# Soft start or vfd



## deakin (Mar 7, 2021)

i no longer have 3ph service and run off of a ph converter. one machine, 10hp - 240v 3ph 1750rpm, starts under a high load. inrush current is 185@ and the 20hp ph converter cannot handle it. (it's running off of a 100@ 1ph sub panel)

soft start. vfd or quit taking in heavy work?  i don't have any experience in any of the three.


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## Ulma Doctor (Mar 7, 2021)

what type of converter are you using? Static or RPC ?
soft starter and VFD's could both be utilized


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## JimDawson (Mar 7, 2021)

VFD is the only way to go.  At 10HP, you will still need the RPC to generate 3 phase for the VFD.  A VFD is much less expensive then a soft star, as well as being very flexible.

I have no problems starting my 10hp spindle off of a 15hp RPC and a VFD.


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## deakin (Mar 7, 2021)

Ulma Doctor said:


> what type of converter are you using? Static or RPC ?
> soft starter and VFD's could both be utilized


rpc


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## deakin (Mar 7, 2021)

JimDawson said:


> VFD is the only way to go.  At 10HP, you will still need the RPC to generate 3 phase for the VFD.  A VFD is much less expensive then a soft star, as well as being very flexible.
> 
> I have no problems starting my 10hp spindle off of a 15hp RPC and a VFD.


i'm not starting a spindle tho' 

this machine starts under a very heavy load


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## JimDawson (Mar 7, 2021)

deakin said:


> i'm not starting a spindle tho'
> 
> this machine starts under a very heavy load



I also run my air compressor with a VFD.  In that case it is loaded, it is set to ramp up over 10 seconds, the starting current never goes over the max running load.

What kind of machine are you starting?


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## deakin (Mar 7, 2021)

JimDawson said:


> I also run my air compressor with a VFD.  In that case it is loaded, it is set to ramp up over 10 seconds, the starting current never goes over the max running load.
> 
> What kind of machine are you starting?


think of a big belt sander with 300# sitting on it when starting.


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## mksj (Mar 7, 2021)

Cost of a VFD will be more than a soft start, if you do not need any of the other VFD features. There is some derating of VFD's when run off of RPC's, typically I just add a DC choke which decreases THD/current peaks. I would look at a soft staarter run off the RPC to the motor. WEG makes some reasonable cost ones would need to see if you need the 30A vs. 45A.  There are also limitations to start/stop cycles per hour, so if more than 4 than may need to look at VFD's or a soft starter that supports that. 








						Soft Starter, Compact, 3 Phase, 10hp, 30 Amps,208-
					

Soft Starter, Compact, 3 Phase, 10hp, 30 Amps,208-480V, Variable Torque, Built In Bypass, Please Note The Suffix Update From EPZ to TPZ Was Only Due to A New Manual Included




					www.wolfautomation.com
				











						Soft Starter, Compact, 3 Phase, 15-30hp, 45 Amps,2
					

Soft Starter, Compact, 3 Phase, 15-30hp, 45 Amps,208-480V, Variable Torque, Built In Bypass, Please Note The Suffix Update From EPZ to TPZ Was Only Due to A New Manual Included




					www.wolfautomation.com
				











						Soft Starter, 34 Max Amps, Chassis w/ Built-InBypa
					

Soft Starter, 34 Max Amps, Chassis w/ Built-InBypass, Simple Start Control w/ Motor Protection




					www.wolfautomation.com


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## deakin (Mar 7, 2021)

mksj said:


> Cost of a VFD will be more than a soft start, if you do not need any of the other VFD features. There is some derating of VFD's when run off of RPC's, typically I just add a DC choke which decreases THD/current peaks. I would look at a soft staarter run off the RPC to the motor. WEG makes some reasonable cost ones would need to see if you need the 30A vs. 45A.  There are also limitations to start/stop cycles per hour, so if more than 4 than may need to look at VFD's or a soft starter that supports that.
> 
> 
> 
> ...


that was also a thought - should i get a larger than 10hp ss or vfd.


