High amp draw

[miniz98]

Hello we have a chevalier 1620 with fanuc drives and motors oimd control. Power is 208 3 phase. We have a problem with when the drives turn on we get 30 amps on each leg from the power coming in. Sometimes it will go away. Majority of the time we get 30 amp draw with nothing running. What ends up happening is it will trip the breaker when the breaker gets hot. We have been in contact with fanuc for over 30 days and chevalier. No one can figure this problem out. Does anyone have a idea of what would draw 30 amps when the machine isnt even running?

[Jim Dawson]

Are the braking resistors getting hot when nothing is running? Maybe a failure of the spindle drive braking system?

[miniz98]

I dont see any breaking resistors. I think this has dynamic breaking in the spindle. I was thinking of unplugging the break with z on a block of wood. I wish i get get ahold of this guy on cnczone he had the same issue back in 2006 https://www.cnczone.com/forums/fanuc...-amp-draw.html

[Jim Dawson]

Something must be getting hot, you can't dump 6200 watts into a system without it going somewhere. If it's not using that power to do useful work like making chips, then it has to be dissipated as heat.

Maybe time to get out the IR thermometer and point it at various places in the panel or motors and see what is getting hot.

[miniz98]

Yea you would think. The only thing getting hot is all 3 wires. Checked all motors nothing else is hot. Except for the breaker at the main panel feeding the power. We tried replacing that too. Everyone is baffled. Fanuc and our electrician. I disconected the brake still high amps. I've disconnected x,y,z and spindle and still high amps.

[Jim Dawson]

Yea you would think. The only thing getting hot is all 3 wires. Checked all motors nothing else is hot. Except for the breaker at the main panel feeding the power. We tried replacing that too. Everyone is baffled. Fanuc and our electrician. I disconected the brake still high amps. I've disconnected x,y,z and spindle and still high amps.

OK, add me to the list of those that are baffled

[cjfisher]

Mini,

When you say that you have disconnected X, Y, Z and the spindle - have you only uncoupled the motors or have you pulled the power to the servo amplifiers and spindle drive as well? Have you checked the temperatures of the heatsinks on the servo amplifiers and spindle drive? Could be a IGBT transistor inside one of the units acting as a big resistor.

CJ

[miniz98]

Fanuc has replaced the drive. its a package unit style. They have disconnected the x,y,z and spindle cables going to the drive.They have not removed any ribbon cables.

[cjfisher]

Hmmm.... well that's the end of that theory... What other loads are there in the machine? Is there a hydraulic unit? Spindle cooler? Tool changer motor? As Jim points out you can't dump 6200 watts into the system and not have something heat up. I would also point out that if this load were going into smaller wires you'd be burning them up. Another thought.. What is the current in the ground return? As you aren't popping the panel breaker I would think it would be 0 amps, but it would be interesting to know.

CJ

[miniz98]

Hmmm.... well that's the end of that theory... What other loads are there in the machine? Is there a hydraulic unit? Spindle cooler? Tool changer motor? As Jim points out you can't dump 6200 watts into the system and not have something heat up. I would also point out that if this load were going into smaller wires you'd be burning them up. Another thought.. What is the current in the ground return? As you aren't popping the panel breaker I would think it would be 0 amps, but it would be interesting to know.

CJ

Yeah it's driving me crazy. Ground has 0 amps. No hydraulics or cooler on this machine. I was thinking the same thing 40 amps would fry them. So upset. Machine has been down for a month. I'll send a photo of the back in the morning. Thanks for all your help.

[cjfisher]

ok.... Does the machine have a bunch of contactors in one of the panels? It would be interesting to disable all of them - and hook them up one by one until you find your problem. One last thought - though I would think (and hope) this would kick out the main breaker - worn insulation on the wires somewhere inside?

CJ

[miniz98]

So the problem has been fixed! They installed a isolation transformer and the high amp draw is gone! Anyone have any answers as to why this works? I am so happy

[regina]

Is the machine still grounded or is it floating now? If floating what is the frame voltage in reference to earth ground?

[miniz98]

the machine is still grounded from machine to the main breaker panel with the isolation transformer hooked up. How would i check frame voltage?

[generaldisarray]

So the problem has been fixed! They installed a isolation transformer and the high amp draw is gone! Anyone have any answers as to why this works? I am so happy

Can we have a picture of the tag on the transformer. for posterity.

[miniz98]

Can we have a picture of the tag on the transformer. for posterity.

Attached.

[generaldisarray]

The old Wye Delta.
Thats the second time (at least) on here someone has used these to solve a problem.(different problem<more insane)

By chance
Do you have measurements of utility voltage to ground?
And
Which way did you go through the Xformer? ie: Is the machine hooked to the secondaries or primaries.

[evdb]

Hi!
I am having the same issue with 4 of my machines. The main transformer blew on the provider side. I've been blowing fuses in my disconnect left and right.
You only added the transformer? Nothing else changed?