# Can a soft start survive? 30+ starts per hour.



## acro (May 3, 2011)

Just brainstorming here trying to save some $$$.


I have a 40hp motor on a feeder that used to be controlled by a VFD that experienced a failure. Replacement is about $5,600 and we have not been able to get it for quite a while.

We have been running it on a full line starter for several months, at the cost of frequent belt replacement. Running it at full speed requires frequent start stop cycles of over 30 per hour possible.

Well, I thought that about getting a soft start for it to save some of the wear and tear on the belts, but see that even 10 starts/ hour might be near the limit for reliability.

Just for $$ I had considered a Stellar SR33 132a($1,100), but I don't have any experience with them, OR any application with this frequent of a cycle.

Is there any hope of finding a decent soft start option for this application?


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## Bbsound (Dec 16, 2011)

I would not recommend it. 

I think it is the perfect application for a VFD.:whistling2:


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## acro (May 3, 2011)

Yea, me too.

I just looked at the PO's and we have spent $2200 for belts since the drive went out.

Probably would have been less than $500 if the drive was working.


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## John Valdes (May 17, 2007)

The first thing you need to do is contact a soft start manufacturer and ask them this very same question.
If this was my project, I would be trying to find out how to keep this motor running and start, stop the application or process instead of the motor.
You did not give any hint as to the reason for the redundant starting, nor have you told us what the application is.
This asking to much IMO for any motor.


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## JRaef (Mar 23, 2009)

Soft starters (at least the good ones) are designed to handle the same starts / hour as the motors they serve. If you are derating the motor to be able to handle 30 starets / hour, then sizing the soft starter to that same motor size accomplishes the same thing.

If however you are NOT derating that motor for the extreme duty cycle, you are going to be replacing that motor in short order. According to NEMA MG-1, a 40HP 1800RPM motor is rated for 4.7 starts per hour, with a minimum off time of 65 seconds between each one. The only way to get more out of it is to use the formula that is inertia dependent, which means over sizing the motor for the interia in order to minimize the effects of rotor heating. So for 30 starts/ hour, a rough guess (without knowing the load inertia) is that if the load is under 7.5HP, using a 40HP motor will allow you that kind of thermal capacity. 

So if you do have a 40HP motor on a 7.5HP load, then the strain on a 40HP soft starter is less as well and it should be fine.

Or you can use a VFD...


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## JRaef (Mar 23, 2009)

acro said:


> ...Just for $$ I had considered a Stellar SR33 132a($1,100), but I don't have any experience with them, OR any application with this frequent of a cycle.


If you are at all inclined to experiment, DO NOT use that soft starter! It is a "2-phase" design, which means it only ramps 2 of the 3 phases, the middle pole is just a piece of busbar. They do this to be cheaper, but the down side of that is that it INCREASES the heating effects in the motor, especially the rotor.

I would not recommend even 10 / hour with that POS.


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## acro (May 3, 2011)

John Valdes;904058
You did not give any hint as to the reason for the redundant starting said:


> acro said:
> 
> 
> > I have a 40hp motor on a feeder
> ...


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## acro (May 3, 2011)

JRaef said:


> If you are at all inclined to experiment, DO NOT use that soft starter! It is a "2-phase" design, which means it only ramps 2 of the 3 phases, the middle pole is just a piece of busbar. They do this to be cheaper, but the down side of that is that it INCREASES the heating effects in the motor, especially the rotor.



When reviewing the specs, I did notice that about the 2 phase control, but had not considered the consequences.

Again, thank you.


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## dronai (Apr 11, 2011)

I dont know if this is correct, but I was told that soft starts are a thing of the past, and that VFD's are replacing them ? If something doesn't need speed control, it seems like a soft start would be a cheaper way to go, especially on large motors.


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## peloflex (Jan 18, 2013)

Your VFD went out for a reason... Having a 40HP motor cycling power 60 times in a hour is not an easy task for any electrical component, have you considered the alternative of putting in a coil activated mechanical clutch so you can just keep your motor runing continously? I am sure Wagner electric could offer a product that suits your application.


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## JRaef (Mar 23, 2009)

dronai said:


> I dont know if this is correct, but I was told that soft starts are a thing of the past, and that VFD's are replacing them ? If something doesn't need speed control, it seems like a soft start would be a cheaper way to go, especially on large motors.


It's becoming true for small HP for sure, you can buy a low-end 10HP drive for the same price as a (good) 10HP soft starter most of the time, and below 10HP drives are often cheaper. But above that the gap widens and at around 50HP a VFD is roughly 3x the price, then at 200HP it's 5x, going up from there. That's why some soft starter suppliers are trying to stay relevant by going to that cheap 2-phase design, even though they know it's bad for the motor.

But also even in small HPs if you don't need speed control, soft starters are a lot simpler to set up, use and troubleshoot in many cases, plus no harmonics issues (once running at full speed).


