Benchtop Variable AC Power Supply Recommendation? - Page 1
Forum section: electronics / testgear

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: October 28, 2022, 04:10:59 pm
content: While there seem to be endless choices of benchtop DC power supplies, I'm having a hard time finding a benchtop variable AC power supply that will provide say up to 30V at 1A or similar, preferably with current limiting. I'm looking for a budget item, not a high-precision device.Can anyone recommend such an item, or better still, point me at where to purchase one in the UK?

author: bdunham7
author_rank: Super Contributor
timestamp: October 28, 2022, 04:14:09 pm
content: Do you mean mains-derived single frequency (50Hz for you) output or variable frequency output?

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: October 28, 2022, 04:22:48 pm
content: Mains frequency was what I had in mind (as presumably that will be cheaper, and I have no specific need for a variable frequency).

author: bdunham7
author_rank: Super Contributor
timestamp: October 28, 2022, 05:00:55 pm
content: The traditional solution is a variac and perhaps a step-down transformer. More sophisticated AC power supplies that would resemble common DC types as far as voltage and current regulation, digital display, etc are not common and not inexpensive. I use a BK 1655 AC Power Supply with an appropriate step-down transformer as needed. There isn't any adjustable current limiting and load regulation is done manually. You can use a large transformer with a small fuse or breaker if you need a stiffer supply with current protection.

author: electr_peter
author_rank: Unknown
timestamp: October 28, 2022, 05:25:46 pm
content: There are some laboratory AC power supplies from PeakTech and other manufacturers on Reichelt site. Maybe they ship to UK. For example,PEAKTECH 5995 AC/DC power supply unit for current and voltage

author: jonpaul
author_rank: Super Contributor
timestamp: October 28, 2022, 06:03:16 pm
content: We use genuine General Radio Variac or Superir Electric Powerstat, sizes 100VA..20 KVA.two metered V, I are common, some are two range current and a three meter with W exist.All are NOT isolated.A separate 1:1 isolation trsf is avaiable eg from Signal Transfporer, sizes 500 VA...multi KW.All heavy and costly BUT appear at ham Radio flea markets.Essential for power electronic design, debugging testing and repair.EnjoyJon

author: voltsandjolts
author_rank: Unknown
timestamp: October 28, 2022, 07:24:21 pm
content: Sig gen and a power amp

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: October 28, 2022, 08:04:17 pm
content: Thanks all for your comments. Variacs tend to be big and heavy, and are usually designed for higher power than I need. Adding an extra step down transformer for voltage limiting / isolation adds to the weight, and does not provide any current limiting, stability with respect to input voltage fluctuations, etc.I was really looking for a small, portable, self-contained benchtop unit, rather like the Peaktech unit mentioned above - but with somewhat lower power - and cost. Anyway, that's a good starting point. Further suggestions along such lines are appreciated.

author: bdunham7
author_rank: Super Contributor
timestamp: October 28, 2022, 09:08:55 pm
content: Quote from: ralphrmartin on October 28, 2022, 08:04:17 pmThe Peaktech unit shown actually is fairly inexpensive as these things go, I'm not sure how it works or is regulated internally. One low-cost option you could consider is a power amplifier designed to be used with an AWG. This one and ones like it will do what you want and have good load regulation at low power levels, but they are not self contained. You would need the AWG for input and a dual +/- DC power supply to power it. They are light and cheap though!https://www.ebay.com/itm/353102212402?hash=item5236882d32

author: Martin72
author_rank: Super Contributor
timestamp: October 28, 2022, 10:28:44 pm
content: Hi,Simply&cheap solution IRegulated transformer and for current limitation several outputs with different fuses (resetable).Simply&cheap solution IIAudio amplifier with sinegen and for current limitation same as before.Not so simple solution:Sinewave controlled PWM, Transformer, Feedback loop to U and I regulation circuit.Or the so called "pure sinewave" inverter, 24VDC to 230/115VAC and then extend the U/I regulation circuitd with external trimmers.

author: BillyO
author_rank: Super Contributor
timestamp: October 29, 2022, 04:47:57 am
content: There is no $50 solution to your situation. The lowest cost solution is an isolation transformer plus a Variac. As far as I can see that would cost you about $500 for a small few watts for the cheapest possible solution. If that is too much, then maybe you could find another pursuit/project?Some things are not "cheap".

