HELP needed; Wire size for minimum voltage drop, etc.; full house 12v lighting off-grid

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  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr
    BB. wrote: »
    Another person here had a long AC wiring run from his genset that failed inside the conduit (never heard how it failed)--Insulation could have been torn during installation... Who knows.

    -Bill

    Hi Bill, was this AC run underground?
    Here we use underground cable reinforced by a steel wire even if it's in a conduit.
    I had a similar thing happen but not with wiring, it was a grey water discharge pipe from our bio septic system (similar to worm farm septic). It didn't break but it came off the outlet connector. This was due to using the excavated material for backfilling the installation. We have predominantly sand here but deeper down you get to clay. The top layer of sand is quite hydrophobic, yellow sand below takes some water and clay retains water like a sponge. The latter is difficult to compact especially when wet. the water table can be as high as 1-2ft under the surface here in winter and is about 50ft below in summer considering most water bores around here are 60ft+ deep.
    The unit is about 14ft deep underground, the base (1ft or so) sits in poured concrete and is also anchored on four sides about half way up by concrete filled 100mm pipes, about 3ft perimeter held by steel cables to stabilise horizontal movement. The backfill material being of different materials (grey sand, yellow sand & clay), even though it was well compacted, settled inconsistently through water erosion. I couldn't believe it could move this much; an inch or so I expected where the flexible poly pipe could probably cope with the movement but the pipe was about 6 inches lower than the outlet!!! The discharge pipe is about 3ft below ground level and I only noticed the fault when water started surfacing at the location of the outlet. Messy digging, I can tell ya!:cry: I think this kind of force could easily stretch cable to a point of failure. Conduit and slack at both ends of the run helps but 6inch is a lot especially if the cable is perhaps twisted in several places within the conduit causing friction but more so the pressure of settling could compress or put a kink in the conduit if settling is isolated, crimping the cable inside which would then put full pressure/weight of the backfill material on the cable itself (pipe in my case).
    I've learned a lesson; don't use all the excavated material to backfill if inconsistent, a bed of sand around the whole installation would probably reduce the movement so I should have used a couple of tons of sand and discarded the excavated material. :blush:
  • BB.BB. Super Moderators, Administrators Posts: 28,159 admin
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    I do not recall who it was, or if it was buried or not (do not think it was).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Hi all,
    I've finished installing the battery bank & UPS/inverter/charge controller and all is running well.8) I've attached photo's to show the insulated & foil wrapped enclosure. There is room for expansion. If I double the battery bank I'd have to tier the battery enclosure which would then unfortunately make it cramped for maintenance; equalize & top-up which at present is great. I still have to install vents for both compartments which are separated and air-tight when the door is closed so at present I don't close the door at all. The first equalize was daunting with the batteries bubbling (open caps) due to higher voltage going in but I just have to get used to that.
    I did a full charge & equalize first thing, set the BMV600 battery monitor at full charge. The system has now been running for nearly two days powering; 210L chest fridge (freezer to fridge conversion), additional 210L chest freezer, 650W water pump with 20L pressure tank, small LCD TV, PC, several lights and laptop/mobile phone chargers and also my son's xBox 360 + fatback 24 inch TV (not all simultaneousy, of course).
    Halfway through he second day the battery monitor is showing SOC (state of charge) 84.6%.
    In the next few days I'll connect a couple of power hungry appliances; kettle & microwave to see how it affects the SOC and remaining Ah. I know I can't run the two simultaneously as that would exceed the inverter rating when UPS is off mains but still have the option of compensating the inverter with mains, once I get the connector & software to program the UPS. The other option is to install a second UPS unit which I already have (two for the price of one) to double the inverter output as the UPS's can be linked to work as one.

    I will keep the SOC above 60% for the time being, still have to set up alarm on BMV600 to notify me of that.
    Batteries are being charged from mains at the moment overnight, through timer when we only pay $0.11/unit and hopefully we will be pushing units back into the grid at $0.47/unit through our 2.2kW GC solar.
    I aim to install an off grid array around 1000W with OB80 charge controller soon and reset the UPS to only use mains power when battery voltage drops to a certain level and/or compensate the inverter when loads are over capacity.

