I just wanted to post a short review of this beast of a Variac. I picked this up about a week ago which shipped from Mastech in California, FedEx Ground at a weight of about 44 pounds! Yes, it's a beast! It is about twice the size as most smaller Variac's but so far it seems worth it's weight. The specifications state that it can deliver up to 250 VAC at 20 amps at a rated 5KVa. After completing my input and output cables which were also rated at 20A/300V I began to test the variable output with both my Fluke DMM and Oscillscope. The voltage across the entire range from 0-250V was smooth and with no real large spikes or noise. The voltage was very consistent and linear across the entire range. Although this unit is rated up to 250V, I was able to adjust and maintain a 315V maximum output which was stable. I have not yet been able to test the full current capabilities up to 250V and even at the Maximum 315V. I will however load test at about 15A across this range soon. Another pleasant surprise was the accuracy of the analog meter on the front of the unit. Having attached my Fluke to the output, it seemed to track the DMM within a few volts across the entire scale. Another interesting fact, I was able to get a minimum voltage of about 1.13 volt with little effort and this was repeatable each time. The output terminals with respect to frame ground are equal to line in which you would expect. Ground isolation appears to be as expected too.
The build quality is pretty good. It seems to be solid, and the handles on top were very capable of holding the weight of the unit. The transformer windings use a glass/epoxy binding agent, and the slider wheel has a very thick carbon pad which looks like it would last quite some time before you would need to replace. The top of the transformer windings were fairly smooth, and the slider pad seemed to move very easy without much resistance but not enough to overshoot for value if you were to move it quickly. The terminal lugs are about 6mm or 1/4 inch. The binding posts seem to be very secure and tight fitting.
So far, I really like this unit, it has the power to drive almost all the items you could ever want. Built well, vented well and does not appear to overheat like some I have experienced in the past although I have not load tested to full capacity yet. It has a smooth ramp of the voltage and fairly accurate and linear also. I am going to perform a test of steps/increments and graph the voltages on my Agilent bench DMM soon. For now, I hope this helps anyone interested in getting a new 5KVa Variac. Links and photos attached.
http://www.mastechpowersupply.com/variac-auto-transformer/volteq-variable-transformer-variac-5000va-0-250v-110v-input-20a/prod_55.html
