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Old May 25th, 2006, 02:23 PM   #1
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Power Inverter for lighting ???

Anyone ever used a power inverter connected to a car battery to run their lighting?

On Ebay I found a 5000 Watt power inverter that connects to a car's battery. I want to run a 1K tungsten off of it but am having trouble with the logic of somehow getting 5000 Watts of 120V out of a 12V car battery.
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Old May 25th, 2006, 05:58 PM   #2
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Don't do it! Your car battery won't sustain that kind of draw. As I recall, there have been a bunch of discussions on this already, with more details than I can give you right now, but, in my experience, you can get a few hundred watts max. I've used a Kino Diva 400 with good results (220W) on a 400 watt inverter, but it was near the edge of what the car could handle. Xantrex makes an inverter/battery combo that looks like it might fit your need. I can't remember the model but I recall it was around 1500 watts continuous. Or, try using the flo's, they save a ton of pwer. I've run a Diva 200 off a small portable battery/inverter bought from costco. Works great and runs for 1 hour on a single charge.
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Old May 25th, 2006, 05:59 PM   #3
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You can do it... just not for very long. Watts = volts * amps, of course. So a 55 amp-hour 12V battery (which weighs about 40 pounds) is good for 660 watt-hours, or about 40 minutes powering a 1K light. Plus you lose some power in the inverter, so a little less.

Needless to say, if you have three 1K lights and you need a few hours of runtime, it gets a little inconvenient carting around 300 pounds of batteries.

Edit:

Just to clarify, you might get into some trouble if you try this with a regular car battery; I haven't actually given it a shot. There are marine and RV batteries which can handle this kind of load, though, as they're designed to be able to power hair dryers and microwaves and such.
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Old May 25th, 2006, 06:09 PM   #4
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A car battery will not sustain that type of draw without being damaged or worse catch on fire, along with the other components in your system like the alternator and the wiring. It's not just about the watts = volts * amps. 55 amps is a huge drain on the system to sustain, because don't forget you are also running the car. The alternator has to recharge the battey or it will die very quickly at that draw. As I said, do a search for car battery ligths or something like that. It has been well discussed before.
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Old May 25th, 2006, 08:06 PM   #5
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Thanks for the advice.

Car would be running, of course. All I really need is 1K for 20 minutes from an 01 Jetta.

I don't understand why they would make a 5000 Watt car inverter if it would damage your car or catch the battery on fire. It's made by Coleman... a large company who probably knows the liability of catching people's cars on fire.
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Old May 26th, 2006, 11:15 AM   #6
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I'm not sure what they are talking about when they say 5000 watts - You better read the fine print. Thay may be for an absolute instant or it's a mistake. Are you sure it's not 500 watts? 5000 watts at 120V is over 40 amps! You don't even have that in your house! That would be over 400 amps at 12 V. Your car battery can do that for a second or so as it starts the car, but no more. 5000 watts would be a huge inverter and would need some serious cooling as well. Look at the product, if it's relatively small and portable, it'sprobably 500 watts.
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Old May 26th, 2006, 05:52 PM   #7
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I have lit a set powered by batteries through an inverter. The answer is fluorescent light. 20 minutes of 1000W would require at least two heavy-duty deep-cycle batteries wired together as one big cell (in parallel to keep the voltage at 12V). The faster you drain a battery, the less overall juice it can deliver. Reduce the drain and the battery can supply a greater overall quantity of electricity (watt/hours). I made multiple-bulb fluorescent light fixtures that were bright enough for shooting with the Sony FX1 which is about mid-range in light sensitivity for DV/HDV cameras. Also, naturallighting.com has 65W fluorescents that fit in large hardware-store clamp-lamps. If you need to match 1000W, you would need three of these. In my area, Lowes has 40W compact fluorescents that only cost $10. I am putting two of these in one light to give me the equivalent of 300W. They seem plenty bright to me. The cool running temperature is a big bonus since the likelihood of fire or burnt fingers is much lower. If you use 4 x 40W fluorescent lights, you will be much closer to safety than if you want to run a 1000W or even 500W tungsten.

Fluorescent light needs a bit less diffusion since it is a big source, so you can gain a bit of lumens from that factor. If you don't want really soft light, no diffusion is necessary at all. Hard light from a fluorescent is only possible if you move the light farther from the talent, so that decreases the strength of a fluorescent. I prefer fairly soft but directional light, so I find fluorescent is actually more efficient for my needs since I can use less gel. Fluorescent can also be matched to daylight without gelling up if you buy the correct bulbs. I get both 5600K and 3200K bulbs for different circumstances. 5600K is good for moonlight and 3200K is close to streetlight and other practical lights. I try to use reflectors during the day, but a bright daylight-balanced bulb or three comes in handy if the reflector isn't cooperating.

The most wattage I would expect to get from a car is about 600W. You must be careful and connect the inverter to the battery as the cigarette lighter plug can not handle much wattage. My inverter has run my 600W refrigerator continuously for two hours and my 5A drill intermitently (600W with more at startup) with no problems. Anything more is asking for trouble.

