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Tailgate Power Supply
Old 08-20-2010, 10:58 PM   #1
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Tailgate Power Supply

My buddy and I are trying to figure out a way to power a tv for tailgating this football season. The tv is a 26in plasma. Every tailgating website reccommends a small Honda generator but they are expensive (~$900). We are trying to figure out a cheaper alternative. Does anyone have any suggestions? The two criteria are 1) It must produce enough power to keep the tv working for about 7 hours and 2) Be somewhat quiet.

Based on this criteria, the problem with most generators is the noise produced. I thought about using a marine battery hooked up to an inverter but was not sure how long it would last powering the tv. I have also seen solar panels that can be hooked up to a battery that look like they might work. Thanks for your help.
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Old 08-20-2010, 11:17 PM   #2
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I did a quick search on the Web and found that a 26" LCD TV typically draws 60 Watts. I have read that plasma TVs use more power than LCD TVs, but let's use 60 W for now.

An ideal inverter with 100% efficiency would draw 5A from a 12V battery to generate that 60W on a higher AC voltage. A typical group-24 marine battery has a rating of 100 Ah, which means it can deliver that 5A for 20 hours. However, I have read that the user should draw down only 50% of a lead-acid battery capacity to prevent shortening its life. So, that means only 10 hrs at 5A.

That would appear to me that your goal of 7 hr operating time is achievable, even after allowing for inefficiency of the inverter. The inverter efficiency can be as low as 7/10 = 70%, and you are still OK. Many inverters claim efficiency of 80% or more.

So, I would try to get a 100-Watt inverter, plug the TV into it, then use an ammeter to measure the current drawn from the battery by that inverter. Knowing the current drawn, you then divide into the allowable 50 Amp-hours to see how long you can operate.

It appears to be feasible.
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Old 08-20-2010, 11:48 PM   #3
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I'm not much of a electrical tech-guy, but I used to be the boss of a group of such folks and they were always crazy to show and tell their latest invention. We bought them several cars/trucks that they loaded up with all kinds of audio visual goodies (recording for later viewing or transmitting live) along with a number of other electronic devices. Reliability and durability was vital. The two things I remember from working with those guys are how antenna polarization works (and why it's so important), and the wonders that can be done with some deep-cycle marine batteries wired in parallel. I don't know what size batteries they bought, but I don't remember them ever needing to use more than two in an application.
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Old 08-21-2010, 07:04 AM   #4
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I would suggest skipping the marine battery. Marine batteries are somewhat more resistant to deep cycling than your average auto battery, but they also cost more per amp hour due to being built to resist salt water conditions. Plus, the majority of marine batteries are not "true" deep-cycle batteries. They're just kind of half-way between regular starter batteries and deep cycle batteries.

What you probably want are a pair of golf cart batteries. They are the cheapest, most readily available deep cycle batteries. The T-105 model from Trojan are some of the most well known ones. They are 6volt batteries with about 220 Amp Hour storage capacities, and they can be cycled (discharged/recharged) hundreds of times. You still want to follow manufacturer recommendations about how far down to drain them to avoid damage, but they can be run down quite low without damage.

With your intended use - just running a TV for a few hours - I wouldn't bother with any sort of solar charging system. It would drive the price of your battery system up by several hundred dollars, and it shouldn't be necessary.

A pair of T-105's wired together to provide you with a single 220AH 12v power source should be more than enough to power a small inverter and run your LCD TV for many, many hours without any fear of causing damage to the batteries or running out of juice even if your tailgate party runs into overtime. For that matter, you would probably have plenty of power left over to run other stuff, if you felt like it.

I'd say build yourself a nice little ventilated, fused battery box to protect your power source from freak rainshowers. Read up on the subject to make sure you use the right type of cabling and fusing. Don't mount an inverter in the battery box! That can start fires. And get a good quality inverter, too. Most of the ones sold in truck stops are pretty inefficient and tend to die on a regular basis.

Other than that, you shouldn't have any issues. Obviously you'll need a way to charge the batteries, but a home charging station is going to be much cheaper than a solar setup, and you don't really need to be able to charge them while in the field if you're just using them for tailgate parties.

Have fun!

Josh
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Old 08-21-2010, 07:29 AM   #5
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What Josh said.

In the RV world using two 6v golf cart batteries is the standard for powering both 12v systems and inverters for light load 110v AC operation. Although the Trojan T-105's are excellent they maybe a little too much $ for your appetite. I'd suggest buying a couple of golf cart batteries from your local Sam's club. They run under $70 each and should be more than enough to power your TV. I've had two in my RV for more than four years and they are still going strong.

EDIT: I'd also recommend getting a quality inverter with the capability for at least 100 watts more than your expected load. Nothing more frustrating than having a system right on the edge, prone to kicking out at a critical point in the game!
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Old 08-21-2010, 08:48 AM   #6
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.

