AC Dummy Load - Page 1
Forum section: electronics / projects

author: skipjackrc4
author_rank: Regular Contributor
timestamp: December 09, 2012, 11:06:39 pm
content: I've been thinking about making an AC dummy load to test UPS's, solar inverters, etc, up to 230V... Does anybody know of any good designs out there?The only thing that I've been able to come up with so far has been to rectify and filter the AC and then use a DC dummy load. It seems like I've seen a better design somewhere in the past, but I have no idea what it was.Ideas?Thanks!

author: nctnico
author_rank: Super Contributor
timestamp: December 09, 2012, 11:27:29 pm
content: I'd use a PFC stage instead of a rectifier to present a load which is close to resistive. The only problem is that most PFC stages output 450V so you'll need a dummy load capable of handling such voltages.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: December 09, 2012, 11:59:13 pm
content: OK, here is another idea I just came up with.Yesterday morning, a family member called me and said that he had found a 3 phase, 6kW variac--virtually unused--at a surplus place for $75. I had no clue what to do with it, but for $75, I told him to pick it up for me.So would a variac with the secondary hooked up to some large, cooled power resistors work as a variable AC load? I've got nothing else to do with the thing...

author: Skimask
author_rank: Super Contributor
timestamp: December 10, 2012, 12:55:04 am
content: Any reason why the lowly incandescent light bulb wouldn't do the job?A handful of various wattages, in series, in parallel, in series/parallel, in parallel/series, maybe using a handful of switches to put them in and out of the load circuit?

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 10, 2012, 01:08:27 am
content: A portable heater is little more than a very large power resistor.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: December 10, 2012, 01:23:45 am
content: Yep, I was completely overthinking it at first. I am designing a DC load, and had the brilliant idea of adding a module to it to allow AC sinking as well.Then I remembered the huge variac. The current plan is to hook up the primary (is it called a primary on an autotransformer?) of each of the three phases to the AC input. Each of the 3 outputs will go to a resistive heating element. This will give me 2kW sinking with no strain at all on the variac, and I can go higher should I need it. Panel meters will monitor voltage and current. I may put individual current meters on each phase so I can be sure that everything is sharing evenly. This will probably wind up on wheels because that is a lot of power to be burning off inside a lab.Thanks for the suggestions and putting up with my brain-dead question. Sometimes I just like to over complicate things.

author: cybergibbons
author_rank: Frequent Contributor
timestamp: December 11, 2012, 11:03:55 am
content: Large commercial dummy loads are just articulated trailers used as a tunnel full of heaters with a big fan at the end. Cheap and easy.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: December 11, 2012, 03:46:20 pm
content: Good to know.