New Battery Bank Project

Yesterday I started running tests on my ancient Optima Yellow Top, because I suspected that after 11 years and various torture through it’s lifetime, it might not be still up to its original factory spec.  My concerns turned out to be valid.  Putting a 20-watt load on the battery sent its voltage down to under 12v, which pretty much means it’s shot.

So I started looking around for a replacement.  I found on Amazon and other retailers that a deep cycle battery with somewhere between 50 and 100 amp hours (at 12v), was going to cost me somewhere in the neighborhood of $1.60 per amp-hour or more.  I figured that since my battery needs weren’t a precise grouping (size) or even capacity, maybe I could get something either free or cheap on craigslist?

I did find a listing of someone that had 40 batteries that were pulled from UPS (uninterruptible power supply) systems that were 3 years old.  They supposedly had a 32 amp-hour capacity each (at 12v), and they weighed 32 pounds each.  He was looking for buyers that would buy at least 10 at time.  If I wired them up in parallel, that’s a theoretical 320 amp hours of capacity, which would be way more than what I need, but it would also give me tons of “breathing room” if the solar panel system doesn’t charge as much as I expect or I use a bit more power than planned.

So I contacted him, and things went smoothly.  This morning we met and I got 10 used batteries and he got $150.  That’s an effective rate of $0.47 per amp-hour, which is way better than my previous best of $1.60.

So here’s what they looked like when they just got home.  The white spots are bits of fresh snow as they were sitting in the back of my truck for the ride home, and we got about 6″ of snow today.

Here I am in the middle of wiring them all up together.  Yes, I realize I’m going to need to disconnect all the wiring in order to load them into the trailer, but I still wanted to do some bench testing and this looked like a fun project.  Hey, to me it’s fun spending a couple hours obtaining the necessary supplies (1/4″ ring terminals and 50′ of 10 gauge wire) and then cutting/stripping/crimping everything to fit.

In the upper left corner of the image above isn’t a TV, it’s a radiant heater.  It’s not meant for use in the garage (doesn’t have the necessary BTU rating), but I figured I’d try it anyways.  Yep, it doesn’t have the necessary BTUs.  It barely made a dent in the temperature in the garage.

Here’s a nice shot of all the batteries wired up together, and I have a battery tender on the whole system.  I ran some quick tests using an inverter and some incandescent lights, which can simulate a relatively high load.  They did OK, nothing spectacular.  I’m a little concerned at how much their voltage dips when a load of 60 watts is placed on them, but I am pleased that at least the voltage does not continue dropping dramatically as the load is left in place for a while.

In my current “camping” build of the trailer for the AZ trip, my highest single load item is the water pump, which can apparently pull 8 amps (96 watts) briefly when at full pressure.  Most of the time when the water pump is running, it’s more in the 4-5 amp range (48-60 watts).  The plan right now is to only use the pump when showering, so that’s a couple minutes a day.  Not a big deal there.

The other load which will be drawing significant power is my laptop.  When it’s charged and only drawing enough power to keep it self running, it’s generally in the 16-20 watt range, unless I ask the CPU to actually do something interesting.  If I’m charging the laptop and possibly working on it as well, it can go up to 85 watts, and stay there for a significant time, so that’s something that will need to be monitored.

There will be other small loads as well: iPhone, Verizon JetPack, LED lights, etc.  They don’t add up to much of anything.

With 320 amp hours of capacity (and of course accounting for the fact that only 50% can be used in AGM batteries before damage will occur), I’m calculating that I should be able to last 12 days without any solar power coming in.  I’m pretty sure that when in Arizona, it’d be really tough to go 12 days without any sun.

BTW, the featured image today was taken while driving the truck on my way home from one of the hardware store runs.  Winter has finally come into full force in Minnesota.