This is a revised article adapted from a tip featured on my prior (now defunct) website. Since I am a Canon owner the tips here are mostly specific to Canon, but there are some Nikon tips too.
- Figure 1: Luggable (9,000 mAh, 10 pounds) Big.
I have built two different rigs for powering my Canon 40D, 50D and 5D Mark II cameras. Each of the beefy battery solutions here can run continuously for up to a dozen hours – and longer. When I say a dozen hours I mean a dozen hours of continuous shooting. One rig I call my luggable weighs about 10 pounds and uses a 12 volt, 9,000 mAh sealed lead acid battery in a box that can be used to jump start a car – it has jumper cables on it. The total capacity of the battery is 108 watt-hours. My second lightweight solution is 7.4 volt, 8,000 mAh (56 watt-hour) combo that is much more portable because it weighs less than two pounds. I explain what “mAh” and “watt-hour” mean in the glossary below. To power a Canon DSLR a battery eliminator is required. Battery eliminators can be purchased from Canon ($$) or after market companies ($) or the can be fabricated (¢) by anyone who knows which end of a soldering iron is safest to hold. See below under “Battery Eliminator” for options.
*If you have a Nikon, e.g. model D200 you may find a somewhat simpler solution – or more complicated depending on your point of view. The D200, for example, can be paired with the EH-6 AC adapter which mates with a DC power connector on the camera. The EH-6 apparently supplies 13.5 Volts to the connector. One D200 owner found that he could attach a 12V battery directly to the DC-in connector and power his camera. And attaching a 7.4V battery seemed to work just fine! Unfortunately the on-camera connector is not a standard size so it seems nearly impossible to get one without plunking down cash.
- Figure 2: Lightweight, Small, Powerful (8,000 mAh, 1.3 pounds)
So why did I bother to build these things? I typically like to hike into the wilderness, set up my rig for star trail work and go to sleep. The shutter will be open nearly continuously for 4, 6 or even 8 hours at a time. While my descriptions are specific to the Canon, a similar approach works for other cameras and camera vendors. Indeed, the Nikon D40 battery, the EN-EL9, is a 7.4V battery, too.
Six hours of run time is more than can be achieved with a single high capacity battery and also beyond the capacity of a battery grip that holds two high capacity batteries. Since I hike with my solution it must be portable.
The luggable rig pictured above in Figure 1 is obviously not ideal for hiking. The “Start It” unit weighs almost 10 pounds. On the other hand, I can keep the jump start kit in my car and perhaps avoid a dead car battery. The “Start It” will fully charge if I connect it to the car accessory power plug for 2-3 hours which is convenient when driving to remote locations.
The lightweight rig at about half the capacity is highly portable. Indeed, two BP-970 camcorder batteries totaling about 3 pounds exceeds the power of the luggable solution. Nontheless I use both solutions.
Let me walk through each solution.
Luggable Jump Start or Car Battery Based Solution
The Jump Start battery solution is good for more than just powering the camera. The heft of the battery makes it a pretty good ballast for stabilizing my tripod. The 12 Volt starter battery is also better suited for use with a dew heater to keep the camera lens from fogging, it can be used with other 12V appliances – anything that plugs into a standard car power socket (aka a cigarette lighter). Sealed lead acid batteries can supply more power in very cold weather (freezing and below) than lithium technology. Oh, and you can use it to jump start your car if needed! The down side, of course, is it’s heavy. Not something you want to hike with for miles and miles (though I have). Also any power solution for based on a jump start battery can also work if plugged directly into a car! Here’s what you need:
- Portable power source one of
- 12V Car battery or jump start device.
- Your car (that power/cigarette lighter socket can come in handy)!
- DC-DC converter because a 12 volt battery is too strong to power a camera which wants to be fed 8.2 volts or less.
- Dummy Battery or Battery Eliminator options are:
- Buy a battery eliminator: eg. the Canon DR-400 $30.
- Cannibalize an old/non-working battery or hack up a new, cheap one.
- Build a battery dummy out of wood, plastic, or similar non-conducting substance.
- Cabling and strapping to carry and secure the rig (I use a bungee cord to attach it to my tripod)
The device I bought, the Jump Start, is a small 12V auto battery with a carry handle, jumpers and a power port (cigarette lighter) socket.
