Hi all,
recently I bought an Arduino Mega clone, a DFRduino Mega, and also got a PSU to run it on when its not connected to the PC. The PSU is rated at 12v 300mah which I believe to be inside the tolerance for the Arduino boards. But after leaving the board connected the the mains PSU for a while, I noticed it had lost power. I then noticed that one of the large yellow capacitors right next to the power adapter had blown its top off, as well as the usual smell of burning, I also noticed one of the voltage regulators was very hot (the one closest to the PSU jack). The component on the Eagle file of the Mega is C6, a 100u capacitor. Do you think the PSU was faulty and put a surge into the board? Can anyone recomend a stable PSU for the boards? The PSU is now dead but the Arduino works off USB power.
Thinking of going to PSU supplier and asking him to pay for a replacement.
To quote "mAh" for anything other than a battery is fairly unusual.
It may be that the supply is unregulated, and knocks out consideralbly more than 12V. Have you tested with a multimeter?
as well as the usual smell of burning
If the smell of burning is usual, I think you need to re-think your power supply issues.
I did try putting a multimeter on the PSU afterwards but couldnt get anything from it which lead me to believe it was dead but I've just had another go now and all I can get is 0.34v reading on the multimeter. I stuck the PSU from a Linksys router on the multimeter and got a constant 12.12v from it.
Interestingly as a test I stuck this PSU in the Arduino and it leaped into life. I've touched the voltage regulator near the power jack and its not even warm.
I wish I had tested the PSU before plugging my Arduino into it. I bet it was putting out loads more than the stated 12v.
So the next question, what is the capacitor on the board used for? Can I solder any normal 100u cap in its place? The capacitor has now crumbled to nothing and there are just the metal terminals left that are not connected to anything yet the board is working.
I was wrong stating 12v @ 300mah for the PSU, it didnt have the 'h' on the end!
Smell of burning was joke - the board did smell after the cap popped but not any other time! Well... not all the time.
Power supply ripple filtering, and meeting the specs for the voltage regulator (voltage regulators like to have a capacitor "near" their inputs (and outputs) to prevent high-frequency mis-behaviors of various sorts. Probably with a good regulated switcher like your linksys supply you don't need anything, but it ought to have a cap. Note that the cap is not in the circuit at all if you're running of USB power.)
Can I solder any normal 100u cap in its place?
Yes. You can probably stick leads of a normal cap in the Vin and Gnd pins of the lower shield connector as quick and dirty workaround. "near" the regulator is a relative thing, after all...
Your metering experiments suggest that the other supply MIGHT have been an AC supply...
Hi all,
The only thing I have been able to find out is that the capacitor that blew was a polarised 100u, but I dont know what voltage it was rated at; what voltage should I make the replacement?
The PSU I used is on this page with the model number LN3071. I got it in an Arduino starter kit from http://www.earthshinedesign.co.uk/ and the guy that runs the site said the Mega is different from the Duemilanove and I shouldnt have used it on the Mega... but on Arduino.cc both boards have the same power requirements and ratings and should have run happily on 12v.
I don't know for the original Mega. But Seedstudios Mega's "equivalent" Capacitor (if you can call it like that) somewhat less than 24V. Quite easy to find out..... if you choose the hard way
Sorry to be a pain, but what's the hard way? Put it under a multimeter? [even more] Google searching? The markings on the capacitor are unreadable and the one next to it, although being a 100n capacitor, it has no marking to show the voltage. The one that blew was polarized, does the replacement need to be?
The "hard way" means allowing the magic smoke to escape from any electronic component by careless or deliberate overloading.
A fried polarized component must be replaced with a polarized component (and with the proper orientation) unless in the rare case where the schematic says an unpolarized replacement is allowed.
A fried polarized component must be replaced with a polarized component (and with the proper orientation) unless in the rare case where the schematic says an unpolarized replacement is allowed.
I don't know if that's true in the case of capacitors. In theory, non-polarized capacitors should be usable anywhere, while polarized caps are only usable in SOME places. In practice, you almost always ended up with polarized caps beyond a certain capacitance value, because the only technology that gave you the needed capacitanace in the space required happened to result in polarized technology. These days, other technologies have advanced, and you CAN get high-value (relatively speaking) capacitors in non-polarized ceramic technology. I have some 100uF caps in something like 1210 SMT size that are a bit mind-boggling, and 10uF in 0805 (TINY!) packages are pretty common (low voltages, though. The input cap on the Arduino and Mega (which ARE the same) should be 47 to 100uF at 25V or so (16V is too low for an unregulated 12V supply, and 25V is the next standard voltage), and needs to be shorter than 7mm to avoid interfering with shields. This tends to narrow the choices a great deal.
just to clearify: 24V with a notebook-adapter with 4A killed it instantly
(on Seeed's Mega)
Just take a xy-µF cap with a max-voltage (+some volts) you don't wanna exceed as replacement. I don't know for sure, but if you feel uncomfortable putting an unpolarized cap as replacement, just take a polarized. Won't be more expensive.
Might? I would put money on the fact that is was, why else would a capacitor blow like that.
Well because the Arduino has a series polarity protection diode and the 100mfd regulator input cap (that makes a half-wave rectifier), I would suspect that one could run fine with a AC input voltage wall wart, as long as the peak voltage was under the caps voltage rating and the current draw was small, as in just the on-board components.
Bottom line, AC input would not damage the cap unless it's peak voltage was high enough to exceed the max working voltage of the cap, same as if using a DC wall wart.
I've plugged in an AC adapter, rated for 12v at some 3.something amps into my Duemilanove, without any damage.
I plugged it in for I'd say 10 seconds or so, I looked at the supply and just read the 12 volts part.. I assumed it was DC. Nothing worked while it was plugged in, which is expected when you're trying to use the wrong supply.. but definitely no damage to the board. Every LED works, able to upload, etc etc.. I use the board for programming my bread-board Arduino's when testing.
But I'd have to agree, only thing that should make a cap blow like that would be too high of a max voltage. (Unless of course, it's a low-quality design, missing some important components:D
@Pumbaa, poor Mega! :X lol most of the regulators on the Arduino's can only handle a MAX of 18 volts, but going over 12 isn't recommended, you'll lose way too much energy in heat.. and a good chance you'll damage the board. (especially if it's NOT regulated.) I have a 12v regulated supply at 1amp, it's from a Linksys router, it measures at 11.49 volts with no load, and a little over 11.50 when the Arduino is plugged in and running.. it gets warm but NOT hot. I've let it run for about an hour.. still was only warm.
EDIT:
If the PSU is dead.... are you SURE you didn't have a short somewhere in your Circuit? Arduino's have a resettable fuse just for that case.. but I'm not too sure about PSU's.. considering if you're playing with anything rated at more than a couple amps.. and you short it out, you're in for a show!
ALSO, the Seeeduino Mega's voltage regulators are rated for LESS max voltage then the Duemilanove's, but they're LDO (low drop out). So anything over 12v is definitely pushing it! (You can get away with as low as 6v though, I believe)
So did you replace the cap? I hooked a universal laptop adapter and blew the cap within a half a second. Looking on mouser for a suitable replacement. I was thinking maybe this:
sorry can't have links in my post... copy and paste
but then I really don't know if it will work?
My electronics knowledge is lacking. But I'm learning, namely not to hook any old power supply to the mega in search of something to power all my servos. :o
