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After a few discussions about fabricating simple power supplies from eBay modules, I decided to go one step beyond. I spotted these cool DC-DC Buck/Boost power modules with tons of features. With an output voltage range of 0.6VDC to 36VDC, and a max output current capacity of over 5 amps, they seem to have pretty much all I'd need in a bench supply. They do constant voltage, constant current, and have a really accurate digital display of both voltage and current. You can also graph the voltage and current output for analyzing external circuit performance, pretty neat.

542001


XYS3580 DC DC Buck Boost Converter CC CV 0.6-36V 5A Power Module Adjustable Regulated Laboratory Power Supply Variable

Of course, one of the little issues is they require DC input as well. I hunted around and found this 120W 24VDC switcher that looked like a good fit to provide the input power. This little gem puts out 24 VDC at 5 amps with 120VAC in.

Both the buck-boost and primary switcher have a host of protection features, so I think this should be a pretty decent source of bench power.

542002

Mean Well EPS-120-24


I shopped around and found a case on Jameco, it was a tight fit, but I managed to get all of the stuff in. I also needed a small cooling fan if I push this unit very hard, so I added that. Banana jacks salvaged from a dead MTH TIU and a power switch round out the picture.

If one of these nice power supply modules is good, two would obviously be better, right? Of course, so two it is!

542003


I actually bought two cases from Jameco, this is the smaller one, and I got a larger one as well. Since I could squeeze all of the stuff into the smaller case, I decided that limiting the bench space it consumed would be a good idea. As you can see, the front panel doesn't have any more room, it really is stuffed! However, I did want to fit the dual banana jacks for ease of use, so this was the only layout that everything would fit in.

542004


The interior is pretty straight forward. Since I had no idea how hot the primary 120W supply might get, I added a fiberglass plate and mounted it on some standoffs to allow ventilation all around.

542005


An 80mm ball bearing fan blows directly on the primary supply and I provided generous exhaust vents to allow air circulation. Since I had the grill laying around, I thought it was a nice touch.

One little disappointment in the primary power supply. It conveniently included a 12VDC fan output, only that output didn't work! So, I added a little regulator module to drop the 24V to 12V for my fan. I thought of a resistor, but the fan consumes 75ma, and it was a pretty big resistor, so I just dropped in the little regulator module.

542006
 

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do you think that the primary supply output of 12 volt not working was a 'one off', or indicitave of the supply ??
 

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Discussion Starter #8
do you think that the primary supply output of 12 volt not working was a 'one off', or indicitave of the supply ??
I'm guessing it might be a one-off, or perhaps it was intended for a specific brand of fan that draws less than 70ma. I wasn't going to try swapping it for that as it would have been more trouble than it was worth. The 24V output managed to put out 4 amps (I have a huge 6 ohm resistor), so I figured to press on.
Parts list?
There's a link to the actual modules in the post, the other parts are just stuff I took out of my parts stock.
Can the buck/boost converters be computer controls or is it all manual?
It's all manual, no computer control. I don't really do any automated testing here, all of that stuff is behind me since I retired. :)
 

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Discussion Starter #10
If you follow the two links, all the "working" parts are there. The only extra is my little 12V module to run the fan since it didn't run on their fan output. This power switch, power jacks, and line cord are all pretty generic. The 80mm fan was one I had from doing computer builds. The case was this one: Jameco 18869 H2505-R CASE,INSTRUMENT,7.9"x6.3x2.5 GRAY CASE/END PLATES BLACK.
 

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Discussion Starter #12
With those components, yes. 20A at 30 volts is 600 watts!

The primary power supply is 120 watts max, and the two panel modules max out at 5.1 amps output power. This wasn't intended to be a welder, rather a bench supply for slightly more delicate devices. ;)
 

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Maybe 20 amps is too high. I need a digital level power supply and something to run motors. Well I did... my O scale motors kinda sit right now. I have a standalone 20v 6 (?) amp power supply I was using for that ... maybe that's enough. But I thought I read those motors can peak much higher.
 

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Discussion Starter #19
John, this is a nice simple project. Well engineered I might say.
Do you have a handle that doubles as a rest. to point the face up.
I didn't add a handle, I really made it for the bench, it's parked beside another power supply and my 'scope. A handle would be a nice touch if you wanted to carry it around.

Ok ok, I was wondering about stalls and peak draw at start up...
A motor stall can exceed 5A, true. If that happens, the power modules all have excellent current limiting and will shutdown. You can also set the max current output for critical applications if desired. One of the screens you can access allows you to set the max temperature for each panel module, if it exceeds that, it shuts down to avoid damage.
 
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