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Wattage for a DC-to-AC Power Car Inverter?


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#1 Nick Norton

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Posted 25 June 2008 - 04:28 PM

Wondering what type of AC Power Inverter i would need to power a 1k Fresnel off of a car battery.

Is this even practical?

Thanks-

Nicholas
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#2 Tim O'Connor

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Posted 25 June 2008 - 10:34 PM

Wondering what type of AC Power Inverter i would need to power a 1k Fresnel off of a car battery.

Is this even practical?

Thanks-

Nicholas


I like to use inverters but the biggest that I've used is 750w and that, like every other
inverter I've used, is the maximum rating, in that it's recommended that you stay a 100w
below that consistently. I also feel that drawing 650w or even 600w off of a car for several hours, while a big help in certain shoots, is not something to do all the time as it does seem to beat on the car a bit.

If you need that much light, maybe you could use a smaller unit that is open faced and then
spot it in and diffuse it if that will get you close to what the 1K fresnel would do for you.

There are some nice small generators too that are really quiet. If recording dialogue, usually the car has to be parked away a distance and it might be easier to carry a small
generator away from your set.
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#3 timHealy

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Posted 26 June 2008 - 05:10 AM

Wondering what type of AC Power Inverter i would need to power a 1k Fresnel off of a car battery.

Is this even practical?

Thanks-

Nicholas


Can you clarify your question for me.

Do you want to power lights using a car battery that is installed in a car that you are shooting in or just using car batteries in general that are not installed in a car to supply power to an inverter?

Best

Tim
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#4 Rob.m.Neilson

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Posted 26 June 2008 - 10:23 AM

Your going to blow the car lighter jack with a 1k off the inverter for sure. I blew one using an inkie in the past! Inverters are rated at their max wattage I think, and at that they will only be able to stand the max load for 15 minutes or so at a time.

Lately Ive had alot of success using duracell portable 600w powerpack inverters (they have a built in light and radio too to play with) and they have been great. I've only used them with kino flo's but they have not let me down.

If you search amazon you can also buy a Xantez 1500w powerpack to run a 1k off of, however I would assume that the 1k would sap the battery pretty quickly. (With the 600w duracell power pack, rated at 28 amp hours gets sapped in 23 minutes powering a 300w fresnel).
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#5 Nick Norton

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Posted 26 June 2008 - 01:13 PM

Perhaps a generator is the better route to take.

I'm a little confused with how much wattage i need the generator to handle.

Is it as straightforward as a 1000watt light needs a 1000watt generator or better?

Thanks-

Nicholas
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#6 Adrian Sierkowski

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Posted 26 June 2008 - 03:34 PM

You'd want one that's a bit higher than you're drawing. I'd take a 1500W genny for a 1K light. Then you can plug in a coffee pot too!
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#7 JD Hartman

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Posted 26 June 2008 - 04:04 PM

It's a simple matter of applying a power calculation. A cig. lighter outlet can only provide so many watts before the fuse melts. Usually they are fused at 20 or 25A, so a maximum of 300 watts is available to convert to 120vac. If you wanted to power a 1k or larger, the inverter would have to be wired into the vehicles primary electrical system with much heavier cable (#2 or 4) and fused to protect the alternator and battery. It's not something to be done with jumper cables either. Can it be done, certainly. Is it worth the time, money and effort for one shoot, no.
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#8 Tim O'Connor

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Posted 26 June 2008 - 05:40 PM

It's a simple matter of applying a power calculation. A cig. lighter outlet can only provide so many watts before the fuse melts. Usually they are fused at 20 or 25A, so a maximum of 300 watts is available to convert to 120vac. If you wanted to power a 1k or larger, the inverter would have to be wired into the vehicles primary electrical system with much heavier cable (#2 or 4) and fused to protect the alternator and battery. It's not something to be done with jumper cables either. Can it be done, certainly. Is it worth the time, money and effort for one shoot, no.




I use a 750w inverter that is fused and that comes with small jumper type cables and I've used it many times. I park the car, leave it running when I'm powering the light(s) so that I'm using the alternator and not just drawing from the battery and lightly gaff the inverter down so that any vibration doesn't slide it off of the flat space between the grille and the radiator frame where I tend to sit it.

There are lots of locations on small shoots where I can drive the car up to the edge of the woods, beach, deserted warehouse and park behind a wall and
run 50' of 12/3 and never hear the car and use a couple of 300w lights or whatever and have done so for an hour or two successfully.