The luggable solution also requires a DC to DC converter. The converter will accept anywhere from 12 to 18 volts and has a dial to select the output voltage with choices of 3/5/7.5/8/9 or 12 Volts. The $19 device lists itself as a 3000mA (3.0 amp) unit. The converter has an inline fuse to “blow” if too much electricity runs through it – this is a good thing as it will help protect the camera and the battery. The device I purchased from Fry’s Electronic is labeled “3000 mA Rhino Intelligent Adapter” but I haven’t been able to match that with anything on the internet or find anything similar. The closest match I found is a 1 Amp unit, or this unit. Many people like me have a big assortment of “cigarette lighter” chargers, and one of them may be able to do the job. Inspect the unit carefully to determine its output voltage and capacity which are often labeled right on the unit. For example the label might read: Input 12VDC, Output: 7.5VDC 500ma which means its output is the right voltage, but at only 500 milliamps it may be too puny to keep the camera fed.
Figure 3: A 3amp 12V selectable converter which includes 7.5 V.
I discovered that an old Nokia cell phone charger, the Nokia LCH-8 converts 12 to 24V from your car battery to 7.5 volts DC at 650 ma. In theory this might be enough except that I’ve read reports on the internet that measured peak usage for the Canon is 1.4 amps (1400mA). Clearly the Nokia can’t sustain that much current, but if it is for a short period there is an electrical trick to allow this – add a big capacitor. I haven’t tried using the Nokia charger.
Other Luggable Soltions
There are other options, too. For example Harold Davis purchased the Vagabond II Portable Power System ($299). This is also a beefy (really beefy) battery which features 12 volt output and a built in inverter for powering a 120 Volt outlet. The battery sports 240 watt-hours. That is huge. The most serious detraction is the weight and bulk. It is a self contained system that weights 18.6 pounds. If the 120 volt output is used, it also means that an A/C adapter for the camera must be used. The Vagabond’s built-in inverter must be paired with an A/C adapter for AC-DC conversion. Converting power from 12 volts DC to 120 Volts AC and then back to a DC voltage will cause as much as 35% of the electrical energy to be wasted – but given the huge size of the battery and the additional versatility the loss of power may not matter. A smaller, lighter cousin is also available the Vagabond Mini. At $240 and 3.5 pounds total weight it is more portable. The unit still has a substantial 130 Watt-hour rating.
Lightweight Camcorder Battery Solution
The camcorder or Remote Control (RC) battery is a lighter and more portable solution that uses off-the shelf parts – but assembly is still required. Lithium technology does not supply as much power in very cold climates as a lead-acid car battery solution. Camcorder batteries are large compared to the 3oz battery for my cameras and camcorder batteries are relatively hefty at almost 1 pound. But, with that weight you get 5 to 7 times as much power! Taking two of these with you on a back pack trip is feasible. Not something you can say about a 10 pound solution! In fact, 8 pounds of Lithium Ion (camcorder batteries) will last longer than 40 pounds of sealed lead-acid batteries.
At its core my lightweight solution is a camcorder battery and a charger suitable for that battery. I blatantly ignored the “do not disassemble” label on my charger. The unit I purchased has two phillips screws located beneath a large sticker on the back. After disassembly I discovered that there was plenty of room inside the case for an additional power jack (6). I wired a power jack into the unit by finding where the spring loaded battery contacts went, carefully cutting the wires and attaching them to the power connector, then attaching wires from the power connector to the place the battery contact wires originally went. The power jack that I added has a “Normally Closed” switch which completes a circuit when there is no plug in the jack. It was probably not necessary to take the precaution, but safety when 120 volts are involved is a good thing.
Figure 4: The components
I purchased these:
- A: a replacement BP-970 Camcorder battery. Several capacities are available. I chose two 8,000 mAh batteries at $31 each from Amazon. I also purchased a charger for this battery.
- B: a camcorder battery charger for the above battery.
This @ $10, or this @$15 seems just fine. I have also purchased another charger: the Lenmar which is a tinkerers dream because it comes with easily modifiable plates to accommodate different batteries.
- (1) 20 or 22 gauge stranded wire. I suggest red and black, but black wasn’t available so I used white. About $6
- (2) M size inline power jack. $4 #274-1577
- (3) M size power connector plug (two needed) $1.50 each #274-1569
- (4) electrical tape for strain relief $2
- (5) 3/32″ heat shrink tubing $3
- (6) M size chassis mount power jack.$3.50 #274-1582
I made these
- B: charger with additional “battery out” power jack (6).
