This is probably the most simple way to convert a speedlite from battery to DC power supply drive.
This Yongnuo YN560IV is needed occasionally in our photo booth, to illuminate the background wall and eliminate shadows from the subject.
There is a lot of information to be found scattered in forums about this kind of conversion, and just a few diy videos. I wanted to share my experience with this project as there were a few obstacles that no one really mentioned or explained as far as I've seen.
There are professionally made dummy battery to dc power supply converter kits that are being sold. You can find them online if you don't want to tinker with wires and soldering.
Step 1: The Converter
I chose a 6V 2A AC/DC converter. They are easily acquired through ebay. This one costed me less than 10 Euro. A 5V converter would probably work as well.
You choose the converter according to the application. A speedlite will have longer or shorter cycle time depending on the Amperage. I figured that 2A would be enough for me, but up to 4A capacity could be more suitable depending on your requirements.
The converter came with a 5,5/2,1mm standard DC male plug, also called LED connector. I had previously bought female and male connectors with screw clamps for wires for another project. These are also readily available on ebay.
The connector is of course optional as you can strip and solder the wire ends together instead, or use any other suitable connector. Just keep track of your + and -
Step 2: Going Through the Battery Compartment!
This way you get a clean and tidy solution without having to open the insides of your device and tamper with the electronics. Usually a small modification to the lid or housing will allow the wire to come out in a good looking manner. .
This speedlite runs off of 4 AA cells that are connected in series to produce up to 5-6V total.
Now you can arrange this in two ways:
1. Either create 3 dummies that just short both ends together, and 1 dummy that is connected to the + and - of the power supply (the professional solutions are usually like this).
2. Create only 2 dummies, one for the + and one for the - ...but you have to determine and somehow remember which goes into which socket. I opted for this solution as it seemed easier to fit the wires in the compartment. The black dummy (blue wire) is connected to the "-" and the silver dummy is connected to the "+"
Use your imagination and whatever you have at hand. I used a piece of round wood and a piece of pencil, and some eletrical tape and duct tape. A screw works as the pole connector. The wires are wound around the screws and hidden underneath the tapes around the dummy.
Step 3: The Current Limiting Resistor
This was the crucial part of this project.
Because I had a 2A power supply, it didn't work! I connected the power supply to the right poles in the battery compartment, but the Speedlite didn't turn on. But there was a faint clicking noise when I held the power button on.
It turns out that when the Speedlite is turned on, it tries to draw more than 2Amps. And when it does, the converter enters "hiccup mode". It turns on and off and on and off... in order to protect itself from overcurrent.
By putting a current limiting resistor on the + between the converter and the speedlite, it is possible for the speedlite to startup even with only 2Amps, but it may take a couple of seconds longer.
Use Ohms law to calculate how much resistance you need. The converter can supply maximally 2Amps, and it drives 6Volts.
6/2 = 3 Ohm.
I did not have a 3 Ohm resistor so I had to create my own wire wound resistor. To do so I used two strands of an industrial steel wire, about 30cm long. This steel wire strand was wound around the pencil core of the dummy battery in three layers, separated by electrical tape and shrink tube.
Note! NiChrome wire is usually used to create a resistive load. However this industrial wire (probably som chrome-steel alloy), worked pretty well too, and it is probably much more easily obtainable (and likely cheaper?). You can just experiment with whatever metal wire you have at home. The thinner it is the more resistance it makes.
Warning! One thin wire strand became quite hot in full load, too hot to touch. Hence by using two longer strands the resistance was kept the same but without the overheating issue.
Tip! Anneal the steel wire strand to make it more pliabel and easy to work with. Anneal it using just a normal lighter or candle.
I hid the resistive wire inside the silver dummy battery. It only rates 2 Ohms of resistance, and not the full 3 ohms that was calculated. The speedlite still turns on, a little hiccupy at first, but then it has smooth operation.
Step 4: Aesthetic Result?
What do you think? Kinda looks integrated.
Step 5: Summary, Important Highlights
Use dummy batteries to supply the power to the speedlite or any other device. My digital camera also uses 4 batteries and it worked this these dummies too.
Be sure to pick a sufficient power supply. With 2Amps the cycle time for my speedlite after a 1/1 blast was 9 seconds. I only use the speelite for 1/32 or 1/64 so for me that didn't matter.
Note that speedlites don't have a good heat disspiation, so don't expect it to work continously during a full day photoshoot just because it is connected to the mains. Speedlites can overheat!.
It is important to use a current limiting resistor if the device can temporarily draw more amperage than the converter is rated for. My converter had overcurrent protection, luckily for me, otherwise I would have probably burnt it on the first try.