solar battery charger/generator

krisman
krisman Solar Expert Posts: 57 ✭✭✭✭
I have a solar panel connected to a solar charger, connected to a marine battery, connected to a 750 watt inverter. i need to put it all underneath the floor. but i will have to keep the inverter in the "on" position at all times with an extension cord running from the inverter to the top of the floor, to keep from constantly running back and forth downstairs. i was needing some advice, on if i could rig up something to where i could turn the inverter off from upstairs like a kill switch or something, to keep the inverter from running my battery down.

Comments

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: solar battery charger/generator

    I hope you are not putting the Solar panel under the floor!

    Seriously,

    A switch controlled relay should be able to figured out fairly easily. On the other hand, the Mornigstar TS 300 (and perhaps others) have an on board remote switching capability.

    Tony
  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: solar battery charger/generator

    I am betting that your solar panel will not be enough to keep the battery charged up with the inverter being on all the time.

    Most of those cheaper inverters are notorious for pulling a lot of standby current even if not using any power from them.
  • krisman
    krisman Solar Expert Posts: 57 ✭✭✭✭
    Re: solar battery charger/generator

    that is exactly right, the inverter does drag a lot of current, its a schumaker, does this mean that if i had a different inverter, that i would be able to run my computer longer off of a charge? yes some kind of relay is what i was thinking too but how would i go about doing that? i mean the extension cord would go up to the top floor which my computer would plug into, then where would the relay go? and what kind of relay exactly am i looking for?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: solar battery charger/generator

    The short answer is that we (and perhaps you) do not have any idea how much power your battery holds, size of the solar panels, size of the inverter, or how much power your computer uses.

    Is this a portable installation (boat?) or an emergency system (home) or off-grid (cabin?).

    In any case... The usual method to figure out your answer:

    1. Reduce all power needs (i.e., use small laptop instead of big desktop system)
    2. Plug into a Kill-A-Watt meter and measure Peak Watts and Watt*Hours per day usage

    wind-sun_2038_172010Kill-A-Watt AC Power Monitor Meter
    P4400 Cumulative Killowatt-Hour Monitor

    3. Size the inverter by ~2x the peak load in watts (or 4+ times if motor such as a fridge).
    4. Size the battery by multiplying Watt*Hours per day x6 (3 days no sun, 50% max discharge) then dividing by battery/inverter voltage:

    XXX Watt*Hours * 6 / (batt Voltage) = Battery 20 Hour Rating (in amp*hours)
    5. Size the solar panel by the formula:

    Watt*Hours per day * 1/(hours of sun per day) * 1/(50% system efficiency) = solar panel wattage


    For a small system, highly recommend looking at this 300 watt True Sine Wave inverter:

    wind-sun_2040_712293Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC

    It also has a small connector where you can install a light weight pair of wires to small remote DC On/Off switch. [update per Icarus/Tony's post below--Thank you Tony. -Bill]

    Batteries, solar panels, charge controllers--take a look at our host's store for a selection of good quality products at reasonable prices. Other than the Administrator (WindSun) of this forum, none of us have any business interest in our hosts store...

    Depending on where you live--a local vendor may be a better choice (local support and reduce shipping costs--glass solar panels and lead acid batteries are expensive to ship).

    Everyone here is more than happy to answer any questions we can about any vendor--but going to the above website is a good start for your research. Besides the products, there are a lot of FAQ's (battery, inverter, charge controller, etc.) spread through the store.

    Also, there is a lot of "junk" out there. At least understand how the good stuff should work before looking for the 20 watt amorphous panel + $12 solar charger + 30 AH gel cell battery + 1,500 watt MSW Inverter...

    Yes the above combination may work--for about 15 minutes at full power, then it will go dead--and probably ruin the battery within a few days or weeks.

    Solar is neat, but it is not cheap unless you are using it 9+ months of the year... If you are using it for a weekend cabin for the summer--it is usually hard to justify versus just using a good quality Honda eu1000i or eu2000i gasoline generator (perhaps charging a storage battery for night time lights and radio).


    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: solar battery charger/generator

    Just to clarify, The Morningstar has the capability to REMOTE switch. A pair of light wires is sent from the inverter to a switch located elsewhere.

    Tony
  • krisman
    krisman Solar Expert Posts: 57 ✭✭✭✭
    Re: solar battery charger/generator

    well the fact is that i am using it 9 months out of the year, at least 6 months. i dont know how much the battery holds but at full charge. powers my desktop for an hour and a half to two hours. the only problem i need help with is finding out what i can plug into my extension cord, going from the inverter, so i can turn the inverter on and off with a click of a button without going outside every time to turn the inverter on and off, still have an outlet for my comp to plug into, and finding out what i should ask for or look for, a kill switch, ac on off switch, breaker or what?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: solar battery charger/generator

    The Morning Star 300 Watt TSW inverter would be a nice fit (it sounds like)...

