Photographer needs advice on his kit

[mrsus]

Hi all,

I am a photographer looking for advice on how to power a studio flash system, on location using a battery/inverter combination.

I have a studio flash pack, about 10-15 years old, with no specification label on it. It is a 240v unit with a 5amp fuse, so clearly it uses less than 1200watts. It is basically a box of pretty big capacitors.

I want to run this from a 12v battery/inverter combination (petrol generators are apparently no good for this due to the dirty (spikey) supply they give, unless you buy an expensive one.

My flash pack is also fitted with a auto sensing input voltage thingy, which means I can plug it into a 110v or 240v mains supply without needing a transformer.

My questions are:

Apparently, one of the issues is that after the flash fires and the pack draws current, the voltage from the inverter drops slightly and confuses the voltage sensor causing it to not work.

Is this true? If I bought a 1500watt inverter, would this get around the problem since it is rated higher than the 1200watt flash pack?

I also understand that it will need a pure sine wave inverter, can anybody recommend a good make that is available in the UK?

Is there likely to be a way to bypass the voltage sensor, since I will only ever use the pack on 240v?

How dangerous to my equipment is it likely to be if I plug it into an inverter as an experiment? It's very expensive kit and I obviously don't want to brick it!

The makers of my lights used to make a switched mode power supply for it, which enabled you to run it from a 12v car battery. They don't seem to be available anywhere, either new or secondhand. Is there likely to be another unit that would work?

The switched mode unit has its' own socket, presumably to bypass the voltage sensor. Could a decent electronics engineer be able to work out what this socket requires and then either buy or make a switched mode supply that will work?

As you may have guessed, I only have a basic grasp of electronics (I'm just a lowly snapper), so I'll apologise now if none of this makes sense or if my questions are stupid!

I have a deadline for this, so I am panicking a little and any advice would be gratefully received and possibly stop me having a heart attack!

Thanks all

 

[NickS]

Interesting.

So if I understand you correctly your "box of caps" can charge from either an AC or DC source. Which means logically that the AC input must have a transformer and be rectifying to DC for charging the capacitors. That also means built in filtering. So what exactly tipped you off to be worried about noisy AC going in? And do you know how clean it needs to be?

Moving on do you know what its output is? AC/DC and how much? I am thinking it would be DC voltage out right off the caps, but it could be stepped or inverted too.

Finally I think the best long term goal would be to either find or have made a DC-DC converter to run it right off a car battery. Even though they don't sell the DC-DC unit anymore you can probably still find a datasheet on it that would have some useful info.
If you could come up with the rated input DC voltage, current and maybe ripple that would be enough info to design a new one.

But for now, if you need it working asap that may not be a good option. If I were you I would look at finding an AC line filter to knock down the spikes and run it off the petro generator(but that is just me).

What you explained about the sag in voltage from the power inverter sounds like the inverter was just asked to do more than it could handle like you observed. It stands to reason that an inverter with higher power handling would do the trick. But it may take a big step up since the in-rush current to a bank of large caps can be huge.

I would discourage trying to remove the input voltage sensor unless you have a schematic and know you can do it without impacting anything else the unit is trying to do.

 

[(*steve*)]

The alternate input is probably for a high voltage DC (possibly current limited) source.

If you could find the specs for that it might be possible to recommend something.

Apart from that, I would try powering it from a 1500W inverter and see how you go. The problem may be that the unit has no power factor correction and is drawing power at only the peak of the mains waveform. That may cause inverters a bit of a problem.