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Old 04-02-2010, 11:25 PM   #1
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12v Television runtime VS 120v

I am going to add a Television in the bedroom area. From what I have read, it seems a 12v unit is the best choice. Or is it? I am wondering how long you can realistically power a 19" LCD TV from the batteries. It seems almost like the two balance out in the end. If I wanted to watch the tv couldnt I get an inverter? I have read several posts here on the forums, and have googled 12V Televisions. The selection is not very good. And they are pricey for what you get. What is the current general consensus on this?
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Old 04-03-2010, 10:09 AM   #2
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Consider that the efficiency of an inverter runs about 90% and, if wired properly, nearly makes up for that in line losses in many cases. Contrast that to the nominal battery variations of 10% or more from factors such as temperature, cycle to cycle variation, use profile, and other things.

What will get you is the continuous drain at rather significant levels. For instance, watching a DVD movie in the evening requires the energy from about 50 pounds of battery (500 watt hours).

The fact is that you just can't get much battery energy storage in a TT. Worrying about a few percent here or there is like using a tin cup to prevent the Titanic from sinking - may make you feel good but isn't going to make much difference in the final result.
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Old 04-03-2010, 10:44 AM   #3
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I have had good luck with it.

I have written about this before in other threads...I bought a Polaroid 19" television with DVD player from Target. It runs on 12 volts. It works great, doesn't use much juice (I've never done any scientific experiments on this) and it cost me $329 about two years ago. I think they have come down in price since then.

Randy Bowman
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Old 04-03-2010, 07:00 PM   #4
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Randy thanks for the reply. If I can buy it at walk in retail then thats a little different. I will check out that tip. I searched all over the forums and for some reason I never saw your post so thanks for re-pointing it out! What is the model number of your Polaroid tv? Target does not carry them anymore but I thought I would search around and see who does.
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Old 04-03-2010, 08:19 PM   #5
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We sometimes watch TV from bed while dry camping. We use a 350 watt inverter to power our 22" Vizio flat panel TV. We set the sleep timer to prevent the TV from running all night and taking down the batteries. The inverter will continue to run, but it draws very little when not running something.

A 12v TV sounds like a good idea, however, I would get one with a sleep timer, otherwise, if you fall asleep, you may run your batteries down overnight.

Not to say you will fall asleep watching TV from bed, just because we always do.
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Old 04-04-2010, 03:37 PM   #6
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The Polaroid TV is Model # TDX-01930B

It is: 19" HD LCD, TV?/DVD Combo

The thing that makes this work in the Airstream is: The television came with a in-line transformer very much like the transformer for my laptop. (Three prong plug into the wall-120v. and 12 volt coming out of the transformer to the television). As it turned out I didn't even use the transformer...I bought a connector plug and a cigarette lighter plug from Radio Shack and used it directly. That way I use the trailer batteries directly without a invertor running using power just to run. I take it that Target doesn't carry this unit anymore. It seems like I saw one at Walmart about a year ago that was, I think, another brand but a 12volt unit.

I hope that the photo shows below. It is the transformer and how it plugs in to the television.

Randy
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Old 04-04-2010, 05:27 PM   #7
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No kidding. I was moving an LCD monitor this morning, and it suddenly dawned on me that maybe MANY TV's can be DC powered, and alot of the smaller ones have this "brick" that you show above. I cant believe it took me this long to realize this.
Thanks!
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Old 04-04-2010, 05:51 PM   #8
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Randy and you are correct. Many of the smaller TV's are DC powered and have a "brick" for AC power. I just recently purchased a new Vizio 23". They make a 19" for under $200 (at Sams Club).
I would also suggest that you consider the new LED LCD TV's. The picture is powered by LED's which use much less electricity. The two Vizio's that I mentioned above are LED LCD TV's.
Good luck.
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Old 04-04-2010, 06:32 PM   #9
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Originally Posted by bryanl View Post
For instance, watching a DVD movie in the evening requires the energy from about 50 pounds of battery (500 watt hours).

Well, not quite. The Polaroid unit I have (discussed in this thread) draws 55W max. (and of course, it's not drawing at max. rate unless the screenis at full brightness all the time and the sound is all the way up to clipping all the time!), but assuming it's run that way ... a 120 minute movie would run 110 Watt hours, and at 12 Volts, that's less than 10 amp hours ... on a sunny day, I get more than that out of my solar panels in an hour.

Or did I miss something in EE 101?
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Old 04-04-2010, 08:07 PM   #10
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For better sound check this thread

http://www.airforums.com/forums/f450...-up-61942.html

I hope this helps you.

Randy
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Old 04-05-2010, 11:37 AM   #11
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re: "Well, not quite." -- yeah, that's rather typical in these discussions, start nitpicking a generality as if it means anything.

If you really want to go this direction, why not get one or two of those DVD players they have for kids in the backseat? They aren't expensive and can run on their own batteries. Then you can leave all lights off (even LED's or flourescents) and save a bit more. Then you can shut down the furnace and the fridge and alarms and whatever else and save a bit more. Then you can make sure that you only watch 90 minute movies and so on.

It is always possible to adapt to the limitations and constraints of an RV off grid and figuring out the best way is often a personal preference matter.

re: " Or did I miss something in EE 101?" -- what they don't teach in EE 101 is client relationships and the problems encountered in figuring out the real problem in real world situations for arbitrary clients who aren't really sure what they are asking for. (another thing rarely found in the entire EE curriculum is lead acid battery technology and how use involves available energy capacity, which are major factors in this consideration)

What I tried to provide was based on real world experience in trying to help a number of folks who get rather surprised by low batteries in the morning.

Pardon the snark, but sometimes it gets really frustrating trying to get across that idea one person's experience and choice is not necessarily the same as another's.

BTW: the 'LED' hype these days is about the backlight and not the LCD. The TV is basically the same except that it uses LED's rather than cold cathode fluorescents as the light source to shine through the LCD to create the picture. This might or might not make a difference in power efficiency depending upon compromises in the TV design. The backlight is the major power hog in TV's which is why smaller (and/or darker) screens often use significantly less power.
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Old 04-05-2010, 01:10 PM   #12
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I bought one of these . . . JENSEN LCD TVs

They are built for the temp swings and vibration of RV's.
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Old 04-08-2010, 07:13 PM   #13
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bryanl you are correct on every point in your post. I havent seen any studies that prove or disprove the LED is more power efficient than CC, however I would think the LED would run much hotter, which may or may not be a good thing. My quest was to get the "right" tv, and not a piece of junk. I think I can get a high quality tv with an external ac power supply, connect it to the 12V rail, and that way I can get a good tv and not break the bank. Im hoping Samsung will have one that will fit the bill
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Old 05-17-2010, 09:59 AM   #14
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I just replaced an analog 14" LCD TV with a digital (Insignia brand from Best Buy) 19" HD LED TV. Both units have 12 volt converters and will run directly on 12 volt DC.

The new LED TV cost $199 plus they offered a 4 year warranty for $24, (plus tax, of course, for our poor State) I don't normally pay for extended warranties, but considering the vibration and temperature extremes in the travel trailer I thought it was a good investment.

I did a test using both TV's on 110 volt AC and a Kill-A-Watt meter. The 14" LCD consumed about 35 watts, compared with 23 watts for the 19" LED TV.

That's pretty impressive, 23 watts is about 2 amps at 12 volts, at that rate you could run the TV all day and night before discharging a normal 100 AH battery 50%!
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