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Lab on a budget 2/3 - Cheap Power Supply: Better than a stack of 9V’s

Part two of my series “Lab on a Budget” I want to talk about the power supply I just bought via Amazon. I was in need of a second power supply for my home lab bench for some time now. Having only one supply was starting to get restrictive and, as I mentioned in previous post, my existing supply is becoming unreliable. I was looking for something with specs close to my existing supply. I wasn’t looking for anything super fancy, a bazillion amps, or super precision or anything like that. I decided to roll the dice on a cheap power switching supply from Amazon – Made in China. $38.71 and Prime shipping. Can’t beat that.

This is a 0 – 30V 5A supply. It has a nice LED volt and amp meter on it with adjustable regulation and current limiting. Pretty slick. A week or so after ordering the supply it comes in the mail and I open it up. The first thing to strike me is the brand name on it. The images on Amazon indicated that there was no brand name on it at all.

When I opened mine, it had a brand name on it (*snicker*).

I guess this power supply isn’t going to be the one I recommend for the high school electronics class a friend of mine teaches.

Anyway, I didn’t have the luxury of voiding the warranty or potentially damaging the unit by opening it up but I assume the internal construction has many MANY technical no-no’s, all kinds of cheap shortcuts and its fair amount of hot glue. What do you expect for $38.71 shipped? I also don’t have the proper equipment to properly load test this thing yet, so I’ll save that for another article. When I have that equipment.

What did I do? I did a low budget, ghetto battery of tests. Consisting of loading it at 1 Ohm and turning up the voltage until the limiter kicked in around 5.25V when the current hit 5 Amps using a Radio Shack power resistor(which seemed about right for a 10% tolerance). I connected various power resistors and limited-out at other voltage levels too. Voltage remained on target. I compared the internal meters with my bench meters loaded at 100 Ohms. The internal meter was within 10mV and 1mA of my bench meter. The most scientific test of all was when I flicked the power on and off REALLY fast with my oscilloscope connected and the voltage set at different levels where, much to my surprise, I didn’t see any spikes unlike my existing supply.

During these tests I noticed 3 things. The first thing was the knobs. They are REALLY REALLY tight. Holy cow! I had to resist the urge to use a wrench or something to turn them. After working them back and forth a bit, they got a little easier, but they are still pretty stiff.

The second thing was the voltage adjustment knobs and their resulting values. Like most supplies, this unit has a fine and coarse voltage adjustment. What’s interesting about this unit, is that if the fine adjustment is all the way up, the voltage will never go to zero. It sits at about 1.2V until you turn the fine adjustment all the way down. Compared to my existing supply, that’s weird. My existing supply, the coarse adjustment will take the output to zero. I think I know WHY the new supply does this, but I’m not going to try to explain it here and expose my ignorance when I turn out to be way off.

The third thing is the fan. It’s REALLY loud. I don’t think there’s anything wrong with it, but it’s just a really loud cheap fan.

It’s a nice looking unit, seems to work well enough for most tinker/hobby types, and with some carefully placed paint on the brand name (to keep the giggling to a minimum), this would work for a basic 6-12 electronics lab. If you need better precision or less uhh…nuance… you just simply need to buy a better supply.

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