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Voltage Conversion

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Drew Fulton

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I am currently working on building a battery for my Nikon D200 DSLR Camera so that it can basically be powered for very long periods of time to do extended (think months) time lapse photography.

I have consulted another photographer doing this in the Arctic so have my design all layed out except for one part. I need to attach the camera to a 12V power source. What this other photographer has done is simply solder two leads to a AA battery tray in the camera, run these leads into a voltage regulator and then the voltage regulator to the 12V battery.

What I need help doing is creating or finding a voltage regulator to conver the 12V car battery to power the camera instead of the 6 AA batteries that would normally be in the trade.

The other option is to run an inverter off of the battery and then into an AC adapter but there is a lot of conversion in there and isn't as efficient (I think).

I should be able to switch out 12V batteries on a regular basis for this application, or I may be attaching a solar panel to trickle charge during future projects.

Thanks for any help.

Best,
Drew
 
Two obvious choices are:

Use a linear regulator which is simple and has about 75% efficiency, which is what the other photographer did.

Use a switching regulator to convert the 12V to the required 9V which is more complex, but can have around 85-90% efficiency.

It depends upon whether the added battery life is worth the extra complexity.

Running a 110V inverter into an AC adapter is likely more inefficient then either of the above.
 
Crutschow,

What is the best way to go about obtaining/making one of these regulators? I should say that these things have to withstand some pretty nasty conditions though they will be housed in a waterproof case with the camera.

Hero999,

I am not exactly sure the current it draws. Looking through the manual it can be powered by the following...

One or two EN-EL3 Batteries or six LR6 alkaline, HR-6 NIMH, FR-6 lithium, or ZR-6 nickel-maganese AA batteries.

the EN-EL3 battery is a 7.4V/1500mAh battery.

Unfortunately, thats all I can find at the moment... I will have the camera in hand next week and should be able to learn more.

Thanks again for all the help.

Drew
 
I am not exactly sure the current it draws. Looking through the manual it can be powered by the following...

One or two EN-EL3 Batteries or six LR6 alkaline, HR-6 NIMH, FR-6 lithium, or ZR-6 nickel-maganese AA batteries.

the EN-EL3 battery is a 7.4V/1500mAh battery.
Does it say how long it will run on any of those batteries?
 
I would suggest you measure the curren by connecting a multimeter in series with it. You need to know the current requirements in order to build a power supply for it.
 
Sounds good. I will have the camera in hand in the middle of next week and will see what I can learn. I'll check back then. Thanks for the help.

Drew
 
I finally got the camera in hand and can provide some more information on the power.

On the bottom of the battery grip it reads 9V ---- 2.5A.

The battery itself reads 7.4V, 1500mAh. The camera can run on 1 or 2 batteries.

The tray I will be modifying holds 6 AA batteries has no information.

So how can I connect a 12 V battery to this camera without killing it. I should preface this that I have very little experience with electronics but I can follow directions well.

Thanks everybody.

Drew
 
On the bottom of the battery grip it reads 9V ---- 2.5A.

The battery itself reads 7.4V, 1500mAh. The camera can run on 1 or 2 batteries.
I don't think the camera takes 2.5A except perhaps in short bursts. You really need to measure the current or else how long the camera runs on a set of batteries in your intended application. Otherwise it's mostly a guess as to how to build the supply.
 
What's the best way to go about measuring the current? I've got all day tomorrow to run the test.

Thanks,
Drew


Hi Drew,
Here's the way I would do it, take the battery from the camera and put a red wire from the positive of the battery to the positive of the battery input on the camera. Connect a black wire from the battery to 1 lead of a dmm then put another wire from the other dmm lead to the negitive input on the camera. Have the dmm set to 10A current and take a pic without the flash then 1 with the flash. these 2 reading will give you the current used in taking a normal pic and 1 with using the flash.

I hope I'm right in the above explanation and if i'm wrong some other member will chime in and correct me I'm sure.

Cheers Bryan ;)
 
Alright everybody, here we go. Camera is hooked up to a digital multimeter and here are the results...

When the camera is just sitting, nothing happens (calling it "sleep" for now), it reads at 0.00.
When the meter is on, it reads 0.30.
When the shutter fires, it spikes to somewhere between 1.5 and 2.0.

Typically, the camera will sit "sleeping" for a while, the meter is activated a second or two before the shutter fires, then the shutter fires, then the meter remains activated about 4 seconds before it returns to the "sleep" mode.

So, thats what I got. Any other measurements I need to take in order to get this going?

Thanks again for all the help.

Best,
Drew
 
Okay. From your results you could use a simple 3-terminal linear regulator to generate the voltage, but the normal bias current draw of typical regulators will drain your battery somewhat over the long period of time you want to operate. For example, the LM317 has a minimum bias draw of 5mA (through the voltage set resistors). This will use about 3.6 ampere-hours per month from the battery. Since a normal 12V car battery is about 50 ampere-hours that may be okay.

