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Thread: solar charge controller and amp hour question

  1. #1
    Join Date
    Apr 2008
    Apache Junction, Az

    Default solar charge controller and amp hour question

    I am putting together a solar panel setup. I have a 80 watt Bluesky panel and a Morningstar 300 watt inverter. I am ready to buy the charge controller and battery but have a few questions.
    For charge controllers I have been considering the Bluesky solar boost sb2000 or Morningstar sunsaver MPPT, anyone have any experience with these controllers?
    Now for the battery I am either going to go with a single 12 volt 100 amp hr diehard patinum or a single 12 volt Lifeline 4D AGM 210 amp hour battery. Any other sugesstions as for batteries? I have even considered going with 6 volt batteries as well but they are bulky and heavy.
    The aux. battery will be used to power my fridge and the small inverter will mostly be used for a radio and to charge my laptop and camera batteries maybe a low wattage light. I would assume in the hot summer the fridge will run a lot.
    What will my amp hour useage be?
    Any ideas or suggestion? I have been slowly ordering parts over the last several months and now down to the last bits and I will finally be back home next week so I can get started putting it all together.

  2. #2
    I am using a blue Sky controller, but the 2512i, not the sb2000. It works well.

    Your fridge likely consumes about 3 amps when the compressor is running, but it will likely not run more than 30 out of 60 minutes or a 50% duty cycle, It will probably run about 20 minutes per hour so figure it will consume 1 to 1.5 amps hours per hour.
    Laptops vary pretty greatly in the amount they consume. Mine can draw 100 watts. It depends on the task it is performing and if the battery is fully charged or not. Watching a DVD on mine takes about 6.5 amps, or more than twice what my fridge consumes when the fridge is running.

    If you buy a Laptop DC to DC converter, bypassing the inverter, you will use 10 to 15% less electricity, and not have to listen to the inverter's fan. Google Laptop car adapter. If your laptop consumes less than 80 watts, you can get a cheap universal Model. Look on your power brick and multiply the output volts times the amps. That will give you the watts the laptop is capable of consuming

    Look into LED lighting. Many places sell replacement LED bulbs for incandesent fixtures. LED quality just keeps getting better. Brighter and uses 1/5 to 1/10 the electricity of incandescents. Do not get the cheapos from E bay, they are 10 year old technology.

    Charging smaller batteries is usually under 0.6 of an amp. Some battery chargers do not like Modified sine wave output from cheaper inverters. Monitor them for excessive heat, or get a true/pure Sine wave inverter.

    Ideally you should have 60 to 100 watts of solar per hundred amp hours of battery, so a smaller battery will be happier being regularly charged by the 80 watt of solar. But the bigger battery can go twice as long before it reaches 50%, which you should aim not to go under.

    Having the bigger battery is good, but it might not get fully charged by the solar each day. As long as you charge it fully when you get back it will serve you well. Either plug it into a grid powered charger, or let the solar take a few days to top it off, Just do not store it less than 100% and you're good to go. Recharge it before the next outing, or just leave the solar to do it's thing. The charge controller will not allow overcharging.

    If you go 2 weeks and each day do not allow the battery to reach full charge, it will start performing badly until you can blast it with higher amps for a long while until true 100% State of charge is reached. How much performance it loses depends on the battery, and how far from full it is and for how long.

    Lifelines are excellent batteries, but the DHP's have a good following of happy owners/ renters here.

    The 2 golf cart batteries together weigh no/little more than than the single 4d, and are designed for cycling deeply, and can be had for cheaper if they are flooded, not AGM.

    Hope this helps

  3. #3
    Join Date
    Apr 2008
    Apache Junction, Az
    Yes a lot of great info! I never thought a laptop would use that much power, but I rarely bring it on trips anyway.
    the power inverter I have is a pure sine wave.

    I have been thinking of connecting the second battery to a isolator so it will charge while driving and then the solar panel will maintain the battery while parked. I mostly camp at the lake for 2-3 days without driving anywhere.
    I also had a idea to install a marine battery charger of sorts so I could charge the battery when I get home but don't know if it is really needed. Even though I do have a roof top tent and fridge I am trying to keep this a simple build without a lot of fu fu stuff

  4. #4
    It's always good to have a grid powered battery charger. You pay a premium for the word 'Marine' though. You got a lot of salt Air in AZ?

    They make some fairly compact portable chargers, No need to hardwire/ mount something. Just use an extension cord when you get home if the battery needs a blast. I have 130 watts of solar, but my batteries very much appreciate a 32 amp blast when I can provide it, when they need it. They really like it when My alternator can hit them with 50 amps for any duration, but unfortunately 50 amps from my alternator is too short lived.

    If you want to keep it simple, and be able to alternator charge, bring a pair of thick jumper cables and have a good method of keeping them safely and tightly on both battery's terminals when driving. Good ole manual isolation!

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