It’s only recently that I have been hearing about Lithium Iron Phosphate batteries. I read about it first on a post made on the Worldwide Radio Forum. Then, a few well known portable QRPers posted about it so I gave it some investigation. LiFe (as they are called) batteries offer really amazing power density, and they are extremely safe to travel with. Doing my research, I found that these batteries are also very popular in the RC market. HobbyKing carries a whole slew of them in their stock. There are a number of varieties and configurations you can get. I’ll go over this first to describe why I purchased what I did.
LiFe batteries come in a number of configurations: 4S1P, 4S2P, 3S1P, and so forth. This naming convention indicates how many cells are in series, and then how many of those series cells are in parallel. For example, a 4S1P battery has one battery in parallel and then four in series. Well, you can’t be in parallel with yourself so it’s just really one series set of four cells. A 4S2P battery has two batteries in parallel, and four sets of these two in series. Simple enough. Only, as you add more cells to a battery pack, your opportunities for failure increase.
In a 13.2V, 4200maH 4S1P battery each cell is 3.3V and has a 4200mAh capacity. That’s very close to the standard 13.8V that most power supplies produce and well within the 9V-15V range the KX3 accepts. However, in a 13.2V 4200mAh 4S2P battery, each cell is still 3.3V but has a 2100mAh capacity. Having two of these cells in parallel is what produces the 4200mAh capacity, and then four of them in series produces the 13.2V. It is the same result, but using more components. Enough of this, on to the pictures.
This is the Zippy FlightMax 4200mAh 4S1P LiFePO4 battery pack, purchased from HobbyKing. It is effectively four 3.3V 4200mAh cells wired in series with a circuit included to allow balanced charging using a charger that can accept the additional voltage inputs. It comes with some kind of generic plugs that I didn’t recognize. It didn’t really matter, as you will see in a moment.
Highly recommended with this battery, I also purchased the Turnigy Accucell 6 balanced charger. It is capable of balanced charging batteries with up to six cells in series. It does not have an internal AC to DC converter so you need a DC power supply.
The first thing I did when I got the battery pack on my bench was to remove the useless connectors that came with the battery and attach some Anderson power poles. This was a little tricky because the cables used are thick with fine strands. I’d guess they were 8 gauge. After I stripped off a length of shielding, I clipped small sections of the exposed strands until I had enough to manage to slip into a 30-amp power pole connector and crimp. Out of pure luck, I stripped exactly the amount of shield to make a flush fit with the power pole housing. I still added some 3/4″ heat shrink tubing over the connections (not pictured) for good measure.
The charger unit came with alligator clips on all the ends for power connection. The wire on the bottom of the picture connects to the charger on the left side… and I guess the alligator clips are supposed to connect to DC terminals to charge. The charger output goes to the right (connected in the picture) and to some kind of small molex connector. Another cable with a molex connector goes to yet more alligator clips. Suffice to say all the alligator clips were removed and replaced with still more Anderson power poles. The alligator clips went into my parts drawer.
Finally, I was ready to charge the battery. I used my recently acquired Powerwerx SS-30DV switching power supply to charge it, as it has convenient front panel power pole connections. This will be the power supply that I travel with for portable operations. A separate review of this will come soon. The power supply will connect to the charger, which will connect to the battery. Also from the battery the five-pin balancing circuit connector (see picture three) will connect to the charger so that it can monitor the voltage of each of the four cells in the battery. It’s pretty slick.
I let it charge, it took about two hours at a 2A rate, which is what the battery pack is rated for. Then I did a power balancing charge. That took only a few minutes. The real test was attaching it to my KX3. The KX3 fired right up and I was able to transmit SSB at 12W, which it will only do when connected to external power greater than 12V.
I’m in business!