For those that said the fuse should not be on the primary must be thinking of something else. This is a variable autotransformer so it has only one winding. The correct place for the fuse is BEFORE power gets to the transformer itself. You can certainly fuse the output but having the input fused is mandatory.

4:30 You can get a LOT more current OUT than you put IN. The power won't change, but as you reduce voltage you increase available current (for a given power). Really it ought to be fused on input AND output; input fusing is basically in case the windings touch the case, it does not protect the transformer itself. It is the OUTPUT fuse that protects the transformer.

It's a death trap, a suicide wrap, we gotta get out while we're young. Baby I was born to Run.

I have this same model, and I'm perfectly satisfied with it. One thing should be noted, however; these are made with 110v input in mind, so when running them on our 120v+ mains, output voltage of the variac will be higher than indicated on the dial. When I use mine, I plug a power strip into it's outlet and the equipment being powered into the strip---this allows me to also connect my AC voltmeter, so I can monitor real-time output

I have a similar unit. Liked the video other than the use of the term primary and secondary. A fuse of the output isn't a bad thing to add. You can easily put out a lot of amps on the output when the voltage is turned down. ie 10A in a 120V can be 100A out at 12V. I actually built an DUT power box into my bench that has an isolation transformer then a variac and dim bulb that are both switchable with volts and amps display on the output. It's proven to be one of the absolute best bits of gear for testing things.

Hi, RJ, Yes, that unit does look better. So glad that you found a descent unit and that it is safe to use. Something to know for future maintenance and repairs... The brush contact for variable autotransformers is very difficult to find. You might want to try to find one now, while your model is current. (Some folks would say that you would never wear one out, in a lifetime. But, just drop the unit off of the counter, once, and you could easily need a new brush. However, I don't imagine that you will find it, even if you could make contact with the seller. And, you can not fashion one from a common electric motor brush. That material simply has the wrong electrical properties, even though you would think the materials to be identical. When I bought my AT, I did a lot of research on the subject. And, I did locate a supplier. However, KZfaq will not allow me to post a link, or even mention where I posted the information. So, I am going to send you an email and you can post it, here. Thanks for the shout-out. HTH.

Auto transformers DO NOT provide isolation, so be careful. Aside from that, they are safe to use and if you dont overload them, they will last for many years. I have a Staco unit that I bought over 40 years ago, and it's still working just like new. If you are unsure about the quality, try running it from 0 to full voltage with a modest load on it, and make sure there are no dropouts visible on the meter (nice feature, BTW) as the knob is turned. Also, see if it gets warm if you run it overnight with no load. Personally, the wires in the video look a bit small for 20 amps but are probably OK when you consider their length (resistance) and the amount of heat they generate at 20 amps.

Good production. Thank you. Quite the gadget you've got there. I admire your friend's polite reserve trying to tell you to sincerely beware of Chinese junk.

Yes, the circuit breaker is to protect the house wiring, not the load. However, at the wall receptacle, you are not plugging in a 12AWG copper cord. That cord appears to be 16AWG. This is one of the flaws of our USA electrical code. That cord now is a fire hazard. This is one of the reasons that the latest NEC (2020) now requires arc fault breakers. If that cord were to start a melt down, it would trip the breaker once arcing between the hot and neutral occurs. The fix I see in the UK standards is to have the plug with a fuse that protects the smaller wire used.

You have great content. Im surprised you don't have a larger subscriber count. Keep it up, i love your videos, and i hope your subscribers increase! You deserve it!

Thanks for checking this device for safety concerns.

Thanks for the inspection. I have tested this model's actual output with a volt meter, and it is not linear with the top ring and the attached meter. So I just use an external volt meter every time with my DUT's.

I have the 10A version that I bought over 5 years ago. I only need it a few times a month max and It's been doing the job I need it to do with no issues. Obviously, there are better ones available at quadruple the price. If I needed it daily, maybe I would have gotten a better one but honestly, if it does what I need it to do and it hasn't failed, what more can I say?

