Do you go portable with amateur radio? Perhaps you have a favorite QRP rig like the Yaesu FT-817/818, or a 100W like the FT-891. What if you don't have access to AC mains? Your power supply becomes useless. What if you don't even have a power supply or you're on a budget? Are you sick of your noisy, awful switching power supply? Can you not afford a large and bulky linear PSU?
Well fear not, because I have the solution for you! What if I told you that for well under $100, you can build a portable, battery-powered power supply from an ammo can? Yes that's right - for under $100, you too can make an almost watertight battery pack that will last you in the field for hours! Did I mention that it comes with a USB port for your phone to charge too???
This is a real concept and I'm making it because I absolutely hate my switching power supply noise (I'm too lazy to put chokes and toroids on it. Chances are it won't work anyways). But that's okay, because today I'll walk you step by step on how to make your own.
Most amateur radio operators have at least one portable power supply. They use it for EMCOMMs, ARES, or even mobile and portable operations where powering a conventional power supply isn't available. SOTA/POTA workers use these too. For them, portable power packs with all the bells and whistles can cost up to $300, and that's for a low-amperage model! Here's the worst part - many of these aren't even waterproof!
This is where the saying "keep your ammo dry" couldn't be any more true. A power supply is a radio's ammunition. It can run out and it "loads" the radio in the form of volts, amps, and watts. The Hammo Can (classic, isn't it?) is basically a battery in a box, but where it differs is that it's almost watertight, stupidly easy to make, and provides protection from the elements if sealed properly. If you're going out to operate and it begins to rain, the battery and your equipment needs to remain dry. If made the right way, the extra leftover space can be used to store cables, interfaces, or even portable QRP radios themselves!
1. Choose the right battery
Battery voltage for amateur radio applications will almost always run at a constant 13.8VDC, though 12V can be used. The most important thing to look out for is amperage ratings. Refer to your owner's manuals for ratings on your equipment. You'll also want to add a USB hub on this thing too since you'll more than likely be taking your phone with you. You have ham radio apps on your phone, right? Keep in mind if you do wire a USB hub, it will draw anywhere from 1A up to 3A of power. A dual port will draw twice those values.
For me, a 15Ah battery is perfect. My TS-660 only needs 4A draw on transmit and only 1A on receive. In addition, my FT-2200 draws 10 - 12Ah on a full 50W transmission.
Batteries are sold in a wide variety of ranges but make sure to use what is most appropriate for your application. You'll also want to ensure that a charger can be bought or supplied with your battery.
2. Buy the other necessary components
Some other components you'll need include
- An ammo box (Harbor Freight sells them for around $3 or $4!)
- Binding posts or Anderson Power Poles
- A USB hub w/ a voltmeter (the two can be separate, but you will need more wire)
- about 6 ft of 12 AWG wire (buy some extra in case you make a mistake, right?)
- Butt connectors
- I/O switch
- Inline fuse or circuit breaker
These components can be easily bought at any store and are readily available online. Most stores sell wire by the foot. As I mentioned before, about 5 or 6 feet will suffice and you'll have some left over if you make a mistake.
Be sure you color code your wires too. Don't use 2 black wires for positive and negative, or a white wire for negative and the black for positive. You'll thank yourself later if you need to maintenance or repair the power supply, regardless of its ease in circuitry.
Circuit protection is also mandatory in this application. A fuse works great and is the cheaper option, but make sure you purchase a fuse with the same amperage rating as your battery. A 15Ah battery requires a 15A fuse. If an application tries to overdraw current (>15A), the fuse will blow and you'll need to replace it. This could help diagnose a fault in the application that you use. A circuit breaker works equally fine, but these are more costlier. The perk with a breaker is that most are made to automatically reset after a fault.
3. Drill holes and add parts
Once you've bought your parts, it's time to get to work. Start by drawing a rough diagram of where you want to place your parts. From there, use a step bit to drill your holes. Make sure the ports fit perfectly and snugly. For sealant, I'd recommend putty or a clear silicone caulking.
Next, you'll need to place the battery in the box. Orient the battery so it won't interfere with any surrounding objects, including accessory ports. If you've done everything correct, you should have some space left over to store items.
To protect the battery and separate it from your stored items, you can add some packaging foam around it on the bottom and top.
To test the Hammo Can out, plug in your radio using the binding posts or Power Poles and power it on. The USB voltmeter should read a bit over 12V. If it's below or at 12V, charge the battery for a while. It's possible that the battery discharged during transit. An ammeter could be added to measure current draw, but I'll leave that up to you.
Congratulations! In just a few easy steps, you've made a useful and important ham radio essential. To make this even more off-grid, you could add a solar panel for recharging the battery. This will make it even more effective should the power grid ever fail. It's very handy when it comes to an emergency situation where communication is crucial.
Here is a simple schematic diagram to illustrate how everything should fit together. More modules can be added by connecting them to the binding posts or by making a centralized power distribution module. Again, make sure you don't exceed amperage ratings:
I'm sure that anyone can make this, and it can be done in 2 hours or even an afternoon. It's simple, effective, and portable in case of a bug out or emergency situation.
One other point of further clarification. Many people aren't sure what Ah means. An ampere-hour (Ah) refers to how many amps a battery can put out in one hour before it potentially loses charge. It's important to know this because an incorrect, low amperage rating will provide poor results. You'll blow fuses or breakers often and you will ruin the battery completely.
As mentioned in the construction, I'd pad the battery's top and bottom with packing foam. This will ensure that the battery will not sustain serious damage if it is dropped. In addition to the battery, try to use something lightweight. You can use the inexpensive, lead-acid types, but these tend to weigh heavier and discharge in a linear fashion. As a result, these tend to die faster. Lithium-type batteries are much more lightweight and can hold charge, but these tend to be priced almost 2 to 3 times as much as lead-type.
As a postscript, I'd like to give a few suggestions. I think these would be good as a door prize for your radio club or other amateur radio gathering, a great and easy gift for a birthday, etc. You also don't have to use these for amateur radio - batteries in boxes have so many other uses too!
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