My Variac / Isolation Xfmr / DimBulb Setup

A few years ago, I started working on vintage Heathkit stuff (mostly mine from the '70s!) and needed a safe way to plug it in. Here's what resulted.
As usual, none of my material is ever sponsored by anyone. And of course, Line Voltage (eg. 120VAC) is potentially lethal, so if you attempt anything you see on my channel, you're doing so at your own risk.

[@orihalcon8693]

I believe that the purpose of the isolation transformer is to isolate the hot line's reference to ground/neutral, which means you could run your ground wire to your output plugs and that won't show a voltage potential between either of your two live wires which you could check with your resistance meter with the unit off, or check AC voltage between the original ground and your two isolated lines with it on . I think the main reason you'd do this is to allow static electricity in/on a device to still be able to dissipate to ground, but I haven't really seen any videos discussing that. Same as your disclaimer goes, I'm just a guy on the internet who has never even hooked up a dim bulb tester (but I do understand the purpose of one)r, so take all of this with a grain of salt haha

[@dtss_smudge]

The isolation transformer is there to isolate *both* hot and neutral. In the US at least, ground is bonded to neutral at the first disconnect (ie. the breaker panel). Also, once you've isolated the device under test, take care with how you power (um, ground) your test equipment. A case for battery-operated DMMs, scopes etc Thanks for commenting.

[@t1d100]

Yes, please, I would like to see the analog volt and current meter build, with schematic, BOM and parts links.

[@dtss_smudge]

My greatest challenge seems to be finding good meter-paper-scale-design software for Mac, to re-label stock ammeters to 0-130 VAC and 0-3A. The actual electronics for extending ammeter ranges and converting them to voltmeters is straightforward Think resistors in parallel or series, respectively. Oh, and rectifiers for AC...

[@Pulverrostmannen]

I have a more compact and refined version of isolation and dim bulb, The Super Isolation transformer I have is a huge 500VA continuous power compact one that came with dual outputs made by Elsund, it has a ground center tap isolated from the mains/chassis ground on the outputs. I modified mine to have a switch for virtual ground so I can completely lift even the virtual ground on the load completely, I added Power switch and a Neon bulb on the transformer as well as a huge MOV for spike protection. my transformer already came with a resettable fuse 240V 6,3A (1500watt) that pops out if you load it too much for extended time but I added extra protection around it too. The dim Bulb addon could not be more compact and I have never seen any design on that like mine. I have re-built a single to dual outlet adapter to have your current limit output that goes through the lamp that is placed on the second output of it instead, the size of this addon is smaller than a Gameboy. you just plug it into any outlet and pick a bulb and it´s ready. I have this plugged into one outlet of the isolation tranny and if I want to disable current limit I simply move the plug to the other output. if I want to use a variac I just plug this into any of these outlets only when I need it instead. mine is big (up to 2000Watt) or 8 amps 260Volt. My version of isolation/current limit is the most compact and simple I have seen on youtube and it is always ready on my bench without taking up space barely more than a 2Litre pack of milk on the table with the current limiter included. The tools are essential to have for any technician of both Tube and modern equipment but I see the trend pretty much everyone make these so big and bulky it is even hard to have it available as a part of your bench at all times. I mean as long as it fits your desires it´s no problem but space is also precious around your workspace :)

[@dtss_smudge]

Sounds like a great unit; why not do a video on it?

[@Pulverrostmannen]

@@dtss_smudge yeah I really should do that some day

[@splitprissm9339]

Possibly, add a ten turn coil that can take a clamp ammeter.

[@dtss_smudge]

That would certainly do it. Thanks for commenting.

[@johnfitzpatrick2469]

G,day from Sydney Australia. I've just recently made a dim bulb. Want to set up V and Amp meters. Want variac and DC controller. You set my mind straight; there (Chinese LED) are a monitor not an accurate meter. 💫🇦🇺

[@dtss_smudge]

Greetings from the USA! Glad you found it helpful and thanks for the comment.

[@Sodbusterrod]

Enjoyed the video. Have you tried the Kill A Watt monitor? I use it on my setup with accurate results so far.

[@dtss_smudge]

As a matter of fact I have a Kill-A-Watt, but I needed something dedicated to the variac/isolation/dimbulb.... Thanks for taking the time to comment! !

[@CoolMusicToMyEars]

No isolation on a Variac its just a tapping off a primary

[@dtss_smudge]

Yes, but perhaps you're commenting on the thumbnail variac picture, not on the rest of the project which has the isolation xfrmr right next to it. Thanks nevertheless for taking the time to comment.

[@orihalcon8693]

They apparently did make some Variacs with isolation built in - they used a separate secondary coil. The one here is an "autoformer" that is definitely not isolated alone, though going through the separate isolation transformer accomplishes the same thing for much less than hunting one of those isolated various down haha.

[@t1d100]

Warning: The BK Precision 1655A is a screaming piece of dangerous junk. No solder mask on the PCB. 1940's circuit design and parts. Horrible construction quality. Useless soldering iron controller. I had three brand new arrive DOA, from a reputable OEM supplier.

[@dtss_smudge]

I had a quick look at this B&K, and putting aside any quality concerns, it seems to have things you don't need (soldering iron temp control) and not things you do need (current limiting)... Thanks for the comments!

[@splitprissm9339]

@@dtss_smudge Probably, the mindset is that overcurrent is supposed to trigger fuses/breakers, NOT be limited - When not in a lab/workshop environment and attended by a competent amateur or professional, a current limiter can cause an accident rather than prevent one (especially if you allow limiting it to an amp or three, as you would need on a 200...500VA capable supply - plenty enough to start fires while keeping any fuse or breaker from interfering).