Bacilonur's post about portable power in a pelican has rekindled my interest in building my own portable battery+inverter system, but I have a question regarding inverter ratings and strobe power.
Now, I'm not an electrical engineer, so please bear with me. I assume that using an inverter with X watts continuous would be sufficient for a strobe pack that is X watt-seconds (e.g. a 1000W inverter for a 1000Ws Dynalite pack).
Would using an inverter with a lower continuous wattage simply raise my recycle time or are there other factors to consider? The reason I ask is because I'd like to power a Dynalite M1000wi, but I'm not too concerned about slower recycle times and an inverter with a lower rating would be cheaper (and smaller).
And before anyone mentions it, yes I know the inverter has to be pure sine wave
It's not just about how many watts an inverter is rated for, it's also highly dependent on the amp draw by the mono/pack, as well as whether the inverter is current limited and the battery's discharge rate.
IIRC, the Vagabond 2's inverter is a 300w/600w surge. It can still power up to 2500ws, but in a best case scenario, it's going to recycle 300-400ws every second. It powers my M1000 and Acute2 1200 just fine, though more slowly than if I've got 3 AB800's connected to it. 400d put together a 24v 600w/1200w unit, which is probably about as fast as you're gonna get it. I'd be interested in renting the Little Genny sometime to see what inverter they use, as Rob Galbraith quoted times faster than AC due to increased output voltage.
kylegehmlich wrote:
Bacilonur's post about portable power in a pelican has rekindled my interest in building my own portable battery+inverter system, but I have a question regarding inverter ratings and strobe power.
Now, I'm not an electrical engineer, so please bear with me. I assume that using an inverter with X watts continuous would be sufficient for a strobe pack that is X watt-seconds (e.g. a 1000W inverter for a 1000Ws Dynalite pack).
Would using an inverter with a lower continuous wattage simply raise my recycle time or are there other factors to consider? The reason I ask is because I'd like to power a Dynalite M1000wi, but I'm not too concerned about slower recycle times and an inverter with a lower rating would be cheaper (and smaller).
And before anyone mentions it, yes I know the inverter has to be pure sine wave
Thanks,
Kyle...Show more →
It's not that simple. The WS of a pack has nothing to do with the current draw. First, there is apparent power and actual power - you don't need to understand this - just the implications. I'll try to be brief and provide some better insights.
A typical flash - monolite or pack has an efficiency in terms of apparent power of less than 50% and about 85% in real power efficiency. An inverter, of any type, only sees the apparent power, as do fuses. What this means is to charge the flash caps to 2000WS, it takes over 4000WS from the inverter. If it cycles in 2 seconds it takes 2000WS per second (2000W) from the inverter. That would seem to indicate a 2000W inverter would do.
But the charge current is not constant - it it much higher at the first part of the charge cycle and lower as the unit charges. This results in a much higher peak charging power than the 2000W indicated above. Here are the real world numbers:
Either of the packs mentioned, with a 120VAC input, draw about 50A at the beginning of the charge cycle. 50A at 120VAC is 6000 watts. Bottom line is, if the inverter or generator or power line is going to maintain it 120VAC output it must be capable of delivering 6000 watts peak current and 2000 watts average (RMS). Most inverters and generators can deliver about twice their rating as peak current. Based on this, it would suggest a 2000WS power pack that cycles in 2 seconds would require a 3000 watt inverter with a 6000 peak rating.
If you now use a 1000WS pack with a 1 second recycle time, the peak and average power don't change. You still need a 6000 Watt peak power rating. This is one huge and very expensive inverter and simply not practical for a Vagabond type system in terms of cost, weight and size.
This is where current limiting comes into play. By allowing an inverter with, say a 900W peak rating, when the light asks for 6000 watts, the inverter just lowers its output voltage so it can charge up the light at a longer recycle time.
But two caveats apply: 1. The light must be able to charge at less than 120VAC input during the initial part of the cycle and, 2. The inverter must be specifically designed to properly reduce its output voltage (current limit) according to the demands of a flash system. Some inverters can do this and some can't. Vagabond is specially designed to do this. Many off the shelf inverters don't current limit, and will simply shut down when their peak power capability is exceed. This includes both pure sine and non-pure sine inverters. (Non pure sine inverters are not recommended because they can damage flash units.
The specs for various off the shelf inverters rarely provide the necessary information regarding these parameters, and most flash systems do not specify how low the AC input voltage can fall before they crash or cease to charge. Most fully analog flash units tolerate low AC input voltages well and most digitally controlled flash units will crash if the input voltage falls below a certain critical voltage. Our next generation Einstein digital units are specifically designed to not crash under these conditions.
