Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerator

fm.109
fm.109 Registered Users Posts: 33 ✭✭
Hello everyone, hope you all are doing well and in great health!

I am back again to asking questions from this respected community of awesome folks with immense solar tech knowledge.

The question is more educational and less on the problematic side.

I am wanting to know all the factors involved in determining a charge controller size (MPPT). It would also be helpful to know how many optimal amps a battery bank would require for charging (Lead Acid & gel)

Second question is regarding Fuse sizing. I would like to know how to size fuses and where are fuses applied to in a solar installation.

Third question is more related to determining how to size an inverter and battery bank for devices such as a refrigerator, freezer, deep well pump (2 HP), surface pump (2HP)

One further addition to my query is how to design a system grounding.

Hope to hear from you all at the earliest and also looking forward to BB's input in this. :D

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    Not Bill but ...

    Off-grid systems are based on loads. The load requirement will determine both the battery bank size and the inverter size: they have to be large enough to supply the maximum power used at any given time and the total Watt hours used daily.

    Then you have a battery bank size, and that determines the peak charge current and total Watt hours needed for recharging. Thus you have the numbers for the array size and charge controller to handle it.

    At that point you can measure the distances between components, know the current, and determine wire size - which set the size of circuit protection for the wiring.

    As you suspect the sizing of inverter/batteries for things like refrigerators and well pumps is a bit of a guessing game. Even in those instances where you can measure the running Amps and total Watt hours using a Kill-A-Watt meter there is still the matter of the start surge. You will see estimating factors for this: 3X to 5X running. But this is not always the case: a motor starting in "free air" uses less current to start than one starting against a load like a compressor or pump. The load on those at start-up will be different depending on the particular device and installation. My best advice is to estimate the maximum draw based on what information you do have and then size the inverter to handle that without including its surge rating.

    The battery bank size is not as critical for a momentary surge as is the inverter: we are talking about a second or so at high current, which will not "flatten" a battery the way a sustain current demand will. Almost any component can handle a momentary high current demand, except an inverter.

    System grounding follows certain rules of good practice and NEC regulations, but in every instance has to be adapted to the particular installation.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    I am BB--And sometimes, I am not sure that is a good thing. :roll:

    I keep referring to this thread as a good beginning point (and anyone is welcome to add useful information/links too):

    http://forum.solar-electric.com/showthread.php?5556-Working-Thread-for-Solar-Beginner-Post-FAQ

    Fusing/breakers/wire size usually starts from two points--Simple voltage drop calculations--which many folks who know 120/230/etc. VAC power get wrong (working at 12-24 VDC, the current is 10x that of the 120/240 VAC circuit). Many have been tripped up by that simple fact.

    The other is--for us in North America, is we start with the code and "Listed" components. The code provides a unified framework so that relatively safe wiring/installations can be built and maintained (by others down the road) and Listed components which are built to specifications over time (tested initially, and the manfacturers are inspected 1-2 times per year via UL and other NRTLs -- Nationally Recognized Testing Laboratories).

    The US NEC (National Electric Code) is pretty detailed and conservative. The ABYC (American Boating and Yacht Council) also has some electrical codes which are pointed at boats--And seem to be (for some stuff) a bit less conservative.

    You are in Pakistan--So, you can start with the codes and regulations that match the majority of wiring/electrical equipment in your country (English or Metric Units, any "standards" organizations in your region, etc.).

    I find it very difficult to answer these types of "questions" in general. That can be a book length answer--And may not even help with a specific question/installation. And serves to confuse more than clarify.

    Starting with a "real" requirement (power, equipment, etc.) and answering to that end usually is easier and clearer. And after you have one of those under your belt (and the exprience of getting the parts and installation them), then we can talk about some more generic issues/questions and scaling methods.

    I can give "better" (but certainly not perfect) answers for North American Code--But for regions I don't know anything about--That is a bit more dicey.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    here is a thread about installing a pump in Pakistan...


    http://forum.solar-electric.com/showthread.php?16078-Help-required-to-design-off-grid-system/page15&highlight=pump+pakistan
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat
    BB. wrote: »
    I am BB--... And I approve this message.
    Paid for by the Nothing for Nobody Committee.
    SMA SB 3000, old BP panels.
  • fm.109
    fm.109 Registered Users Posts: 33 ✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    Alright I understand everyone's opinion on the subject and based on that I would like to tell you what exactly I am wanting to do.

    Last time around I was looking to power a house with Air conditioner that would run on solar power. Unfortunately the costs were extremely high for doing so mainly because of immense power outtages (16-20 hours a day on a daily basis) and secondly the over all system cost was way out of that family's budget.

    This time around though I am wanting to do something that is more on the cost effective and realistic side of the solar world.

