240 volt television

[David Schweizer]

I suspect that this has been covered previously but I cannot find it, so here goes.

 

My existing 12volt TV is getting a bit old and I want to replace it with a newer model, I would also like to upgrade from a 10" screen to a 14" or 15" screen. However, I was a bit taken aback when I found out how much they cost, so I thought why not get a 240 volt model and run it through an inverter. This is where my technical knowledge bcomes a bit challenged. A typical 240v TV will use about 60/70 watts per hour, so I will need an inverter that will easily permit that, will a 150 watt inverter be big enough and does it have to be a pure sine version or will a quasi sine type work ok? Also if I am using a 60watt TV through a 150 watt inverter will the demand on the 12volt batteries be 5amps per hour, based on the demand of the TV, or 12.5amps per hour based on the rating of the inverter?

 

The other question is, should I run a new cable to supply an inverter or will the existing 30amp cable be adequate, the only other item on this supply is the fridge which draws about 4amps per hour when on.

[Richard Bustens]

Hi David

Some TV seem to work with Quasi but others do not if you have a inverter try it first and then if it does not work you will have to get a pure sine, if you dont sterling will sell you a quasi and exchange it if it does not do the job.

It would be better to get a 300W unit then you should have a bit of le-way if you need to add a VCR or DVD later

Keep the cables from the battery to inverter as short as poss 2-3 foot and run 2.5 neg and pos and earth to the point you need the supply.

Edited January 11, 2005 by Richard Bustens

[ChrisPy]

as long as we talk about watts per hour or amps per hour we will remain confused. Those technical units DO NOT EXIST.

they are instantaneous measurements.

 

it would help if you mean watt-hours to say just that. watt-hrs = watts multiplied by hours. watts per hour means watts divided by hours, and is meaningless. same for amps.

 

sorry to be pedantic but our government spent hundreds of thousands of pounds at today's values to teach me that.

[nbtafelberg]

I have a 17" samsung LCD flat screen that runs for HOURS and HOURS on my 1kw inverter.

 

I think its a lot better on the batteries using and LCD because it doesn't have to generate all that heat....

[Gary Stacey]

I have a domestic TV that works just fine on a cheap 300w inverter from maplins (cost aprrox £30)

 

Gary

[khaffra]

I had a 14" portable TV on the old boat they take more watts when first turned on than stated on the back panel (this is there average running watts),

I had a 150W invertor that would sometimes turn it on and sometimes not so that is very borderline I would go for at least a 300W if not a 600W. I ended up with a 600W invertor (as the 150W one expired pretty quick) never had any problems with that.

If your invertor is a long way from your batterys you may end up with it cutting out due to low voltage as there could be a significant voltage drop over the length of the boat on 12V when putting the invertor under load, If possible mount the invertor close to the batterys and run a 240V cable along the boat as you wont get any significant voltage drop at 240V

[dor]

I have a Sterling 150watt quasi-sine wave inverter. This will happily run my 39 watt TV and a DVD player which I think has a similar or lower rating. Most of the power used by a TV is to run the CR tube. You must have the inverter close to the battery and run 240V to the TV otherwise you will get low voltage cutouts - more likely the more current you draw. If your TV is going to rated at over about 90 watts, then go for a 300 watt inverter. Unless you are going to use it for other things, there is no point in getting more capacity than you need due to increased quiescent current. However it is one of those rules of life that no matter what size inverter you fit, you will soon wish you had bought a larger one as you will find something else to use it for. If you are not going to use the TV much, and you have plenty of battery capacity, then maybe the extra current drawn will not be a problem.

 

Incidently, my 110watt "electric broom" will only run off the 150watt inverter when the engine is running.

[John Orentas]

I have a Sterling 150watt quasi-sine wave inverter. This will happily run my 39 watt TV and a DVD player which I think has a similar or lower rating. Most of the power used by a TV is to run the CR tube. You must have the inverter close to the battery  and run 240V to the TV otherwise you will get low voltage cutouts - more likely the more current you draw. If your TV is going to rated at over about 90 watts, then go for a 300 watt inverter. Unless you are going to use it for other things, there is no point in getting more capacity than you need due to increased quiescent current. However it is one of those rules of life that no matter what size inverter you fit, you will soon wish you had bought a larger one as you will find something else to use it for. If you are not going to use the TV much, and you have plenty of battery capacity, then maybe the extra current drawn will not be a problem.

