimped, therefore he's not getting anything like he expects.Not to mention Amps * turns capacity of the core.But this is something in the direction of what the anodizing guy wants.Edit: Gosh, it's hard to force the forum software to NOT insert direct video images. Remove spaces in URLs.

author: langwadt
author_rank: Super Contributor
timestamp: May 22, 2015, 12:28:08 pm
content: Quote from: JohnnyP on May 22, 2015, 11:44:48 amone wire taking a few turns around each toroid effectively putting all the "secondaries" in seriesyou'll have to look at the spec for that transformer or measure how many volt per turn to figure out how manytransformers/ turns per transformer to get 25VAC

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 22, 2015, 12:38:20 pm
content: Sounds like an interesting project.However -It's an anodizing / plating / processing facility. There are probably a lot of other people there. Various chemicals. Much of which is probably insured.Sure, one could piece together equipment to do the job. (My vote is for the welder transformers. Arc welder or MIG? Need to research. Note: welders often have a fair amount less than 100% duty cycle.) But would the equipment be safe for operation? Would it be built and installed to all applicable codes? Of course, in no fashion would it be approved by or listed with an agency. Slight problem if there is an insurance claim.It kind of sounds like your vendor is looking for a $2000 substitute for a $20,000 piece of equipment.

author: HighVoltage
author_rank: Super Contributor
timestamp: May 22, 2015, 12:46:30 pm
content: Take a high voltage transformer from a microwave oven,Remove the secondary high voltage winding completely.And add a heavy cable and wind yourself a high current, low voltage transformerIt works very wellYou just have to play with the quantity of windings to get to 25V

author: langwadt
author_rank: Super Contributor
timestamp: May 22, 2015, 12:54:53 pm
content: Quote from: HighVoltage on May 22, 2015, 12:46:30 pmit's got to be one beefy microwave to get a 25*500 = 12500VA transformer

author: KenGaler
author_rank: Contributor
timestamp: May 22, 2015, 12:56:46 pm
content: If he's plating I'm surprised he wants AC instead of DC. I've designed DC supplies for plating but never heard of using AC. I wonder if he really needs DC but doesn't know it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 22, 2015, 01:25:37 pm
content: AFAIK, anodizing is a current limited process, as the voltage rises over time, corresponding to the thickness of the layer. Hard anodize being the highest (around 100V I think?), and typical protective layers being 20-30V.He would need a rectifier after that transformer, yes.A welder rated for continuous duty (or cycles in the many minutes at least) would seem quite reasonable. In the 10kVA range, you'll be looking at 3 phase, certainly, which is fine for both an industrial grade machine like that, and for an industrial factory that's already got it available.One plus: if you do it by transformer alone, you can use a six pulse rectifier to get continuous DC -- full wave rectified 3 phase draws a power factor somewhere around 0.8-0.9 (not unreasonable, though still runs afoul of .eu harmonics regs if that's a concern) and gives output ripple around 20% (who needs filter chokes / caps?).Tim

author: TerraHertz
author_rank: Super Contributor
timestamp: May 22, 2015, 01:29:36 pm
content: Quote from: KenGaler on May 22, 2015, 12:56:46 pmSince he's a professional anodizer, I'd expect he'd know the difference.I'm curious too. It might be something to do with pre-cleaning surfaces? Or doing some treatment to the chemical solutions maybe?Or, maybe he has a huge rectifier bank lying around spare. But typically the systems would be three phase transformers and rectifier banks.Final possibility: he's teasing JohnnyP, or testing to see if he knows anything at all about anodizing.

author: rolycat
author_rank: Super Contributor
timestamp: May 22, 2015, 01:42:27 pm
content: A quick Google shows that AC anodising is definitely possible, although not common. Some recent papers and patents suggest AC or combined techniques offer some advantages over purely DC methods prior to adhesive bonding.Maybe the OP's friend has some such scheme in mind?

author: OldNeurons
author_rank: Regular Contributor
timestamp: May 22, 2015, 02:17:19 pm
content: Probably DC instead of AC if it is for anodisation.I know this company located in Germany.http://www.plating.de/en/home.htmlI have been using their products for the development of automated plating systems working 24/24.Very compact and reliable.They are also flexible, and can build a power supply according your exact requirements.I know also a sweedish company doing the same. They are more expensive. I can't recall their name right now.

author: rolycat
author_rank: Super Contributor
timestamp: May 22, 2015, 02:31:55 pm
content: Quote from: OldNeurons on May 22, 2015, 02:17:19 pmAs it happens, the company you mention demonstrates that AC can indeed be used when anodising.From the relevant page of their website:Quote

author: OldNeurons
author_rank: Regular Contributor
timestamp: May 22, 2015, 02:49:01 pm
content: Quote from: rolycat on May 22, 2015, 02:31:55 pmWith a need for 500 Amps, in a production environment, I would leave the 'old style' systems on the side. It would need huge transformer, huge rectifiers, etc ...Go for a modern solution !!! The power supplies from Plating Electronics that I have been using, weighed 12kg, not bigger that my HI-FI amplifier, and deliver 250A over 18 Volts.All that for a price which is certainly less than an 'old style' system (copper is more and more expensive).

