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Tv Draw In Amps


sampvt
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I know my old 12v tv which was 25watt used to draw 2 amps when run on the battery (ohms law volts into watts etc) But how many amps will a 240 volt domestic 25watt tv take when run through a 1500 watt pure sine wave inverter hooked up to the battery.

 

I know I need to factor in the inverters needs as well as the tv,s but how can it be calculated.

Im back to motorhoming with a scooter on the back again.

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25W is 25W, doesn't matter where it gets it from i. e. 2. 1A @ 12V or 0. 1A @ 240V (assuming it's designed to work from these voltages, of course!!). Yes, there are losses using the inverter but PSW inverters are usually pretty efficient. Mine is 93%, others will be similar.

 

Remember that the TV itself does not operate internally at 240Vac. The TV will reduce this to something like 12Vac then rectify it to get DC - you'll probably find more losses in this conversion than within a PSW inverter, imho.

 

My inverter usually draws about 10W no-load (0. 8A @ 12V) i. e. just having it switched on but it soon switches to a 'low power mode' drawing abut 5W (0. 4A @ 12V) if the load stays below a configurable threshold (I've set it to be 58W) for more than a few seconds.

 

So I would reckon total battery drain would in the order of: 2. 1A (TV) + 0. 8A (inverter) + 0. 2A (losses) = 3. 1A. A 110AH leisure battery will supply this for around 18 hours* (you shouldn't discharge a lead-acid battery below 50% SOC), less if you have other things running e. g. Alarm (0. 1A), water pump (4A), circulation pump (1A) etc.

 

 

*110AH / 50% = 55AH / 3. 1A = approx 18 hours.

 

Edit: added missing calculation.

Edited by tictag
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25W is 25W, doesn't matter where it gets it from i. e. 2. 1A @ 12V or 0. 1A @ 240V (assuming it's designed to work from these voltages, of course!!). Yes, there are losses using the inverter but PSW inverters are usually pretty efficient. Mine is 93%, others will be similar.

 

Remember that the TV itself does not operate internally at 240Vac. The TV will reduce this to something like 12Vac then rectify it to get DC - you'll probably find more losses in this conversion than within a PSW inverter, imho.

 

My inverter usually draws about 10W no-load (0. 8A @ 12V) i. e. just having it switched on but it soon switches to a 'low power mode' drawing abut 5W (0. 4A @ 12V) if the load stays below a configurable threshold (I've set it to be 58W) for more than a few seconds.

 

So I would reckon total battery drain would in the order of: 2. 1A (TV) + 0. 8A (inverter) + 0. 2A (losses) = 3. 1A. A 110AH leisure battery will supply this for around 18 hours* (you shouldn't discharge a lead-acid battery below 50% SOC), less if you have other things running e. g. Alarm (0. 1A), water pump (4A), circulation pump (1A) etc.

 

 

*110AH / 50% = 55AH / 3. 1A = approx 18 hours.

 

Edit: added missing calculation.

 

Question 1: how do you tell when a battery is below 50% charge without using a hydrometer.

Question 2: what is the point of a leisure battery other than the fact that it is not damaged if it is discharged flat - other than unless it is very smart an associated charger may not be able to restart it?

Question 3 to the OP: why a 1500W PSW invertor? This will be the only thing in the van that does not run off 12V or gas, so a 150W or even 100W would be more than adequate.

 

If the TV mentioned has an external power supply have a look at its output voltage. If it is nominally 12Vdc as many are you can but a switching regulator from such as the Alfatronix DDi which will take any input voltage in the range 8. 5-15. 5V and are 93% efficient. They have the advantage of having a lifetime guarantee and cost about £25. You will have to check with the manufacturer as they give a nominal output of 13. 6V (they are designed for use with mobile radio) but I'm sure I remember that there is a way to adjust them down to 12V.

2018 Passat B8 Estate 150GT TDi150 towing a 2018 Bailey Unicorn S4 Seville

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Question 1: how do you tell when a battery is below 50% charge without using a hydrometer.

 

The open circuit terminal voltage of a lead-acid battery is directly proportional to the state of charge, in other words:

100% = 13. 2V

50% = 12. 1V

0% = 10. 5V

 

Question 2: what is the point of a leisure battery other than the fact that it is not damaged if it is discharged flat - other than unless it is very smart an associated charger may not be able to restart it?

 

All leisure batteries are damaged to some degree by discharging to flat. Depending on how long it stays in this state, the battery could be rendered irrecoverable (due to sulphation). Some chargers purport to recondition sulphated batteries (e. g. CTEK range) but I have no experience of these myself. The main reason a leisure battery is better suited to caravan use (as opposed to a starter battery) is because their physical build is optimised for deep discharge cycles at relatively low current draw. A starter battery is optimised for maximum current draw over a relatively shorter time. Cross purposing these batteries will (might) work but the life of the battery would be significantly reduced.

 

If the TV mentioned has an external power supply have a look at its output voltage.

 

I would tend to agree with the argument that if the TV supports a 12V supply then it would be more efficient to use this, rather than supplying via an inverter.

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