Yaesu FT-727R lithium-ion conversion part one

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Modern technology makes an old amateur radio new again.

In part one of a three part series this Yaesu’s chassis interface will be designed and printed. I purchased this old Yaesu at the Pacificon swap-meet in 2018. The Nickel-cadmium 500mA battery had long since perished making this portable radio not so portable.

This radio accepts a supply Voltage varying from 6-15 VDC. a 3S configuration (11.1V) was chosen for packaging and the ability to charge from a vehicle. The 18650s chosen are of the 2800mAh variety. These cells were purchased used on Ebay. They however will not fit in the original enclosure so a new one will have to be designed. First in making a new enclosure is copying the original batteries’ interface with the radio:

3D printing just the bracket speeds up prototyping time and reduces wasted material. This is printed from PLA. After a revision or three the interface was working pretty good:

From here the main body will be designed. Yaesu’s low battery indicator was designed for Ni-Cd technology and is below the cut-off threshold of the charge controller therefore it will not work. A new battery indicator utilizing a couple LEDs and zener-diodes will be used. The original batteries’ location for the charge jack was on the bottom of the radio, it will be moved to the side so that the radio can remain vertical while placed on a bench.

In Part Two the battery body will be printed and the electronics test fitted.