Where to buy an isolation transformer ? - Page 1
Forum section: electronics / beginners

author: lordvader88
author_rank: Frequent Contributor
timestamp: August 14, 2018, 09:33:02 am
content: I want to be able to a scope and repair household electronics, so I guess 500W should cover most things.But where to get 1 ? Searching 'isolation transformer' and my hometown doesn't come up with much at all. There's not many electrical supplies places here, I can start phoning around to places.There's not really anywhere with used industrial machinery for sale that I could salvage a transformer from.On ebay Canada they are +100 for 300W, $180 for the 1st 500W

author: Kjelt
author_rank: Super Contributor
timestamp: August 14, 2018, 09:55:05 am
content: You know any ham radio clubs in the vicinity or old crt repair shops that went out of business, there you can pick them up sometimes in a variac version almost for free. Shipping is usual the costs, those things are heavy.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 14, 2018, 10:11:52 am
content: Beware of the variacs, many of them are autotransformers, so the output is not galvanically isolated.At 500W, it can rather make sense to use a handheld oscilloscope, or to float the oscilloscope instead of floating the DUT (Device Under Test).I made an improvised DYI isolation transformer out of two identical 220V/2x22V (they were meant for a stereo audio amplifier with independent power source for each channel) connected secondary to secondary, and the remaining primary windings were used as isolated input/output.220V/2x22V -> 2x22V/220VSince each transformer has symmetric 22V secondary winding, I can also connect the 22V secondary from the first transformer to the 44V of the second transformer, so in the end I can get an isolated 220V/110V, too.

author: lordvader88
author_rank: Frequent Contributor
timestamp: August 14, 2018, 12:03:39 pm
content: I have a 2000W auto-transformerI just phoned around and most suppliers don't have them at all or deal with anything as low voltage as 120V or 240V. The only price I got was +$200 for a 120/240:120/240 500W unit

author: ebclr
author_rank: Super Contributor
timestamp: August 14, 2018, 12:16:17 pm
content: Pick 2 microwave old transformers, and make yourself, Just Cut the 2 high voltage coils, and maintain the 2 primary coils on the same core, Will work like a charm

author: Jeroen3
author_rank: Super Contributor
timestamp: August 14, 2018, 12:23:03 pm
content: Newark has the Block ST 500/11/11 for $90. Do they deliver to you?

author: lordvader88
author_rank: Frequent Contributor
timestamp: August 14, 2018, 12:42:38 pm
content: Well see I did that, I have both primaries on 1 core. People said I should add another 20% to each coil, so as to overcome the saturation/heat issues with MOTs. And then get it welded back together, hopefully I could find someone/shop to do it for free or $5, it would take them 5 seconds.So thats about 15/20ft of 14 gauge wire, times 2. And I haven't gone looking for that yet. I might be able to get 14/1 wire for $0.30/ftThat would do for now, if I can get the wire for cheap and welded for cheap.

author: Kjelt
author_rank: Super Contributor
timestamp: August 14, 2018, 12:56:54 pm
content: How about safety? Is the isolation of the wires adequate? An isolation transformer is more about safety than just functionality.

author: lordvader88
author_rank: Frequent Contributor
timestamp: August 14, 2018, 01:15:42 pm
content: Yeah IDK.....so I want a real 1 for sure for.The newerk store has 1's like I can get locally, thanks

author: rhb
author_rank: Super Contributor
timestamp: August 14, 2018, 03:43:54 pm
content: Quote from: lordvader88 on August 14, 2018, 12:42:38 pmThere's no need to weld it. That's just done to avoid the expense of screws.Putting the primary from a 2nd transformer will provide isolation, but you might not get the voltage you want if they are not identical. However, if you're using it to isolate an autotransformer, it may not matter.

author: Cliff Matthews
author_rank: Unknown
timestamp: August 14, 2018, 04:11:36 pm
content: Out where you live, you can make a constant duty 500-watt unit for under $150 with some low-tech work and get a ship-load of spare parts to boot. We've talked about MOT's before, so be patient with this old guys rambling:1)Get 4 large MOT'sby posting a free kijiji want-ad saying "deliver me your big old micro-wave and get $20 cash" (buy 5 or 6 to make sure you get decent size matching). That's the fun part in getting all the goodies.2) Use a hack-saw to cut off one side of all the secondaries and knock them out of the other side (do not cut the primaries..)3) Screw all 4 MOT's to a piece of plywood in a square formation with the primary terminals facing outward.4) Wire the primaries in series and attach the usual fuse/switch and power cord to the the line-side. Wire the secondaries to a good quality DPDT switch (so you can have a useful 60v/120v output in series or parallel) and attach a fuse and receptacle.5) Buy some #4 welding cable at Princess-Auto on 410 Stavanger, and neatly stuff all new secondaries full in a loop (same turn quantity on each and same turns direction).Once everything's running the way you want (including maybe some switches for secondary taps to control output voltages) run it for a few hours on various loads and then transfer it to a box. Of course, this is not a project for well-healed or lazy types, but if you have the time it'll be fun.