    Is the SOC minimum 60% OK, too low or can I go deeper?
    Where do I install the battery temperature sensor; last batterie's negative pole or the negative bus?
    If I install the second UPS would it be advisable to double the battery bank?
    Can I put off the charging to once a week if SOC is still above recommended or is it better to charge more frequently?
    With both units connected I could effectively power all appliances with the exception of tankless water heaters.
    I wish I went for terminal mount fuse blocks rather than the inline kind as I'll have to disconnect the cables from the terminals to be able to open the fuse holders. :blush:
    I was initially going to bus the two battery bank halfs at the + switch and - shunt but I'd be using more cable so installed bus as close as possible to the batteries.
  • mike95490mike95490 Solar Expert Posts: 8,020 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr
    Sascha wrote: »
    Hi all,
    I've finished installing the battery bank & UPS/inverter/charge controller and all is running well.8)......

    Halfway through he second day the battery monitor is showing SOC (state of charge) 84.6%. .....

    I will keep the SOC above 60% for the time being, still have to set up alarm on BMV600 to notify me of that. ...........

    Generally, by noon, solar should have gotten the batteries well into bulk, and starting into absorb. (80%)

    But every day that you can, you need to get above 80%, to prevent sulfation of the batteries. Daily discharge down to 60% will shorten your battery life.

    And if you have grid, why are you cycling batteries ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr
    mike90045 wrote: »
    Daily discharge down to 60% will shorten your battery life.

    Thanks Mike. I mean SOC 60% which would be 40% DOD I assume. I'm trying to avoid charging every day, would every other ay be sufficient? At the moment I'm down to about 90% SOC per day.
    mike90045 wrote: »
    And if you have grid, why are you cycling batteries ?

    Because I can use the stored power during the day when electricity from grid costs $0.42/unit peak and $0.21/unit off-peak then charge overnight when electricity costs $0.11/unit between 9pm and 7am. Also have power during grid outage for essentials.
    I'm installing off-grid solar + charge controller in the near future to keep batteries charged during the day with loads connected.
    This would cost me about $2000 extra for 1000W array + OB80 charge controller but should be able to pay for itself soon considering any units we return to the grid are paid at $0.47/unit due to the government 10 year buy-back scheme compensation. I know the fact to charge batteries uses more power than what then becomes available to use but the $/unit are quite extreme at different times.
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Hi Marc,
    I hope you are well.
    I could do with some advice if you're up to it. :D
    Hi all,
    I've finished installing the battery bank & UPS/inverter/charge controller and all is running well. I've attached photo's to show the insulated & foil wrapped enclosure. There is room for expansion. If I double the battery bank I'd have to tier the battery enclosure which would then unfortunately make it cramped for maintenance; equalize & top-up which at present is great. I still have to install vents for both compartments which are separated and air-tight when the door is closed so at present I don't close the door at all. The first equalize was daunting with the batteries bubbling (open caps) due to higher voltage going in but I just have to get used to that.
    I did a full charge & equalize first thing, set the BMV600 battery monitor at full charge. The system has now been running for nearly two days powering; 210L chest fridge (freezer to fridge conversion), additional 210L chest freezer, 650W water pump with 20L pressure tank, small LCD TV, PC, several lights and laptop/mobile phone chargers and also my son's xBox 360 + fatback 24 inch TV (not all simultaneousy, of course).
    Halfway through the second day the battery monitor is showing SOC (state of charge) 84.6%. I assume this is equivalent to 15.4% DOD?
    In the next few days I'll connect a couple of power hungry appliances; kettle & microwave to see how it affects the SOC and remaining Ah. I know I can't run the two simultaneously as that would exceed the inverter rating when UPS is off mains but still have the option of compensating the inverter with mains, once I get the connector & software to program the UPS. The other option is to install a second UPS unit which I already have (two for the price of one) to double the inverter output as the UPS's can be linked to work as one.

    I will keep the SOC above 60% for the time being, still have to set up alarm on BMV600 to notify me of that.
    Batteries are being charged from mains at the moment overnight, through timer when we only pay $0.11/unit and hopefully we will be pushing units back into the grid at $0.47/unit through our 2.2kW GC solar.
    I aim to install an off grid array around 1000W with OB80 charge controller soon and reset the UPS to only use mains power when battery voltage drops to a certain level and/or compensate the inverter when loads are over capacity.

