Charge controller for 24v 120w

davidwillis
davidwillis Solar Expert Posts: 104 ✭✭
in Off Grid Solar & Battery Systems #1
I have a small portable solar panel I use to charge two 12v batteries. The are connected in series, so it is 24v. I would like to be able to have the charge controler mounted on the solar panel and just clip the wires to the batteries to charge. However every charge controller I look at (the small cheap ones) say I need to connect the battery first, then the solar panels. This means I have to take dissconnect the wires to the solar panel, connect the battery, then hook the panels back in. The problem is that I keep forgetting to do this (at least I think that is what happened)... anyway I keep burning up the charge controllers.

Is there one that can just be connected and work even if the order is not correct? Or at least not destroy the controller when I forget?

Thanks
David
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Comments

  • boomadge
    boomadge Solar Expert Posts: 25 ✭✭
    #2
    you could always place a 15 amp inline breaker on the + side of panel lead before it gets to the CC. Doubles as protection and a way to kill the power..
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
    ? don't use a charge controller and just clip panels to the batteries ? All the decent charge controllers have "brains" and need proper treatment. A few more expensive replacements and you should learn.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    It is a problem... There was one or two charge controllers that said to connect the panels first.

    The problem is that many 12/24 volt charge controllers "set" their operating voltage from the connected battery. With the panels connected first, it is possible for leakage current to set the "wrong" voltage. But given that your batteries are 24 volts--I am not quite sure why the controller is frying.

    Another possibility is charge controllers expect around 30 volts maximum on the battery output. Again, leakage current from the panels can get you to 42 volts or more (Voc-cold). It is also possible that is causing the controller's battery side to "fry". Remember, for electronics, over voltage only requires a few micro or milliamps for an over voltage fault to damage the silicon devices (and capacitors, etc.).

    Placing a Panel Disconnect is probably the "right solution"--You can do what we did with aircraft for remove before flight stuff (control locks, etc.)--When the battery is disconnected you move an orange flag/streamer from the battery connector to the disconnect switch (or something similar) so you get in the habit of turning off the panel before disconnecting the battery.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #5
    Thanks. I guess I will just have to pay attention to what I am doing and make sure I connect everything in the correct order. I did find the Morningstar ss-20L-24v charger that is only 24v, but even with it it says to hook the battery first.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #6
    I believe ASC (Specialty Concepts) charge controllers don't require a special order, but are voltage specific, While not cheap they aren't too pricey and do come with a 10 year warranty.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #7
    Thanks. The ASC charge controller may be what I am looking for. It is about 4 times as much as the cheap ones I have been blowing, but if it will hold up, and allow me to just connect the batteries, it is worth it.
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