If this is acceptable to you than I suggest a simple LM317 regulator with resistors selected to provide the desired 9V. If you look at an LM117/317 data sheet it will show how to calculate the required resistor values for 9V and connect it up.

Since the camera instantaneous current draw is high, you will want a large capacitor on the regulator output to supply the transient. I suggest at least several hundred microfarads (electrolytic type).

If you think you need a lower bias-current regulator, than you may need to build one using a zener diode, a low power op amp and a power MOSFET pass transistor. That could keep the bias current well below a milliamp.
 
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Crutschow,

I am not worried about the minor bias current as in any instance where I will be set up for very long periods of time (aka over a month) then I will either be able to rotate batteries or hook up a solar panel. However, for what I am doing right now, even the solar panel isn't needed.

So it sounds like a LM317 will work perfectly for me. Now here is where my ignorance comes into play. I don't even know how or where to start. Would you mind treating me like a total novice and pointing me in the right direction?

Thanks,
Drew
 
Here's the data sheet for the LM317. Take a look and see if you can make any sense of it especially the sample circuit.

I'm a little busy at the moment, but I can work on it a little later if you need additional help.
View attachment LM117 Adj. + Regulator.pdf
 
Crutschow,

Thanks for the help and especially the patience. So lets see if I understand this or am totally oblivious. Basically, I buy a LM317 package and then assemble it. I assume this means assembling various resistors and capacitors on a circuit board?

Is that the basic idea? If so, can I pick a kit up locally like at a radio shack or is this something I will need to order?

Thanks!
 
Basically, I buy a LM317 package and then assemble it. I assume this means assembling various resistors and capacitors on a circuit board?

Is that the basic idea? If so, can I pick a kit up locally like at a radio shack or is this something I will need to order?
Yes. It's a simple circuit with only a couple resistors and a couple capacitors besides the LM317 so you can assemble it on a small perforated board from Radio Shack. The LM317 won't be dissipating much power so you don't have to use a heat sink.

Have you soldered before? If not you should practice soldering two wires together until you get the hang of it. Generally you don't want to apply more heat than you have to, especially with semiconductors, and you don't need a lot of solder, just enough to wet the joint smoothly, not globby. You need to tin the tip with solder before using. A small damp sponge works well for cleaning the tip before each solder application. Touch the tip to the joint and apply the solder between the tip and the joint. Applying a small amount of rosin (not acid) flux to the joint before soldering makes it easier and helps insure a good joint.

They sell small heat sink clips that you put on the semiconductor leads to minimize heat transfer but you probably don't need to do that with the LM317 since it's a power device.
 
Crutschow,

Alright, I am slowly figuring this out but I still haven't figured it all out. My understanding is I need a LM317 and two transistors. I think I understand the formula except for one part, the Iadj(R2) part. I don't understand what the ADJ stands for and then how to calculate the two resistors.

I stopped by one of our two local Radio Shacks today and they were out of the LM317's but I will try the other store tomorrow. I'd really love help putting together a shopping list. Here is what I have so far...

LM317
Resistor A (need to know what to get)
Resistor B (need to know what to get)
Capacitor (size?)
Perforated board

The other thing I need to consider is how to attach this whole thing to the camera and battery.

So what else do I need to get? I hope to finish this all up tomorrow. Now I am off to practice some soldering.

Thanks again.
Drew
 
For 9V out:
R1 = 240 ohms
R2 = 1.46k ohms
C1 (input cap) = 0.1uF for circuit stability (20V or greater rating)
C2 (output cap) = 470uF or larger for output filtering and transient current supply (10V or greater rating)

Since you probably can't find an exact 1.46k ohm resistor you can use a 2k trimpot and adjust it to give the desired voltage. (connect the pot wiper to the cw end of the pot so the voltage will increase with cw adjustment of the pot wiper).

You might want to add a two wire connector to the camera connection so you can easily disconnect the regulator. A simple plastic connector such as they use in car wiring would be fine.

For the battery you can buy battery clips that attach to the battery terminals.

Any wire 20 gauge or larger should suffice.

Also need rosin core solder and a tube of rosin flux.

Double check your connections to make sure you wire the LM317 correctly. An incorrect connection can blow the device.

If you want to get fancy, you can put the board in a little electronic box. Otherwise just wrap the whole board assembly in electrical tape so it won't short out if it touches any metal.

Good luck.
 
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Carl,

I just got back from Radioshack with all of my supplies except for the resistors. When I got there I got confused. First, there weren't any 240s, just 220s. Second, there were several different ones with different current capabilities. I wasn't sure which one to pick. And third, you completely lost me with the 2k trimpot part. Can you explain a bit more? Thanks!

Drew
 
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