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Looking for help connecting variac to 120vac

retireddiy

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Hello everyone I hope all had a good holiday. I have acquired a Staco Energy 1010b auto transformer (variac) and is uncased. It is a 5 pin model and I need help connecting to mains. I have tested it and it works but from o it starts at 130vac and turns down the wrong way. I have searched here and online, any help would be appreciated.
 
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rlitman

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Do you have any small low-voltage transformers (not DC power supplies, but just a plain transformer)? Say a 16VAC transformer from an alarm panel or maybe a doorbell? Something you can safely play with before you test this out on line voltage... You can easily supply this Variac with 12VAC and get 0-13VAC out without risking anything. Just saying...

The spec sheet is here:

Since it is a Variac, there are various ways of wiring it. Are you looking for 0-120VAC output, or 0-140VAC out of it? Depending on what you want (output voltage and direction of shaft rotation to increase voltage), you should reference the chart in the bottom right of the drawing, and use the listed inputs and outputs. There are no jumpers, and every configuration uses three terminals with one being common for two wires.
 
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rlitman

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24 AC transformers are pretty common too.
Exactly. Something where you can safely touch the terminals without getting buzzed, and that doesn't have the energy to blow up in your face if you short it. I actually use a 24VAC 45VA transformer to supply a Variac (even though it is rated for 0-130VAC) to power my hot wire cutter. It's just a transformer, so you can always feed it low voltage AC, and in my case, that means that if the wire breaks, I don't get zapped.
 
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retireddiy

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Everyone here is awesome! Thank you all very much. I paid $40.00 and when I get this wired up correctly it will be helpful. I want to go 0 to 130v. Then build a box for it and add outlets, lighted on off rocker switch and fuse. Trying to choose a digital volt/amp meter.
 

dogdog

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eBay have plenty of digital panel meters that does ac and amp sensing
 

nadogail

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IMHO, Your biggest problem will selecting between which of the many connection options you want for either Clockwise or Counter Clockwise rotation for voltage increase.
 
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retireddiy

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Thanks for advice every body. I will be using it for power tools that I haven’t used treadmill motors on. It’s something I haven’t tried yet.
 

rlitman

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Everyone here is awesome! Thank you all very much. I paid $40.00 and when I get this wired up correctly it will be helpful. I want to go 0 to 130v. Then build a box for it and add outlets, lighted on off rocker switch and fuse. Trying to choose a digital volt/amp meter.
For 0-140V, you would use terminals 4 & 5 for 120V line in, and 4 & 3 for 0-140V out for CW knob rotation.
For 0-120V (so you don't overspeed motors), you would use terminals 1 & 4 for 120V line in, and 4 & 3 for 0-140V out for CW knob rotation.

I would wire terminal 4 to the neutral as the common, and consider using a switch to connect line to either 1 or 5 so you could choose 0-120 or 0-140 out. If you use a DPDT with center-off, you could have 0-120 OFF 0-140. ;)
Thanks for advice every body. I will be using it for power tools that I haven’t used treadmill motors on. It’s something I haven’t tried yet.
Keep in mind that this has a 10A limit. If you run it over 10A for too many seconds, you will let the smoke out. I would suggest using something like this with it rather than (or in addition to) a fuse:
 

Innovate1

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For 0-140V, you would use terminals 4 & 5 for 120V line in, and 4 & 3 for 0-140V out for CW knob rotation.
For 0-120V (so you don't overspeed motors), you would use terminals 1 & 4 for 120V line in, and 4 & 3 for 0-140V out for CW knob rotation.

Keep in mind that this has a 10A limit. If you run it over 10A for too many seconds, you will let the smoke out. I would suggest using something like this with it:
A fuse or some sort of protection on the output is useful to prevent overloads. Since it is a type of transformer you can get lots more current out (at lower voltage) than the current at the input. For intermittent use going to the 10A limit is ok. I always try to derate for any long term use - something like 50 - 75% of the rating.
 

rlitman

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...Since it is a type of transformer you can get lots more current out (at lower voltage) than the current at the input...
No. This is an auto transformer, and not an isolation transformer. This is only one coil, so the current in the coil is the current you are concerned with, and that's that. It's not like there's an input and output coil with different currents. In an auto transformer, there is a common connection between the input and output (terminal #4 in this case) that carries a good deal of the load without ANY current at that point passing through the coil.

Being a Variac, my guess is that the coil can handle more current than the wiper, which is usually the weak link and the part that is most in need of fuse protection.
 
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retireddiy

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Should the fuse be In conjunction with the breaker and should it be a slow or fast blow?
 
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Innovate1

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No. This is an auto transformer, and not an isolation transformer. This is only one coil, so the current in the coil is the current you are concerned with, and that's that. It's not like there's an input and output coil with different currents. In an auto transformer, there is a common connection between the input and output (terminal #4 in this case) that carries a good deal of the load without ANY current at that point passing through the coil.

Being a Variac, my guess is that the coil can handle more current than the wiper, which is usually the weak link and the part that is most in need of fuse protection.
I suggest you read up on this a bit... If the output is set to 50% of input the output current will be about twice the input current - input power is approximately equal to output power so the currents must be different. An output fuse will protect the wiper. If you look at the link to the manual that someone earlier posted on the first page under precautions it states to fuse the output. Also see page 10 on this link that recommends an input and output fuse:

https://www.stacoenergy.com/images/...st-sets/stacovt/brochure/designengine_bro.pdf

I was amused by a recent post I saw on another site where someone said they posted their question and then, under a different user name, posted a wrong answer. Their theory was that many people liked to correct others more than help others so this increased their chance of getting responses... My observations tend to support this... :)
 

Innovate1

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Everyone here is awesome! Thank you all very much. I paid $40.00 and when I get this wired up correctly it will be helpful. I want to go 0 to 130v. Then build a box for it and add outlets, lighted on off rocker switch and fuse. Trying to choose a digital volt/amp meter.
You got a great deal! Where I work once had a box like that which included an isolation transformer on every workbench. They decided to pitch them and I now have one for home use.
 
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retireddiy

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I suggest you read up on this a bit... If the output is set to 50% of input the output current will be about twice the input current - input power is approximately equal to output power so the currents must be different. An output fuse will protect the wiper. If you look at the link to the manual that someone earlier posted on the first page under precautions it states to fuse the output. Also see page 10 on this link that recommends an input and output fuse:

https://www.stacoenergy.com/images/...st-sets/stacovt/brochure/designengine_bro.pdf

I was amused by a recent post I saw on another site where someone said they posted their question and then, under a different user name, posted a wrong answer. Their theory was that many people liked to correct others more than help others so this increased their chance of getting responses... My observations tend to support this... :)
Just an ole dog trying to learn new tricks, lol.
 
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