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My primary fascination with the DIY aspect of amateur radio is building antennas. What good is a radio without a decent antenna? Likewise, what good is a portable radio station without power?
Power for portable operations can come from a variety of sources like generators, solar generators, shoreline outlets, solar and battery. The primary choice of portable operators is battery, supplemented with solar. And the overwhelming choice of battery power is the LiFePO4 chemistry (Lithium [Li] iron [Fe] phosphate [PO4]).
There are a couple reasons why LiFePO4 is superior to Lithium Ion (or Li-Ion) batteries. Number one is safety. The LiFePO4 chemistry has a much greater degree of thermal stability over Li-Ion, and will remain cool at room temperature while charging, while the Li-Ion heats up faster and may potentially suffer from thermal runaway.
Next is the voltage supplied to the radio. Fully charged, Li-Ion charges to 4.2V per cell. With 4 cells in series (4S), the battery pack comes in at 16.8V. That's much to high for today's transceivers. For Li-Ion cells with 3 cells in series (3S), the fully charged voltage is 12.6V. While this might seem OK, we need to look at the nominal voltage of both the 3S and 4S packs. Nominal, or resting voltage, of those cells are 3.7V, making a working voltage of a 4S battery 14.8V, and a 3S pack 11.1V. While these batteries will eventually drop to the nominal voltage working condition after a bit of use, the initial 16.8V of the 4S pack would need to use a DC-DC voltage drop converter to be safe to use. With that being said, the 3S packs can be ideal for use with smaller QRP rigs, and I do indeed use a few 3S Li-Ion packs with a couple of my QRP radio like the KX2 and the QCX-mini. With the KX2, the voltage will start and remain at 12.6V for a good hour of operating, and I have only seen it as low as 11.8V after a couple hours.
With LiFePO4, each cell is fully charged at 3.6V per cell. With 4 cells in series (4S), a typical of LiFePO4 battery, the battery pack comes in at 14.4V. Nominal voltage is 3.3V, making the working voltage about 13.2V. PERFECT for a 100 watt transceiver.
Next, both batteries will maintain a very flat voltage curve, compared to an sealed lead acid (SLA) or absorbent glass mat (AGM) battery which will start dropping voltage right from the beginning. Run time on an SLA or AGM will be drastically shorter than a comparable Li-Ion or LiFePO4.
Lifespan is also greatly increased with both lithium batteries compared to the SLA or AGM batteries. The latter will give you less than 300 cycles (charged, discharged, then charged again) at 80% DoD (depth of discharge). LiFePO4 on the other hand, are generally rated at 3000-4500 cycles at 80% DoD, and will far outlast their SLA and AGM counterparts.
Weight is another huge factor for portable operators, especially for SOTA operators (some of whom are really just mountain goats trapped in a humans body hi hi) who summit peaks to activate, and POTA operators who might find themselves hiking a ways to their spot, or just lugging gear across a the grass to the nice shady spot. Lithium batteries are very energy dense which causes them to be much smaller and lighter. The average weight of a 10Ah SLA battery is about 6-7 pounds. Compare that to a 10Ah LiFePO4 at just under 3 pounds!!
Price. People are lured into buying an SLA, for example, because of it's price. A 10Ah SLA can be found in the neighborhood of $25 +/-, while a 10Ah LiFePO4 will cost around $100 - $125. On the surface, the LiFePO4 is 4-5X the price!! But when you take into account the lifespan of each type of battery, the LiFePO4 will last 12X longer! Look at it this way..... you could take a fully charged LiFePO4 battery, completely discharge it, then recharge again EVERY DAY FOR ALMOST 10 YEARS, even longer if they are not completely discharged with each use. With an SLA battery, a complete daily charge/discharge cycle will leave the battery ready for the recycling center in less than a year. The phrase "buy once, cry once" certainly comes to mind here.
Lithium batteries will also hold a resting charge much longer. LiFePO4 are typically rated at 5% discharge per month, meaning it would take about 6 months to reach the same state of charge that an SLA battery would reach in about 30 days.
Much lighter weight, a flatter more consistent voltage curve, can be stored seemingly forever with very minimal voltage drop, much more stable and safe to use, and has a far greater lifespan. And there are more reasons yet why the LiFePO4 is far favorable over traditional batteries, but I don't want to bore you to death. Bottom line, after making the switch, I cannot see any good reason to NOT go with a LiFePO4 over a traditional battery.
As I eluded to earlier, I have built many of my own LiFePO4 and Li-Ion battery packs. The ones I have bought are a variety of used cells or assembled batteries that were once used in medical gear. With these, there is a good chance they were never used/cycled except for maybe a few times here and there to test the equipment. It seems most hospitals and medical facilities use an 18 month time frame to replace all batteries regardless of their current state. For us, that means cheap batteries!!
Below is my POTA portable battery box, some of the batteries I have built from new components, recycled medical packs, and one that might just surprise you.
