Confusing power consumption

[Boldly]

Have been and got a replacement inverter from Toolstation to replace the one that blew up in Spain. I then remembered I had bought old one at a car boot several years ago. Both connected to a spare battery and the wife's hair dryer worked fine on each. I have one of those energenie testers to supposedly save electricity costs. The old inverter from the shed showed 425w the brand new inverter 350w and lastly plugged into the mains 523 w. Does this tell me anything or would you expect similar readings?

 

[Lenny HB]

I expect your inverter is a quasi sine wave (modified sine wave) so the reading you are getting when using the inverter don't mean much.

 

[autorouter]

Not very surprised at this variation. The hairdryer is a 'dumb' resistive load, which doesn't draw more power to compensate compensate for voltage variations. The mains is likely to be at least 240V in the UK, and an inverter will probably be 230V or 220V. A 10% drop in voltage results in about a 20% drop in power for a resistive load.

Another variable is the waveform shape. House mains is a nice smooth Pure Sine Wave, and the inverter, the old one anyway, will probably be a 'Modified Sine Wave' type. I don't know the details of the tester you are using, but it's likely to be inaccurate if it's not a pure sine wave.

 

[Boldly]

So when trying to work out how many battery amp hours I'm using is it safe to assume the watts as recorded from the mains?