Variac Isolation Transformer. Are Variacs Isolated?
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- Опубліковано 29 чер 2024
- This Variac isolation transformer has stirred up controversy. Is it really isolated? Let’s do some tests and open it up.
NOTES & MORE CONTROVERSY: New models with the genuine Variac brand seem to be no longer sold. In 2004, Instrument Service Equipment obtained the name Variac. They sell Variable AC transformers under the name Staco. The unit shown in the video is from PHC. www.phcenterprise.com/isolatio... The word Variac is printed on the front, but I’m not certain it’s an officially brand-licensed product or they’re using the word generically.
The term Variac is often used generically, and often as a substitute for autoformer. This is incorrect. Variac intended the name to mean variable AC (Vari-AC) not necessarily autoformer.
Also, thanks to some viewers, it was brought to my attention that the dial on the Variac in the video may actually be using a “percentage of input voltage” scale and not an output voltage scale. In other words, at the “100” mark, voltage will be 100% of input voltage (about 120 volts) and not an output of 100 volts.
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NOTES & MORE CONTROVERSY: New models with the genuine Variac brand seem to be no longer sold. In 2004, Instrument Service Equipment obtained the name Variac. They sell Variable AC transformers under the name Staco. The unit shown in the video is from PHC. www.phcenterprise.com/isolation.html The word Variac is printed on the front, but I’m not certain it’s an officially brand-licensed product or they’re using the word generically.
The term Variac is often used generically, and often as a substitute for autoformer. This is incorrect. Variac intended the name to mean variable AC (Vari-AC) not necessarily autoformer.
Also, thanks to some viewers, it was brought to my attention that the dial on the Variac in the video may actually be using a “percentage of input voltage” scale and not an output voltage scale. In other words, at the “100” mark, voltage will be 100% of input voltage (about 120 volts) and not an output of 100 volts.
The original factory calibrated scale on the front side of that plate you changed, may actually have been calibrated to the voltage output under a FULL (10 AMP) load instead of essentially NO load, as you were testing it here.
I would tend to think that may be the case, rather than a percentage of input, simply because it's not mentioned or labeled anywhere with a percent (or %) scale, plus it does say on it that the output volts are from 0-130 volt AT 10AMPS, and that is what the dial numbers range from also.
No, you are incorrect. The scale shows percentage.
I love your videos and I just subscribed 🙂
And I believe you that the Vvariac is fully isolated.
*_BUT!!!_*
What happens if a fault sends 240 VAC from the mains into the Variac? What output voltage will you get if the Variac is set to 120 VAC?
This is why I'm looking for a true isolation device, like a motor-generator with an insulated shaft.
WoW! Love the quality of your videos. You take a lot of pride in your work and production of these tutorials.
Keep up the good work. I will keep enjoying 👍
Nice video! My autotransformer is not isolated so I run it after an isolation transformer. I bought a nice TrippLite hospital grade model but it's only 250 watt. After using that for around a year I opened it up. Turns out the secondary neutral and ground were connected! So turns out my isolation transformer was not isolated in the manor I expected! I could have been zapped but was lucky to not have been. I promptly factory deleted that wire and it is truly isolated now! So turns out my isolation transformer was only going to be noise isolation and not electrical isolation as I expected. Oh well! I didn't get zapped so it doesn't matter. But for my autotransformer I used sharpie to mark the voltage on the dial. My dial is printed on and in percentage of output 0-100%. There is a switch to change 120V or 140V output. I need to build a current limiter at some point. So I just change fuse sizes on the autotransformer to approximately what I expect to pull to prevent direct shorts drawing a ton of current.
The plastic track also helps to stop the carbon from the brush shorting the windings over time.
Warning to viewers: there are many variacs for sale out there that look exactly like Flux’s from the outside (even that fire engine red color) but are not in fact isolation transformers. Check the specs, the schematic, and test, test, test.
Looks like there is enough room in front beside the plug to add a scavenged power supply mains switch, and have it in line with the ground wire, allowing the lift without the cheater plug. Since condensing the isolation transformer and variac into one unit, might as well keep going! Great video and teardown displaying the guts of the unit.
The safest way to check the isolation is to short the primary windings, and also the secondary windings, then check the continuity between the two shorted windings with an insulation tester capable of 1000v output or greater. I wouldn't trust the low voltage from a DVM to confirm the isolation, especially with Chinese transformers. Even Fluke DMM's are not designed to do the job of an insulation tester.
