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LAN_403

Part Scavenger

Mon Jul 13 2015, 03:01AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Do you guys have any idea where to get EI Cores? I'm making a couple small custom transformers. I can't find anybody that sells them on the Internet, unless I want to wait for a shipment from India or order large quantity.

I don't want to use MOTs because I need the screw holes, and I don't need a cross sectional area that large. I don't have any other transformers I want to tear down.

I've also tried eBay, Amazon, mouser, with no luck.

Thanks

mister_rf

Mon Jul 13 2015, 03:51PM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

IMO modifying some old transformer is the optimal solution.
Try for example here:

maybe they are offering discounts.

Later edit
also see here:

Ash Small

Mon Jul 13 2015, 04:32PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

As far as I'm aware, we, in Europe, have to import our laminations from USA, as we don't have our own suppliers anymore.

I think there are a couple of US companies. I'll try and find out who and where they are.

radiotech

Wed Jul 15 2015, 04:09AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Just what size core do you want? If you are after very small, ie wall wart size, up
to about 15 watt, go to a thrift shop. They usually have a bin of adapters for
50 cents each. Most aren't potted.

Part Scavenger

Sat Jul 18 2015, 04:22PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

I intend to make a transformer with about 12 sq cm core area and up. I think I'm just going to cut them myself and see what happens. The worst that will happen is it will saturate earlier than I expect or get too hot. Going to try getting some 1/16" steel from the scrapyard and see how bad the eddy currents are if I build it a little big and keep my field strength about .8 Tesla.

Also, I was on a battleship the other day, and noticed that most of the transformers are made like the attached which would be a pretty feasible option with MOT sections.

GrantX

Sat Jul 18 2015, 05:34PM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

Part Scavenger wrote ...

I intend to make a transformer with about 12 sq cm core area and up. I think I'm just going to cut them myself and see what happens. The worst that will happen is it will saturate earlier than I expect or get too hot. Going to try getting some 1/16" steel from the scrapyard and see how bad the eddy currents are if I build it a little big and keep my field strength about .8 Tesla.

Also, I was on a battleship the other day, and noticed that most of the transformers are made like the attached which would be a pretty feasible option with MOT sections.

That's very interesting. I assume it's a forced air cooling system to guide the airflow through the windings? Any idea what the transformer's job is?

When I rewound a MOT for use as a mini spot welder I found that the magnetizing current was pretty bad (3.5A or more), due to my method of assembly. I cut the original welds, removed the shunts and rewound the secondary, then simply placed the two core halves back together (with a 5kg weight on top) and re-welded them with my MIG. Afterwards I noticed there was an approx 0.25mm air gap, despite the weight used while welding. I guess it was caused by thermal stresses or the welding current / feed rate was a little high. If I had clamped the core in a vice I might have gotten better results, but unmodified MOTs already have large magnetizing currents.

1/16" (1.5mm) is probably a little thick for the laminations, but if your design doesn't require a low magnetizing current, or is only for intermittent duty, you might get lucky.

Ash Small

Sat Jul 18 2015, 05:35PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Try looking on Ebay for a cheap, big, old transformer, and rewind it. It will probably cost less than steel from a scrapyard, which will be pretty useless unless it's under 0.5mm thick and is alloyed with silicon.

Hamfests are also good places to pick up big, old transformers for next to nothing. At the last hamfest I went to people were giving them away for nothing.

Carbon_Rod

Sun Jul 19 2015, 12:58AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

If you are trying to do something unique, than perhaps a local water-jet cutter service can help.
For low frequency stuff, the FEMM cad material models do seem to work rather well.

On craigslist one can usually find cheap welders, car battery chargers, and old 3-phase commercial stuff.

Your local recyclers/scrap yards will tend to charge a premium on anything containing copper, but regularly get a few kw+ step-down transformers.

Perhaps you may be located near a company like this:

Cheers,
Rod

klugesmith

Sun Jul 19 2015, 09:25AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Part Scavenger wrote ...
...Going to try getting some 1/16" steel from the scrapyard and see how bad the eddy currents are if I build it a little big and keep my field strength about .8 Tesla. ...

Give it a shot. How are you going to cut the sheet into E's and I's?

Have you considered using steel sheet intended for roofs, gutters, or flashing?

It's much thinner than 1/16" and usually comes with durable paint on both sides.

Even if you match the thickness of conventional transformer laminations, I bet that ordinary steel material will make a much lossier transformer. I tried it once, when I was new to the 4hv forums.

Lower permeability. Much higher coercive force and hysteresis loss. Much lower electrical resistivity, so more eddy current loss. Here is one brochure about transformer steel.

Dr. Slack

Sun Jul 19 2015, 09:52AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Making your own transformer laminations from random steel sounds like one of those tasks that you really don't want to do. There's so much technology in a decent lam, thickness, insulation, several magnetic and resistive properties, that a transformer made from nails or angle-iron is going to be little more than a science-fair proof of principle demo item.

How about you widen your scope of where to get a rewind candidate? Almost any mains powered boat anchor

will contain a transformer. With SMPS replacing iron and halving the weight of all sorts of things, a lot of stuff is being obsoleted, try skips outside factories.

I've always found Es'n'Is very difficult to rework, if you can find C-cores they are sooo much easier

If I read your OP right, you don't want to drill holes in MOT laminations, but subsequent posts suggest you are prepared to make something inferior from scratch?

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