OBSERVATIONS FROM SCOTLAND                            28 May 2008                                GM1SXX

A better battery pack for the FT817 transceiver

As anyone who owns an FT817 knows, the standard battery pack sucks!  It's rated at 1300maH and only runs the radio for a limited period.  When I bought my 817, it came with a charger, the standard battery and an empty cell case intended for Alkaline types.  I don't like spending money on chuck-away batteries. It's hardly eco-friendly not to matter the cost so my thoughts turned to how I could make the spare cell holder work with Ni-Mh types.

Now the FT817 Ni-Mh pack has five wires running to it from the connector so my first task was to see exactly what they did.  That was easy, a quick snip with a pair of small sharp scissors and I had the shrink-wrapped cover off the cells for a look.  Here's what's under the wraps.

The two red wires from the connector go to the battery positive and the black ones to the battery negative while a thermal fuse at the half voltage point is connected in series with the two 'strings' of four cells.  Nothing clever there. 

The connector is wired as follows--- With the connector facing you... looking into it (leads facing away from you as in the photo below) and the two small polarising bumps LOWERMOST ...

NC, RED, RED, BLK, BLK.

(NC = No Connection)

This equates as follows.

The sense line is used by the radio to detect when non-rechargeable or no batteries are fitted. When the Ni-Mh battery pack is installed, there is no voltage present on the sense line and when Alkalines are used in their special holder, the sense line is at half the supply voltage.

Notice how in the photo below, there is no connection to pin 5!

In the photo above, the connector has the polarising bumps facing downward.  The thermal fuse is also clearly visible.

The empty cell case for the alkaline batteries is wired rather differently..   I took a close look at the Alkaline battery pack to see how it was wired  Here's what I found.

Alkaline Battery Holder

You can clearly see the difference from the 'standard' Ni-Mh connector.  That extra green wire tells the radio that you are not using the standard battery pack. It sits at half the supply voltage.   I peeled off the sticky tape, clipped out the green wire  that goes to the battery holder. (its not needed). Leave half an inch protruding from the connector end then glue a piece of insulation (from a bit of scrap connecting wire) over it to avoid possible shorts.

Do remember that this modification, should you wish to do it is done entirely at your own risk.  I should also point out that since there is no thermal fuse fitted, overcharging could have serious consequences.  I don't plan to fit a thermal fuse, but if you can find one, it should be connected in series with one of the connections and should be in intimate contact with the battery cells and the leads well insulated.

When I bought the 2500maH battery cells, I got a really good price so I actually bought four packs of four cells, enough for two complete battery packs.

For my second pack, I didn't even waste my time buying another battery holder. I just used bare 5A fuse wire to interconnect pairs of cells soldering the cells into four strings of two, wrapping a layer of PVC tape around the joined cell ends to keep them neat and to avoid possible short circuits. The four sticks of cells were taped together side by side in the correct order (positive and negative ends alternating!) and interconnected by short links of insulated hookup wire. I found a suitable 5 pin connector in an old computer printer at work and just used that to connect to the radio. When sure it worked OK, I wrapped a couple of  layers of tape around the edges of the battery pack to hold it all together.  providing you only use a few layers of tape, this WILL fit because you don't have the additional bulk of the battery container to deal with. It'd probably best to fit a 'grab loop' or similar so you can easily remove the battery pack if you need to. Things are tight in there and and a tab or tape is a good idea.

I used the same sort of arrangement several years ago to make Ni-Mh battery packs for my Yaesu FT290's and my FT790 radios using Ni-Mh 'C' sized cells.  These batteries are now a few years old and have served me very well. One of their best features is that they always work, unlike batteries housed in spring-type holders where the slightest 'whiff' of oxidation or even severe vibration often stops them in their tracks.

If you do decide to make your own battery packs for the FT817, remember that even a stick of pen-lite Ni-MH AA cells can do real damage if short circuited.  Their low internal resistance means that if short-circuited, the  current flow will be very substantial and can cause fire and serious burns.

Take care and play safely.

A more suitable battery technology for the FT817 would be Lithium Polymer. This has the highest power density of commonly available battery types and would allow extended operating.   YAESU/VERTEX if you are listening.... please do a LI-PO retro-kit for the 817!

73 Al.

GM1SXX