    Is the SOC minimum 60% OK, too low or can I go deeper?
    Where do I install the battery temperature sensor; last batterie's negative pole or the negative bus?
    If I install the second UPS would it be advisable to double the battery bank?
    Can I put off the charging to once a week if SOC is still above recommended or is it better to charge more frequently?
    With both units connected I could effectively power all appliances with the exception of tankless water heaters.
    I wish I went for terminal mount fuse blocks rather than the inline kind as I'll have to disconnect the cables from the terminals to be able to open the fuse holders.
    I was initially going to bus the two battery bank halfs at the + switch and - shunt but I'd be using more cable so installed bus as close as possible to the batteries.
  • DillDill Solar Expert Posts: 170 ✭✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    I'm not Marc, but I'll knock a few of your questions out, and he can comment on the others.

    Is the SOC minimum 60% OK, too low or can I go deeper? This is OK occasionally, but I wouldn't do it on a daily basis. The less you discharge your batteries, the longer they will last. I tend to want to charge mine back up when they reach 70%
    Where do I install the battery temperature sensor; last batterie's negative pole or the negative bus? On the battery pole, the purpose is to measure the temp of the battery which will compensate the charging profile.
    If I install the second UPS would it be advisable to double the battery bank? probably, as it will maintain your current usage and not overly deplete your batteries.
    Can I put off the charging to once a week if SOC is still above recommended or is it better to charge more frequently? sure, it all depends on the SOC though. You don't want to leave your batteries discharged or they will sulfate
  • BB.BB. Super Moderators, Administrators Posts: 28,159 admin
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    As Dill said, it would be best to recharge your batteries that evening--It will help reduce battery sulfation over time (the lower the state of charge, the more/faster sulfation occurs).

    Regarding how deep to discharge... You can use a smaller bank and a deeper discharge... But perhaps you will have to replace the smaller battery bank every 2-3 years instead of every 5-7 years or so. Overall the costs are not that much different (i.e., 2x larger battery bank replace a little less than 1/2 as often).

    You might setup a financial model for your system... I.e., how much does a battery bank cost divided by how many kWH per 3-5 years you time shift (remembering your system is probably around 54% efficient--AC to battery charger to battery bank to AC inverter to AC load--That means, at worst case you can be using 1/0.544=1.83x as much power to recharge your battery bank at night).

    Regarding the temperature sensor, some bolt right to the positive post... Or you can take a hunk of Styrofoam, hollow it out, and glue the sensor+foam to the side of one of the batteries in the middle of the bank (foam keeps sensor closer to battery temperature).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Thanks Dill & Bill ;)
    Went down to just over 70% SOC last night before recharge but will try to keep this closer to 80% SOC from now on. So, if I adjust the charger-timer to only charge 1-2 hours a night during the week to go back to 100% SOC and do the full cycle including absorb & float every weekend would this greatly affect the bank's life? As you said Bill, the efficiency of the system is a concern so if I had to charge for 9 hours every night it would probably cost more to cahrge than what I'm gaining. I think we'll agree the way to go is hooking up an off grid array + charge controller to keep the batteries happy during the day with moderate loads attached and use the UPS/inverter/charge controller primarily as an inverter and back-up in case of grid failure.
    We are nearly breaking even with the 2.2kW GC with the last three bills being $30, $80 and $5, normally $280-$300. The $80 bill was in summer when I used a portable air-con to cool my delivery van when stationery (I sell confectionery & dry goods and the van is always stocked up, doubles as storage) but this will not be required once we move into the house as the van will be parked in it's own insulated part of the shed.
    Without going into complex calculations the winter sun is pretty good here, possibly better on a clear day than summer due to less heat on the panels.