I'd have probably just enlarged the holes in the dial a bit to allow it to be rotated to give accurate readings, since it was pretty close to 3v off in most positions.
I really appreciate the level of detail in this video. I think experts often underestimate what trips up those less experienced.
Thanks, Peter. Very much appreciated.
@@FluxCondenser I likewise appreciated you explanation of that different components of a “system” are in an earlier episode. I though it was great for the younger demographic. :) I played it for my son for a test. You and I are audio geeks of about the same age, my son is 18 and has little interest :(. His first comment “what’s equalization?”
@@peterk8978 Glad you enjoyed that video about system components. It’s not just for teens. I have a friend my age that recently got a turntable as a gift and he asked me if I had any videos introducing component hi-fi to newbies. I sent him to that video and he told me later that he learned a lot. Not every male our age is an audio geek like us, I guess!
Great video, keep it up.
I have two suggestions,
1: Lose the cheater plug. Replace it with a GFI, connect the ground of the GFI through a switch to the neutral side of the isolated output. This will give you a fully isolated ground through a GFI for protection.
2: The meter can be adjusted. It has two helical Springs, one of the front, and one on the back Of the shaft. By increasing or decreasing the tension of these Springs together you can adjust the movement versus voltage. Be careful, they are very Delicate.
Stay safe.
Thanks for the tip about the meter. I might look into that, but it’s so tiny and cheap I’m afraid it’ll break if I look at it the wrong way! I’ve seen some digital meter mods for these Variacs that I might consider, though. Even if it was accurate the analog meter on this thing is so tiny and provides so little granularity that it’s not especially useful. A nice bright LED display on the other hand would be pretty great.
A GFI won't work behind a true isolation transformer.
I have tested this with a 10mA portable GFI.
For a GFI to work, you need a Hot and Neutral , a isolation transformer doesn't have a neutral on the output, but has 2 Hot wires.
To create a neutral on the output of a isolation transformer, you must connect one of the 2 Hot wires to the neutral of the input (primary side),
but by doing that, you bypass the benefits of having a isolation transformer.
The only way to add protection against electrocution behind a isolation transformer, is to use a socalled "Line Isolation Monitor", but these are not cheap.
These devices monitor the impedance between both Hot wires from the output, and the isolated ground to your DUT (Device Under Test).
A example of such a device is the older model Tektronix A6901 :
w140.com/tekwiki/wiki/A6901
Keep in mind if you connect a device like a SMPS (laptop charger etc....) to the output of isolation transformer, and the input of this SMPS has X and Y filter capacitors on the input, that there will be a very low current leakage of mains voltage to ground.
Normally when the ground is connect to a wall outlet, this very low current leakage becomes almost zero volts, but with elevated ground on the output of the isolation transformer, 50% or more of the voltage will be present on the ground pin.
Some laptop chargers have the negative of the DC jack (which you plug in the laptop) directly connected to the ground of the input of the charger,
so the negative of this DC jack isn't zero anymore , but can carry 50% (or more) of the supply voltage.
Another fact is, when the ground of the output socket of the isolation transformer is disconnected, that there is a "Ghostvoltage" between each hot from the output socket and the metal chassis and housing of the isolation transformer, this is due the capacitive coupling between the primary and secundairy side.
This "Ghostvoltage" is also low current leakage, enough to light up a neon bulb, but also can damage sensitive circuits connected to the output of the isolation transformer.
Great video Sir , if you choose one with digital reading , would it be more accurate than the meter type ?
Don't forget about parallax errors when reading analog meters as in the comparison between the built-in Variac meter to the digital meter. The Variac panel appears to be closer on the right side than the left as indicated by the position of the fuse holder. If the settings remained the same, but the viewing position was shifted to a position which was perpendicular to the meter face, the meter would have shown the needle slightly higher than 100v and closer to the 114v indicated on the digital meter.
All readings of the Variac were done from directly overhead which, as you stated, is necessary for accuracy. For the video, many, many shots of me hovering over the Variac to ensure this were edited out to the cutting room floor.
Sorry, I was referring to the segment near the end of the video when you were complaining about the accuracy of the little meter on the side of the Variac.
I see. Yes you’ve got to be careful with meters, as yeah, the angle can make a difference. I love analog meters with a mirror background to help line up the needle and ensure straight-on accuracy. Again, when viewing the voltage meter in the video, the results I state are from viewing straight on. The meter is horribly inaccurate.