This battery box is my constant companion for my POTA activations. It has everything I need, and nothing I don't need. Inside is an EcoWorthy brand 30Ah LiFePO4 (about $150 at the time). Also mounted inside is a MPPT solar charge controller. Not the quietest in the world RFI-wise, but it's also not noisy enough that it messes with my ability to still hear weak signals. Also stored inside are a number of things I might need during an activation: 12V/USB adapter, 10' cord to run to the solar panel, extra power cord for the FT-891, inline noise suppressor, charging cord for my phone and one for my MFJ-223 antenna analyzer, a small 150 DC to AC inverter, and a 4-way Power Pole power strip with a 2' cord. The meter on the outside lets me monitor the battery's health. Below it are two outlets that both run through the meter. On the back it a master on/off switch that shuts off power to the meter and the two outlets. I chose to use a guard on the switch to prevent it from accidentally getting turned on while bouncing around in the back of the truck. Above the switch are the charging ports: orange/grey for solar, and blue/black for the wall charger. All of my solar panels and related solar cables use orange and grey power pole connectors to avoid connection the solar straight to the battery.
While this battery box is primarily for radio use, it would also be very handy during a power outage to keep cell phones and laptops charged up, run some low draw LED lights in the house, etc.
OK, so I didn't build this one specifically for POTA, but for now that's what I'm going to use it for. This is just one of four 12v 200Ah batteries I will be making as part of a future 48v 200Ah battery. The 48v setup will be installed in the basement as a backup battery bank to go along with the 8000 watts of solar on the roof.
The cells are 3.2v 100AH pieces from seller Liitokala on AliExpress. To balance all the cells before assembly, I cut and drilled buss bars from some scrap aluminum I had in the shop, and connected them all together in parallel, which essentially made a 3.2v 800Ah battery. Since I wasn't going to be getting to this project right away, the cells sat like this for about a month. This allowed the voltage between all of the cells to balance out among themselves. After that month had past, I set up my power supply to charge them. I adjusted the bench top power supply to 3.5v, connected it to the pack, and set the current to 10A. When the power supply dropped to 1A, I shut it off to prevent over charging the cells. Once this was done, I started the process of assembling the cells into a 12v battery.
If I were start this project all over again, I would have just bought larger 200Ah or maybe even 280Ah cells. I believe the project would come out to about the same price, if not a little less.
As I was trying to figure out how I would haul this thing around, I lucked out and found this large 5.56mm ammo can at the gun shop when teaching a class one weekend. The completed pack ended up fitting PERFECTLY inside. The eight cells are banded together for some compression to prevent them from expanding during charging, wired in 2P4S (2 in parallel, then 4 in series), along with a Daly 100A BMS. The balancing function did not seem to be working correctly on the BMS so I added a separate active balancing board (the small PCB) which did the trick. They all stay within .100 volts of each other now. I'll probably replace this BMS soon. The buss bars are made from 1/2" copper pipe that I hammered flat, cut to length, then drilled holes. Then I stacked 2 per connection.
To protect the cells on the sides and bottom, I used a couple cheap 88 cent Walmart cutting boards (the same ones I use to make wire winders from). The BMS fits perfectly in the gap left on the one side of the can.
I still have a few things left to do; notably add some protection to the balance wires to prevent them from rubbing on the buss bars, install a dual power pole outlet and the battery monitoring gauge, and install a clear acrylic sheet over the top of the buss bars to prevent anything from getting shorted out. Then it will get a fresh coat of paint, and a couple decals.
Once it is all together and ready to go, I'm thinking I will start using it on activations, and see just how many activations I can get out of it before it needs to be recharged! I will be keeping notes on things such as modes and power setting used, length of the activation, and the number of watt hours used at each activation. Should be a fun and interesting experiment.
All said and done, I'll have right at $440 in this 12.8v, 200Ah battery. The cheapest commercial battery of this size that I have found starts at $800, and can be as much as $1600 or more! The best part of this build is that anyone can put one together with no special tools needed, like the spot welder I use on my smaller Li-Ion and LiFePO4 builds. Click HERE if you would like to follow my build steps, including links to the cells and other pieces used.
This was one of the first battery packs I put together. It uses 4 Headway 8Ah LiFePO4 cells that are rated at a whopping 200 amps each! These cells have been used to jump start a dead vehicle, and with the right sized cables, I could certainly do that too. But I won't, I already have a proper jumper box lol. This battery is a little larger, heavier, and more expensive than I was hoping for in a battery of this capacity, and there are certainly other options.
I have about $65 give or take into the battery; the cells are $8 each, $14 for the end caps and bus bars, and about $20 for the BMS (battery management system). The BMS is a MUST on these batteries to keep the charge and discharge parameters in check. This particular BMS is called a dual port, which means it requires a charging connection seperate from the load connection. All of my other batteries after this use a common port BMS, so the charging and useage are done from the same connection.