EDIT: I'd also recommend getting a quality inverter with the capability for at least 100 watts more than your expected load. Nothing more frustrating than having a system right on the edge, prone to kicking out at a critical point in the game!
+1, a unit of 200W or 400W isn't going to cost much more. You need to know the draw of the TV - if <100W you can probably get by with the cigarette lighter adapter (most are fused at 10A; 10A*12V=120W, maybe 100W to the TV after losses)

But I don't understand the need for extra batteries for an occasional use. Doesn't 'tailgate' infer there is a vehicle attached to that tailgate? Why not just use the vehicle battery? Check the voltage after a few hours just to be sure, run the car for 10 minutes or so to top it off, and carry some jumper cables, JIC. Or move the plug to another vehicle for the next 2 hours or so. Seems like there are plenty of people around to give you a jump. CAUTION: Jumping is far more dangerous than most people think (acid, hydrogen, sparks) - combined with adult beverages, not so good. You might want a designated jumper.

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Old 08-21-2010, 08:50 AM   #7
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I think it would be great if you could integrate solar and wind power into the system.
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Old 08-21-2010, 09:08 AM   #8
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I think it would be great if you could integrate solar and wind power into the system.
Yeah, maybe something like this:
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Old 08-21-2010, 09:22 AM   #9
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Google:

battery charger stationary bike

If you took turns, the bike would offset (if not fully eliminate) the power drain from the battery. You can drink beer and ride a stationary bike at the same time, and if not, time to stop both!


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Old 08-21-2010, 09:36 AM   #10
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Re the inverter, be careful to get one that produces a true sine wave, not a stepped sine wave. The cheaper ones produce a stepped sine wave, in which the voltage does go up and down at 60 Hz, but in steps, not a true smooth wave.

The issue there is that the steps produce eddy currents in the power supply and transformers which in turn produce heat, which shortens the life of whatever you're running significantly.

That's one of the main advantages of the small Honda generators in that the inverter ones produce a true sine wave. Alas, that's why they cost so much.
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Old 08-21-2010, 09:55 AM   #11
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Although the Trojan T-105's are excellent they maybe a little too much $ for your appetite. I'd suggest buying a couple of golf cart batteries from your local Sam's club.
Heh. You are probably quite right. The setup I was suggesting is slightly overkill. I tend to equip for an outing as if I am going on a week long camping trip when all a normal person would pack is a picnic basket. I get a lot of enjoyment out of knowing that a given device will do a lot more than I normally need it to, though - just in case.

As for the comment about modified square wave vs. true sine wave inverters... I've read that LCD TVs work pretty well with your standard, less costly, modified square wave type, but I can't verify that with any personal experience.

Whatever battery system is decided on, at least it will be a lot quieter than a generator!

Josh
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Old 08-21-2010, 09:57 AM   #12
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Re the inverter, be careful to get one that produces a true sine wave, not a stepped sine wave. The cheaper ones produce a stepped sine wave, in which the voltage does go up and down at 60 Hz, but in steps, not a true smooth wave.
True to degree, but this is from a web site that sells both types:

Inverter FAQ - DonRowe.com - Frequently Asked Questions about Power Inverters

Quote:
If you mostly want to run lights, TV, microwave oven, tools, etc, a Modified Sine Wave inverter is fine for your needs.
OTOH, a 300/500W Pure Sine Wave inverter on that same site is only ~ $160. At this power level I think I would go Pure Sine for the extra assurance that it will work with anything in that power range.

Actually, the "modified Sine Wave" term is quite 'generous'. It doesn't look anything at all like a sine wave. It is not 'stepped' (well, one step, I guess). It is actually very much like a Square Wave, but the ON time is ~ 30% narrower. That is the only difference from a square wave. This makes the Peak and RMS values match those of a Sine Wave (otherwise Peak would RMS, instead of RMS=70.7% PEAK). But anything that relies an the 'gentle' slope of the Sine Wave will likely be confused by this, there is no slope on the "modified Sine Wave" inverters (or technically, a very steep one).

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Old 08-21-2010, 11:16 AM   #13
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Couldn't you get a portable power station with a built-in inverter like this?

Duracell Powerpack 600 | Portable Generator | Duracell

Or would that not have enough juice and run time?


http://www.tailgatelot.com/gadgets/t...?currentPage=5


If you go this route, what I'd do is do a trial run. Plug it in for 7 hours and see if the powerstation lasts. If not, get a second one to switch to at halftime?
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Old 08-21-2010, 12:24 PM   #14
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Actually, the "modified Sine Wave" term is quite 'generous'. It doesn't look anything at all like a sine wave. It is not 'stepped' (well, one step, I guess). It is actually very much like a Square Wave, but the ON time is ~ 30% narrower. That is the only difference from a square wave. This makes the Peak and RMS values match those of a Sine Wave (otherwise Peak would RMS, instead of RMS=70.7% PEAK). But anything that relies an the 'gentle' slope of the Sine Wave will likely be confused by this, there is no slope on the "modified Sine Wave" inverters (or technically, a very steep one).
-ERD50
Spoken like an EE.

