learn from my error, variacs need 2 fuses..the output is rated for the same current as the input.. imagine variac set to 12v (easy math) if output shorted 3a in = 30a out so output blowes. mine blew at the common terminal so could be repaired... have seen others with bottom 1/4 or so smoked.
Great project. I think it needs to be mentioned that the variac does not provide mains isolation for the high voltage outlets. I would be adding an isolation transformer between the variac and the outlets.
Absolutely. Also by using that meter in the way you have, compromised isolation. There is possibly a fault path through the relay and the meter from the tap on your variac straight through to the 30V binding post.
You can get a Variac from tme.eu if you live in Europe (listed in the Transformers -> Autotransformers category). They have the lowest shipping rate out of all the big online shops. Digikey, Mouser and Farnell also have autotransformers but their shipping rates are quite high. Don't recommend them if you're buying just a few parts.
Hey, fantastic. Where can I get a Variac? I have searched eBay etc. No luck. I am going to build one at 240v in, need about 120v Out. Thank you for your time in sharing. David (Aus. down under)
Hi, I like your set up. Could you use you a adjustable power supply to fix or trouble shoot some power tools with. What I'm intending is to set a safe ac current to run through the power tool, so there is less danger while looking for shorts and testing out tools that use ac. Also please let me know if you think testing out tools with lower ac voltage is a good idea. I don't see how it could hurt a tool running it on a lower voltages. If you plug a 220 tool, in a 110, it just runs slower. I'm not sure how that would work out with a tool that uses circuit boards, but even then its usually just a thysister, a op amp chip, some resisters and a couple capacitors. This could really show case the usefulness of having an adjustable ac power source.ThanksRandy
If you were to run a power tool at lower voltages for an extended period of time, it could possibly cause it to overheat under certain circumstances, but for simply testing tools out it sounds like a great idea. If you use a non-isolated power supply, be sure to isolate yourself and the tool by standing on a good rubber mat while testing the tool. Then use a small wattage mains-powered incandescent light bulb grounded on one of its leads, with the other lead having a metal probe on it to touch the tools with so that if there is an internal short to ground inside the tool, the light bulb will light up and warn you. Don't forget to try turning on the tool to test for shorts to ground while energized also.
Very nice DIY project. I am doing something similar, but I do have to ask, why waste the time and expense of a 28v transformer? Just bring your variac out to the binding posts as well (you all ready have the relay) and have 0 to whatever voltage out there. The small DVM looks cool. Thanks for sharing.
+saturn5tony My primary goal was to build a 0-30 VAC benchtop supply. I didn't want the risk of someone inadvertently turning the knob up and sending 120 VAC out the binding posts to a project that was intended to only work from low voltage. Using the transformer also allows me to get a bit finer control out of the variac for the range I was interested in. The receptacle on the back and the relay to switch between the two ranges was a bit of an afterthought -- I figured it will come in handy powering up old tube radios and such.
Auto-transformers are not isolated from the mains, so looks can be deceiving. Imagine this: autotransformer set to 5V, but the plug is not polarized like in germany, so while it can be safe to have some 5v(a bit of the winding) and neutral, if it's plugged the other way will have 230v and 225v .. still 5V but in reality there is no ground, and if you provide a short path to ground you get electrocuted from either terminal, one has 225v, one has 230v.. so a big no, no. Also the equipment you are powering might be grounded and if you supply 5v but with 230v difference to ground potential, you might get into arcing from those presumably 5v to ground. So a tiny circuit that runs at 5v must be insulated from ground as if it was 230V. Any autotrasformer must have a conventional transformer grounded (even 1:1, or whatever suits to improve range and resolution) to provide galvanic isolation, and have those 5v or whatever voltage will be absolute from the ground potential. So it's a must to have the second transformer. AFAIK autotransformer stuff is not available in consumer electronics - too many dangers. With respect and knowledge it can be handled safely by providing isolation right next to it.. so have a proper setup between auto-transformer and transformer and put it in a sealed box and never mess with what's in it, only what's out of it. Also the second transformer must have primary winding properly insulated for mains max voltage and not the autotransformers max voltage
Enjoyed your video. I could not read your comments as they quite dim. What is the Brand of Auto Transformer, is it VariAC? Also what is its amperage capability. It does look nice and compact. All VariAC's are Auto Transformers but not all Auto Transformers are VariAC's :D
VARIAC INFO - went to Scott's webpage (noted near the end of the video - www.smbaker.com) and looked up this project, the variac used here is available from www.Jameco.com and the part number is 149324, $64.95 USD (Jan. 2021). BTW, Scott has SEVERAL projects listed on his site, looking forward to checking them out.
learn from my error, variacs need 2 fuses..the output is rated for the same current as the input.. imagine variac set to 12v (easy math) if output shorted 3a in = 30a out so output blowes. mine blew at the common terminal so could be repaired... have seen others with bottom 1/4 or so smoked.
Wow that's a genius idea, really simple but sadly no current limiting
Great project. I think it needs to be mentioned that the variac does not provide mains isolation for the high voltage outlets. I would be adding an isolation transformer between the variac and the outlets.
Absolutely. Also by using that meter in the way you have, compromised isolation. There is possibly a fault path through the relay and the meter from the tap on your variac straight through to the 30V binding post.