    If I install the other UPS I already have, so double the inverter to 6000/12000, keep the battery bank 24v/440Ah, add 1000 watts of panels off-grid + OB80 charge controller...;
    Would this give us autonomy considering the off-grid would keep the batteries topped up + serve loads through two inverters during the day and then use some of the stored power to run loads between sunset and say 10pm?
    This would cost about $2000 extra. :D
    If not, then double the battery bank, add 2000 watts of panels off-grid + ??? charge controller? What kind of charge controller do you recommend for this?
    This would cost about $3500 extra + ??? charge controller. :cry:
    $2000 we can afford now but if doubling is advised I'd rather leave it until we can afford the lot instead of doing half now and add later.

    With rising costs of electricity in mind for the near future we'd eventually like to be self sufficient and we are working on ways to minimise consumption in the first place. We are very happy with the 'chest-freezer-to-fridge-conversion', LED lights throughout, switching off stand-by appliances at the socket, etc..
    It's always better to preserve than to try and re-gain right?
    We don't pay for water as we have a large 270,000 liter rain water tank and will be instslling another one soon for some of our 5 acres irrigation. The household only takes about 35,000-40,000 liters/year and the tank we have has never gone below 80% capacity given all the roof space we have. Water heating is another thing I'm looking into; double the plumbing inlets (cost about $300 extra for installation) and run the hot pipe through coils on the tank or house roof to heat up during the day. Before we built the main shed I had a caravan (RV) and a small shed with camp shower and I'm telling you; I had to wait a couple of minutes for the water to cool down before taking a shower, it heated up so much through the 40 meter hose pipe from tank to shower.

    We have recently added a power consumption monitor, which I highly recommend, only thing bugging me is the fact it measures the pulse of units going both ways so having GC solar it measures power going in as well as out-no true reading during the day! :grr
    It'll be good when we are in the house, then I can install it in the sub-panel which will measure the units from the main panel to the sub-panel- one way only, treating the GC as part of the grid.
    BB. wrote: »
    Regarding the temperature sensor, some bolt right to the positive post... Or you can take a hunk of Styrofoam, hollow it out, and glue the sensor+foam to the side of one of the batteries in the middle of the bank (foam keeps sensor closer to battery temperature).

    -Bill
    The manual says: The temperature sensor is isolated and must be mounted on the batteries minus pole.
    I didn't know which of the 8 batteries to attach it to; last in line or one of the centre two or does it matter if they are regularly equalized? I prefer your suggestion as the sensor should measure average temperature of all the batteries, is this correct? The end of the sensor has a brassy 8mm ring connector. Do I glue this to the side of the battery in the centre of the bank with styrofoam slightly compressed between the two batteries, pressing the sensor against one battery or hollow out the foam and keep the sensor central between the two batteries, inside the foam?
  • BB.BB. Super Moderators, Administrators Posts: 28,159 admin
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Sounds like you are getting your system and power costs under control there... I don't really have any idea what to say about a larger system. I always like to start with your loads and work back towards your battery bank--then solar array. And finally, start picking hardware to support your needs.

    Regarding the temperature sensor--Don't over think it. Ideally, you want the sensor to measure the warmest battery--where ever that is (and, you really want all the batteries about at the same temperature--so there should not be a big temperature difference between batteries anyways). Worst case, if you have a high charging current and cool temperature sensor, you could get thermal run-a-way. As the batteries heat up, their charging voltage requirement drops. If the temperature sensor misses the "hot battery bank", then it is possible for the charge controller to think that the battery needs more charging current/Amp*Hours (bank gets even hotter, etc.). But, unless you have very unusual setup/conditions, it is not a common failure mode.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Hi Bill,
    I know your way of assembling a system is the best way to go, a proven method! I've kind of done it half-way so probably not as bad as some who start the very oposite to your way and then wonder why the system can't support their needs/loads. I have room for expansion which will be needed once we are in the house and can deptermine the loads more accurately. I'll have a go at calculating the loads in the meantime, using the plans and appliances we intend to install.
    If I charge the bank every other night when we reach 80% SOC for 2-3 hours (bulk & absorbtion) and then full charge once a week (bulk & absorbtion + float), equalize once a month, will this keep the batteries happy?

