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Voltage & Wattage Question


Dan Stone

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We're having a hypothetical debate in the studio this morning around the concept of Jumbo lights (wiring 28V ACL lights in a series). We're not electrics so we won't be wiring anything ourselves but had a question about the concept.

 

Assume we have 4 x 28V/600W ACL bulbs wired in a series. We'll end up with 112V and 2400-ish Watts, which is 21.4 Amps. Not powerable by a 20 Amp household circuit.

 

Is my electrical knowledge correct, here? Thoughts? Voltage and Watts add up in a series. Then Watts divided by Voltage to get Amperage.

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Yes.

 

My thoughts: I wish that Iwasaki still made their 150W par36 metal halide stuff, it does this sort of thing so well and for about 25% the power.

 

If you wanted to homebrew it, it is increasingly plausible to homebrew LEDs at this sort of power level, depending what sort of radiation pattern you wanted.

 

P

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Thanks! And agreed on the metal halide lamps.

 

I put together 3 x 50" off road led light bars a while back. It was a good amount of light but for some reason they interfered with everything wireless. They also made a high-pitched whistling sound when on. They were cheapies from Amazon.

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We're having a hypothetical debate in the studio this morning around the concept of Jumbo lights (wiring 28V ACL lights in a series). We're not electrics so we won't be wiring anything ourselves but had a question about the concept.

 

Assume we have 4 x 28V/600W ACL bulbs wired in a series. We'll end up with 112V and 2400-ish Watts, which is 21.4 Amps. Not powerable by a 20 Amp household circuit.

 

Is my electrical knowledge correct, here? Thoughts? Voltage and Watts add up in a series. Then Watts divided by Voltage to get Amperage.

Not hypothetical. Was done a lot in 90’s with Mole Richardson Dino Lights. Vittoria Storaro still does it with some of his lights.

 

Tim

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We're having a hypothetical debate in the studio this morning around the concept of Jumbo lights (wiring 28V ACL lights in a series). We're not electrics so we won't be wiring anything ourselves but had a question about the concept.

 

Assume we have 4 x 28V/600W ACL bulbs wired in a series. We'll end up with 112V and 2400-ish Watts, which is 21.4 Amps. Not powerable by a 20 Amp household circuit.

 

Is my electrical knowledge correct, here? Thoughts? Voltage and Watts add up in a series. Then Watts divided by Voltage to get Amperage.

 

More like 2400w/120v=20a. I don't think you're going to meter less than 120V anywhere (USA) even under load. Not even in Harlem, NYC in the Summer. A 20a breaker doesn't trip at exactly 20.001 amperes. Why don't you try your 4 bulb ACL setup in a see how long it takes the breaker to trip. If you think you are going to run your light on the end of a 100 foot stinger, then all bets are off.

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Not hypothetical. Was done a lot in 90’s with Mole Richardson Dino Lights. Vittoria Storaro still does it with some of his lights.

Tim

I think I should clarify, when used in a big light like a Dino, one would not change the connectors. So a Dino usually has 6-60 amp connectors. One connector powering 4 120v 1k bulbs. If you replace with ACLs, one 60amp plug can easily power 20 amps worth of ACLs. The breakers never trip.

 

Other big lights may even have camlock so a piece of 5 wire banded would power up a large light.

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If you really want to get the exact theoretical numbers you apply 2 formulas from Ohm’s law. The lamps are basically fixed resistors that you put in series.

Voltage Squared / Power = Resistance - 28x28 Volts / 600 Watts = 1.3066 Ohms

You have 4 of these resistors in series - 4 X 1.3066 Ohms = 5.2266 Ohms

Your voltage for calculation purposes would be what you can measure with a meter in your specific setup and not what the combined rating of your series elements is; i.e. not 112V. At 120V supply voltage your setup would result in the following current flow:

Voltage / Resistance = Current - 120 Volts / 5.2266 Ohms = 22.95 Amps

At a lower voltage than 120V they would draw less current. Note that rated lamp power vs. real lamp power and also utility supply voltages can vary with as much as +/- 5% or more.

Bottom line is that you will be over or dangerously near the rating of a 20A breaker.

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  • 3 weeks later...

So I was curious and threw together a fake Molefay ("Folefay"). Ordered nine 9" 185 Watt LEDs from Amazon (they actually draw closer to 110 Watts each). Ended up only using six because they're insanely heavy. This Frankenstein weighs about 50 lbs.

 

Color is about 6300K and, from eyeballing what it's doing to the inside of the room, it's comparable to an M18 with a 1200 globe on spot in terms of brightness. Total cost (excluding the unused lights) is about $500.

 

Not sure what I was thinking because I would probably never use this on set unless I needed to hang something high up in a tree in the woods. In Billy Madison's words, "I drew a blue duck because I've always wanted to see a blue duck."

 

333eov4.jpg

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Nice idea. Don't supposed you managed to get any CRI or, better, TLCI numbers for it? I fear if it was that easy everybody would have one.

 

This could be done with high quality LEDs with a bit of ingenuity but it would require forced air cooling.

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Nice idea. Don't supposed you managed to get any CRI or, better, TLCI numbers for it? I fear if it was that easy everybody would have one.

 

This could be done with high quality LEDs with a bit of ingenuity but it would require forced air cooling.

I've been searching for this info as well. I haven't been able to find much in the way of technical data for any brand. I'm guessing that as these lamps are generally attached to pickup trucks and other vehicles, brightness is more important than color rendition.

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