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I want to make an external power supply for my Godox TT685N, and I have two questions:

  1. There are 3 pins on the connector (I found, that this is same conector like Canon) What is the pinout of this connector?

  2. I found that the voltage on this connector is about 300V. Is this correct?

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Yes, the voltage is approximately 300 volts and here is a diagram showing the pin connections:

enter image description here

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You can buy a complete unit for as little as $30. It doesn't make sense to try and design your own. The have complex electronics inside.

Ebay Flash battery packs

enter image description here

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  • \$\begingroup\$ Why is this voltage so high? How can I DIY make left pin "Output logic control signal..."? \$\endgroup\$
    – marcel3032
    Dec 26, 2017 at 16:14
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    \$\begingroup\$ They are high voltage in order to charge the flash faster. I wouldn't bother trying to design one yourself. It would be much simpler to buy one from ebay for as little as $27. ebay.com/sch/… \$\endgroup\$
    – Mike Sowsun
    Dec 26, 2017 at 17:14
  • \$\begingroup\$ Is that diagram looking at the plug of the battery pack, or the prongs on the flash? (I need to convert a Nikon plug into a Canon plug.) \$\endgroup\$
    – Bruce
    Nov 23, 2020 at 19:50
  • \$\begingroup\$ That diagram represents the pins on the flash body. I added a photo above showing the battery pack connection. \$\endgroup\$
    – Mike Sowsun
    Nov 23, 2020 at 21:05
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The flash works by discharging a capacitor into a xenon tube, when ionized by a very high voltage pulse to allow conduction. The energy, E, stored in a capacitor is E = CV²/2. Because of the square factor, it's much more productive to increase V (volts) than C (capacitance). With C = 750 µF, V = 283 Volts, you get the 60 Joules of a typical high end cobra flash.

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  • \$\begingroup\$ Yes, but capacitors become disproportionally more difficult to build - and larger! - when you increase the voltage they can handle. \$\endgroup\$
    – rackandboneman
    Oct 16, 2021 at 15:18

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