This was a great video on the misconceptions about some VARIACs, on the lack of accuracy of the Chinese-made clones, and the fluctuations of our power at different times of day. My solution: buy an older American-made VARIAC and use a Tripp-Lite Isolation transformer with the ground mod. I did this and spent 30 minutes total on the project and I didn't give the Chicoms any money. My VARIAC brand autotransformer is still dead on after decades.
Thanks, Ross. Glad you enjoyed the video. As a side note, the Variac shown in the video is not a clone. While it’s made in China, it’s a genuine Variac. There are some good options out there for isolation transformers, but having the isolation and Variac in one unit (for me) is invaluable and I’d be hard pressed to give it up.
I did a little more research on this, and I think you’re correct that the Variac I show in the video is not actually from the brand Variac. It appears to be a product of PHC. www.phcenterprise.com/isolation.html
I sharpie’d mine .. too lazy to pull out the Dymo labeler, lol. Great review and great advice.
Variac dials are usually calibrated as percent of input voltage. That's why 100 read 122.
Some are and some are not. Either way I always monitor the voltage with another device.
My variac is a Staco and the dial is 0 to 100. The unit says on it that the dial is a percentage of output voltage. I've also seen some older American made variable transformers with scales like yours that were labeled as percentage of input voltage. They are all just approximations and there should always be an accurate voltmeter monitoring the output. Even yours set to 130 was close to the 156 the 130% of 120 volts would be.
@Robert Gibbons I double-checked the math using the indicator dial as a percentage scale, and you’re correct that as a percentage scale it’s far more accurate. This is based on the readings I state in the video. For most positions on the dial, it fairly accurately represents about that percentage of 120 volts.
There were two outliers, though. For example, at the 20 mark actual voltage was 30 while 20% of 120 would only be 24. At the 70 mark output was 90 volts, while 70% of 120 would only be 84.
And while the instructions for Variacs state that the dial should be used to indicate voltage, I think you must be correct that the original intention for the scale used was probably to indicate percentage. That’s great input and I appreciate you bringing this to my intention.
Nonetheless, Variac is certainly not clear about this (again they state it’s a reference to actual voltage and most people would assume that’s the case) and a percentage scale isn’t particularly useful.
As an aside, while I originally thought the Variac shown in the video was a genuine Variac-brand product (Variac is printed on the front). That appears to not be the case. I did a little research and looks like it’s a product of PHC. www.phcenterprise.com/isolation.html
I don't know if it's a marketing arrangement or what, but if you go to the PHC website their catalog lists what you have as a Variac.
The newer SC-10T models have a two prong AC input cord so there is no connection to the earth ground at all. No need for a 'cheater'. I got mine in the mail today and it is very nice. Thanks for this video. It sold me on this model.
My recollection was the numbered dial was not for voltage but is a rough indication of percentage and the analog meter should show the correct voltage. Therefore when the dial position is pointing at 100, the output should be close to mains level.
I learned a lot from your video.
Thank you!
Glad to hear that, Mark! Thanks for taking the time to comment.
The Isolated Variac output amplitude will also depend on the load. I know you were doing all of that just to make some other points. In general I measure all of my equipment outputs with a DMM/scope and assume the instrument's display is "for reference only." Making your own scale is a nice reminder to everyone that we have the skills to make and modify our own tools for our purposes.
Good video, good content, peace.
Yes, transformers can sag under load. The Variac shown in the video is capable of 10 amps and in my tests running with a substantial load (far greater than any equipment I’d ever test), the voltage did not sag and my new dial remained accurate. As you do, I will continue to use this Variac while monitoring the voltage with an accurate meter (I keep my old Heathkit line monitor calibrated). But having the dial now give a good indication of actual voltage is going to be helpful.
Would you explain how you set up your current limiter. Does the switch in one direction have the bulb in the circuit (100 watt bulb would limit to about one amp) and the switch in the other position just directs the variac output to the plug directly, with the bulb out of the circuit? So you start with the bulb in circuit to detect a short, but then you just switch it out of the circuit when no short or unusual current draw is not detected?
Dave, I should do a quick video showing how I made the dim-bulb limiter. It could be wired to switch the bulb on and off as you describe, but mine’s not as complex as that. The bulb and switch are in series with the AC in and out so the switch is just a convenience for me to quickly switch my device under test on and off.