 

Incidently, my 110watt "electric broom" will only run off the 150watt inverter when the engine is running.

<{POST_SNAPBACK}>

 

Dor.

 

That little problem must surely be voltage drop on the DC side, you need to beef up your inverter input cables, 10mm if they are not too long.

[John Orentas]

David.

 

Use an inverter that is at least double the required wattage, they loose efficiency towards the top end of their range, obviously keep the input cables as short and big as possible. A modified or quasi sine wave type will be ok for a TV, the input goes straight into transformers and regulated circuits anyway.

 

Look around for a TV with a low consumption, as has been said the flat LCD screen types are very good for that, it was the old cathode ray tubes that took all the power.

[dor]

I agree John, but it is only a little inverter, run through a cigar lightter socket, with 4mm cables run 2 metres from the battery, then the 1 metre supplied lead which are probably 2.5v.

 

Firstly it is no big deal so I haven't bothered increasing the cable size - I really need a larger inverter! Secondly, didn't want to cut off Mr sterling's nice wires until the warranty had run out.

[David Schweizer]

Thanks for the swift responses, you have answered most of my questions very helpfully. One question remains - will the power used be related to the rating of the TV or the inverter, I think I can guess the answer but would like to know for certain.

[David Schweizer]

I have just thought of another question, when you talk about a flat screen, I assume that you mean a TV with an LCD screen? I have a flat Screen TV at home but it has a big fat tube which I assume uses the same sort of power as a conventional screen.

[John Orentas]

David.

 

As you no doubt anticipate, the power consumption will be relative to that of the TV plus any losses, call it 10% to be on the safe side. As the TV will be in use for lengthy periods and it will be around for several years, spend some time studying the small print in the specifications for both units, there can be vast variations in efficiency, look at the off load cunsumption too, that can be significant.

 

The 'flat screen' refers to the very small dimension front to back, and yes a LCD type, a big advantage in itself. A friend of mine has one in his motorhome, he's fixed it to the wall.

Edited January 11, 2005 by John Orentas

[David Schweizer]

Thanks John. that is what I had assumed. By off load I assume you mean the consumption of the inverter when it is not being used, but is still connected to the batteries. Presumably I could introduce a switch into the 12 supply circuit to disconnect the inverter from the batteries when it is not being used, or will this damage the unit?

[Gary Stacey]

The inveter should have a switch on it to cut the power

[Martin]

If you are buying both an inverter and a TV from scratch, I would certainly consider an LCD TV or an LCD computer monitor with an external tuner - there is a link to these boxes on another thread.

The size of LCD screens is as important on a boat as the power it uses and I will certainly take that route when I replace my Sony 14" CRT TV.

On the inverter side - consider what else you might like to run before you buy one just for the TV.

If there is a possibility that you will want to run power tools, take their demands into account now and buy a big enough inverter first time.

You wouldn't want to buy a 600W one now only to discover six months down the line that a 1000W one would have been better as it would have run your new orbital sander as well.

[rustyduck]

But not forgetting that the 1000w inverter will only work (reliably) if your orbital sander is around 300-400W.

 

When sizing for inverters you should add up the requirements for resistive loads (lights, TV, toaster etc) and add at least 25% of the total for a healthy margin. For inductive loads (fridges, power tools, hoovers) add around 200%. Inverters really don't like inductive loads, before you even account for the startup surge that can be huge.

[ChrisPy]

All this stuff about sizing an inverter may be misleading, taking into account Charles Sterling's warning about different manufacturers rate them. I believe that a Sterling 1800W inverter would support a continuous 1800W load at 40C and a start-up surge of about 3000W.

