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Old May 29th, 2009, 07:46 AM   #1
bosko
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Soft Start and VFD with bypass

Hi everyone

I'm looking for recommendations for soft starters and/or VFDs with bypass built in. To clarify, a bypass to me would include a switch of some sort to completely bypass the soft start/VFD module, and start the pump across the line. My search for "Soft Start bypass" has only led me to products that claim they have a bypass, but it is only engaged once the device is running at a nominal speed. What I'm looking for is something that can get the pump running in bypass in case of Soft Start/VFD failure without having to integrate an external bypass.

Thanks for your suggestions!
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Old May 29th, 2009, 07:59 AM   #2
just_lionel
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The way we have done it in the past is with contactors and a selector switch. In Bypass mode a small control contactor pulls in which pulls in a larger motor contactor straight to the motor. In VFD mode, a different contactor pulls in that pulls in another large contact that ties into the output voltage side of the drive.
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Old May 29th, 2009, 08:01 AM   #3
bosko
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Thanks for your reply. We have done similar things, but now I'm looking for a product that has that functionality built in.
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Old May 29th, 2009, 08:06 AM   #4
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Got ya didnt read that part. Friday morning and been staring at ASP code all morning...so forgive me!
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Old May 29th, 2009, 08:12 AM   #5
rdrast
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Many manufacturers have integrated VFD/Automatic bypass capabilities, generally in what they call the "HVAC" lines. I only have a link to ABB's handy, but AB, Parker/SSD, Telemechanique, and others have similar offerrings.

ABB's packaged solutions:
http://www.abb.us/cawp/usabb046/46d9...000529a76.aspx
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Old May 29th, 2009, 08:16 AM   #6
OkiePC
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We use RAM industries DBS soft starters for our refrigeration compressors. They are so reliable, my only time spent even thinking about them was during the commissioning phase. Their customer support is outstanding. They even took the drawings of our old wye/delta panel and made the interconnecting wire numbers match which made installation very easy.

They have the bypass functionality built in. They provide simple instructions to operate DOL in the event that the control board should completely fail. IIRC, it involves adding a couple of jumper wires and moving a wire or two, then starting the system normally.

I highly recommend the RAM DBS

Paul
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Old May 29th, 2009, 08:16 AM   #7
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If you're going to do "bypass" with a VFD, remember that you can NEVER, NEVER, NEVER connect line power to the output terminals with your contactor arrangement.

You must use 2 contactors, it is best if they are "mechanically interlocked", and only pull one at a time. Many manufacturers purchase "reversing contactor sets" because they have everything you need to set up an "either/or" circuit, and many come with the "mechanical intrlock" mechanism built in.

Most of the soft starters that I have worked with CAN be bypassed with a starter that is sized for cross-line staring of the load. This starter can perform double duty as a bypass for AFTER the soft starter is up to load AND to start the load in the case of soft-starter failure if it is properly SIZED. As mentioned, you just need a bypass switch in that case.

There is usually a "bypass" terminanal on the soft starter to pull in the contactor when the soft starter is up to speed. The type of bypass you are describing just requires a switch to ETERNALLY energize that terminal since it will already be wired to the coil of the contactor, either by you or the manufacturer.

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Old May 29th, 2009, 08:22 AM   #8
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We have a softstart with bypass from Saftronics. I don't know about VFDs as we didn't look into that. This controls a 450hp motor.
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Old May 29th, 2009, 08:37 AM   #9
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And one more thing about using a bypass on a VFD:

Many motors are dual rated. One HP/FLA for VFD and another of across the line running. Usually the later is LARGER than the former.

So you must make sure your fuse / wire / etc is sized to handle the non-vfd HP/FLA rating.
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Old May 29th, 2009, 09:00 AM   #10
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you guys are awesome! I'll do some research into your recommendations.

Thanks again.
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Old May 29th, 2009, 09:24 AM   #11
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Smile

I think some things need to be clarified

Are you looking for a soft starter that has a built in bypass contactor if so these are built into the soft start in most cases and work by engaging and putting the motor load across the contactor and the scr’s turn off. So from a stopped state the scr’s bring the motor up to speed soft and smooth then after a time delay and the motor is up to full speed it switches the load to the contactor.

Or are you looking for a bypass in the terms of if the soft start goes bad you can “Bypass” and start across the line. If this is what you are looking for then do some reading on 2 and 3 contactor bypass as 3 contactor bypass is the best method. But as far as a turn key product primarily for pumps and fans mostly for hvac use myself have never seen a 2 or 3 contactor bypass panel with a soft start but you could “roll you own” it is the same concept as with a vfd.
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Old May 29th, 2009, 09:26 AM   #12
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Here is a soft start with a built in bypass contactor.

http://www.ab.com/industrialcontrols.../smc-flex.html
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Old May 29th, 2009, 11:18 AM   #13
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plc noob- I definitely need to be able to start/stop the pump in bypass mode in case of soft start failure. It is the entire purpose of the bypass in the client's eyes.

Thanks again!
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Old May 29th, 2009, 11:21 AM   #14
bosko
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Quote:
Originally Posted by plc noob View Post
Here is a soft start with a built in bypass contactor.

http://www.ab.com/industrialcontrols.../smc-flex.html
I was looking at this one... how would one start this in bypass mode if the soft starter was fried?
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Old May 29th, 2009, 12:04 PM   #15
Gil47
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I read this and say, all very well to make the bypass arrangement for the situation where you have a VFD or Soft start failure, along with a panel twice as big and you want one that is intergrated, now for the but.

You add the needed contactors and controls, overloads fuses, larger panel, and so on,
now you have a VFD or soft start that needs serviced.
Please explain how you remove it safely, from the jumble of added controls, and switch gear, as well as more points of failure, and then you need to find an Electrician that would confidently work on it without a full isolation.

In the very few occasions, we might have the need to run existing machinery when failure of Vfd or soft starter would be a problem, we have a convetional starter feed the VFD or Soft start, and by link wires swap the way its started after removing, then linking motor leads from VFD with the supply leads to the VFD.

If fast swap is required, I believe a back reserve pump or capacity of what ever, is the best, wisest, safest option.

Now did I mention cost of building this arrangement.
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