Joe's 1000x600x200 steel and aluminium router started

[devmonkey]

Thanks guys, lots of inspiration here.

The DDCS has two estop inputs but one is difficult to access on the MPG port. I have an idea how to sort this now. Currently I use the output of the safety relay to switch the low side of the contactor coil and also signal low to the DDCS estop input which is configured to go into emergency stop if this signal is high. I was looking to integrate the alarms on the estop switch side of the safety relay but this is wrong, instead I can put them on the output side. Take a resistor to +24v then series the NC alarm outputs via the same safety relay contact to ground. Take the DDCS estop input from the resistor.

With this configuration the alarms will only estop the DDCS not the contactor, but when the safety relay is tripped both DDCS and contactor will estop. Million dollar question, do I need a diode to prevent current flowing from emitter to collector through the alarm NPNs into the DDCS input when the safety relay is open? My analogue electronics is extremely rusty.

[Kitwn]

Analogue is easy, just work out where the current will flow. Ohm's Law plus Superposition Theorem equals The Answer.

[devmonkey]

Good news machine is moving, very nicely indeed, I will post some video tomorrow.

I have a question about a potential issue I've discovered with the 24v dc smps I'm using for powering the controller and proximity switches. The unit is a high quality double insulated (no earth connection) TDK-lamda din rail SMPS and I've used them in automation projects before. However this is the first time I've noticed this issue.

Basically you get a slight tingle (barely noticeable electric shock) when touching both DC ground and mains earth.

I believe this is down to the 'Y' capacitor used in the SMPS to reduce EMI, it is a small capacity capacitor that couples input to output (when there is no earth connection) and is required by all SMPS to meet EMI regulations, however it has the nasty side effect of raising the DC output to around half mains voltage wrt mains earth. The capacitance is tiny so it isn't dangerous.

I noticed it whilst leaning on the earthed machine and holding the shield of my db37 cable which is connected to dc ground.

I've checked the unit with a megger to prove to myself it is properly isolated.

So do other people see this, does it matter? What do other people use for the 24v side of their systems? I might substitute it for a small power supply with an earth connection (class1??).

EDIT:
Just ordered a class1 meanwell unit MDR-60-24, this has an earth connection and the datasheet shows it's 'Y' capacitor is connected to it.
https://www.meanwell.co.uk/pub/media...DR-60-SPEC.PDF

Cheers, Joe

[Neale]

Good news machine is moving, very nicely indeed, I will post some video tomorrow.

I have a question about a potential issue I've discovered with the 24v dc smps I'm using for powering the controller and proximity switches. The unit is a high quality double insulated (no earth connection) TDK-lamda din rail SMPS and I've used them in automation projects before. However this is the first time I've noticed this issue.

Basically you get a slight tingle (barely noticeable electric shock) when touching both DC ground and mains earth.

I believe this is down to the 'Y' capacitor used in the SMPS to reduce EMI, it is a small capacity capacitor that couples input to output (when there is no earth connection) and is required by all SMPS to meet EMI regulations, however it has the nasty side effect of raising the DC output to around half mains voltage wrt mains earth. The capacitance is tiny so it isn't dangerous.

I noticed it whilst leaning on the earthed machine and holding the shield of my db37 cable which is connected to dc ground.

I've checked the unit with a megger to prove to myself it is properly isolated.

So do other people see this, does it matter? What do other people use for the 24v side of their systems? I might substitute it for a small power supply with an earth connection (class1??).

EDIT:
Just ordered a class1 meanwell unit MDR-60-24, this has an earth connection and the datasheet shows it's 'Y' capacitor is connected to it.
https://www.meanwell.co.uk/pub/media...DR-60-SPEC.PDF

Cheers, Joe

Why leave the 24V supply floating wrt earth? Take the 0V connection to the control box star point and all will be well. Can't see any reason not to ground it. That's what would normally be done - my control box has a 24V smps and a 5V+12V smps and all the 0V connections go straight to the star earth.

[devmonkey]

Why leave the 24V supply floating wrt earth? Take the 0V connection to the control box star point and all will be well. Can't see any reason not to ground it. That's what would normally be done - my control box has a 24V smps and a 5V+12V smps and all the 0V connections go straight to the star earth.

Is that really recommended? Doesn't it defeat the purpose of the galvanic isolation?

[devmonkey]

Should add the noise is coming from the stepper drivers as it only happens when the stepper is moving, so basically the EMI filter in the 24v smps is filtering what comes into it and coupling it to the 24v DC output which causes the DC output to float relative to mains earth because the neutral and earth are coupled at the electricity company's box in the street. I will fit an EMI filter in front of the toroidal stepper PSU to suppress noise returning back up the supply and into the 24v SMPS (and the rest of the house).