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## mksj (Mar 7, 2021)

You have not defined what machine it is, how often it needs to start, and the running load/draw/voltage. With a VFD, there are two options, one run off of the RPC vs. one run from single phase. Recently went through a similar discussion of sizing a VFD for a 15Hp compressor running off of single phase. I am not sure a straight 10 Hp VFD would run off an RPC to drive a 10 Hp motor, really depends on the model,  the output under heavy load and the overload % rating. I probably would go with a 15 Hp to give you some head room. The price of the Fuji's compact series is hard to beat.
Fuji 10 HP LSLV0075C100-2 is HD rated for 10 Hp, so should work with a DC choke and runs $405. https://www.wolfautomation.com/vfd-hd-10hp-32a-200-240-vac-3-ph-ip20/
The Fuji 15 Hp which could also be run off of the RPC runs around $570 https://www.wolfautomation.com/ac-drive-15hp-230v-3-phase-33386/
If running single phase input (no RPC) then a Fuji 20 Hp FRN0060C2S-2U will run $650 https://www.wolfautomation.com/ac-drive-20hp-230v-3-phase-33387/

If running a soft start, then would need to address frequency of starts and any derating or configuration for running off of a RPC. The AuCom is not limited with regard to soft starts, the WEG is. Cost wise it is a close call, but a VFD would take up more space and be a bit more complex to install in the end. The soft starters like the AuCom soft starter would be their 10 Hp model would probably be the easiest to install and also has overload protection for both start and run, but still needs to run off a breaker or fusing. Probably worth discussing with Wolf technical to find what the best fit is for your application, and get a warranty. It looks like the Fuji LSLV0075C100-2 running off your RPC might be your least expensive option, otherwise you might consider 20 HP VFD with single phase input. Another factor may be availability/stock, many distributors are out of VFD's.


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## deakin (Mar 7, 2021)

i thought i described it.  a large belt sander that starts with a big chuck of iron resting on it.  10hp runs at about 30@ but inrush at start is 185@

frequency of starts depends. you would have to stop it to check progress. could be done in one start or may take several. i could squeeze by with 4 starts an hour with the job taking about 5-15 minutes with all the starts

i'm thinking whatever i go with i should probably at least double the rating if not more. i assume a 20-30hp ss or vfd would not be detrimental


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## mksj (Mar 7, 2021)

The SS does not need to be up rated, the AuCom is not limited to starts and is rated at 34A continuous. If going with a VFD, I do not see the need to upsize if it is not needed and there are some other limitations as to fusing and input wiring.  If going with a 20 Hp VFD then I would skip the RPC.


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## deakin (Mar 7, 2021)

with the SS  how is the machine started? with the SS or is that just in series. 

right now there is a foot switch that operates a contactor. it would be two monkeys with a football if both had to be switched at the same time


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## Larry$ (Mar 7, 2021)

JimDawson said:


> I also run my air compressor with a VFD. In that case it is loaded


An air compressor should not be started under load!


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## mksj (Mar 7, 2021)

SS and VFD are in series with the input power to the motor power. A SS has a bypass which closes (pass through) after the soft start and the AuCom  also have a ramp down speed (soft stop). With high centrifugal loads there is always the issue of stopping and dissipating the energy. With a VFD you would use an external braking resistor to help dissipate some of the energy. The SS as to wiring, you would need to look at the directions for each unit.  They typically use 2 wire or 3 wire control similar to VFD's, depends on how they are wired into your application. Trigger voltage can be low or high voltage for the SS, VFD is low voltage per the inputs. Depending on the route you decide, Wolf Automation technical would probably be the best source of information for sizing and installing.


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## deakin (Mar 8, 2021)

got it
thanks


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## sdelivery (Mar 8, 2021)

I would probably modify your machine to start the motor fee of the load, then engage the load.
Everything on the machine will thank you, hell your electric bill will thank you.


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## deakin (Mar 8, 2021)

sdelivery said:


> I would probably modify your machine to start the motor fee of the load, then engage the load.
> Everything on the machine will thank you, hell your electric bill will thank you.


can't work that way unless you want to lose some fingers or hands along with destroying the work piece. can't set a 50-300# (+) workpiece on a moving belt


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## deakin (Mar 8, 2021)

well wolf tech knew absolutely nothing about soft starters and they didn't have the product or know when they could get it. (must be covid)
aucom rep tho' verified it should work although he said it was a 6-10 cycle per hour. (which is ok)
i ordered a SR33-41 from automation direct. their selection chart says it should work and was in stock so i'm told
fingers crossed


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## Flyinfool (Mar 8, 2021)

Larry$ said:


> An air compressor should not be started under load!


Not all compressors have an unloader valve, mine don't , so it always starts under load. 
It looks like deakin's machine also needs to start under load.


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## mksj (Mar 8, 2021)

Disappointing about Wolf Automation technical, seems like who you get, others have have mentioned they have been more helpful. Might go to some third party these days.  The AuCom seemed to check all the boxes. I like Automation Direct, I use them a lot for automation/control system parts, so glad they could provide more information. The SR33-41 should work if you motor draws 29-30A under full load, the load would be rated class 20 from the description. SR33-55 would be indicated it your motor FLA is over 30A. Frequency of starts is 5 per hour, but this will also be influenced by many other factors, the rated starting capacity for class 20 is 4X the motor current for 19 seconds, I would assume if one shortens the starting time or decreases the starting current it would lower the thermal impact and allow more start stop cycles. Still seems like a SS is an easier install than a VFD.