    I'll take your advice and mount the temperture sensor somewhere in the middle, between two batteries, assuming that's where the highest temperature may be as the walls and door are insulated, thanks for that.
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    If I charge the battery bank every other night when we reach 80% SOC for 2-3 hours (bulk & part absorbtion) and then full charge once a week (bulk & absorbtion + float), equalize once a month, will this keep the batteries happy?
  • BB.BB. Super Moderators, Administrators Posts: 28,159 admin
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Here is an older post that I keep pointing back at:

    I like Dave Sparks' post:
    I learned this strategy from Dave Surrette (Rolls) in the late 70's. Pretty much the bible on how I design my systems for off-grid.

    Assume that the system will never reach more than a 90% state of charge.
    Try not to go below 50% SOC, ever! Complete absorption over 90% of the year

    Use the energy stored from 70% to 90% SOC for your daily cycles.
    Save the energy from 50% SOC to 70% SOC for aging to get long battery life.

    I know Surettes has changed their recommendations over the years but I also know they are in the business of selling batteries! If you do the above you will get 10 to 15 years on their batteries with decent maintenance.

    The OP is making it complicated by mixing battery types and not really stating a lot of information that would allow decent specific advice.

    Oh yea, I am really happy that Surrette and Trojan are making L16's with 1000 AH capacities @20HR. Been bugging them for many moons to do batteries less than 125LB's!

    And, my two cents... If your batteries are using a bit of distilled water per month--you are probably OK. If you are using none, or a lot per month--then you are probably under or over charging.
    • Undercharging and operating for long periods (below ~75%) is damaging to lead acid batteries.
    • Overcharging is less damaging to flooded cell batteries (at the cost of distilled water and wasted energy).
    • Overcharging sealed batteries (AGM, Gel, VRLA, etc.) can be fatal to those types (venting electrolyte).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Thanks Bill,
    Can I rely on the BMV600 battery monitor for SOC? it has been manually reset to 100% after batteries took initial full charge cycle + 1 hour equlization.
    If I achieve 100% SOC (BMV600 reading) within 2-3 hours every other night (charged when reaching nol lessthan 80% SOC), can I assume the battery bank is full?
    If this is good do I then still have to do a full 3 stage cycle once a week and equalize once a month or can this be done less frequently?
  • BB.BB. Super Moderators, Administrators Posts: 28,159 admin
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Equalization is "hard" on a battery bank... Do it when needed and only do it as long as needed (when batteries SG from high to low differ by ~0.015 to 0.030 SG or more). Start equalization (should not be more than 5% of battery bank 20 Hour Rating), and measure the SG every 30-60 minutes. When the SG stops increasing, stop equalization. (AGMs can be "equalized" by just extending the Absorb charging voltage a few hours--always refer back to your battery's manual/instructions).

    Battery Monitors are "estimates" only... The longer they go between "re-sync" (typically over 14.x volts for y hours), the further they will diverge from "true state of charge". Also, battery capacity itself changes over time (increases the first 30-60 cycles or so, decreasing with sulfation or other failure modes)... I like monitors because it much more accurate than watching battery voltage, and much easier for non-technical folks (spouse, kids, guests) to understand the state of charge (i.e., below 75% state of change, watch loads and start genset next morning if cloudy day forecast; below 50% start genset/cut loads call you for help; below 20%, turn everything off)...

    Typically, Lead Acid battery charging becomes slower/less efficient in the 80-90% state of charge range. And over 90% SOC, the charging current tapers down to 1-2% of bank AH rating. As you approach 100% SOC, much of the energy is used to electrolyze the water into Hydrogen and Oxygen. Don't want to do too much of this.

    Because of the low current, this is where solar panels are pretty nice... Quiet and no fuel use... Vs running a Genset with a very light load for the AC Battery Charger (not very fuel efficient with a genset sized for larger loads/full current charging).

