During my holidays, I always bring a “holiday radio”. On the camping sites we are used to stay, we always have 230 VAC @ 10A net power, so full 100W output. It is OK, but not very exiting to be honest, so… I’ve challenged myself to improve my CW skills and explore QRP’ing from /P locations during the holidays.
At first I wanted to buy a FT-817D radio, but as my FT-897D can hold batteries as well and power can be set as low as 5 Watts, I decided to first upgrade my FT-897D with one or two battery packs. The FNB-78 4.5 battery however sets you back $124 (around €100+) and bear in mind you probably want/need two and also need a specific (Yaesu) charger to go with it which probably sets you back another $100 or so.
Browsing the internet I say many people are making these batteries themselves so I decided to homebrew a battery myself as well. I started with ordering 24 NiMH “sub-C cells” (smaller dan normal C cells) with 6000 (!!) mA capacity that seemed exactly the right size. The 24 batteries were only $35. Maybe they’re rubbish, but for that amount you’re not taking a big risk I guess. Here are the batteries I ordered:
The batteries arrived today (only 6 days from Hong Kong China to The Netherlands!!) but unfortunately the packing they were only packed in a bubble plastic envelope so 12 of the batteries were dented. I raised a case via eBay and mostly those Chinese sellers refund or replace the goods (if not: eBay’s buyer protection works pretty well). 12 of the batteries seemed fine so… let’s get started. I was thrilled to all 24 batteries will fit the FT-897D’s battery compartment so… two 14.4 VDC @ 6000 mA batteries for 35 bucks… Not bad at all!
After writing this article, I was made aware of the fact that a healthy MiMH cell can be charged up to 1.5V so my series of 12 FULLY CHARGED CELLS CAN POTENTIALLY PUT OUT 18VDC WHICH EXCEED’S YAESU’S OPERATING VOLTAGE TOLERANCE OF 13.8V + 15% = 15.87V!! After less than one hour of charging, the Voltage went up to 15.8 VDC which is on the edge of reason. Please be aware that I HAVE REMOVED ONE CELL FROM THE SERIES CELLS!! THE TOTAL NUMBER OF CELLS IS NOW 11. Max. Voltage would be (theoretically) 16.5VDC, “working Voltage” should be around 13.2 VDC.
I soldered a series of 6 batteries in series and soldered the two of these 6-battery-series in series as well (are you still with me?! HI). !! I HAVE REMOVED ONE CELL SO NOW 6 + 5 = 11 IN SERIES !! Then I used a glue pistol to kinda glue them together and packed them in very thin PCB material that I got years ago at a ham fair. Wanted to use is as a point to point component board for guitar amplifiers, but the material was waaaay too thin. Always kept it because it seemed pretty sturdy, very well isolating and can be cut with normal scissors. In Holland we tend to say “wie wat bewaart, heeft what” and now, years later, it comes in very handy. So… glued the batteries and packed ‘m in the PCB board:
As you can see in the picture below, 24 of these batteries fit the FT-897D nicely:
(BUT ONLY 2 X 11 = 22 ARE REQUIRED!!)
Solderded the battery’s (+) to the LEFT pin of the A connector and (-) to right PIN of the A-connector, took out the batteries on the right side (just to show you what a nice fit they are), closed the FT-897D and fired it up…
Oh yeah! 14.6 VDC on the meter, excellent. I worked the local repeater from Utrecht with only 5W output, the Voltage dropped to 13.8 I think. I’m now listening to the radio for about 2 hours and Voltage is 12.8VDC on receive and 11.8VDC on transmit, still pretty good I guess. I’m now awaiting a 1A intelligent NiMH charger AND (!!) 10W solar panel (already got the charge controller) and then the real fun starts… QRP from my back yard in CW on a random length of wire tuned by a simple L/C tuner. What an adventure HI.