Grounding/Earthing Morningstar SureSine/SunSaver MPPT

jp3djp3d Registered Users Posts: 9
I am setting up a small AC system for an off-grid cabin using SureSine inverter and SunSaver MPPT controller. I could use some clarification on the grounding system. I will have an earth grounding electrode connected to a grounding bus. Connected to the ground bus:

1. SureSine inverter ground terminal
2. Negative battery terminal? (SureSine manual does not show this connection, SunSaver manual does)
3. "neutral" side of my AC wiring coming from inverter

I am not sure if these circuits need to be connected to the common ground as well:

4. Negative side of PV array input to SunSaver MPPT?
5. Negative side of SunSaver MPPT DC load (connects to 12V electric fence charger in my case)

Extra credit: Do you have any advice on how the ground system of the electric fence charge should relate to the 12V DC / AC grounding? Should they be connected so that any stay voltage that might find its way onto the grounding electrode can flow back to "ground" of the fence charger?

Thanks for your help!

Comments

  • jp3djp3d Registered Users Posts: 9
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    basically my main question is this:
    Attachment not found.
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    Pretty much you are correct...

    The typical installation would be--Think of the "ground triangle" as the top of the ground rod. Run a 6 awg cable from the battery negative to the ground rod. And run a 6 awg cable from the inverter chassis ground to the ground rod. And run a 14 awg cable from the "neutral" to the ground rod (or if there is a "main panel", run the ground from the neutral bus to the ground rod. And the neutral bus is tied to the metal box/safety ground in one spot--typically in the main panel).

    Electrically, this is all the same as you have drawn. The only difference is where the ground connections are typically made.

    Functionally, you could do the whole thing without any grounds--But it is "not to code" and you would have some safety issues (i.e., if the chassis of the AC inverter becomes "hot", there is no ground path back to the battery to trip the DC fuse/breaker for the inverter... Etc.

    Lastly, I am never sure why they have a 3 amp fuse on the output of the AC inverter--I don't think it is needed unless you are using something a lot smaller in diameter than 14 AWG wiring. I think the fuse is just another point of failure--And it is a bit too small. The inverter can output 600 watts for 10 minutes--which would require:

    600 watts * 1/110 VAC * 1.25 NEC derating (wiring and fuses) = 6.8 amps

    If you run the inverter near its maximum ratings (300 watt continuous, 600 watts for 10 minutes), a 3 amp fuse may false trip.

    The inverter should limits its maximum output (by shutting down or browning out).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    Welcome to the forum.

    The PV (-) and LOAD (-) do not need separate grounding as they are a pass-through connection to the battery (-) on the SunSaver. Ground that and you've got them all.

    Keep the fence charger's output isolated from the rest of the system as much as possible. Connecting it to the other ground would be like introducing stray Voltage to the system.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT
    Keep the fence charger's output isolated from the rest of the system as much as possible. Connecting it to the other ground would be like introducing stray Voltage to the system.

    Tell me more about your fence charger... Will it be powered from your cabin system? If so, 12 volt DC or 120 volt AC? There may be a role for surge protection.

    As far as the fence charger output is concerned, other than following Cariboocoot's advice, you could do this:
    http://www.premier1supplies.com/detail.php?prod_id=591&cat_id=44

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • jp3djp3d Registered Users Posts: 9
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    Thank you both for the help!

    Thinking about this again I am having second thoughts about grounding the battery, as this would make the (+) side "hot" with respect to earth correct? We are so used to working with ungrounded batteries someone is likely to accidentally try to connect/disconnect wiring to the (+) terminal while the negative is grounded, which I'm guessing would result in an extremely unpleasant shock. What safety does the grounded battery provide? I suppose I could attach a warning note to the (+) terminal if there is no other way.

    The cabin is located ~100ft from the location of the solar power system, and the solar power system is within the electric fence perimeter. Would it be okay to have no earth grounding at the battery/inverter site and simply ground everything including AC "neutral" and ground to the battery negative terminal? Would it then make sense to place a ground rod for the AC wiring at the cabin? Seems like this would minimize problems from stray electric fence voltage. Maybe I'm over thinking this/don't know what I'm talking about :p

    We are planning to use a Blue Sea double terminal block fuse holder with 100A and 30A fuses and DC disconnect switches to connect the battery to inverter and controller. AC cabin wiring is 12AWG, so I couldn't see any point in the 3A fuse either.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT
    jp3d wrote: »
    Thank you both for the help!

