Input power for Profoto D4 4800

[Songyun]

I know the output is 4800 Ws, how about input power? To use it in the field, How much power do I need from power generator?

[Daniel Stone]

I'd get something OVER a 5K genny.

make sure to not have the "fast" or "turbo" mode on, you might break the generator.

These big packs are best used on ac(aka wall power) unless you have a tow-behind-the-truck generator at your disposal ;).

-Dan

[E. von Hoegh]

I know the output is 4800 Ws, how about input power? To use it in the field, How much power do I need from power generator?

"Ws" means watt-seconds, and is the output power dumped by the capacitor, not the average power going into the device. Look on the label of the device, it will specify the input power in watts, or the input current in amps. Multiply volts by amps to get watts, or divide watts by volts to get amps. 5000 watts at 120 volts is just under 42 amps; you won't be getting that out of any 120v wall socket - so the input power will probably be on the order of a few hundred watts. The generator will be protected by a circuit breaker.

[Mark Woods]

If the unit has a 20 amp plug, a much smaller generator is called for. I've shot on sets with a putt putt generator and had no problems.

[Neal Chaves]

Consider an AC inverter for mobile use rather than a generator. The new models are inexpensive and many produce true sine wave power (although modified square wave is fine for strobes). Get one that can supply 2KW continuous. These inverters will connect to a 12VDC auto battery or you can make up your own rechargeable battery pack. When you travel to locations with a generator you need to take along gasoline and deal with noise, exhaust and starting problems. Generators can produce voltage spikes that damage strobe electronics if not properly filtered. Once you use an inverter, you'll never use a generator again.

[E. von Hoegh]

Consider an AC inverter for mobile use rather than a generator. The new models are inexpensive and many produce true sine wave power (although modified square wave is fine for strobes). Get one that can supply 2KW continuous. These inverters will connect to a 12VDC auto battery or you can make up your own rechargeable battery pack. When you travel to locations with a generator you need to take along gasoline and deal with noise, exhaust and starting problems. Generators can produce voltage spikes that damage strobe electronics if not properly filtered. Once you use an inverter, you'll never use a generator again.

An inverter and battery that will deliver 2kw will weigh much more than a generator of equivalent capacity. 2kw from a 12v battery is a drain of around 170 amps. That's assuming 100% inverter efficiency. You'll need 4 average car batteries to supply that kind of current, even then you'll only get the full 2kw for a matter of some tens of minutes. What do four car batteries weigh?

I don't know, but I'm guesstimating his flash draws 300 - 500 watts maximum, with an idle draw of much less. If he wants 2kw, a generator is the way to go. The Hondas are quiet, sip gas, and are fairly clean waveform-wise.

[Songyun]

checked last night, can not find it.

"Ws" means watt-seconds, and is the output power dumped by the capacitor, not the average power going into the device. Look on the label of the device, it will specify the input power in watts, or the input current in amps. Multiply volts by amps to get watts, or divide watts by volts to get amps. 5000 watts at 120 volts is just under 42 amps; you won't be getting that out of any 120v wall socket - so the input power will probably be on the order of a few hundred watts. The generator will be protected by a circuit breaker.

[E. von Hoegh]

The power consumption must be listed somewhere, maybe on the maufacturer's website. And, I forgot to think of whether or not you'll be using modeling lights. Say you have four 250w modeling lamps, that's a continuous Kw right there, over and above what the flash unit draws.

[Sevo]

I'd get something OVER a 5K genny.


The charge circuit for the capacitors could be driven almost arbitrarily high - the caps could be safely charged as fast as they can be discharged, deep in the kA territory. The makers however won't try to exceed the household circuit limit, or the flash would be useless in real life. Hereabouts flash generators with 230V plug accordingly are limited to 16A grid load, as they would blow the circuit fuse otherwise. Something similar, perhaps with other values, will have to be considered everywhere. Don't dimension the generator any smaller, or you may fry it. Ideally, plan in at least 50% headroom - some of them take rather unkindly to complex overload patterns...

[Neal Chaves]

Inverters in the 1990s were heavy, but new models are much lighter. Only one car battery is required. Large strobes draw up to 100 A in a spike as they charge or recycle and then "float" on much less current when ready. Use of modelling lamps, which draw continuous power, should be kept to a minimum. A 100 A spike on the 120V side is 1000 A on the 12V side. Use adequately sized battery power cables on the inverter and attach them securely to the battery posts. Keep the vehicle running if possible.

Some rental houses may still have the power management device called "The Magic Bus", developed by photographer David Mendelsohn and me in the 1990s and marketed by Saunders. With this unit, up to four large power packs can be powered from one 15 A source. System recycle time is lengthened, but tremendous flash output (4 X 4800 WS) is available at the end of a single long extension cord, or from a small generator or inverter.

[polyglot]

Stop pulling numbers out of your arses, people.

You can approximately figure the peak power consumption from the recycle time. Specs say it's 4.4s and the flash energy is 4800Ws (4.8kJ), that means you need 1100W... plus inefficiencies so say 1500W on average while it's recharging. It might be uneven, e.g. a big initial peak of 2kW or 3kW that falls off to lower numbers near the end of the recharge - it depends how smart the charging circuitry in the flash is. You must also add on the total power consumption of your modeling lights (less so if you set the pack to turn the modeling lights off while recycling); the pack supports up to 2kW.

A small 5kVA generator will not struggle with this at all, even with 4 of 500W modeling lights attached and running continuously. A 2kW inverter will probably be fine with it if you turn the modeling lights off.

A small car battery (e.g. for a 2L car) can supply about 300A (3600W) instantaneously, but only for a minute or so. Keep in mind that the capacity of a battery goes down rapidly as the load current goes up, which means that if you can halve the load current, you can probably get double or more total capacity from the battery. This is why there are power-packs designed for use with batteries; they charge more-slowly so as to maximise battery capacity, and they do direct flyback switching DC-DC conversion from 12V (or 48V or whatever) to 300V for the flash, no need for sinewave inverters, PFC and all the inefficiencies involved therein.

If you want to use several car batteries, be aware that connecting them in parallel will cause significant current to flow between them if their charge is not perfectly equalised. Keep your batteries as a set and only disconnect them from each other for transport; leave them connected to each other at all times during use and charging.

[Leigh]

The power consumption must be listed somewhere, maybe on the maufacturer's website...
Power consumption, if listed at all, would be meaningless for a cylic load like a strobe. It only draws power while charging.

The parameter of interest is the peak current. That determines the size of the generator or invertor required to power it reliably.

Modeling lights are a different story. Those consume power continuously, and the rated power can be used for calculating generator load.
In this case watts = volts * amps, so a 250-watt bulb will draw just over 2 amps on a 120-volt circuit.
That current should be added to the peak current required when the strobe is charging in order to determine proper generator size.

If the generator capacity is insufficient, the voltage will sag and it will take longer for the strobe to reach full charge, but it will do so.

- Leigh

[polyglot]

If the generator capacity is insufficient, the voltage will sag and it will take longer for the strobe to reach full charge, but it will do so.

- Leigh

If the generator is completely inadequate, it can even stall! I found that one out the fun way when plugging a big amplifier (1kVA of toroidal transformers, a few kJ of filter capacitors and no soft-start control) into a little 5kVA generator for a party out in a paddock. The flash of course

[Sevo]

If the generator capacity is insufficient, the voltage will sag and it will take longer for the strobe to reach full charge, but it will do so.


It is a bit more risky than that - the generator frequency and waveshape can drift from the standard, which may overload the flash inverter or caps.