20 replies to this topic

[John Crow]

So, I've always wondered this: I read in one of my lighting books that by increasing voltage one can increase power output, thereby increasing wattage and hence luminosity. I've never had an opportunity to try this and I was wondering if it's true. How can this be achieved? Do you just dial up the voltage on the genny? It seems that could be a danger. Would the the higher voltage simply result in a lower amperage to maintain a balance with the wattage, or would the wattage actually increase? And can it be done with HMIs or Kinos - lights with ballasts that regulate voltage? I've noticed lights sometimes dim when voltage gets low, but I've never seen the opposite effect..

[Ralph Keyser]

Yes, you can increase the wattage of a tungsten bulb by upping the voltage. Basically, the filament in a tungsten bulb is a resistor, and by upping the voltage applied to it you are causing more current to flow through it. This gives you more light, but drastically shortens the life of the bulb. The big genny's that I've worked with do have a control that will let you set the voltage, so yes, you basically just dial it up. I've only seen this done once with a string of practical bulbs that we just needed to get a little more "oomph" from. The danger is that you are pushing more amps through something that's not designed for it, so you have the possiblity of things overheating and burning out. I'd say you can do it, but it sure is hard on the equipment.

This does not apply to HMI's or Kinos. The ballast regulates that voltage that reaches the lamp, so you might damage the ballast with enough voltage, but you won't get anymore light out.

[Dan Salzmann]

Just wanted to underline that this is just an emergency measure and for tungsten only.
To increase the power of practicals it is much better to just insert higher wattage globes.
Not too long ago we increased the voltage for some practicals in a house in a remote area on a weekend and they blew out very quickly with around a 25% voltage increase.
Since it was night there were no shops open and we just about made it with our spares.
Beware!

[timHealy]

On a film set one shouldn't mess with the voltage. A normal 110 volt range on a US film set is 110 to 120 volts (110 is interchangeable with 120). If a genny reads 119 or 121, you are fine. You could turn up the voltage to 130 but then not only do you start to run the risk of blowing bulbs, but you could start blowing sound and video equipment on your set as well.

Some people start turning up voltage when experiencing voltage drops. When you put a load on, and the voltage drops as you add lights, some crank up the voltage, but as you turn off lights the reverse happens, and the voltage could pop and blow bulbs or other equipment.

It is just safer to run your genny at proper voltages and with proper cable runs.

Best

Tim

[Adrian Sierkowski]

Essentially, if you need a bigger light, you need a bigger light. . . Trying to get 'round that by changing voltages is an exercise in danger. Right tool for the right job... and when that failed make the best of it. My 2 cents.

[John Crow]

Thanks for the input, I think you've answered my question. I asked because I'm going to be gaffing a small budget project soon, and they just don't a have a sufficient lighting package for what needs to be done, not enough big guns. I was going to consider juicing up the volts as an option, but in lieu of what your posts I may just skip that and hope for the best...

[Adrian Sierkowski]

It's always a pain on the smaller budgets. But, you can only do what you can do, you know? Let the DP know any concerns you have, and I'm sure you can figure something out. Hell, it's the most fun part of the day when you make something work that really, by all account, shouldn't.

[Jamie Metzger]

First of all, I think that the only way that you could do this, is stated above; with a genny capable of producing more voltage.

Second: this is a terrible idea. DO NOT TRY IT.

Bulbs are rated a certain watt, at a certain volt (120) for a reason. There really isn't a safety factor built into them, letting you get away with X amount of %. Granted peaks in voltage coming from the power station are normal, but they hardly exceed 121/122. That's for a reason.

You can decrease voltage by the use of a dimmer, but you can not increase the voltage past the rating for a product. A lot of people all ready posted some serious concerns for other peoples gear as well... Good points.

[Matthew Parnell]

Recently did a shoot in an older building that was getting mains power that we were metering at 257-261v besides our generator power of a perfect 240v. Because of budgetary constraints, we had to run of house power even at those voltages.

When we put the lamps on house power they did throw about a 1/4 stop more light, however on that job we were going through an average of a par globes, two tweenie globes and a pup globe every two days. Of those lamps we only had 8 pars, 4 pups and 2 tweenies out of the truck! Went through a lot of prac globes as well.

