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01-19-2018, 06:36 PM   #16
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Thanks Bob 245. My opening post pointed out the difficulty of deriving stored capacitor energy from guide number. I'm familiar with the electro-optical issues. This thread deviated from energy to guide number -- an interesting subject but a red herring for my goal. My goal was and is creation of a <<simple>> electrical load on the QTB that will simulate the load from the flash so that I can discriminate between relatively fresh QTB batteries and end of life batteries.

"It would be an easy matter to calculate the energy output if you know the size capacitor that the AF500FTZ uses." Indeed. That is the point of my recent post above yours, and why the values for the Nikon flashes above provide a useful starting point pending tear-down of an AF-500GTZ.




01-23-2018, 10:12 AM   #17
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Now I see your goal in a different light. If you could determine what energy is pulled from your power pack for each flash, it would be easy to figure a simple resistive load that could be applied to the pack and figure battery condition from the amount of time that load would take to discharge the pack. Is that the correct assumption?

Since you know the voltage of the power pack (330V), the power dissipation in a resistor (Vsquared/R), times time in seconds would be the net energy removed from the pack. For example, if one flash was 100 Ws, you could use a 1090 Ohm resistor applied for 1 second to simulate that same thing (that resistor would have to be rated at 100 Watts or better). A 10,900 Ohm resistor (10 Watt rating) applied for 10 seconds would be almost equivalent and more practical (time would be easier to measure).

I would allow some time in between simulated "flashes" to prevent overheating the power pack batteries, and then you could count the simulated flashes to a dead pack to determine its capacity.

Sound like what you're after?
01-23-2018, 09:45 PM   #18
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QuoteOriginally posted by Bob 256 Quote
Now I see your goal in a different light. If you could determine what energy is pulled from your power pack for each flash, it would be easy to figure a simple resistive load that could be applied to the pack and figure battery condition from the amount of time that load would take to discharge the pack. Is that the correct assumption?

Since you know the voltage of the power pack (330V), the power dissipation in a resistor (Vsquared/R), times time in seconds would be the net energy removed from the pack. For example, if one flash was 100 Ws, you could use a 1090 Ohm resistor applied for 1 second to simulate that same thing (that resistor would have to be rated at 100 Watts or better). A 10,900 Ohm resistor (10 Watt rating) applied for 10 seconds would be almost equivalent and more practical (time would be easier to measure).

I would allow some time in between simulated "flashes" to prevent overheating the power pack batteries, and then you could count the simulated flashes to a dead pack to determine its capacity.

Sound like what you're after?
Yes. Actually, I tried a 10 kohm 10W wirewound just for preliminary testing about a week ago. It will work on the dc output early QTB units (red 25% dot), but for that case the resistor really needs to be set up closer to a load of 50 W-s per 10 seconds to keep the heat in check.

On the newer units (green dot), this load hardly draws any power due to the pulse output. I believe it will need a capacitor in parallel with the resistor. Due to illness I haven't had a chance to see if I have an appropriate cap at hand, but hunting one down is on my to-do list.
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