Joe's 1000x600x200 steel and aluminium router started

[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?