Variable frequency drives are now ubiquitous in the motor control industry, with dozens of large to small-scale players offering ready-built products. With just a few quick Google searches you can find drives to meet almost any need. However, like the proverbial square peg in a round hole, sometimes an off-the-shelf drive just doesn’t fit the use case.
To help motor control engineers determine when developing a custom VFD makes sense we have created a Custom VFD Checklist that outlines the considerations we work thought when consulting with our clients. While we specialize in building custom AC motor drives, going the custom route is not our first choice if it can satisfactorily avoided.
There are trade-offs for going down the custom path. You get exactly what you need, but it will typically cost more than off-the-shelf, unless substantial volumes are involved. Cost factors may include non-recurring engineering costs (NRE), UL certification costs if required, packaging costs, and/or higher per-unit costs. There is also a timing factor; anything which must be first engineered and developed naturally takes longer than pulling something off the shelf. Other considerations include ownership of intellectual property associated with a new drive, assuming it is truly a one-off design.
Case Study – Oil Burner: Recently Invention House created a custom VFD for an OEM that manufactures oil burners used in HVAC applications. Our client needed a 110v single phase drive capable of 80Hz to drive the combustion fan of a portable oil burning heater. The burner is a world-ready unit that must be able to operate between -40 and +130F(55C). In addition, it had to be very rugged to withstand truck transport and rough delivery conditions. Invention House designed a single board drive in an open 3″x 2″x 7″ aluminum frame. The drive responds to commands for high and low fire rates (100,000/200,000 btu/hr). It has several on-board relays to energized the fuel solenoids and the fresh air blower. The drive has custom adjustable relay timing to avoid flame outs during transitions and to avoid blasts of cold air to the user. The drive’s main function is to create the correct frequency for the combustion fan. This is done using an on-board altitude sensor that allows the drive to maintain the correct air /fuel ratio. There is also a on-bard tilt sensor for safety. These sensors would have been difficult to do using convention PLC’s and a conventional solution would never have fit in the necessary space. The true befit of the combustion solution came at then end of the development when the specification suddenly changed wanting combustion at 14,000 ft. This required 120hz operation and more voltage. Invention House simply reprogrammed the drive for 120hz and designed an small transformer to boost the input voltage to 160vac. The product was successfully tested at the top of Pike’s Peak and has endured operating many thousand of hours in harsh conditions.
As the above case study illustrates, if your situation is one where unique factors are involved, such as those outlined in our Custom VFD Checklist, then going down the custom path will be a rewarding one. You end up with a drive tailored to your specific requirements and in the size and shape that fits your design specs. In addition, because the drive is tailored to your product’s specs, there is usually less installation time as the unit comes programmed, tested, and with wiring terminals and other factors that make installation more of a plug and play install.
One remaining important factor to share…gaining a competitive edge. If your company is competing with similar products and all those products employ off-the-shelf drives, you can gain a competitive edge by going the custom route. Your product will be unique and have a performance curve that beats the competition and helps create stronger vendor-customer bonds.
In summary, don’t be afraid to look at developing a custom variable frequency drive, especially if your product meets one of the 5 key custom VFD decision factors outlined in our free guide. If you have that round hole situation, build a round drive. You’ll be more satisfied in the end and so will your customers.