AC lab / bench power supply - Page 1
Forum section: electronics / testgear

author: MrQuan
author_rank: Contributor
timestamp: September 19, 2014, 12:40:26 am
content: G'day!I'm on the market for an AC bench-top power supply, and haven't been able to find anything suitable.First I'll give you the scenario: I'm developing hardware that is to run on AC supply (nominally 12-24V) and a battery backup system. I've been testing using my DC supply, and a standard 240V primary / 24V secondary transformer. However, now I would like to:Test performance (efficiency and thermal) over a range of voltages,Simulate brown-outs,Simulate surges,Test the battery backup in greater detail (loss of AC power, etc.),Test half-wave rectifier with grounded secondary neutral,Test full-wave rectifier,Test protection on device power input,Test protection on device I/O terminalsFor this purpose I'm looking for a supply with the following features:Adjustable output voltage from 0 to 60VAC (0 to 30VAC would be ok),Adjustable current limit from 0 to 100W (0 to 40W would be ok),Isolated output, with ability to ground secondary. This could be done externally with a ground lead, as long as I don't blow up the supply!I've searched the forum and found a mentioned to the B&K Precision Model 1653A (http://www.bkprecision.com/products/power-supplies/1653A-150v-2a-ac-power-supply.html), but this doesn't offer the accurate current control I require. It has buttons to switch between amp ranges (I believe this is just switching transformer windings).I'm looking for the ability to accurately adjust the current limit with a dial, in the same way most DC supplies operate (no switching or interruptions to the supply). It would be great if this could also be programmable or software controlled, but I imagine something like this would be way out of my budget!Does something like this even exist? Can it be bought for a reasonable price? I'm hoping to spend $500 or less.I was thinking of building my own AC supply, perhaps some form of sine-wave inverter. But I'm too busy and really just need something fast and off the shelf.Another idea I had was to use an isolated variac and connect a big rheostat in series with my test device. Would that work?Any advice would be greatly appreciated, especially if you have experience with this sort of testing.

author: robrenz
author_rank: Super Contributor
timestamp: September 19, 2014, 01:00:24 am
content: Look at a Kepco BOP supply. These are 4 quadrant supplies that come in various V and A capacity and behave like a huge op amp. You would need to drive it with a FG to set the frequency and amplitude but there is independent current limit. Very hand bit of kit in general and also work at DC.I have athread hereabout the Lambda version of them called BOSS

author: MrQuan
author_rank: Contributor
timestamp: September 19, 2014, 01:13:17 am
content: That's a really interesting solution! Driving with function gen would obviously allow me to test over different frequency ranges too.Thanks for the suggestion and link. I have some reading to do, but it looks promising :-)Update:This looks like it would do the trick, but it's probably beyond my budget at the moment :-( They are mostly in the States (none in Australia) and the cheapest go for around $600 + $100 shipping. I'll keep looking for better deals.Although cheap and nasty, is the variac + rheostat a viable solution?

author: edavid
author_rank: Super Contributor
timestamp: September 19, 2014, 03:24:18 am
content: Quote from: MrQuan on September 19, 2014, 12:40:26 amThe buttons only change the meter range. It does not have current limiting (how would that work?), just a circuit breaker.

author: macboy
author_rank: Super Contributor
timestamp: September 19, 2014, 11:49:58 pm
content: If you want to test with 60 Hz, you could use an audio amp together with a signal generator set to 60 Hz sine.With a 100W (8 ohm) audio amp, you should be able to get roughly ~30 Vrms, or roughly 80 + Vpp. You can usually drive a transformer to get higher voltage and correspondingly lower current. Most audio amps will sense an over current and disable themselves to prevent damage to itself/load, though I wouldn't trust that implicitly.

author: eurofox
author_rank: Unknown
timestamp: September 20, 2014, 12:08:39 am
content: Maybe you need something like this one?http://www.clarke-hess.com/828.htmlI got one

author: edavid
author_rank: Super Contributor
timestamp: September 20, 2014, 03:31:52 am
content: Quote from: eurofox on September 20, 2014, 12:08:39 amIt's nice, but only 10VA output...

author: VintageTekFan
author_rank: Regular Contributor
timestamp: October 07, 2014, 07:48:18 pm
content: Quote from: macboy on September 19, 2014, 11:49:58 pmI hate to say this, but thats what we did for a one-off test bench. Used a commercial grade audio amp, and a mux board to take feedback from the output, a 60hz ref signal sine, and a 4-20mA control input for amplitude. We were able to vary from ~90 to ~200V on one mode, and ~160 to ~320 on another. The second audio channel provided an inphase current between 0 and 10A. But only because the voltage and current sense were not common-ed on the Device Under Test.But, it works quite well.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: October 07, 2014, 08:35:36 pm
content: An audio amplifier was what I was about to suggestDecent sized PA amplifier... or you may even be able to get away with bridging the channels on a smaller amp (by inverting the input to one channel) seeing as you don't need a heap of power.