Electronics advice please

Phate

Phate

Phate

Caporegime
Joined
1 Nov 2003
Posts
35,691
Location
Lisbon, Portugal
Right, I'm rubbish with electronics, amps, volts, gigawatts etc :p - So I need some help :)

Right my plan is to power 2 x studio lights from a van.

The info I have is

They are 2 x 250w studio lights, and the sticker on each one stating 2.5A so 5.0A in total?

(In case you don't know studio lights run a continuous 100W bulb and then when fired the 100W bulb goes off, and the flash fires, then the bulb comes back on) (I'm also going to guess that the the light peaks at a 2.5A draw when being fired)

I'm looking at buying a Leisure battery, I can get it wired up for a split charge from the van so it'll charge when I'm driving and I'll buy an inverter so I can plug a long extension lead in to power the lights away from the van.

So,

If I wanted to power these lights for a full day, say 5/6 hours with moderate usage (IE 300 photos), what sort of battery would I need before having to start the van and get a peasant to put his foot on the throttle to give it a charge :p

Cheers all :)

Jake
 
I take it the van is running a 12v system? If so, then 500 watts is roughly 42A/hr (not including inverter losses). I think the average car battery is rated at 70/AH, more for diesels but still you'll need most of that current just to crank the engine. So I can't see a single battery being able to power those lamps continuously for more than 20 minutes before needing to start the engine to charge it back up.

Don't most inverters come with a 'low battery' cutoff or audio sounder anyway? This will signal when you need to start the engine.
 
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I would have thought a vehicle type battery would be bad for this kind of thing since its life would drop pretty quickly with being drained so often, maybe a small generator would be an alternative option?
 
i think i agree with a small generator as it can run strait 230V AC and no inverter is needed.

and yes a car battery wouldn't hold out long as it is not a deep cycle battery, its not meant to be drained to 0%
 
benftl said:
I take it the van is running a 12v system? If so, then 500 watts is roughly 42A/hr (not including inverter losses). I think the average car battery is rated at 70/AH, more for diesels but still you'll need most of that current just to crank the engine. So I can't see a single battery being able to power those lamps continuously for more than 20 minutes before needing to start the engine to charge it back up.
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Hmm ok...not that it's an issue if I need to do this. The only thing I can think of (thought of this in the shower) is that you can get battery 'packs' for studio lights and power them all day as I described, let me find the details on them...

...dammit, can't find the technical details on them, but they'll power 2 lights upto 250 flashes. They can't be that different from a car battery? or can they?
 
Oh I see, so continuous use is only 100w per bulb and the flash brings up momentarily to 250w?

I'm inclined to agree with the above posters, a small generator might be the better option depending on the cost of inverters / installation of new batteries versus running cost of the generator.
 
ill say again, car battery are not meant to be drained completely as they are not deep cycle.
http://en.wikipedia.org/wiki/Deep_cycle_battery

A deep-cycle lead-acid battery is designed to be regularly discharged to most of its capacity. In contrast, starter batteries (e.g. most automotive batteries) are designed to deliver sporadic high current for cranking the engine, and to be frequently discharged of only a part of their capacity.
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benftl said:
Oh I see, so continuous use is only 100w per bulb and the flash brings up momentarily to 250w?
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I THINK that's how it works. As the continuous is only a 100W bulb.

I'm inclined to agree with the above posters, a small generator might be the better option depending on the cost of inverters / installation of new batteries versus running cost of the generator.
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Yeah, problem with a ginny is that they are noisy as anything. Trying to concentrate with that thing whirring in the background will be difficult :(
 
Fair point. So if that battery is rated at 70Ah, and you have 2x 100w continuous load then that makes it 17Ah. You should in theory get around a couple of hours use, the peak '250w' load when you flash is negligible really, though you'll need to check the inverters continuous and peak rates. What inverters are you buying, any decent make should have a low battery cut out.
 
benftl said:
What inverters are you buying, any decent make should have a low battery cut out.
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That's my next step which I haven't researched at all yet.

What inverter would people recommend? I want one I can wire basically straight to the battery if possible to stop me frying the vans electronic system! :)
 
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