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Using a Staco Variac with rectifier to make a variable DC power supply?

PaulCrabtree

New Member
Hi, I'm looking for some help with the circuit and parts to turn a Staco 3PN variable autotransformer into a variable DC voltage output. I bought some 25A rectifiers from Amazon(https://www.amazon.com/dp/B07TG18DDB?psc=1&ref=ppx_yo2ov_dt_b_product_details) and I have a 590mfd 200V capacitor. I am a beginner at electronics and would like a simple circuit that will work. The rectifiers aren't well marked, one side has AC at one corner and + at the other. Is this doable with what I have?
 

Papabravo

Well-Known Member
I think you may have some safety issues with what you are attempting. I'm not clear on whether an autotransformer's output is isolated from the mains. [EDIT: It is not isolated] If not, you could sustain a potentially lethal poke. Connecting a ground lead from an instrument has the potential for sparks. I would be extremely careful with this setup. Normally a bridge rectifier is used with a center tapped secondary winding, where the center tap becomes the DC ground on the secondary side. I urge you to avoid experimenting with this setup. IMHO it is extremely dangerous and potentially lethal.
 
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crutschow

Well-Known Member
Most Helpful Member
Exactly how do you anodize Titanium?
 

PaulCrabtree

New Member
Anodizing Ti- water bath is the cathode, Ti piece is the anode, apply voltage to oxidize the Ti. Controlling the voltage controls the thickness of the oxide layer because the oxide insulates the Ti as it forms. The thickness of the oxide determines what color you see by refraction.
 

danadak

Active Member
I think the forum is not a fan of electrocuting folks, not sure why but they are not keen on
that outcome.

No kid can get a hold of the loaded gun w/o a lock (in your case a hot tank without safety controls) ?

Rubber gloves fine for you, everyone else trained on this ? Family, pets, mother-in-law (maybe pass
on training her)......

Just a thought, might want to buy a gravesite early.....just in case your rubber gloves have a pinhole
leak in them and it fibrulates your heart. And if you feel generous feel free to put us in your will if
there is anything of value you wish to leave behind.


Regards, Dana.

PS : Go to the dump and pick up a microwave oven or two, and rip out transformer and
rewind secondary to build an isolation transformer. Youtube several have done so.
 
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crutschow

Well-Known Member
Most Helpful Member
I agree that what you are trying to do is too dangerous.
It's tantamount to dropping a hair dryer into a tub of water.
Buy an isolated supply and be safe.
 

Diver300

Well-Known Member
Most Helpful Member
I share all the others' reservations about the safety. Do you know what voltage is needed?

Variable autotransformers, usually called variacs, are often used to run a step-down isolation transformer to give a variable power supply. In a previous job we needed around 150 A at 3 V, and that was done with a variac feeding a step down isolation transformer. As the voltage of the output was so low, and isolated from the mains, we didn't have to have any safety isolation to stop someone touching it when in use.
 

PaulCrabtree

New Member
Thanks all, I am aware of the safety issue, it's in my studio workshop, not home, and I have used this set up for 30 years. System went down and I was troubleshooting. Fixed now.
 

Papabravo

Well-Known Member
Post #3 OP acknowledges safety issue.

Forum, myself included, went off on him because we are all self absorbed DUMBASSES :)

Regards, Dana.
In the absence of complete information we acted prudently and responsibly. You can call yourself whatever you want, but calling me one is rude and offensive.
 

danadak

Active Member
Timeline :

#1) OP Posts
#2) Papabravo discusses safety
.
. Myself and other(s) continue to discuss what OP has already acked.....
.
.
#14) Papabravo rudely to OP - "So you knew the answer before you asked the question. Good form."
.
.
.
Yes, I am a member of the rude club. And so are they who shall not be named....


Regards, Dana.
 

KellyGreené

New Member
It's nice that you have it all sorted out. But would it be possible to let me know about your progress and the steps that you ended up taking? I might want to try something like that later in the future and would like to start when I know what I'm doing.
 

danadak

Active Member
The use of vulgar expressions certainly puts you in an exclusive club.

Yep, this surely meets the vulgar test, welcome brother -

#14) Papabravo rudely to OP - "So you knew the answer before you asked the question. Good form."

Definition of vulgar


1a: lacking in cultivation, perception, or taste : COARSE
b: morally crude, undeveloped, or unregenerate : GROSS
c: ostentatious or excessive in expenditure or display : PRETENTIOUS
 

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