Ammo Box PSU


Sometimes you need a power supply that can be thrown into the back of a car and taken into the field. [BadWolf] didn’t want to take his bench supply, so he whipped up this very portable power supply made from a computer PSU. To ruggedize his build a little, he put it in a 50 caliber ammo can making it more than able to handle the roughest field work.

While not a proper adjustable power supply, this ammo can is more than capable of delivering a whole lot of current in a number of different voltages. There are a few bells and whistles – a ‘plugged in’ and ‘on’ light, as well as a few very cool looking toggle switches that are sure to arouse the suspicions of unsuspecting bystanders.

[BadWolf] kept all the safety features built-in to the computer PSU, so this ammo box power supply is still protected from short circuits, and over-current, making it much safer than its appearance belies. It’s also a great example of what can be done if you don’t have a proper bench supply, so we’ve got to tip our hat to [BadWolf] for that.

30 thoughts on “Ammo Box PSU

  1. If he had put all the switches and ports etc. under the lid, it would have been much more rugged – dustproof and fiarly waterproof. I thought that was the point of using ammo boxes.

    1. FWIW: This is what my “ammo box” power supplies look like– one AC powered, one battery powered for field use. They were fabricated as accessories for an old army radio.

      Note that when the lid is replaced and closed, the package is airtight. You can just about run over these thing with a small car. You can throw them into a swimming pool and no water leaks in (I’ve tried it.) Since nothing is exposed, nothing can get hurt.

      In each case, the chassis easily slides in and out of the can for service. The handles on the face of the control panels prevent the chassis from sliding back and forth inside of the can, and they provide spacing to protect the switches and connectors from damage.

    1. Actually, it is a 50 Caliber ammo can. It just happened to be used to ship 5.56mm ammo. The military only uses a few different sizes of ammo cans to ship all their different munitions. This one is indeed a 50 Caliber size can.

  2. I’d always thought it was a bad idea to use a switching power supply for a bench supply. Switchers are designed to be used with a defined current use. If you go much outside the design specs (too low) then you’ll burn up your output transistors since they’ll sink most of the current.

    1. I once tried using a PC power supply to run some high current PWM application. It blew up after a few hours of use. On the other hand, I’ve used commercial, general purpose single voltage switching power supplies to do the same, and they’re still working fine. I’m guessing PC power supplies are designed with the specific load of a PC in mind.

  3. I only have two.5 criticisms of this otherwise extremely cool project as well as a story of my own ammo box build:

    1) None of the components used on the exterior are designed for the same hard use environment that the ammo box is and will likely get broken or sheared off completely if simply thrown anywhere.
    I would look to a marine supply place as an easy source of weatherproof hard-wearing external componentry along with the use of simple guards.
    I’ve used drawer pull handles on either side of more fragile externally mounted stuff in the past to act as guards to great effect.

    1a) RCA connectors are NOT my first choice for anything other than audio, and to be frank I wish I could do without them even for audio applications based on past experience.
    Almost any other rugged polarized connector is better for power supply use.

    2) I don’t see any extra fuses on the outputs or additional protection added to take into account the adverse situations/environments one might expect to use this device in.
    This is a great application for circuit breaker switches, in that you get protection without getting stuck without a replacement fuse, although admittedly there is lots of room in that case for a stash of spares.

    Those things considered it’s a very cool project!
    The case certainly has room to add future refinements and is tough as nails.
    I think everyone who hacks hardware wants to take on building some ultra hard-core…thing…using an ammo box at some point.

    I built something kinda-sorta like this years ago (still in service today), but made everything to go inside the ammo box.
    Just open the top to access everything.

    My version is an uninterruptable 12VDC supply for amateur radio use and consists of a small 12 volt, 7-amp switching power supply, a fully automatic battery charger, a 12v 7ah SLA battery and a relay as a transfer switch with circuit breaker switches controlling everything.
    When plugged in to the AC mains the battery is kept automatically maintained by the battery charger while the power supply provides 12volt output for use with relatively low power two-way handheld amateur radios or anything else requiring 12 volts at just under 7 amps.
    If used in the field away from AC power or if AC fails, 12V output is automatically switched over and provided by the battery.
    I even managed to design in cord storage.

    Mine was designed so that the ammo box takes the brunt of abuse when getting moved around, with controls and connectors kept safely inside the case.
    My configuration isn’t as convenient for field use, and requires a very short set up time, but it has kept everything working as good as the day I built it.
    The advantage of this project’s design is that everything is accessible and ready to go, with the trade off being that the connectors and controls are put in harm’s way.

  4. Meh. RCA connectors are good for 2A @ 34V, and don’t short out when you plug them in. I use them for power all the time. Around our house you always check to see what the other end of something is connected to before you plug it in. Coffee table LED lights? RCA. Computer speaker power supply? RCA. Hacked PSU? RCA.

    Do you people even bother checking a goddam datasheet before you whine? Damn.

    1. LM317 circuits aren’t hard but a bypass LM723 is nicer. Here is one I built with adjustable voltage, and current.

      As the URL suggests it outputs a fair amount of power too. Sorry, I didn’t build it into an ammo box. The box I made for the transformer (the light tan colored box) is pretty rugged though.

      I didn’t cover what is inside there, but here is a peek in it:

      I custom made that barrier strip to handle all of the wires coming out of the transformer (salvaged out of a PDP 11/34).

      Although if LM317 is really your thing I got you covered here:

      Now there is a crappy case!

    1. RCAs have limited current capability. The shield connector can be prone to making intermittent contact. They don’t lock into place, meaning it’s easy to partially pull them out, disconnecting the shield while leaving the center part connected. It’s very hard to tell, just by looking, when this has happened. They’re not commonly used for power, which means custom adapters for almost everything.

      If you need a coaxial signal connector, BNC is widely available and superior to RCA in every aspect I can think of. They positively lock in place. But they’re still not commonly used for power, and they’re not for really high current. They’re primarily designed for RF signalling, but work very well for audio, as well.

      For power, i’d prefer 5-way binding posts, or plain banana jacks on 0.75″ centers. I also like Anderson Power Poles, especially for 12V power connections. Any of these options are secure, reliable, and capable of high current. They’re also widely used for power, meaning that if you buy another power supply, you can continue to use your same cables to power all your gadgets.

  5. I like, the only thing I would have done differently, I would have probably painted the side with the controls and connectors a solid color. It gets busy with labels, connectors and the original stenciling and any confusion here could be potentially disastrous. Otherwise, great job.

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