A few months ago, i began to look for a battery for my FT-817 because my 7Ah SLA weight too much into my backpack.I use my FT-817, mainly, to transmit from Sota summits and geodetic points (called “Vertices geodésicos” in Spain). So, the weight is very important.My three candidates were LifePO4, Li-Ion and LiPO.But i rejected LiPo technology, due it is dangerous, mainly in the charge and discharge process.So, the two choices are LiFePO4 and Li-Ion.
And here are the LiFePO4 batteries from A123Systems. Finally we have bought and mounted several packs of them.
The LiFePO4(Lithium-Iron-Phosphate) batteries are relatively new in the market. They are on the market from 2-3 years ago. So, they are becoming known now.
The best known are those made by A123Systems (http://www.a123systems.com/) and are manufactured in 3 sizes (32113, 26650 and 18650)
However, despite being a newer technology, these batteries provide a current capacity smaller than well-known battery Li-Ion.
While a cell Li-Ion 18650 can provide 2.000mAh, the same size in a LiFePO4 will give us aproximately 1.100mAh.
Then, why do not we do the batteries with Li-Ion cells instead of LiFePO4? It’s simple. The LiFePo4 have many advantages over Li-Ion or Li-Po batteries.
- They have a huge current capacity.
- Support many more cycles of charge and discharge than others lithium batteries
- They are very permissive with charge and discharge. The charge current recommended by the manufacturer is 3A for a single cell.
- Is almost impossible it explode, while the Li-Ion batteries are sensitive not to mention the Li-Po.
Look its impressive features:
- Weight: 72 grams (26650 cell). 39 grams (18650 cell)
- 2.300mAh capacity (26650 cell) and 1.100mAh (18650 cell)
- Recommended charge current 3A in 45 minutes (fast charge 10A in 15 minutes). Impressive and without the problems of other lithium batteries.
- Max. continous current of 70 amps (26650), 35 amps (18650)
- Max. current of 120 amps in 10 seconds (26650), 70 amps (18650)
There is also a third size, the biggest, which provides 4400mAh in a single cell, but is too expensive for me.
To build my battery pack, I have chosen the 18650 format, because it have better cost/performance ratio than 26650 size. Perhaps, some day, i will build a pack with 26650 cells for transmit with my FT897 at full power.
I bought 16 cells from a chinese seller on eBay. The seller sent me 4 blocks of 4 cells in parallel. Each block is as shown in the photo shown above.
The 4 blocks were joined with melt glue. Then 3 tabs were soldered to connect all of them and build a 13,2V and more of 4000mAh battery.
The pack have been inserted in a plastic container from a local supermarket chain.
Anderson Powerpole 30A connectors were installed and 3 solder points ready to install the connector needed to balance the battery in the charging process, if so decided in the future.
And this is the final result. The photo shows the charging process:
If you would like to check the discharge capacity of these batteries, you shoud see this video:
The container is a fudge, but cheaper is impossible.
The pack weight 640 grams (22.5 oz)
The total cost was under 30 euros, including the 16 18650 cells and two Anderson Powerpole connectors (the Anderson Powerpoles are too expensive in Spain).
If you see this video, you can check the discharge capacity of these batteries
But if you want something faster and aesthetic, just enter to the Buddypole web page and buy one of its batteries, which are made from the same cells that we have seen here (26650 cells). For 165 USD plus shipping, you will have about 200-300mAh more, only. You can see these batteries at http://www.buddipole.com/portablepower.html