RV Solar

I have been using solar a couple of years on a truck camper, and have now purchased an older Trek motorhome, and am installing my 80 watt Kyocera/Morningstar Sunsaver 10. Questions relate to my desire to use the system remote--My experience here in Oregon suggests that my single panel is notably more efficient used as a remote vs. permanently mounted---given tall trees/shade, sun angles, etc. (1) I am using about 25' of 10 ga. wire--I want to be able to plug/unplug from the battery. I have plugs with 10 ga. wire. Will this be okay, even with a "hot" PV? I have been doing this, but worry about the regulator. (2) What do I need to do to put gauges between the panel and controller, and to measure the batteries (2 6v) capacity? I am considering using simple analog voltmeters. (3) Is there anything I'm missing? Thanks in advance........Chuck

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: RV Solar

    chuck,
    nearly any connector will work as long as it is rated for the current passing through it. it is also possible if you only just wish to shut off the current from the pv to use 1 connector for either the positive or negative, but a switch is easier than that. do know that if pulled often enough that these and other connectors can wear out especially when done with live current, but won't be terribly expensive to you with only an 80w pv's power going through it.
    the sunsaver should be fine, but if in doubt put the connector between the pv and the controller. if you still wish the connector going between the controller and the battery, but you needlessly worry about the pv power still on it you can put a switch there to shut off the power to the controller. if not using a switch use a fuse to do it.
    for measuring voltages, it not a big deal unless the voltage source to be measured is far away. the resistance in the wires add to that of the analog meter and can change the readings somewhat. analog meters are fairly inaccurate anyway so if you have them and can live with the innaccuracy then use them. digital meters do well to measure remote voltage sources and are very accurate regardless of being remotely used or not.
    on the subject of the meters and your wishing to roughly measure battery capacity you could learn to know by the voltage readings or get a meter that can measure in vs out amps like that of the trimetric. try here to see them and there accessories.
    http://store.solar-electric.com/metersmonitors.html
  • System2System2 Posts: 6,290 admin
    Re: RV Solar

    Niel--Thanx!! Alright, so I can use the plug and fuse I have been using--and stow the PV the rest of the time. Now, I was not aware that analog gauges are less accurate than digital gauges--I'll take your word for it, though I don't understand why this would be so.... I want to make my own monitering system using either a single or 2 gauges, such as those found at NAPA. Is this adviseable, and do I need shunts to do this?? Cost IS a consideration, but I want accuracy. If you have further advice on designing an inexpensive monitering system, I'm all ears!! ChuckD
  • BB.BB. Super Moderators, Administrators Posts: 32,642 admin
    Re: RV Solar

    Niel is correct about Digital Gauges being more accurate than Analog... First, it is just easier to read to 3+ decimal places on a digital scale than to try that on a precision analog meter (I probably still have a few meters from the days where there was a mirror stripe behind the needle to make sure that you don't read parallax). Also, temperature compensation, earth's magnetic field, and shock/vibration all lead to more accurate and rugged digital meters. Also, digital meters typically have higher input resistance which makes more more accurate readings too in some instances (also less self-discharge than analog meters on a battery system).

    Another reason that, if you are interested in accuracy of your battery's condition, you should pick one of the meters that Niel suggested is that it is very difficult to find out how much capacity of battery you have used (or charged) by just watching current and voltage. There is also battery temperature, chemistry, resting conditions and such that all affect the voltage readings of the battery.

    The meters that Niel linked to also include totalizers--basically, monitor current over time (possibly current*voltage over time--that I am not sure about)... Basically, this is how you would know that you have used 50% of your 100 amp*hour battery's energy as these meters will simply read 50 amphours of current consumed. And, the meter will also track how much you have charged your battery too--makes it much easier to really know what you are doing to your batteries.

    Lastly, shunts... Basically, if you have a current meter without a shunt, you have to route a heavy gauge cable to the meter and back to the bus to read the current. With a shunt, you place it with a short piece of cable between the battery and the bus bar and route very small gauge wire (properly protected with fuses and/or resistors) back to your monitoring point. You will have a better installation with a shunt because you will have shorter runs, need less copper, fewer losses, and a much safer installation due to less chance of shorts (ask me how I know that running wire from the battery to the amp meter and back to the battery on our old 4WD truck).

    You can build your own system, but unless you find/make an analog DC current totalizer (like the kWatt*hour meter on the side of your house), you will be missing one of the most important pieces of instrumentation for monitoring your battery use over time. Also, because batteries are not idea systems, the people like Xantrex put routines in their totalizer gauges that reset to zero/full after a period of time on charge (time and voltage)--and some of them allow you to program in the bank capacity so that they can display percent capacity--handy for those users (like wives) that may not care about the details.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: RV Solar

    Niel and Bill--You guys sortof leave me in the dust on this stuff....Okay, so I will install a Trimetric and shunt---anything else I need? thanx....ChuckD
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: RV Solar

    the wiring of the trimetric can be confusing so follow the instructions carefully.
  • System2System2 Posts: 6,290 admin
    Re: RV Solar

    Right
    Thanks!!
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