snubber board
snubber board
(OP)
we recenlty experienced a dc drive occasionally tripping on regen stops,
I scoped the current output from the drive during motoring and regenerting conditions and all pulses were present every time i checked. the drive would trip on speed feedback error. initially i thought the encoder coupling but because of the way this system works that cant be the case as once it had slipped it would never run again.
looking at the way it derrives a speed feedback error it is a calculation based on armature volts, current and speed which narrows it down to just about anything really.
Because this doesnt happen all the time i decided to change the snubber board thinking a failure may be causing erratic armature volts on occasion, the fault hasnt occured since but i really expected to see a blown component on the board which has resistors varistors and capacitors on it.
from your experience do snubbers go bang or do they fail silently?
was it a good guess to change this board first or do you think i have just been lucky and desturbed a loose connection
cheers
I scoped the current output from the drive during motoring and regenerting conditions and all pulses were present every time i checked. the drive would trip on speed feedback error. initially i thought the encoder coupling but because of the way this system works that cant be the case as once it had slipped it would never run again.
looking at the way it derrives a speed feedback error it is a calculation based on armature volts, current and speed which narrows it down to just about anything really.
Because this doesnt happen all the time i decided to change the snubber board thinking a failure may be causing erratic armature volts on occasion, the fault hasnt occured since but i really expected to see a blown component on the board which has resistors varistors and capacitors on it.
from your experience do snubbers go bang or do they fail silently?
was it a good guess to change this board first or do you think i have just been lucky and desturbed a loose connection
cheers





RE: snubber board
Varistors - MOVs absolutely wear out. Usually dramatically.. Hence the shrink wrap on them all the time.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: snubber board
Power film capacitors are commonly made of metalized polypropylene film and any insulation breakdown in the capacitor will cause the local metalization to be vapourised. These capacitors are often described as "self healing" and will slowly lose their capacitance. It is possible that the value of the capacitors on the snubber are much lower than they used to be.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: snubber board