VARIAC - Page 1
Forum section: electronics / testgear

author: EEVaditya
author_rank: Regular Contributor
timestamp: January 29, 2015, 12:07:05 pm
content: What are the specifications to be considered while buying Variac?

author: nowlan
author_rank: Frequent Contributor
timestamp: January 29, 2015, 12:26:15 pm
content: I believe they have1. voltage2. kva3. ampereDepending on your load, you may need a larger one (kva)

author: helius
author_rank: Super Contributor
timestamp: January 29, 2015, 03:40:36 pm
content: Additionally, some are designed to sweep 0-100% of input voltage, and others 0-110%.Often this can be changed by the wiring, if the autotransformer is multitapped.Some are designed to be mounted on the rear of a panel and rotate counter-clockwise.

author: jbryan2
author_rank: Contributor
timestamp: January 30, 2015, 05:57:31 am
content: The voltage and current that your load requires.It took several tries a couple of years ago for me to get an unbroken one. The sellers didn't appreciate how much the copper and laminations weigh and underpacked them. They were reputable sellers and I got refunds, but it was really heartbreaking to get beautiful, never-used variacs all busted up in shipping.

author: Shock
author_rank: Super Contributor
timestamp: January 30, 2015, 06:22:19 am
content: Some other differences:Max voltage 120v, 240v, 280v, 480v, 560v (the larger ones are normally ganged)50Hz or 60Hz or bothAdditional output taps on the winding (e.g. 240v gives you set outputs at 110/120/220)Sustained verses peak current ratingOutput socketIf it has a voltage or current meter or both (some cheap models have these so beware)Replaceable brushesEnclosurePanel mountable or reversibleCheap vs quality models

author: Electro Fan
author_rank: Super Contributor
timestamp: January 30, 2015, 07:59:54 am
content: Not sure where you are located but if you can call David Riddle. His company makes a large array of variacs including some beautiful units.http://www.ebay.com/itm/NEW-GENERAL-RADIO-240-VOLT-MAINS-METERED-VARIAC-TUBE-AUDIO-AMP-MCINTOSH-C22-/111183396920?pt=LH_DefaultDomain_0&hash=item19e30c0038If you call him he will walk you and talk you through whatever you want to know about variacs.

author: rickselectricalprojects
author_rank: Regular Contributor
timestamp: January 30, 2015, 11:58:04 am
content: the main things are:safetyis it from a reliable sellervoltage (input and max output (like on some variacs the overwind might be 30 volts so the max output would be 270 volts)max currentmax KVAi hope i helped and i am only 14 so please dont be to harsh if i got something wrong.

author: LaurenceW
author_rank: Frequent Contributor
timestamp: January 30, 2015, 01:23:46 pm
content: No-one has spelled it out, yet (perhaps it's obvious to all reading, here?) but remember that the output of a variac is REFERRENCED TO THE MAINS NEUTRAL SIDE andNOT ISOLATED!Worse still; wire the variac primary into the main power supply incorrectly, and the entire output will be referrenced to Mains Live! ZZZT....Also many units - even quality ones - may be supplied as "open frame" - that is, not contained in a safe end-user case, but designed to be built into an equipment cabinet of some kind.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 30, 2015, 01:33:56 pm
content: Some units are isolated like my EJ901V. However, I think a GFCI at the wall or bench is a must have option.It has a rectified dc output that may be of benefit.I was leery of some of the new units that are being sold with high current specs. 20A models with 15A outlets and plugs do not seem to be a good combination.

author: avvidclif
author_rank: Regular Contributor
timestamp: January 30, 2015, 02:05:08 pm
content: Quote from: ManateeMafia on January 30, 2015, 01:33:56 pmNothing wrong with that, having excess capability is good. Think of the opposite, a 15A Variac with a 20A socket!!!!!

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 30, 2015, 02:16:23 pm
content: Agreed. The units I have seen have 20A fuses with 15A receptacles!

author: saturation
author_rank: Super Contributor
timestamp: January 30, 2015, 08:45:45 pm
content: As variacs are electrical devices, its specs depend heavily on the quality of its materials and assembly.If you buy a no-name I'd derate it 50% at least and test it thoroughly before deploying it.