At the risk of opening Pandora’s Box I’m going to present some calculations for (respectful!!!) comments because I am confused as hell! The example I will present will use the figures from the attachment. I will assume a 220V single phase supply and will also assume 100% efficiency in the VFD and a power factor if 1 to keep things simple.
Rated Output: 2.2kW
Input: 220V single phase
Output: 220V 3 phase
Rated Input Current: 23A
Rated Output Current: 10A
Power Factor(PF): 1
At the input:
Input Watts: W = V x I = 220 x 23 = 5060W = 5.06kW
Output Watts: W = V x I x PF x 1.732
2200 = 220 x I x 1 x 1.732
Solving for I: I = 2200 / (220 x 1 x 1.732) = 5.77A (per phase??)
5.77 x 1.732 = 10A (3 phase current)
Output using a PF of 0.85:
2200 = 220 x I x 0.85 x 1.732
I = 2200 / (220 x 0.85 x 1.732) = 6.79A
The numbers are not adding up.
Looking at it differently, a Watt is a measure of energy. 1W= 1 joule per second. It shouldn’t matter if the energy is created by single phase or 3 phase electricity or even a GE CF6 jet engine burning jet fuel, energy is energy. So for a VFD that has an efficiency greater than 90%, it should not take more than 5kW to output 2.2kW.
At 90% efficiency, 2.45kW x 90% = 2.2kW. So for a 220V supply, 2450W/220V = 11.14A. So why does the VFD require a 13A supply?
I keep trying and can’t make the numbers add up, there has to be a reason why all the manufacturers list the input current so high. It’s not being consumed by the spindle and it’s not being dissipated as heat so where is it being used?
I hope someone can explain this to me in simple terms because it’s driving me crazy.
My brain has now exploded and I need to take a nap.