vfd old condenser retrofit

[codgy]

Anybody ever converted from fan cycling to vfd? I have a customer w/ 2 15hp larkin hot gas defrost units each one has a 4' single belt drive fan, 3 phase condenser motor. They have had some stress cracks develop due I think to rapid fan cycling during winter operation. I thought about using A350 series 0-10vdc to modulate speed control but wondered what suggestions you might have.

[BDOLIN]

Fairly easy to do but be careful, older motors with class A insulation or sleeve bearings will die quickly on VFDs.
Most VFDs (we use Yaskawa) have built in motor overloads and these should be set for the motor you have. Keep wire between VFD and motor as short as possible and make sure they are in conduit and grounded well.
Set the vfd to prevent the motor from going below about 20 hz, about 30% of full speed.

If you watch the details in installation, VFDs will give you significant energy savings and better control of head pressure. Savings of 50% over step control are possible and most utilities will give substantial rebates for installing them

[codgy]

What controller would you advise for this setup. Will it directly control the drive?

[BDOLIN]

Most drives will accept a 0-10 volt or 4-20ma analog signal to control the speed. You can use a pressure transducer with those types of outputs and set the parameters in the drive to read the pressure and control to that pressure.