Soft Start- Noise
Soft Start- Noise
(OP)
I have a Motortronics 500hp soft start.The unit has been in service for 5 years.When starting the unit it has always made a humming noise for about the first 5 seconds.Recently this noise has gotten much louder.The unit appears to still be working.Ramp time is 10 seconds,60%intial voltage,200% intial current,400%max current.Output current and voltage are balanced when up to speed and also when under load.The unit does not make noise during operation only starting.
Iam looking for ideas on where to look for cause.
Iam looking for ideas on where to look for cause.





RE: Soft Start- Noise
RE: Soft Start- Noise
Is the duration of the noise related to temperature? is something loose when at room temperature, but as bypass heats up from current flowing through it it "tightens" up?
Is it a buzzing noise-two things rattling together?
Or is it an electrical hum? 60/50 hz type sound?
None of these will specifically solve your problem, but they might help you see the forest for the trees. Or however that old saying goes..
RE: Soft Start- Noise
It is not a rattling noise,more like a loud humming.The noise only occurs in the first 5 seconds of start when the current is the highest.The application is on a hog grinder.
while grinding when the current goes up and down,sometimes as high as a 1000 amps the noise does not happen.
RE: Soft Start- Noise
RE: Soft Start- Noise
I'm really just guessing at this point but other things to look at:
If you haven't changed the programming of the soft start recently, do you have any sort of PM records on motor current vs. time at startup.
If the startup is limiting the current at startup to no more than 400% is the soft start needing to stay in one of the harmonic switching frequencies longer than it used to?
Have you verified the program hasn't been changed? Curious fingers or loss of memory in the eeproms.
Good Luck!
RE: Soft Start- Noise
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Soft Start- Noise
There is a small chance that the problem is electrical rather than mechanical.
RE: Soft Start- Noise
Is it a "static" like sound, or a mechanical rattle?
RE: Soft Start- Noise
RE: Soft Start- Noise
RE: Soft Start- Noise
RE: Soft Start- Noise
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Soft Start- Noise
Motortronics mounts the SCR stacks off of the back panel using glastic isolators, referred to as "apples", which can get loose over time. It's quite a job to get at them to tighten them though, it involves both removing the stack and removing the back panel.
It would be prudent to just go around and double check tightness of all of the bolts you can see. Be careful of the ones holding the stacks together on the SCRs though, they are critical and if overtightened you can damage the SCRs themselves. They have specific tightening requirements that must be followed to the letter. Before enbarking on that, check the resistance across each stack (power off of course). They will all be high, but if one is extremely different (lower) from the others, it may be getting loose. But before tightening them, get instructions from Motortronics based on your serial number because over the years they have changed the clamp design on that stack and some of them are done by numbers of turns, others have a gauge built in.
Also check the compression lugs on your line and load leads as well while you're at it, they tend to loosen over time.