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## JRaef (Mar 23, 2009)

peloflex said:


> Your VFD went out for a reason... Having a 40HP motor cycling power 60 times in a hour is not an easy task for any electrical component, have you considered the alternative of putting in a coil activated mechanical clutch so you can just keep your motor runing continously? I am sure Wagner electric could offer a product that suits your application.


It's generally a good idea, but for rock crusher feeders, clutches burn out in a matter of weeks because of the dust. People have tried hydraulic drives, eddy current drives, mechanical varidrives, everything under the sun, but most technologies fail in short order or come with other problems, like hydraulic fluid leaks that can ruin a mining process, that they can't live with.

Acro,
VFDs have been the solution that seems to be consistently working well for that application, as long as you don't get cheap on protecting them from dust and heat, which is a real challenge. What you will want is a good Vector drive, one that has DC bus regulation (because the vibrator can cause regeneration that trips the drive on DC bus high voltage) and one that offers a "fins out" heat sink design option so that you dont need fans and filters, because NOBODY will change the filters often enough out there. Thats likely why yours failed, but a lot of these options are only more recently available so what you had may have been the best they could do at the time. Done it dozens and dozens of times and the only ones that have failed have been when the users were unwilling to spend the extra it takes to do it right, because some dingbat supplier convinces them they don't need it.


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## acro (May 3, 2011)

peloflex said:


> Your VFD went out for a reason... Having a 40HP motor cycling power 60 times in a hour is not an easy task for any electrical component, have you considered the alternative of putting in a coil activated mechanical clutch so you can just keep your motor runing continously? I am sure Wagner electric could offer a product that suits your application.



I suspect heat and dust had a lot to do with it. It was in an unventilated 36x36x12 cabinet in an extremely dusty environment. Once I even had to take the display apart and clean the dust from the back side of the screen. I sealed it up with some silicone when I put it back together.



I am going to install a 107cfm fan and 10x10 filter, and have also installed a line reactor. I had the fan laying around. Think it will be adequate?




I never considered the clutch. But we did finally get the approval for the new drive. I think it is about a 2 weak lead time on it.


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## acro (May 3, 2011)

JRaef said:


> Acro,
> VFDs have been the solution that seems to be consistently working well for that application, as long as you don't get cheap on protecting them from dust and heat, which is a real challenge. What you will want is a good Vector drive, one that has DC bus regulation (because the vibrator can cause regeneration that trips the drive on DC bus high voltage) and one that offers a "fins out" heat sink design option so that you dont need fans and filters, because NOBODY will change the filters often enough out there. Thats likely why yours failed, but a lot of these options are only more recently available so what you had may have been the best they could do at the time. Done it dozens and dozens of times and the only ones that have failed have been when the users were unwilling to spend the extra it takes to do it right, because some dingbat supplier convinces them they don't need it.


We ordered another AB Powerflex 70, which is what was there originally. I am sure you are familiar, but has a built in fan. Pretty sure the DC bus is regulated on it. Correct?

I built the fan enclosure myself and it will use 10x10 furnace type filters. Just slide right in and out. I think it will be way easier than any of the ones the cabinet mfg's have. Most of them have at least one nut or bolt that must be removed. And the filters are way cheaper too.

That's the plan anyway.



Is Vector a brand? maybe I will google it later.


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## peloflex (Jan 18, 2013)

acro said:


> I suspect heat and dust had a lot to do with it. It was in an unventilated 36x36x12 cabinet in an extremely dusty environment.  Once I even had to take the display apart and clean the dust from the back side of the screen. I sealed it up with some silicone when I put it back together.
> 
> 
> 
> ...


Dust is electronics worst enemy. it affects heat transfer (cooling) tremendously! most definitely that was the reason why it went down. 

Best of luck with your repair, it seems like the worst part is now behind.:thumbsup:


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## JRaef (Mar 23, 2009)

"Vector drive" has to do with how the drive regulates speed and / or torque. A basic drive tells the motor what speed to run at, but doesn't know if it is actually running at that speed or not. A Vector drive does, so for example if it tells it to run at 50% speed and it sees the shaft speed is only 48%, it tweaks the way it pumps power into the motor to correct the error and get it back to 50%.

The PF70 is a Vector drive. No problem there.

The DC bus regulation is also there on a PF70, although the PF753 would be better at it for this type of application. Still, if it was working, it must have been fine for your machine.

There is a "Flange Mount" version of the PF70 available, it looks like this:








It allows the heat sinks to shove out the back of the box and maintain a NEMA 4X seal, so the box may not need to be vented at all and the dust stays out. I would highly recommend it if you haven't already bought it.


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## denny3992 (Jul 12, 2010)

Might want to rethink the fan and go with a compressed air cooling system and pressurized enclosure..... No dust gettin in and will def keep ur drive happy and cool!