author: chemelec
author_rank: Contributor
timestamp: August 14, 2018, 06:18:35 pm
content: Somewhere I have a 110VAC Hammond Isolation transformer and you could have it for Free, Other than the Shipping cost.Not sure on the wattage, But Should be in the 300 to 500 watt range.Just need to Find it.I am in BC Canada

author: CCB
author_rank: Unknown
timestamp: August 14, 2018, 07:42:45 pm
content: Builders used to use isolation transformers for outside work like mixing concrete, are these suitable? Nowadays I guess they use RCD devices.Also how about 2x UPS transformers with the secondaries connected?

author: lordvader88
author_rank: Frequent Contributor
timestamp: August 14, 2018, 07:51:44 pm
content: Quote from: rhb on August 14, 2018, 03:43:54 pmWell I'd have to bolt it back together super tight tho, but yeah I never even considered that because I'm hoping some garage would just do it for free, or I'd offer $5Right now it's like a 60Hz clapper with a big loud heavy lid

author: lordvader88
author_rank: Frequent Contributor
timestamp: August 14, 2018, 08:02:27 pm
content: Hi Cliff Matthews, thanks but thats a lot more work and overall would weigh a lot more. And I'm impatient so I'm going to buy 1. But I'm going to use the MOT IT I've almost finished.....I'm assuming MOT's must have very good insulation on them. And 14/1 14/2 wire that I add should be just fine, why wouldn't it be ? I'm not planning to use this in a lightning storm. (And sadly we barely get any)What % of people on here have an IT ?Quote from: chemelec on August 14, 2018, 06:18:35 pmWell thanks and I'd gladly pay shipping for such a thing, if I could pay with paypal for safety, if u could make it a private sale on ebay.ca, I'd cover their charge to u as well, thanks.

author: chemelec
author_rank: Contributor
timestamp: August 14, 2018, 09:53:27 pm
content: Here is a Picture of this Isolation Transformer.It is Rated at 300VA and Weighs about 20 Pounds, Possibly More When Wrapped to Mail it.I have No Interest to Post anything on Ebay or accept PayPal.I Will accept a Postal money Order or a Personal Cheque.Want to check me out further, go to chemelec.com

author: Cliff Matthews
author_rank: Unknown
timestamp: August 14, 2018, 11:25:56 pm
content: So on that MOT you've got,1) have you added about 35-40 more turns to the primary? (so it doesn't run the core so hot and saturated)2) what room would you have left to install a new secondary of 100+ turns? (since MOT's are cheap, that's why I'd use two: way more room for winding a secondary, and unsaturated running with untouched primaries each running cool at just 60v)The option mentioned was to leave all primaries untouched and back-to-back link 2-pairs of transformers with the big welding cable because it's bang-up quick to wind 15 turns on each (about 40 amps max on secondaries) and only one solder joint to connect the whole dang loop together. But nothing saying you can't do the same with 14 gauge and 2 MOT's (you'll get tighter regulation too) but don't kink while winding ~50-60 turns on each or you could get hot spots later on.Hey come visit Ontario, you can stop by and grab some of my spares

author: rhb
author_rank: Super Contributor
timestamp: August 15, 2018, 02:43:32 am
content: Quote from: lordvader88 on August 14, 2018, 07:51:44 pmWhy does it need to be "super tight"? The construction is intended to reduce losses due to eddy currents. The weld increases them.Merely welding it will not make it quieter. It has to be clamped tightly wen welded.I suggest you do a bit of reading on transformer construction.

author: Jwillis
author_rank: Super Contributor
timestamp: August 15, 2018, 03:57:47 am
content: Not sure which side of Canada your on but you could tryhttp://www.a1parts.ca/out of Toronto orhttps://leeselectronic.com/en/in Vancouver.Both supply transformers . Lee's are more generic and A1 has Hammond.Usually takes less than a week to ship to central Canada for both.

author: Gregg
author_rank: Super Contributor
timestamp: August 15, 2018, 03:27:56 pm
content: Here is one in Canada with free shipping:http://www.adamsstore.top/index.php?main_page=product_info&products_id=6872

author: exe
author_rank: Unknown
timestamp: August 15, 2018, 04:01:56 pm
content: I'd check the forum about safety of isolation transformers. It seems nowadays it is suggested to use RCD instead of an isolation transformer:https://www.eevblog.com/forum/beginners/rcd-or-isolation-transformer-what-is-best-to-use-for-safety/