Regarding "pure sine wave" inverters, these are a fairly new development that was made economically possible by inexpensive fast and powerful MOSFET devices. In shopping for an inverter for my RV, I was surprised to find even large 2 kW ones with reasonable prices. On eBay, one can see many el-cheapo no-name ones from the Orient being offered for dirt cheap. But in researching on the Web, I read horror stories about them blowing up due to poor design. For technical reasons, a "pure sine wave" inverter is more complex and harder to design than the garden variety "modified sine wave" type, which actually outputs a "modified square wave" like ED50 described.

I have several smaller inverters of the cheaper type, from 100W up to 400W and did not have any problem with them. Again, these are simple and have less to go wrong. For the 2-kW true-sine-wave job for my RV, I decided to go with a name-brand one and bought a Xantrex. Will exercise a heck out of it in the upcoming trip.
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Old 08-21-2010, 01:24 PM   #15
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But I don't understand the need for extra batteries for an occasional use. Doesn't 'tailgate' infer there is a vehicle attached to that tailgate? Why not just use the vehicle battery?
I just bought a "dual-purpose" battery called Optima YellowTop.
It can provide enough current to start the car, but is also deep-cycle.
It was expensive ($150 or so) but I needed a new battery anyhow
(I had ruined the previous one by draining it too much, car camping
and the like). But it's only 48 amp-hours.
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Old 08-21-2010, 01:27 PM   #16
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I swear I need to get you guys to spec out my power needs for the boat. It would be a lot easier than doing all the math myself, LOL!
Ditto on the golf cart batteries, though--easier option than a gen.
Having said that, one of the justifications I'm trying out for buying the Honda generator for the boat is that it could be used for other stuff, like on the RV and around the house if we had a power outage or hurricane.
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Old 08-21-2010, 01:31 PM   #17
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For the 2-kW true-sine-wave job for my RV, I decided to go with a name-brand one and bought a Xantrex. Will exercise a heck out of it in the upcoming trip.
How long does the warranty run on one of those units? You think you'll actually take a trip before it expires?
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Old 08-21-2010, 02:04 PM   #18
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Heh heh heh... Any day now...

The order for the toad wiring parts, i.e. the coiled cord, the receptacle to be mounted on the toad and the wire, is still at the UPS warehouse to be delivered on Monday. Two days ago, I finished wiring up that inverter to the power distribution box, using 115VAC relays for the auto-switchover function.

When shore power is not available, the entire 115V circuit in the RV automatically switches over to this powerful inverter, with the exception of the AC and the battery charger: the AC, because we all know there is no battery bank large enough to run it, even if one spends many thousands to buy a stupendous inverter (they exist for home solar installation), and the charger because it is of course dumb to draw from the battery to generate 115VAC, then use 115VAC to generate 12V to charge back to the battery. It is all checked out and works great.

The inverter is hidden in the counter cabinet, under the gas stove. I reverse-engineered the remote switching circuit of the inverter to make a remote on/off push-button switch for it, which is mounted on the kitchen cabinet front. It's a 1" square lighted push on/off switch, whose little indicator incandescent lamp I replaced with an LED to cut the power from 3W down to 0.5W. Other than this innocuous switch, there is no indication that there has been any modification to the RV wiring. All the heavy-gauge wiring, 12V and 115VAC is done under the floor. Heh heh heh...

When drycamping, every little watt counts, heh heh heh... Just finish retrofitting an LED light into the 12V light fixture above the bed to allow reading late into the night without draining the battery. I may need to log off to go out to do a couple more. Thought about adding 2 more batteries to the existing 2-battery bank, but I need to see if I really need it, and also to save some work for later. What if I run out of things to do and have to sit around twiddle thumb all day?

There's no way CampingWorld can even do something like this. And if they do, the labor would cost so much one cannot afford it. Heh heh heh...

DW was getting antsy and asked if we can leave next week. Heh heh heh...
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Old 08-21-2010, 02:13 PM   #19
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The inverter is hidden in the counter cabinet, under the gas stove.
Great! What could possibly go wrong with that...

Seriously, sounds like a spiffy upgrade job. I'm betting you add those two additional batteries if you do much boondocking.
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Old 08-21-2010, 02:24 PM   #20
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Hey, that's another reason I bought a brand-name inverter!

I will test the propane detector just in case, by blowing an unlit propane torch at it.
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