Earthing the machine
Posted: Sat Nov 09, 2019
So I don't know how typical this is, but ...
I've just taken delivery of a new laser, a largish-bed Chinese special from Ebay, and I was giving it the once-over before switching it on. I found a few things:
1) I recall seeing Russ saying his wiring was pretty neat, and mine is too, but being the cynical type I disassembled the earthing-pole connection from the mains inlet to the chassis. After taking it apart completely, there is no bare metal for the connection between the earthing-pole and the chassis itself, so the "earth" connection is really going through the paint on the sheet metal before it gets to a real earth. On my Fluke multimeter it was reading 230 ohms resistance between the "earth" and true ground. I sanded down to the metal and now it reads 0 ohms.
I wonder how many machines are poorly earthed like this ? I mean, it's not a huge resistance, and a dry human body is about 100k ohms, but a wet/damp hand is ~1000 ohm and high-voltage currents quickly reduce the resistance of the human body to ~500 ohms; I personally wouldn't like to be part of that potential divider when there's 15,000 volts hanging around.
[vent mode=on]
2) The buggers sent me a 220v laser cutter when I specifically asked for a 110v system, being in sunny California. It's not the end of the world, they shipped a 110->220v transformer as well, but I've heard bad things about the residual currents and getting shocks after it's powered off with those things. I have 220v in the garage, I'll just have to get the electrician to come and wire up something I can use. It's just bloody annoying.
The only way I found this out is by sticking a cell-phone underneath the PSU to snapshot the label that is otherwise hidden. No documentation, no "wire it like this", nothing. Oh well.
[/vent]
I guess the point of this post is "always check", even when it seems stupid. I had even switched the machine on (but not the laser yet) and it was working (presumably because the other psu's are auto-switch), homing and panning the head. I'm waiting on a real water cooler (the CW-3000 they send is pretty awful) and some ducting for the vent/filtering - otherwise I might have jumped in there and possibly screwed up my laser PSU...
Enough. I'm going back to see if there are any other surprises
I've just taken delivery of a new laser, a largish-bed Chinese special from Ebay, and I was giving it the once-over before switching it on. I found a few things:
1) I recall seeing Russ saying his wiring was pretty neat, and mine is too, but being the cynical type I disassembled the earthing-pole connection from the mains inlet to the chassis. After taking it apart completely, there is no bare metal for the connection between the earthing-pole and the chassis itself, so the "earth" connection is really going through the paint on the sheet metal before it gets to a real earth. On my Fluke multimeter it was reading 230 ohms resistance between the "earth" and true ground. I sanded down to the metal and now it reads 0 ohms.
I wonder how many machines are poorly earthed like this ? I mean, it's not a huge resistance, and a dry human body is about 100k ohms, but a wet/damp hand is ~1000 ohm and high-voltage currents quickly reduce the resistance of the human body to ~500 ohms; I personally wouldn't like to be part of that potential divider when there's 15,000 volts hanging around.
[vent mode=on]
2) The buggers sent me a 220v laser cutter when I specifically asked for a 110v system, being in sunny California. It's not the end of the world, they shipped a 110->220v transformer as well, but I've heard bad things about the residual currents and getting shocks after it's powered off with those things. I have 220v in the garage, I'll just have to get the electrician to come and wire up something I can use. It's just bloody annoying.
The only way I found this out is by sticking a cell-phone underneath the PSU to snapshot the label that is otherwise hidden. No documentation, no "wire it like this", nothing. Oh well.
[/vent]
I guess the point of this post is "always check", even when it seems stupid. I had even switched the machine on (but not the laser yet) and it was working (presumably because the other psu's are auto-switch), homing and panning the head. I'm waiting on a real water cooler (the CW-3000 they send is pretty awful) and some ducting for the vent/filtering - otherwise I might have jumped in there and possibly screwed up my laser PSU...
Enough. I'm going back to see if there are any other surprises