VSD or Soft Starter – which is right for you?
Many people use Variable Speed Drives (VSD) to start their fixed-speed motor applications – why?
Distributors/resellers/installation engineers will propose a solution that is good for them, not necessarily what is right for the end-user or their application. Why wouldn’t they? – We’re all in the business to make money!
It may be that historically, engineers only ever used VSDs – so they stick with what they know – or perhaps they are unaware of how intelligent and fully-featured the modern soft starters are. There is another train of thought that distributors and resellers ‘force’ the customer to have the more expensive VSD – there is more margin to be had.
Generally, a variable speed drive is more expensive than a soft starter – could be twice as much, could be 5 times more, dependent on the size/power of the motor in the application.
For example.
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SS (7.5kW / 37kW / 75kW)
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VSD (7.5kW / 37kW / 75kW)
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Initial Cost
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£1,050 / £1,500 / £2,250
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£2,100 / £5,100 / £10,300
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Additional Eqpt required
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None
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Yes
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Maintenance
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None
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Regular
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Energy Saving
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Yes
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Claimed but consider additional running costs
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Initial Cost
As an example – a middle-of-the-range soft starter for a 55kW crusher application is priced at £2,250. I’ve taken only a couple of examples but VSDs for the same application are listed at £8,600 to £10,300. Installation on a soft starter (from Motortronics) can be very quick and inexpensive. Actual ‘wiring-in’ for both items is about the same but a soft starter – even a highly intelligent unit can take up to 1 (ONE) minute to set-up. VSDs generally take between 45 and 120 minutes. And transferring settings from one unit to another is as simple as plugging in a USB drive to record the data and settings.
“The touchscreen user interface is so simple to use and the built-in application sets make setting up a breeze – under a minute and you’re ready to go!” – one of the many comments that we have had regarding our VMX-synergy soft starters.
Additional equipment
Additional equipment for VSDs can include larger enclosures and more powerful fans to assist with air flow and circulation to ensure that the equipment does not overheat and ultimately fail prematurely.
Downtime and Maintenance
The potential for longer downtime and greater maintenance costs are increased with the addition of any element into the enclosure, no matter what the size or cost. Filters and fans that are required for VSD enclosures are just an example of what may be classed as ‘consumables’.
Energy saving and environmental considerations
Variable Speed Drives (VSDs) are promoted as energy savers by reducing operational speed, thus lowering running costs. However, operating motors and drives below their designed speed can increase the hardware cost of larger enclosures and fans and also the energy costs to running equipment at sub-optimal speeds. Soft starters, once the application reaches the required speed, activate an internal bypass to ensure no extra power is used and no extra heat is generated. VSDs constantly generate heat when adjusting the frequency/speed of the application.
Variable Speed Drives are not needed in all applications, with fixed speed loads, a soft starter is a better option.
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Applications that are suited to soft starter usage are lightly loaded and not those that are using continuous power. Pumps, conveyors, presses, fan and compressors all fall into the good applications for soft starter use category.
Our website gives you access to a powerful selector tool to advise, without obligation, which soft starter is most suitable for your application. We have other tools available which will allow us to show how much savings you could potentially make.
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