1336 Force

This is not a PLC issue but I'm hoping someone can offer some help.
We have 2 axes with 50 HP motors and 1336 FORCE drives. One axis has been faulting out beacuse the braking resistors are overheating. The drive was replaced, chopper module swapped, the usual stuff. What's odd is that on the axis that's faulting both direction LEDs are on simultaneously (before and after the drive was replaced). According to the manual the direction LED should only indicate the direction of motor rotation for the axis. This may not be related to the braking resistor problem but I would like to know why it occurs with one axis and not the other identical axis.

from the sounds of it i would check your inputs..from the indicator lights you are saying are on it looks like the drive is tying to go in two directions!!.. I didnt think a drive would allow that so it might not be the problem..But you never know..Its where i would start for sure..specially if its doing it on both drives.. the 1336 force was the newer of the 1336 drives was it not?

The inputs are configured the same for both drives. Even though both LEDs are on the drive is not responding as though it is actually reversing direction each time (when running the RPM on both drives varies by roughly the same amount). The fault is only occurring sporadically, it will run for several days at a time. I think the LED must light under another scenario which is not elaborated in the manual. I couldn't find anything on the A-B site but I'm hoping someone has encountered this before.

i understand both are configured the same but have you checked if they are both calling at the same time..i don't know what your input is but for example lets say it 4-20 ma

4ma..slow speed
20mas..fast speed

if you have 20 ma on forward direction you should have 0 on reverse..
what happens if the logic controlling it is defective in some way and is sending 3ma or 4ma or even 5 on the reverse??.. The drive will always be trying to brake the unit to run backwards..becouse it trips intermittently you might be right on the border between 3 and 4 ma..perhaps 3ma is enough to turn the led on but not enough to get the drive to work..every once and a while it spike to 4 or 5 ma and the drive trips...

Again this is all if and or but i still think its worth spending time on..

I see now; that sounds like a good suggestion. Hopefully the remainder of the shift will be quiet enough for me to check it out. Thanks.

let us know...

Ward, it is possible that the speed loop tuning on the 1336 is so unstable that the torque is swinging positive and negative continually. I only work with AB drives occasionally but I can see that lighting both LEDS possibly.

I would compare the speed loop gains, P, I, and D, to see if they are the same in the two drives. After recording the settings, I would drop the gains on the problem drive in half and see if the LEDS behave the same way. If it stops, the high gains were the problem. Instability would likely result in regen energy flowing back to the DC bus causing the overheating brake resistor too. Check the drive metering parameter for DC bus voltage to see if it is running high. If the brake resistor is heating up and the bus is under about 760Volts, you have brake module problems.

It appears to have ben a drive tuning problem. Although the issue hasn't been resloved yet we started noticing other problems with that axis under no-load conditions.

mr>rockwell

wel if boyh lights come on does it have a encoder on it ?

If the direction input is changed, whether by reversing the polarity of an analog input or by turning on a different DI, the current direction LED will remain lit and the other direction LED will light (flashing?) until the drive is able to stop in its current direction and turn around. Several years ago, we installed fourteen 1336 Impact drives and had to manually tune each and every one of them due to similar issues. The auto tune function works fairly well with standard motors, ours were 6 pole high torque high slip motors. Try looking at some of the 900 (Ha Ha) parameters that may affect this. Look at the zero speed threshhold (i forget it's specific name in the AB manual).

paul c

A-B is also suggesting the encoder is the problem. Lately it has been working OK so there hasn't been an opportunity to replace it. Older 1336 manuals mentioned this possibility for the LEDs but not the newer one. Thanks for the input.