[Found] WTB [EU]: Low Voltage AC Bench Power Supply  - Page 1
Forum section: electronics / general

author: hp3310a
author_rank: Regular Contributor
timestamp: October 06, 2025, 10:26:28 am
content: I'm looking for a bench power supply (that doesn't bankrupt me) for low voltage, starting at 0-12V AC minimum, low power output (lets say 20VA). Must have isolated output, frequency setting optional. Voltage display or current limiter not necessary, if it needs a DMM connected for fine tuned setup that's fine.Optionally a variable transformer with isolated secondary winding with the ability to fine adjust low voltage setting.

author: Gertjan
author_rank: Frequent Contributor
timestamp: October 06, 2025, 10:51:02 am
content: Hi hp3310a,The standard budget solution is a normal variac (0....240V out, auto transformer), and after the variac a normal mains step-down transformer. (e.g 240V to 30V)The second transformer takes care of the isolation, and transforms the voltage setting range to what is needed (in this case 0V...30V)This concept is also commercially available. Regularly I see them for low prices at radio rallies. Inthis postyou can see mine.regards, Gertjan.

author: hp3310a
author_rank: Regular Contributor
timestamp: October 06, 2025, 02:09:30 pm
content: Thanks for the tip, I'll keep an eye out for those. The fairy tale €10 prices I keep reading about appear to be a thing of the past.

author: Zucca
author_rank: Unknown
timestamp: October 06, 2025, 03:31:15 pm
content: Also consider for variable f up to 20Khz at low power, to hookup a audio amp to the secondary of a trafo.... and use the primary as output.You can feed the audio amp with anything you want, and use the volume knob to adjust the amplitude.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 06, 2025, 04:52:18 pm
content: Quote from: hp3310a on October 06, 2025, 02:09:30 pmIf you can find a variac, I can send you a ~100VA 240V->24V toroidal for the price of the postage (naturally the practicality of this depends on what country you are in)

author: hp3310a
author_rank: Regular Contributor
timestamp: October 07, 2025, 05:36:06 am
content: Quote from: AVGresponding on October 06, 2025, 04:52:18 pmThanks for the kind offer! I found a variable transformer that would perfectly fit your toroidal (https://www.conrad.com/en/p/thalheimer-ess-104-variac-1-x-230-v-1000-va-4-a-516511.html), just need to find a good case for it. I'll send you a PM shortly.

author: Gertjan
author_rank: Frequent Contributor
timestamp: October 07, 2025, 01:55:18 pm
content: Quote from: Zucca on October 06, 2025, 03:31:15 pmBeen there, done that. Mostly for speed-varying turntables and tape recorders.Be sure to use a sturdy amplifier. Preferably with current limiting on it's power supply.That is because a transformer is a nasty inductive load for the amplifier. Even more when the transformer gets saturated.And an inductive load like a motor does not help either.... I managed to destroy a Quad 405 that way.Also, the output level of the driving ARB of function generator is less stable then the average power supply.So yes, use this solution by all means when needed. But use it with caution. And I think this setup is less appropriate for a general use AC bench supply.@ hp3310a: Good to read you found a variac, and got offered a matching transformer!regards, Gertjan.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: October 09, 2025, 01:41:22 am
content: I had fun with TDA2050 + diff. kind of transformers + Fun. gen ... till it dieplanning 2x20V 65W laptop PS bricks and bridge 2xTDA2050 ,

author: Electrodynamic
author_rank: Regular Contributor
timestamp: October 09, 2025, 04:19:12 pm
content: hp3310aQuoteI was having major issues with isolation and ground interaction so I used an old 200w 1:1 transformer on the 120v input of a $40 30v/5A power supply off amazon. Have also used a 12v battery and 500w inverter for power input isolation in a pinch. It depends on how much we would use or need power isolation. In my case it was rare so I improvised.

author: hp3310a
author_rank: Regular Contributor
timestamp: October 09, 2025, 07:56:12 pm
content: Thanks guys. I ended up buying a used 24V toroidal transformer, a variable transformer (linked above) and all the components for building a complete unit except for the case.Cases that fit the contents are surprisingly difficult to find and extremely expensive. The best I found is thishttps://uk.rs-online.com/web/p/general-purpose-enclosures/2777624?gb=s&searchId=490121f1-dfbc-408b-8615-e29263f00b62from Hammond. If someone knows a good source for acceptably looking metal cases, let me know.

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 09, 2025, 08:25:50 pm
content: You might be able to find something like this cheaper:https://www.amazon.com/dp/B09XWM5P21/There are a lot more options than that Hammond available, and that specific series from Hammond with the angles is more expensive than regular boxes.

author: hp3310a
author_rank: Regular Contributor
timestamp: October 10, 2025, 06:01:21 am
content: That one I know, but it doesn't have the required height. It needs to be at least 170mm high, 220mm wide and 160mm deep (usable inner space). There are tons of rectangular boxes that are not high enough. The best other match was a 4 HE rack case, that's of course 4 times bigger than it needs to be.

author: _Wim_
author_rank: Super Contributor
timestamp: October 10, 2025, 04:32:24 pm
content: Quote from: hp3310a on October 09, 2025, 07:56:12 pmFor that price I would go for something like this instead:https://nl.aliexpress.com/item/1005006651105114.html?spm=a2g0o.productlist.main.1.259a3decwIUhjo&algo_pvid=e42da09f-0792-49e2-9ff9-c403fffc8ea4&algo_exp_id=e42da09f-0792-49e2-9ff9-c403fffc8ea4-0&pdp_ext_f=%7B%22order%22%3A%22-1%22%2C%22eval%22%3A%221%22%2C%22fromPage%22%3A%22search%22%7D&pdp_npi=6%40dis%21EUR%21119.66%21107.69%21%21%21135.16%21121.64%21%402103985c17601133615748251e9310%2112000037927804824%21sea%21BE%21161137670%21X%211%210%21n_tag%3A-29919%3Bd%3Ab5808fe0%3Bm03_new_user%3A-29895&curPageLogUid=POIimJMNzFh5&utparam-url=scene%3Asearch%7Cquery_from%3A%7Cx_object_id%3A1005006651105114%7C_p_origin_prod%3Aif link does not work correctly, search for "206 Shell Aluminum Enclosure Case Empty Box for HiFi Audio AC Power Filter Power Purifier Isolation Transformer" on Ali-express...

author: hp3310a
author_rank: Regular Contributor
timestamp: October 10, 2025, 04:37:02 pm
content: Quote from: _Wim_ on October 10, 2025, 04:32:24 pmThat's much better, thanks very much for sharing this one!