DIY Flash battery pack
I Have The Power!
Anyone who uses a speedlight knows their voracious appetite for batteries. No sooner do you put in a fresh set and start shooting than the recycle time seems to start climbing! It's one of the main reasons I tend to avoid using this lighting if I can. I like to maintain something of a rhythm during a shoot and having the ability to take a coffee break whilst the flash recharges, tends to break the flow. A lot of the time I'm using studio flash, however there are times when that is just not feasible and so I need something that has the portability, without the problems associated with AA batteries. An external battery pack seems an ideal solution and there are commercial versions available. The cheapest just add extra AA batteries, and better versions tend to start getting expensive. So I decided to look into a DIY solution.
The Answer
My research lead me to the Sealed Lead Acid battery (SLA). These batteries are used in a selection of items such as RC models burglar alarms etc.They are available in different powers, most importantly 6 volts (4x AA @1.5v each=6v) and various capacities.
They have some very significant advantages. Firstly they have a much higher storage capacity. The one I chose is 4.5 Amp-hr. I've not really pushed mine yet, but from what I've read from others with a similar set up, it should be fine for at least 500 full power flashes. More storage is not a problem as for example you could get a 12 Amp-hr unit. This would give a far longer use or perhaps power two flashguns. As I often use this type of lighting via slaves and set some distance from each other, a single pack for each flash is better for me.
Another, major advantage is the voltage they supply will fall off far slower than an equivalent normal or rechargeable AA battery. I practical terms it means that the flash recharge time is not going to increase much until the battery is almost empty. A final possible plus is that these batteries are also designed for use in such things as emergency lighting etc. Therefore if you use an intelligent charger it will recharge the battery and once it is full it will switch to a trickle charge that will keep the battery at full power until needed.
Another, major advantage is the voltage they supply will fall off far slower than an equivalent normal or rechargeable AA battery. I practical terms it means that the flash recharge time is not going to increase much until the battery is almost empty. A final possible plus is that these batteries are also designed for use in such things as emergency lighting etc. Therefore if you use an intelligent charger it will recharge the battery and once it is full it will switch to a trickle charge that will keep the battery at full power until needed.
Putting it all together
WARNING
Mistakes and incorrect wiring could lead to damage or destruction to the flash, battery, or harm to yourself.
I have tried to make this article as straightforward to follow by a non technical minded person as possible. However I accept no responsibility for any damage caused. If you have any reservations, please seek help.
Connecting the flash
There are two approaches to getting external power into the flash. Some flashguns already have an external power socket, however this is often not a direct replacement for the normal 6V rather than a connection to the capacitor to allow a higher voltage to charge it quicker. Therefor the first option is to add your own connection. This would mean dismantling the flash (BEWARE even if not used for a while, the capacitor could still hold a substantial charge) and wiring a socket to the power leads.
For my prototype I opted for making a set of dummy batteries that would take the place of the normal batteries. This has the advantage of straight off working in any of my (or others) 4xAA flashes. Care must be taken to make sure they go into the correct battery bays inside the flash, as usually two of those will be connected together which would short out the battery.
To make the fake batteries I cut 2 pieces of wooden dowel to the correct length. I then drilled a hole down the centre of the wood so that it came out the side. Passing the wire through the hole, I soldered it to a drawing pin that I then hot glued onto the end. Finally I cut a small notch in the battery cover to allow the wire to exit. I used some standard power cable cut to a suitable length. A thicker and shorter cable will allow more current and quicker recharge of the flash. At some point I will probably replace this with a coiled cable for tidiness.
The battery side
At it's very basic, that would be all that is needed. Just connect the leads up to the correct terminals on the battery and it's ready to go. However there are at least a few additional items you'd probably wish to include...
Firstly I added a switch to the positive side of the circuit to allow me to isolate the power from the battery. I also terminated the output suitable socket to allow me to unplug the flash and plug in the charger. The connector needs to be polarised so it cant be plugged in wrong, and the flash power lead (and charger) needs a corresponding plug.On the prototype I used a standard 2.5mm power connector, however in future I will use something locking to prevent it accidentally pulling out.
Optional extra
Although not strictly needed I decided to add a voltage display to enable me to monitor how the battery was performing and when it required recharging etc. An LED voltmeter unit can easily be bought via eBay for about £3 (less if from China). It connects between the positive and negative power. I added a non latching push to make switch so that it only displays when pressed and does not draw any extra current from the battery.
