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how long would a 75 watt tv operate with a 75 watt tv using a 600 watt inverter

oops no edit button should be with 75 ah battery

A 75Ah battery means it will supply 75A for 1 hr or 1A for 75hrs (as a rule of thumb).
So the inverter converts your 13.8VDC to 230VAC but the Watts remain the same with the inverter efficiency added.

Let us say your inverter had an efficiency of 90% (average for this size) then 75W for the TV would be 75/0.9=84W from the battery.
This translates to 84/13.8=6A which for the 75Ah battery would give you around 12.5hrs (and completely drain the battery, so 10hrs would be more practical I suggest).

in theory your right thats what i came up with --------but for some reason with an inverter it only works for 5 hrs ----was told at place where i bought the 600 watt one to double the watts of tv etc -- a 300 watt would work a 75 watt tv he says would need 150 watts to start

That's interesting ... I was told by the fella in Dick Smith (who REALLY did know what he was talking about) that a 150w inverter should be ok for mine.

I was going to run it from the car and into the van as I have a dual set up in the car; thus leaving the van battery for lights. Might have to check it out again.

Current draw of the TV was only 4amps ... is that the same as yours Kevin?

Scol.

waiting on inverter to be delivered from factory who make them in adelaide ---peformance shop.com.au --$84.50 plus delivery for 600 watt $62.50 for 300 watt ---decided to go to the bigger one in case i might want to run something else --------check out the website has most things used and what inverter is needed.
thats where i got the info direct from maker. He also told me it uses minium power when connected on its own but to always turn it off after use ---in other words not to leave it running on its own.
dick smith ======== some of them are only salespeople

Hi Kevin,

I suppose you would also have to factor in the "standby" current of the inverter as this would be it's energy usage for the internal electronics.
As you go up in size, this becomes quite substantial which adds a larger drain on the battery and hence reduces the running time.
For the typical 150W - 600W inverters it seems to be about 0.3A but jumps upto 0.8A for the 800W models and obviously higher for larger models again. A 24V/2500W inverter can have an "idle" current of 2.5A

would say you would be right ---this is what i was told also---will run tv with full charged battery and tell you what the results are

keviny6 wrote:dick smith ======== some of them are only salespeople

Yes. that's been my observations too ... which is why I specially mentioned this fella as he was very knowldgeable and was able to tell me things about my van's electical system that I didn't know ...

I'll wait and see what your experience is with the bigger inverter.

Good luck!

Scol.

Batteries are rated in Ah for a discharge rate that will discharge them in 20 hours. For a 75 Ah battery you can draw 3.5 A for 20 hours (3.5 x 20 = 75) If you draw less current than C/20 (battery capacity in Ah divided by 20 hours) you will be able to draw more Ah from the battery. If you draw more current than C/20 you will get less Ah out of the battery. It is all explained in Peukerts Law http://www.caravanandmotorhomebooks.com/articles/peukerts_law.htm - there is too much explaining for me to post the details here so go to the link and read it.

The rule of thumb when powering things from an inverter is to divide the stated AC power in watts by 10 - not 12. This takes into account the inefficiency of your inverter and power loss in the DC cables etc. In the case of the 75 W TV this gives a current draw of 7.5 A. This may look a little high but not when you consider you are using an inverter that is far too large, you may find the current to be in excess of 7.5 A. Then when you take Peukerts Law into the calculations you may have an equivalent of over 10 A drawn from your battery, hence what you are finding with your battery capacity is no surprise to me.

PeterD