I'm working on a project to charge my handheld radio battery through USB-C. The battery has flat contacts and charges via a cradle that outputs 8.4v at 1000mA, while the battery itself has a nominal voltage of 7.4v. I want to skip using the bulky cradle and charge it directly via USB-C instead. I've seen several boards online that output the required voltage but they all have USB-A connectors for the wall plug and USB-C for the board. I found one trigger board on Amazon that can negotiate the voltage, but it only supports an output of 9v, which is too high. Is there a way to drop that voltage to 8.4v using a silicon diode, and if so, which diode should I use? Also, does anyone know of a USB-C board that negotiates properly and outputs 8.4v?
4 Answers
You can find 2S lithium ion charging circuits with USB-C connections; however, they typically require USB-A as input. Your best bet might be to combine a USB-C trigger board that can negotiate the voltage with a compatible 2S charger.
Just a heads-up, that 8.4v you're referring to might actually be the peak voltage when charging a lithium-ion battery. Instead, look for a USB-C 2S lithium-ion charging module like the DDTCCRUB, which is designed for this. It may well serve your needs without complications from triggering voltage downs.
Thanks for the suggestion! I’ll look into it, but does that one accept USB-C from the wall? I keep finding models that only work with USB-A.
If your cradle is stepping down the voltage from 12v to 8.4v for the radio, it likely isn't a simple power adapter. You'll need to implement a 2S charging circuit directly inside the radio; this effectively simulates what your cradle does. You'd feed it a higher voltage through USB-C PD and let it manage the charging process. Just make sure to look for USB-C trigger boards that can handle power delivery to ensure compatibility.
You might want to check the specs of your current wall adapter. If it's a standard wall wart, it could be supplying 9v or 12v, while the charging cradle does the regulation. If it's 9v, consider getting a USB-C female trigger board that outputs 8.4v directly. Try to avoid using adjustable types unless you're confident with soldering, as the pads are pretty tiny and tricky to work with.
Good point! Also, make sure to double-check the current rating if you're switching components around.
That sounds like the route I need to take! Thanks for the guidance!