- C: power cable using stranded 20 or 22 gage wire (1) with 3/32″ heat shrink tubing (5) at the ends and in the middle for strain relief and a (2)
power jack. I also used a velcro cable tie for neatness (Home Depot?)
- D: BP-511 battery eliminator – I gutted an old BP-511A battery unsoldering the circuit board with a low wattage iron. I then soldered a length of red wire to the “+” lead and length of white wire to the “-” lead. I tied a loose knot on the inside (strain relief) and passed the ends through the battery case by making a hole with my soldering iron. I used the barrel of a recently turned off soldering iron to shrink the tubing until it was tight and made sure that where the wire entered and exited the battery it did so through the heat-shrink tubing. I the glued the
battery case back together with hot melt glue along the corners on the inside.
- E: Power connector (used M size power connector (2))
- F: “Cheater” power cable – basically a length of double wires with a part number (3) soldered at each end.
*** You may be wondering why I didn’t just put a plug (3) at the end of the battery eliminator – it’s because a DC-DC converter will normally provide a PLUG not a socket. I can also make a longer or shorter cheater cord if need be.
The two screws that hold this unit together are underneath the big sticker on the back. I poked holes through the sticker using a phillips screw driver.
If you are uncomfortable with messing with the guts of the charger, you can modify a plate from the Lenmar charger instead. The Lenmar comes with interchangeable plates to accommodate different batteries. or you can get a cheap travel charger. I find it convenient that my charger and “battery connector” are the same unit. And the charger is quite light.
Not shown, but also required:
- low wattage soldering iron.
- Small gauge wire stripper.
- Diagonal cutter or needle nose pliers with cutter,
- small parts holder (chip clips will work).
- A drill (and drill bit of the appropriate size for the chassis mount jack (6)).
- You may also need a phillips, hex or regular screwdriver to disassemble the battery charger.I originally purchased a sub-mini audio connector and tried to use that as the power connector but the connection was not crisp or reliable.
- And finally you may also need contact cement and/or a hot glue gun to reassemble the battery eliminator and possibly the charger as well.
The Battery Eliminator
Unless your camera or battery grip has a power connector any “big battery”solution will require a battery eliminator (parts C, D and E) or a DC input plug (hooray to Nikon for getting this part right, boo for the lack of availability of those connectors!). You can buy a battery eliminator – see more below – for many cameras but I found it easy to make a battery eliminator for my BP-511 battery out of a junk battery. For Canon cameras the battery eliminator plugs in where the battery goes and wires exit through a rubber gasket and are then connected to an external power source. While making a BP-511 eliminator was easy, I also tried to make an LP-E6 battery eliminator from a new (but cheap) LP-E6. I gutted the battery and soldered wires. The outcome was less than stellar as the contacts in the LP-E6 are small and very close together.
Those who fear the soldering iron can purchase an ACK-E2 or a cheaper knock off. Had I found the $20 knock off I would not have bothered hacking up a battery. The ACK-E2 includes a battery eliminator and an AC power adapter to power the camera from a 110 volt outlet – I almost never am near wall power, but I can use the battery eliminator. For my other camera, the 5D Mk II Canon sells the ACK-E6AC. Cost is about $140. Like the ACK-E2 the ACK-E6AC includes a battery eliminator and an AC wall unit. However I found an equivalent unit for $39. No need to struggle with disassembling and soldering a battery eliminator!
My two cautions about these knock off units are:
- I doubt the AC components are UL listed. The knock offs certainly feel cheap.
- The connector between the AC unit and the dummy battery is not standard. Different manufacturers use different connectors. The connector on my ACK-E6AC knock off matched the Radio Shack M size power plug I had already been using. Oh happy day!
NOTE: Some camera models, like the Canon 5D Mk II have batteries with “chips” in them to help the camera know the current battery state. Your camera may – or may not – require this chip. Without the chip the camera nags you whether it is “ok” to use a battery that it can not talk to. Just say yes.
Figure 5: The homemade BP-511 battery eliminator installed in a Canon 40D camera.
