Building a Beefy Power Supply for your Canon*

I have built two different rigs for powering my Canon camera continuously for up to a dozen hours (maybe longer, I haven't tried). When I say "a dozen hours" I mean a dozen continous hours of shooting. One rig I would call "luggable" it weighs about 10 pounds and uses a 9,000 mAh sealed lead acid battery in a box that can be used to jump start your car (it has jumper cables on it!). The other is much more portable because it weighs less than two pounds. It is a 7,000 mAh solution - though it could easily be bigger with a beefier battery.  Both solutions require making a "battery eliminator" which is not that hard to do if you know which end of a soldering iron is the business end.

*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 the 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.

Luggable (9,000 mAh, 10 pounds) Big.

Lightweight, Small, Powerful (7,000 mAh, 1.3 pounds)

So why did I bother to build these things? I want a PORTABLE rig that I can use to power my Canon 40D or 50D for 6 hours of continuous unattended shooting (e.g. star trails). This is more than can be achieved with a single high capacity battery that is usable IN the camera and is also beyond the capacity of a battery grip that holds two batteries. Of course my solution must also be portable. A similar solution can be used for long timelapse sequences without having to intervene and replace a battery.

I want to be able 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, the same approach works for other cameras and camera vendors. Indeed, the Nikon D40 battery, the EN-EL9, is a 7.4V battery, too.

The luggable rig pictured above 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 Cigarette lighter for 2-3 hours which is pretty convenient when driving to remote locations.

A considerably lighter solution is use a large capacity battery like a camcorder or a remote control vehicle (RC) battery. For example, the BP-970G battery used in Canon camcorders is a high capacity, 7.4V battery. I have seen versions of the BP-970G up to 8500mAh. That capacity weighs about 1 pound and is way easier to carry than the Start It battery weighing almost 10 pounds! Given these advantages, the "Lightweight" rig was born.

Let me walk through each solution for you.

Luggable Jump Start or Car Battery 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 to 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 cigarette lighter.  Sealed lead acid batteries can supply more power when very cold (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). A power solution for your camera that works with a jump start battery can also work plugged in directly to your car, too! Here's what you need:

  1. Portable power source one of
  2. DC-DC converter since a 12 volt battery is too strong to power a camera which wants to be fed 8.2 volts or less.
  3. Battery "dummy"
  4. Cabling and strapping to carry and secure the rig (I use a bungee cord to attach it to my tripod)

Lighweight Camcorder Battery Solution

The camcorder or Remote Control (RC) battery is clearly lighter and more portable solution and uses off-the shelf parts - but assembly is still required and it does not supply as much power in very cold climates as the lead-acid car battery solution. Camcorder batteries are large compared to the 3oz battery for my camera 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 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 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. For a little electrical safety, I connected the additional power connector so that when a plug is present, the charging function is disabled. 

Parts

I purchased these:

I made these

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 get a plate instead. There are some charger units 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:

  1. low wattage soldering iron.
  2. Small gauge wire stripper.
  3. Diagonal cutter or needle nose pliers with cutter,
  4. small parts holder (chip clips will work).
  5. A drill (and drill bit of the appropriate size for the chassis mount jack (6)).
  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.
  7. 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.
  8. Patience.

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). You can buy such a thing for many cameras, but I found it easy to make one out of a junk battery. The battery eliminator usually plugs in where the battery normally goes but provides a wire to an external power source.

NOTE: Some camera model batteries have "chips" in them to help the camera know the current battery state. Your camera may - or may not - require this chip. If it does, you probably cannot easily build a battery eliminator.

My 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! 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 devices.

 

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. Bottom line is that 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 your 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.

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 you 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 you multiply the amp-hours by the working voltage. If starting with milliamp-hours you 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 you have a charger for that camera battery doesn't mean you can use the charger 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, you have to have a pump that exerts 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 doesn't have to supply much current, a trickle is all it needs to slowly charge the battery - just as you can use a bicycle pump to 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 you to realize that ANY voltage in the range of about 7 to 8.5 volts will make your (Canon) camera happy IF it can also supply enough amps.

Jump Start Solution Details

I bought a "Jump Start" device (basically a small 12V auto battery with a carry handle, jumpers and a cigarette lighter jack). My neighbor gave me a "last legs" BP-511 battery which I disassembled and soldered some wires to.

I also a DC to DC converters. 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 amps) 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.  If you're like me, you may have a big assortment of "cigarette lighter" chargers, and one of them may be able to do the job. You'll have to carefully look for the "output voltage" and capacity which is often labeled right on the unit. It might be labeled, for example: 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.

Curiously 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.

    NOTE: I have replaced the wiring on my battery eliminator. The one here used fine solid wire and did not stand up to use.

 

If you look carefully, you'll notice that I put hot glue over the selector dial of the DC-DC converter. I also taped the connector on the end of the cable so that the polarity will not be able to be easily (accidentally) reversed.

Products

DC-DC Voltage Converters and Reducers

Circuits

Batteries

Image mA Hours Voltage Weight (oz) Dimensions Type Cost Link / Description
7,000
7,200		 7.2
7.4		 ?
?		 ?
70.34 x 38.34 x 59.86mm		 LiIon
LiIon		 $40
$30		 Sony NP-F970 7.2V 7000mAh
NP-F960 7.4V 7200mAh

Can use a "normal" battery charger for the device, e.g.

This charger ($13)
6,000 7.4 13.8 2 3/4 x 1 1/2 x 2 3/8 LiIon $21 NP-F960 Battery and Charger from Amazon marketplace.
The 960 is the "older" model.
10,000 7.4V 56   LiIon $180 Includes over and under voltage protection, built in fuse.  Requires $23 charger.
13,600 12.8V 62.4   LiFePO4 $239 Awesome power, but a little pricey and heavy.

Line Power Solution

Canon CA-400 Power Adapter
plus
DC-400

Discussions

Timescapes.org has a lot of great discussions.  http://www.timescapes.org/phpBB3/viewforum.php?f=12&st=0&sk=t&sd=d&start=0&sid=505b281a852b8d8822981253470bbb49

 

Results

Below are some images achieved with these rigs.

 

4 Hours in Pleasant Valley [6047-6109]  4 Hours.  Pleasanton Circular File [5_018700-20] Almost 3 hours (not longer due to clouds!)

 

 

 

 

 

 

 

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