author: eneuro
author_rank: Super Contributor
timestamp: May 22, 2015, 02:58:05 pm
content: Quote from: rolycat on May 22, 2015, 02:31:55 pmThat is interesting, but never tried AC for anodizing, while quite bulky trafo I've used has synchronized rectifier for anodyzing.Anyway, there is some equipment available-used their hints for anodizing and they know what are talking about.http://www.anodizeusa.com/anodizing-systems-hard-coat.phpQuoteBTW: PC motherboard teardown close to 12V CPU power stages can be source of nice synchronized rectifier drivers - three in the case of ASUS motherboard

author: SArepairman
author_rank: Frequent Contributor
timestamp: May 22, 2015, 04:01:00 pm
content: What about creating +-12V rails with PWM then using driver? a bit more modern then massive inductors12500 watts is alot though

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 22, 2015, 04:07:17 pm
content: Any way you slice it, 12.5 KVA is orders of magnitude beyond the scope of DIY for amateurs.A 12.5 KVA transformer is the size and weight of a large truck or earthmover engine.

author: SArepairman
author_rank: Frequent Contributor
timestamp: May 22, 2015, 04:10:54 pm
content: Quote from: Richard Crowley on May 22, 2015, 04:07:17 pmidk though, people made 30kVA home made induction forges that use IGBT. Possible to do this entirely solid state with no coupling magnetics. apart from the final impedance matcher

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 22, 2015, 04:15:23 pm
content: Quote from: SArepairman on May 22, 2015, 04:10:54 pmSure, there are clever solutions for certain applications. But we don't know enough about the requirements here to assume that any of those novel work-arounds would work here.

author: eneuro
author_rank: Super Contributor
timestamp: May 22, 2015, 04:18:41 pm
content: That is interesting what kind of anodizing they want to do with this thing, while when we assume 30 ASF for type III anodizing, than 500A could do ~1.5m2 (square meter) anodizing.When we put additionaly this recomendation into account:http://www.anodizeusa.com/aluminum-cathodes.phpCode:In addition the ratio of 3 sq feet of anode to 1 sq foot of cathode gave the most consistent anodizing.this would mean that cathode for 500A current could be ~0.5m2.Is it possible with 1.5m2 anode (anodized part area) and 0.5m2 cathode @ 25VAC only get 500A current between those plates in sulfuric acid bath containing 180-200 grams per Liter of acid?NOTE: I assumed type III anodizing in those estimations based on linked data.

author: technix
author_rank: Super Contributor
timestamp: May 22, 2015, 04:28:58 pm
content: What I can think of is a huge multi-phase non-isolated switch-mode power supply that draws 20A from the mains...

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 22, 2015, 04:32:13 pm
content: Quote from: technix on May 22, 2015, 04:28:58 pm12.5 KVA is 31.25 A @ 400V assuming 100% efficiency.

author: OldNeurons
author_rank: Regular Contributor
timestamp: May 22, 2015, 04:44:37 pm
content: Quote from: OldNeurons on May 22, 2015, 02:17:19 pmKraftPowercon:http://www.kraftpowercon.com/This is the name of the Swedish company that I also contacted for the project I mentioned before.There products are more expensive than those from Plating Electronic, but they are also experts.I am smilling when reading the last posts. Are we still talking about an industrial and viable solution?Do you really want to help JohnnyP?

author: N2IXK
author_rank: Frequent Contributor
timestamp: May 22, 2015, 04:53:59 pm
content: Simplest solution is a custom wound 480:25 transformer. If the guy is serious, he should send an inquiry to a place that specializes in such things. One possibility is P.W. Dahl/Hammond, who make similar transformers for operating the filaments of huge transmitting tubes:http://www.pwdahl.com/index.html

author: Gyro
author_rank: Super Contributor
timestamp: May 22, 2015, 07:03:50 pm
content: Surely his 480V supply is going to be a 3 phase one???Isn't he going to need a 3-phase transformer? I wouldn't have thought he'd want 25kVA hanging off just one of the phases.

author: N2IXK
author_rank: Frequent Contributor
timestamp: May 22, 2015, 07:15:27 pm
content: If he needs a DC output, then a 3 phase transformer (and 3 phase rectifier) would be preferable as far as load balancing.If he needs a single phase AC output, then he needs a single phase transformer. To get 480V, it would be fed from 2 legs of the incoming 480V feed.

author: Gyro
author_rank: Super Contributor
timestamp: May 22, 2015, 07:44:47 pm
content: Absolutely on the DC case.On the AC, of course it would be, sorry. 25kVA between 2 phases is still quite hefty, but I guess that sort of thing is quite common in industrial buildings depending on how the other loads are distributed (and powered on and off). I guess the utility company must have some sort of maximum spec to be met. No simple way around it anyway.

author: Zero999
author_rank: Super Contributor
timestamp: May 22, 2015, 08:00:37 pm
content: If it's DC then an SMPS will probably be the best solution.For AC though, you need a transformer.Either way, it's quite likely it will need to be a custom made product.

author: rickselectricalprojects
author_rank: Regular Contributor
timestamp: May 24, 2015, 08:52:27 am
content: your best bet is a (or a few) old welding transformers. that's probably the cheapest way to get 24v at 500ahope this helps