Motor chattering when contactor off

I'm using a (now obsolete) LDC1430 to power a winch motor from a nominal 12V battery. I am using a contactor to isolate the 2 Vmot lines as recommended. I am switching Pwr-Ctrl to battery 0V to disable the controller, and battery +12V to keep the controller alive if the contactor is off.

I am running in closed-loop position mode. Usually there is a residual loop error of 2 or 3 encoder counts when the system comes to rest. I have been unable to reduce this to zero.

If, when the system has stopped, I open the contactor, the motor chatters. Here is a zipped recording made with my iPhone -- it's a bit quiet, but you can hear the click as I switch the contator off, then the chattering, then the click as I switch it back on.


All inputs have been disconnected except the RS232, which is going through a 3-line opto-isolator.

The encoder itself is powered by the +5V on the D-SUB connector, and is connected to the D-SUB ground too. There is no connection here to the battery 0V.

Do you have any idea how to eliminate this annoying chatter?

cheers,
Richard

Hello Richard,

Is the motor throwing an UnderVolt fault when you shut off power to VMot?

Hi Gabriel,
yes, it is showing undervoltage. I get it in the reported flags as well as in the flashing light pattern (though that is irregular). The voltage reported is between 4 and 5 volts (not constant).

cheers,
Richard

If it has an undervoltage fault, it should be shutting off power to the output stage. It seems like voltage is still leaking out though. This could be a bug in the firmware or a hardware problem, but since we no longer support the LDC1430 there is nothing I can recommend for a fix.

Hi Gabriel,

Thanks for your diagnosis that it may be either a firmware or hardware problem (ie, RoboteQ's fault).

I am less impressed by your statement that since this device is no longer on sale, RoboteQ is not able to offer any support to fix the problem. Particularly since it seems that changes in your product portfolio in this area are largely cosmetic.

Cleary this is counter-productive. It gives the clear message that it's not a good idea to purchase any of your controllers because the moment the controller is declared obsolete (which the buyer has no control over) the support disappears.

If I choose to buy any of your controllers today, you might declare it obsolete tomorrow, and support vanishes.

Frankly, I'm disappointed. I have now invested in three generations of your controllers, and even though the latest of them is only 4 years old (and was a new product when I bought it), you can't support it.

I have spent all of of my career n the aerospace business, and in my experience any company which refuses support for recent products like this will not survive. Buyers quickly learn.