Need soft start recommendations.

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You need to be careful when adding a Soft starter because they have lower torque limits, unlike a VFD. You would need to take a look at the torque versus speed curves to see if at the reduced voltage (using a soft start) you would have enough torque. Like I said because of the differences in softstart versus VFD, the VFD's do not have this same issue since it provides a Volts/Hz output.
 
kingpb said:
You need to be careful when adding a Soft starter because they have lower torque limits, unlike a VFD. You would need to take a look at the torque versus speed curves to see if at the reduced voltage (using a soft start) you would have enough torque. Like I said because of the differences in softstart versus VFD, the VFD's do not have this same issue since it provides a Volts/Hz output.
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I think both ASD's and SSRV starters have starting torque limits. ASD's have more potential for adjustments. SSRV have a starting torque kick feature. Neither can provide more starting torque than the FVNR starters.
 
When starting under reduced voltage, it reduces the available torque to the driven load by the square of the voltage. Such a condition would dictate that the total system inertia be limited to a minimal initial torque requirement and marginal inertial load. Many loads are designed to start under full load and attempts to start with no load could cause the motor to overspeed, causing motor protection devices to trip and possibly damage the motor. They lack the inherent variable load-speed control that Variable Frequency Drives (VFD?s) were designed for and do not possess the capability of continuous precision torque/speed rate control.

Certainly all devices have limitations, there is no one size fits all, but if you have starting torque concerns, the VFD will have a much wider range of capabilities to overcome it. As far as VFD torque limits, it depends on the product as to what the lower limit may be.
 
A variable speed drive permits the torque/speed curve of the motor to be shifted to different speeds. A suitably sized VSD could in theory run a motor with full break-away torque right at zero speed, providing far more starting torque than a full voltage starter.

With a normally sized ASD, you are capable zero speed torque that is between 150% and 200% of normal full load torque, time limited by the VSD for between 30 and 60 seconds. This may or may not be greater than the normal full voltage stall torque of the motor.

With a reduced voltage starter, the stall torque will scale at roughly the square of the applied voltage. If you halve the voltage for starting, then you will get 1/4 the torque.

-Jon
 
weressl said:
I wonder if you would say the same if the money would come out of YOUR pocket?
Uh-oh......I forgot.....It actually DOES come out of your pocket......
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Ha ha :grin: it basically comes down to being alright with paying a little more for the quality. If I wanted practice changing parts I would use a different brand. Cadillac or Volkswagon?????
 
Strahan said:
Ha ha :grin: it basically comes down to being alright with paying a little more for the quality. If I wanted practice changing parts I would use a different brand. Cadillac or Volkswagon?????
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Actually AB's quality record is on par - at best - with the mediocre performers on most product and practically the only thing they excell in in their PLC's, even though since they abandoned direct support, it sucks too.......
 
Strahan said:
Ha ha :grin: it basically comes down to being alright with paying a little more for the quality. If I wanted practice changing parts I would use a different brand. Cadillac or Volkswagon?????
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I think VW has better reliability than GM
 
Strahan said:
Check out the SMC Flex 150. And yes our company is standardized to AB that may be why I prefer AB over other brands regardless of price.
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OMG, when I was working for an AB distributor years ago, I LOVED guys like you! You are the the type of user who keeps them in business, because not all of their products are all that great yet loyal customers buy them almost blindly. Their soft starters, while not junk, are nothing special either. Moderate functionality, low flexibility (despite the name), maximum price, horrific replacement parts cost. I'd give them a B- overall, but certainly not worthy of "regardless of price". Even if I had a plant standardized on AB automation, which I recognize requires a substantial investment in training, I'd make them prove themselves worthy of my other business. Soft starters are too simple to forgo trying to find the best value for your money.
 
Jraef said:
OMG, when I was working for an AB distributor years ago, I LOVED guys like you! You are the the type of user who keeps them in business, because not all of their products are all that great yet loyal customers buy them almost blindly. Their soft starters, while not junk, are nothing special either. Moderate functionality, low flexibility (despite the name), maximum price, horrific replacement parts cost. I'd give them a B- overall, but certainly not worthy of "regardless of price". Even if I had a plant standardized on AB automation, which I recognize requires a substantial investment in training, I'd make them prove themselves worthy of my other business. Soft starters are too simple to forgo trying to find the best value for your money.
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Don't be so quick to jump. Obviously I feel this way and my company due to the fact that they have backed there product. Quality and reliability is number one. Maybe due to the fact we are one of the biggest (ok the biggest) food manufacturers in the world we get better support than what the everyday contractor would. Its only from years of dealing with this line that I feel that way obviously everyone has there own brand they feel comfortable using. I will note some of there products are being made a little cheaper than years ago but tell me one company that is not trying to earn that extra buck.
 
iwire said:
Thanks Marc.

Still would like some more input here.

Anyone?
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Ralspeed is my preferred supplier.
Unfortunately, that would mean import for you.
In my experience, it is well built kit.
If you want, send me a pm and I will give you their details.
 
Iwire,

My two cents.

A soft starter for a starting a reciprocating air compressor is a good option....but how will the load-unload cycle's effect on voltage drop be taken care ?

As you are aware all air compressors work with a set span of air pressure ( let us say 3 bar to 4.5 bar) and load and unload themselves using a unloader valve, or in new microprocessor based compressors with setpoints fed into the console.

Now, whenever the compressor will load itself (at 3 bar pressure) there will be a voltage drop, and this drop will not be taken care by the softstarter as the compressor is already ON.

Hence i would suggest a VFD with two set points 3 bar and 4.5 bar as digital inputs (using pressure switches) and two preset speeds.

You would also have energy saving when the compressor is running in unloaded mode.

Cheers.
 
This compressor stops and starts based on pressure, it is not a continuous run type.

When I said the unloaded works I meant the unloader the relives the pressure in the cylinder when it shuts down.
 
chaterpilar said:
Ok.

How many start stops would there will be in a an hour.

Softstart manufacturers have a limitation of that also.

cheers.
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Few, likely less then one per hour. It is a compressor in large truck repair shop but they only have a 3 bays and do general repairs, no body or paint work.
 
weressl said:
I think both ASD's and SSRV starters have starting torque limits. ASD's have more potential for adjustments. SSRV have a starting torque kick feature. Neither can provide more starting torque than the FVNR starters.
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I thought about this for a while. I'm a new here and from a different country to most of the contributors to this forum. And I don't want to create discord. Enough of the preample.
I just don't agree with your point that an an adjustable speed drive can't provide more starting torque than a full voltage fixed speed starter.

The full voltage applied from standstill will provide locked rotor torque. That torque depends on motor design. For NEMA, that would be about 150% FLT for arond 500-600% FLC from the supply.

By contrast, a variable frequency drive can produce 150% torque at standstill at far lower supply current.

The difference is the slip at which the two systems operate.
 
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