10HP VFD

Features:

• 200V and 400V class inverters
• UL and CE version available
• V/f (volts-per-hertz) control algorithm, selectable for either constant or reduced torque loads
• Convenient keypad for parameter settings
• Built-in RS-422 communications interface to allow configuration from a PC and for field bus external modes
• Sixteen programmable speed levels
• Two-step acceleration and deceleration curves
• PID control adjusts motor speed automatically to maintain a process variable value
• Output frequency range from .5 to 360 Hz
• Continuous operation at 100% torque within a 1:10 speed range (6/60 Hz / 5/50 Hz) without motor derating

A VFD consists of a rectifier/filter section which converts the incoming AC to DC. This high-voltage DC is then converted back to AC with additional controls which provide the speed control. The problem with single-phase AC power is at the input side of the VFD, the part that converts incoming power to DC. When you rectify a three-phase power source, the output voltage from the rectifier never drops below 50% of the peak voltage. This makes it real easy to filter and provide pure DC to the rest of the equipment.

However, when you rectify single-phase power, the output voltage of the rectifier drops to zero 120 times a second. The task of filtering this to provide pure DC is much more difficult. The standard rule-of-thumb is to derate the VFD by 50% when operating from a single-phase source. Thus, if you want to run a 5HP motor, you need a VFD rated for 10HP. I would not recommend operation of any VFD on single-phase power unless such usage is proper according to the manufacturer. If not discussed in the owner's manual, you can always contact the maker's technical support department and ask for assistance.

A VFD drive supplied from a 3 phase system will have a bank of rectifiers at the input feeding a capacitor bank. The capacitor bank serves two purposes --- to filter some of the input ripple from the rectifiers, and to absorb some energy during deceleration. Rectifier-capacitor input filters produce non-sinusoidal pulses of current in the input lines. This means the RMS input current is higher than if the same energy was transferred from a DC source. If you take a VFD drive designed for a 3 phase input and use it on a single phase system, then the diodes and the filter bank may be under sized. This is why you may need a 3 times larger VFD. It is not because of the DC to AC conversion electronics, but because of the input diodes and capacitors.

VFDs typically run on single phase power and convert it to three phase power to the motor. Three phase is preferred for speed control as it is easier to implement and maintains near 100% torque at low speeds Bottom line. Buy a VFD, connect it to a 3 phase motor, plug it into 120 or 240 single phase outlet and you are good to go. BTW, I have a couple of Rob's units, one for my KMG and another for the 9 inch disk grinder. They are top quality and easy to set up and if you do have a problem Rob is always there to help.