Does this power pack look dodgy?

Using Arduino General Electronics
1

I've been running a Uno for years in a dedicated location (garage door open detection). In the last few days it has failed repeatedly. I swapped over the processor board (the Uno) with no effect. Then I tested the power pack which supplies 9 V to the power-in jack. With AC coupling the input looks like this:

Those spikes look a bit of a worry? Or not? That's about 360 mV every 285 µs. Does that look normal? Or not?

The supply itself looks a bit the worse for wear:

Maybe it is a bit tired. What do you think?

2

Do you have a backup power source to try?

Paul

3

I've plugged it into a USB charger plug-pack-thing instead - using the USB input. That's probably better than giving it 9 V and having it turn 4 V into heat day in and day out. So far it's been OK, but it has taken a few hours to fail in the past few days.

4

Wonder what might be living in that PS, one of those badass Aussie spiders maybe?

5

Good suggestion. A red-back maybe!

6

It just failed again, so out of the three major parts:

  • Arduino Uno
  • Power supply
  • Ethernet shield

By a process of elimination, it appears the Ethernet shield is faulty.

7

A common problem is el cheapo switch mode power supplies is dodgy electrolytic capacitors which go hi ESR over time, and stop acting like capacitors.
That voltage spike in the waveform is a sign of a hi esr capacitor.
Sometimes you can physically spot them as they start to bulge.

8

Dont skimp and get cheep power supplies, especially not mains ones, I've seen some
dangerously unsafe units emanating from China with 4mm clearance between 240V and
low voltage side (some idiot routed a trace under the opto-isolator reducing the clearance
from 12mm...)

9

MarkT:
Don’t skimp and get cheep power supplies, especially not mains ones, I've seen some dangerously unsafe units emanating from China with 4mm clearance between 240V and low voltage side (some idiot routed a trace under the opto-isolator reducing the clearance from 12mm...)

I would be equally concerned about what sort of insulation is in the transformer that you cannot see.

10

Careful the smoke might leak out......

Tom..... :slight_smile:

11

The picture seems to show its red back.

TomGeorge:
Careful the smoke might leak out......

Good idea, smoke out that spider !

12

Did you break the case trying to fit it into an Aussie socket? :slight_smile:

Russell.

13

MarkT:
Dont skimp and get cheep power supplies, especially not mains ones, ...

Well, it came from Adafruit, so it wasn't a el-cheapo from eBay.

Did you break the case trying to fit it into an Aussie socket? :slight_smile:

I used a travel adapter.

14

And a hammer? :roll_eyes:

15

Actually I think that is the second such power pack that has basically disintegrated. It's a bit of a worry because if you pulled it out of a live power point, and the case just crumbled, then your fingers could touch 240 V mains.

16

[quote author=Nick Gammon link=msg=2329344 date=1437777431]
Actually I think that is the second such power pack that has basically disintegrated. It's a bit of a worry because if you pulled it out of a live power point, and the case just crumbled, then your fingers could touch 240 V mains.
[/quote]Seriously, please report it to your supplier, stressing that it is a serious safety issue. I can't be certain just from the picture but this sort of plastic moulding usually consists of ABS with a talc + carbon filler. The filler improves the strength but if too much is used (to save cost) it becomes brittle.

Russell.

17