Very neat design, with a few more things added into this this could have been even better! great work
Nice little project. Likely good to limit the output of the front panel binding posts.
where do you get the variac transformer from?
Can you please link me this variac,please...?
You can get a Variac from tme.eu if you live in Europe (listed in the Transformers -> Autotransformers category). They have the lowest shipping rate out of all the big online shops.
Digikey, Mouser and Farnell also have autotransformers but their shipping rates are quite high. Don't recommend them if you're buying just a few parts.
Does it make a difference if you use variac transformer or transformer variac if you didnt need the high output from the back? Great video
Cool stuff! Were did you get variac?
Why are the Amps not adjustable ?
Hey, fantastic.
Where can I get a Variac? I have searched eBay etc. No luck.
I am going to build one at 240v in, need about 120v Out.
Thank you for your time in sharing.
David (Aus. down under)
Newark Electronics has them.
Ty Denis for the variac info lol.
Hi, I like your set up. Could you use you a adjustable power supply to fix or trouble shoot some power tools with. What I'm intending is to set a safe ac current to run through the power tool, so there is less danger while looking for shorts and testing out tools that use ac. Also please let me know if you think testing out tools with lower ac voltage is a good idea. I don't see how it could hurt a tool running it on a lower voltages. If you plug a 220 tool, in a 110, it just runs slower. I'm not sure how that would work out with a tool that uses circuit boards, but even then its usually just a thysister, a op amp chip, some resisters and a couple capacitors. This could really show case the usefulness of having an adjustable ac power source.ThanksRandy
If you were to run a power tool at lower voltages for an extended period of time, it could possibly cause it to overheat under certain circumstances, but for simply testing tools out it sounds like a great idea. If you use a non-isolated power supply, be sure to isolate yourself and the tool by standing on a good rubber mat while testing the tool. Then use a small wattage mains-powered incandescent light bulb grounded on one of its leads, with the other lead having a metal probe on it to touch the tools with so that if there is an internal short to ground inside the tool, the light bulb will light up and warn you. Don't forget to try turning on the tool to test for shorts to ground while energized also.
Very nice DIY project. I am doing something similar, but I do have to ask, why waste the time and expense of a 28v transformer? Just bring your variac out to the binding posts as well (you all ready have the relay) and have 0 to whatever voltage out there. The small DVM looks cool. Thanks for sharing.
+saturn5tony My primary goal was to build a 0-30 VAC benchtop supply. I didn't want the risk of someone inadvertently turning the knob up and sending 120 VAC out the binding posts to a project that was intended to only work from low voltage. Using the transformer also allows me to get a bit finer control out of the variac for the range I was interested in. The receptacle on the back and the relay to switch between the two ranges was a bit of an afterthought -- I figured it will come in handy powering up old tube radios and such.
Auto-transformers are not isolated from the mains, so looks can be deceiving. Imagine this: autotransformer set to 5V, but the plug is not polarized like in germany, so while it can be safe to have some 5v(a bit of the winding) and neutral, if it's plugged the other way will have 230v and 225v .. still 5V but in reality there is no ground, and if you provide a short path to ground you get electrocuted from either terminal, one has 225v, one has 230v.. so a big no, no.
Also the equipment you are powering might be grounded and if you supply 5v but with 230v difference to ground potential, you might get into arcing from those presumably 5v to ground. So a tiny circuit that runs at 5v must be insulated from ground as if it was 230V.
Any autotrasformer must have a conventional transformer grounded (even 1:1, or whatever suits to improve range and resolution) to provide galvanic isolation, and have those 5v or whatever voltage will be absolute from the ground potential. So it's a must to have the second transformer.
AFAIK autotransformer stuff is not available in consumer electronics - too many dangers. With respect and knowledge it can be handled safely by providing isolation right next to it.. so have a proper setup between auto-transformer and transformer and put it in a sealed box and never mess with what's in it, only what's out of it.
Also the second transformer must have primary winding properly insulated for mains max voltage and not the autotransformers max voltage
Nice design. Where did you get the variac from ?
Enjoyed your video. I could not read your comments as they quite dim. What is the Brand of Auto Transformer, is it VariAC? Also what is its amperage capability. It does look nice and compact.
All VariAC's are Auto Transformers but not all Auto Transformers are VariAC's :D
did you use an AC Display or did you rectify a DC source for it? thanks for the video.. great build!
Display is 6 volts AC thus the center tapped 12vac transformer(small one).
G Dizzle
Parts list?
Hi so stead of a variack can i use a 10 amp 1 face dimer on the primary of a transformer?
nope
can I have the schematic please?
do you have a printable version , and do you know if this will work a burnmaster or razer tip pyrograph my pens are 10ohms at 15volts at ac
what if wanted to fix more than 1to2 or madebe even 3 hook ups
VARIAC INFO - went to Scott's webpage (noted near the end of the video - www.smbaker.com) and looked up this project, the variac used here is available from www.Jameco.com and the part number is 149324, $64.95 USD (Jan. 2021).
BTW, Scott has SEVERAL projects listed on his site, looking forward to checking them out.
Variac link - www.jameco.com/z/PSV-203-R-320va-Variable-AC-Power-Transformer-110VAC-Input-0-130VAC-Output_149324.html
Digikey
Quite a Lame Video with no parts list.