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Bad power supply unit might kill your MCU, do not buy!

Tags Grind My Gears  AliExpress  FNIRSI DC580 

On my balcony I have a very small solar panel setup that I use to keep a small car battery charged up. This battery is wired into some USB plugs into my home office desk. They are powered from 12V battery and provide 2 powered USB sockets. I got two models installed; one normal USB and one that supports quick-charge.

plug Normal

plug Quick Charge

These are advertised as ‘marine’ plugs, you can find them for around € 10-12 on amazon.

This setup has been working great, I use it to charge all my mobile devices (Watch, Phone, bike clock, etc.). In general i produce more energy then I consume this way.

Given that I often do small electronic experiments for work, I thought it would be nice adding a small power supply in my desk. I have used the RD DPS3005 modules before, but these can only step down (buck converter). So after looking around the FNIRSI DC580 looked nice.


It has the right input/output range. After installing it on first looked fine but I saw some oddities on it own voltage measurement when turning it on (it showed a higher number, then stabilized to the right value).

So some measurement where in order. A quick test (without load) showed:

3.3 v 5 v 12 v 32 v

As you can see there is some ridiculous overshoot happening. On 3.3V, that I often use for micro controllers, it overshoots by 4.3V providing it with 8.3V.

Now this measurement is not completely fair, as there is no load on the power supply. So I hooked up a 100Ohm resistor, this is a higher load then I would normally add to it.

3.3 v 5 v

As you can see the overshoot goes to the correct value a lot quicker, but it still very high (> 2x).

If we zoom in a bit:

5 v

We see a huge 40ms over voltage, then some ringing that drops to 1/2 the requested voltage. This is not good, and if you have sensitive electronics could easily kill it.

Now if we compare it to another (switched) power supplies:

3.3 v 5 v

It is a bit slow to ramp up, but no overshoot.

Now if I compare this to a quality brand power supply (also switched power supply):

5 v

While this is not a completely fair comparison as this one still cost around 300$ in damaged state on e-bay (Delta SM 7020-D), it does show we can do better.

But even a simple delta power supply from 1978 does this way better:

5 v

(As you can see, this is not a switching power supply.)

Now the comparison with Delta Electronika Power supplies is not fair. We are talking about order of magnitude more expensive supplies. But having said that, what the FNIRSI DC580 produces is not acceptable and can possibly damage the device your working on. I would not use this beside maybe charging a battery or running a little motor. I have reported it to the FNIRSI and waiting for a reply from their engineer.

But the conclusion is simple, DO NOT BUY.

To show that a cheap Chinese can do a lot better, this is what my DPS3005 does:

5 v

That is closer to to the high end power supplies.

On a side note, they have a nice wired out serial port that I thought I could use, but they don’t make the protocol available. Unless you run windows and want to use their software, that is useless.

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