Current Draw from an Inverter

Thanks Peter,
Sounds like a fair estimation to calculate load. This would equate to an inverter of an 80% efficiency rating, yes?
Cheers,
Alex

Alex

Had no bothered to work out the exact efficiency figure. It is just a convenient divider that is commonly used in the industry that is fairly conservative & safe to use.

PeterD

Hi,
You will find the inverter will draw a certain idling current when it is switched on with no load, the pure sinewave ones up nearly 1 amp.
Connecting a 12 Watt flouro lamp will increase but not necessarliy double that current. The higher the load up to the inverter's maximum rating, the less significant the idling current becomes, of course.The "modified sinewave" types are little more efficient, but have other disadvadvantages.
As for the 12V flouros that can run straight of your battery, I have had a nasty experience with 2 of them that went up in smoke and stank the place out. They have a small 12V/300V inverter build into the base, hence the much higher initial cost, but I have the found less reliable.
Cheers

Hi Beau,
Thanks for your thoughts. Yeah, I do have both 12v lights and 240v lights. The example with the 12W lights was more for illustration purposes. I.e. it's easy to calculate in ones mind the current draw under both 12v and 240v when 12W is connected (1A and 0.05A). My 600W inverter is used for many more things than just lighting but with a formula I'm comfortable to work the others out.
Thanks again,
Alex

The high efficiency flouros work more efficiently off an inbuilt inverter. These devices operate at around 25 KHz and the higher frequency current seems to get the same light output for for less 12 V input. The 14 W 2D tubes in my van only draw around 1 A

PeterD

I've always been a bit confused by the wattage figure on these lamps, my Jaycar 12V 20W one draws about 1A2 (less when it's warmed up) rather than the 1A66+ a true 20W should draw yet it produces more light than a 20W filament lamp?

Maybe there is an AC component to it's current draw? I'll try to remember to look at it on the scope.

Mike Harding

Mike the wattage of a fluorescent is stamped on the glass of the glass tube itself and doesn't actually have much to do with current draw of the fitting. The number (many years ago) used to relate to the light output compared to an incandescent test lamp but these days with different types of phosphors inside the lamp you are getting more light output for less power consumed.

The power figure printed on the lamp is the power drawn from a DC or 50 Hz power source (in the case of a fluorescent tube it only applies when it is fitted into a fitting with power factor correction - the cheap fittings often do not have PF correction and draw more current.)

The different types of tubes have different efficiencies. Their light output is generally related to a standard incandescent globe.

A QI globe produces around twice the light output.

The older fluoros produce around 2.5 times more. The old 40 W tubes produced the output roughly the same as a 100 W globe. The new tubes that fit that fitting draw less.

The high efficiency fluoros produce 5-6 times more (the PL or 2D tubes.) That's the marvels of modern technology

In addition, the PL and 2D tubes seem to be more efficient when operated on power that has a frequency higher than 50 Hz. That is why the caravan manufacturers are turning towards them. The 14W 2D tubes in my van only draw around 1 A. The inverters in these fittings operate at a frequency of 25 KHz or higher.

PeterD