Flash Watt.Second based on capacitor size.

[BeBu Lamar]

I have this Novatron 240 which is supposed to be 240WS. I found 4 capacitor of 480μF and rated at 400V. So assuming that the voltage will be 350V (I think they don't charge the capacitors to their rated voltage) and using the formula E=1/2CV² so it's only 117J or 117Ws wich is about half of what is rated? Did I make wrong calculations somewhere?

[AJG]

I can't evaluate your calculations but I do remember lots of ads for White Lightning monolights back in the 1980's and 90's comparing their flashes favorably with a thinly disguised Novatron flash outfit for light output and generally higher quality.  I bought the White Lightnings then in part because they were monolights so that I wouldn't lose all of my flash units if one power pack went out, as well as avoiding more cables to trip over in my studio. Thirty+ years on, I've been happy with my choice.

[hjoseph7]

I doubt that Novatron would downgrade their monolights by half, that is outrageous ! Novatron was my second choice for Monolights before I decided to go Alienbees. They make good products. Have you tried using a flash-meter to determine the output ?

[ben_hutcherson]

Out of curiosity, have you stuck a voltmeter on the capacitors to see what voltage they are charging to? I agree that I can't imagine them going all the way to the rated voltage. 350 even sounds high to me-330V is common for a lot of shoe mount flashes, although I realize monolights are a different beast.

Just playing around with the equation a bit, I get 240J exactly if I plug in 500V, but I can't imagine that they'd go over the rated voltage of the caps.

Alternatively, could there possibly be a few more caps hiding in there? 8 total 480µF caps at 350V gives 235J, which sounds close enough to 240 for marketing purposes for me.

Just playing with some other numbers, those are what I come up with to get in the range of 240...

[BeBu Lamar]

I think I made some mistakes. I don't feel like to power it up with the caps outside of the case. The caps may be rated for 480V now I am not sure. I will have to take it apart again later. Thanks for all the replies. This is not a monolight. It's a power pack capable of 3 heads. 

[BeBu Lamar]

My mistake. I got it right now. The caps are rated at 500V not 400V as I said. The step up transformer secondary is about 350VAC RMS with 120VAC input from the outlet. This voltage is rectified and charge 1 or 2 banks of 2 caps. It would charge 1 cap for half of the cycle and charging the other cap the other half of the cycle. It's a voltage doubler circuit.  The fully charge caps has the voltage of 487VDC (this because the peak of the AC cycle is 1.414 times the RMS value). These 2 caps are connected in series and thus gives the total voltage of 975VDC. There is a choice of 120ws or 240ws. If the choice is 120ws then only 1 bank of caps is charged. So the 2 480uF caps in series makes them 240uF. Parallel that to the other bank makes it 480uF again but the voltage rating is now 1000V instead of 500V.

So at 975VDC and 480uF the energy is 228J which is close to the rating of 240ws.

[rodeo_joe1]

975V to get a pitiful 230 Joules!

So that's why, if we're sensible, we don't use old studio flash equipment from the Jurassic era. Or from before the big bang - literally. 

[ben_hutcherson]

On 1/28/2024 at 3:47 AM, rodeo_joe1 said:

 

So that's why, if we're sensible, we don't use old studio flash equipment from the Jurassic era. Or from before the big bang - literally. 

Joe,

 

I know you often speak ill of old studio flash equipment-what do you prefer as its alternative?

And for full disclosure, I am not giving up my Normans any time soon. Yes the power settings are weird, but after 5 years of owning and using them quite a bit, I know how to work around them and get almost always get the result I want the first time, and I love the quality of light.

A little more recently I've been playing with Lumedynes, which look like they were put together in someone's garage(probably because they were, or at least some of the oldest stuff) and the whole system is clunky. I love how small the light heads are, though, especially for the amount of power they can throw, and also simplicity and built-in a-garage design means I can often repair it myself..

[BeBu Lamar]

I much rather using Jurassic stuff than Chinese made stuff. 

[rodeo_joe1]

To put 230 Joules into perspective; it's only the same energy as 3 decent speedlights, be they Chinese YN560s or Japanese Nikon SB25, 28, 800, 900, etc. or their Canon equivalent. But capacitor energy is not exactly light output. Because the tubes are smaller, with a lower retaining voltage, and their reflectors are far more efficient, speedlights put out a fair bit more light than a studio 'strobe' of the same energy rating. 

So a 200 watt-second strobe in a softbox is roughly equivalent to the same size softbox containing two speedlights on a twin mount. And without the trailing cables if you use wireless + optical triggering.