Some basic questions

I have a rather simple solar hookup in my toolshed that I use mainly for recharging drill batteries and such. As you will be able to tell, I'm a newcomer to this topic. I have 3 15 watt solar panels that I bought from Harbor Freight, a 12 volt deep cycle dry battery that I got on ebay, a 7 amp voltage controller that i got from Northern Tool and a 45 watt power inverter. My technique is that I connect the solar panels to the battery (through the controller of course) with alligator clamps until the controller tells me that the battery is fully charged. Then, I disconnect the leads from the solar panel and substitute leads to the power inverter, then plug in the drill charger to the inverter. The system seems to work ok as is, but I'm thinking that all that connecting and disconnecting can't be good. Anyone have any comments or suggestions?


  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
    Re: Some basic questions

    I had a big post going--but trashed it by accident...

    Short answer, first the power into your battery system (from solar panels) must be (slightly greater) than the power you require out of the system (for charging your tools).

    Also, I had a warning about disconnecting your battery terminals--don't get in a habit of doing this... You should permanently wire your devices so as to prevent arcs and sparks on top of the battery--Hydrogen explosions and sulfuric acid burns are not fun.

    Second, you will probably need a Sine Wave type inverter for your chargers--the standard cheap square wave inverters are known to damage many of these types of chargers.

    Wind Sun has quite a few good FAQ's sprinkled around their store's site. Here are a few places to read through.

    Charge Controllers
    (look for LVD-low voltage disconnect options).
    Inverters (look at Exeltech--good low price sine wave inverter).
    Batteries (read Battery FAQ)

    You will need to monitor your battery's state of charge--drawing it down to less than 50% of charge, or storing for more than a few days at less than 80-90% of charge can drop years of life off of your battey.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Some basic questions

    It's fine (actually adviseable) to leave solar PV panels connected while charging. It will lessen the draw off the battery by a little bit, and extend battery life. Be sure to switch the inverter off when not needed, it's standby draw is still likely above what your 3 panels can supply.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Some basic questions

    i'll first comment that if that inverter is modified sinewave (i'd bet the house it is) that it's a wonder that none of the chargers blew out on you as many dislike modsine. know that in the future you could blowout any new tools if they are sensitive to this type of inverter and you may never know until it happens as i'll bet even the company that makes the tool wouldn't know what you're talking about so this makes researching this difficult ahead of time.
    now as to your other dilema, i would think a switch is in order like: ,but there isn't any reason i can think of that would necessitate them being switched at all. why can't you just connect them together allowing both the main battery and the small tool rechargables to charge similtaneously? you could still seperate the tool batteries once in a while to insure the main battery does receive a full charge.
    it would also be a good idea to fuse the controller outputs to the battery and fuse the outputs from the battery to the inverter if there is not one there already. some may even suggest fusing the input to the controller from the pvs as you never know.