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The question is - is there an inexpensive oscilloscope I can use to measure DC voltage and current to see why my battery pack is failing to power a DSLR?

In order to take long time lapse photos with long (night time) exposures in cold weather, I have built an external camera battery pack. However, after a period of time (15 minutes to a couple hours) the camera stops. If for even an instant the camera does not get sufficient power, it stops the series and once stopped, even if it gets restarted manually, the time lapse cannot because of the gap that gets created.

The battery pack initially was a 12v 12Ah AGM battery connected to a buck converter to supply the camera with 8.4v which is the voltage of a fully charged Nikon EN-EL15 battery. When even this failed, I tried connecting two smaller batteries in case one could not supply the needed current. (I tried the two in both series and parallel even though creating a 24v battery and then down converting to 8.4v seemed futile. It was.) I have also added two small 5W 12V heating pads to keep the battery from getting too cold.

The camera is a Nikon D750. There is not much I can find about power consumption although 2.5A is written on it somewhere or other. Long exposures are the highest energy drain on a camera as the sensor needs to stay on and the mirror needs to be held open. (I have not yet tested current usage but now that I think of it, I should with a multimeter.)

I was hoping an oscilloscope could be used to determine if it is the voltage that is dropping or the current is insufficient. My guess is the current is briefly inadequate as the bucks should keep it at 8.4v as even a discharged 12v is around 11v.

Mostly I want to understand the issue. But if not and my guess it is the current, what about a capacitor in the circuit? How would I choose the right size capacitor for this? (I do realize the capacitor would drain the battery when not in use but could be easily disconnected from the power until needed.)

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    \$\begingroup\$ For your needs an oscilloscope will be overkill, what you need is a DC voltmeter with logging capabilities. An alternative is to use a microcontroller based solution like an Arduino. Measure the voltage using the built-in ADC and write a program that logs the voltages and write the values to an SD card. There might be examples of similar projects, for example: youtube.com/watch?v=oei3Y6tOhVI But why not simply eliminate that the battery is the issue by powering the whole thing from a power adapter, just to make sure it actually is the battery. \$\endgroup\$ – Bimpelrekkie Feb 10 at 13:04
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    \$\begingroup\$ You might also want to include a schematic of your setup, just to be sure what you're doing makes sense. I have also added two small 5W 12V heating pads to keep the battery from getting too cold. My choice would be to not waste that power on heating the batteries but design the system such that it can still deliver the required power even when the batteries are cold. On the whole that will be more power efficient. \$\endgroup\$ – Bimpelrekkie Feb 10 at 13:10
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    \$\begingroup\$ How cold are we talking about? What is the operating temperature range of the camera and if the buck converter? \$\endgroup\$ – Edgar Brown Feb 10 at 13:51
  • \$\begingroup\$ INA219 voltage/current sensor and an MCU or an Arduino for which there is already a library. If you need to test in the field as an API flash for data storage. Keep in mind many battery types do badly in the cold, and your heaters mean a huge drain themselves. \$\endgroup\$ – Chris Stratton Feb 10 at 16:00
  • \$\begingroup\$ 1. Test via AC adapter. I'm setting that up to test right now. The camera is rated by Nikon to 0°C. (I am operating at up to -10°F (-23°C) so clearly out of spec. But I have used many Nikon bodies in this cold for many years without problems other than the battery. \$\endgroup\$ – RadOD Feb 10 at 17:43
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The standard EN EL15 battery is rated for roughly 2.5 Ahr, and is good for about 1200 shots. That a 12 Ahr battery will show problems after 15 minutes (although you don't say what the exposure rate is), suggests something else is going on.

I'd be inclined to look very closely at your external battery wiring, and particularly at the connector you're using. Removable connectors can do odd things, particularly when you are using them well outside of rated conditions.

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I agree, that the reason of malfunnction is in voltage drop due to high current bursts made by camera. Possible reasons:

  • converter is not capable to supply needed burst current (what current it rated for?, what is minimum input voltage, at which it rated for that current?)
  • poor connection between converter and camera: poor contacts, high resistance of wires (too long? too thin?)

Large capacitor may help to supply high currents bursts (try 4700uF and more). Place the capacitor as close to the camera as possible. But having enough power of converter is more important.

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  • \$\begingroup\$ Specs:Non-isolated buck-boost synchronous rectification Input voltage :DC 6-32V (Rated Power, input voltage equal to 9V; if input 6v, output about 90W) Lowest dropout: 0V (seamless automatic switching buck-boost, no minimum pressure requirements) Output voltage :DC 0.8-28V (adjustable) Output Current: 15A (MAX) Output Power: 150W (MAX) Efficiency: Up to 97% Soft-start time: 500mS Output ripple: 1% (MAX), 20M-bandwidth Operating Temperature: Industrial (-40°c to +85°c) Load regulation:± 1% Voltage regulation: ± 0.5% Dynamic response speed: 5% 200uS \$\endgroup\$ – RadOD Feb 12 at 13:43
  • \$\begingroup\$ 15A seems well enough! So, connection between the output of converter and the camera is under suspect. What kind of wires and contects do you use for the connection? BTW, do you know about existing solutions like this? \$\endgroup\$ – Eugene K Feb 12 at 20:37
  • \$\begingroup\$ Nikon AC adapter rated as 9V 4.5A, so I think camera will drain less. Try to load your supply by that current (using about 2 Ohm power resistor) and make sure voltage does not drop. \$\endgroup\$ – Eugene K Feb 12 at 20:53
  • \$\begingroup\$ No, I did not know about that product. I had found one previously but they would not ship from Europe because of the batteries. Still, this project has grown because it is built into a waterproof case (sometimes I put my tripod in streams and lakes), because extreme cold will kill performance in LIPo batteries too, and I don't know about that product, but every USB type lithium battery pack I've ever owned has auto-shutoff unless sufficient power is being used which tends to shut off the camera if the interval between exposures gets too long. Plus, I'm interested in understanding the problem \$\endgroup\$ – RadOD Feb 13 at 1:20

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