Hot swapping batteries

haroldina
haroldina Registered Users Posts: 3
Hi, there. I'm the equipment manager for an autocross club and I've been tasked with coming up with a solution for keeping some batteries charged in a way that doesn't require people to take them home after an event. I'm completely new to PV systems, so I'm hoping someone here can shed some light on this for me.

I've got a 12V SLA I need to keep charged for a wireless display and I'm trying to figure out how to do that with a solar system. The battery will need to be unplugged from the charger to place it with the display and I need to set it up so somebody can just walk up to it and unplug the battery to place it since it's for a club with about 200 members and it's unlikely we'll be able to train everybody to disconnect panels before pulling the battery.

While I'm installing that system, I'd also like to have another permanently-mounted battery to run some lights in the trailer for a couple hours until the sun comes up since we set up events pretty early in the morning. Is there a dual-channel controller that could handle 2 15Ah batteries and also allow us to hot-plug one of them? I haven't been able to figure out how that would be listed in the specs on any of the ones I've seen.

Thanks,
 Harold

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    The problem with hot plugging batteries with Solar Charge controllers is that most charge controllers use the battery as their power source (run the cpu, keep memory/history, etc.). So just pulling the battery with the solar panel powered up (under sun) can "confuse" the charge controller (typically, you turn off the solar array first, then disconnect/connect the battery, finally turning the array back on again).

    But, you can get a DC to DC battery charger (solar system charges a main battery bank, then the DC converters charge your individual batteries).

    Anyway, 15 AH @ 12 volt battery is not very large--But it would be helpful to understand how many batteries you want to charge, how many AH/WH per day, how many days for display (i.e., 2 days to 50% discharge, 4 days to recharge, where will the system be used--hours of sun per day, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • haroldina
    haroldina Registered Users Posts: 3
    Ideally, I'd have one battery permanently mounted and attached to the charger just to run some lighting that would be used for ~2 hours two days in a week at peak usage. I haven't gotten into what kind of lighting I'd be using, so I don't really know what the draw would be on that one. 

    The battery for the display has run the display for 4 events without being charged before, but I've never checked the SOC on it after an event. Our standard practice used to be to have somebody charge it after every event, including between days on a 2-event weekend.

    Between events, the trailer will be parked where the panels would have southern exposure and the batteries would only be in the trailer between late March and late October. Over the Winter, they'll be stored inside.

    It sounds like a DC-DC charger is what I'm looking for on the display battery.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    One thing to watch out for is trying to parallel a fully charged and an uncharged battery on the same charger output. The voltages of the two batteries will be different and the current flowing from the charged battery into the discharged battery will be far greater than your design charging current. This can damage wiring and the batteries themselves.

    SMA SB 3000, old BP panels.
  • haroldina
    haroldina Registered Users Posts: 3
    Yeah, I was planning on having the permanent-mount and removable batteries on separate circuits, anyway.