Newbie with an Ohm's law, battery question

[Dave S]

Hi. I took two 12 volt batteries, wired them in series. Produced 26 volts. Hooked it up to a 24 v inverter. Then I put an AC device on inverter that draws 200 watts. When I took an amp reading. meter says I draw 16+ amps. 200 watts at 12 volts should be 16.6 amps...I would think 200 watts at 24 volts would be 8.3...Why is my reasoning wrong? Thanks

 

[sunshine_eggo]

Likely causes:

equipment error
user error
instrument error
inefficiency issues
voltage drop

Did you MEASURE a 200W load, or are you assuming?

Inverter is also consuming power. Bigger inverters consume more. Remove the 200W load, and you should have a non zero current.

If the 200W is a small fraction of the inverter's rating, efficiency may be very poor. Peak efficiency is at about 30% of rated. Above 30%, it's a slow loss of efficiency. Below the peak, it can drop of rapidly at very low power.

My high-end Victron inverter/charger is only about 65% efficient when I'm only using 100W vs. its 5kVA rating.

A more accurate estimate that assuming 85% efficiency:

200/24/.85 = 9.8A

 

[Dave S]

Okay. Great. Thank you. I just bought cheap 24v inverter. I imagine it is probably that. I was just wondering if I misunderstood the math/ohms law.