Additionally, I really don’t tend to not use a current limiter when servicing equipment, so there’s not much need to switch it off. The only time I might have an exposed device on my bench without the current limiter is in the preliminary-final testing phase to quickly check performance at full current. I could see how being able to instantly switch the limiter on and off could sometimes be useful, though, and I’ve seen other UA-camrs using designs that have the feature. However, one potential problem with such a design is that the user may believe current limitation is in place, but the switch is in the wrong position.
My final performance tests are done with the unit’s covers fully in place (for safety and to reduce hum) and the device plugged directly into my home’s AC (no Variac, no current limiter).
Would your measurements of the variac output voltage have been different if you had a reasonable load on the unit?
Another great question, Dave. I tested this by hooking up a large air filter which draws a lot of current to the Variac. The output voltage didn’t budge even with the filter in its highest setting. As shown in the video, the transformer is mammoth and can supply lots of current without sag (10 amps).
You videos are so professionally done 👍
Mine changes a lot when under load
the dial indicator is in %. your voltage @ 100 on the dial was 122 volts which is normal household voltage
Thanks, Murray. Yes, this has already been discussed in the comments. Please see the pinned post. Appreciate your input.
Good evening, I wanted to ask if it is possible to measure an amplifier with an oscilloscope, without galvanic isolation, or in which case it is not possible, if the case still has only 2 pins, thanks to any knowledge, I am a beginner, I would like to understand, thank you very much.
You're a good man, Charlie Brown. Good choice with the 126ers too.
Very well detailed and interesting.
I see a lot of these variacs on ebay. Is that where you got yours? One ebay seller's location is listed at (Perth Amboy, NJ) which is only about 30 minutes from my home at the Jersey Shore...
As I mentioned on your current limiting video, I am looking for a variac (10 amp) to use with guitar amplifiers any info welcome. You explain things very well. All the best.
Phil
No, I believe I got mine from Amazon. But the manufacturer no longer be in business and I’m not aware of any new “Variacs” that have the isolation feature.
The ones I see on ebay with a TDGC in the model # are not isolated. The one shown in this video (model SC-10T) is 4 times the price of the TDGC models on ebay of the same current rating, but they are a single wound transformer and the one here is a double wound. There seems to be a concern if the is insulation of the transformer construction will give complete isolation but only a few could test that.
I think that puts to bed the issue of isolation with your transformer for good. Well done.
We’ll see ;-)
They now sell the Sc-10T-2, which has a digital Voltage meter incorporated within
Until I saw this video I never knew isolated variacs existed. Being such a novel idea I decided to buy one and check it out. The SC-10T wasnt available so I purchased the SC-15T. From the outside it looked really nice and worked as seen in the video. However when I checked its ground isolation I found that the chassis over the transformer/variac was not grounded yet the cover holding the pwr switch, fuse, receptacle and meter was. Not good. So I decided to discect it. What I found was typical Chinese crap. Soldering was substandard and wiring and lead dress was very poor. What shocked me most was their use of a cheap 5-15R receptacle with the GN ground wire jammed into its ground terminal with an oversized lug. Note: no UL, CSA or CE markings were on the receptacle. If only an isolated ground receptacle was used and the GN wire was secured to the chassis .....With the chassis ungrounded and the output receptacle grounded this wonder of modern science is an electrocution hazard out of the box. BTW-my background is in design of industrial transformers.
Intersting, but I wouldn’t assume that the SC-15T is of the same quality and circuit design as the one I show.
Did anything change when you put a large load on it?
The indicator seems to be showing the PERCENTAGE of your line voltage, not the voltage itself
Scary to see that dial reading inaccurately.
Lately I only buy UL rated products as I’m concerned about fire and shock hazards from poor quality electrical products.
I also tend to buy audio products made in the USA, Europe or Japan out of concern about a fire burning my house down because of something made in a country where regulations are lax or nonexistent.
i have one of these variac andf it goes noisy and gets very hot when i put it to feed a full bridge rectifier only at 50 volts it goes to 100 c temp is that normal ? i can even smell the varnish
It’s hard to say, Amir, but if the rectifier is working correctly and isn’t shorted, then yes, I agree, that doesn’t seem like typical operating behavior and caution should be used. Make sure the Variac has a fuse and the correct value is installed.
Well demonstrated, albeit hard to find type of Variac.
Thanks. Yeah, it’s a shame that this model no longer seems to be available.
