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  • Re: best approach to string 12 2 volts agm batteries

    Then there is no choice. With 12x2v cells, you will have a single series string of ~700ah @ 24v. There is no parallel option.
  • Re: South Dakota experiences

    I could make a pretty good case for trackers if I ever did grid-tie solar at my city place.

    In spring/summer, there's a pretty wide azimuth range at my lat. Although pv may be cheaper these days, real estate with viable solar certainly isn't, so more panels isn't a realistic possibility.
  • Re: Advice on buying a good used laptop?

    I just put debian linux on an old Vista laptop in a dual boot config. The windows filesystem is easily accessed from linux, and I can still boot vista if I really want to run a windows application. I also did a vista desktop, but added an SSD as the boot drive. Boy, does that ever make a difference.

    I'm also running Raspbian linux on a raspberry pi. It runs off a micro-sd card in a board about the size of a credit card. Even with ethernet, wifi, hdmi, and 4 usb ports, it's about the size of a pack of cards and costs <$50. Draws ~100 milliamp at 5v (plus whatever for monitor), and does pretty much everything the laptop can. I haven't tried youtube videos on it, but I suspect they'd run ok. Video intensive games maybe not so much.

    My first computer had 640K ram and a 10MB hard drive. Oddly enough, I still had it 15yrs later, and needed it to handle a job in which source data had been stored on 5.25" floppies, and nothing else could read them. With stuff in the cloud now, maybe it won't be an issue, but I still wonder if we'll be trying to find a way to access stuff stored today in 15 years from now.
  • Re: Mistake in Startup Construction Project

    There's probably not much you can do about shading other than plan for some loss of output. I have a treed ridge to the south that means basically no sun from early Dec to early Jan., so had to install a couple of winter float arrays to maintain batteries when I'm away, and have to run a generator if I'm there.

    Likewise, you can't change the weather. We've had weeks of temps <0°F, which is pretty normal for this time of year here. DC shouldn't be nearly as extreme, so you may be able to get away with charging cold. The problem is apparently lithium plating of anodes charging cold, which is permanent damage. The battery should generate a bit of heat when charging, which may mitigate the issue to some degree. Locating the battery out of the wind, or even insulating it may help.

    Lead acid can be charged at much colder temps, and won't freeze until very cold (-70ish) fully charged. In this application though, I'd be concerned that a partly discharged battery might sit overnight in temps cold enough to freeze it in the discharged state. Charging a frozen lead acid battery is potentially dangerous.
  • Re: Mistake in Startup Construction Project

    > @westbranch said:
    > I see one major calculation error, you did not use  the standard ,  50%,   derating for  the amount of power you can draw from the battery. Going below is the fastest way of killing any battery. 

    Being a LifePO4 battery, the charge/discharge profile is a bit different, generally kept between ~10% and ~90% is recommended, vs ~50 to 100% for lead acid. Lithiums are apparently happiest sitting in a 50% or so SOC, whereas a LA battery won't be happy at all sitting at 50% for long periods.

    One possible issue with using lithium in this application though is they don't like being charged in freezing temps. Discharging is okay, but they should be warmed to 0°C to charge. The battery may have self-protection to prevent low temp charging, or possibly even some sort of internal preheat, which may be a factor in current performance issues?