Problem- Electrical short?

[dsnellen]

I posted this under General Topics but here may be a better location. I really need some help/ideas.

I have a new P-C 690LR router. To do a tool zero, I put a clip on the bit and G31 down to the touch pad. The routine wasn't working. I tested the circuit by touching the clip to the pad and the circuit worked fine. As I continued to work with it, I noticed that touching the clip to the bit was causing sparks! Never had that happen before. The clip is connected to 5V and the zero pad is connected to pin #11 (C10). The touch pad works flawlessly with other routers. The computer, electronics and router have a common ground.

I used a voltmeter to do some testing.

1. There is a 6v DC flow when touching the 5V clip to the router body when the router is plugged in (but turned off). It's the same whether plugged into the Relay Board or directly to a wall socket. This makes some sense as I am connecting 5V DC to ground.

2. The voltmeter also shows a small AC voltage. This is puzzling as the Relay Board is switching the black wire so logically there is not an AC circuit unless there is a current leak between the common and ground wires.

3. I have a solid ground among all the parts. The Ohm meter show 0 between the router body/bit and the table. The ground between the router and table also exists when the router is plugged into the wall socket. I have what Al calls a "ground star".

I'm thinking the sparks are caused by the 5V DC C10 circuits coming in contact with a small AC charge. Although the router will start and run, I am thinking it may have an internal short/electrical issue somewhere and that I should return it. Anyone have any thoughts?

Thanks for your ideas.

Dave

[dsnellen]

Come on guys, I need some input here. Al, where are you?

Today, I tested the ohms between the ground & the hot and neutral wire. Nothing. So why the current flow mentioned above? I am sending the router back tomorrow as being defective. I put the old router back on and the tool zero work flawlessly. No extra current flows. Why the difference? I need some help from the electrical experts.

Help

Dave

[WoodSpinner]

Originally Posted by dsnellen Come on guys, I need some input here. Al, where are you? Today, I tested the ohms between the ground & the hot and neutral wire. Nothing. So why the current flow mentioned above? I am sending the router back tomorrow as being defective. I put the old router back on and the tool zero work flawlessly. No extra current flows. Why the difference? I need some help from the electrical experts. Help Dave

the 690 series of routers are case grounded to the mains, just like your computer, so attaching a 5v+ lead to the bit effectively shorts it to ground.

John

on mine, I use a pull up resistor on the pin I use for sensor, so the bit touching it would ground it giving the signal.aka active low

[Al_The_Man]

Makes sense what John said, if you have 5v direct from the supply and its common is at earth ground then the 5v will short out when contacting any part of the machine?
Al.

[dsnellen]

Thanks John and Al.

I don't know what "case grounded to the mains" means. Is this unique to the P-C 690 series router? Is this something I should be concerned about>

John, can you explain this further :
"on mine, I use a pull up resistor on the pin I use for sensor, so the bit touching it would ground it giving the signal.aka active low"?

LSS, is the router safe to use? Meaning should I send it back? If I modify the wiring to use a pull up resistor will this work on the other routers I may use? Since I use the same circuit for touch probing, will modifying the tool zero circuit invalidate the probing tool? Why would one P-C model differ in its electrical configuration from other models? The sparks have me concerned.

I put the PC 75182 back into production. The only problem with it is that it is heavy and and the Z axis is not repeatable meaning a "G31 Z-2 F10" can vary +/- .009. This creates ridges/groves when doing a bottom surface on a sign. With lighter routers, like a RotoZip, a Craftmans, etc, the Z axis is dead-on accurate meaning bottom surfaces are at the exact same level with no height difference.

Maybe I am trying to fit the wrong problem. The issue is Z axis repeatability. Lighter routers mean better accuracy. Maybe I should address the Z axis itself. Thoughts?

Thanks for your input.

Dave

[WoodSpinner]

Originally Posted by dsnellen Thanks John and Al. I don't know what "case grounded to the mains" means. Is this unique to the P-C 690 series router? Is this something I should be concerned about>

no, just something you need to take into account. the housing and bit are grounded at the wall outlet, since the computer and probably everything else is also grounded to the wall outlet, then connecting your 5v lead to the bit, shorts it to ground, hence the spark.

John, can you explain this further : "on mine, I use a pull up resistor on the pin I use for sensor, so the bit touching it would ground it giving the signal.aka active low"?

this part is a little harder for me to explain, I dont know the proper way to do it, I dont use a bob, or opto isolation. I just have a hobby cnc board and it puts a pullup resistor on the input leads, this means that when its not grounded the input pin goes high, aka 5v, when the router comes down and touches the touch off plate it grounds it and makes the pin go to 0v. with it set up this way you have to tell your controller software that it should look for active low instead of active high.

LSS, is the router safe to use? Meaning should I send it back? If I modify the wiring to use a pull up resistor will this work on the other routers I may use? Since I use the same circuit for touch probing, will modifying the tool zero circuit invalidate the probing tool? Why would one P-C model differ in its electrical configuration from other models? The sparks have me concerned.

it would appear that the other routers are double insulated or some such and hence are not grounded at the wall. in those cases you would need to attach a ground lead to the bit with a clip when probing.

I put the PC 75182 back into production. The only problem with it is that it is heavy and and the Z axis is not repeatable meaning a "G31 Z-2 F10" can vary +/- .009. This creates ridges/groves when doing a bottom surface on a sign. With lighter routers, like a RotoZip, a Craftmans, etc, the Z axis is dead-on accurate meaning bottom surfaces are at the exact same level with no height difference. Maybe I am trying to fit the wrong problem. The issue is Z axis repeatability. Lighter routers mean better accuracy. Maybe I should address the Z axis itself. Thoughts? Thanks for your input. Dave

I have no idea on this, perhaps you have too much flex in your router mount/zaxis/gantry for the heavier router.

John

ps if I got anything wrong I hope someone can correct me/explain it better
I'm still a newbie

[Al_The_Man]

Originally Posted by dsnellen Thanks John and Al. I don't know what "case grounded to the mains" means. Is this unique to the P-C 690 series router? Is this something I should be concerned about>

It means the machine is connected to Earth ground which is correct practice, grounded mains would refer to one side of the main supply (neutral) also connected to earth ground.
Al.

[dsnellen]

John,
Thanks. Your explanation of "case grounded" was far better than everything I found on the Web. I will keep the router and rework the circuits. It was unnerving to see sparks! Thanks for your input.
Dave

[gslcnc]

Originally Posted by dsnellen Come on guys, I need some input here. Al, where are you? Today, I tested the ohms between the ground & the hot and neutral wire. Nothing. So why the current flow mentioned above? I am sending the router back tomorrow as being defective. I put the old router back on and the tool zero work flawlessly. No extra current flows. Why the difference? I need some help from the electrical experts. Help Dave

If you got 0 ohms between ground or neutral and hot, you have a short. resistance should have been infinite (megaohms). I hope you are not using your ohmmeter on live wires.