My off-grid solar system. Comments and Feedback welcome

Discussion in 'Boondocking' started by EdZilla, Jul 9, 2018.

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  1. EdZilla

    EdZilla Member

    53
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    Sep 19, 2017
    Denver
    I purchased an E1 which had a simple Yakima rack. I moved my solar panels from my previous camper (Starcraft Starflyer) and I managed to get a couple 100W panels mounted and actually still have room for the bikes.
    My goal is to recharge and maintain my batteries when off grid, charge phones and kids (and Dad’s) electronics and to be able to run a few higher power A/C appliances (blender, power tools, etc) when the sun is hitting the panels. It’s not a complicated system, but i'm hoping it's adaptable. It all started when someone gifted me a camper ('94 Starcraft Starflyer) with minor electrical issues and got two free 100w panels. So I ordered cables and a charge controller and started hacking.

    The main idea is to maintain two group 24 marine batteries so they are always fully charged. My E1 didn’t have them so I wired up 12v and USB adapters around the cabin to run or charge most small electronics. I also added an inverter to run A/C appliances.

    It all works well, but I haven’t boondocked for more than 3 days at a time so it’s not yet really battle tested.

    The solar panel cables are run from the panels on the roof through the shore power port to the charge controller (Grape Solar GS-PWM-40BT) which regulates charge to a marine battery in the battery box.


    Although the GS-PWM-40BT has a built in control panel, it also has a Bluetooth interface so the solar charge system can be fully monitored even when the E1 is closed up. Because of the Bluetooth interface, I rarely need to look at the control panel, and so the controller can be mounted inside and out of the way.


    The separable battery box is normally connected to the solar charge controller. Note the battery box has 2 USB, two 12v ports, external cable connections and a voltmeter. Also, with a group 24 marine battery inside it, there’s still room for an inverter or it’s own charge controller or jumper cables.

    The idea is that this battery is separable from the E1 and so it can be removed to power items outside of the camper but in “boondock” mode it’s connected in (balanced) parallel with the E1 primary battery. Both are maintained by the solar system when in “boondock” mode, else only the one in the battery box.

    Balancing batteries in parallel
    http://www.smartgauge.co.uk/batt_con.html

    I like having this battery separable from the E1 primary battery because it can be removed and used away from the E1. Another reason is that if the E1 is parked in the shade, you could carry a panel and the battery where it has better sun exposure and recharge it.


    Since the E1 primary battery is normally maintained by either the tow vehicle or by shore power, so I've kept the two systems normally separate unless boondocking for extended periods of time.
     
    Last edited: Jul 10, 2018
    Overland likes this.
  2. rabird

    rabird Howdy!

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    Mar 3, 2006
    TX
    Love it!

    I like to connect in balance but that might prevent you from moving batt2 around, happy camping.
    Balance batteries connected in parallel! for 2 batteries it means
    "Finally, if you only have 2 batteries, then simply linking them together and taking the main feeds from diagonally opposite corners cannot be improved upon."
    http://www.smartgauge.co.uk/batt_con.html

    I know the temp displayed on the app never changes but the controller does adjust voltage for temp measured by the controller.
     
    EdZilla likes this.
  3. mpking

    mpking Active Member

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    Jun 17, 2014
    Raynham, MA
    The grape is a nice unit.
     
  4. EdZilla

    EdZilla Member

    53
    2
    Sep 19, 2017
    Denver
    Yes, balance. Exactly. It's important to balance them correctly. I'll get there, but currently I like having them separate.

    Thanks Rabird. Actually it was based on much of your posts and feedback to my previous posts that I went with the Grape 40BT. It's so nice to be able to monitor things remotely.
     
  5. EdZilla

    EdZilla Member

    53
    2
    Sep 19, 2017
    Denver
    The temp measured by the controller is the temp at the controller, not the temp at the panels, yes?
     
  6. rabird

    rabird Howdy!

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    Mar 3, 2006
    TX
    yes, ideally it would be the temp of the batteries. In the heat the temp compensated voltage is lower and in the cold it is higher
     
  7. EdZilla

    EdZilla Member

    53
    2
    Sep 19, 2017
    Denver
    The solar panels efficiency is also derated with higher temperature, yes?
     
  8. rabird

    rabird Howdy!

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    Mar 3, 2006
    TX
    No, not with a PWM controller. Yes with an mppt controller.

    The panel can make power over a range of voltages from 0-22v
    The peak being 17-18 (spec on the back sticker). As the panel heats this peak goes down but as long as the peak is above battery voltage and the battery is in Bulk charging then all the power goes to the battery.

    Once the batt gets to 14.6 (or whatever the set pt is adjusted for temp) it is held at 14.6v by connecting and disconnecting the panel to the battery to keep 14.6 constant for 2 hrs, Boost. Current tapers by letting the OFF time become longer and longer (the batt is getting full and does not need as much power to maintain 14.6v). During boost the panel voltage is battery voltage when ON and Voc (~20v) during OFF. The controller displays panel voltage, during boost it will be an average of batt and Voc based on how long it ON/OFF, so at 50% on/off the panel voltage should read (14.6 +20)/2 or 17v, as the off time increases, panel displayed voltage will increase up to 20v.

    The same thing happens in float but the set pt is 13.8v or whatever.
    Looking at your screenshot above, panel V ~21 and only 2w is needed to maintain 13.7v float at the battery. That suggests to me that the OFF time is much longer than the ON time. Turn on a light or 2 and the off time will shorten so more power goes to the batt to maintain float.
     
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  9. bobinfleet

    bobinfleet Active Member

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    Sep 2, 2011
    Hampshire UK
    Neat set up, I've just got started with a 100w solar set up
     
  10. roybraddy

    roybraddy Well-Known Member

    1,555
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    Mar 23, 2016
    King George, Virginia
    I am going to eventually do some solar on my off-road RT14 roof... Just makes sense to do that...

    I want something that will give me around 20AMPS DC current when in high sun.. Have room for two 120WATT on opposite sides of the fantastic fan and maybe a 200 watt or large across the rear of my trailer roof.

    Since the POPUP roof can be lowered it sure looks like it would neat to work on things - maybe play with some portable panels...

    My large Battery Bank will take a good 55 AMPS DC current when first being charged and I will do that with my 2KW generator. Then after about 30 minutes or so the DC CURRENT will tapper back and eventually be around 6 AMPS DC Current per 12V Battery being charged... This would be great to just let the solar panels take over at this point and can stay online as long as there is high sun available...

    I know if I would remove my very seldom used Air Conditioner mounted on the roof I could have a real good solar panel setup as well as two fantastic roof fans... Since most of my camping is OFF GRID the Air Conditioner just never gets used anymore... The very cool night air in the woods is all I need anyway and a couple of fantastic fans can pull in a bunch of cool night air thru the window flaps...

    My game plan at any chance...

    Roy Ken
    [​IMG]
     
  11. WVhillbilly

    WVhillbilly Active Member

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    Jun 6, 2018
    WV
    If I may hijack.
    Are those the Amazon bike mounts? [BY]
     
  12. EdZilla

    EdZilla Member

    53
    2
    Sep 19, 2017
    Denver
    No, they are old Yakima bike mounts. I'll be replacing them as fast as I can because I don't feel like they secure the bikes very well.
     
    WVhillbilly likes this.
  13. inthedirt

    inthedirt Active Member

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    Aug 28, 2012
    SW Montana
    I have the same battery box on my boat for the electric trolling motor. Comes in handy having all the 12v/USB hook-ups and the display.
     

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