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Variable voltage power supply.

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Arcstarter

Tue Aug 26 2008, 12:31AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

I know this might be hard to come by, but i am looking to make an either 0-50 or (preferably, but unlikely) 0-80 volt dc power supply. It does not hav to be regulated, but at least smoothed. I would use a rewound large mot(large for more turns) and a good 5 to 10 amp output would be awesome. This would be VERY expensive to buy, so i will make the transformer, but the variable part is what gets me... I would use a large bridge rectifier capable of 35 amps and i have some large smoothing capacitors.

So, is there any way to hook voltage regulators in parallel for higher current carrying capacity, or is there any relatively cheap variable voltage regulator that could handle the job? Or is there another way that i do not know about to vary the voltage, other than a variac?

Shaun

Tue Aug 26 2008, 01:26AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

I would go for something SCR-based, like Dr. Conner's solid-state variac. You'd need some pretty big SCRs and sinks to carry that amount of current continuously, but it shouldn't be too hard. You might not even need a transformer at all...

Electroholic

Tue Aug 26 2008, 07:01AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

can;t you just use a variac thru an isolation transformer and smooth the output?

quicksilver

Tue Aug 26 2008, 05:04PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Find a junked arc welder! They are available if you search. Occationally they are junked because some dolt left them in the rain and THOUGHT they were wasted but still have goodies working.

Arcstarter

Wed Aug 27 2008, 12:15AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Electroholic wrote ...

can;t you just use a variac thru an isolation transformer and smooth the output?

Sure, if i can find a big variac that does not cost 800 bucks(a brand new 22 amp 120 volt vavriac costs 808 bucks) And an isolation transformer that can handle 10 amps that is not huge, expensive and does not weigh 3.125 tons(idk..).

Can i parallel regulators? I could just get a few 30 volt 3 amps regulators and make a nice and juicy 30 volt power supply, but i am really going for 50 -80 volts.

EEYORE

Wed Aug 27 2008, 04:52AM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Variac is going to be the way to go. Look on ebay as they are plentiful there. A regulator would suck for this I think.
matt

Electroholic

Wed Aug 27 2008, 06:31AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

sure a huge regulator would work, i mean why not? do you have any idea how much power you are going to burn? power dissipated by regulator can be calculated like this, very simple.
( Vin - Vout ) * Iout

Real Linear Regulated Power supplies usually have a multi tapped transformer, and the taps goes to the same regulator thru some relays. So while the regulator still has to pass the current, the voltage it has to drop is less.

btw, I have a 7.5A variac sitting on my desk, and its not big. It would easily fit in a box 15x15x15cm^3.

0 to 80V, 0 to 10amps, is really not that much power if you think about it. If you have balls, design a forward converter from scratch, it would fit in a box smaller than my variac. If not, i really think variac is your best bet. And the fact that you don't mind the non regulated output? it's perfect!
As far as isolation transformer goes, while not exactly easy to come by, they are not as heavy as you think. hack you can even do it with two mots. or leave it out for all i care, you are obviously not too concern about safety seeing as you like to pull CW VTTC arc with your hand.

quicksilver

Thu Aug 28 2008, 11:37PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Why take a chance? Mouser has Isolation transformers for about $80.

Arcstarter

Fri Aug 29 2008, 02:00AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Well i want an isolation transformer because i don't want it to kill low voltage stuff like logics and stuff. I know nothing of variacs and regulators, so...yea.

quicksilver

Sat Aug 30 2008, 05:58PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Just out of curiosity I checked Mouser for actual prices and found some for MUCH less! The Triad brand Mouser stock # 583-XXXX is around $60 depending on what level of output current you want. Stancor brand is a lot more (starts @ about 80 but is higher quality). (PP1864 in the catalog or type stock # search online)

There is nothing wrong with trying your luck and asking the actual companies (Stancor or Triad) if they have factory 2nd's or blemished units they would sell to a starving student. You can get very lucky sometimes.

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