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Old 30th May 2009, 07:10 AM   #1
miallen is offline miallen  United States
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Default Radio Shack Transformer 273-1512

I've been hunting high and low for a ~24V center tap transformer to make a standard LM317/LM337 adjustable bench power supply. After searching the usual sites it seems the cheapest is actually from Radio Shack:

http://www.radioshack.com/product/in...ductId=2102703

It's only $10.49 USD. Supposedly it can put out 2A, it has an all metal enclosure and it comes with clips and wire leads. A similar part on digikey or mouser is over twice the price.

Has anyone tried this transformer? Is this a case of "you get what you pay for"?

If it's considered crap, what is a good transformer with similar specs or at least what manufacturer should I look for?

Mike
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Old 31st May 2009, 01:01 AM   #2
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The RadioShack Transformers are great.

I have used SEVERAL of them. The 24V ones and the 12V ones. They are reliable, never had one fail. NEVER a failure, even with short circuits and pulling over the rated amperage.

They are excellent transformers. They can take overloading well, and don't get too hot under normal loads. They also work great for charging batteries.

I recommend these transformers. For a nice project with a split supply, it can't be beat, especially for under $20.
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Old 31st May 2009, 02:40 AM   #3
star882 is offline star882  United States
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Look for some used laptop power supplies, particularly the ones for obsolete (Pentium 1 or 2) computers. They're built very well and you don't need to do any line voltage wiring. They're also rectified and regulated.
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Old 6th June 2009, 02:07 AM   #4
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I hope you don't mind me asking a quick question, but I might have found a better deal for you.

Quote:
Originally posted by EWorkshop1708
The RadioShack Transformers are great.

I have used SEVERAL of them. The 24V ones and the 12V ones. They are reliable, never had one fail. NEVER a failure, even with short circuits and pulling over the rated amperage.

They are excellent transformers. They can take overloading well, and don't get too hot under normal loads. They also work great for charging batteries.

I recommend these transformers. For a nice project with a split supply, it can't be beat, especially for under $20.
So then which do you think is a better deal, the radioshack trafo or this:

http://www.antekinc.com/AN-0512.pdf

13$, which would be 23$ after shipping (If I'm reading the page right) in my area.

I'm asking this because I'm trying to figure out which one to buy for my project here:

Will this work?

If I'm reading the datasheet right, floating output is 11.8V, so it doesn't look like you can make a 12V regulator with this. If you want to put it through a reg you should probably use the 15V version, which is the same price.

http://www.antekinc.com/trans.html

Wait a sec, I'm looking at the 50VA ones. The 20VA ones will supply 1.8A, and are 11$. They are also toroidal, maybe better emissionwise.

Thank you,
- keantoken
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Old 8th June 2009, 05:01 PM   #5
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Quote:
Originally posted by keantoken
I hope you don't mind me asking a quick question, but I might have found a better deal for you.



So then which do you think is a better deal, the radioshack trafo or this:

http://www.antekinc.com/AN-0512.pdf
Thank you,
- keantoken
The RadioShack transformer is the better deal. For one, it's local, an no shipping. Two, it's ~50VA for only $11. Three, I've used the RadioShack transformers for YEARS, and have not had even ONE single failure!

I've charged batteries with them, and run stuff with them pulling well over the rated current. Never any current or short circuit protection, and never burned one out. I even accidentally dead-shorted a 12.6V 3A version one time a few years ago, and left it on for 15 minutes, and you could smell the transformer burning from another room, but the transformer STILL WORKS to this day!

The 25V, 2A, transformers will have plenty of power, and if you really need more, then get two of them. Unloaded off the bridge rectifier gives me +/- 19.5V on a RS 25V transformer. You can easily get +/-12V or +/-15V from that.

I used a 25V RS transformer in my ~350WRMS DIY amplifier for powering the control and fan circuits, and preamp circuit too. It runs 6 powerful fans, runs all the logics and relays, and feeds my 7812/7912 regulators for my preamp on +/-12V supplies. I'm only filtering with 2,200uf on the rails, and it runs everything fine from that transformer, with power to spare.