I think all of my future battery builds for portable radio will be based around this cell. The is a 32650 LiFePO4 cell from Battery Hookup. www.batteryhookup.com The 32 in 32650 is the diameter of the cell in millimeters, and the 65 is the length, or 1.250" x 2.56". This battery is in my FT-891 kit, and can always get me through a POTA activation if I forget the battery box at home. And since I'm awfully forgetful, I has been pressed into service more than once!
In the photo of the two partially assembled batteries above, the 4 cells laying on their side is the finished battery pack pictured to the left. The unfinished pack with a total of 12 cells is put together in a 4S3P configuration, which will be a 15Ah battery when it is completed.
There is an initial expense to building these types of cells into a completed pack, and that is the spot welder used to attach the strips connecting each cell. I have built, and plan on build many many more batteries, so the expense has been well justified.
Looking beyond the spot welder, I have less than $30 into this battery including the BMS, wire and power poles, and heat shrink. As for the 15Ah battery, I will will have about $55 into it. You will not find another 15Ah battery wrapped in blue for that price. Battery Hookup also has these same cells in a 6Ah variety, so I could have built a 6Ah and an 18Ah battery for an additional $3 and $9 each, respectively. I just didn't happen to notice they had them at the time I ordered, although I should have.... grrrr.
I said I had one that would surprise you. Well, here it is. These are surplus 3.75V 5Ah batteries originally used in Ring doorbells as a backup power source! Each cell pack contains a 2.5Ah pouch cell wired in parallel to make a 5Ah cell. Wire three of those in series, and you get a battery with a nominal voltage of 11.25V, fully charged voltage of 12.6V. As an added bonus, each cell pack has it's own BMS and they have been tested to a full discharge at 2 amps. This is perfect for low draw QRP rig like a KX2, and this battery sees a lot of use with my KX2.
Here's the best part..... each cell pack was $1.35. Add in a small bit of wire and a couple power poles, and I have about $5 into this battery! I have used it a lot, because I always seem to leave the KX2's internal battery at home on the charger. This ridiculously inexpensive battery has never failed to perform!
One other place I use these.... we have a gas fireplace in the living room, and one in the basement. These fireplaces have a battery backup system on the igniter so if we loose power, we still have the ability to use the fireplaces for heat. The OEM battery backup system was 2 D-cell batteries in a plastic tray, which would of course leak and corrode themselves to the point they wouldn't work. So I replaced the D-cell packs with one of these on each fireplace. Works perfectly, and I don't have to worry about any leakage, or the batteries being dead when I need them the most.
These are among some of the funkier timed-out medical batteries I have purchased through Battery Hookup. These are four 3.7V Lithium-polymer 10Ah pouch cells wired in series. Fully charged voltage is 16.8V, and nominal voltage is 14.8V. These were $10 each, and since I had a specific use for them in mind, I bought several.
I bought a bunch of LED light strips from Amazon that produce about 600 lumens at about .75 amps. In all of the rooms throughout the house, I have a battery with two LED light strips rubber banded to it. If we loose power (and we do often in the winter), we now have the ability to have light in each room of the house. And since these batteries hold there charge for a very long time, I don't need to worry about them being dead when the time of need comes around. An unlike AA or D batteries, they won't leak anything out either.
The green packs in the far right picture are representative of what I received when I ordered these from Battery Hookup. These are once again, timed out medical packs. They are 14.4V 6.6Ah Li-Ion packs that contain 12 of the 18650 cells rated at 2.2Ah each. At a cost of $7.99 per pack, that breaks down to about 67¢ for each cell, not including my labor. But for me, the labor is my "alone time", my time to decompress. I disassembled each pack, removed the labels (they are damaged in the tear down process), installed new heat shrink labels, and did a complete charge/discharge/charge cycle on all of them. I have hundreds of these individual cells!
The next picture shows three of them in a cheap and simple plastic 3-cell holder from Amazon along with a power pole connector installed. When fully charged, this gives me a 12.6V battery at 2.2Ah that pairs perfectly with my 5 watt QCX-mini 40 meter CW transceiver.
The next picture is of a battery I had just completed before wiring up the BMS, then wrapping with heat shrink. The next picture shows it fully completed and ready for use next to the 5Ah LiFePO4 battery shown earlier. This battery is a 12P4S battery..... in laymen terms that equates to a 14.4V 26.4Ah battery (16.8V fully charged).
* When I say something like 4S3P, that means:
- 4 cells in series, which adds the voltage
- 3 cells in parallel, which adds the capacity (amp hours, or Ah)
The way the cells are arraigned is what determines the final total voltage and amp hour capacity of the battery pack.
I have another battery using these cells that is in the planning stages right now; it will be a 24V battery with the purpose of supplying power to a DC to AC inverter for power out situations to run select small appliances.