So the whole issue is very iffy for the customer to predict. This is why we make Vagabond and our lights consider all these potential issues so they work together. This is also why we can't say with accuracy whether or not a Vagabond will successfully power a particular competing light system
Can't write a book on this here, but these are the high points. Hope they helps. I will remind readers that, prior to Vagabond 1, there was no commercial available system to power AC flash units from a battery/inverter combination that I am aware of.
So, just to be clear, as long as the inverter can handle the current load put on it by the strobe pack, the actual number of watts the inverter puts out will only limit the recycle time and not do any harm to the pack's circuitry? (again, I'm not an engineer )
The only number I can find for the M1000wi's amp draw is the average power consumption: 13 amps. I'm also having trouble finding inverters that list whether or not they're current limited.
I'm considering the Samlex 300W inverter, as I've heard that will work. Can anyone confirm this?
I saw that Little Genny linked to in your thread, pretty sweet little item. Unfortunately it's a little out of my price range, lol.
Paul, I posted my last reply before I'd seen your post.
Thanks for that wealth of info! I'd assumed there was a lot more to it, I just had no idea what it was. You definitely cleared up a few things for me. Surprisingly after tons of searching I was never able to find that info anywhere else, even with so many people discussing DIY portable power. Maybe I just wasn't using the right keywords.
I've considered the Vagabond quite a few times, but since I haven't actually NEEDED battery power for my strobes as of yet I've never actually made the purchase. This is more of a geeky, "let's see if I can make this work" kind of project, assuming I actually go ahead with it.
Definitely a lot to consider. It's easy to see why there are so few Vagabond-type products out there.
Innovatronix make sine wave inverters specifically for powering strobes. This link is for the Innovatronix Explorer XT 230/50 version (for Australians like myself) but they have 110 versions too. They have compatability charts for various strobes too. It's worth having a look at as I doubt I could make some thing similar for less and it seems quite flexible and well though out. They have been on the market for quite a while too, I first heard of them several years ago.
Innovatronix showed up a couple of years after we introduced Vagabond. We tested them and found them workable. I don't want to go further than that here.
JohnJ wrote:
Innovatronix make sine wave inverters specifically for powering strobes. This link is for the Innovatronix Explorer XT 230/50 version (for Australians like myself) but they have 110 versions too. They have compatability charts for various strobes too. It's worth having a look at as I doubt I could make some thing similar for less and it seems quite flexible and well though out. They have been on the market for quite a while too, I first heard of them several years ago.
JJ
Yep, and the Tronix Explorer XT is pretty darn nice. I've owned both the vagabond and the tronix, and I prefer the tronix. The hard metal case, multiple outlets, nicer bag, and fans for ventilation are the big advantages. The vagabond is a bit smaller, and doesn't have fans (which is admittadly, nicely quieter).
That, plus the fact that they have a compatibility list to tell the consumer whether or not their lights will acutally be compatible with the battery unit.
cathpah wrote:
Yep, and the Tronix Explorer XT is pretty darn nice. I've owned both the vagabond and the tronix, and I prefer the tronix. The hard metal case, multiple outlets, nicer bag, and fans for ventilation are the big advantages. The vagabond is a bit smaller, and doesn't have fans (which is admittadly, nicely quieter).
That, plus the fact that they have a compatibility list to tell the consumer whether or not their lights will acutally be compatible with the battery unit.
Use my Tronix XT to power my Speedo 2403B (2400 w/s pack) just fine. I use the 102 heads with the fans switched off to minimize draw on the XT.
That meant a mod to each head replacing the simple model lamp ON/OFF toggle with a DPDT ON/OFF/ON. Now I can have model+fan ON, model+fan OFF model OFF + fan ON.
kenyee wrote:
JBPhotog: any details/pics of the mod for that DPDT switch? Those 102 fans are friggin *loud*
Swap 'em out. I replaced the fan in one of my Dynalite 4040 heads, it wasn't too hard. I got an identical replacement, but you could swap it for one with similar voltage and current specs but with a lower dB rating. $10 on Newegg, tops.
As long as you're here, do you know of any reason why I couldn't use your Vagabond II Portable Power System to power my Photogenics 160 and 320 monolights??
kenyee: Remember, the fan has a purpose so unless your running off an inverter I'd let them do their job. A cool flash tube and model light means longer life. Also the 102 flash tube cover wraps around the tube and model lamp so cooling is particularly a good idea. However, not running the fan is not a no-no since Speedotron's own Explorer 1500 battery pack disables the fan circuit.
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