This is the sort of job I can put off for YEARS.

You might recall that back in December a neighbor invited me to haul off these four oldish 6-volt batteries.

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I was certain they were no good, and only picked them up to be neighborly. I figured sometime I’d find some salvager who’d be willing to give me a few bucks for them. But they’re Trojan T-105’s, which have a very good rep in solar power systems. And they took a charge just fine, and tested fine, and held their charge fine for, like, months. I really didn’t want to go to the trouble of replacing my two 3-year-old known-good batteries with four maybes, but months passed and I couldn’t find anything wrong with them. Believe me, I tried.

With the weather having turned so beautiful and warm I was just completely out of excuses. It wouldn’t cost anything but some effort and a few new cables to check them out. There was one problem, though…

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When I built my powershed in 2012 I was still working on the “spend no unnecessary money” paradigm, and the powershed was made entirely with scrounged materials. Entirely – even when that turned out to be quite unwise. Every time I walk in there I’m a little surprised the floor hasn’t collapsed, and I would not have bet anything that it would survive doubling the battery weight in that corner.

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So before I could do anything with the batteries I had to pull everything out of the shed – including the old batteries – and replace the floor with plywood that would bear the weight. That took an hour right there – and don’t forget, Joel, to get the plywood cut to size before you completely disable your power system. Okay?

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Then I took the Jeep over to Ian’s place, where I had the new/old batteries stashed. Loaded them up – and damn but deep cycle batteries are heavy – and also cut a piece of surplus plywood to increase the size of the table a little. Dragged the batteries into my powershed, got them set in place…

…and then came the scary part. I am not an electrician. At all. Mostly because I’m afraid of sparky things that shock me.

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But I’m also not an idiot, and as long as you’re careful it’s not rocket science. Also I’ve got this book that has a very simple diagram for how to wire up a series-parallel circuit. :)

So everything’s working. That’s good. Of course I won’t know until this evening – and then recharging the whole thing tomorrow – if I’ve actually improved anything or if I end up putting the old batteries back.

But at least I got a stronger powershed floor out of it, and that needed to be done anyway. Now for lunch, and then I’ve got to put all that crap back where it belongs. Some of it could really use a scrub first.

About Joel

You shouldn't ask these questions of a paranoid recluse, you know.
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13 Responses to This is the sort of job I can put off for YEARS.

  1. coloradohermit says:

    I don’t know what T-105s weigh, but the 12 L-16s we had at the forest house weighed 108 pounds each. That doesn’t sound like a great project for your shoulder. I hope they work out!! I miss a few things about the forest house, but batteries aren’t one of them.

  2. Joel says:

    Are L-16s those big red Rolls Surrette things? Because yeah, those are strictly two people or one person and a stout handtruck. I think the T-105s weigh 65 pounds – which is doable, but I didn’t finish putting the powershed back together this afternoon because I’m exhausted and my shoulder is calling me bad names.

  3. coloradohermit says:

    Our L-16s were Trojan, but yes they are big honkers. They look about the same as yours but are 17″ tall. Hope your shoulder doesn’t call you bad names for very long. Doesn’t this ageing process just suck….

  4. Ben says:

    What are your plans for your original two batteries?

  5. Joel says:

    Nothing, until I decide whether I’ve done more good than harm. I’ve treated those batteries gently, they should have 3-4 more years left in them and I’m reluctant to abandon them when I really don’t trust these that I just installed.

  6. Malatrope says:

    Don’t abandon the old ones, but don’t let them die from just sitting, either. Acquire and use a trickle charger (“battery keeper”), or dedicate one solar panel to keeping them up to charge.

    A year of sitting, discharged, will destroy them.

  7. Ben says:

    Joel, is there any reason why you can’t have three strings? Yes, I know all of your batteries are supposed to be matched, but I have harmlessly ignored that rule many times. (On the other hand, one cell going bad can effectively drain them all, but you seem to watch your voltage pretty close, so you would detect that in time to avoid damage to your remaining batteries.)

  8. Joel says:

    Ben, the thought has occurred to me. It’s against the rules, but I’m a rebel and I’m not sure there’s enough difference between the Interstate batteries and the Trojans to do any harm.

    On the other hand I’m also not sure I have enough panels for that much battery. This is one of those situations where it would be nice to be able to do the math, instead of just sorting out what works empirically. But I don’t even have a way of measuring the panel wattage, so I’m just going to see how this goes before I mess with it more.

    Tell you what, though, it’s 8:30 as I write this and the voltage is certainly holding a lot more firmly than I’m used to. I’m at 12.5 with the computer on, which is not normal.

  9. Ben says:

    To me the math seems easy, you have three times the panels you had before, so you should be able to support three times the battery.

    (But this is the Internet, where anybody can play at being an “expert”. You, on the other hand, must deal with the actual hardware, and live with the actual outcome.)

  10. Joel says:

    It ain’t the size or number of the panels, it’s the wattage. Those four new/old panels are *old* and unevenly deteriorated. I tripled the number of panels but didn’t do more than (and maybe not quite as much as) double the generating capacity. And there may be other pitfalls I haven’t stumbled into … yet. I’m learning this business empirically, which makes for a slow, shallow and occasionally painful learning curve.

  11. Goober says:

    Do not hook the interstates back up until you’re certain these new batteries are good. If they’re not they’ll drag the interstates down with them and you won’t have any batteries at all.

  12. Norm says:

    This may be completely unfeasible, but is there a way to run two separate (and different) battery banks in “disconnected” parallel ? Devote panel output to Bank 1 until you get float, then shift output to Bank 2. That – might – keep both banks charged, or one fully charged and one partially, which would both test the batteries and provide some degree of backup.

  13. Cosmostrator says:

    Don’t you have one charge controller for each bank of panels? You could divide your system into two, and have a backup for low power days, or accidents when lights or inverters get left on. Or you could have one system for 120 volt and one hooked to the 12 volt system.

To the stake with the heretic!