Variable isolating transformer suggestions - Page 1
Forum section: electronics / testgear

author: davorin
author_rank: Unknown
timestamp: March 01, 2025, 08:53:27 am
content: Good morning (o;Have an old isolating transformer from the former GDR company RFT, which runs fine...but the power output is limited.Anyone have experience with those Voltcraft VIT isolating transformers like the VIT 1000?Or are there better devices out there who can handle up to 1000W or even a little more?

author: Kean
author_rank: Unknown
timestamp: March 03, 2025, 02:41:14 pm
content: You can buy separate a isolating transformer and variac/autotransformer to do the same thing but cheaper.You just need to size them both appropriately, maybe add a small V/I display module, and ensure you use them in a safe manner.Note that the VIT-1000 can output a max of 4A, so the 1000VA rating only applies at 250+VAC.My own setup is a 240V 2.5A 600VA isolating transformer, a 4A variac, plus a KWS-AC301 20A Power Meter, to give me 0-270VAC at 2.5A max.

author: madires
author_rank: Super Contributor
timestamp: March 03, 2025, 03:11:04 pm
content: If you don't like to build one yourself and want something long-lasting with good quality:- second hand from TV/radio repair shop (e.g.Grundig or Nordmende)- BLOCK- ThalheimerIIRC, both have standard models with 1 kVA and 2.x kVA.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 03, 2025, 03:23:31 pm
content: There are several manufacturers, but be prepared to spend some decent amount of money for non-Chinese brands.

author: Kean
author_rank: Unknown
timestamp: March 03, 2025, 03:39:42 pm
content: These items also weigh a lot... like that Voltcraft VIT-1000 apparently weighs 22kg.So the shipping costs can be quite high, especially internationally.

author: davorin
author_rank: Unknown
timestamp: March 03, 2025, 04:16:37 pm
content: Seems the Variac and isolating transformer in series is the cheapest solution...a case for it might add up to the price substantially.What do you use for front panel digital voltage/current readouts? Are there any modules that can be interfaces with a microcontroller like ESP32 for WiFi readout?

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 03, 2025, 08:26:40 pm
content: I acquired at a good price an old Voltech PM100 power analyzer. Therefore I can read not only volts, amps and watts, (the most common setup) but power factor, THD, frequency, VAr and other variables.There are some Chinese modules which read volts, amps and watts, but which cannot accurately handle distorted waveforms.

author: Kean
author_rank: Unknown
timestamp: March 04, 2025, 01:58:27 pm
content: Quote from: davorin on March 03, 2025, 04:16:37 pmAs I mentioned, I use a KWS-AC301 20A Power Meter on my "Green Dot" variac. Not sure if I've seen a WiFi connected meter, but Atorch have a model with Bluetooth.I was trying to get a Voltech PM100 some time ago as I had used one at a client and seen Daves video on it, but instead bought a Tonghui TH3331. I use that when I want more accurate measurements or to take a look at harmonics. I can pair it with my ITECH IT7321 programmable AC PSU so I can select different mains frequencies and even simulate waveform disturbances. But the variac is quicker to set up, though heavy to move.

author: JimKnopf
author_rank: Frequent Contributor
timestamp: March 05, 2025, 05:40:27 am
content: I use an EA-STT 2000 B 4,5A.

author: johansen
author_rank: Super Contributor
timestamp: March 05, 2025, 06:50:55 am
content: the amazon link i found a while ago is no longer available but the same product... may or may not be available herehttps://www.rpelectronics.com/sc-10t-1000w-variac-isolated.htmli think that for 300$ i could be tempted to wind an isolated variac myself. bridgeportmagnetics used to sell toroidal transformers with just the primary winding. --if they still do, you could then 3d print a template to help you wind a second variac type secondary over the primary, using a 3 layer winding through the ID of the toroid.normally variacs have a 2 layer winding in the middle of the core which is in a sense incredibly wasteful in the sense that you can't put much copper in the transformer because you are limited to a single layer winding on the outer diameter of the core.if you were to get really creative you could build a jig to bring out every other turn of the variac so you could fit twice as much copper at the expense of increased resistance losses in the carbon brush.