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Questions about solenoid bed probes

Posted by Nprod 
Questions about solenoid bed probes
September 11, 2016 06:50PM
Hey there, i'm trying to add a compact solenoid bed probe for my printer based on a design from the ROBO3D forum here - [community.robo3d.com]

It seems like solenoid probes aren't as popular and i haven't been able to find much info on them. My main question is regarding the circuit - from what i understand an arduino board can't supply enough current to drive the solenoid, so a 12V->5V step-down board and a mosfet are required. Wouldn't it be easier to skip the step-down converter and just use a 12V solenoid hooked up directly to the PSU (as opposed to the 5V one proposed in the thread) with the same mosfet? Perhaps a 12V one would have too much holding force that it wouldn't allow the metal chuck to go upwards while probing? Please share some info on this!
Re: Questions about solenoid bed probes
September 12, 2016 10:12AM
I agree, a 12v solenoid would make more sense - except that quite a lot of people use 24V electronics these days. I was working on a solenoid activated probe a while ago and I got as far as finding a suitable 12V solenoid. But I abandoned it when I got the differential IR probe working well.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Questions about solenoid bed probes
September 13, 2016 07:35AM
I looked at the ROBO3D's specs and it seems to use a regular 12V supply. My guess would be that they probably couldn't find a suitable 12V solenoid on Sparkfun or Adafruit and went with that 5V one instead. I'll give these "Shindengen" 12V ones a try (pictured). They're roughly the same dimensions and about 2$ a piece.

Re: Questions about solenoid bed probes
October 08, 2016 08:25AM
Okay, the 12V solenoids just arrived and they work pretty well! They do get slightly warm when active for longer than a minute or two, but that's probably normal. Actuation force is small, so the only option when using a mechanical microswitch would be the way it's shown in the ROBO3D forum, with a lever and set up in the normally-open position. Opto-endstops probably make much more sense here. My next question is this - since it's 12V, would it be better use a relay and BJT transistor to activate it or would a MOSFET do the job just as well?
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