The inaccuracy in the scale is due to the fact they try to adjust for a load being drawn. As even with a 10th of the max load the voltage will vary quite a bit
This is not a traditional variac. It is a variable isolation transformer with separate pri and sec as seen in the schematic. Sec voltage is adjustable via a brush instead of individual taps. Being isolated the transformer will exhibit a voltage drop from no load to full load ( phenomenon is called regulation ). The dial scale is probably graduated in % input voltage which will change with the load. The carbon brush of the wiper does not contact individual turns of the sec but probably two at a time. This would represent a short circuit however with only a couple volts per turn on the windings the brush probably dissipates the heat generated. The business of the unit overheating with the use of a rectifyer is likely due to the fact that the AC current is higher than the DC load current by.....I believe 1.8X.
A lot of those dials ment percent of line voltage. I noticed when you had it at 100 it read 122. That may be 100% of your line voltage.
Thanks, Multimood. You’re correct that the original plate for the Variac read in percentage scale. Please see my pinned comment in this video for more on this.
An adjustable or variable transformer and an autotransformer are two different types of variation on a transformer, a transformer can be one, the other, both, or neither. A variable transformer basically has a very high number of taps and a way to change between them more easily, it serves voltage adjustment or regulation. An autotransformer is a way to more cheaply build a transformer that has pros and cons. Many variable transformers are autotransformers, but not all.
For many years 30+, I have used CVTs, constant voltage transformers, to provide isolation and current limiting. I have 125, 250, and 500 VA transformers. If the current exceeds the output current spec of the transformer the voltage will fold back to maintain that current level. The big advantage of these transformers is they regulate the supplied voltage and will suppress voltage spikes and noise. I sometimes hook the variac to the CVT's output If varying the voltage is needed. The 125 VA transformer is good for most radios and the others are used as needed by the test units rated power consumption. Always use an isolation transformer.
So what do you think of this combo of isolation and variac? Would you use it if you had limited space?
There's another acronym being hijacked. Today, CVT is used for Continuously Variable Transmission, lol. (We won't talk about the hijacking of our dear acronym CRT!)
There should be multiple taps available within the enclosure. Sounds like to me that it's not set at 1:1. Also, the dial represents the percentage of line voltage out. 100 on the dial should equal 1.1.
Thanks, you're correct, the scale represents percentage, not voltage as I had once thought. This issue has been addressed in the comments and video description.
I always knew that the numbers on the adjustment knob indicated the percentage based on the input voltage. when you do the math it works out. I have one at 220v and it has numbers up to 130 and not 290v which is the maximum mine reaches.
Would it not make more sense to label the output as percent voltage rather than output voltage?
I kinda like the unit because it would take up less bench space than both my isolation transformer and my Staco Variable Autotransformer. But then what would I do with those two units? Decisions, decisions. 😜
Exactly, Darth. The practical advantages of having the variable AC and isolation in one unit can’t be overlooked. No matter how big your space, bench and shelf space always seems to be limited. To power a device under test I often have to have the Variac (with its bulky 10 amp power cord), current limiter and AC line monitor on my bench (along with the DUT, other test gear and tools) which is already a lot. I’d hate to have to add one more bulky device with another bulky cord to that mix. Still, your Staco is probably built like a tank and will last forever, so I’m not sure I’d look to replace it and your isolation unit unless your bench space is really limited.
Isn't it showing you the percentage on the dial, not the voltage? (Because it doesn't know what your wall voltage is.)
It's showing you the winding ratio, I believe. If you put 100V AC into it it would align.
Yes, that’s correct. Please see my pinned note in the comment section for more details.
Ah, you've noted that already. Good. Yes.
The numbers around the dial DO NOT represent the voltage at the output. It represents the PERCENTAGE of the INPUT to the variac being presented to the output. ie: If your house voltage is 122vac, you will see 122vac on the output when you turn the dial to 100 (meaning 100% of the input is now at the output).
It's impossible for the dial to show accurate voltages because it depends on the voltage being applied to it. If you want your variac dial to be accurate, just apply 100vac to the input. Then when you turn the dial to 100, you'll have 100vac at the output. If you turn the dial to 50, you'll have 50vac at the output. So that dial you made is only accurate for the place you plugged it in. If you take it somewhere else and the house voltage is 110vac, your dial is no longer accurate.