I worked on a film for German tv on which the gaffer had a real high quality inverter (don't know the brand) which he mounted on the hood of the picture
car, connected it to the car battery with temporary jumper type cables and powered a small HMI off of it (which he mounted with a suction cup and a spud) and that car was driven by an actor.

I have used cigarette lighter outlets to power lights for illuminating the car interior/actors, but they're 12v small on camera video lights of say 25w
which can do a lot in that small space and I have run only two at once.
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#9 timHealy

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Posted 26 June 2008 - 06:19 PM

Personally I prefer to play it safe when dealing with picture cars. (especially when some of them may be older models)

Though it sounds like some have gotten away with it, tying an inverter into the picture cars (or any car for that matter) car battery runs the risk of depleting the battery or damaging your alternator.

It is a standard practice on larger films to use two 12 volt marine or gel cell type batteries in parrallel hooked up to a true sine wave inverter. The type you may find on a boat or something. The largest I have worked with is about 2500 watts and they work well. You can put them in a trunk, the back of a van, or ratchet strapped to the roof depending on the vehicle.

It is a tried and true method that leaves the electrical department of any film out of the picture car owners hair.

Best

Tim

Edited by timHealy, 26 June 2008 - 06:21 PM.

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#10 John Sprung

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Posted 26 June 2008 - 07:38 PM

OK, 1000 Watts at 120 Volts would draw 8.33 Amps. Rule of thumb for a safety margin, make that 10 Amps.

To get the same power from a 12 Volt system, you'd have to pull 100 Amps. Rule of thumb for sizing batteries, you want to pull no more than one tenth as many Amps as the battery's Amp-hour capacity. Or think of it as discharging at no faster than the ten hour rate. In this case, to use the inverter, you'd want to parallel enough batteries to have 1000 Amp-hours available.

Regular car batteries are not the best choice for this. They're designed for brief heavy loads (cranking the engine to start it). What you want are the kind of deep cycle batteries they use in golf carts and fork lifts. We're talking 2 - 4 batteries here, very doable in the trunk of the car.

Bear in mind that the color temp on your incandescent or halogen lamps will go down as the batteries discharge, HMI's go up IIRC. That's why you need a whole lot more hours than you'll actually be shooting.



-- J.S.
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#11 chuck colburn

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Posted 26 June 2008 - 07:45 PM

What John says.
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#12 Tim O'Connor

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Posted 26 June 2008 - 08:14 PM

Personally I prefer to play it safe when dealing with picture cars. (especially when some of them may be older models)

Though it sounds like some have gotten away with it, tying an inverter into the picture cars (or any car for that matter) car battery runs the risk of depleting the battery or damaging your alternator.

It is a standard practice on larger films to use two 12 volt marine or gel cell type batteries in parrallel hooked up to a true sine wave inverter. The type you may find on a boat or something. The largest I have worked with is about 2500 watts and they work well. You can put them in a trunk, the back of a van, or ratchet strapped to the roof depending on the vehicle.

It is a tried and true method that leaves the electrical department of any film out of the picture car owners hair.

Best

Tim



Yes, I agree. I use the inverter for my own personal productions, the really no budget short films on which I may be the entire crew and
want to get some light into a place where power is not easily accessible.

Newer cars have such sophisticated electronics that running an inverter for a long time may raise issues that wouldn't have come up with older cars.
Plus, if you're paying somebody to use his brand new top of the line Jaguar and a week later it's in the shop with an electrical problem, and the guy
happens to relate the story of his car being in a movie and powering lights; you could likely be blamed for a problem with the car and if it's something funky even Scotland Yard and the FBI mightn't be able to say what caused it.

Older cars might not be up to the added stress on an electrical system with a lot of hours on it.


Currently I'm waiting for my patent to be approved for my 1 mile (yes, 1 mile long) extension cord that has virtually no drop to it due to
revolutionary new technology. Each one is handmade so get your orders in now.

Coming soon will be a metric version, the Kilocable. It's like the above, except that it's .6 of a mile long.
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#13 Brian A Garnell

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Posted 06 July 2008 - 10:12 AM

You'll be much happier with this geny from Honda. Super quiet, carry it with one hand, runs a 1200 HMI no problem.
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#14 Glen Alexander

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Posted 06 July 2008 - 11:48 AM

If have a GOOD alternator, you can run it off your engine while car is running. IF your alternator is weak, you'll ruin it.

Cheap inverters are very noisy electrically, bad harmonics, and inefficient. Sensitive equipment will not work.

Person above is right, get some deep ocean marine batteries in parallel or big one. They're heavy but you can mount them any direction and they take shock and drops.

or use the quiet Honda.
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