The RS transformers have been around for years, and I can see why. They are really good. I built a 6V/12V 12Amp PSU out of 4 of the RS 12V transformers a few years back, and it still works great.

For the hassle of looking around for a transformer, and the costs of shipping, it's easier just to pick up two or 3 RS transformers locally.
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Old 8th June 2009, 05:50 PM   #6
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Quote:
Originally posted by EWorkshop1708


The RadioShack transformer is the better deal. For one, it's local, an no shipping. Two, it's ~50VA for only $11. Three, I've used the RadioShack transformers for YEARS, and have not had even ONE single failure!

I've charged batteries with them, and run stuff with them pulling well over the rated current. Never any current or short circuit protection, and never burned one out. I even accidentally dead-shorted a 12.6V 3A version one time a few years ago, and left it on for 15 minutes, and you could smell the transformer burning from another room, but the transformer STILL WORKS to this day!

The 25V, 2A, transformers will have plenty of power, and if you really need more, then get two of them. Unloaded off the bridge rectifier gives me +/- 19.5V on a RS 25V transformer. You can easily get +/-12V or +/-15V from that.

I used a 25V RS transformer in my ~350WRMS DIY amplifier for powering the control and fan circuits, and preamp circuit too. It runs 6 powerful fans, runs all the logics and relays, and feeds my 7812/7912 regulators for my preamp on +/-12V supplies. I'm only filtering with 2,200uf on the rails, and it runs everything fine from that transformer, with power to spare.

The RS transformers have been around for years, and I can see why. They are really good. I built a 6V/12V 12Amp PSU out of 4 of the RS 12V transformers a few years back, and it still works great.

For the hassle of looking around for a transformer, and the costs of shipping, it's easier just to pick up two or 3 RS transformers locally.
I have a 7815/7915 handy that I could use to power my bench. Would I be able run a class A amp, 750mA bias current and 1.5A max current with the rails still not going below 15V?

You're starting to win me on this one... Our local RS used to hold these but they stopped carrying a lot of their inventory, to my dismay. I had planned to get some of their Kynar wrapping wire but it was gone.

Okay, we should look at this I think....

http://www.radioshack.com/product/in...gs#showReviews

Maybe the ones you get are good, but it seems like there may be a quality control problem. One person says they run very hot. I can't imagine how hot they get at the power you run them at. Running them hot is not an option for me because my bench is close to the ceiling and I'll be frying too.

- keantoken
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Old 8th June 2009, 06:07 PM   #7
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I've used the radioshack trannies for a long time, too. I've used them for heater power supplies in pre-amps, and also as back-to-back for getting isolated HV with wall-warts.

I've never had a problem with them, either. The only time I've had them run hot is when i've hit them with way too much draw, usually from the small 600ma variants.

If you only plan on drawing 1 amp per rail, I'd say the 25.2VCT would be fine. But, if you want the transformers to run really, really cool and not have to worry about voltage drop from a loaded rail, I would go with two of the 12.6VCT 3A transformers.
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Old 8th June 2009, 06:33 PM   #8
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Would the Antek run cooler?

- keantoken
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Old 9th June 2009, 01:24 AM   #9
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If you're worried about temperature, upsize the transformer. The lower the load you put on it, the cooler it will run. The one nice thing about toroids is they generally have good regulation, so you won't be dissipating extra heat on your regulators because the voltage drifts upwards on the EI cores from Radioshack.

If space isn't a constraint for you, I would just go buy a pair of the 12.6VCT 3 amp transformers instead, and put one regulator on each tranny. It will cost you less than the Antek, you don't have to wait for shipping, and you'll have plenty of headroom.
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Old 9th June 2009, 05:26 PM   #10
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Sounds good. I will do that.

This also gives me the benefit of having 6V outputs.

- keantoken
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