Is there a primary and secondary? All variacs I've seen in my country are autotransformers. I have burnt one that had no output fuse. Sure, it took less than 10A in, but because the tap is at lower voltage (and P=UI) at same power I got much more amps at lower voltage out and it burnt the coil. Autotransformers are dangerous in my country because we can put plug in two ways and you are not sure which is L or N. It is also never isolated. I run my variac after an isolation transformer and with a fuse in input AND on output.

Hi RJ, I just came across your channel and subscribed. I'm looking forward to watch all of your videos. Wondering you if you remember me Rick (rrowan) from a few years back doing light shows. Take care and I hope you and your family are doing well.

BEWARE: On the unit that I have, the switch is single-pole-double-throw and when switching off, it takes the primary and connects it to ground/neutral. My switch failed after a few months of normal usage and I think was because the full energy of the primary being dumped through the switch if the user gets unlucky when switching off. I would have liked to see a snubber circuit instead of the SPDT switch to ground like I had. My work-around was to disconnect the switch and use the power plug to turn it on/off.

Do believe the UL marking are genuine? What gauge cord is on it?

for mains devices, I always prefer spade terminals. solder seems amateurish to me. (at least they should have used shrink tubing) one other thing I question on Chinese instruments is wiring. they don't use real copper whenever possible. I've seen so many examples with aluminum or copper coated aluminum.

There is no secondary, it's an autotransformer. The "auto" part means "self". (Some company in China makes one that's also an isolation transformer and that one does have a secondary, but this doesn't appear to be that - they're rare. Also, if it was an isolation transformer it would be defeated by the continuous ground from input to output and you'd have to add a cheater plug adaptor to ensure your DUT is isolated from the mains.)

I don't understand why there is a 20 amp fuse when it has a 15 amp plug.

Excuse my confusion, I thought the earth on the secondary should not connect to the earth of the chassis or the mains earth. Everything should be separate on the secondary side..There should be no earth on the secondary side as you only have hot and neutral wires as that is all you need. The earth in the mains is because it is used as the neutral return to the grid.

As far as I can tell the secondary winding is also floating, meaning it’s a bit less likely to kill me…

What are the core losses?

You are wrong. The fuse on the primary side don't protect the secondary, if the secondary is set to a lower voltage the secondary curent can be much higher than the primary current. This is probably the most likely fault situation and it is unprotected. If you conect a DUT with a short circuit and increase the voltage slowly then when you reach e.g. 10 V you can draw 50 A on the secondary while only drawing about 5 amps on the primary. That can release the magic smoke very fast. A fuse on the primary side is good to protect against internal faults but labb equipment definitely needs to be protected against faulty DUTs and that requires a fuse on the secondary side. I would definitely add a fuse on the secondary side if it was mine.

There is something odd about these cheap Chinese variable autotransformers. A few years ago I bought one on Amazon, it was a LVYUAN Variable Transformer rated at 1.0kVA. I also bought a used one on eBay, a Staco Inc Industrial Variable Autotransformer model 3PN1010 rated at 1.5 kVA. Testing and comparing the two, the Staco (an American company I think) was about half the size and weight, yet it outperformed the super cheap Chinese product, which was twice the size and weight as the Staco. These two autotransformers are electrically the same yet the smaller American made one performed 50% better than the cheap Chinese one. I assume the difference is in the exact way the laminate core is constructed. Nearly all Chinese technology has been copied from the West and so its not surprising that when they manufacture a copy of Western technology it comes out like an imperfect facsimile, having the appearance of the original without its substance.

"Is It Safe to Use?" Yes.

You keep saying primary and secondary winding and I think that's a mistake. My variable transformer which looks exactly like this one has only one winding with a moveable tap. You can confirm this by checking if there is any isolation between the plug and the outlets on the device. With one winding - any point about fusing the primary or secondary winding is moot.

I would not own a Chinese Red autotransformer Period. I own several (big & small) classic Variacs™But that's just me. Thank you for the video. You RoCk!

Its 20 Amps.. ?????WTF TWENTY AMPS ???/ . hahahahahahahah nothing to see here.

That's an irrelevant way to test earthing there was no test current there, you have to load the earth bond with a decent test current like 10a or 20a for a few seconds I use 12v psu and halogen lamps as dummy loads for this, you get sparking from earth lugs that are paint Contaminated even when there's a shake proof washer cutting through the paint