Internal FT-817 NiMH battery option

Hi all,

A while ago I wrote about options for internal batteries in the FT-817. As detailed in that post, some are trying out LiPO options in the FT-817, and HobbyKing sell a 2600mAh 3S option. Provided operators watch the voltage level on the FT-817 screen to avoid excessive discharge, that would work well.

I still prefer keeping the LiPOs out of the radio – I am more than happy to use them as an external power source and often do. However, the internal battery is not great weight bank for gram. It has a 1400mAh labelled capacity. Mine would still be delivering the vast bulk of that even though I have extensively used it. It gives about 1 hour 20 minutes to 1 hour 30 minutes action when doing a SOTA activation with TXing at 5 watts. I have a BHI noise filter which is a little expensive on the juice, the 817 is drawing about 420mA on RX.

In my previous post, I highlighted that many NiMH batteries do not make the grade in the FT-817. They might get close to their labelled capacity (2100 to 2500mAh) typical on lower currents, but they struggle when 2A is called for. I did notice that the HobbyKing 2400mAh AA cells could handle a 2A load, so I was interested in trying them. That time had now arrived.

I used the 8 AA battery holder that comes with the FT-817 and loaded it up. This holder needs to be put in the radio either empty or with 4 or less cells as otherwise it jams. Care also needs to be taken that the cable does not get jammed as well. The holder can be subject to open circuit faults and I had a little bit of trouble with this.

HobbyKing AA cells in a FT–817

After sorting out those issues, I got on VK3REC, a local repeater, and proceeded to rag-chew at 5W FM. This would present the highest current load on the batteries. I was able to operate for nearly 3 hours before the batteries got to the end. Nice result, and the HobbyKing cells had no trouble throughout the discharge cycle.

Near the start, the 8 cells would present about 10.1V on RX and 9.1V on 5W FM TX on a multimeter. The FT-817 display would show 9.6V and 8.4V at this time. The 8.4V on TX remained at that level for about 90% of the discharge cycle. The final part of the discharge cycle was more graceful than the internal battery, with the RX voltage slowly drifting down from 9.2V FT-817 display to 8.8V. The multimeter was about 0.2V above each of these levels. The 5W TX was at 7.8V when I stopped the cycle. The FT-817 will power off if it drops below 7.5V.

On the whole, I am very happy with the AA cell’s performance and can recommend it for use with the FT-817. I would suggest charging the cells individually in a NiMH smart charger. Alternatively, two lots of 6 hour charges in the FT-817 should fully charge the 8 cells from flat. The green cable in the battery pack needs to be disconnected for the FT-817 to charge the pack.

73, Regards, Wayne VK3WAM