We’ve all seen those cheap bench power supply units (PSUs) for sale online, promising specifications that would cost at least a hundred dollars or more if it were a name brand model. Just how much of a compromise are these (usually rebranded) PSUs, and should you trust them with your electronics? Recently [Denki Otaku] purchased a cheap unit off Amazon Japan for a closer look, and found it to be rather lacking.
Major compromises include the lack of an output power switch, no way to check the set current limit without shorting the output, very slow drop in output voltage while adjusting due to the lack of a discharge circuit, and other usability concerns. That’s when the electrical performance of the PSU got tested.
Right off the bat a major issue in this cheap switching mode PSU is clear, as it has 200 mV peak-to-peak noise on its output, meaning very little output filtering. The maximum power output rating was also far too optimistic, with a large voltage drop observed. Despite this, it generally worked well, and the internals – with a big aluminium plate as heatsink – look pretty clean with an interesting architecture.
The general advice is to get a bench PSU that has features like an output power button and an easy way to set the voltage and current limits. Also do not connect it to anything that cares about noise and ripple unless you know that it produces clean, filtered output voltages.
I have a similar one 30v 10A . Its ok for simple stuff and is better or just as good as most mid priced units .
all in all I would not use it certify anything but but its ok for mucking about semi seriously. If one is looking for low noise specs then maybe non switching power supplies would be better.
There are probably a bunch of rebranded ones that are essentially the same. I started with one that was good enough, then a couple months later it totally crapped out. Without too much to go on, and mains supplied power supply not exactly something I feel comfortable messing with, I bought … another one. Then I picked up a lab quality one at a ham fest for probably $50, maybe $100. It’s massive over kill for what I need so far, but definitely a personal case of buy twice, cried once (the second d cheapo still works) and was also proud of myself once. TL:DR for same $$ thereabouts get a used good one. About zero down side.
Used lab PSUs usually need replacement of most electrolytic caps, relays and pots, cleaning all connections and switches to work as intended. And they are hard-to-find things – I spent months to find one in decent condition. And then spent many hours to clean and service it properly. Fortunately I had all wiring diagrams and spare parts.
Honestly, today I would prefer to buy cheap Chineese one and add missing filters and features. This will give me much smaller, more effective and more powerful device.
Old stuff is nice and have it’s own aestetic value, but it’s not the best choice today. Especially if you buy some cool used lab stuff for cheap and then find out that to make it up and running, you have to find some unobtanium, or original spare part cost more than plane wing, or you have to buy another one for spare parts in hope it will not have the same problem. Of course you could win in that lottery, and get high grade equipment for cheap, but that’s not for certain.
Just adding filters won’t make a crappy supply into a good supply, usually the current control loop is useless, load regulation is horrible and gets worse when you add filters, and some have overshoots during power-on or power-off.
Good lab supplies regularly get replaced because of age, or because of simple defects like a broken knob. I recently got a really nice supply from TTI that blew fuses, it just needed 2 new diodes in the PFC rectifier.