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Hi Dukedog,

The reason the figures didn't make sense were, I believe as follows:the battery was not fully charged,the output volts were less than 200v but the bulb was indeed 40w,I have retested the inverter plugged in to the 12v power outlet in my van(with engine running 12.8v) and 40w bulb as follows:12.8v x 3.75A=48w,output volts drop to 201(inverter rated 150w @ 230v) hence the previous readings,it trips if I insert a 60w bulb,I estimate it is less than 50% efficient, it is a Power-Inverter I don't think you will rush out to buy one!

I refer back to the original question re running 240 v equipment from 12v battery as is shown the drain on the battery is considerable and you need a large inverter to cope.

Why spend all that money use ELH?

To measure the efficency of an inverter, you really need to accuratly know the output voltage and current into the load, measuring these at mains voltage is not for the faint of heart.

A bulb might well be 40W at 240v, but its resistance wont be linear, it will vary depending on the temperature of the filament (which depends on the current running thru it of course).   

 is to use a resistor of suitable power rating and measure the mains voltage across it, this being easier thaIts always going to be difficult to measure the efficiency of a power inverter,

Quote: Originally posted by srnet on 18/09/2004

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To measure the efficency of an inverter, you really need to accuratly know the output voltage and current into the load, measuring these at mains voltage is not for the faint of heart.

A bulb might well be 40W at 240v, but its resistance wont be linear, it will vary depending on the temperature of the filament (which depends on the current running thru it of course).   

 is to use a resistor of suitable power rating and measure the mains voltage across it, this being easier thaIts always going to be difficult to measure the efficiency of a power inverter,

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 Yes I agree Stuart, Obviously you need to know the voltage before you can calculate the power. and of course a propper dummy load would be ideal, I supose it all depends how accurate you want to be. 

Regards Frank