Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: kolias on January 28, 2011, 12:50:07 AM
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I’m in the final steps of wiring my new CNC and I have a question:
About 1.5 years ago I had a problem on my 1st CNC with the Z axis plunging uncontrolled and Hood had suggested installing a 0.1uF ceramic capacitor on the limit switch I had installed on the Z.
This capacitor fixed the problem and now on my new CNC I wonder; is it a good practice to install one of this capacitor in all of my Limit / Home switches, as per attached schematic, or it is better to wait to see if I have any problems?
Thank you
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Yes, you better connect a 0.1uF between input and ground, it will filter any small voltage variation or noise pick up by the wire and use shielded cable.
Jeff
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Not lucky lately..... I have 3 capacitors left from last time and each is 104 0.1uF. So I went to the store BUT they dont have these any more and the give me one which with my magnifying glass I can see 102, 003, RAV, C5K (102 is clear but the other ones may not be correct - very fuzzy).
I also received my 36V, 9.7A power supply unit from China today and I'm ready to adjust what needs to be adjusted and connect the motors to the control station and....we will see what happens next.
My question: is it ok to use this 102 capacitor in one axis and use the other three 104 on the remaining axes?
Or just leave one axis without capacitor?
Thanks
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There is some information on the capacitor code markings here http://www.csgnetwork.com/capcodeinfo.html
Tweakie.
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There is some information on the capacitor code markings here http://www.csgnetwork.com/capcodeinfo.html
Tweakie.
That is cool Tweakie but still dont know if I can mix capacitor size or if the 102 value is good or not
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Basically the 102 (0.001uF) will not have the desired effect so don't bother with it.
Best get some of the 104 (0.1uF) like you used before. ;)
Tweakie.
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I will do that, thanks
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Dear Friends:
I have the same problem with the Z axis limit switch. Sometimes the limit switch input activates itself. But the worst thing that in other 2 occasions has been generated an overvoltage that has burned the input of the breakout board because of the Spindle. For this I designed an additional circuit with optocouplers in order to protect this input. For this, it requires incorporating a 0.1uF ceramic capacitor to see if this can attenuate these voltage surges as explained in the attached image. The circuit usually works quite well. The problem that when incorporating the capacitor and activating the limit switch, the system does not activate. However, when the capacitor is removed, the circuit is activated normally. Is it possible that the capacitor is wrongly connected or some other component is missing in the circuit? I am not an expert in electronics and it is likely that I am making some basic error in this. For this reason, I ask for your help. I have also incorporated shielded cable in the spindle and in the limit switch of the z axis to solve this problema.
Best regards
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Yes, the cap is in the wrong place. It should be across the opto input.
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Thanks for your answer. I have a doubt. The led should stay on once the limit switch is disconnected for a short time. This due to the energy stored by the capacitor? This would suggest that the circuit works well?
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The delay on switch opening is a few tenths of a millisecond at most. The Spice Simulation shows the switch input (yellow) and the opto current (red).
The point at which the opto output opens depends on the version of the PC817 used. Peak OPTO LED current is about 15 mA. If the turn-off point is 2 mA then the delay is 0.1mS.
Diode D10 is in the simulation to make the V1 voltage pulse generator behave like switch contact. It isolates the voltage pulse generator when low to simulate the open switch contact.
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Thank you very much for your kind response. And for taking all the trouble to explain it to me as well as you have done. I have nothing but one last question. Do you think that the implementation of this capacitor in this circuit can protect my breakoutboard from burning out due to overvoltages produced by the spindle?
https://youtu.be/_qTjYUyNpGs
Best regards