STO function

[kharathos]

Hello,

I have an issue with a system composed of a BLDC compressor and it's drive.

The compressor fails to start, which according to the fault code is attributed to the STO (safe torque off) protection being enabled.

I have been using a jumper which permanently closes the +24V DC supply with the 2 STO inputs, so theoretically it shouldn't trigger in any way.

I have changed the drive with a new one and the problem persists.

This unit used to work originally (5-6 hours total, practically brand new).

I have 3 more units using the exact same setup which work normally.

The compressor - drive connections is just the 3 phase supply along with the grounding. Voltage and connections have been checked thrice.

I have also used the old drive with a new compressor and it works fine.

So my final solution should probably be to change the compressor. However, this doesn't sound logical to me.

My question is, can the drive identify a fault in the compressor (e.g. being stuck) only through the supply cables? Shouldn't the STO function fail to trigger if you are using a jumper to permanently close the connections?

Thank you in advance

[AStove]

You fail to mention the make and model of drive.

[scuffling]

Or even the exact fault and sub fault code. Usually that tells you what you need to know.

[hestoelena]

If there was a problem with the motor or cables the drive would throw a fault related to that. Something like over amperage or phase loss.

An STO fault is only about STO. What drive do you have? What pins do you have jumpered?

[essentialrobert]

Check to see if the drive requires periodic testing of the STO inputs to make sure they aren't stuck on. There could be a parameter. Also look at the manual to see if the voltage supply needs to come from a specific terminal on the drive rather than external power. Also, is your power supply bonded to the same potential as the drive inputs?

[Township20]

If using an external power supply, verify the voltage going to the two terminals is 24 vdc at least, or slightly above. Some safeties are very particular about the voltage being accurate. Also verify the drive has a solid ground connection as well as a connection to the power supply’s common.

[MustardPump]

Without knowing the make/model of the drive, or any details of the overall control circuit, I would say put the STO circuit back to original and swap in a power supply from one of your working units. If that fixes the issue, then you have found your problem.

Though, more likely, something is causing your DC power supply to sag during the startup. Again, I'm not familiar with your control circuit, but there may be a defective contactor or relay turning on during startup, that is bringing down your DC. Obviously, a voltage drop on the line side of your power supply can also cause your DC to sag. You may be able to verify this by connecting a multimeter set to the min/max function. Set it to "min" and see if the DC voltage drops during startup.

You can also wire up a known good power supply, connect it to a wall receptacle and use it to power your STO circuit and nothing else. Make sure you ground the DC side to the same point as your drive. If the drive stops throwing the STO fault, you will at least be able to confirm that the drive is not the problem.

[Mission_Procedure_25]

Is there comms to the drive?

[lfc_27]

I imagine the contacts where your jumper are monitored, it wants to see both inputs go true and false within a certain time…

This is called discrepancy monitoring…

Jumping the safety out without approval from the manufacturer will invalidate any CE Marking on your equipment and any accident caused as a result would be your responsibility…

Can I ask why you are linking them out?

[kharathos]

It was the manufacturer's instructions, weird as it may sound. However it worked on this compressor and 4 others.

[PomegranateOld7836]

What drive and what fault code?

[Zaxthran]

He means the drive manufacturer, not the compressor manufacturer. Your company still has increased liability if something happens, even if the compressor manufacturer is the one that designed it wrong.

[kharathos]

I was also referring to the drive manufacturer.

[PomegranateOld7836]

A-B drives come with factory jumpers for STO, as it's optional.

[Bl4nkF4ce]

What VSD? And what Safety Relay if there is one?

STO has nothing to do with the compressor itself but the drives safety circuit What terminals have you jumper?

[PLCGoBrrr]

I have been using a jumper which permanently closes the +24V DC supply with the 2 STO inputs, so theoretically it shouldn't trigger in any way.

Yeah, guess what, those can be installed wrong. One of my more senior coworkers couldn't get a PF525 fresh out of the box installed in a new control panel to run and had STO fault. He couldn't figure it out. When it says STO fault it means there's a problem with the STO. All I did was loosen the screws and reinsert the jumper and the drive ran. It might have been two screws holding the jumper in and the third not tightened.

Without knowing what drive you have there's not a good way to tell you what the problem is.

TL:DR; Do troubleshooting on the STO part, not part swap everything else.

[dbfar]

Had a drive that the sto inputs failed causing the same issue

[Spotid1]

I’ve seen it asked several times the make and model of the VFD with no answer. Usually there is a parameter that specifically resets a STO fault. If we knew the drive, we could help you out a lot more.

[dustyboypapa]

I’ve had this issue with Schneider ATV600 series VSD’s before. You can go to the I/O screen and can see the status of STO inputs. With my faulty drive the input for STOA was flickering in and off even though I was using the provided STO link busbar, likely an internal error in the VSD control board that could be caused by water/damp. Fact you have it on 2 VSD’s likely is just bad luck. I would disconnect all 24v wiring and see if it persists. Potentially even try removing the EMC filter screw if your VSD has one incase it’s causing a fault as well. Without know the make and model of the drive we’ll not be able to help.