Canon cameras have a little rubber gasket that allows a cable to exit the battery compartment. If you build your own eliminator make sure your cable exits your battery eliminator where it will be able to be routed out of the battery compartment. If you do it wrong, you’ll have a battery eliminator that does not work because most cameras do not supply power to the camera electronics unless the battery door cover is fully closed. This is also true for most battery grip attachments.
Voltage, Amperes and Stuff: Background Data for the Electronically Challenged
The typical Canon BP 511 battery supplies 7.4 volts** to the camera and boasts a 1390 milliamp-hour rating. 1390 maH means that if the camera draws 1.39 amps it could run for an hour. That kind of power is possible with lithium batteries – the most power for the least weight of any currently available options. It’s also possible with SLA (Sealed Lead Acid) and a variety of similar battery chemistries. The battery you have in your car is a suitable choice, it’s just quite a bit heavier than most people are willing to carry. Smaller lighter versions of that same battery are available for things like lawn tractors and, “Jump Starters”.
**First you need to know a little secret.
A “12 volt” battery is really around 13.8 volts when fully charged. Likewise the Canon 7.4V battery is about 8.2V when fully charged. During use the voltage will drop to the point where it will no longer be able to service the camera. At that point it is wise to stop using the battery… going further, especially with a lead acid type battery, may permanently damage the battery.
Using a 12 volt car battery with a camera that expects 7.4 volts is, well, a possible cause for problems. The camera probably CAN sip from the 12 volt supply, but it would be kindler and gentler to chop that voltage down using a “voltage regulator”. In particular a “DC to DC” regulator is best here. A DC to DC converter (sometimes called a “buck”) drops the voltage down to a manageable level.
Confused about Volts, Amps, MilliAmps?
Voltage = “pressure”. Imagine a ball. It’s useless unless filled – to the proper pressure with air. Fill it too much and it will pop, too little and it won’t bounce. The
electrical equivalent of “air pressure” is “voltage”. Just as car tires require more air pressure to work than soccer balls do, so do some circuits require more voltage than others.
Amps (or milliamps) = “flow rate”. It will take a lot less time for a tire to go flat if there is a huge hole where lots of air can escape than it will for a pin-prick sized hole. The “rate of escape of air” is the electrical analog of current which is measured in amps. A milliamp is a thousandth of an amp.
Resistance. In our analog, the “size of the hole” is a good example of the electrical term resistance. And it’s not a surprise since the volume of air that can escape in a second will depend on the pressure and the size of the hole the air can pass through.
Capacitance. A capacitor is a device that can hold a charge. In the air pressure world, a tire is a capacitor. You can fill a tire with air, then use the pressure in the tire a little at a time – or all at once – to inflate something else like a balloon.
mAh – an abbreviation for milliamp-hour.
Milliamp-Hour is one milliamp of current for one hour. Milliamp-hours or amp-hours describe how much energy a battery can supply and for how long – under normal conditions, that is.
Watt-Hour is another format for specifying the capacity of a battery. To convert from Watt-Hours to Milliamp-hours divide the Watt-hours by the working voltage and then multiply by 1,000. Thus a 34.2 watt-hour (wH) 7.2 Volt battery has a 4,750 mAh capacity. To convert from amp-hours to watt-hours multiply the amp-hours by the working voltage. If starting with milliamp-hours first divide by 1,000. A 7.4 volt battery with 7,000 mAh rating is equal to 7,000 / 1000 * 7.4 which is 51.8 Watt-hours
Here is another important tidbit… just because a charger for a camera battery is available does not mean the charger can be used in place of the battery. There are two reasons for this. The first reason is that chargers MUST supply more than the normal maximum battery voltage. Using an air-pressure analogy: to fill a tire, the pump must exert greater air pressure than the current pressure in the tire. Likewise to charge a battery, a greater voltage must be applied than the final voltage the battery will attain. The second reason is that the charger does not have to supply much current, a trickle is all it needs to slowly charge the battery – just as a bicycle pump can inflate a truck tire. The camera, however, sometimes takes “gulps” of current – more than the charger may be able to supply.
Knowing that a 7.4V battery is really about 8.2V helps makes it clear that ANY voltage in the range of about 7 to 8.5 volts will make a (Canon) camera happy IF it can also supply enough amps.
Timescapes.org has a lot of great discussions.