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## sdelivery (Mar 8, 2021)

deakin said:


> can't work that way unless you want to lose some fingers or hands along with destroying the work piece. can't set a 50-300# (+) workpiece on a moving belt


Then put a clutch on the moving belt drive? 
Or maybe on the motor to the drive.
The rest of the industrial world has learned to stop and start the largest equipment safely.


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## deakin (Mar 8, 2021)

mksj said:


> Disappointing about Wolf Automation technical, seems like who you get, others have have mentioned they have been more helpful. Might go to some third party these days.  The AuCom seemed to check all the boxes. I like Automation Direct, I use them a lot for automation/control system parts, so glad they could provide more information. The SR33-41 should work if you motor draws 29-30A under full load, the load would be rated class 20 from the description. SR33-55 would be indicated it your motor FLA is over 30A. Frequency of starts is 5 per hour, but this will also be influenced by many other factors, the rated starting capacity for class 20 is 4X the motor current for 19 seconds, I would assume if one shortens the starting time or decreases the starting current it would lower the thermal impact and allow more start stop cycles. Still seems like a SS is an easier install than a VFD.


auto direct had a selector guide. one question was elevation above sea level. that was never covered in my 60's electronics classes


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## sdelivery (Mar 8, 2021)

Flyinfool said:


> Not all compressors have an unloader valve, mine don't , so it always starts under load.
> It looks like deakin's machine also needs to start under load.


Even the cheapest compressors have an unloader. With some it is on the head(valves) some Its built into some of the pressure switches.


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## deakin (Mar 8, 2021)

sdelivery said:


> Then put a clutch on the moving belt drive?
> Or maybe on the motor to the drive.
> The rest of the industrial world has learned to stop and start the largest equipment safely.


easier said than done. would have to be a slipping clutch or the workpiece and i would be thrown across the room


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## mksj (Mar 8, 2021)

Yes, they have a nice calculator to determine the size of the SS. As mentioned the calculator may be based on maximum values, so there may be some wiggle room on the start/stop cycles. The AuCom is not limited to starts per hour.




__





						Soft Starters Selector | AutomationDirect
					





					www.automationdirect.com


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## sdelivery (Mar 8, 2021)

You mean like a part on an old VTL?
Many of the large lathes used a mechanical clutch to start the load , this way the operator could ease it up to speed.
Many cranes are using both friction clutches as well.
Monarch lathe company uses an easy to make style, I know of 30 HP on one of them. And adjustable when it starts to wear.


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## deakin (Mar 8, 2021)

sdelivery said:


> You mean like a part on an old VTL?
> Many of the large lathes used a mechanical clutch to start the load , this way the operator could ease it up to speed.
> Many cranes are using both friction clutches as well.


think of an engine block on a very large belt sander. two hands holding on to the block, one foot on the switch, the other foot keeping the operator vertical - out of hands and feet


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## sdelivery (Mar 8, 2021)

deakin said:


> think of an engine block on a very large belt sander. two hands holding on to the block, one foot on the switch, the other foot keeping the operator vertical - out of hands and feet


Sounds like someone needs to stand back and engineer some solutions to the process.
It also sounds like it is just a matter of time before someone gets hurt.


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## deakin (Mar 8, 2021)

sdelivery said:


> Sounds like someone needs to stand back and engineer some solutions to the process.
> It also sounds like it is just a matter of time before someone gets hurt.


they have been using this type machine in eng rebuilder shops for a long time. i bought this new in 1985. used it almost daily back in the day. never got hurt. can't say the same about dirt bikes.

i don't believe it is nec to reinvent it. only issue with it now is power or lack of


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## deakin (Mar 10, 2021)

got the soft start in. has a label that says be sure it has control voltage before starting so i called auto direct tech support. now i'm more confused. apparently :
i need a 24vdc power supply (no problem)
i need a toggle switch to turn the SS on but the sequence is critical
i can't turn on the SS then turn on the motor on with the foot sw
i can't bypass the contactor because one leg feeds power at all times from the SS os the motor would have one leg hot
i can't shut the power off to the motor before shutting off the SS or i will destroy the SS

so what i left with was i would have to put the SS on the output side of the contactor and immediately after pushing the foot switch i would turn on on the SS. then i would have to remember to turn off the SS then the foot switch.
not enough hands and feet


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