author: LinuxHata
author_rank: Frequent Contributor
timestamp: October 29, 2022, 05:27:01 am
content: If not mistaken, Linear (or TI), have a quite juicy opamp, with up to 1A of output current, up to 25V. (it was available in TO-220 case even, just I don't remember the P/N) Very few external components would be required to build adjustable voltage/current PSU with that way.

author: LinuxHata
author_rank: Frequent Contributor
timestamp: October 29, 2022, 05:28:54 am
content: Here it is - LT1970Ahttps://www.analog.com/media/en/technical-documentation/data-sheets/1970afc.pdf

author: inse
author_rank: Super Contributor
timestamp: October 29, 2022, 06:41:31 am
content: A cheap solution, but not quite reaching the 30V might be a adjustable model railroad transformer.Isolated secondary, short circuit protected…

author: J-R
author_rank: Super Contributor
timestamp: October 29, 2022, 08:57:30 am
content: The best budget solution with minimal DIY seems like a variac plus a step-down transformer and some resettable fuses as desired. I do not see this being very big or heavy (and why does that matter since it's going on a bench anyway?), and the output should have no issues reaching 30V/1A (or even 100W+). Neighborhood of $100 USD. Maybe a little more if you want to put all the parts in a nice enclosure.A signal generator + audio amp is for sure legitimate, you can get one of the toy sig gen kits and rescue a car amp for maximum savings.And to clarify, I have had both of these solutions for quite some time, no issues assuming you keep children away.

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: October 29, 2022, 03:55:33 pm
content: Thanks for all the further suggestions. I have an AWG, so using an LT1970a is an appealing solution as it also has adjustable current limiting. It only goes up to 0.5A, but the data sheet gives a circuit for external current boost to 5A, so it should meet my needs.Edit: the OPA548 looks like a good bet, too. It's even possible to buy small modules with one on cheaply...

author: mawyatt
author_rank: Super Contributor
timestamp: October 29, 2022, 04:31:17 pm
content: Quote from: ralphrmartin on October 29, 2022, 03:55:33 pmIf you need a higher voltage level the APEX PA441 or dual 443 might be considered. These utilize an external resistor across a Vbe junction to set the current limit. An LM3866 may also work, but with lower voltage capability and you'll need to configure the overcurrent utilizing the mute function. Here's link to some possibilities.https://www.eevblog.com/forum/testgear/awg-buffer-amp/msg3368650/#msg3368650https://www.eevblog.com/forum/testgear/hv-buffer-amp-for-awg/msg3623953/#msg3623953https://www.eevblog.com/forum/testgear/cheap-diy-high-powervoltage-awg-buffer-amp/msg3449784/#msg3449784Here's the APEX PA443 Dual in a AWG HV Buffer Amp config with built in +- HV supply all operates from a single +12VDC input from a few years back. Apologies for the jumpers, we didn't read the chip package layout correctlyIf you don't want a DIY AWG Buffer , the low cost & Voltage Juntek DPA-1698 can supply 1A peak at 40VPP and uses a pair of LM1875 chips.Anyway, hopes this helps.Best,

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: October 29, 2022, 07:24:30 pm
content: Thanks!

author: Swake
author_rank: Frequent Contributor
timestamp: October 29, 2022, 07:45:16 pm
content: For about 410€ you can buy the Matrix APS-4000A from eleshop.euPower 350 VAVoltage range 0-150V, 0-300VMaximum current 3AFrequency range 45 - 250 Hzhttps://eleshop.eu/matrix-aps-4000a-ac-power-supply.html

author: LinuxHata
author_rank: Frequent Contributor
timestamp: October 29, 2022, 08:26:16 pm
content: Kindly note, most cheap modules with "OPA548" are fakes. They have relabeled something like TDA2030 or similarSo I strongly suggest buying it only from digikey, mouser and other, reputable suppliers.

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: October 30, 2022, 06:33:09 pm
content: Thanks on both counts:I'd rather NOT have something that can go over 30V, to reduce the chance of a bad accident (to me, or devices).Noted the comment about fake modules (although some come with a circuit diagram, with clear provision for current limiting, and are not a 5 pin device).I will probably make my own, then I can include a digital potentiometer / micro to control the current limit, as appropriate display. This should still come in well under the cost of a commercial device.