A cheap bench supply, measured
I bought one of the generic 30 V / 5 A switching bench supplies sold under a dozen different brand names. My old linear supply is heavy and only does 2 A, so I wanted something for higher-current work. Before trusting it with anything I care about, I measured it.
Setup
Load: an electronic load in constant-current mode. Voltage: a handheld multimeter I trust more than the supply's display. Ripple: a scope at 20 MHz bandwidth limit, measured with a short ground spring rather than the long ground lead.
Display accuracy
| Set | Display | Meter |
|---|---|---|
| 3.30 V | 3.30 V | 3.27 V |
| 5.00 V | 5.00 V | 4.96 V |
| 12.00 V | 12.00 V | 11.93 V |
| 24.00 V | 24.00 V | 23.86 V |
It consistently reads about half a percent high. It's close enough for most things. When it matters I check with the meter anyway.
Ripple
At 12 V I saw roughly 15 mV peak-to-peak with no load and around 40 mV at 2 A, mostly switching spikes. That's fine for motors, LEDs and charging. For audio or anything analog and sensitive I'll keep using the linear supply.
Turn-on overshoot
This was the main thing I wanted to check. I set it to 5 V, disconnected the output, and toggled the mains switch. I saw no visible overshoot on the scope. Toggling the output enable button was also clean. Good.
Annoyances
- The fan runs at full speed all the time and is loud.
- The rotary encoders skip a step now and then if you turn them fast.
- The banana jacks are a bit loose. I'll probably replace them.
Overall it's worth the money as a second supply. I just wouldn't make it the only one on the bench.