I want to buy an inverter-generator to run my Trane heating system in case of a power outage. The Trane is on a 20 amp circuit. The sticker says it needs a minimum of a 15.2 amp circuit.
My question is, how do I determine (not estimate) the surge amperage of the 1 hp blower motor in my Trane heating system?
The inverter generators I have seen have max outputs of 2,000, 3,000, or 4,000 watts. I am trying to figure out if any of these will run my heating system. It seems the critical issue is the starting current of the 1 hp motor.
How might I go about measuring the starting current of my heating system?
Update: My HVAC 1 hp fan motor is constantly running- on low if not providing heat and on high if it is providing heat. Based on that, it seems to me that I need to use the in-rush amperage, since the theoretical calculations are all not relevant to my situation. Thanks.
Best Answer
Measuring the startup load is as easy as using a clamp on meter and turning the air handler on and off.
The startup load will be high for a split second, then drop down to a steady load.
Use Ohms Law to calculate the wattage.
Watts/Voltage = Current
As mentioned in my comment, the invertors peak load is a good indication of the invertors motor starting current.
Edit
To get the most accurate motor startup load readings from your meter, you may need to use one that supports "in-rush" readings.
Meters like the Fluke 374, 375 and 376 support "in-rush" readings.
Edit 2
I did some digging around and found the formula to calculate inrush current.
Take the NEMA assigned letter to your motor, in which case yours is letter B, and plug that into this equation:
You can ignore the square root of 3 if your voltage source is single phase.
Bottom line is your invertor needs a surge rating of at least 4000 Watts
NEMA Motor Letter Table