    Thinking about this again I am having second thoughts about grounding the battery, as this would make the (+) side "hot" with respect to earth correct? We are so used to working with ungrounded batteries someone is likely to accidentally try to connect/disconnect wiring to the (+) terminal while the negative is grounded, which I'm guessing would result in an extremely unpleasant shock. What safety does the grounded battery provide? I suppose I could attach a warning note to the (+) terminal if there is no other way.

    It's 12 Volts: you won't get a shock from it even if you wet two fingers and stick 'em on the battery posts.
    The cabin is located ~100ft from the location of the solar power system, and the solar power system is within the electric fence perimeter. Would it be okay to have no earth grounding at the battery/inverter site and simply ground everything including AC "neutral" and ground to the battery negative terminal? Would it then make sense to place a ground rod for the AC wiring at the cabin? Seems like this would minimize problems from stray electric fence voltage. Maybe I'm over thinking this/don't know what I'm talking about :p

    Think like this: single point ground. One rod with everything that gets grounded connected to it via shortest possible route. Since the battery cables to inverter should also be as short as possible, you want to keep this all in one location.

    What you do not want to do is introduce multiple grounding points on the same system. If the panels are far away (and I hope they aren't because you have a 'direct 12 Volt' system here) then a second ground rod is sometimes used for their frames/mounts.
    We are planning to use a Blue Sea double terminal block fuse holder with 100A and 30A fuses and DC disconnect switches to connect the battery to inverter and controller. AC cabin wiring is 12AWG, so I couldn't see any point in the 3A fuse either.

    That all sounds good. :D
  • jp3djp3d Registered Users Posts: 9
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    Hmm I'm still a bit scared by all the power contained inside a large 12V battery. I guess the resistance of a human is too high for much current to flow through you, but a short through good conductos can create some scary looking arcs. I'll try to remind myself of that :)

    The solar panel may end up about 50ft from the battery. I thought it would be a good idea to keep the inverter and charge controller electronics back in the shade away from the sunny and sometimes excessively hot clearing where the panels will need to go. The system also needs to feed our existing 12V fence charger. I am using two 100W 12V panels in series which should operate around 36V with the SanSaver MPPT. Here is a picture of the setup:

    Attachment not found.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    Okay, with the two panels in series on a SunSaver MPPT you should be all right over 50' with a wire of 10 AWG.

    But, 200 Watts of panel may not charge a "large 12 Volt battery". You will likely see about 12 Amps max from that, and that would be enough for about 120 Amp hours @ 12 Volts. This leads to the question "how well have you evaluated your loads?" That's roughly a max of 700 Watt hours available, and the panels may not manage that much (depending on how much daylight they receive).

    Don't be concerned about the SS15's "200 Watt" limit; that is usable Watts. You can actually "over-panel" it without fear and get the maximum 15 Amps output. In fact you will probably find it cheaper to buy one "grid tie" panel of 250 Watts than two "standard" panels @ 100 Watts each. For example: http://www.solar-electric.com/solarworld-sunmodule-sw250-monocrystalline-solar-panel.html
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    Be careful with the 12v fence energiser. Some units specifically say, do not connect to mains power. Mine also says that its earth stake should be at least 10m from a power or other earth stake. I get the feeling, just a hunch, that these things are not good for inverters. Mains rated energisers maybe better, dunno.

    Our 12v unit is on its own little PV, 10W or so, had it laying around, attached to a shed.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    I think they don't want the ground stake too near any 120/240 VAC power because if there is a short somewhere in the home power system and the ground rod becomes "energized" (can happen, ground rods do not sink that much current at 120-240 volts)--You could energize the fence with the "Hot Ground" and then your horse or cattle 1,000' away could get a 120-240 VAC shock with significant current and get electrocuted (or some human touching the fence wire too).

    Cattle and other four legged animals have even gotten killed just by standing next to a power pole with leaking voltage/current. The cow has legs at the four corners, so any current is directed through the heart region. For a human, our legs are closer together (less voltage gradient across the ground, lower possible voltage) and the current path does not go through our heart region (leg to waist back to leg).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jp3djp3d Registered Users Posts: 9
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    Well we already purchased two 100W panels and most of the other components. We were told the larger panels could not be shipped via UPS - would have been an all-day drive to the nearest supplier.

    This is a summer-only cabin and we have propane water heating, refrigerator, and a light. We just want to add some more convenient lights, power a laptop and small radio for a few hours.

    We are going to use the 12V marine battery that's been powering the electric fence for now, then upgrade to two 6V golf cart batteries.
  • jp3djp3d Registered Users Posts: 9
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    CONSTRUCTION STRATEGIES FOR MINIMIZING STRAY VOLTAGE ON DAIRY FARMS
    By: Tom Wilson, Keith Tinsey & Truman Surbrook
    Agricultural Engineering Department
    Michigan State University
    http://www.egr.msu.edu/age/documents/news_archives/et/construction.pdf
    What is the proper way to install an electric fencer?
    In order for the animal to receive a shock, the animal must touch the fence wire and complete the circuit from the "hot" terminal of the fence energizer, through the animal to earth, and back to the "ground" terminal of the energizer.

    An improperly installed electric fence system can result in unintentional shocks to livestock at grounded equipment such as at waterers, feeders or even in a milking barn. The most frequent cause of unintentional shock is due to improper grounding of the energizer. The energizer must have its own grounding electrode located well away from any other grounds or metal object in the earth (50 feet minimum recommended). An energizer must never be grounded to the farm electrical system grounds, to the utility system grounds, to metal water pipes, or to metal objects in a building such as stalls, fences, or dividers. Such improper grounding puts the metal objects and livestock in the electric fence earth return path.

    An energizer should be placed at a location where it is possible to maximize separation of the energizer grounding and electrical wiring system grounding. The best place for the
    energizer may be outdoors away from animal buildings and grounded equipment.

    Interesting... So in theory I should try to isolate the two "ground" systems, but I have never been shocked while touching the grounded parts of the fence, so I'm guessing it is probably extremely unlikely that there would actually be a problem installing the ground rod for the electrical system "near" the electric fence.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    It's the whole problem of the unknown and variable resistance of the Earth between the two grounds. That causes all sorts of trouble, not just with fence chargers.
  • jp3djp3d Registered Users Posts: 9
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    Attachment not found.

    Hooked everything up. Does this seem reasonable? The power system ground it within 5ft of the electric fence, but the fence doesn't seem to be causing any problem.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT
    jp3d wrote: »
    Attachment not found.

    Hooked everything up. Does this seem reasonable? The power system ground it within 5ft of the electric fence, but the fence doesn't seem to be causing any problem.

    Is the white box a lightning arrester? It's a little confusing to see so much red wire carrying PV neg and battery neg. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT

    You have some nice equipment there (MPPT MorningStar controller and AC inverter). Enclosure going to keep relatively dry?

    The 25 amp breaker/switch to fence charger appears to be a bit oversized for the wiring (need 12 or 10 awg minimum for 25 amp circuit).

    Is that the fence "hot wire" going down through the wood board at the bottom (in parallel with fence ground)??? I get solid automotive ignition wire to route the high voltage from the fence charger to the fence wire. When it gets wet, the cabling you have may short out to the wood/local metal connections. Normal wiring insulation is rated only to ~1,800 VAC maximum and a fence charger can get 25,000 volts or so...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jp3djp3d Registered Users Posts: 9
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT
    vtmaps wrote: »
    Is the white box a lightning arrester? It's a little confusing to see so much red wire carrying PV neg and battery neg. --vtMaps

    The white box is just a bus bar that came with a little cover for the common bonding point connecting the inverter equipment ground, battery (-), and the cabin 115V AC ground/neutral together and to earth. I agree the red wire is confusing. I labeled both ends of the negative wires with black tape to try to make it saner.
  • jp3djp3d Registered Users Posts: 9
    Re: Grounding/Earthing Morningstar SureSine/SunSaver MPPT
    BB. wrote: »
    You have some nice equipment there (MPPT MorningStar controller and AC inverter). Enclosure going to keep relatively dry?

    The 25 amp breaker/switch to fence charger appears to be a bit oversized for the wiring (need 12 or 10 awg minimum for 25 amp circuit).

    Is that the fence "hot wire" going down through the wood board at the bottom (in parallel with fence ground)??? I get solid automotive ignition wire to route the high voltage from the fence charger to the fence wire. When it gets wet, the cabling you have may short out to the wood/local metal connections. Normal wiring insulation is rated only to ~1,800 VAC maximum and a fence charger can get 25,000 volts or so...

    -Bill

    There is a bit of a temporary roof on it for now and we are going to build an enclosure around it eventually, although everything claims to be weather proof besides the fence charger that has survived 15 years outdoors so far.

    I got the 25 amp breaker/switch to go along with morningstar's wiring diagram, but I see now it doesn't serve much purpose besides as a switch. I'd forgotten the charger had such small gauge wire leads. The Sunsaver MPPT does have short circuit protection for its load terminal, so I think it is pretty safe as is. I think I have a little inline automotive fuse holder lying around I could add.

    I routed the fence wires that way to distance them from everything else as much as possible. Using spark plug wire is a good idea. I'll take a look at the local agricultural supply stores as well for high voltage wire.

    Thanks again for your help everyone.
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