Transformer - Page 1
Forum section: electronics / general

author: GK
author_rank: Super Contributor
timestamp: July 11, 2014, 04:37:45 am
content: I need one 240V pri. 18V sec. 800VA transformer. Toroid or E-I, don't care. Can't find one off-the-shelf from anyone at all down here. Suggestions?

author: calexanian
author_rank: Super Contributor
timestamp: July 11, 2014, 05:05:38 am
content: Look harder..... They are very common.

author: calexanian
author_rank: Super Contributor
timestamp: July 11, 2014, 05:11:46 am
content: Now that I read it back it sounded harsh... Just hear Mr Miyagi saying in this time! hahahaha... 18 volts is a common voltage for 12 volt regulated power supplies. Also most toroids these days have dual primaries. Being in Australia my source is not really useful to you, but just to do them a solid, I use Antek in Arlington new jersey. You may have to do an Ali Express or a Ebay china type thing to get a reasonable price, otherwise you will pay like Farnell or Element 14 price and that might permanently peel your eyelids back.

author: IanB
author_rank: Super Contributor
timestamp: July 11, 2014, 05:19:44 am
content: I get the feeling that 800 VA is quite big for a low voltage transformer. The secondary has to provide 45 A, which means it will not be copper wire so much as bent copper bar...

author: calexanian
author_rank: Super Contributor
timestamp: July 11, 2014, 05:32:54 am
content: Quote from: IanB on July 11, 2014, 05:19:44 amThey typically have multiple windings you can parallel. Also the actual length of wire in toroids is relatively short so you have less resistance loss. you can really get the amps out of 16 or 18 ga wire. Use 4 sections in parallel and now you really have something. Also you can then have parallel rectifiers, caps, etc etc.

author: GK
author_rank: Super Contributor
timestamp: July 11, 2014, 05:34:20 am
content: Quote from: IanB on July 11, 2014, 05:19:44 amCorrect. 18V or 18V+18V is common but not at 800VA. Not a stock item anywhere here that I can find.I can get 225VA and could put four in parallel, but that isn't very elegant.

author: rob77
author_rank: Super Contributor
timestamp: July 11, 2014, 06:48:44 am
content: what's the application ? isn't a SMPS suitable ?

author: nanofrog
author_rank: Super Contributor
timestamp: July 11, 2014, 08:08:02 am
content: Quote from: GK on July 11, 2014, 05:34:20 amAny custom winding shops around you by chance?Not sure where you're located, but I found aexamplein Bayswater, Vic, and even one in Christchurch, NZ (here). Finding at least one within reasonable driving distance would be ideal IMHO. Worth a shot at any rate.Hope this helps, and good luck.

author: GEuser
author_rank: Frequent Contributor
timestamp: July 11, 2014, 01:10:37 pm
content: Large battery charger transformer (old type not a inverter)orWelder transformer (old type not a inverter) ..Poke around a recycling centre or equivalent .

author: VK3DRB
author_rank: Super Contributor
timestamp: July 11, 2014, 01:30:52 pm
content: Quote from: GK on July 11, 2014, 04:37:45 amTry 3 of these if you have roomhttp://www.ebay.com.au/itm/18V-18V-300VA-TOROIDALTRANSFORMER-/390802002956?pt=AU_B_I_Electrical_Test_Equipment&hash=item5afd9d540c&_uhb=1They look OK.Your photo is fake. No girl looking like that would be after a 800VA transformer. Now if she was after some gallium arsenide field effect transistors for a home brew low noise RF preamp, then maybe I'd believe you.

author: AlfBaz
author_rank: Super Contributor
timestamp: July 11, 2014, 01:55:21 pm
content: I'm not sure of the price, it's been many, many years but I do remember thinking they weren't as expensive as I thought. We use to get transformers made up all the time herehttp://www.coastelectrical.com.au/known at the time as Illawarra transformers. A couple of days turn around if I remember correctlyI don't know where in OZ you are located but I'm sure there'd be a similar outfit near you somehwere

author: GK
author_rank: Super Contributor
timestamp: July 12, 2014, 06:38:03 am
content: I'm in Adelaide. We used to have TAD transformers locally and ever Arlec I think, but they closed shop many years ago. I last used TAD for a re-wind ~15 years ago.I rummaged through my junk and found two 225VA 18V+18V transformers which have a current E14 part number. It would make sense to make use of them and my cheapest option so far would be to just buy 2 more of them. It's free delivery at least.

