2000VA Variac (Variable AC Transformer) - Page 1
Forum section: electronics / testgear

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: October 08, 2013, 08:09:15 pm
content: I am looking to add a new Variac to my lab for transformer ratio calculations and design. I have been looking around and found several ranging from 60 bucks to about 500. I finally settled in on this one. Seems like it has what I need and won't break the bank. Does anyone have any experience with this brand? If not, can you make recommendations on a good Variac with a fair price?Thanks in advance!http://www.automationtechnologiesinc.com/products-page/variable-ac-transformer/tdgc-2km-metered-variac

author: Fsck
author_rank: Super Contributor
timestamp: October 08, 2013, 08:12:28 pm
content: never seen it, but I'm not a fan of variacs with fuses. I prefer circuit breakers.

author: MarkL
author_rank: Unknown
timestamp: October 09, 2013, 12:37:14 am
content: I have what looks like exact same model of "Made in China" No-Name brand 20A variac, which I purchased here:http://www.allelectronics.com/make-a-store/item/SC-20M/20-AMP-VARIABLE-TRANSFORMER/1.htmlWithin a few days of using the unit, the fuse holder broke, the outlet cracked, and when trying to adjust the voltage under a 15A load, the wiper arced and caught on fire. That last event pitted the transformer windings/contacts, and now setting the voltage in that area no longer works reliably even after fixing up the damaged area (no surprise there).I thought it was a great deal price-wise, but it turned out to be a disaster. Don't go near it, would be my recommendation.If you need a variac, stick with an established name-brand like Staco. They can be pricey, but, as I found, you get what you pay for. Surplus Sales of Nebraska in the US (http://www.surplussales.com) have a decent selection of salvaged variacs (and other heavy electronics).

author: eevblogfan
author_rank: Frequent Contributor
timestamp: October 09, 2013, 05:11:01 am
content: HeyI have no huge experience , But I saw Variac here and there ..I won't touch the chinese ones , I once forgotten one plugged in ( turned to 0V and the output switch was off ) only for one night ...One day after, the Variac was 40~60C ( I didn't measured , but it was hotter then 40C for sure , it wasn't pleasant to touch , Hence around the 50C or so ... )and that is not so good in my opinion . actually , quiet bad one .DO NOT think yo can get 2KVA transformer for cheap , unless it is USED ,If you need it for professional use or for characterizing transformers over night/few Hours without your supervision . please at least thermally protect it ..cheap chinese ones are okay , but they are usually smaller and can handle half or third of the value marked on them , that's bad choice if you are going to power some 600-1000VA transformers for more then 24Hrs ,as for the actual transformers , please at least be there for the first 30 minutes ... 1 Hr is better ... and after that , try and get some thermal overload device ( automated to switch some relay(s) )I first loaded 150W marked transformer with .... well .... 150W ... 2Hrs lated the room was smelly with perhaps enameled wire burned ... ( no OTP fuse there .. )I understood you need to measure ratio(s) , for that you can use small transformer and measure mV AC on the other side , it is okay , but when High ratio transformers are the DUT , it may be some problem ..Good luck

author: saturation
author_rank: Super Contributor
timestamp: October 09, 2013, 12:17:03 pm
content: These are copies of the Staco design. They are ok so long as you derate them 50% as their QC is unknown. Only the true Staco ones can be operated at rated VA, a good used one from eBay is enough. I have reviews of one in the eevblog archives.

author: robrenz
author_rank: Super Contributor
timestamp: October 09, 2013, 12:29:33 pm
content: This is the oneI am going to try when I finally buy one. As I mention in the thread the 5000 gets me 2500 with a 100% derating for Chinese quality.

author: fcb
author_rank: Super Contributor
timestamp: October 09, 2013, 12:31:58 pm
content: 2KW variac$100What could possibly go wrong...........

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: October 09, 2013, 12:44:42 pm
content: Thanks for all the great info! This really helps in my research to find the right one. In the meantime, I used a power transformer from an APC UPS to build a basic low voltage high current AC test signal of 14.6 volts. From what I can see, I can get more than enough current to get me by until I either buy or build one, but I will not leave this unattended since I have basic protection such as a circuit breaker. But for the current needs I have this should not be a problem for now. Maybe, I will just take my time and design and build my own!

