Paul C. Buff, Inc. Technical Forum

Hi there, Tech Support:

So I just got my VML last Thursday and have tested it out on a couple of shoots, and am a little concerned about the amount of power it holds. So I have a few questions:

1) When it was shipped to me, it appeared to be fully charged (3/4+ light was lit up). Is this normal? (I ask because in the manual it says the FIRST thing you should do is charge it, so I thought they would arrive without much of a charge.)

2) I did two shoots over the weekend of about only 40 shots each shoot with my old WL5,000 strobes over the period of about a half hour and at the end of that shoot, the power level indicator on the inverter had dropped from 3/4+ to the 1/4 level. That seems like a big drop. How accurate are the power level indicators?

The WL5,000 is only 125WS at full power (I was using only one strobe), and even though I DID have the modeling bulb on, it is only a 60 watt bulb. Could the modeling light have drained it that much over a period of about thirty minutes?

Is there a way that I can test the discharge rate on my own (without having to take hundreds of flashes???)

Thanks in advance.

First, was the light still plugged in and running? The battery indicator is not necessarily accurate under load. Secondly, the three LED's indicate 3/4+. Of the ~110Wh available, this could leave as little as 82Wh in actual charge. 30 minutes at 60 Watts is 30Wh, which would leave 52 Wh. Subtract the amount of power consumed by flash, and factor any temperature impacts, then it is not unreasonable to believe it went from 3/4 to 1/4 in that time considering the continuous model lamp.

Also, we do charge the batteries, and do apply some use to them. So there will be a significant charge to them, but not a true full charge.

Thanks so much for the response:



Yes, I believe it was, but don't want to swear by that.

I would note that when I turned on the inverter this morning (with the battery in it but with nothing plugged into the outlets), the 1/2 LED light was lit (where as yesterday when I noticed it the 1/4 LED was lit). So you might be right about the inverter charge status being different under load and when not under load.



Ahh... I think I see what you are saying.

Just so I understand the math / science a little better (I am using round numbers to make the math easier):

Does a 100WS flash from a single strobe equal to .02777... Watts? I am guessing it would be 100WS divided by 60 (seconds per minute) divided by 60 (minutes per hour) = .02777...

That is again assuming a 100WS flash from a single strobe WITHOUT running the modeling lamp.

Thanks in advance.

That would be .027777 Watt-hours, yes. The deliverable amount of Watt hours in VML is about 110 max. This will vary on how long the unit is allowed to run without actually having something draw power from it (i.e. it will run itself out of power, eventually).