Holding everything together
One of the slight disadvantages of the SLA battery is it's weight, so it ideally needs to all be enclosed in something that could be hung from a shoulder/light stand or clipped to a belt etc. I found an old camera case I had that the battery fitted perfectly. Some old plastic sheet was cut and folded to fit over the top of the battery and the various switches mounted to the top. Finally it slipped into the bag perfectly to be hung from the belt or over my shoulder
In Use
Although I've yet to really put it through it's paces, it's so far a huge improvement over the normal batteries. Fully charged the recycle time is about 2 sec at full power and after about 100 flashes it show's absolutely no sign of increasing as the voltage drop has been negligible! At less than full power the recycle drops to become pretty much instantaneous keeping up with the burst mode of the camera. However caution needs to be used as the flash can start to heat up if overused which can damage it.
The exact cost is hard to say as this prototype was put together using a lot of items I had to hand. The battery was about £8 via eBay and a charger (which I had) could cost anything from under £10 to over £30 depending on the type. However excluding the charger, I would estimate the battery pack could probably be put together for about £20-£25. A huge improvement on AA batteries! lol
WARNING
Mistakes and incorrect wiring could lead to damage or destruction to the flash, battery, or harm to yourself.
I have tried to make this article as straightforward to follow by a non technical minded person as possible. However I accept no responsibility for any damage caused. If you have any reservations, please seek help.
Connecting the flash
There are two approaches to getting external power into the flash. Some flashguns already have an external power socket, however this is often not a direct replacement for the normal 6V rather than a connection to the capacitor to allow a higher voltage to charge it quicker. Therefor the first option is to add your own connection. This would mean dismantling the flash (BEWARE even if not used for a while, the capacitor could still hold a substantial charge) and wiring a socket to the power leads.
For my prototype I opted for making a set of dummy batteries that would take the place of the normal batteries. This has the advantage of straight off working in any of my (or others) 4xAA flashes. Care must be taken to make sure they go into the correct battery bays inside the flash, as usually two of those will be connected together which would short out the battery.
To make the fake batteries I cut 2 pieces of wooden dowel to the correct length. I then drilled a hole down the centre of the wood so that it came out the side. Passing the wire through the hole, I soldered it to a drawing pin that I then hot glued onto the end. Finally I cut a small notch in the battery cover to allow the wire to exit. I used some standard power cable cut to a suitable length. A thicker and shorter cable will allow more current and quicker recharge of the flash. At some point I will probably replace this with a coiled cable for tidiness.
For my prototype I opted for making a set of dummy batteries that would take the place of the normal batteries. This has the advantage of straight off working in any of my (or others) 4xAA flashes. Care must be taken to make sure they go into the correct battery bays inside the flash, as usually two of those will be connected together which would short out the battery.
To make the fake batteries I cut 2 pieces of wooden dowel to the correct length. I then drilled a hole down the centre of the wood so that it came out the side. Passing the wire through the hole, I soldered it to a drawing pin that I then hot glued onto the end. Finally I cut a small notch in the battery cover to allow the wire to exit. I used some standard power cable cut to a suitable length. A thicker and shorter cable will allow more current and quicker recharge of the flash. At some point I will probably replace this with a coiled cable for tidiness.
The battery side
At it's very basic, that would be all that is needed. Just connect the leads up to the correct terminals on the battery and it's ready to go. However there are at least a few additional items you'd probably wish to include...
Optional extra
Although not strictly needed I decided to add a voltage display to enable me to monitor how the battery was performing and when it required recharging etc. An LED voltmeter unit can easily be bought via eBay for about £3 (less if from China). It connects between the positive and negative power. I added a non latching push to make switch so that it only displays when pressed and does not draw any extra current from the battery.
Holding everything together
One of the slight disadvantages of the SLA battery is it's weight, so it ideally needs to all be enclosed in something that could be hung from a shoulder/light stand or clipped to a belt etc. I found an old camera case I had that the battery fitted perfectly. Some old plastic sheet was cut and folded to fit over the top of the battery and the various switches mounted to the top. Finally it slipped into the bag perfectly to be hung from the belt or over my shoulder
In Use
Although I've yet to really put it through it's paces, it's so far a huge improvement over the normal batteries. Fully charged the recycle time is about 2 sec at full power and after about 100 flashes it show's absolutely no sign of increasing as the voltage drop has been negligible! At less than full power the recycle drops to become pretty much instantaneous keeping up with the burst mode of the camera. However caution needs to be used as the flash can start to heat up if overused which can damage it.
The exact cost is hard to say as this prototype was put together using a lot of items I had to hand. The battery was about £8 via eBay and a charger (which I had) could cost anything from under £10 to over £30 depending on the type. However excluding the charger, I would estimate the battery pack could probably be put together for about £20-£25. A huge improvement on AA batteries! lol
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