Made MOT Isolation Transformer - Page 1
Forum section: electronics / projects

author: lordvader88
author_rank: Frequent Contributor
timestamp: July 29, 2018, 11:56:47 pm
content: So I took 2 pretty similar microwave oven transformers, and cut them both open with a hacksaw. Then carefully and fairly easily got both primary coils out and put them onto 1 core. I put the shims back in, not sure if I need them there or not.The coils are about 3/8" or 6mm apart. And for now the core /cover is just strapped back together, so it's just basically sitting back together.I put 117VAC in and get 103 out so thats 0.88 or 1.14 giving 132V the other way. Thats all fine, I have an auto-transformer that goes up a bit aswell.However it hums at probably 50dB (I can't guess that) but it's way too loud for now. I guess if I weld it back together that should mostly go away ?1 trans was a jmot-n 95A0-16T. I never thought to write down anything about the MOs these came from. But they were mid-sized.I only want to use this for SMALL loads, like an unloaded computer PSU that might use 50W (IDK) so I can use my scope on stuff.I can try a 100W light bulb, and see what the core temp does. Any thoughts on this creation ? I'm quite pleased, except for the noise. There's all kinds of small stuff this should be perfectly safe with....right ?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 30, 2018, 12:17:47 am
content: No, no shunt, that intentionally makes regulation worse.Add more turns to reduce noise. Shoot for 20% more (estimate primary turns from what you can see around the winding). It's running in saturation, to save weight at the expense of noise and heat.Tim

author: lordvader88
author_rank: Frequent Contributor
timestamp: July 30, 2018, 12:40:06 am
content: Right I forgot about the whole saturation thing and the way they run them in MO, never got to that in school.The gap is more like 1/2" right now, about 1/4" is just air.So I could get some 14 gauge household wire, with it's insulation intact.The 103V out coil is about 11t high x9t wide so 99turns. It looks like 1.3mm gauge for sure.The other coil is maybe 0.8,0.9mm comparing it to solder. It's about 11t x 10t =110 or so, that sounds about right.So u mean add secondary turns ? Or making it closer to 1:1 add to the other 1, but more over all even if I add to both ?

author: Cliff Matthews
author_rank: Unknown
timestamp: July 30, 2018, 01:24:25 am
content: Up on the rock you have 240v access, add one more MOT and you can run 3 with the primaries in series without modification. I did some testing some time back and logged it to a thread. If project continues in the future, it'll will wind-up (pun intended) as a 2000-watt kick-ass lab isolation transformer.https://www.eevblog.com/forum/projects/diy-1kva-isolation-transformer/

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 30, 2018, 01:32:42 am
content: Add primary turns.But then you need to add secondary turns to keep 1:1. So, both.Tim

author: lordvader88
author_rank: Frequent Contributor
timestamp: July 30, 2018, 08:18:52 am
content: ok thanks

author: james_s
author_rank: Super Contributor
timestamp: July 31, 2018, 07:11:44 pm
content: Have you tried swapping which winding you are using as the primary and the secondary? It's possible that one has more turns than the other so you might get a different output voltage if you switch them. Of course that might also make the saturation situation worse, although as soon as you put a load on it, it will be less likely to saturate.