Variac used as step down xformer? - Page 1
Forum section: electronics / beginners

author: fourierpwn
author_rank: Regular Contributor
timestamp: January 23, 2016, 03:42:43 am
content: Hi all,I am wanting to power a piece of Japanese equipment, which runs on 100Vac. I am in Australia where we use 240Vac. The only thing I have that can supply 100Vac is a variac (this one here:http://www.svtechparts.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/i/m/img_1199.jpg)Is it safe to use a variac as a step down transformer?

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 23, 2016, 04:13:19 am
content: "Is it safe" is a loaded question. If I say "sure, go ahead" and then someone comes along and turns the knob up to 240..... will you blame me for blowing out your Japanese electronic device?On the other hand... sure, go ahead. A Variac is a variable stepdown (auto)transformer, that's what it is for, generally speaking.But don't blame me if someone accidentally turns the knob and blows out your Japanese device. I also wouldn't trust the analog meter on the Variac to be completely accurate.

author: fourierpwn
author_rank: Regular Contributor
timestamp: January 23, 2016, 04:35:30 am
content: Thanks for the reply. I understand what you mean.I thought a quick check with a multimeter to ensure it is actually at 100Vac would be wise.

author: station240
author_rank: Unknown
timestamp: January 23, 2016, 09:42:36 am
content: Quote from: alsetalokin4017 on January 23, 2016, 04:13:19 amEasy fix, remove the knob.

author: Ian.M
author_rank: Super Contributor
timestamp: January 23, 2016, 11:14:07 am
content: Theoretically, its not safe because you are connecting a device with insulation designed for 100V RMS to a 240V RMS circuit, and if anything fails on the neutral side of the circuit before the Variac, the insulation to case or exterior metalwork has to withstand the full supply voltage. In practice, under the direct control and supervision of a competent person, its fine for bench testing and if the knob is locked, for general use by said person *AFTER* they have satisfied themselves that the equipment's insulation, creepage distances, clearances etc. are adequate for 240V - beware of cheap & nasty rocker type power switches!If anyone else in the household without an EE/EEE background is going to use it, either convert it to 240V operation (if its possible to safely do so) or get it a voltage conversion transformer, preferably *NOT* an autotransformer.

author: andre_teprom
author_rank: Regular Contributor
timestamp: January 23, 2016, 02:50:23 pm
content: Although the Variac, strictly speaking is an equipment designed for withstand power applications and the manufacturers specifies sufficient wattage ratings that may comfortably fits your load requirements, its use is not recommended as a "permanent" transformer, because of thelivecontacts on the windings w/o finishing, which can oxidize over time more rapidly in the presence of current all the time.

author: SteveyG
author_rank: Unknown
timestamp: January 23, 2016, 03:21:49 pm
content: The other question is what is the piece of equipment? If may be easier to just modify it to work on 230V