The dial as a percentage scale has already been discussed and explained in my pinned post. Additionally, obviously the output voltage is relative to the input voltage. This was also explained in the video. This doesn’t mean a dial scale showing voltage can’t be used and in fact, some Variacs have just that. No, the scale will not be 100% accurate, but will be reasonably close and certainly more helpful than a percentage scale for many users.
The voltage in my home varies from 120-123 volts. Changing the dial scale to read voltage has been a tremendous improvement to the functionality of the Variac. I can quickly get the voltage in range using the dial now, and then more precisely adjust voltage using the meter.
@@FluxCondenser Anyone who hasn't seen your "pinned post" wouldn't know about the percentage thing. IMHO, I don't think it's reasonable to expect everyone watching this video to have seen the other video. I'm sorry if I ruffled your feathers. I would, however, like to see this other video (pinned post) you're talking about. Could you provide a link that I might see it? Thank you
No feathers ruffled and I don’t mean to ruffle yours. The pinned post is in the comments. Pinned just means that it will be the first comment you’d read. I certainly apologize if I came across as abrupt, but admittedly, I do sometimes get frustrated when people comment without reading the other comments first. This would be ideal as the same info wouldn’t have to be repeated. Honestly, though, I’ve been guilty of that myself in the past and only now that I have my own channel have I curbed my ways.
I wonder if the marking are calibrated for full load.
Ian, the markings are actually marked as a percentage of input voltage. So, if the input voltage is 120 volts, at 100, the output will be 120 volts. I wish they had put a % symbol on there as it was quite confusing.
Wouldn't an unloaded transformer winding read a bit high? Nice recalibration too:)
Brilliant solution for dial accuracy
Thank you.
I have a hobby Lincoln welder 20 amp 110v so I got this one only newer model to help drive my welder and not kick breaker. Hope it work order it be in 4 days
Well, if you try to pull more amps than the Variac is rated for, you’re just gonna blow the fuse on the Variac. The Variac in the video, for instance can only provide 10 amps. To drive a 20 amp welder, you’ll need at least a 20 amp Variac and a 20 amp dedicated circuit in your home to plug it into.
Load the variac with its VA rating before making an output voltage measurement. Open circuit conformance is not a valid measurement to make output voltage/dial setting conform.
Can you change voltage on full load?
Yes.
if you don't test it with a nominal load at the output you don't read the output voltage as on the scale... the Mr. Ohm law do apply also to this kind of equipments
mount a small digital volt/amp meter to the side and you will have all the info you need with out looking on top.
Yes, I have that, but having the dial match improves things further.
Scale is not in voltage. It should indicated % of line voltage. Also, marking in voltage will be inaccurate as the line voltage can vary slightly and the voltage from the variac will also vary slightly due to the size of the load you put on it. Best to always use a volt meter.
Thanks, Val. Yes, this has been discussed in the comments.
Excuse me Mr. In Israel there is no isolation between the input & the output in any variac & in Israel the cycle is 50HZ & the outlet power A.C. in any socket is 230Volts
The scale was in percent of the line voltage.
Yes, this has been discussed and explained.
Are these available in 240v
Steve, I can’t even find this isolated model in 120v anymore. It was on the market less than six months ago, but now the links to it seem to be dead. Good luck finding something. I see some single-phase 220v Variacs available on Amazon, but nothing 240v. If that would suit your needs and you also need isolation, you’d also have to find a 220v isolation transformer to pair it with.
Thanks for your speedy reply. I enjoy your video's. Keep them coming!
My pleasure. Always glad to help.
Do you think you could do a video on making up an isolation transformer?
Steve, possibly, but it wouldn’t be that interesting. An isolation transformer really is just that. A transformer. To build one, you’d simply be putting a transformer in a case and adding a power cable and some outlets (and maybe a fuse and switch). Considering the effort and expenses of buying the transformer and parts, I think it might end up being an exercise in futility as well-built, complete isolation transformers are readily available at a reasonable cost. I guess the only way I’d consider building one myself would be if I happened to have a suitable transformer laying around collecting dust. But I don’t have one of those.
I just don’t think there is a practical way to isolate this unit. IMO you are better off modifying a so called isolation transformer available almost anywhere. I have yet to see anything available that is fully isolated at a reasonable price. I hope to see a link if you know.
This unit is isolated. Not sure what you’re talking about.
You are measuring with no load. I think the dial is calibrated so that when the device is under load it will be more accurate.