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## JRaef (Mar 23, 2009)

denny3992 said:


> Might want to rethink the fan and go with a compressed air cooling system and pressurized enclosure..... No dust gettin in and will def keep ur drive happy and cool!


Very true, but only if you have oil free dry compressed air... which is unlikely at a jaw crusher feeder.


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## acro (May 3, 2011)

Correct - no air available and I guess the enclosure it is is would be nema 3 at best.

Interesting about the flange mount option. I was not aware of that, but it is too late for that on this one.

I do hope the fan helps and they keep an eye on the filter. It will be on the side of the enclosure facing the door, so it will be very easy to see. And as long as they keep a box of filters on hand, should be fine.


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## JRaef (Mar 23, 2009)

acro said:


> Correct - no air available and I guess the enclosure it is is would be nema 3 at best.
> 
> Interesting about the flange mount option. I was not aware of that, but it is too late for that on this one.
> 
> I do hope the fan helps and they keep an eye on the filter. It will be on the side of the enclosure facing the door, so it will be very easy to see. And as long as they keep a box of filters on hand, should be fine.


Good luck with that, I rarely see filters that are properly maintained in relatively clean environments, let aloe a crushing plant. It could be that your plant has a conscientious crew with good PM skills though. At the very least when the drive trips out on over temperature, that should act as a notification for them to change the filter, but that puts a lot of stress on the drive. I'll take a look in the manual tomorrow and see if the PF70 has a temperature WARNING level that can be programmed to an output relay, but I don't think so. If not, you could set off a light with a simple little thermostat set at a temperature below the critical air temp of the VFD (104F), say 95F, so there is a little head room.


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## acro (May 3, 2011)

Good idea, though I also don't think there is a parameter for the temperature alarm.

A separate relay and t-stat could be something to consider.


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## JRaef (Mar 23, 2009)

acro said:


> Good idea, though I also don't think there is a parameter for the temperature alarm.
> 
> A separate relay and t-stat could be something to consider.


You're right, no Temp limit alarm, only trip. But here is a free convoluted work around if you have not used one of the Digital Outputs. 

Program the Drive OL parameter (150) response contition to "Both-PWM 1st", which will reduce speed if the heatsink temperature gets too high, then program the unused Digital Output (380 or 384) to change state on At-Speed (selection value of 9). Then you can wire up an alarm light to the NC contact of the output relay. What will happen is that if the drive starts to over heat, the response will be for it to artificially reduce the speed so as to reduce the heating of the transistors and heat sink. But if you have the Output programmed for At-Speed, it will compare the speed you have TOLD the drive to run at against the actual speed command it is giving to the motor, and the relay will change state. By wiring to the NC contact, the light will be lit when you first accelerate, but will go out once it gets to speed. Then if the temperature gets too high, the speed will drop and no longer match your commanded speed, so the relay will drop out and the light will go on again. It will take some training of the operators to understand that if the light goes off AFTER it is running, that means they need to change the filter.


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## acro (May 3, 2011)

Interesting.

Thanks .


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## acro (May 3, 2011)

With the current ambient temps, I have not worked on the temp alarm stuff yet, but when configuring the new drive, we(vendor tech support and I) came across something that was quite strange and the tech had not experienced before.

What's your take on it?

Grounded B phase installation and I removed the jumpers. Again, this is an elliptical type feeder installation where the load drives the motor for part of it's revolution but strict speed control is not required and no braking resistor in place.


After completing the somewhat automated initial motor setup, I proceeded to the more involved settings. And I referred to my notes and your previous comments on this subject.

I set this up with 3 wire control, and with my 1st error, I had to disable Dig in 3.


The rotation test was fine, but when I tried to start the motor for real...
Immediate Decel inhibit fault, so I disabled Bus Regulation - 161/162.
Then it faulted on over voltage. I looked around and tried a few other things, but could not get the drive to run the motor more than a fraction of a second.

So I got ahold of someone that knew more than me. We changed 161 back to default - 1. Still faulted.
So he had me change bit 6 in parameter 238 to 0. He said this basically turns off the "check engine light"

This got the drive to operate the motor without faults. However.... I found that I could not stop the motor!


Not sure if it was related, but in my inital setup, I set the minimum speed to 20hz, and the maximum to 60hz.

The drive was "seeing" the stop command from either the remote station or the keypad. But all that would happen was that the motor would slow pretty quickly to the 20hz, and then very slowly coast down to around 10hz, but would never shut off or stop. The drive was continuing to supply the motor with power. Press either of the start buttons, and right back up to 60hz maximum. Press the stop, and back down to about 20hz and lower.

I thought I had set 155 to 0 in my initial configuration, but we checked it and it was set at the default 1. so we changed it to 0, and the drive then would stop normally.


So, have you seen any cases where an improper configuration basically would not allow the drive to shut off using the keypad stop?


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