Normal inverter power consumption

mshahmshah Registered Users Posts: 1
I just finish setup a small offgrid solar system. I connect 12v battery to china brand inverter(it says 1500w but i believe its a low end inverter). In between, i put dc voltmeter to monitor the power consumed from the battery. When I turn on the inverter without load, the voltmeter shows 10-12w consumed. But when i connect 20w load(lamp) the meter reading hike to 53w before slowly down and stop at 45w.
As for me the beginner, i not sure if this is normal. Because in my calculation it should be 10+20=30w. Is the inverter consume more power when load connected on top of the initial(10w) power it consumed? Any idea and helps very much apreciated. Thanks

Comments

  • BB.BB. Super Moderators, Administrators Posts: 28,144 admin
    Can you tell us a bit about what you meter(s) are using to measure the AC and DC power/watts/VA/amps/etc.?

    In general, if you measurements are accurate to within 5%, you are doing pretty good. Even to within 10% accuracy is not bad...

    And to measure True "Power" (Watts), you need a "power meter" (that measures both RMS Volts and RMS Amps, and the phase between the two) at the same time.

    Accurately measuring AC and Pulsing DC current (and Watts) is not easy (or cheap).

    To get better, you pretty much need lab grade instrumentation.

    Add the issues between TSW and MSW (true/pure sine wave vs modified square/sine wave) inverters, and using "simple/cheap" peak reading meters and true RMS reading meters--Can make it difficult to equate readings of power between the AC and DC sides of your inverter. 

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bill von novakbill von novak Solar Expert Posts: 814 ✭✭✭✭
    mshah said:
    I just finish setup a small offgrid solar system. I connect 12v battery to china brand inverter(it says 1500w but i believe its a low end inverter). In between, i put dc voltmeter to monitor the power consumed from the battery. When I turn on the inverter without load, the voltmeter shows 10-12w consumed. But when i connect 20w load(lamp) the meter reading hike to 53w before slowly down and stop at 45w.
    As for me the beginner, i not sure if this is normal. Because in my calculation it should be 10+20=30w. Is the inverter consume more power when load connected on top of the initial(10w) power it consumed? Any idea and helps very much apreciated. Thanks
    This is normal.  High power inverters are very inefficient when run at low powers.

    How are you measuring current?
  • ThomThom Solar Expert Posts: 185 ✭✭✭
    Love my 300w inverter. 
    Off grid since 1984. 430w of panel, 300w suresine , 4 gc batteries 12v system, Rogue mpt3024 charge controller , air breeze windmill, Mikita 2400w generator
  • stmoloudstmoloud Registered Users Posts: 63 ✭✭
    edited December 9 #5
    The inverter will have a self-consumption of watts. A 1500w will consume more than say, a 300w inverter. So that difference of 23 watt you are measuring could be the intermittent expense of what it will cost you to power a 1500w inverter. 
    310W panel array, 2 x 6v 220 ah Crown batteries, no name PWM controller,  no name 600 PSW inverter, grid backup but not for long 
Sign In or Register to comment.