Parker 890 drive HOT fault.

Hello Mr. Holt,

Thank you for your reply.

As per our observation also, it seems to be frequent failure of PCB AH500819U001/1. But please suggest us why this PCB fails so frequently causing the same fault again & again. And, is there any way that you can clear "STO Test Record" fault for our newly purchased PCB (AH500819U001 04) remotely through teamviewer.

If not, please suggest how to start the process of RMA for repair/correction.

For your questions:

We are using STO inputs/features.

Our drives are installed in an enclosure & well spaced.

The enclosure is properly cooled with panel air conditioners.

We are located in Muscat, Sultanate of Oman. 

Hello.  We do not have any repair center in the Gulf or Middle East, but we do have a factory and repair center in Europe.  You could set up a repair RMA through your nearest distributor, which appears to be in UAE:

PARKER MIDDLE EAST FZE
Sales Company Middle East
Jafza View 19, Office 2205,
Dubai, United Arab Emirates

Phone: +048127100
Fax: +048865401

It looks like there is some serious damage to that board, more than a simple thermistor failure.  The components in your photo are all low-voltage circuits.  Some are part of switched mode power supplies for various components in the power stack and others are just miscellaneous I/O features (brake relay).

If these traces are burning up, I would be concerned about your power and grounding situation.  Questions:

1. What is this drive's input voltage?
2. What is the drive's ground lug connected to?  What are you using as ground in your facility?
3. What kind of line service does this drive have?  Is your main service a center-grounded Y (preferred), a floating delta or a high-leg delta?
4. Do you have any kind of line reactor or isolation transformer on the line side of this drive?

Hello Mr. Cliffe,

Thank you for your reply.

Answers to your questions:

1. The drives input voltage is 3-phase 410V ac.

2. The drive's ground lug is connected to common ground for the panel, which is connected to earth pit.

3. Our main service is center grounded Y.

4. There is no line reactor or isolation transformer on the line side of the drives.

That all sounds fine.  Perhaps there is something wrong with the motor that is damaging the drive.  Have you checked out the motor recently?  I would perform a resistance check on all three phases to make sure there are no phase-to-phase shorts.  I would also perform two megohmeter tests:

1. Check the strength of the insulation between the phases and ground.
2. Check the strength of the insulation between the phases and the thermistor.

I am wondering if your thermistor's insulation is failing, which would explain the HOT faults and could also explain the damaged circuits you found.

Hello Mr. Cliffe,

As I have mentioned before, the drives which have failed are installed for different motors.  Still for your doubt we checked the resistance of the motor which drive failed lately and the results as follows:

1. The resistance between phases and ground are 950 MΩ, 970 MΩ and 985 MΩ

2. The resistance between phases & thermistor are out of maximum limit.

The insulation resistances were checked with Megger device at 500V.

And please note that every time a drive fails with "HOT" fault, we replace the faulty drive with new drive without making any changes in the motor and the drive gives no fault for next 8-9 months. Suddenly one day the drive fails with HOT fault and again the same story. Currently we have 6 faulty drives with the same HOT fault.

Thanks for testing that.  It should rule out the possibility of a thermistor insulation issue.  There could be other power-related issues in the machine.  Do you have a schematic for this machine I could review?

Daniel and I have reviewed the basic drive/motor schematics and nothing stands out.  Is it possible for you to provide some current pictures of the inside of the enclosure where these drives are installed?  Also, motor specifications (pictures of the inside of the enclosure being the more useful), something that shows the general installation/orientation of the drives relative to each other and other components above/below, so not specifically zoomed in on any 1 of the drives directly.  Trying to get some perspective.

And also, take a measurement of the actual AC voltage showing on the L1, L2, L3 terminals relative to each other to verify the AC input voltage being used.

Finally, along with the motor specs, some specs on the motor brake used, specifically how much current it requires.  The brake terminals are only rated up to 2A.

Finally, along with the motor specs, some specs on the motor brake used, specifically how much current it requires.  The brake terminals are only rated up to 2A.

Thanks for reviewing the schematic. The actual AC voltage for incoming supply of drive are: L1-L2: 410V, L2-L3: 412V, L3-L1: 410V.

As suggested by you we checked the current rating & actual current being drawn by the brakes. We found both currents higher than the ratings of brake terminals. The current rating of each motor brake is 4.2 A & during operation it is drawing 3.6A . As you mentioned in your last message, the motor brake terminals are rated for 2A only. May this be the reason behind HOT fault?

I have attached the pictures of enclosure showing drives' installation, motor nameplate & brake nameplate for your reference.

Yes, this makes some sense as potentially being behind the multiple drive failures (that result in a persisting HOT alarm - due to parts/traces burning up on the board). 

3.6A is higher than the contact (and also internal trace) ratings (2A), but not so excessively high that it would fail immediately, especially if under a managed ambient temperature as you previously described.  This kind of hard failure mode would take time, each time the brake transitions (maybe also not that often in that system?) to 'off' and you have current flowing it is degrading the contact in that connector and possible overheating the internal traces that lead to it (depending on how long current if flowing through that connector to the brake).  

Your 8-9 month "time to failure estimate" is similar to what I would estimate in situations where a bit too much current is flowing through a circuit like that.   The controlled ambient and actual amount of time current is flowing in that circuit would also factor in to that time frame.  Each time current is flowing, the connector and traces leading to it heat up beyond what they are rated for, even in a controlled ambient temperature.  This eventually leads to a thermal runaway condition.

From some of the earlier pictures Daniel noted actual damage to the circuit board inside (burning/browning) so we believe the HOT alarm isn't the actual 'failure point'.  Instead, it is simply indicating that the brake control circuit failure is also damaging the heatsink temperature monitoring circuit when the brake control circuit fails.

So - number 1 recommendation is to add an additional relay that can be controlled by the brake output circuit and has a coil rating of 2A or less, with its output contacts rated for at least 4A or more, suitable to the brake's current requirements.

Please note that drives that have already been exposed to this excessive current condition in the brake output circuit may have already been degraded and/or started to fail so simply adding the relay to existing drives won't absolutely prevent additional failures in the future, unless added to brand new drives of course.

This is our best theory at this point based on the details you've provided so far.  It is definitely something that should be corrected in either case.  

Dear Mr. Holt,

Thanks a lot for your troubleshooting. As of now, we will modify the circuit as per your suggestion, and monitor the performance with new drive. Will get back to you with the results. Once again, thank you & Mr. Cliffe for your valuable guidance & support.