FT-817 Internal battery ideas

These days, FT-817ND units are supplied with the Yaesu FNB-85 battery pack. This pack consists of eight NiMH AA cells in a shrink wrapped package. The rated capacity of the pack is 1400mAh. NiMH cells have a nominal voltage of 1.2V, so 8 times this is 9.6V.

The capacity of this pack gives me about an 1 1/2 to 1 3/4 hours during a SOTA activation. SOTA activations at the moment can involve a lot of CQing, so my rough estimation is that I would be looking at a TX duty time of at least 30%. I also have a BHI filter installed, so my 817 is heavier on current draw on receive – about 417mA with the volume down, and 430mA typical on receive. Obviously more on TX. This leads me to believe that at the moment, I am getting capacity “in the ball pack” of the rated capacity.

Quite a number of my trips involve multiple activations on a single day or trip, and the internal battery is not enough to keep going the whole time. At the moment, I supplement the operating time I get from the internal battery by using either LiPo packs or three LiIon 18650 cells in series in some PVC pipe, and then plugged in via the external DC jack. This is meeting my needs for the moment.

There is no doubt that by using 3 cell Lithum technologies, there is plenty of options for external power. What about internal – when the FNB-85 dies sometime in the future, I will want to replace it, but I want something better. Given that it is working well at the moment, it would be a little indulgent of me to replace it now, so I won’t – but it is nice to have a plan. It is also nice to have more capacity than 1400mAh. Something north of 2000mAh, perhaps even 2500mAh should be achievable.

A LiPo pack in the internal battery slot

Glenn, VK3YY experimented with putting a Turnigy LiPo inside the FT-817. See his picture below:

Turnigy LiPo 2500mAh battery

This battery can be found at HobbyKing at:

http://www.hobbyking.com/hobbyking/store/__23814__Turnigy_nano_tech_2500mAh_3S1P_5_10C_Transmitter_Lipo_Pack_.html

It has a lower C rating than many LiPos as it is optimised for RC transmitters, rather than the boat, plane, helicopter at the other end that could be drawing 100A plus. The FT817 is going to only hit it with 2A, which is only 0.8C – a walk in the park given its 5C discharge rating. The voltage of the pack would be 12.6V fully charged and 11V or so when discharged – so the voltages will be perfectly fine for the 817. Some care is needed as the battery will provide some additional operating time down to 9V, but this is not recommended. The operator needs to pay attention to the voltage display on the 817 screen. The 817 cutoff is 7.5V which would drive the LiPo pack too low – this is 2.5V per cell if it was perfectly balanced. If even a little unbalanced, one cell would be even lower, which is not good.

The LiPo is is a good solution, but it is a higher maintenance solution given the cut-off issue above. The FT-817 is also not designed to charge LiPo packs, so the LiPo needs to be taken out to be charged. It really needs a proper LiPo balance charger to keep the cells in line with each other. Care would need needed if this battery was installed fully charged and an external DC power supply be attached, as unless the green battery cable is connected to a meaningful voltage, the FT-817 will trickle charge 10mA into the battery. This is bad for a fully charged LiPo pack!

NiMH solution

The 817 is supplied these days with the FBA-28 battery holder. This is designed for use with Alkaline cells. These cells are not going to handle a 2A current draw very well, so I can’t imagine that there are many in the world who are using this holder in this way. The holder is pictured below:

FBA-28 battery holder

I have put in a number of Energizer 2450mAh NiMH battery cells into the holder. Eight are needed to complete the pack. The pack is a little difficult to get into the 817, but the trick is to put the holder in first empty, and then put the batteries in.

Yaesu do not recommend using rechargables in this pack. The main reason for this is suspected to be the risk of a short. The Cathode of a rechargable AA NiMH is the outer shell. Aside from the last cell in the pack, this will have a voltage difference to the case, and some of the cells can rest against the case. The only protection against disaster is the outer label on the cells, and this can be scuffed away. The picture shows that there is a plastic tab that will cover about 2/3rds of the lower 4 cells, but some electrical tape put over the exposed cells will also aid in providing the necessary protection. I would not think it needs to be comprehensive coverage, but two strips over the top 4 cells, top and bottom, and one strip over the 4 bottom cells at the exposed tops should be enough. (Of course half the cells are facing the other way so their top will be the other cell’s bottom, etc).

One final modification is the green cable. This is connected between cell 4 and 5 in the pack. If this cable remains connected, the FT-817 will not charge the pack. This cable needs to be cut and secured, and then everything will be ready to go.

Appropriate NiMH cells

My picture above shows Energizer NiMH cells. These are rebranded Sanyos. They work well in many applications, but unfortunately, not this one. Even though fully charged, the voltage drop when the 817 hits them with near 2A is too much, and so the effective life of the pack is much lower than the 1400mAh Yeasu pack. The labeled 2450mAh capacity sounds real nice, but the real world experience would suggest much different. I have tried them in non-radio applications with current draws of around 500mA, and they work ok there.

I found that HobbyKing sell NiMH cells, including some low discharge 2400mAh cells. This is a great capacity for a low discharge cell. I have also read that some have tested these cells at 3A and they work well. I am getting some of these cells to give them a test, but if they can handle 3A, they would be a great cell to use in the Yeasu battery holder. The 2400mAh capacity nearly matches the 2500mAh LiPo pack. Both solutions should give nearly 3 hours of heavy SOTA activation time, but the NiMH solution can use the internal Yaesu charger (2x 6 hour charges back to back), and there are no concerns about damaging the pack if taken to 8V or so.

Regards,
Wayne VK3WAM