[rustyduck]

I agree with the comment about various manufacturers ratings, but with the risk of getting too techie, try this lot regarding modified sine wave inverters and inductive loads:

 

"Heavily inductive loads tend to demand current that is strongly shifted in phase relative to the inverters output voltage pulses. This makes it hard for the inverter to cope, because the only energy available to the load between pulses is that stored in the internal transformer."

 

"Inductive loads can also produce voltage spikes caused by a back-EMF, which can cause damage to the primary circuit."

 

"Fluorescent lights can be even worse as they have shunt capacitor circuits that can put huge loads on the poor little inverter."

 

So to para-phrase: Inductive loads want lots of power during a part of each cycle when the inverter isn't actually producing any, and may produce voltage spikes that can knacker up the inverter, whilst fluorescent lights can pull the guts out of it.

 

And just as an afterthought - a correctly sized capacitor can eliminate the problems found with the inductive load, effectively turning into a resistive one!

 

Why are these things never straight forward?

 

I'm off for a lie down in a dark room.

[Richard Bustens]

I dont understand what rusty said.

But you should not use the surge readings for usual start up if you have a itim that requires 1000w to run with a start up requirement of 3000w you should have a 3000w inverter, the surge is for protection not every day use.

A mains fridge that runs at 120w has a start up of 900w

[John Orentas]

Richard.

 

Surely that is not quite right, your inverter will have a 'surge rating' usually about 200% so in your example, a 1500 watt unit would be ok. I keep hearing about these 120 watt fridges with a start-up of 900 watts. I have always found that very hard to believe, has anyone ever measured that or seen it in the manufacturers spec.

[David Schweizer]

I never thought I would generate so much discussion with such a simple question. Some of the technical stuff is lost on me, but fortunately I do not need an invereter to run anything except a TV. From what has been said it seems that a Sterling 350 watt inverter will be more than sufficient for this.

 

Armed with all the information gleaned from your responses I visited a couple of TV retailers today and discovered that I can get quite a decent conventional 240v. 14" or 15" TV, with a rating of 44 to 46 watts, for well under a £100, and I think I have found a couple that will fit inside the cabinet I built for the old (10") TV. However whilst discussing my requirements with the sales assistant at one establishment I discovered that most LCD TVs run on 12vDC and use a transformer to operate on 230v AC, so I am now wondering whether it would be possible to run one of these directly from the boat's 12v DC supply. The one thing that puzzled me is that the LCD TV's seemed to use far more power than their conventional counterparts, which is contrary to what has been sugested by some people on this and another thread about TVs. We could not find one 14" model rated less than 70 watts. The assistant electrical engineer at the establishment was suprised that I though the LCD tv's used less power and stated that they use a lot more, encouraging me to put my hand on the screen to feel the heat generated. He then made some philisphical point about not being able to create heat without using energy.

 

Your further thoughts and suggestions would be most welcome.

[John Orentas]

I had forgotten the 12 volt bit, my friend with the motorhome discovered just the same thing. The best thing is to look at the specification stickers and the manual, you will no doubt find a voltage rating, e.g. 10.5 to 15 volts D.C.

 

Remember you may have as much as 14 volts with the engine running, any voltage drop will probably work in your favour, it is the voltage measured at the set with it switched on that is important. I am surprised at the consumption, I would certainly have thought an old style set was less efficient.

 

Heat without energy, thats not philosophy thats phisics.

[Richard Bustens]

Hi John

I always thought 3-4 times run for start up but when i asked the man at Comet guess what he did not know, so i got him to ring the manufactures, and they gave me the 120W running and 900W start up

So in that example i will need a 1000W inverter to run it. now add a freezer and that is about the same again so a 2000W inverter coz sods law says they will both start up together from time to time, though a 1800W sterling would do.

Edited January 12, 2005 by Richard Bustens

[dor]

My 17in widescren LCD TV at home uses a transformer to supply 12Vdc to the tv, although the power plug has four pins. Can't recall what the power rating is, but I though it was quite low - about 40W.

 

I have heard that LCD tv's are very sensitive to over voltage which can occur if the power supply is not stabilised to 12 volts. Hence the gizmo's that I mentioned in a post some days ago.