U4 burning on new Mesa 7i76e

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15 Sep 2019 10:18 #145227 by Sebigamer4
Hello,
I'm curious if anyone can help me.
A friend and I are going to build a Linuxcnc driven Plasmacutter and we want to use named mesa to control it.
But we've experiencing some strange issues.
First, we have both an electrical background, so we've got some experiences in this stuff.

A few weeks ago, we've got our mesa, everything worked fine, but after we interfaced something on the IO (and there, we made a
mistake on our own: we've connected an Optocoupler and forgot the resistor needed bec of the 24V field power).
Nevertheless it worked fine for our first test, but the next day, when we turned on the mesa Power, U4 (driver chip) burned down with
lots of magic smoke. We've tried then to power the FPGA only, and that looked still good.
We don't know if this was our fault (too much current on output, despite the integrated overcurrent protection) so we took the pill and ordered a second one.


This time we only connected 24V on VIN and VField, and Ethernet going to our linuxcnc pc.
(See attached Pictures, jumper are placed like the schematic, both power-wires are 24V, generated from a sitop supply, polarity checked. The power is turned on and off through a DC line breaker on Powersupply Ou, both powerlines are switching on at the same
time ( they're connected in parallel after the breaker).)
And U4 burned instantly.
(Remember: No Wiring on IO, or anything else...)

At this point, we don't know what to do...
A third mesa isn't really in our budget and i don't see the point there...

Had anyone here similar issues/experiences in the past?
or has anyone a clue, what had gotten on with the second mesa (the one in the pics)?

What next steps should i take?
(i mean beside contacting the seller and mesa, it's just a little complicated because we are in Germany, the seller in Portugal and mesa is somewhere completely else)
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15 Sep 2019 14:10 #145248 by PCW
Replied by PCW on topic U4 burning on new Mesa 7i76e
if you use a relay or switch in the 7I76E field power you are very likely
to damage the power components

Here's the relevant section of the manual:

Field power must have a ramp up rate of less than 10V/Millisecond. This
means that you cannot switch the field power connection with a switch or relay.
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15 Sep 2019 14:16 #145249 by tommylight
That is valid for the drives also, never switch the DC side of the power supply.
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17 Sep 2019 20:57 #145440 by andypugh
Is U4 easy to replace?

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01 Dec 2019 11:54 #151652 by thefabricator03

tommylight wrote: That is valid for the drives also, never switch the DC side of the power supply.


Tom,

How do you turn the power off to the drives in your systems for safety? I have read else where that putting a switch between the power supply and motor drives is not a good idea as it will destroy the drives.

I have noticed with my toroidal power supply, when power is cut off on the ac side it still has residual power and does not cut off instantly.

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01 Dec 2019 13:26 #151655 by tommylight

thefabricator03 wrote: Tom,

How do you turn the power off to the drives in your systems for safety? I have read else where that putting a switch between the power supply and motor drives is not a good idea as it will destroy the drives.


That depends a lot on the machine and the used electronics:

-For stepper systems
--a simple mains ON/OFF switch for the power, a circuit breaker inline with power supply, enable from Linuxcnc wired to enable on the drives
---The reason for this is that no matter what happens to drives in the event of a failure, the motors can not spin on their own.

-For DC Brushed servo systems
--a mains switch, circuit breaker/s ( single or 3 phase ), a 4 pole relay (2 pole for single phase, but i buy 4 poles so i use that) controlled by Linuxcnc from E-Stop and relays wired as Extreme Limits and physical e-stops. When using toroidal or normal "box" transformers that is all i use, since the energy stored in the capacitors is not sufficient to do any damage to the machine in case of a runaway and they are not affected much by back EMF in case of abrupt stopping of the motors or cutting the power. For switch mode power supplies another circuit is needed to short the drive power rails with a relay and a resistor used to dump the stored energy or back EMF. There was a nice schematics on the geckodrive website, but the picture is missing :
www.geckodrive.com/support/servo-drives/...chanical-e-stop.html

-For AC or DC 3phase brushless systems
--they already have plenty of protections included so the only important thing is having Linuxcnc disable the drives on any error, especially on feedback errors, limit switches wired to the drives also when possible as it does not allow turning on the side the switch is tripped. Also most have dump resistors or have terminals for them, can not run away in case of a failure or the power stage.

food, eating, later.

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03 Dec 2019 20:24 #151899 by Benb
Replied by Benb on topic U4 burning on new Mesa 7i76e
I don't know what type of IC is U4,.However, I suggest you google FPGA dv/dt damage and MOSFET dv/dt damage.

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04 Dec 2019 07:20 #151954 by Sebigamer4
"Is U4 easy to replace?"

It depends if you got the right tools for SMD desoldering and soldering, but if you find the right ICs, its 'Replacable'.

"tommylight wrote: That is valid for the drives also, never switch the DC side of the power supply."

We`ve learned that lesson. For now, on the DC Side, theres a Blow-Fuse and an Switch at the primary side of the DC- Supply for the Mesa.

"thefabricator03 wrote: Tom,

How do you turn the power off to the drives in your systems for safety? I have read else where that putting a switch between the power supply and motor drives is not a good idea as it will destroy the drives."

We are cutting off the Drive Power Supplys, as tom wrote, that results that the drives a unable to turn something by their own, no matter whats happening.
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