Off that experience one can definitely assume doing this on purpose does not work out cheaper or more time efficient, especially for a gain of about a 1/4 stop!

[Jamie Metzger]

Recently did a shoot in an older building that was getting mains power that we were metering at 257-261v besides our generator power of a perfect 240v. Because of budgetary constraints, we had to run of house power even at those voltages.

When we put the lamps on house power they did throw about a 1/4 stop more light, however on that job we were going through an average of a par globes, two tweenie globes and a pup globe every two days. Of those lamps we only had 8 pars, 4 pups and 2 tweenies out of the truck! Went through a lot of prac globes as well.

Off that experience one can definitely assume doing this on purpose does not work out cheaper or more time efficient, especially for a gain of about a 1/4 stop!

HERE HERE! Don't do it!

[Gus Sacks]

From the most recent ASC Mag article on The Curious Case of Benjamin Button:

Along the ceiling were crisscrossed strings of vintage clear 60-watt bulbs. "I barely got a T1.4 or even a T1 out of the whole tent being lit up," recalls Miranda. "We had to crank the voltage up to a 140 to get some sot of exposure out of them. The bulbs got very, very warm."

So, of course it is done, and even people with I'm sure unlimited resources turn to doing it. Just an example when it worked.

[Walter Graff]

If you have a variac you'll notice it goes up to 130% and offers some fine over wattage.

[John Sprung]

Utility companies here in the U.S. are generally required to provide nominal voltage plus or minus 5% as measured at the service entrance. Building codes generally allow no more than a 3% drop from there to your plugs and sockets. So, a 120/240 system should never show you more than 126/252. There are 277 volt three phase systems out there, and if one is running on the low side, it could look like the 257 - 261 that you found.

Bear in mind that while overvoltage is bad news for light bulbs, undervoltage is bad news for motors. Motors make up for low voltage by pulling more amps, and running hot. That's why motors are often rated 115/230 instead of 120/240.




-- J.S.

[Matthew Parnell]

John,
I am in Australia where we are purely based on a 415/240v three phase system. Was an old building in an old area.
Cheers,
Matt.

[John Sprung]

John,
I am in Australia where we are purely based on a 415/240v three phase system. Was an old building in an old area.
Cheers,
Matt.

Wow, do you guys have three phase in your homes? Here the DWP will only sell single phase 120/240 to residential customers, even if there's three phase on the pole. Three phase motors are much more cost effective than single phase -- no capacitors or starting crap.

As for the overvoltage, if the building was big enough, it might have its own multi-tap transformer that was set up correctly for a full occupancy load, but ran high if you were the only users in the place.




-- J.S.

[Matthew Parnell]

Three phase is rare in homes over here, you can get it, but you have to specifically get it installed and its really a pain to do. Only really keen guys with serious home workshops using three phase lathes and welders seem to be the only guys keen enough to do this.

We were in a hall in the middle of an older industrial area. We never did work out what the problem was, so your theory might very well be right.

[David Auner aac]

Wow, do you guys have three phase in your homes? Here the DWP will only sell single phase 120/240 to residential customers, even if there's three phase on the pole. Three phase motors are much more cost effective than single phase -- no capacitors or starting crap.

Hi John,

three phase power (380V) is pretty common here. We had it in my parents house from the start. Numerous other people who have hobby workshops would also have it. And out in the country is pretty much everywhere as nearly every one who does farming or gardening on a larger scale has a couple of appliances for three phase power.

Cheers, Dave

[John Sprung]

Thanks, guys -- I'll have to keep Austria and Australia in mind as good places for a machinist to retire.... ;-)




-- J.S.

[David Auner aac]

Thanks, guys -- I'll have to keep Austria and Australia in mind as good places for a machinist to retire.... ;-)

Another advantage is quality of tools made here in Austria and of course Germany.

Cheers, Dave

[DJ Joofa]

Three phase motors are much more cost effective than single phase -- no capacitors or starting crap.

Hi John, a small refresher , not all single phase motors have a capacitor for starting, some that come to mind right now are split phase motors that produce torque by having 2 stator windings; shaded pole motors; reluctance motors, and hysteresis motors.