VIN under-voltage event only after M84

[Poent]

Hello,

I've had a new issue crop up after rebuilding a Delta style printer. After power cycling or resetting the printer it homes and moves normally - and can progress through an entire print without issue. If I let the motors idle timeout occur however, or manually send the M84 command, the next home event will cause all steppers to skip and trigger the following console error:

VIN under-voltage event (9.5V)Error: Attempt to move motors when VIN is not in range

I can see that the VIN readout under Machine status does indeed fall to around that range during the issue.

I can sometimes get the printer to recover to normal voltage levels by sending M84 and retrying, and it has always worked immediately after a power cycle, but I can't seem to find the root cause.

The power supply worked fine not but a day before the rebuild and I've confirmed that there are no loose wires or screw terminals. I can also proceed through a several hour long print as long as I start it before the motor idle timeout.

Could anyone recommend some other things to check?

I'm using a Duet WiFi 1.02, firmware version 2.03, wifi version 1.21, web version 1.22.6
Power supply is a 12v/30A supply running off 115v mains.
I've attached my current config file for review. config.g

Thanks

[SIam]

Are you sure that you have a 30A (360 Watt) power supply? Own you a multimeter ? If yes can you measure The Voltage directly at the output of your power supply to see if there the Voltage goes down to 9,x Volts? What have You all connected to this power supply? And how much watt they need (heat bed etc.)
Something seems to consume a lot of Amps or your Power supply does not deliver 30Amps or it is dying. Is something getting hot on the duet board?

[Poent]

For the power supply, I'm only as confident as the sticker on the side. I do have a multimeter and have used that to ensure that I'm getting 12v from the supply. I have not yet measured the voltage coming from the supply when the issue is occurring however - I will see if I can capture that.

The PSU is powering the Duet board, 3x Nema17 motors, one small fan, and a large heated bed (though the heated bed has been disabled/off for all of my testing).

I'm not sure the best way to test if anything is getting hot on the duet board, but gently touching the drives and what I think is the voltage regulator, they do not seem to be producing a concerning amount of heat.

[alankilian]

You can try editing your config.g and only defining one axis, no hot-end, no bed heater and try again.

Then configure two, three etc and see if it comes back.

I had a power-supply that held 12 Volts just fine most of the time, but would drop to 10 Volts under even a light load.

So I replaced it and everything was fine.

[Poent]

@SIam

I just had a moment to test with the multi-meter and when replicating the issue VIN measures at 10.49v. VIN through the Duet Web GUI reads 9.5v. Confirming the Low-Voltage reading.

[alankilian]

It sounds like your power supply has failed to maintain its voltage under a small load.

It happened to me and I needed to replace the power supply.

[Phaedrux]

Can you provide a M122 before and after that error message?

[Poent]

Sure thing.

Here are the results from each:

M112_Before.txt
M112_After.txt

The specific steps I took to replicate the above were:

1. restart the Duet
2. Home all Axis (worked normally without issue)
3. send M84
4. Home all axis (Undervoltage error, steppers begin skipping repeatedly until endstops are hit (5mm away, skipped steps take a long time to hit endstops).
5. M84 is sent again to stop skipping steps (can hear the steppers skipping while holding idle until m84 is sent again).

[dc42]

If it's a PC power supply (e.g. ATX), these have minimum load requirements. If the load is too low then on the cheaper power supplied especially, the output voltage may rise too high and the over-voltage protection will cut in.

[Poent]

@dc42

I'm currently using a dedicated 12v 30a switching power supply, though it is certainly a cheap Amazon supply and wouldn't be surprised if it's failing.

Is there a power supply you recommend? I've already ordered a replacement 24v switching power supply to test with, but would be interested to know your recommendations.

Thanks

edit: I've found the "choosing a power supply link" in the wiki, so nevermind!
https://duet3d.dozuki.com/Wiki/Choosing_the_power_supply

[Poent]

Replaced the power supply and the issue was instantly resolved.

Nothing more than an odd coincidence with the rebuild!

[alankilian]

Awesome!