grounding in van pv system

gbschreiber
gbschreiber Registered Users Posts: 2 ✭
in Off Grid Solar & Battery Systems #1
Hi all, I have a b-class van to which I am adding a 200w pv system. The system includes two-100w panels, a bluesky 3000i charge controller, 300w pure sine inverter and a vmaxtank battery. Shore power is completely isolated from the pv system. My question is what needs to be grounded? I have a good chasis ground lead. Should I ground the inverter only? Should I ground the battery only? Should I ground both(would that result in a ground loop)? I am only a beginner so I apologize if this is a simple question. I've had trouble finding a suitable answer elsewhere. Thanks in advance for your thoughts!

George
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #2
    There are two sorts of grounding. One could be called "the working ground" and the other could be called "the equipment ground". Basically, the working ground is required for the stuff to work, whereas the equipment ground is for safety in case something shorts out in the equipment and electrifies the case/chassis of the equipment.

    For DC, you have the positive and negative and very rarely also have a chassis ground for safety. (In DC, the equipment ground is commonly already connected to the negative inside the equipment, so no extra safety ground is needed.) The negative is also often called ground. It shouldn't be called that, since it doesn't connect to the planet, but people call it that anyway.

    So for the solar, there will be a positive and negative from the PV module(s) to the charge controller, and a positive and negative from the charge controller to the battery. Looking at the manual for the Bluesky 3000i, I don't see any connection for an equipment grounding conductor, so just positive/negative from PV and same to battery. Done deal easy peasy.


    For AC, you have the hot, neutral and ground. The hot and neutral are required for the electricity to flow, the ground is the equipment ground for safety. In the electrical code, the neutral and ground are tied together in the main electrical panel (service entrance) and so they should NOT be tied together anywhere else. Also, due to the way many inverters work, you almost never connect the neutral and ground together.

    You didn't specify the model of your inverter, but it will need regular positive/negative to battery on the 12v side. It might also have an equipment grounding lug somewhere, which usually just connects to somewhere convenient on the chassis for safety in case the thing shorts out internally.

    For the 120v side, if it already has an outlet (plug) and if you don't intend to mix it in with your existing shore power 120vac system, then no worries - you're done.

    If you want to power the entire 120vac system that is already installed in your van, then it gets a bit more complex. In which case, we'll need more details. What sort of Class B do you have? Falcon? Airstream B190? What is the make and model of the inverter?




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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    edited July 2016 #3
    And to answer the next question before it appears...

    Can you just plug your shore power into the inverter?
    Depends. Does your shore power electrical distribution box also supply 12v? Does it feed power to the battery to charge it?

    If so, then no, you can't just plug the shore power into the inverter because you'd be drawing power out of the battery to power the inverter, which would be powering a battery charger putting power back into the battery.

    If you tried it, your van would probably end up at Warp Speed 6 in the Omnicron Delta Dimension.
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  • gbschreiber
    gbschreiber Registered Users Posts: 2 ✭
    #4
    @dwh Thank you! the inverter is a gopower gp-sw300-12 and does have a grnd lug. I will plan on connecting that to the chasis ground but not grounding the battery. The RV is a airstream B190 1991. The inside has been stripped. My shore power is a panamax surge protector connected via extension cord. I thought to keep these systems separate for simplicity. I figure whatever shore power I plug into will hopefully be grounded(the panamax has a ground ok indicator) I don't plan on connecting the inverter to the shore power. Does this sound proper to you? Thank you again!


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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #5
    Well...you have to ground the battery.

    If it's being charged from the vehicle alternator, then it'll have to have the negative connected either to the chassis or to the negative of the primary battery, which will be connected to the vehicle chassis anyway, or it won't charge.

    Also, the purpose of the equipment ground/safety ground is so that if say the inverter's negative to the battery breaks, and then there is a short inside the inverter which applies positive power to the chassis of the inverter...well, the fuse won't blow because there is no path to ground to complete the circuit. Until someone happens to touch both the chassis of the vehicle (or anything grounded to the vehicle chassis) and also happens to touch the case of the inverter at the same time. Viola! Now the human who did that becomes the ground for the inverter and lights up like the main attraction at the Burning Man festival. (Well, not really, but they could get bit hard enough to have a story to tell around the campfire.)

    But, with the equipment/safety ground, even if the negative to the battery is broken, if something inside the inverter shorts positive to the chassis, the safety ground will complete the circuit and cause the fuse to blow.

    But it won't happen if the battery isn't grounded to the vehicle chassis.


    But yea, what you've described will work. If you've removed the original Magnetek(?) (pretty sure the B190s had a Magnetek) load center, then you've already solved the looping problem, and if you don't intend to mix the two systems then no worries.

    My advice would be to invest in a good multi-stage shore power battery charger of at least 25 amps capacity (and double that would be even better) so you can charge the battery while connected to shore power.

    And yes, you can run the charger to feed the battery at the same time you are running the inverter to drain the battery. They won't butt heads. Of course, if you are feeding 15a (per hour) to the battery , and sucking out 25a (per hour) with the inverter, guess what happens to your battery? Yup, it drains at 10a (per hour).


    Now as to that itty bitty 300w inverter...
    Wow, that's a nifty little unit.

    Pros: GFCI on the front and built-in Anderson PowerPole connection on the back for the 12v input. Even has a connection for a remote on/off switch.

    Cons: Not very big, and no reverse polarity protection so if you hook it up backward, you'll blow the internal fuse, possibly toast the inverter and certainly void your warranty.

    Still, 300w / 12v = 25a so a 25a battery charger would keep up with it even if the inverter was fully loaded, and if the inverter was less than fully loaded the charger would have amps leftover to charge the battery.

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