8i20 spindle drive hardware issues

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26 Oct 2019 03:35 #148811 by blazini36
I'm trying to figure out what happened to my spindle drive/motor setup or at least what's still wrong with it. A week or 2 ago I noticed my brake resistor blew out, like it obviously damn near caught fire while the mill was sitting idle. I used the mill and it was fine then I left it sit powered on for a day or 2 when I noticed the brake resistor was cooked, this is a 500w 50R brake resistor

I replaced the resistor and some wiring, the 8i20 seemed fine. Not quite sure how the resistor smoked out, even if the resistor was faulty, the 8i20 still would have had to have been dumping voltage to it while it wasn't running. It's all back together but it doesn't run for sh!t. The motor runs away hard at full current if it's phased correctly. I checked the resistance between phses and all 3 are at about 3-4 ohms which seems pretty short to me. With no power to the motor It cogs when spun by hand.

I'm thinking the motor is trash but I'm curious if there's any way I can check that the 8i20 is in good shape.

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27 Oct 2019 11:08 #148869 by tommylight
That seems odd for sure as the brake resistor should be on only during deceleration to dump the back EMF from the motor.
Bumping this up, maybe someone who can help missed it.

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27 Oct 2019 14:47 #148885 by blazini36
I have the drive running again, there were some issues with the BLDC component direction, the 8i20 phasing and the encoder direction that I didn't expect since it was a running setup but it's sorted now.

I am still a bit uncertain about why the motor has such low resistance between phases but I suppose that's just the way this BLDC motor is. But yeah, I'm still lost as to how the brake resistor cooked itself in the first place. As I said I tend to leave the mill powered on and the 8i20 HV power was enabled but the mill is just sitting there, with no current request. I didn't find any evidence that something shorted out other than the resistor itself, no wires were burned or arced or anything.

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27 Oct 2019 14:56 #148886 by PCW
What are you brake on and brake off voltages set to?

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27 Oct 2019 15:27 #148889 by blazini36
Brake voltages are stock, nvbrakeonv = 36000 nvbrakeoffv = 34000. It's a 340vDC power supply (8i20 reports ~350v unloaded)

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27 Oct 2019 16:02 #148893 by PCW
OK I guess I would bump the on/off voltages to say 380/370

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09 Jan 2020 04:23 #154398 by blazini36
Well I found out the various items the fill break resistors with! it's either some kind of oil or sand in the case of the 2nd one I just cooked, and I mean literally coooked.

Now I have for a long time been running Gmoccapy with a bus voltage and current display coming directly out of the hal pins from the 8i20. Even if it reached the brake on voltage it certainly never stayed above the brake off voltage, Yet I walked away from this machine again without thingking about setting the Estop or realizing the 8i20 was still dumping current to the brake resistor but it obviously was (machine wasn't actually being used anymore, just left on.

Fairly certain in both cases the last operation was rigid tapping where the drive does tend to get stressed but I can't imagine how it was seeing bus voltage high enough to keep the break resistor output on long enough to melt it. Like the thing literally must have been dumping to brake for an hour after stopping the mill if I can clean up and walk away from the machine without noticing anything funny yet,

Maybe there should be some firmware patch to disable the brake if on for a specified time for safety? Either that or my 8i20 has an issue. These were large brake resistors that must have took quite some time to cook.

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09 Jan 2020 04:31 #154399 by PCW
Did you set the brake-on and brake-off voltages to the higher numbers I suggested?
360 for brake on and 340 for brakes off are too low for a nominal 350V power supply

(Just a 7V rise in 230VAC line voltage will keep the brake cycling forever)

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09 Jan 2020 05:04 #154403 by blazini36
Yes, they were setp'd in hal as opposed to setserial-ing them as I did previously with some different values. I didn't think much of it since the hal parameter showed the new values the few times I checked them when I first did it.

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