Homebuilt variac

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Here is my latest project, took 2 days to build and finish.
Unit has a 10 amp variac but I won't be using it for more than 6 amps.
This is just a teaser photo, I'll take some better ones today.
DSC_0821.jpg
 
Try getting a small audio transformer that you can pass the hot wire to the outlet between the coil and the core. Put a resistor on the output and connect it to a BNC connector that way you can look at the waveform of the current draw!

Along the lines of simon7000's idea, you can get current sampling transformers for just this purpose. I have some in my basement that I removed from scrapped equipment from work. Not sure how many are down there, but I may have some extra.

Peace,

Dave
 
Hello SirByrd, one thing you could do in your schematic/wiring, put an SPDT switch on the incoming power line to the right side of the variac windings. That way you can switch between a 120 volt and 140 volt output.

In regards to the suggestion that simon7000 made about the current sampling transformer, the primary side would wire in series with the current ammeter(s) you have.

Peace,

Dave
 
Why would I want to switch between 120 and 140? To get more finite of a control when set to 120?

Hello SirByrd, being able to adjust the voltage above the incoming line voltage can be useful when you are designing things. Sometimes you want to be able to raise the voltage a little higher. I can't give specific examples, but at some point will find it useful (at least I think so).

Peace,

Dave
 
The "140" is relative. it only will be 140v when the mains is in fact 120v. If the mains drops to 108v because it is 110 degrees and all of the city is using electricity for air conditioning, you can dial up the variac past the nominal 120v to compensate. If you want to. If you wire for 120v maximum, then the output is limited to whatever voltage the mains provides at that moment.
 
The "140" is relative. it only will be 140v when the mains is in fact 120v. If the mains drops to 108v because it is 110 degrees and all of the city is using electricity for air conditioning, you can dial up the variac past the nominal 120v to compensate. If you want to. If you wire for 120v maximum, then the output is limited to whatever voltage the mains provides at that moment.

Thank you Enzo for reminding of something I was forgetting!
:cool:

Peace,

Dave
 
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