Isolation Transformer
The Ingredients...
DIYShopTools.com - Homemade Isolation Transformer For Nothing
The Process...
I've been wanting a power station for my workshop ever since I started building it. When I say "power station" I mean like my own dedicated circuit breaker box, isolation transformer, variac, step-up transformer (or simply 220-250VAC outlet right from the breaker box, or even a 120VAC in -250VAC out variac for my variac. Just some way to power the higher demand powertools), variable bench DC power supply, uninterruptable power supplies, remote switches for stationary tools (table saw, bench router, dust collecter, etc.) and that kind of stuff. Basically a unit that provides all of the power to my workshop as well as test anything I'm working on while also providing the safety that I need/want. While going through my accumulated stock to build another project, I noticed that I had two nearly identical transformers that had all E plates and I plates unmixed, allowing me to simply split the transformers and remove the coil without destroying the core. I've seen a good deal of "isolation transformers" that were actually a pair of transformers joined ath the out on the secondaries so the circuit goes into Transformer 1(Mains Voltage > Transformed Voltage) over to Transformer 2(Transformed Voltage > Mains Voltage) and then to the outlets. I had originally planned on doing the same, but noticed that I could split the cores and the secondaries are wound around the primaries which cover the entire inside of the cores. Which means I can join the E parts and create one EE core from two EI cores. I had originally planned on just removing the secondaries but thought it would be really convenient if I could keep the original secondaries, resulting in 4 cores with multiple voltages allowing me to power other items like cooling fans. So I started working toward that end while also searching online to make sure my theory would work in reality. I wasn't able to find any example of what I had planned, but it sounded plausible at least. So I cut the bases off of the transformers and then cut the Es and Is apart. Noticing that the bobbins prevented the cores from fitting flush against one another, I shaved them down until they fit flush against eachother. Using a stainless hose clamp to hold the E core sections together I fastened them into one EE core transformer with 4 coils. I grabbed my multimeter and a power cable and plugged it in to test it. Honestly, I was surprised to find out that it tested perfectly. Now I'm trying to decide how I want to approach the case. In one sense, I want to give it it's own specific small case that's easy to move around. In another, I want to build it into one big power conglomerate with a variac, DC lab PSU, 120v, 240v, isolation transformer, and hopefully an oscilloscope and signal generator soon, all basically on their own subpanel on the circuit. I want one location (at my bench) capable of handling all of my electrical needs. I'm lazy. I don't want to have to go to multiple stations or collect all the components. I kinda put this on hold for a minute while I figured out what I would do for the enclosure. While cleaning out and organizing some of my other gear, I came across my old rework station that was pretty well trashed (only the hot air gun worked anymore). The size seemed pretty good to fit the isolation transformer, it already had multiple switches installed in locations I liked, had a power input jack, and even cutouts for voltmeter and ammeter displays. Ideally, I'd like to have 2 displays that show voltage and current, one on the input, and one on the output. We'll see what space allows for, but I should be able to make that work. I don't have any AC voltmeters and/or ammeters, so I'll have to buy them, but the upside is I should be able find a perfect fit that way. The trickiest part is likely to be figuring out how to use the other two dozen taps on the transformer. As far as the isolated mains out, I'm going to put two outlet plugs and a pair of banana jacks. The others, I'm likely going to either keep them on the spring-loaded jacks or put at least some on cheaper banana jacks from my recovered parts bin. My main debate with these outputs is whether I want to put them on a bridge rectifier for DC or not.
  • Back
And I'm done...  At least for now. I'm almost positive that I'm going to end up rectifying some of the smaller outputs to have easily accessible isolated DC voltages as well. Though for the time being, while I'm without a variac, isolated lower AC voltages could be handy for testing older electronics and powertools that haven't seen power in a long time to avoid blowing up any components with a fast charge of such a high voltage. But anyways... here are some pics of the newly finished portable isolation transformer (I plan on making another that will go inside my powerstation at my workbench):