Converting 125VAC Monolite to Battery?

Enclosed is a photo of one of my monolites I'm trying to make more portable for real estate work. It's just a Chinese cheapo, but it's actually pretty good. The downside is that as far as I know, no schematic paperwork is available on it. So even though I am a ham a radio man, I'm not sure enough about the circuitry on this flash where I can tap in and modify it for a battery pack.

So, I wonder if there is a portable battery-to-AC inverter I can hook it up to. I wonder about how many watts this would draw. (It's a 600W/S flash). Certainly there must be a small inverter with self-contained batteries I can hang off the lightstand when going on location. I wouldn't need very many flashes out of it on one job. Thank you.

 

Edited September 29, 2019 by henry_finley|1

Paul Buff offers/offered a battery+inverter package called Vagabond. I used a 1st generation version once or twice and had good results. In any event you will need to ensure that the inverter is a "pure sine" inverter to avoid damaging the flash.

Not my field of expertise. For Americans Paul Buff's "vagabond" stuff seems a solution, if you can live without modelling light.

Flash tubes need in the region of 350 volts DC to work efficiently, and in mains-powered studio strobes this is derived in one of 3 ways:

 

1) For 230/240 volt mains areas the incoming AC is simply rectified to give 325 to 340 volts DC to the storage capacitor bank.

2) For lower voltage mains supplies a voltage doubler or multiplier circuit may be used.

3) The higher voltage may also be derived from a transformer - usually an auto-transformer to save bulk.

 

None of these circuits/methods lend themselves to the injection of low-voltage DC at any point. Therefore your only option is to use an (external) inverter, which incidentally is how all battery-powered speedlights get the high voltage needed to operate a xenon flash tube.

 

The 'power' (actually energy) of the flash expressed in watt-seconds is pretty much irrelevant. It's how much current it draws while charging or recycling that determines the inverter needed. That, and how quickly it's required to recycle.

 

So you need to look at the mains fuse rating of the flash, or at its mains power rating. These should be stated or labelled somewhere. For example: A fuse rating of 5 amps @ 125 volts would mean an absolute maximum power draw of 625 watts, and you could probably get away with an inverter rated at 500 watts continuous. However, allowing for efficiency losses that's going to draw a peak current of over 60 amps from a 12 volt battery. Meaning you need a fairly hefty battery as well as the inverter. And that battery will have to be periodically recharged as well.

 

All in all it might save expense and weight to buy a system designed to run off batteries from day one. These can use a high-frequency inverter with better efficiency, and will usually sacrifice some recycle time for using a smaller and lighter battery pack.

Yes you can make it more efficient with a nice little ferrite core transformer inverter running at 20kHz or so.

 

But it will be much less work to buy an existing inverter to power it,

the battery will be somewhat big in any case.

Although the flash is designed to plug into a household outlet it's going to draw less than 15A. To know for sure you can measure the current draw using an amp meter. That way you know how big an inverter and how big a battery you would need.