I currently have a 75hp motor on a VFD. I did not install it. The problem is that when the equipment goes down under load it is next to impossible to start. Is there a setting I’m missing somewhere. Usually we would have a bypass contactor for this problem but one is not installed. Should I put one in?
VFD and bypass contactor
- Thread starter Jsmith811
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What's the application?
It’s actually a Grain Leg that carry’s product up 160ft…when it goes down it actually has a backstop on the gear box that does not allow it to spin backwards….thus leaving one side completely full. Other facilities use soft starts with bypass contractors with a HOA switch for plug conditions. This one for some reason for a VFD installed on it with no bypass
Not an application I'm familiar with. Sorry........................
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Stops operating because of a fault/failure or because of a command to stop? If a fault, what is it?
With the VFD?
We can start with
Is the VFD correctly sized & programmed for the application?
What's the startup ramp time?
Does it usually start when unloaded?
Is the "backstop" some sort of ratchet or does it need to be disengaged like a brake? (Is that happening?)
If you disconnect the auger from the motor, will it start/run?
Assuming the VFD is there for a reason, I'm not sure a bypass contactor would be useful in this situation.
Soft-starts often have bypass contactors since they're used for starting but not speed control, so you can bypass them once the motor is running (there are several threads on the forum here about bypass contactors).
Correction on the first post…it is actually a Altistart22…not a VFD…and the backstop is actually mechanical within the gearbox that only allows rotation of one direction…it does usually start unloaded but when product backs up there is 160ft worth of product in the machine and the motor will not start with the soft start…I was for sure it was a vfd because it didn’t have a bypass but turns out it wasn’t
ptonsparky
Tom
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- EC - retired
From experience, fix the the backup problem first. Proper interlocks should help.
I haven’t worked with a 75 hp leg but you need to open the bottom up and let it all drain out. Shovel work. It should start after that.
I haven’t worked with a 75 hp leg but you need to open the bottom up and let it all drain out. Shovel work. It should start after that.
- Location
- San Francisco Bay Area, CA, USA
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- Electrical Engineer
But adding a bypass to a soft starter is a good idea for more reasons than that.
Yeah that’s the problem with the mechanical backstop…won’t empty out the product…legs without them just roll because of the weight and empty it out but this one just allows the product to be in suspension
ptonsparky
Tom
- Occupation
- EC - retired
Even so the 30 hp and others would start full up. Not at 160’ though
Is this an OEM-designed system or home-brew?
It just sounds like a bad all around design.
ptonsparky
Tom
- Occupation
- EC - retired
That is the typical design. Older ones would coast backwards.
Those are the only ones I’ve seen.
That seems like a better approach that something that can’t be restarted.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Still not clear to me, is the motor just locked or does it move at all? Does the SS try to move it and give up (maybe throwing a code)?
Depending on motor curves/etc, can you crank up the max start time and accel time to accommodate the load?
Depending on motor curves/etc, can you crank up the max start time and accel time to accommodate the load?
- Location
- Wisconsin
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- PE (Retired) - Power Systems
Decades ago, I had a situation with an old Altistart 23 that required us to implement their 'e-boost' function? In sub zero weather the bearing grease would harden and need an extra kick to get started. The e-boost applied full voltage and current for a very brief time period, but it was enough. I don't know if this function is still offered on Altistart.
petersonra
Senior Member
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- Northern illinois
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- Semi-retired engineer
I don't think I have ever used a soft starter without a bypass contactor.
It might be that the reduced voltage and current the soft starter is putting out at first just can't get the motor turning, but one would think that after it got to full voltage the motor would start producing max torque. It might be that the motor is just under sized.
It might be that the reduced voltage and current the soft starter is putting out at first just can't get the motor turning, but one would think that after it got to full voltage the motor would start producing max torque. It might be that the motor is just under sized.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
If the soft starter goes into current limit and never finishes accelerating, it will likely trip on a "Stall" condition. How they typically detect that is for the current to go beyond some value, like 200%, for a number of seconds, then drop down to 100% or less. If it never finishes accelerating, the current never drops and the soft starter will trip on Stall (or Over Current on Acceleration). If there is a Bypass Contactor that is rated for Across-the-Line starting, you can often just command it to go into bypass on a Stall, but I'm not sure if the Altistart 22 is that sophisticated, I doubt it is.
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