Circuit Boards Safety

Okay, I have most of the parts for the circuit boards and I'm getting ready to start plugging them in. But I am looking at this 50V 4700uF capacitor and I'm concerned about safety. Here is what I know: Big capacitors can hold a charge long after they are powered down which can kill someone who isn't careful. I have limited room in my studio apartment so I'll likely be taking things apart after I play with them and putting them away.

Is this thing safe to touch after I power it down? The rest of the capacitors are small enough I don't consider them a major concern.

I'd love to know your thoughts on safety. And if there are some guidelines I'd happily write them up and make them ready for the wiki - or have I missed them?

Thank you!

Corey Cox.

i'm not entirely 100% sure, but i think its fairly safe for a couple of reasons:

1. the 50v rating is just maximum voltage, the project itself uses 12v which is pretty safe.

2. when you power down the device, you can tell the capacitor drains, because the light stays on for a couple seconds then slowly fades out.

you should be safe, although i wouldnt deliberately touch it just to be safe.

Yup, as Zach says, the supply voltage is 12V. 12V is safe. You can touch the power capacitor leads directly (while switched off or even while running) and you won't feel anything.

Strictly speaking, there are a couple of places where higher voltages can occur, which is in the serial comms and back-EMF from the motors. The comms signals are very low power and can't cause a shock. The back-EMF is suppressed as much as possible. It is possible that if you could get your fingers in the motor circuit of one of the larger motors while it is running, you may feel a little tickle on your fingers, but it wouldn't be dangerous.

The most dangerous part of RepRap is probably the heating element, which can obviously get quite hot. You could potentially burn yourself on some of the motor drivers too. And getting your hair caught in a motor assembly could be unpleasant. If you put your tongue across the motor connector while it is running, you could have some fun

If you use a PC power supply to drive a RepRap, that can be quite dangerous. They are switched power supplies and internally have extremely high voltages that also carry high currents. They can kill. Capacitors in mains power supplies can also store dangerous voltages. As long as you keep it nicely tucked away in its original caging though, you will be fine. Never open a PC power supply if you don't know what you're doing.

The heating element is no more dangerous than a soldering iron, in fact considerably less dangerous in my opinion in that it is in a fixed mount and not being waved around by some dude with an itch to solder components on a PCB. :-D

I've fried myself far more often on my soldering iron. So far I've yet to hurt myself on the extruder barrel. As well, I've touched my extruder barrel many times with no more than a slight scorch and mine runs at twice the temperature of the Mk 2's that extrude CAPA. About the only bit that can brand you is the leads from the nichrome heating coil to the to the 12v copper leads. The bits of nichrome hanging free in the air can get red hot.

A kill switch would be a good safety requirement.

that ones pretty simple... just pull the plug and the machine will grind to a halt.

of course... you're welcome to make that as fancy as you want, with an actual button of some sort.

i'm not familiar with the interface software, but it would be a good idea to add a 'pause/stop' feature to it when you're printing (if its not already there)

Some PC power supplies (particularly older ones you're likely to scavenge) have a power switch on them. It's not quite the big red button kill switch, of course... That would look much fancier.

The software has an option to pause after each layer or after each segment, and can be turned on at any point during production. So that gives you a way of pausing if you want to, although it's a few mouse clicks away.