Use VFD or Contactor for 5HP Blower.

[dani90]

Customer want to use contactor for their 5HP motor blower application.

im leaning to VFD.

anyone use contractor for blower application?

thanks in advance.

 

[Old Man]

VFD, just explain the benefits. Should be easy choice.

 

[mburtis]

5 horse isn't that big, if all they need is simple full speed why complicate it?

 

[dwoodlock]

Yeah if they intend to run full speed all the time seems like contactor is probably the way to go.

Just from a cost and simplicity perspective.

 

[robertmee]

Moat centrifugal blowers run full speed...no advantage to varying speed, and the drive would be set to v/hz anyway for that application. So it comes down to control. Is ethernet or discrete preferred? You could even do both using an E300 type electronic overload with contactor so you can monitor OL trips and running amps, and remotely reset OL trip faults.

 

[Old Man]

So many variables to be considered?
What is blower used for? Do you need to know when it is running? Do you need to adjust speed? Do you want a "ramp up" & "ramp dn" this will
extend life of motor tremendously. Do you need to record "trends" for Hz, Amps, Voltage. Fault Logs, Etc.

All of this can only be done with vfd. But by all means keeps it simple.

 

[JesperMP]

Yes, we use contactors for blowers.

Blowers comes in all sizes, up to gigantic.
VFDs have become quite inexpensive, but for the larger size blowers, it is still a much more expensive option.

 

[Puddle]

Go in the middle, soft starter. Half the cost of VFD with the same mechanical benefits on starting.

 

[BOWILLY]

The application and the customer's wallet will dictate the design. There are definite advantages to controlling the blower with a VFD but if they are of no benefit to the customer, why would he pay for them?

 

[JesperMP]

For 5 HP DOL start is fine.

One hot topic these days is energy savings. If the blower must not operate at 100% at all times, then using a VFD to regulate the air flow instead a throttle or bleeding air can provide savings. One has to make a calculation if it pays off. Take into account that VFD operation incurs its own energy losses.

 

[JankyPLC]

Contactor keeps it simple. VFDs on high inertia loads like blowers can open a whole new can of worms generating faults that would never happen with a contactor. Could it be stopped and started before motor coasts down(flying restart)? If so you may end up with a braking resistor in addition to the VFD cost.

 

[Tom Jenkins]

I've done blowers from little guys like yours up to 4,000 hp. I can't tell you what is best for your application, but I can tell you what to look for.

First, the process needs to dominate the decision. Will the process benefit from a variable flow rate? Can you optimize the flow rate at one point, or is a continuous modulation capability advantageous? If everything works best with a constant design flow rate then it's hard to justify a VFD on energy savings.

5 HP is really too small to justify a reduced voltage starter unless there is some special sensitivity to the inrush current in the rest of the system. That's usually a consideration beginning around 30 hp or 40 hp.

Finally, look at a life cycle cost analysis. Does energy saved with a VFD offset the incremental cost? Based on the owner's power cost how many years will it take to pay back the higher cost with energy savings?

You don't identify the type of blower. Different considerations are required in using a VFD on a positive displacement blower versus a centrifugal blower.

 

[lfe]

What type of fan?
If it is an axial fan or a low pressure centrifugal fan you will not have problems with a contactor.

If, on the other hand, it has a turbine with a lot of inertia and a large diameter, a standard motor protection will not work well, the thermal protection will trip. In this case, I recommend using a soft starter, cheaper than a VFD.

My experience is that Siemens Sirius starters work well for those types of loads.