    In the end, I am not an "off grid" person--So take what I say with a grain of salt. There are others here with many decades of battery experience--So they can give you better information than I.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Thanks Bill,
    The system has only been running 4 days now so I yet have to monitor the use of distilled water. When all was wired up i decided to do a full charge cycle + equalize just to make sure all batteries are in sync. Prior to installation I had 4 of the fully charged batteries standing for 6 weeks and 4 batteries for 2 weeks.
    So will it be OK to charge to 100% SOC within 2-3 hours every other night and only do a full 3 stage cycle once a week or can the full cycle be done less frequently?
    I need to understand the basics of battery charging; bulk, absorb & float and what effect occasional skipping of float and only part absorb would have on the batteries to determine the frequency need for a full charge cycle.
    Thanks for the tip on equalizing. Do I need a hydrometer for reading the SG? For the time being, is it safe to assume all batteries' cells are equalized since they are all new?
    Am I being too meticulous with all this?
    Solar will be an advantage and a bonus to virtually eliminate the charging through the UPS, at the moment I'm trying to find a sweet spot in terms of charging time through the UPS's mains input as I don't want to use more grid units to maintain the batteries than what I use from the stored energy. This would not impress the missus, hehe! :blush:
    I'm looking at an array of 2.2kW OG through an OB-FX80 and double the battery bank to 24v/880Ah, also install the other UPS- Victron MultiPlus 24/3000/70 for more inverter capacity. This way we should produce more than we consume and the existing 2.2kW GC should then theoretically sell back all it produces to the grid with the exception of 4 x small tankless water heaters installed at points of use which will remain on the GC or optionally run through the two UPS's as they have power assist built in to compensate the inverter capacity with grid power if needed for heavy loads.
    Would you advise I keep the two UPS's separate or would this make no differece to the power they consume if no loads are being used?
    By the way, the batteries are lead acid, high density plates GC2-6V as per link: http://www.supercharge.com.au/products_special_deep.php

    Our average consumption calculated for the past year was 16kWh per day but this will be reduced by a large amount as we get more energy wise. Example; two months April & May this year we used 611kWh as opposed to April & May last year when we used 1092kWh. I think we are on the right path here. 8)
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    PS; The reason I'm charging the battery bank from the grid is the fact we pay around $0.42/unit peak times, $0.21/unit off peak (average $0.30/unit daytime) and $0.11/unit at night. The charging is done at night. Sell back of unused units to the grid is $0.47/unit.
  • BB.BB. Super Moderators, Administrators Posts: 28,159 admin
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    You have to keep a close watch on power used (UPS idle current, conversion efficiency, charging efficiency, etc.)...

    I understand the desire to load shift out of peak power cost period (mine are $0.09 vs $0.30 per kWH at bottom tier, can approach peak kWH costs of $0.40 to $0.50 for people with A/C and other high power usage needs in summer afternoons).

    The conversion losses and cost of replacement batteries, with my SWAG's for my home, seem to, at best, come out to a small loss of money (cost of batteries, hardware, energy losses) vs the savings of time shifting using a UPS/Backup power system.

    In the end, it was just better to go grid tied + GT inverter and no batteries, with a pretty good 1 year net metering plan--But not every utility allows grid tied solar or 1 year net metering (commercial billing is usually much worse terms vs residential).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Hi all,
    We have now further reduced our mains usage to an average of 9.5 units/day. Considering we are still building so power used would be slightly higher than when the house is completed I think we are doing well.
    For the same period we used to average 14.5 units/day in 2010 and 14.3 units/day in 2011. :D
    Mind you, we are not in credit currently as the solar is generating about 47-48% in winter as opposed to the max reading in summer so in summer we should be well in credit.
    We are currently producing an average of 2.9 units/day from solar while in summer we produced an average of 6.1 units/day.
    I think we need to incorporate wind power as well as we do get strong easterly winds thorughout summer, especially overnight when solar is asleep.
    It took some time to adjust our minds to preserve at any opportunity and we are still constantly trying to improve.
    Our mains supply cost has gone up again as of 1/07/2012, total of 57% increase since 2008!!!:grr
    I'm hoping part of the increase is used to protect the grid from EMR and similar even though the official reason for the increases is always maintenance, etc.. I think the government is afraid to tell the people they are spending money on protection in case nothing ever happens as far as solar flares and the like as they don't want to be ridiculed.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr
    Sascha wrote: »
    I think we need to incorporate wind power as well as we do get strong easterly winds thorughout summer, especially overnight when solar is asleep.

    Before you make that leap, investigate very thoroughly the posts and references on this forum on wind power. There are a lot of scams out there, and the single most common error people make is in estimating the average wind speed. "Strong" just does not cut it. Ideally you should install a recording anemometer at same approximate location and height that you would use for the turbine. Then you will be better able to make a good decision.

