Author Topic: Unregulated Bench AC/DC PSU: necessary?  (Read 1704 times)

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Offline Catfish Stevens

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Unregulated Bench AC/DC PSU: necessary?
« on: June 10, 2015, 11:28:09 pm »
This is a pretty newb question but I suppose I'm in the right place.

I recently ordered this from Amazon:
http://www.amazon.com/gp/product/B0002DT0GU/ref=olp_product_details?ie=UTF8&me=
and got what I thought was a pretty good deal using Warehouse Deals, with a claim that only the packaging was damaged.

Problem is, I received this instead:
http://www.amazon.com/gp/product/B0002DVEZA/ref=olp_product_details?ie=UTF8&me=

Technically I guess I'm getting a pretty good deal as it's selling for almost triple the price I paid.  It did not work when I received it, had a blown fuse that I replaced and now it seems to be working.. obviously if there's something wrong with it I'll be returning it.  I've been pretty unhappy with Amazon lately and this doesn't help matters, but I digress.

What it comes down to, though, is will this unregulated power supply be of any use to me as I continue to learn electronics?  Is it something that will be needed on my bench?  For that matter, what do people use an unregulated bench supply for?  I plan to do a little bit of everything but will definitely be focusing learning about and building power amplifiers and restoring vintage audio equipment.

If it makes any difference, I already do have a DC regulated PSU (one of the Korad 30V/5A DC ones).  I liked the kit because it gave me another DC source and a little AC to play with.  I can order another one if I actually NEED this unregulated unit.

Any advice would be appreciated, thanks.
 

Offline jeroen79

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Re: Unregulated Bench AC/DC PSU: necessary?
« Reply #1 on: June 11, 2015, 12:21:48 am »
Personally I would have gotten a second Korad or similar regulated power supply with adjustable CC and CV.
Maybe a dual supply with the option to set them up in a series or parallel master/slave setup.

The unregulated PSU you received seems to be intended to demonstrate the basic principles of electricity to high school students.
Based on the description it seems to me that it contains no more than a variac, a rectifier and maybe a capacitor.

The one you ordered would be slightly better but I would guess that it has just a pair of LM317 and a 7805 inside.
The 6.3VAC reminds me of a transformer for old tube equipment.

Edit: I guessed right:
http://www.elenco.com/admin_data/pdffiles/XP720Kweb.pdf
Edit 2: Well, partially. The XP-625 has a dimmer instead of a variac:
http://www.elenco.com/admin_data/pdffiles/XP-625_REV-F.pdf
« Last Edit: June 11, 2015, 12:33:36 am by jeroen79 »
 

Offline Cliff Matthews

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Re: Unregulated Bench AC/DC PSU: necessary?
« Reply #2 on: June 11, 2015, 12:29:05 am »
Be careful - this is just a transformer run by a dimmer circuit.
Yes, you have isolation but 40-60volt peaks are still present!! (it only chops waveform to reduce the effective RMS value)
« Last Edit: June 11, 2015, 01:13:57 am by Cliff Matthews »
 

Offline Catfish Stevens

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Re: Unregulated Bench AC/DC PSU: necessary?
« Reply #3 on: June 11, 2015, 01:33:28 am »
Thanks for your answers.  So basically this unit is actually potentially dangerous and could have fried something important if I hadn't realized they sent me the wrong item?  I don't know much about unregulated bench PSUs beyond skimming some articles but it sounds like this has zero use for me. 

I wonder why this thing is over twice as expensive as the one I ordered?  I even thought I was getting a nice deal for the original one at $50 just for some damaged packaging.

I hate returning items to Amazon but I have a couple of other items they've packed badly that have been damaged, so I guess I'll be dropping off one more.
 

Offline Richard Crowley

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Re: Unregulated Bench AC/DC PSU: necessary?
« Reply #4 on: June 11, 2015, 01:43:50 am »
No, it is not "dangerous", but simply rather crude.  Yeah, MAYBE you could have "fried something important" if you were working on some very sensitive circuit. Since we don't know what kind of circuits you propose to play with, we are unable to evaluate whether you could still use it or not.
 

Offline Cliff Matthews

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Re: Unregulated Bench AC/DC PSU: necessary?
« Reply #5 on: June 11, 2015, 01:53:41 am »
It's more expensive likely due to:
1) Much bigger transformer, 2) Dual meter movements, 3) probably has stud diodes or a 10 amp bridge and 4) likely is higher duty.

I don't imagine they'd sell too many either. Newarc sells bigger 15amp / 600v quadrac's at just $2 each.  Hmm.. the circuit gives me ideas of what to do with an old microwave transformer and a custom-wound secondary..
 

Offline kingofkya

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Re: Unregulated Bench AC/DC PSU: necessary?
« Reply #6 on: June 11, 2015, 03:02:08 am »
You might check ebay you can get cheap 3amp current and voltage controlled ones for around $50 USD mark.

 


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