More polyfuse-related troubles.
Originally shared by Mark Zimmerman
I let some of the smoke out of my Prusa Mendel this morning and was wondering what the problem might be. It looks like it was just the 12vdc input filter cap as everything continued to run while I scrambled for the plug. Are these caps easily popped or is this typically indicative of another problem?
So glad I bypassed my 12v polyfuses in favor of an inline automotive fuse.
The polyfuses cause so much trouble, pity there are thousands of RAMPS out there. Really time for a new iteration, RAMPS v2 anyone?
Too much current coming in or being drawn. Something is wrong somewhere on the board, or devices it powers. What is the rated current the board can supply, and what is the draw current of the motors? Did a motor stall and start drawing a lot more current?
@Daniel_Joyce stalled steppers don’t consume any more power than when turning, and if something had started drawing way too much much current, the fuse would have opened up and sat there with zero heat produced.
Instead, what these fuses tend to do, is that they develop a marginal resistance under perfect conditions, which makes them heat up, which in turn further increases their resistance until they end up in an unfortunate equilibrium where the fuse burns some of the voltage that could instead heat the heated bed or hotend, but instead only heats the fuse. Some setups simply have their heated beds taking forever to heat, others, like this one, kill the fuse.
Personally, i’ve simply shorted the fuses on my RAMPS - the idea behind that is that the over-current protection on my PSU will shut it down if anything really short-circuits.
Or you can but fuses between your PSU and the ramps. That’s how all my CNC machines are done. I always though it was strange the fuses resided on the board, but I guess it forces the safety measure instead of assuming the user will implement it.
throw out the broken fues and switch the Heated bed with a Relay instead of the Mosfet on the RAMPS.
Could even use a solid state relay, with a good duty cycle, would avoid temp spikes. But I don’t know how massive the plate is.
sure. The Prusa heated bed 2 variants I have in use on my printers draw between 10 and 12 A at 12 V, so 120-144 W. I switch them with a finder Type 40.61 relay. It is rated for 250V AC or 30V DC 16 A and costs a whopping 2.60€ when bought in small numbers.
voir pour la modification du filtre avec un plus gros condensateur