Submitted: Tuesday, Jun 22, 2004 at 01:32
ThreadID: 120627 Views:3306 Replies:5 FollowUps:0
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Hi All, Could any electrically minded bogger out there tell me how you work out
the current being drawn from a 12 volt battery by an inverter that is
putting out say 1200 watts ( 5 amps ) on the 240 volt side? I'm am trying to determine if it is feasable to run my 240 volt T.V &
DVD through an inverter while free camping, or if the drain on the
batteries would be too great & therefore I could justify the cost of
a 12 volt T.V & DVD player with the 'BOSS'.
Thanks for any input on this in advance.
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Reply By: Turist - Tuesday, Jun 22, 2004 at 01:34

Tuesday, Jun 22, 2004 at 01:34
I can't wait until our new site is up and running with a search engine built in..
Just type "inverter" and the answer would be there.
A very good rule of thumb, divide the load current by 10 to obtain current draw.
ie, 1200 watt radiator (240v) would pull 120 amps (12v) from your battery when operated via an inverter.
Collyn would argue that this is not absoutley correct as no allowance is made for the angle of the hypotenuse when parked on a south facing hill or some other high falutin totally useless equation but in practice accurate to about 2 decimal points.

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AnswerID: 562487

Reply By: Deleted User - Tuesday, Jun 22, 2004 at 01:35

Tuesday, Jun 22, 2004 at 01:35
Baygypsy, To compare the two, it will be about the same given a small loss by the inverter, as the source voltage is still 12v. The best way to understand it a little better is to look at the watts used by the appliance you want to plug in. As an example take the TV and DVD wattage drawn would be about 40 watts for each. Now we know the draw of the appliances lets see if 12v supply or 240v supply wins the race !! This should make it a bit clearer and help determine the best way... Watts divided by volts equals amps used. So 80 watts drawn a 12v battery will use 6.8 amps per hour. So 80 watts drawn from 240v will use .34 amps per hour This looks great until you realise that the supply of the 240v has to be provided by the inverter changing the voltage from 12v to 240v so in effect you are still drawing 80 watts from a 12v source. The inverter only changes voltage it does not create energy in fact they usually show a 10% loss when converting 12v to 240v. 240v divided by 12v gives a factor of 20 times .... so .34 amps at 240v multiplied by 20 gives the same amps .... 6.8 amps. If you think of it this way ... look at the source voltage and look at the end wattage to determine amps used. So to answer the question the 12v items will draw less because of the invert losses but 5-10% loss does not justify spending money to save a little amps with 12v appliances. There is another reason to stay with 240v stuff through the inverter. The inverter can act as a voltage filter for the end appliance. That is makes 240v out even if the voltage in wavers a little. It probably doesnt worry most 12v stuff but if you are using a 12v appliance and the charger or solar is in boost the appliance can be receiving 14.2v or above. This may be detrimental to some 12v that needs 12v rather than 14 or above and therefore may shorten their working life. Clear as mud .... hope not ! [smile] Sorry if I killed the new purchases !! ??? [smile] Now if you're talking 12v because it is smaller/lighter as in LCD screen verses CRT tubes and the 12v DVD fits in the overhead cupboard ....Thats another question !!! Go the 12v every time !!! Regards Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker
AnswerID: 562488

Reply By: Deleted User - Tuesday, Jun 22, 2004 at 01:36

Tuesday, Jun 22, 2004 at 01:36
Thanks for that Anthony & Turist. I'll need some time to digest all this and at least I have a better understanding of what I am weighing up now...... Thanks again.
AnswerID: 562489

Reply By: Noosa Fox - Tuesday, Jun 22, 2004 at 01:37

Tuesday, Jun 22, 2004 at 01:37
We only have a 240volt TV and when it is run via the Inverter it uses about 5 or 6 amps, so you should be able to use it without a problem. In reality though, we find that when we are bush camping, we don't get around to watching TV anyway. There are just too many other things to fill in the day and when the sun goes to bed we often go to bed a short time later, ready for an early start the next day when the sun gets up again. On a side note, Make sure that you carry your TV in a place where it is free of virbrations. We used to carry ours fixed to a bench, and last week had to put it in for repairs for a 4th time. They just don't like lots of corrigations. We told the repair man in Broome that we were in town for a week, so when we hadn't heard from him at the end of the week, we went to pick it up and he told us that he sent it to Perth to get fixed, only 2254 km away, and that it should be back towards the end of next week. Just as well we know other BT owners in WA and were able to get it delivered back to their place so we can collect it when we get there. With a large number of Bushtracker Owners now fitting a TV tuner in a cupboard and running it to a LCD screen, usually on a swing arm, I just hope that they are made better than our Orion TV was, and that they don't have the trouble that we have had with ours. I think a good place to carry the TV is on the back seat of car, if able, or on the bed where it can get some cushioning from the mattress. Brian
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AnswerID: 562490

Reply By: Deleted User - Tuesday, Jun 22, 2004 at 01:38

Tuesday, Jun 22, 2004 at 01:38
Brian I carry my TV on the bed all the time now after many failures. LCD are in many ways more prone to failure from corrugations than conventional TV sets. Trouble is with LCD the trouble is more likely to be fatal. I know of three LCD's that have failed from permanent mounting. If LCD are not subjected to vibration the reliability seems to be great and superior to conventional tube TV's.
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