author: eponte5
author_rank: Newbie
timestamp: May 18, 2018, 05:08:55 pm
content: Quote from: eevblogfan on October 09, 2013, 05:11:01 amI'm not for or against the actual variac in question (I do own a staco and a Chinese variac), but being that the primary was connected and secondary was open, you are left with just the excitation of the core and the core losses.This will obviously increase the variac's temperature. But by how much and what is acceptable depends on preference (for what is acceptable) and flux density that the core is running at. (which in turn depends on the turns of wire, voltage, freq and cross section area of the core.)So I wouldn't think 50°C on the core of a transformer that is just excited is unusual.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 18, 2018, 06:53:40 pm
content: Terabyte,The variac you linked to says 2KVA @ 110V with a 20A fuse. Simple math says that the unit will be overloaded before the fuse blows. Not good. Also, what kind of plug does it have? A 20A fuse should have a 20A plug but there's no indication of what type of plug is attached or what wire gauge is used on the line cord. It doesn't really look like 12 gauge.Ed

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: May 18, 2018, 07:12:36 pm
content: Quote from: edpalmer42 on May 18, 2018, 06:53:40 pmTakes me back! I never bought that one actually settled on one that was quite a bit more expensive and built a bit better, in-rush was a bit of an issue sometimes but I that's been rectified since then. Thanks for the follow-up!

author: CopperCone
author_rank: Super Contributor
timestamp: May 18, 2018, 07:12:58 pm
content: I have a rather large variac only rated for 3 amps, american made. I think the Chinese like to over rate their things.It's slightly smaller size as a '10 amp' isolation transformer I put in the chassis, also made in china..Primary fuse is 10A for the transformer and 3 amps for the variac output.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 18, 2018, 07:37:37 pm
content: The Mastech 2kVA I got is quite good - it is still holding very well without the smell/temperature increase.Photographs are here:https://www.eevblog.com/forum/buysellwanted/mastechvolteq-variac-comments-on-quality/msg161815/#msg161815

author: rhb
author_rank: Super Contributor
timestamp: May 18, 2018, 10:51:52 pm
content: This one weighs 25 lbs and is rated for 1.5 KVA, 250 V and 6A. also no question about quality, it's American made and at *least* 60 years old.I was discussing this with a friend the other day. We think it's a theatrical lighting unit. Obviously not safe to use without a proper enclosure and other enhancements.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 20, 2018, 03:05:31 am
content: Quote from: rhb on May 18, 2018, 10:51:52 pmI have a vintage Australian made/licensed version of that Powerstat above in an 8 amp rating at 240 volts and it will handle 10+ amps at 240 volts short term without issue or 'skip'Quality windings with solid arm that makes excellent contact, with beefy precise cut carbon brushes that track perfectly,good thick wiring and control wheel for fast or gradual voltage swings from 0 to 290,housed in a strong metal frameworkProbably 60 years old when I got it, and after a good dust off, TLC, capping off exposed terminals, a proper mounting base with handles and input/output gear,this 1960s? beast is good for another 60 yearsTip:when not in use, suggest to cover up the top of variacs so dust doesn't sneak in and settle on the top of the windings, acting like wet n dry sandpaper,giving the carbon brushes more work than they need, hurdling over obstaclesPlastic shopping bags work for me, total wrap over, keeps the variac operating good as new every time, and TLC freeThere is no way one of those red half baked MIC 'potentiometers' on steroids will see my credit card unsheathed, I've seen what's inside them,it's-How OneHungLow can you go?quality all the way...or if you really have no choice, buy a 2kva model, de-rate, re-fuse and re-label it to 500va, cross your fingers, and don't leave it unattended in useThis is after opening it up to check and or correct any cheapassedness that will be there in 99% of cases.Sometimes you can get lucky and score a well made unit with everything anchored down properly, probably due to one day in the OS working week that isn't a FridayReality humor aside, it's old school variacs for me that kick ass, no matter what they cost, weigh or fugly they areSame deal with isolation transformers, no cutting corners where electrical manipulation is called for

author: rhb
author_rank: Super Contributor
timestamp: May 20, 2018, 03:17:39 am
content: I plan to put it in a stout, grounded metal case with a circuit breaker, fan and voltmeter. Hopefully also with an isolation transformer of suitable rating. And stout handles on the side if I need to move it.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 20, 2018, 04:10:16 am
content: Check the brushes are in good shape, even and making good contact on the top through all the travelPut a 1kva load on it, lamps, heater, kettle etc and with an analogue needle meter, sweep back and forth anywhere and everywhere from 0 to 120v (not over, so you don't over voltage the load!)and see how it performs. It should be smooth with no jitters or skips displayed on the meterFWIW if the unit is uber heavy, park it on a small cheap timber movers or planter 4 wheel dolly to move it from A to B, and or roll/park it somewhere when not needed.Another option is to have it on the floor propped up a few inches to reach down comfortably, dial up and get the job done, without it hogging bench space too