# 12v V 240v



## Pudsey_Bear (Sep 25, 2008)

Whilst doing my morning ablutions, It crossed my mind how much power do inverters use in use, compared to taking the supply direct from a 12v battery.

I have 300 watt inverter, and it's only used to power a PVR and a TV, the TV could be supplied by 12v.

Assuming I just want to watch the TV (No PVR) which is rated at 120 watts via the inverter for one hour, how much more power does it use than if I just used it via with 12v, disregarding the power the inverter takes to run itself, would it use more, less or the same amount of power.


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## chapter (May 1, 2005)

most tv than run 12v/220v have a internal/external transformer so they run on 12v regardless of the power source 
chapter


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## geraldandannie (Jun 4, 2006)

Hi Kev

The answer is: it all depends  

Inverter efficiency varies depending on the make, and how much of the rated power that's being used. I would guess your inverter, at 120W / 300W, could be around 80-85% efficient, so would take 25% more power (10/8) from 12V than the TV would take on its own. If it was being 90% efficient, it would take 10/9 or 11% more power.

Just guessing, though :wink:

Gerald


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## GerryD (Sep 20, 2007)

chapter said:


> most tv than run 12v/220v have a internal/external transformer so they run on 12v regardless of the power source
> chapter


My thoughts entirely. There is no point in generating electricity only to convert it back to where it came from.
I make sure that everything electrical for the motorhome is 12V compliant unless I intend to us it solely on site with EHU. As we only tend to use one proper site per year, 240V equipment is not a priority. If I can't use it on a rally with a 40W solar panel then it stays at home.
Gerry


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## phil4francoise (Jun 21, 2008)

A much debated subject As most small LCDs are 12v anyway in theory yes you can run straight from your 12v leisure .The problem is that that supply is not stabalised and could cause problems
We went down this route and the tv packed up after a few months ,I dont know if this was the reason
We are now running a 1500 watt invertor which does the tv and pc and all the mobile chargers etc at the same time . I have noticed no difference in battery drain .We have even left the invertor switched on overnight several times which has been fine and the 60watt solar panel recharges the batteries with ease .In fact I cant remember the last time we needed a hook up on camp sights even though we have to pay for it but thats a whole new can of worms.


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## Wytonknaus (Jun 18, 2007)

I am going down the solar panel route and inverter but I am not sure what size I need inverter wise.
I wish to use the microwave if possible which is an 800w output and according to the manual it is a 1200w input would a 1500w inverter cope or should I go bigger?
Any help appreciated.
Thanks
Tim


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## fdhadi (May 9, 2005)

Kev_n_Liz 

Much better to use an inverter. This will keep the supply to the tv @ 12v.

If the tv is wired directly to the battery and used on the move the power will be more than 12v. If not used on hook-up, when the battery power drops the tv will not get the 12v it needs.

One of the clever (ok "cleverer") people on here will be along soon and explain this properly. There lots of treads on this subject.


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## bigtwin (May 24, 2008)

To answer the OP's question; If you disregard the only other load (the inverter) it will use the same power (current). However, it's an irrelevant question since you do not have that option in practice!
If you include the inverter then clearly you will use more power. It will always 'cost' more (in amps used) to run 240v appliances from 12v than would be the case for similar 12v appliances.


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## DABurleigh (May 9, 2005)

Kev,

Have a read of the MHF inverter guide. An inverter's efficiency is mostly dependent on its load as a fraction of its maximum output. From 50% to 100% modern inverters are over 90% efficient.

Dave


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## Pudsey_Bear (Sep 25, 2008)

Thanks all, It's amazing what pops into my head in the morning.

I'm glad I wasn't too far off in my thinking that overall, the inverter route makes more sense, I did look at 12v to power everything, but the fluctuations and stuff packing up made no sense at all.


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