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I need my camera (Canon EOS 7D Mark II) powered in terrain for a long period of time (10 + hours, mostly idling.)

I bought a dummy battery with a 5V to 8V boost converter (camera uses a 7.2 Li-ion battery,) which "almost works". I can turn on the camera, switch on live-view, record video, but I can't take pictures.

I suspect the DC-DC converter cannot handle the current spike needed (it should be up to 3 A) for taking pictures. I did not crack open it for now, so I have no idea what it consists of. Prior power source should not be problem, as I tried a powerful powerbank and also a mains adapter. But that is not the issue now.

I decided to switch the provided DC-DC converter with a more powerful one. I bought a DC-DC boost converter based on the XL6009E1 IC (image and schematic below.) Note that I am not certain with 0.1 microF capacitor values, but other should fit. It should handle input current of 4 A according to product description (it would burn without heat sink/cooling I guess, but I only need short spikes of high current.)

enter image description here enter image description here

Problem:

After hooking up 5V to the input of the boost converter, setting 8 V on output, and delivering it to the camera through the dummy battery - nothing happens. The camera won't even turn on. I measured 8.00 V while connected. There is also small current: 0.01 - 0.02 A.

The measured current could be no-load current (18 mA according product description.

The polarity was correct. I suspected boost converter to be defective, so I hooked up a small DC motor on the output. It ran, measuring almost 1A of current.

Questions:

  • Why is the boost converter not delivering enough current to the camera?
  • Am I doing something wrong?
  • What should be changed?

I do not believe that there is more than 1 A of current needed for turning on the camera. The smaller (and assuming also weaker) original boost module was capable of it.

Update:

I measured the current flowing to the camera when switching on with the original boost converter that came with the dummy battery. It slowly rises to 0.7 A @ 8V. It was measured only with a multimeter several times, this was the peak. Also, I tried to take a picture and it spiked to 1.5 A @ 8V then an error message appeared on the camera.

While this error message is really most probably caused by an insufficient prior power source, it does not explain why the camera is not even turning on with the XL6009 boost converter. It can successfully output 1.5 A @ 8V (tested on a bigger DC motor.)

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  • \$\begingroup\$ In my experience, Canon cameras are very fussy about the voltage. The ones I have need it to be very close to 7.3 V. I'm not sure why you chose 8.0 V. \$\endgroup\$
    – Dave Tweed
    Sep 25, 2020 at 15:44
  • \$\begingroup\$ Also, 4A input current cannot provide 3A output current at these voltages. \$\endgroup\$
    – user16324
    Sep 25, 2020 at 15:49
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    \$\begingroup\$ "Prior power source should not be problem, as I tried powerful powerbank and also mains adapter." Are you sure? If the camera sometimes pulls 3A at 8V as you say, the input of the DC/DC converter would have to get over 5A from your power source. Can your power source deliver that? The camera pulls a rather large current at start-up too. \$\endgroup\$
    – ocrdu
    Sep 25, 2020 at 15:55
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    \$\begingroup\$ You can't combine power adapters! \$\endgroup\$ Sep 25, 2020 at 17:19
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    \$\begingroup\$ You are missing the fact that you cannot parallel power supplies. Realistically this project is beyond your current level of electrical understanding and experience, and has many opportunities where things could go dangerously wrong. You should try to purchase a finished solution, purchase a spare battery pack to switch to, or similar. \$\endgroup\$ Sep 25, 2020 at 17:59

2 Answers 2

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The XL6009 boost converter module is a non-synchronous boost converter and has been notorious for its lack of safety features, resulting in damaged electronics in some DIYers. It does not have overvoltage protection, undervoltage lockout, or thermal protection. This means that it is possible for the module to output deadly voltages, especially during transients.

The transient response of a boost converter is the stability of the output voltage during quick current surges throughout the operation and in your case most importantly during startup of the camera. The transient response is related to the switching frequency, and higher the frequency, the faster the transient response. However, the XL6009 module has a switching frequency of 400 kHz, a switching current limit of 4A, which may not be fast enough to handle transients. Even if you use huge bypass capacitors at the Vout of the module, it might still not be stable enough to power the camera properly.

A better option would be to use another ready-made boost converter module based around the Texas Instruments TPS61088. This IC comes with 10A switching current limit and usually 1 MHz switching frequency, which can handle transients better. You will also need a 1S BMS for the undervoltage protection.

TPS61088 synchronous boost converter module

The TPS61088 also has overvoltage, overcurrent, and overtemperature protection features, which are not found on the cheap XL6009.

Therefore, if you are looking for a boost converter option, the TPS61088 is may be a better option than the XL6009.

XL6009 TPS61088

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The reason the camera is probably rejecting turning on with the XL6009 boost converter is that the dummy battery includes more than just the boost converter. The battery has internal thermistor, and exposes one leg of it on a pin, that the camera reads. The other leg is likely connected to battery -. The thermistor is likely 10kΩ @ 25°C, but be sure to check it.

Thus your minimal schematic needed for the camera to be happy, may be something like this:

schematic

simulate this circuit – Schematic created using CircuitLab

Adding the 1000µF cap is likely not truly needed, but I'd add it to help with any transients.

I'm using a similar setup as yours for a timelapse, but it is a different model of camera, and I'm actually using 2 Li-Ion cells in series (so the camera actually sees a real Li-ion chemistry), which are constantly being charged in by a CC/CV charger. C1 and R1 are soldered on a small PCB very close to the camera battery bay, so the wires from the cap to the camera internals are short. I'm not using a DC-DC converter, but even if I did, I'd probably opt for a 12-to-8V conversion with a buck converter. Anyhow, your setup should work, provided that you supply the extra components that the camera expects.

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