This guy wanted a UPS for his two computer controlled lathes. The nameplate on each lathe motor was 9.5amps at 208volt. So he asked for our APC 5000va UPS since the total VA or volt-amps was 3952. Fortunately he shared his purpose before we shipped it to him. Why?
a ) 19amp x 208volts is indeed 3952 volt amps, but that is based on FLA or full load amps. Lathes have motors and have a startup amperage of 2-5 times the FLA that must be considered in the UPS
b) the computer lathe had other components, not just the main motor. Displays, servos, etc, dont take up too much power, but must be included in load calcs
c) both motors could be starting at the same time, so its possible to have extended startup amperage.
d) VA isnt the same as wattage. On non computer loads is very important to understand the factors that influence wattage.
So, I am pretty sure the 5000va unit would not have met his needs, because each unit probably demands 20amps to start, meaning 40amps potentially.
Our solution, was to a) get the real startup amperage using a MinMax multimeter {peak 14.6a} b) sell him two 3000va ups units so as to limit the chance of dual startup and c) switch to Powerware UPS system since they often can handle 125% of load for a brief period.
Bottomline, even if you have been told about a certain UPS, feel free to ask for our opinion. We want you happy and your equipment working well.
