Cheap Low Voltage AC Power Supplies - Page 1
Forum section: electronics / general

author: techie1234
author_rank: Regular Contributor
timestamp: August 06, 2016, 01:41:52 am
content: Here’s a suggestion from one of my other hobbies: if you are looking for a simple 8-20V variable voltage AC power supply that’s not regulated, rather than rigging something up yourself you might want to consider just buying a used Lionel model train transformer. Although most are now 50+ years old, they were built very solidly and most work just fine today. Most (although not all) have a circuit breaker in them and some are even U/L listed. And if something is wrong, they’re easy to repair with specs and parts readily available.You can pick up a single control 25-75W unit for +/- $10 on Ebay. I keep one on my workbench for testing train equipment but also use it from time to time in my electronics as well.

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2016, 06:26:40 am
content: That is a great idea. Further, the parts are available to refurbish things like the carbon wipers.

author: techie1234
author_rank: Regular Contributor
timestamp: August 06, 2016, 02:27:57 pm
content: Quote from: David Hess on August 06, 2016, 06:26:40 amHehe...I actually have the Lionel "Type V" transformer that my father got in the late 1940's on my bench right now to clean and replace the carbon rollers. It's going through its twice-a-century maintenance...

author: techie1234
author_rank: Regular Contributor
timestamp: August 06, 2016, 02:39:55 pm
content: Here's an example 75W one - it's the one I have on my workbench and does have a circuit breaker:http://www.ebay.com/itm/LIONEL-4150-BLUE-TOY-TRANSFORMER-75-VA-LOOKS-AND-WORKS-GREAT-/112080177122

author: bitseeker
author_rank: Super Contributor
timestamp: August 07, 2016, 04:53:08 am
content: Good idea. I've got a red Lionel one somewhere...

author: SeanB
author_rank: Super Contributor
timestamp: August 07, 2016, 09:04:43 am
content: I have an old 12V downlight toroid and a small variac in a box as an AC source. Works well as an adjustable voltage source, giving up to 50VA of power. Variac is a 115VAC 400Hz one, so derating to 12VAC 50Hz is perfect, and it is rated at 5A as well.

author: David Hess
author_rank: Super Contributor
timestamp: August 07, 2016, 02:39:51 pm
content: That is the way I do it. I have several variacs and hook up an appropriate 120 volt power transformer as needed to make a variable AC power supply.

author: retrolefty
author_rank: Super Contributor
timestamp: August 07, 2016, 03:44:48 pm
content: Quote from: David Hess on August 07, 2016, 02:39:51 pmAnd with the added advantage of (if desired) isolation from the input neutral/ground of the input source.

author: Back2Volts
author_rank: Unknown
timestamp: August 07, 2016, 03:54:27 pm
content: Quote from: techie1234 on August 06, 2016, 02:27:57 pmWhether it needs it or not! Preventative maintenance is a best practice!

author: Back2Volts
author_rank: Unknown
timestamp: August 07, 2016, 04:02:06 pm
content: Quote from: retrolefty on August 07, 2016, 03:44:48 pmIs the transformer to provide isolation? Are there variacs with separate primary/secondary windings ?

author: techie1234
author_rank: Regular Contributor
timestamp: August 07, 2016, 04:09:37 pm
content: Quote from: retrolefty on August 07, 2016, 03:44:48 pmA classic Lionel "train transformer" is little more than a power transformer with a wiper/roller on the secondary to select voltage. The output is isolated from the mains and they all have two-prong plugs. While I wouldn't bet my life on their absolute isolation, we are talking about low voltages on the output side. In fact, quite a few people with layouts that have mains current devices (e.g., overhead lights) in proximity to their track purposefully connect their output common to earth ground as a safety measure in case the track somehow accidently gets "lit up" by the mains.

author: techie1234
author_rank: Regular Contributor
timestamp: August 07, 2016, 04:15:20 pm
content: Quote from: Back2Volts on August 07, 2016, 03:54:27 pmTechnically, I guess it's in for its thrice-a-century maintenance. My dad (a ham guy who should have known better...) let the original cord and plug get pretty dodgy. When I was about 8 or 9, I got a 110V wakeup call that taught me respect for electricity at an early age. A bit chagrined, he changed the cord that evening.

author: David Hess
author_rank: Super Contributor
timestamp: August 07, 2016, 04:37:16 pm
content: Quote from: Back2Volts on August 07, 2016, 04:02:06 pmVariacs with separate primary and secondary windings do exist but are both rare and expensive; most are autotransformers with one winding so for safety, an isolation transformer should be used and if you want a low voltage output anyway, then a standard power transformer can provide both and boost the output current. The Lionel train transformers are one of the few examples of a variac with separate windings.

author: bitseeker
author_rank: Super Contributor
timestamp: August 07, 2016, 09:03:21 pm
content: Most of the isolated variacs I've seen consist of a regular autotransformer (aka, variac) behind a regular isolation transformer -- nothing fancy, just more expensive when they're both in the same enclosure. So, if you already have a variac, just add an isolation transformer to it. (Then, put them both in a single enclosure to boost their value)