I found this very helpful, thanks!. However, you should note that what is true about your Variac is apparently NOT true of MOST currently available Variacs. Based on their schematics, most models are NOT ISOLATED. I just bought a new Variac knock off that appears to be a clone of the one that you have, a model number SC-10T. The included schematic confirms that it is isolated (with the use of a cheater plug as you describe) and I get the same results that you do when testing for isolation between the line and output neutrals. However, and AFAIK, the SC-10T may be the only of the commonly available import Variacs (including a number of models that have nearly identical cases) that provides isolation. You might want to change the title of the video to be more clear on this point. Assuming that just any Variac provides isolation could be a dangerous mistake. I am no expert and everyone should do their own testing, but viewers please don't assume that if you have a red one that looks something like the one in the video that it is actually isolated. It may well not be.
Thanks, Jeff, glad you enjoyed the video. I don’t feel I need to clarify things any more than I have. In the video I state very clearly that not all Variacs are isolated and that most aren’t. The title doesn’t state all Variacs are isolated and the thumbnail graphic makes it clear the subject is controversial.
"Controversy"? An autotransformer is by definition not isolated. If there is an additional component that is an isolation transformer, and it's isolated. Nothing could possibly be controversial about it.
Nonsense.
Is this a good safe variac I keep reading on the web do not buy these cheap Chinese variax they will mess up your equipment is this true ?
I know a lot of Chinese stuff is rubbish bye got a variable transformer device marketed as a fan speed controller rated it 3 amps. It's nothing but a power input and output and a dial and a riveted metal box. It's completely made down to a certain price and was £100 in British money. I was so sceptical I expected it to kill me straight away. But the casing is earth the plug sockets are urged and it works really well. Tiny adjustments in the dial alter the voltage. I actually did have an old-fashioned 10 amp Berco variable transformer. No doubt it was far better made but you also have to bear in mind that some of the old equipment was made at a less stringent safety standard. This unit has large air vents which you know if you just push up against a piece of metal you've got a live wire. Point is I don't have much experience but my one experience of buying a budget Chinese variable transformer has been a very good one left me impressed
A variac is not isolated .Only an isolation transformer is isolated .Soon as you bond the ground and neutral together you are not isolated ..If you have one that has both a primary and secondary autotransformer ..Now when you were testing test the case as reference .
Variac - 1. isolated 2. non-isolated
Your Isolation variac is still not isolated , even with a cheater plug , you have a earth ground going to your receptacle ...... Earth ground meets up with your neutral wire in your breaker box ....... If that green and yellow wire were to disappear for some strange reason from that recep then you would be isolated ..
It is fully isolated with a cheater plug.
You know I’m sure that you have an isolated Variac I’ve seen that model before, but your video would have been more convincing if you had the dial actually set to a number besides zero or maybe you had it past the full amount idk, but it looks like it’s between zero and the full amount so you can’t tell, so maybe if you set it at 50% it would be better, I’m sure it was an over sight. But at zero wouldn’t you expect no continuity on the output?
If that’s what you think, then you do not have an understanding of how transformers work. Think about it.
@@FluxCondenser it not the transformer that I don’t have a understanding of, it’s the tap I don’t have a understanding of, it could be build so the brush goes off the coil on zero. I guess if that’s the case the other lead would have still made contact. Anyway like you said it’s isolated.
There are two types of variable transformers. One is isolated and the other is not.
Buyers and users Must be sure they know which one they are dealing with.
Since there is a physical ground connection this is not fully isolated and not as safe as you think it is. Why? Because that ground ends up making a neutral wire connection to circuit breaker panel/box. Therefore one mistake and 'you' will complete the circuit, hence electrical shock. Even if the output ground were connected to the chassis, still not enough. The workaround is to us a cheater plug(3 prong to 2 prong) to the variac output to eliminate ground connection altogether. Then this is fully isolated and more safe.
Dude, that’s all covered in the video.
Variac are not isolated, a Variac is like a potentiometer or a light dimmer connected to a light source, there are no isolation.
You are incorrect. Most Variacs are not isolated. Some are, though, as is the one shown in the video.
@@FluxCondenser Well which part of my comment is incorrect? In general term a Variac as an auto transformer which only regulate an output from its input have no isolation between the input and the output.
So my comment is not incorrect at all, it doesn't mean that , you can't get an isolated Variac, what it means is if you now go to an Electrical components shop and find Variac on the shelves at least 90% of them if not all will not have isolation.
@@CMTEQ Every part of your statement was incorrect as you wrote that Variacs aren’t isolated.
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