This whole project started when I decided to pursue the "Holy Grail" of time-lapse photography. For those of you that don't know what the Holy Grail time-lapse is--In short, its a time-lapse from sunset through the night to sunrise. Sounds awesome right? After doing a ton of research on the actual exposure programming and getting gear together, I realized something that nobody really talks about. POWER! Time-lapse on long exposures is a massive battery drain, especially here in Connecticut when it's cold. I'm planning on doing the holy grail at the beginning of the New Years on a backpacking trip through the mountains. Here's where the problem lies--Backpacking, can't exactly bring a generator with you and you don't have access to a wall outlet in the middle of the woods. Many suggested getting the AC/DC power adapter for my bodies--but that doesn't work for the middle of nowhere. My only other options on the market were to bring a 12v marine/car battery and an inverter (highly inefficient) or just use a lot of batteries for my body and camera grip. Both solutions don't really work for time-lapse and hiking. Changing out batteries leads to the possibility of shifting the camera, marine battery means LOTS of extra weight and no guarantee of longevity.
Solution: I'll create my own solution
Step 1: Supplies
Before you tackle this project, you need a few things
-Cheap battery grip ~$40 from eBay. This instructable is specifically for my D700 MB-D10 but I've also done the same modification for my D800
-2x 5000 mAH NIMH batteries $30 each or cheaper. You can pick these up from you local RC hobby shop or search online of them. I chose NIMH batters since they are a little more stable in lower temperatures and not nearly as many risks involved with charging them or transporting them
-1 Male TRX style battery connector (or whatever style battery connector is on the brand you bought)
-DC/DC step down voltage regulator from DROK. 6$ off Amazon
-Battery Charger. Again from your RC hobby shop. I had a few around the house since I have other hobbies with RC cars
-Wire. I used about 20' of 20ga wire for this build
-Heat shrink/electrical tape
-Electrical wire butt connectors appropriate for 20 gage wire
-1/8" male and female MONO headphone jack (radioshack cheap)
-Soldering iron and solder
-Drill and drill bit specified for you 1/8" headphone jack
-End cutter for a bit of plastic removal
Step 2: Making the Modification to Your Battery Grip
I never use the supplied AA battery holder for my MB-D10 grip--so it was the perfect tray to use
-Remove the contacts for the AA batteries closes to the side with the tray latch
-Find a suitable place to drill your hole that won't interfere with the latch or the actual frame of the battery grip
-Drill your hole: CAUTION: Recommend using a vice to hold the battery tray while drilling, whatever you do DONT have your hand anywhere near where that drill bit will come through.
-Do a dry fit of the female headphone jack. I went a size smaller than the recommended hole size so I could thread the jack in--If you went a little big, just get some epoxy to set the jack at a later step.
-I cut away some of the AA battery supports to make the wires fit a little better.
Step 3: Solder Connections
Get some of your 20ga wire and cut it to length. Just long enough to reach the contact terminals to the back side of where the headphone jack will sit.
Strip and tin both sides of your wire.
Tin the female end of the headphone jack--Outer pin is the ground. If you bought a mono headphone jack, center pin will become the Positive terminal. If you bought a stereo headphone jack--use either of the 2 center pins (just make a mental note of which one you used so you use the same on on the male side)
-Solder your wires to the headphone jack
-Insert both wires and female jack into your previously drilled hole
-Use some fast set epoxy to set the jack in place if you need to at this point
-Tin the battery terminal connections and solder the other end of your wires to it--positive to positive, negative to negative
-Put the battery tray to the side since your done with the hard part
Step 4: Making the Jumper Cable
Now we're going to make our power supply cable
-Make this cable as long as you see fit--I made mine 6.5' long, max height of my tripod is around 5'5" plus some slack in the cord
-Strip both ends of your wires (positive lead and a negative lead)
-Tin one end of the wires
-Tin your male headphone jack connections
-Dont forget to put the plastic/rubber cable hood over the wires first before soldering them to the jack
-Solder your positive lead and negative lead to the male headphone jack pins
-Slide the plastic hood over your newly made connections
-I like to heat-shrink the entire jack for a little bit of extra support and durability
Step 5: Installing Your DC/DC Transformer and Making the Connection to the Batteries
-The DC/DC step down transformer is a very simple and critical part to this build. Luckily it is cheap and readily available on amazon for ~$6
-With the stripped end of your jumper cables, tighten them into the output of you transformer
-Cut an additional length of wires for the input side of your transformer (only need to be about 6")
-Strip both ends of those wires
-Attach one side of your wires to the input side of the transformer
-Crimp some butt connectors to the other end of the wires
-With your MALE TRX quick disconnect (or whatever style connector the batteries you bought use) Strip the leads and crip them to the other side of the butt connector.
