How much does an Inverter drain the battery?

07-12-2012, 10:27 PM

I know there's a lot of variables, but I was wondering how much drain on a battery is there if (for example) I was using a 500W sine wave inverter to power a 21 inch tv for 2 hours? I'm not sure how many watts the tv would draw, I would guess around 150W....

I know you can't be exact, I mainly want to know if it's a little, a lot etc...

Thanks

Barb&Tim · 07-12-2012, 10:56 PM

Hard to calculate accurate values. Inverters are typically most efficient around 2/3 max load. Could be much less efficient at low loads -- 50% or less.

Taking a guess because of so many variables--> anywhere between 12.5A and 20A DC for a 150W load.

Tim

**ShrimpBurrito** · 07-12-2012, 10:59 PM

Alot.

150 watts for a 21" TV is probably reasonable. Watts is a measure of power (energy), so it doesn't matter if it's AC or DC. 150 watts DC is the same as 150 watts AC. Since you're using an inverter, you'll actually draw more than that because the inverter is not 100% efficient - probably more like 90% for a good quality sine wave unit. So you're really drawing maybe 165 watts for your 150 watt TV.

Ohm's law is:

Power (watts) = Current (amps) * Voltage (volts)

...so:

165 watts = ? amps * 12 volts

That comes out to be 13.75 amps (let's say 14 amps).

If you run a 14 amp load for 1 hour, you draw 14 Ah.

If you run it for 2 hours, you draw 28 Ah.

The typical battery that comes with trailers is probably 100 Ah (or less), and you can only conservatively use say 60% of that at best before you start to really degrade long-term battery life. So you only have ~60 Ah of "useable capacity" at your disposal. So by using your TV for 2 hours, you would deplete your battery nearly 50%.

Dave

07-12-2012, 11:05 PM

Thanks! That tells me what I need to know...

**Bill** · 07-13-2012, 07:37 AM

In my opinion (and it's only that, based on my experience), 21 inches is a pretty big TV for a TM. Perhaps an Elkmont needs something bigger than a folding TV needs, or perhaps you would consider stepping down to a 19-inch class. But there are other things to consider. A bit of research may make you a much happier camper.

If you rummage around sites like Best Buy or WalMart, you'll find that you can buy a 19-inch LCD 720-HD TV for a bit above $100. A similar 1080-HD TV is only a bit more. You will pay more than that for the inverter you are contemplating.

If you look for one that is Energy-Star rated, it will draw as little as 25 watts - considerably less than the 150 watts you are contemplating.

Some of them will operate directly from 12-VDC, eliminating the need for an inverter entirely.

If you insist on bells and whistles like Internet-ready, Ethernet-ready, a dozen different inputs and a dozen different outputs, volume levelling, the price increases, but IMO, a simple TV with a digital tuner should be adequate for camping.

You can get a TV with a built-in DVD player. I'm not sure of the cost impact, but if you watch DVDs on the road, it is worth considering.

Just my thoughts and experience. But I would say that an inverter in the 500-watt class is nowhere near your best solution, if TV is its only purpose.

Bill

07-13-2012, 10:33 AM

One word of caution when looking for inexpensive LCD TVs. Be sure to view the TV from several angles in the store before purchasing one. The lower end TVs use low end displays and generally have very narrow viewing angles. As the TM is not large, a TV sitting on the Fridge or stove can have a significant viewing angle problem from one end of the sofa to the other.

07-13-2012, 05:23 PM

We have a SAmsung 19" tv with a built in DVD player, I was just guessing on the watts. I need to pull out the manual and see what the exact draw is. I'll do that tonight.

After a day of being active, we enjoy relaxing with a movie, but I do not think that it is justified in this case due to the cost of a good inverter and the fact that I really have no other use for the inverter. The 12V tv may be money better spent. Thanks again to all for the input.

**ShrimpBurrito** · 07-13-2012, 05:42 PM

If all you want to do is watch a movie occasionally, take a laptop. Plus, they can be both recharged and run with a cheap $20 inverter than runs 100 watts (we've done it, works great).

It doesn't take a fast laptop, either. You could buy a used one from somewhere - our very old one that is probably worth no more than $50 would do just fine - and just keep it in the TM.

We pull out our sofa, lay down together, and I put the laptop on my lap. Works perfectly.

Dave

07-13-2012, 10:35 PM

I guess I'm brain dead sometimes...thanks Dave for the suggestion. We used to do that in the 2619 sometimes, we'd put the lap top on a plastic milk crate between us and watch a movie.

Any recommendations for one to charge the laptop?

**ShrimpBurrito** · 07-13-2012, 11:16 PM

Quote:

Originally Posted by Redhawk

Any recommendations for one to charge the laptop?

Our laptops don't run on 12V (I think they use 20V), so we just use a $20 inverter rated for ~100 watts. Since the laptop "brick" converts the AC back to DC, you get no advantage from a true sine wave unit, so save your money. Take your pick:
http://www.amazon.com/s/ref=nb_sb_no...+watt+inverter

Most laptops I've had run about 60 watts when charging and running. They take about half that maybe when doing only one of those things (including running with a fully charged battery). Of course, leave the house for a fully charged battery, and with a new battery, you should be able to get 1 full length movie before needing the inverter.

If your laptop happens to run on ~12V, then you don't need an inverter.

Get yourself a Kill-a-watt to measure power loads -- they are very handy if you plan on using an inverter for other appliances. One of the best $20 I have ever spent.

Dave