    Remember that the power available in clear undisturbed air goes up as the third power of the wind speed. That means several major things:
    1. Winds in the 5 MPH range produce nothing at all, even if they can get the turbine spinning.
    2. A difference of 1 MPH at 20 MPH means a difference of over 15% in output. Accuracy of measurement is critical.
    3. The nameplate power of a turbine is *usually* measured at a wind speed of 25 MPH. But some manufacturers may use a reference speed above or below that. And some manufacturers (or distributors) just downright lie about the power output.
    SMA SB 3000, old BP panels.
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Hi guys,
    Would this work (pic attached)? I can't get my head around it. Friend of mine would like to achieve a bank of 24v/440Ah using 4 x 12v/220Ah batteries and this kind of mixed serial & parallel is an alternative I haven't come across before. It doesn't look right!? The 4 x 4' should be 2 x 4' (typo).
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    My suggestion was as attached.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    With the first drawing, why the 'X' in the middle? That won't help anything. In fact it causes the polarity to reverse. This won't work at all.
    Your attached PDF version will certainly work; two parallel strings of two 12 Volts in series.
    You can also do it with the simple "diagonal" wiring rather than create two common point connections elsewhere as per your drawing. Smart Gauge method #2 http://www.smartgauge.co.uk/batt_con.html Modify so that there are only two parallel connections and each is two batteries in series.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr
    Sascha wrote: »
    Hi guys,
    Would this work (pic attached)? I can't get my head around it. Friend of mine would like to achieve a bank of 24v/440Ah using 4 x 12v/220Ah batteries and this kind of mixed serial & parallel is an alternative I haven't come across before. It doesn't look right!? The 4 x 4' should be 2 x 4' (typo).
    No, this will not work at all. He's got 4 batteries connected in series, two pointing one way and two the other. Its output voltage would be zero volts.
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Thanks Marc and thanks ggunn for confirming that.
    Marc, would wiring as per your attachment still need two fuses? Would you still fuse both + terminals on the LHS to isolate the two strings in case or just the one at the top, conecting to inverter/charge controller?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    How safe do you want to be? :D
    With the diagonal wiring like that you can consider the four batteries to be one big battery, as the only secondary over-current risk is between the two parallel sets. This is usually about one foot of wire so there isn't as much risk of an accidental short from the second string to ground as there is with multiple parallel sets where longer wires go to a common connection point away from the battery.

    True, you might short one battery in one string causing the other string to discharge through it. But when you're dropping wrenches on top of batteries you can hit any two posts, including several combinations that won't cause any trouble at all. And some that will cause trouble even if there's a fuse on the (+) of each string.

    Personally with a tight install I would use only one fuse and treat the group of batteries as one unit. But there's no reason you can't or shouldn't put a fuse on each of the two strings.
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Thanks Marc,
    I think he'll go with one fuse on + terminal to inverter/charge controller. I've redone the layout of his batteries to shortern the wires by placing them head to head as terminals on these batteries are both on one side of the battery unlike some that have terminals placed diagonally. See attached.
    BTW, how have you been holding up? Taken that road trip yet?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Whoops! There's a problem with that diagram; you're connecting the (+) and (-) of the inverter to the same string. That would have the batteries "laddered" rather than diagonal. Move the negative inverter wire to the "lower" string's (-) terminal.

    I'm doing as well as can be expected under the circumstances. Traveling too much, and got to travel more.
  • SaschaSascha Solar Expert Posts: 121 ✭✭✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr

    Gotcha, thanks Marc. Does the negative inverter wire have to be the same length as the positive?
    One can never do too much travelling!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: HELP needed; Wire sze for minimum voltage drop, etc.; full house 12v lighting off-gr
    Sascha wrote: »
    Gotcha, thanks Marc. Does the negative inverter wire have to be the same length as the positive?

    No. Wire lengths need to be the same length when they're in a parallel circuit so that each 'branch' has the same resistance (as close as possible). Within any single circuit it all adds up the same.
    One can never do too much travelling!

    Yes, you can. Believe me you can. :roll:
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