Alinco DJ-F1T NiMH Battery Charger

I’m as cheap, er, frugal as the next ham radio operator, so I’m loath to throw out my old Alinco DJ-F1T 2-meter handy-talkies just because their old NiCd batteries wore out.

New NiMH batteries are available for this venerable radio from various sources, and I ordered a couple from these folks.  The power capacity (mA-h) is almost twice my old NiCds, with the same physical size!  NiMH batteries aren’t as toxic as the old NiCds, either.

Trickle charger
Original desktop trickle charger

I also wanted a smart charger for the batteries, since all I had was the original Alinco desktop trickle charger with wall-wart, and that would take about 20 hours to charge the new high-capacity batteries.

My plan was to use the desktop charger base with the smart charger, so I could keep the convenience of snapping the radio into the base with the advantage of fast, smart charging.

I ordered a smart charger from the same battery vendor, took apart the original desktop base, wired in the smart charger instead of the wall wart, and… nothing.  It didn’t work.

A little further investigation revealed that Alinco must have used a diode inside their battery packs to only allow current to go into the battery from the exposed tabs which connect to the charger base, and smart chargers need to both charge and briefly discharge the battery.  Alinco’s was a sensible safety measure, to prevent the battery or radio from being destroyed if you accidentally short the exposed tabs while using or transporting the radio, but it prevented my smart charger from working.

There is another set of tabs on the inside surface of the battery pack which connect directly to the battery without the diode.  These provide power to the radio when the battery is snapped into place, but they’re only accessible when the battery is removed from the radio.

Always happy to find a new project for mechanical CAD, I grabbed my micrometer and began designing a charging cradle to fit the battery (latching lever not shown).

Cradle in CAD
Cradle in CAD (handle not shown)

I planned to 3D print this in plastic and fabricate some tabs from stainless sheet metal to fit in the + and – wells shown which would contact the battery direct connections.  The wells are slightly cantilevered so the tabs would snap in.  There are holes at the bottom of each well and channels leading to the top of the cradle on the bottom side for wire routing.

3D printing is amazingly easy these days.  I uploaded the .stl files from CAD to a vendor I found on and a week and $32 later I had two complete cradles on my bench.

Raw parts
Raw parts from the 3D printer

Unfortunately the quality wasn’t what I’d experienced from previous 3D printers.  There were rough edges with slag, loose threads of PLA plastic, and the pieces were hollow!  You’d think if they charged by the cc they’d send a solid part.  To their credit, the printers refunded my money when I complained.

Battery snapped in place
With battery snapped into place for charging

Anyway, after spending some time cleaning things up with a file and Dremel, installing the latching lever using a nail for the pivot, fabricating and installing the tabs, and connecting up the smart charger, I had a fully functional smart charger and high-capacity NiMH batteries for my old radios.