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Home Forums Technical Discussion Charge Controller Size? – Help Please

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    I currently have 18W solar panel for charging 72Ah leisure battery as part of my offgrid living. I am intending to buy either 1 or 2 130W panels giving me either 148W or 278W.

    Can someone recommend the size of a charge controller for:

    a) 148W, and

    b) 278W



    Nick Rosen

    I am just starting my first solar run with two 85 wpa (>170 wpa) modules,

    and I am told a 20 amp charger will do nicely for both

    of them (I am using 2 130 ah each gel batteries – I have a generator backup

    and an additional charger for a bad weather scenario.

    All in all, my equipment is on the generous side

    (what else do you NEED to run but a medium-sized computer system?)

    – a 10 amp solar charger might do, too.

    Remember that batteries do not like to be charged rapidly

    but slowly, and that they do not like to be discharged below about

    80 percent (even good ones, never mind car batteries).

    I would have used a 170 wpa panel and one 250 ah battery,

    but these items are bulky and heavy and I thought it best

    to get items that one person alonecan still handle – one of

    my batteries weighs about 40 kilos, but the bigger one

    would have been more than 75 :)

    Remember that the batteries should always be the strongest part

    of your setup (but if I had gotten the batteries that would have lastet me a dozen years, I would have had to lay out about 3000 Euros for that alone…)

    so I chose the cheaper gel type, they should last about 5 years maybe,

    constantly but cautiously used.

    ccna test

    The main function of a regulator or controller is to keep your leisure batteries fully charged by regulating the flow of electricity to the battery without allowing overcharging of the battery. They also prevent leisure battery current flowing back from the battery to connected items at night. Without overcharge protection the life expectancy of batteries are reduced. Solar Charge Controllers vary in type from simple controllers to more sophisticated controllers that utilize pulse width modulation (PWM) or maximum power point tracking (MPPT) to assure the battery is being and kept fully charged. These more sophisticated controllers use special monitoring software, to control charging by monitoring in real time the state of charge.

    Solar charge controllers or regulators are recommend to avoid battery damage from overcharging or deep discharge. The Steca range of regulators are designed for simplicity of installation and can be used with GEL, AGM (absorbed glass matt), sealed and non-sealed lead acid batteries. They should be protected from the weather and located within as near as possible to the battery bank. We will be offering the 100% waterproof Steca range of charge controllers in eary 2008 for any customers using solar solutions based on rivers, or waterways ccnp training. All models featured below include a Low Voltage Disconnect (LVD) facility, to ensure batteries do not get over-discharged.

    ccie training | ccsp


    I think a typo crept in because you said “All models featured below include a Low Voltage Disconnect (LVD) facility, to ensure batteries do not get over-discharged” How does low voltage disconnect when the problem is high voltage from over charging?


    You had better do some reading up on alternative energy systems. That is a very large amount of power in PV and would require several large charge controllers. The wind generators have their own at their site.

    They would need a large battery bank system(like over 30 L16s or equivalent), and a shunt to heat water with excess power.

    Normally that much power goes to 24 or 48VDC systems. The panels are close enough in peak voltage, but not totally compatible in all ways with some charge controllers. I would give Xantrex a call.


    There are several better choices in companies than Xantrex. In fact a manufacturer is not as good a source as a multi brand distributor for giving advice. Reason they will always attempt own company brand to your situation rather than giving you the best advice then fit a product to the application.

    South west Wind Products is one such example who have given me good advicce in the past. Xantrex has had several turn overs recently wherin their best people went elsewhere like Outback and Magnum. Independent distributors are your best bet for more impartial advice in both wind and solar power applications.


    I agree with elnav. Don’t just depend on one outfit for advice. Real Goods could help. Outback has the best deals on outstanding charge controllers like this one;

    However, I have found that you should oversize your charge controller by 30% or more. So, even though, technically you could get by with two, you would really need three. I had a 30 amp charge control (BZ) that burned out with 18 amps coming in. Luckily I caught it and covered the panels in time to prevent shorts. I replaced it with a C40.


    A lot of Charge controller sites will have a calculator to help you.  I use Midnight Solar Product.  here is there link for there calculator  It will help you know how to string up your panels.  If series, parallel or series/parallel.  With my system of 4 Astronergy 250watt 24volt panels, 4 Surr 6v, 400 Ah S530 (9600wh), MSC 200, Magnum MM-1524AE 1500 watt inv/chr MS, Cotek SK series 1000w 24v P Sine-wave Inverter and the electrical boxes and fuses.   and future add is 2 more panels  I run 2 strings of 2 in parallel to get my voltage and amps up so I should see 32 peak Amps, or about 8% rate on the 400 Amp hour bank. That’s a nice ‘comfortable’ rate. (The array would be about Vmp 60, Imp 16.).

    For wind power you must have the dump load and I would like to use a normal CC but I have found that at Missouri Wind and solar has a good all in one CC for like 279.00 that does 10000 watts and 440 amps made for wind and solar but I will use it for my wind and growth on my solar if required.  link to it

    I hope this information helps you in your decision making.  Or at least gives you some good reading.

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