Most cars have about a 90Amp alternator. 90A x 13.8V = 1242 absolute maximum watts. Never run a system for several minutes at full load = 900W available. Subtract the energy needed to run the car leaves you with probably no more than 700W available if all accessories in the car are off. If your radiator is an electric fan, take off another 100W.

Keep car batteries well ventilated so inadvertent sparks don't make the hydrogen sulfide gas explode. If you smell a rotten egg odor from your batteries, stop what you are doing. If your cables get hot from electrical resistance, stop what you are doing. Carry a fire extinguisher when dealing with electricity. Don't reverse the polarity. Make sure your car does not overheat. I left the hood open and monitored my car when running my fridge during a power outtage. Be careful and I accept no responsibility. Stay withing the limits of your technical knowledge.
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Old May 26th, 2006, 11:59 PM   #8
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They do make some very large current inverters such as the one you mention.They do have 2 ratings... maximum surge load and maximum continuous load.However,they are not intended to be used at maximum continous capacity installed to a car.They are intended for buses,motorhomes and trucks with systems designed specifically for this.Vehicles that have 2 or 3 large capacity batteries (double that of a normal car)and charging system able to support that.As others have stated the battery,alternator and the WIRING of a car are not designed for 5000w loads.Each specific vehicle is different as some may support up to 1200watt loads but not many.More would be in the 600 to 800 watt range.
Now you can use a higher rated inverter but you should keep the load in the range your vehicle is able to support.
Constant high current loads will also reduce the life expectancy of your battery and charging system.
Marcus has a good alternate solution
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Old May 27th, 2006, 12:26 AM   #9
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Thanks for your input, guys.

I had considered fluorescent but had decided against it due to breakability and the fact that I'm a clutzy idiot -- but I think I'm going to give the 5500K compact fluorescents another look. Either that or I'm going to just get a generator and run a couple of HMIs.

For the record, that inverter is definitely a 5000 Watt - although it's 5000W peak and only 2500 continuous. It's huge (18" long) and has 2 cooling fans on one end - comes with clamps for the battery. Modified Sine Wave and all that jazz. Makes sense about it being made for RVs and buses, etc.

Thanks again, everyone!
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Old May 27th, 2006, 01:04 AM   #10
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You aren't going to fry your car's wiring by attaching a large inverter directly to the battery. Electricity, like water, always takes the path of least resistance. If you have a load of 2500 watts directly clamped to the battery, most of the current being supplied by the battery will go to 'that' circuit, not to the vehicle's wiring harness circuit.

You might destroy the battery by pulling a maximum load which will generate internal heat, which will buckle the plates until the cells short out internally. When that happens, the battery will no longer accept a charge.

You could blow the alternator fuse (most modern vehicles have one) as it goes to max output trying to keep the battery charged while you draw that big load from the battery. That's why emergency vehicles often come with 200 amp alternators so when they are sitting at an accident scene at night in a driving rain storm they can have the windshield wipers, the headlights, the emergency lighting, the radios, etc. all energized (with the vehicle running of course) for possibly an hour or more.

If you do decide to use that big power inverter, I suggest you go buy a pair of deep cycle marine/rv batteries and hook them up in parallel (ie positive to positive and negative to negative) and charge them with regular battery chargers designed for deep cycle batteries.

regards,

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Old May 27th, 2006, 04:04 AM   #11
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If you rent an HMI, a 400W is brighter than a 1K tungsten (~32,000 vs. ~22,000 lumens). There is a 1000W Honda generator (model EU1000i) that is quiet and one of the local film rental places here has them. They sip gas and are as quiet as an idling car. With long and heavy extension cords, you could easily power an HMI from one of those and forget it is around. There is also a 2000W model. Both use an internal inverter to get 120V. I worked on a commercial where we ran crt field monitors with these and they worked fine. Ask your rental house if their HMI ballasts like inverters. Some are supposedly better/cleaner than standard generators that use an alternator. Honda claims true sinewave.

Don't worry about breaking compact fluorescents. They aren't that fragile. Don't be careless, but there is no need to feel paranoid around them. The real problem is their size. Until better fluorescent science comes around (supposedly in two weeks), they are quite large for their output. An 80W "compact" fluorescent is about 11" long and 4" in diameter. A multiple-bulb fixture is the best answer for conventional bulbs. Think fluorescent maxi-brute. You could also rent something like a Kinoflo Diva400 that gives light in the neighborhood of a 1K softbox. It isn't as easy to control as an HMI, but should be cheaper.
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Old May 30th, 2006, 05:45 PM   #12
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The EU series of Honda generators are really marvelous as a low-budget source of power for shooting. While not a quiet as a "real" generator, they are quiet enough with a little sound baffle around them. Easily portable and very fuel efficient. The 2000 model will handle a 1.2 KW HMI. I've found RV and small engine places that will rent them at pretty reasonable prices.
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Old May 30th, 2006, 07:12 PM   #13
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I have run a 900w arri from a 1000w inverter through my car no problems. It was never on for more than 10mins. You can draw between 50-90amps through your cars battery/alt/wiring. In the future I will be using a 650w arri with a 800w inverter just to be safe, but I havn't had any problems!
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