    To use your existing inverter (does not look like Schumacher has any remote control models)--you need a heavy duty DC relay between the + battery terminal and the + input on the inverter.

    Here is a website that describes the basic relay function and wiring (this is for off-road vehicles--but it is the same for you).

    Now, we still need to know how larger your inverter/load is... DC current is actually quite difficult to switch on and off--need much bigger contacts and special designs to prevent arcing (AC switches are easier to make).

    Here is an example of low cost automotive style relays (don't know anything about vendor or their products--just what to look for).

    Guessing that your computer runs 500 watts peak (starting)... then the inverter input current (maximum) would be around:

    500 watts / (10.5 volts min bat * 85% inv eff) = 56 amps...

    So, with my guess, the minimum size relay you should use is ~60 amps.

    The other issue is that relays draw current--so just having your relay "turned on" may draw another 10 watts or so (guessing) which will reduce your battery run time somewhat.

    You could also search for marine or RV relay solutions too. Many do not list how much current/power the relay coil takes--you might have to ask.

    -Bill

    PS: To size the relay for the full 750 watts (if the manual does not say what the peak current is):

    750 watts / (10.5 volts min bat * 85% inv eff) = 84 amps...

    Not a small amount of current...
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • krisman
    krisman Solar Expert Posts: 57 ✭✭✭✭
    Re: solar battery charger/generator

    that is going to be really tough, is there any other solution that i could use to have the battery out of my bedroom floor to underneath the floor but the inverter still in my room? the length to my room to under the floor is about 6 feet or a little less.

    i was thinking number 6 wire but that will require some pretty big holes in my floor.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: solar battery charger/generator

    6' of #6 wire would require a how of ~1/2",, maybe less. 6' would probably be fine, depending on you draw. #6 will carry ~75 amps safely,, ~900 watts @ 12vdc.

    Voltage drop would be pretty small in 6'. See the sticky above with the voltage drop calculator.

    Tony

    PS Make sure you fuse it!
  • krisman
    krisman Solar Expert Posts: 57 ✭✭✭✭
    Re: solar battery charger/generator

    hey i was wondering if i could get a female cigarette lighter plug, run it from the battery, and then an inverter that had a male cigarette lighter plug on it, if this would work?

    and if it wouldnt, what kind of 750 watt inverter could i get that i could keep on all the time without it draining power from the battery? if they even make one.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: solar battery charger/generator

    At best, cigarette lighter/plugs are usually protected by a 10 amp fuse (maybe 15 amps in some cases?).

    If you run a fuse at 80% capacity (recommended to prevent false over current tripping):

    10 amps * 0.80 * 10.5 volts (inverter cut-out) * 0.85 inv eff = 71.4 watts maximum

    If 15 amps:

    15 amps * 0.80 * 10.5 volts (inverter cut-out) * 0.85 inv eff = 107 watts maximum

    Nowhere near the 700 watts you want/need.

    If you look around, you might find others that are similar to the Morning Star 300 watt / 600 watt peak (10 minutes):

    wind-sun_2040_712293Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC

    From the Data Sheet (PDF Download), it has a low power standby mode that is not bad at all:
    Self Consumption
    Inverter On (no load) 450mA
    Inverter Off 25mA
    Stand-by 55mA
    Stand-by: 0.055 amps * 12 volts = 0.66 watts
    Per day: 0.66 watts * 24 hours = 16 Watt*hours per day

    And it also has a DC Inhibit (25mA) which is even 1/2 the Stand-by power consumption.

    I don't recall the size of your solar panel--but that stand-by power loss is the equivalent of ~15 watts of wasted PV panel power (in Winter, assuming ~2 hours of sun and 50% derating factor).


    I am not sure you will find anything out there that is much better... You might even want to run two of the Morning Star inverters if your loads are larger than 300 watts continuous (put 1/2 the loads on one inverter, and 1/2 the loads on the other).

    I would also double check what your AC loads look like when they are turned off... Many computers draw standby current which will keep the inverter on. Also, it is possible that a power strip with surge suppressors may look like a load to the inverter and keep it running at the higher "On" current (450 mA).

    You may need to install a power strip (without surge suppressors) or a simple AC switch to turn-off the computer/electronics standby loads and get the inverter into its low power standby ("sleep") mode.

    -Bill

    PS: As I think I have said before, this is a True Sine Wave inverter--a very nice device all the way around.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset