Do off grid inverters neutrals carry only the unbalanced load?

rainwater01rainwater01 Registered Users Posts: 7 ✭✭
Maybe not to advanced of a question but I'm going to be running a solar system in Haiti and we have to go about 250' in wire feeder length and I want to make sure that I'm sizing my wire for voltage drop properly. I am planning to run 60 amps (30 amps @ 220 volts) of total power to 12 rooms in a guest house. we're figuring 5 amps @ 120 volts per room. I figure I'll run a 20 amp 120 volt circuit to each room which will balance out the neutral pretty good.

The feeder will be 250' of 4/0 aluminum URD to an outdoor loadcenter and then #10 copper on a 20 amp breaker to each room to help with voltage drop and conduit fill adjustments. Voltage drops look great right now if the neutral currents do indeed cancel which I assume they do. That's the most important question to me right now, that the neutral carries only the unbalanced load which will cut my wire length calculations practically in half.

Thanks for your input. The building is below as a reference :)


Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    In general, yes the L1-L2=N current will work OK. In theory, you could run into issues if the L1 rooms were running Motors/Old Computer power/etc. supplies with poor power factor, and the L2 rooms were running new computers and hair dryers. The poor power factor loads would not cancel (part of) the good power factor loads. But I would not expect any such issues.

    https://www.amazon.com/s?k=AC+Amp*Hour+Watt*Hour+meters&ref=nb_sb_noss (general AC power meters)
    https://www.amazon.com/CrocSee-CRS-022B-Frequency-Multimeter-Transformer/dp/B07K3S4K9L (example of a nice meter?)

    With a cost of $15-$20 per meter... If these are guess rooms for "random" visitors that stay a few days/weeks (vs 6+ month volunteers/workers) that you cannot really "train" and monitor--I would think that installing a bank of 12 of these meters at $240 (or more--office? Another for "Mains" power... Or just get a pair for L1/L2 mains power--And if things don't look right--Go knock on doors) and a metal "break out" electrical box to hold all the current transformers/monitors) would let you keep an eye on the system would let you watch for folks that use extra power (such as a hair dryer) or leave stuff on (laptop, lights, etc.) and drain the system--Without having to go into each room and check.

    Other ideas may be to use timers or motion detectors for room lights, perhaps even outlets (timer) to "remind" guests that power is not unlimited here.

    https://www.amazon.com/s?k=ac+timer+wall+swtich&ref=nb_sb_noss

    "Motion detectors" and timers that turned off the lights every 30 minutes "after work" were hated for lights at several companies I worked at... Engineers who came in late / worked "late" were plunged into dark every 1/2 hour (and many of the emergency/night lights had failed over the years--So there was little ambient light until people tripped over stuff until they could get to the local light switch to turn lights on again... Was a big mess (people use coffee stirrers to hold switches on--burned out relays that were designed for just a push on, engineers came late, left "on time", had to fix emergency lights, etc.).

    If you do the automated lights--I would think some sort of room night light (low power LED) would be nice (and not draw much power). Either a light switch with nightlight, or a plugin night light...

    Probably 90% of the time, you will not have issues--But those few times when one or two people don't follow the program, it could save you a night without lights/power, or a dead battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MichaelKMichaelK Registered Users Posts: 218 ✭✭✭
    Since you mention the use of aluminum wire, I think it's appropriate to warn you to make very sure you are using the correct Al bonding paste recommended by the manufacturer to guaranty you don't get aluminum oxide weakening your electrical connections.
    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
  • rainwater01rainwater01 Registered Users Posts: 7 ✭✭
    BB. said:
    In general, yes the L1-L2=N current will work OK. In theory, you could run into issues if the L1 rooms were running Motors/Old Computer power/etc. supplies with poor power factor, and the L2 rooms were running new computers and hair dryers. The poor power factor loads would not cancel (part of) the good power factor loads. But I would not expect any such issues.

    https://www.amazon.com/s?k=AC+Amp*Hour+Watt*Hour+meters&ref=nb_sb_noss (general AC power meters)
    https://www.amazon.com/CrocSee-CRS-022B-Frequency-Multimeter-Transformer/dp/B07K3S4K9L (example of a nice meter?)

    With a cost of $15-$20 per meter... If these are guess rooms for "random" visitors that stay a few days/weeks (vs 6+ month volunteers/workers) that you cannot really "train" and monitor--I would think that installing a bank of 12 of these meters at $240 (or more--office? Another for "Mains" power... Or just get a pair for L1/L2 mains power--And if things don't look right--Go knock on doors) and a metal "break out" electrical box to hold all the current transformers/monitors) would let you keep an eye on the system would let you watch for folks that use extra power (such as a hair dryer) or leave stuff on (laptop, lights, etc.) and drain the system--Without having to go into each room and check.

    Other ideas may be to use timers or motion detectors for room lights, perhaps even outlets (timer) to "remind" guests that power is not unlimited here.

    https://www.amazon.com/s?k=ac+timer+wall+swtich&ref=nb_sb_noss

    "Motion detectors" and timers that turned off the lights every 30 minutes "after work" were hated for lights at several companies I worked at... Engineers who came in late / worked "late" were plunged into dark every 1/2 hour (and many of the emergency/night lights had failed over the years--So there was little ambient light until people tripped over stuff until they could get to the local light switch to turn lights on again... Was a big mess (people use coffee stirrers to hold switches on--burned out relays that were designed for just a push on, engineers came late, left "on time", had to fix emergency lights, etc.).

    If you do the automated lights--I would think some sort of room night light (low power LED) would be nice (and not draw much power). Either a light switch with nightlight, or a plugin night light...

    Probably 90% of the time, you will not have issues--But those few times when one or two people don't follow the program, it could save you a night without lights/power, or a dead battery bank.

    -Bill
    Thanks so much for all the valuable advice. We're not sure what we'll do with the building yet. It was going to be a guest house but could turn into conference rooms, offices or even an addition to the school so having those meters would be an incredibly good idea. I would like to get some for all of our campuses! It would be good to see how much electricity we're producing with the generators too.
  • rainwater01rainwater01 Registered Users Posts: 7 ✭✭
    MichaelK said:
    Since you mention the use of aluminum wire, I think it's appropriate to warn you to make very sure you are using the correct Al bonding paste recommended by the manufacturer to guaranty you don't get aluminum oxide weakening your electrical connections.
    Thanks for mentioning that. I carry it on my truck here in the states but it would be real easy to forget to take some and not be able to find any while I'm there!
  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    As Michael says--Besides the AL "grease", you may also want to look at AU/CU compression connections/Compression-Crimping tool (such as used by our local utilities for connecting AL pole drop to CU building wiring). They are rated for both AL/CU and weather tight.

    Just use one end for AL, and bring some CU pigtails for transition to CU building wiring (generally, compression connectors have a relatively small range of acceptable AWG/Diameter wiring... You may need to use a "heavy" CU AWG cable for compression connector, and then transition to smaller AWG copper building wiring (with locally available splicing connectors).

    In addition to kWH meter(s) for genset--You might want to look into some sort of fuel totalizers too... We see smaller AC gas/petrol gensets get something like 3-5+ kWH per gallon of fuel (diesel should be more efficient)... You can keep track of genst/battery/power usage and watch for anyone that is "out of the typical range" (using 10 kWatt genset run  tens/hundred watts of lighting, somebody siphoning fuel from tanks, short fill, etc.).

    https://www.amazon.com/s?k=fuel+totalizer&ref=nb_sb_noss_2

    I have not used a Fuel Totalizer--So I know even less than typical about them.  :*

    Just using Amazon links for pointers... I have no opinion one way or the other about the product(s).

    It sounds like you know a lot more about this stuff than I.  :)

    Let us know how it all works out (the good and the bad).

    Take care,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,076 ✭✭✭✭✭
    What inverter are you going to use? Some are better than others and the Low Frequency Design type will tend to be better at unbalanced loading.
     Also there is a basic need as an electrician to balance the loading at the panel as best as one can. The more you can shift 120 loads to 240 loads the better the system will perform.

    Large unbalanced loading can shut down an inverter until someone can restart it. Often this is an undesirable issue!

    If I am misreading this, it has been a long day!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • rainwater01rainwater01 Registered Users Posts: 7 ✭✭
    BB. said:
    As Michael says--Besides the AL "grease", you may also want to look at AU/CU compression connections/Compression-Crimping tool (such as used by our local utilities for connecting AL pole drop to CU building wiring). They are rated for both AL/CU and weather tight.

    Just use one end for AL, and bring some CU pigtails for transition to CU building wiring (generally, compression connectors have a relatively small range of acceptable AWG/Diameter wiring... You may need to use a "heavy" CU AWG cable for compression connector, and then transition to smaller AWG copper building wiring (with locally available splicing connectors).

    In addition to kWH meter(s) for genset--You might want to look into some sort of fuel totalizers too... We see smaller AC gas/petrol gensets get something like 3-5+ kWH per gallon of fuel (diesel should be more efficient)... You can keep track of genst/battery/power usage and watch for anyone that is "out of the typical range" (using 10 kWatt genset run  tens/hundred watts of lighting, somebody siphoning fuel from tanks, short fill, etc.).

    https://www.amazon.com/s?k=fuel+totalizer&ref=nb_sb_noss_2

    I have not used a Fuel Totalizer--So I know even less than typical about them.  :*

    Just using Amazon links for pointers... I have no opinion one way or the other about the product(s).

    It sounds like you know a lot more about this stuff than I.  :)

    Let us know how it all works out (the good and the bad).

    Take care,
    -Bill
    Thanks for the crimping tool idea. I've been thinking about that for another project that the village is working on. They want street lights all around the village for safety reasons and they'll be running that overhead. I've been looking for a good affordable crimping tool and splices that won't cost a fortune. Do you by chance have any recommendations? If I take it down there I'll be leaving it there. Right now when somebody needs power from the local grid they just climb the pole, strip the wire and wrap their copper wire around it a few times which is obviously a terrible practice but they have no other way to do it.

    As for this project I don't expect to need the crimping tool because I'll be going underground and landing it in a subpanel. I think I'll go ahead and go over the general plans when I answer Dave in the next post if you're interested in hearing more of the details.

    We will have two diesel generators. I'm not sure if stabilizer helps in those or not but we use enough diesel between the 4 campuses that have generators already that it's totally worth looking into!
  • rainwater01rainwater01 Registered Users Posts: 7 ✭✭
    What inverter are you going to use? Some are better than others and the Low Frequency Design type will tend to be better at unbalanced loading.
     Also there is a basic need as an electrician to balance the loading at the panel as best as one can. The more you can shift 120 loads to 240 loads the better the system will perform.

    Large unbalanced loading can shut down an inverter until someone can restart it. Often this is an undesirable issue!

    If I am misreading this, it has been a long day!
    So this is what I'm thinking of using right now but I'm open to ideas from others as this will be the largest system I've installed yet.

    First I'll give you a broad overview of the site. I'll give as much info as you guys are interested in hearing but I'll try and keep it as short as possible until then :) If you don't want to read until the end I'm thinking of using 2 schneider Electric Conext XW Pro 6848 Inverters

    The building in the photo was wired with 2 main panels (one for a/c, one for everything else) on the far left  side of the building that is the farthest possible point away (additional 150') from the solar/generator building. They paralleled out of the main lugs and fed a small 12 circuit GE panel in each of the upper 6 rooms. Each lower room is fed from the panel in the room above it. They ran their conduit in the attic and junctioned above each panel.

    We really only need to use one generator at a time so I was thinking of running both 50kw generators to a transfer switch that feeds a 200 amp panel. That panel would feed the inverters to charge the batteries and run everything else in the generator building.

    Then I would run 2 sets of 4/0-4/0-4/0 Aluminum cable (4 wire w/ground if I can find it) underground to the back side of the building where I will land one in a subpanel and refeed all the 12 mini split air conditioners (generator power only). The other cable will feed a subpanel with (6) #10awg 20 amp multiwire branch circuits running up the back of the building into the attic in 1-1/2" or 2" conduit and refeeding each of the 6 electrical panels.

    Hopefully that was clear as mud :) That's the best plan I've come up with yet. I probably do need that crimping tool to reduce my 4/0 cable down to #2 copper to land under a 100 amp or less breaker for the solar.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,076 ✭✭✭✭✭
    edited March 2 #10
    Schneider XWP would be my choice for Inverters. I have yet to find one that is at good at a wide range of Offgrid Issues and has the high voltage charge controllers that make easy installation and easy to expand later. The Insight local and cloud monitoring is as good as it gets.

    The mini-splits are 240vac right? You can buy  4/0 to #2 bus screw connectors from Midnite or a good hardware store. Tape them and install in a JB.  Are you shipping to Haiti or ?  Good Luck !
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    Regarding crimps and tools.. I really do not have any practical experience to help here...

    I had a lineman reconnecting my home drop (after fixing some water ingress issues to may meter box) with something from Makita like this (I think):

    https://www.rapidlockingsystem.com/products/tools-jaws

    For crimp splices--I guess something like this?

    https://rexel-cdn.com/Products/Penn-Union/BCUA2-0.pdf?i=E4C360A9-8E78-4A46-ABB1-13055BB1C082

    I have no idea if the above are correct for your application or cost effective... Just what I understand as starting points for your searches/research. Working with your local supply house or even talking with a local utility worker about what they use may be helpful.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rainwater01rainwater01 Registered Users Posts: 7 ✭✭
    Schneider XWP would be my choice for Inverters. I have yet to find one that is at good at a wide range of Offgrid Issues and has the high voltage charge controllers that make easy installation and easy to expand later. The Insight local and cloud monitoring is as good as it gets.

    The mini-splits are 240vac right? You can buy  4/0 to #2 bus screw connectors from Midnite or a good hardware store. Tape them and install in a JB.  Are you shipping to Haiti or ?  Good Luck !

    Yes they are 240 volt mini splits. Usually what I do is buy what I can in country and bring in what I can't get there. Last time I had an outback 3648 inverter in my carry on, an e-panel, pv combiners, breakers and other solar stuff in my other 2 70lb bags.

    Are the schneider charge controllers smart enough to not overcharge my batteries if I size my system heavy on solar and a little light on batteries? I figure if the price is too high for them then I could use less batteries since we have a generator that I should be able to wire to come on when the battery power is low. But if I have a large solar array then I should be able to produce what we need even on a cloudy day?



  • Dave AngeliniDave Angelini Solar Expert Posts: 6,076 ✭✭✭✭✭
    Would be hard to fit a couple XW's in checked baggage let alone carry on   ;)   Use an agent or drop me an email.
    The mppt -80 or -100A will do what you program in and not overcharge the batteries!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • rainwater01rainwater01 Registered Users Posts: 7 ✭✭
    Ha. I have had systems flown there before but it costs us $1.50 a pound so that adds up pretty quick!
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