author: G0HZU
author_rank: Super Contributor
timestamp: July 12, 2014, 01:39:32 pm
content: There must be someone local who could make one?When I was a student here in the UK I had a special toroid transformer made that was about 700VA. It was for a big PSU I was building. IIRC the output was rated at 16.5V 43A. I think it was made by a local company in Kent (UK) called ILP.They still appear to be in business but I don't think my xfmr is on their current standard list. But they do appear to offer custom transformers on a reasonably short lead time and they distribute worldwidehttp://www.ilpelectronics.com/images/pics/transformers_mains.pdf

author: SeanB
author_rank: Super Contributor
timestamp: July 12, 2014, 02:14:43 pm
content: With the weight of them your buying from E14 probably will be the best. If I was doing one I would look for an old oil cooled welder, and cut it apart to get the core out, then rewind the secondary side without any magnetic shunts and with a minimal air gap to give the best regulation. Then put back in the box and seal it up again, either by welding or by placing a inner spacer and using some oil resistant sealer to make it oil proof again.I made a battery booster addon to my air cooled welder using a big press fit rectifier I had lying around and an old 45A circuit breaker to do thermal limiting. Not great to run the core with a DC current through it but it will boost a car battery up in about 3 minutes from stone dead to being able to start. I added a 230V fan as well to cool the welder as well, as there was a convenient set of mountings for it but no fan fitted from new. Only thing is the stray field when welding locks the fan solid until I stop, when it cools the core and windings down nicely. This welder is about 20-30 years old now, and has aluminium wire on the primary and secondary side, so attaching new leads was rather interesting, but very large crimp lugs and a little work with a hammer and a very blunt cold chisel to crimp them onto the existing stumps worked well.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 12, 2014, 02:17:05 pm
content: Rewind a pair of microwave oven transformers. Connect the primaries in series to reduce the magnetizing current.

author: G0HZU
author_rank: Super Contributor
timestamp: July 12, 2014, 02:26:51 pm
content: One other thing to perhaps bear in mind is acoustic noise levels from the transformer, especially from a big old toroid. Is this likely to be an issue?My 700VA ILP toroid is relatively small (but heavy) but it does produce quite a bit of hum noise even at very light loading. I can easily tell if the PSU is switched on/idling from across the room if the room is otherwise quiet. It's not noisy enough to be annoying but the drop in noise level in the room when it is switched off is quite easy to appreciate if the room is fairly quiet.

author: AlfBaz
author_rank: Super Contributor
timestamp: July 12, 2014, 02:54:53 pm
content: If you give me some specs I could get a quote from the previously mentioned company.Just checked with Australia postage calculator 10kg 150x150x150mm package regular mail (5-6days) $26, 40 bucks for 20kg.

author: G0HZU
author_rank: Super Contributor
timestamp: July 12, 2014, 03:21:47 pm
content: The 700VA one I had made had the ILP part number 9T845 but this dates back to the 1980s so this number may be meaningless today. 9T845 referred to a custom ILP spec that was purchased by a few people making versions of the classic Marchwood PSU in the UK in the mid 1980s. I looked up the spec and it uses two 21A 16.5V windings in parallel to give 16.5V at 42A (approx. 700VA)I would expect that they could make something rated at 800VA but I don't know how much it would cost. I think I paid about £60 for mine but that was 25-30 years agoIt's a very pretty transformer and quite small. My first impression was that it looked a bit too small for 700VA but it seems to work fine and I've been using this PSU since the 1980s and it's never ever failed.google for9t845 marchwoodand then select 'images' to see a similar toroid to the one I ordered.

author: GK
author_rank: Super Contributor
timestamp: July 13, 2014, 01:35:10 am
content: Quote from: AlfBaz on July 12, 2014, 02:54:53 pmOh that's OK, I already put the order through with E14 for two more of the 225VA transformers that I already have in stock:http://au.element14.com/multicomp/mcfe225-18/transformer-225va-2-x-18v/dp/9531963?Ntt=9531963Nicely potted; no hum from these ones. They are for the 20A +15V linear regulated supply rail of my digital computer. I already had the eight 105mm X 300mm heatsinks required and a box of 16A TO-3's. Heatsinks are now being mounted on the lower front panel of the rack, below where the control console will mount. Will double as a nice leg warmer when you pull up a chair to program the machine.

author: GK
author_rank: Super Contributor
timestamp: July 13, 2014, 01:38:58 am
content: Quote from: G0HZU on July 12, 2014, 01:39:32 pmNope. I'm in "The City of Churches" here.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 13, 2014, 08:40:45 am
content: You can take an old high voltage transformer, take the secondary windings off and wind your own wire on it.It will work perfectly for this.At one time, I even built a low voltage spot welder with this kind of setup.

author: calexanian
author_rank: Super Contributor
timestamp: July 14, 2014, 05:23:28 am
content: Again, these guys are in the U.S. so it may not be of much use to you, but for those over here i find them to be good.http://www.antekinc.com/grids/