Vivitar 2800D investigation, (Made some progress, but still needs more investigation) Options

[dkirk]

Dug into a Vivitar 2800D last night and thought I would quickly document what I found.

The Inverter is always running (Similar to the Vivitar 2000), and when the flash cap is fully charged it draws 65mA continuously. The pins on the Hot Shoe are at various low voltages (5 volts or lower), and if anyone of them is connected to the yellow wire pin, then the unit will flash.

The problem with this unit is that without the battery connection the unit will not fire. Therefore you can't take advantage of the power saving feature that the slave controller boards offer (could use the 5 uA day/night circuit but the current draw is too high and would discharge the batteries pretty quickly).

I was able to get the unit to operate with just the main board (and able to fire without battery connection) by moving the flash tube trigger wire over to the top of the trigger pulse transformer connection (and finding a new location for the trigger wires (similar to the high voltage trigger Vivitars that we normally use). I was not happy with the rate of discharge of the main flash capacitor so went a step further and removed almost all of the components in an attempt to reduce the rate of discharge. I did achieve my goal, but now the idle current is too high (approximately 150 mA) with the battery connected so I feel that I removed one too many components (I basically removed everything except for about 10 parts on the main board).

I probably need to hack one more 2800D using the knowledge that I gained on this first one in order to provide the least intrusive hack. I would currently advise staying away from the 2800D if at all possible for the moment.

Just FYI,

Don

This post has been edited by dkirk: Dec 30 2006, 07:18 AM

[Acrowe]

Thanks for all of your research and information.

[MJM]

The knowledge on the board is just unbelievable! I do not understand 90% of the R&D discussions, but I do appreciate the work thats put into it and the information that comes out of it. Thanks to DKirk and all of you other innovators, I figure if I keep reading it all, something is bound to stick!

Thanks again

Mark
AKA "Just learning to paint by numbers"

[tree sight]

Nice work Don, thanks for your time and effort on these flash guns, much appreciated. Got a question for you. Most 3 volt flashes will only have a guide # of 60 or less and I fill this is the minimum for ir unless you are shooting something up pretty close to the camera. The 2800 has a guide # of 80 and this works much better but is a 6 volt flash. Could the 2800 be changed to a 3 volt system so we could double the mah with the same # of batteries to increase our run time? I wonder if the guide # would still be at 80 though?

tree sight

[dkirk]

Hello Treetop,

In general most of the flash tubes are designed to run around 300 volts. Therefore the inverter transformer is designed to have the correct ratio of secondary to primary turns to take the battery voltage and transform it up to the 300 volt level that is required. Therefore if you cut the battery voltage in half, you will cut the generated high voltage in half since the transformer ratio has not been changed.

As an example, the 2800D that I have hacked generates 154 volts using 2AA NiMH batteries, and it generates 311 volts using 4 NiMH batteries (it's designed for 4 AA batteries).

The energy that is stored in the flash capacitor that we then dump into the flash tube to generate the light can be calculated as follows using the value of the capacitor and the voltage that the capacitor is charged up to.

Energy (in units of Joules) = (Capacitance x Voltage x Voltage)/2

Reduction of the capacitor voltage has a large impact on the energy that we dump into the flash capacitor and therefore the brightness of light generated.

Generation of the same light intensity will require approximately the same amount of energy regardless of the battery voltage. A flash unit designed to use two AA batteries will have half of the stored energy that a flash unit designed for four AA batteries would have (because there is half the amount of batteries) so they will only last half as long (will yield half the amount of flashes).

There is more to this issue regarding energy, power, and battery capacity ratings in units of mAh but I will avoid that for the moment.

Don

[tree sight]

Thanks for the reply Don. So if we were to use alkalines instead of rechargeables would we end up with a higher guide# because of the slightly higher volts of the alkalines? If so could three rechargeables be hooked up with one diode inline on a three volt system to try and equal the volts of the two alkalines and elevate the guide# above what two rechargeables would yield? Would this work and would it be safe? Would it amount to a hill of beans? You are always an interesting read, thanks again for your expertise.

tree sight

[dkirk]

Hello Tree Sight,

Yes, at first the Alkalines do typically allow the Slave Flash unit to charge up to a slightly higher voltage if you leave the power on until it reaches its peak charging voltage, but this does not last long because Alkalines do not have a flat voltage profile (their voltage starts dropping down pretty quickly and does not flatten out whereas NiMH batteries level off at around 1.25 volts and hang there for a long time during their discharge cycle.

In many of our trail camera slave flash applications, you sometimes don't get the maximum amount of light output because the unit flash is not always fully charged up (again depending on many factors). When using a refresh time of 10 minutes for 10 seconds, the first 10 second charge after a picture is taken normally does not allow the slave flash unit to charge up to the maximum voltage it would charge to if left connnected to the battery for a longer period of time. Therefore a picture taken after the first slave flash charge cycle (before a second charge cycle happens) normally results in a darker picture because the slave flash is not really topped off. Also depending on how much time you have between refresh periods and when you fire the flash between refresh periods will cause variation in flash intensity (because the flash capacitor is slowly discharging between refreshes).

You can indeed run with 3 NiMH batteries using a diode to deliver the voltage available from approximately 2.5 batteries if 2 NiMH batteries is not allowing your slave flash unit to charge up to the maximum design voltage of the slave flash unit. Whenever changing the battery configuration you should double check the voltage that the slave flash cap is charging up to in order to make sure you do not exceed the working voltage of the flash capacitor.

As always many factors to consider and hard to give one statement that solves all our ills.

Don