Fast circuit breakers

Are there any available, fairly cheap circuit breakers that would protect and arduino project from unexpected current surge ?

hsteve: Are there any available, fairly cheap circuit breakers that would protect and arduino project from unexpected current surge ?

Well while on USB power the board and project is protected by an on board 500ma thermofuse. Most simple fuses and circuit breakers do not operate fast enough to ensure no damage to downstream components, they are designed to protect the voltage source from over current draw.

It's basically a truism that the $5 MOSFET will usually blow first to protect the 10 cent fuse. ;)

Lefty

Can you be more specific on the type of failure you're trying to prevent? An example or something would help. :)

Any over current demands produced by motors, servos, or faulty connections (my incompetence basically). I'm building a r/c aircraft using xBees, motors and servos to move the controls and I don't want to overload the Arduino. I'm using a 9V battery and a Ardumoto motor driver, but Ill be adding things down the line, leds, camera module etc and I want to protect all this if I add too much stuff.

Your best protection against high current failure in electronics is to build the electronics to be very, very robust and basically short-circuit tolerant for at least 10x longer than the time it takes a fast-blow fuse to blow.

Fuses are not there to protect the electronics, they are there to stop a fire. And the closer you are to the fuses rated current, the longer it takes to blow. So 1A in a 1A fuse may take 10 seconds to blow, to throw out a rough, wildly inaccurate number.

BTW, if you mean a little 9V battery with the snap connector, they won't put out much power, and not for very long. That is really just six AAAA cells inside there.

No, it's a 9V LIPO from an R/C car, and thanks for the info.

I've not looked for one but you could use an electromagnetic fuse which pops with too much current is passing through.

I'll have a look for an em fuse.

So how about surge protectors on power points, they must do a similar job, protecting against lightning strikes etc ?

Inside a surge protector is the em fuse sure.

Protection against lightning? Maybe an expensive power block, but most don't .. if you look inside you'll find an Inductor coil and maybe a couple of Capacitors to smooth out and prevent small surges/flux.

Lightning would kill it along with everything else in a direct strike, if it's some distance away the then sure the surge protector works.. but never rely on it to save you in a lightning storm unless you buy one specifically higher end UPS can.

Well, there are a few things to consider here:

1) The power supply. If you're using the Arduino's built-in voltage regulator to convert 9v->5v, and you run your devices on that 5v rail, you can overload and damage the onboard regulator. Easy fix for that: Don't use the onboard regulator for large loads.

2) The I/O pins. There are a few things that can lead to an I/O pin's untimely demise -- namely, sourcing or sinking too much current from/to it, and excessive voltage. The pins are protected with diodes to either rail, so over/under voltages kinda end up being over-current problems. The fix for this depends on what's connected to the pin, but in general, you can help matters by using as much resistance between the pin and your peripherals as the application will tolerate.

Anything more specific depends too much on the details of what's-connected-to-what.

Fuses and circuit-breakers have their purpose, but they aren't a cure-all. Using one on an I/O pin would be pointless. You would have to get one rated to blow at like 30mA to do much good, and at that rating, you'll have to deal with nuisance trips on a regular basis. Not helpful. The better option is to limit the current that can flow in ordinary (but still fault) conditions, and accept that catastrophic failures can't be prevented with any certainty. At some point, you will let the smoke out. Wear it like a badge of honor, and then don't do that again.

cjdelphi: I've not looked for one but you could use an electromagnetic fuse which pops with too much current is passing through.

Yes, they are called circuit breakers, that is how they work.

Well I was not sure..

I've seen thermal fuses, regular fuses, em fuses, polyfuses...

Ughhh I don't like fuses lol

http://en.wikipedia.org/wiki/Crowbar_%28circuit%29

[quote author=Jack Christensen link=topic=209219.msg1537369#msg1537369 date=1389153995] http://en.wikipedia.org/wiki/Crowbar_%28circuit%29 [/quote]

Nice.... I'll stick to a polyfuse for now.

I guess a simple ntc thermistor could also be used..