You can make an enclosed case for you transformer which I highly recommend to protect it from being broken or incidental contact with a metal object therefore shoring it out. I made my case from a small plastic box I had around the house and wrapped it in tape.
Step 6: Making Up the Battery Pack
Most NiMH battery packs you buy will be 7.1 volts. This simply doesn't work for Nikons. Most camera battery packs run off 7.4v batteries. Knowing that using the 6 AA batteries in the MB-D10 battery tray, this comes out to 12V maximum voltage you can supply to the camera safely. I DO NOT RECOMMEND GOING ANY HIGHER THAN 12V with a Nikon. I chose NiMH batteries as opposed to LiPo for a few reasons. LiPo (while I do have a lot of them for my RC hobbies) require a somewhat expensive balanced charger, have a higher probability to leak and possibly explode if not cared for properly and sometimes have output voltage oscillations due to temperature shifts. They are also about 25% more expensive than a NiMH.
With that said, we need to do some slight modifications to our battery leads by wiring the 2 battery packs up in series to double our output voltage from 7v to 14v. NiMH batteries have no problem charging in series and tend to self balance individual cells.
-Cut the leads ONE AT A TIME so you don't create a short between the battery leads. Cut the leads directly in the center of the wire length coming from the battery to the quick disconnect.
-Strip your freshly cut wires from the battery and the connectors being careful not to touch the leads of the same battery together and create a short.
-To make this a series setup, attach a butt connector to one of the negative leads and connect it to the OPPOSITE batteries positive lead.
-Take the remaining 2 leads (one positive, one negative) crimp a butt connector on each
-With one of the cut off FEMALE battery connectors, crip it to the other side of the butt connectors. Make sure you hook up positive to positive negative to negative.
-Once all your connections with the batteries are made--Get some electrical tape and tape em together.
-You have now created a 12 cell 14v battery ALMOST ready for use
-In my pictures, I have an extra connection (the white one) that I plan on using for future plans (connecting more batteries if needed)
Step 7: Initial Charge
Now were going to charge this battery pack for the first time.
-The batteries typically come with some charge on them, however since you just made 2 battery packs into one big battery pack....The packs probably aren't equalized and they are usually shipped in a "storage state of discharge" meaning they only have about 25% of a charge to them.
-Hook up you battery to your charger. For this first charge I recommend using a charge rate of 2amps to let everything equalize out. I don't recommend ever going over 4amps. For the first few minutes check that everything is going smoothly and the battery is charging properly then just let it do its thing.
Step 8: Testing It Out and Making the Connections
When your battery is fully charged, remove the battery from the charger. It may be a little warm but shouldn't be hot.
-With everything thing disconnected from your camera (important)
-Plug your power lead with the voltage regulator into the battery. The regulator should power up on its own. Set it to 12 volts on the output. Do not go any higher than 12v.
-I like to double check everything, especially on a build like this where I'm plugging in a DIY power pack into a $1,000 camera body. Check continuity, voltage, resistance...everything before plugging it in to your camera.
-Slide the AA battery tray into your battery grip
-Plug the male headphone jack into the battery pack
-Power on the camera and check your battery level--should indicate FULL!
--Once everything is tested out, wrap all your exposed butt connectors in electrical tape for protection and durability.
-You will notice in my pictures I have an extra connector coming off my battery pack. This give me the ability to add more batteries if I need them in the future without disconnecting everything and interrupting my time-lapse.
-Theoretically this gives me 10,000mAH of battery life as opposed to the stock ENEL3E battery at 1400mAH or even the extended battery at 2000mAH. Add this battery pack to the battery in the camera already and we have somewhere around 8x the battery life in theory. I will update over the next week with my actual results and performance.