Mastech/Volteq variac,  Comments on Quality? - Page 1
Forum section: electronics / general

author: robrenz
author_rank: Super Contributor
timestamp: October 26, 2012, 03:42:46 pm
content: Thinking of getting this variac from mastech power supply. I have had good success with the actual Mastech GPC3030D power supply from them but this is "Volteq" brand. I have no delusions of drawing 20 amps at 240V on a 110V input. I am thinking that it would have a greater chance of lasting a long time if it is over speced by at least a factor of two. I also am looking at this as a kit and would replace the connection box with fusing and a safe connection/grounding scheme.Anyone have experience with Volteq or think I am off track here?http://www.mastechpowersupply.com/variac-auto-transformer/volteq-variable-transformer-variac-5000va-0-250v-110v-input-20a/prod_55.html

author: SeanB
author_rank: Super Contributor
timestamp: October 26, 2012, 05:48:12 pm
content: Replacing the terminals with a box and an outlet will be good. I will add to that a 10a breaker on input and output ( as well as a ground fault interrupter for a panel on the input as well) and a dual socket marked with the voltage range. High power variacs have a good use, though you do not use them often, but they are the best for a variable Ac source that is not isolated from mains input. Add a indicator to prove the input voltage is not swapped line to neutral and it will be a lot better.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: October 26, 2012, 06:26:31 pm
content: Quote from: robrenz on October 26, 2012, 03:42:46 pmSir ,I Would Say Don'nt you have a company near you making variacs .In india we have many people making this .I wanted to test the ups setups i was repairing so i made one with 230 volt input and 0 ~ 325 volt output .Do Not Remember the Amps .BTW when ever anyone buys these i would say just rip them open and inspect mod as necessary and use for a lifetime .

author: robrenz
author_rank: Super Contributor
timestamp: October 26, 2012, 07:04:35 pm
content: Quote from: SeanB on October 26, 2012, 05:48:12 pmThanks SeanB,Since this can do 250 from the 110 input won't I need a 20 amp input and 10 amp output (I only want to use this at half its rated capacity).With a US three prong grounded input plug permanently wired in I don't need the neutral indicator do I? I know all my outlets are correctly wired.

author: robrenz
author_rank: Super Contributor
timestamp: October 26, 2012, 07:06:40 pm
content: Quote from: Amarbir[Lynx-India] on October 26, 2012, 06:26:31 pmNot that I know of. Even if there was it would cost at least 4 times more including the shipping.

author: SeanB
author_rank: Super Contributor
timestamp: October 26, 2012, 07:26:38 pm
content: Breakers are wiring protection, either trying to draw more than the input or more than the output can safely supply according to your derating spec.The indicator will save you the first time you get an improperly wired extension cord or outlet, and the GFCI will save your life. Added protection to the user is good if done at the design stage, and I know you are quite capable of adding the required devices neatly and in a well designed enclosure.

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: October 26, 2012, 07:30:59 pm
content: Quote from: SeanB on October 26, 2012, 07:26:38 pmSir ,whats a gfci ?

author: saturation
author_rank: Super Contributor
timestamp: October 26, 2012, 07:52:14 pm
content: I think you can wing the China version, robrenz, but I derated mine 50%, and I operate it to a max of half its rated power. I don't know this particularly model but one can easily tear down the unit and check the build quality. The reason I chose a staco copy is at least I had a model to which to compare the build quality.The US leader in variacs is Staco.~ $350.00 BTW, these units can be found still working over 50 years old, used as light dimmers in theaters and such still using incandescent lights.http://www.stacoenergy.com/variable_transformers.htmhttp://variac.com/Chinese look-a-like from mpja.com, $50. and they add a barely adequate voltmeter.Quote from: robrenz on October 26, 2012, 07:06:40 pm

author: robrenz
author_rank: Super Contributor
timestamp: October 26, 2012, 08:08:59 pm
content: That is what I planned, this is a 5000W unit 20A at @240V. I will probably never even use 5 amps but I would rather spend a little more once and have the extra capacity and it should last longer being less stressed. This unit has nothing but binding posts for input so no money was wasted on junk meters, switches, fuses etc that I would throw away anyway.

author: JuiceKing
author_rank: Regular Contributor
timestamp: October 26, 2012, 08:34:28 pm
content: Wow, that's a lot of variac for $169. For $149, I bought a used General Radio Variac (W10MT3A) which I like very much but it's 1/4 the power - 110V @ 10A. It's fully fused and has usable voltage and amperage meters. I noticed that the Mastech/Volteq vendor warns you that their product occasionally gets damaged in shipment and that this is something they will help you fix by sending replacement parts, and not to order if this spooks you. If they can't pack it right, it makes me wonder what other corners might be cut to get the price so low.

author: SeanB
author_rank: Super Contributor
timestamp: October 26, 2012, 08:52:21 pm
content: This is mine.....Not too clear, but I reused the wooden box it came in as the housing. No ratings really, but it handles 15A no problem. The board is for the output meter, using a 723 to make a stable 7V reference used to offset the zero on the AC voltmeter I built to show output voltage. Range is 60-360VAC, the variac is wired to give from 0-350VAC from a 230V mains input.I fed the mains in to a tapping about 3/4 of full scale, and am tapping a 60VAC from another tap to drive the metering. Not visible is the other board with the inrush limiting, this unit has a switch on pulse big enough to trip breakers every so often. A bank of 33R 10W resistors and a relay to short them out solves this, takes about 0.5 seconds to close and around 100mS to open on power off. 130C thermal fuse on them for those unforeseen moments.

author: robrenz
author_rank: Super Contributor
timestamp: October 26, 2012, 09:01:25 pm
content: Very nice, your metering made me realize I should put shrouded banana jack sockets on 3/4 spacing in the control panel to meter voltage with a meter

author: rsjsouza
author_rank: Super Contributor
timestamp: November 10, 2012, 05:30:51 am
content: Robrenz, I have a 0-250Vac 2kVA Mastech and it works very well. I put some serious loads on it (4 or 5A @ 120V) and it held up without fuzz.I agree with your comment below regarding the cheap switches, fuses, etc, although the unit has a scale on top and a cheap voltmeter in the front. I simply bought a 15A extension cord, cut in half, soldered the round connectors to the posts and isolated everything. You can see it in action inthis postand detailed pictures are below.Is it a Staco? No, but it did not cost me an arm and a leg and serves the purpose.I would say that a variac is absolutely wonderful for someone that has to deal with mains voltages. I have my share of blown up things that not only cost a lot of money to fix but also were very close to end up badly.

author: saturation
author_rank: Super Contributor
timestamp: November 10, 2012, 01:40:58 pm
content: Thanks for the big photos, build quality looks quite good. Note for eBay folks, if you can wait used good quality variable AC sources do come on line from Heathkit, Sencore and BKPrecision that still should work quite well, if the watts be right.http://www.ebay.com/itm/BK-Dynascan-Precision-1653-Variable-AC-Power-Supply-B-K-Variac-/321017956982?pt=LH_DefaultDomain_0&hash=item4abe294a76I never bought them because they can cost more than buying your own newisolation transformer and a separate variac, both from China.

author: robrenz
author_rank: Super Contributor
timestamp: November 10, 2012, 02:27:44 pm
content: Thanks rsjsouza, nice job on the heavy extnsion cord for the in/out. My pressing need for a variac has subsided but when I need one i will try this one.

author: Monkeh
author_rank: Super Contributor
timestamp: November 10, 2012, 03:42:46 pm
content: Quality connections on that. I guess a cover and some strain relief is too much to ask for these days.