There are a ton of battery box builds explained on ham radio blogs. But I recently came into a source of “free to me” recycled batteries. There’s nothing like getting something for free to motivate you to spend more money. So there’s also that!
This box build is based around three (3) 12ah AGM batteries wired in parallel to yield a 36ah bank at 12vdc. They never reach that, of course, but that’s the base. I used a resin Ammo Can picked up at a local Academy Sports but they are branded as Wise Outdoors Tall Utility Dry Box on Amazon ($23). There’s a Bill of Materials (BOM) link here.
I added a Powerwerx dual port power output, offering 12v via two sets of Power Poles. An inexpensive LCD Digital Volt-Watt-Current Power Meter with a blue back-lighting for reading in the dark. The plus power supply was fed using 12AWG Silicone Wire with two 30A blade fuses wired inline to the Power Pole port. A master SPST switch was inserted to shut down the power. I chose one with a waterproof “hood” on the toggle handle to lessen moisture getting into the switch. Silicon wire helps with any heat issues for current but I used the next larger AWG gauge for the current involved in the system.
To charge the batteries, including when they’re in use and being discharged, I included an inexpensive Solar Charge Controller. I purchased this item via eBay and it was listed as an MPPT type (CMTP02-20A Solar Charge Controller 12V 24V Controller 20A Solar Regulator). However, later research showed that, indeed, it is a PWM design (see http://diyprojects.eu/cmtp02-disassembling-solar-charge-controller/). Hmm. Given the service cycle for a portable battery bank like this, I’m not sure that the Maximum Power Point Tracking Solar Charge Controllers (MPPT) greater efficiency would make that much of a different over the Pulse Width Modulation (PWM) variety. In any case, we will find out!
This was my first battery bank to build. The performance will tell how it turned out. I built this for my friend, Mike N5DU, and he will put it through some paces very soon. The weight of this box it not trivial but it’s easy to carry short distances, like from a truck or auto to a picnic table or cabin. I’m not terribly confident in the solar charge controller after I learned that it was mislabled as an MPPT design. However, it’s built into a resin tray just under the lockable lid. The form factor that it presents is very similar to better known models. So, I can change the charge controller out fairly easily should that need to happen.
For now, it’s done. I’m off to designing a larger four (4) battery bank consisting of 24ah Panasonic AGMs. It will be in a DeWalt rolling tool chest that says it can hold 100 lbs of tools. We will see…