    For this system we need a backup of 12+ hours only (power outtages occur after every one hour i.e. one hour on and one hour off). So in case of cloudy days the person will switch and bear what the grid has to offer.
    He would run 3x90W fans, 2x25W day lights, 2x10W night lights, 1xfridge, 1x60W TV, 4x10W routers, 1x50W Laptop, 2x Mosquito mats totalling to around 710 watts. PV panels will be mounted on top of the roof (2nd floor), a distance from gf floor level of around 30 vertical feet and say some 10 - 20 horizontal feet.

    So we can say that roughly 710 Watts/hr is the consumption of this household for 12 hours a day. The battery bank backup is required for 1 day only.

    There is almost 6 to 7 hours of sunlight incident onto the surface here in Islamabad, Pakistan.

    Based on my calculations, This person would require Solar Array Watts of 2209.772798 Watts

    I was thinking more of a 48 Volt battery bank for this and if that were to happen then I suppose he would need roughly 400Ah @ 48 Volts

    And this is the part where I do not know how to use the rate of charge for battery. As in should I use 5, 10 or 13% as he would also be consuming from it during day time.
    However based on my calculation these would be the following array sizing for this house:


    5 Percent ROC" 1485.569986 Watts Minimum Required Array



    10 Percent ROC" 2971.139971 Watts Nominal Required Array Size



    13 Percent ROC" 3862.481962 Watts Maximum Required Array Size


    Now I have reached the point of awkward confusion lol. I know that MPPT are bought on the basis of output current & voltage since the mppt would take in larger voltage and dial it down to up the amps in order to effectively charge batteries. The problem for me is that I am not sure as to what is the best way to determine a charge controller for battery type and solar panel type.

    Also since this system would charge from both solar and the grid power, what do you all think should be the best way to charge batteries.

    Also what sort of fuses would be used for such a system and where would they be applied. A general description on fuse sizing would also be helpful.

    I am more into looking for a very detailed description like A to Z of how the system can be effectively designed.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    First question: 710 Watt hours per day or 710 Watts for 12 hours per day? There is a huge difference between the two. 710 Watts for 12 hours is 8.5 kW hours; a very large amount of power to come up with.

    This is what needs to be absolutely correct to begin with. The battery bank size will depend on that. A 400 Amp hour 48 Volt battery can supply approximately 4.8 kW hours @ 25% DOD or 9.6 kW hours @ 50% DOD. This leads me to think you were planning on 710 Watts for 12 hours.

    Normally you'd base the array on 10% of the capacity (for 25% DOD usage): 40 Amps @ 48 Volts / 0.77 (typical derating) = 2493 Watt array.

    Check this against the hours of equivalent good sun (not just daylight hours) and you should have something like this:

    2500 Watts * 5.5 hours * 0.52 (over-all derating) = 7.1 kW hours AC

    As you can see that would in fact fall short of the 8.5 kW hours required. Maybe you can squeeze a bit more out, maybe not. Actual hours of good sun on the panels will affect this, as will power loss from high panel temperatures.

    Along the way you need to round the numbers in the right direction to give yourself enough margin for error. For instance batteries won't be available in precisely 400 Amp hours, so you round that number up to what is available. Then you recalculate the array size based on that actual battery capacity.

    At that point you round the panel capacity up to what is actually available. These two rounding up procedures give you a little extra power capacity which may make all the difference in the world.

    Charge controllers are rated by their output current, which is usually the same for any system Voltage they are designed to handle. So an 80 Amp MPPT controller can handle 80 Amps @ 12, 24, or 48 Volts. The other number to watch out for is the input Voltage: it needs to be high enough at the array Vmp to charge the system (as in 70 for a 48 Volt system) and low enough at Voc under coldest conditions not to exceed the controller's maximum (usually 150).

    In general, if you've gone to the expense to install solar use it whenever you can. Panels with sun on them doing nothing are a poor investment. And the sun does not shine 24 hours a day so making use of grid when there is no sun is advantageous.

    Wiring and fuses/breakers are the last thing to be determined. The wire has to be sized to handle the expected current, and be large enough to keep the Voltage drop over the distance involved to a tolerable minimum. Circuit protection is sized to suit the wiring.

    You can think of an off-grid system as being three (or four) separate but inter-acting circuits: array to charge controller, charge controller to batteries, batteries to inverter (and four would be the AC side). Each of these will have their own Voltage and current requirements a well as distances which will determine wire size and needed circuit protection.

    How are we doing so far?
  • fm.109
    fm.109 Registered Users Posts: 33 ✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    Firstly thank you cariboocoot for the input and yes although I wasnt clear, I require 710 watts for 12 hours per day. Which makes it 8520 Watts per day.

    Secondly yes my DOD was based on a 50 percent calculation.

    Monthly Averaged Radiation Incident On An Equator-Pointed Tilted Surface (kWh/m2/day)
    [FONT=fixedsys]Lat 33.726
    Lon 73.07
               Jan     Feb     Mar     Apr     May     Jun     Jul     Aug     Sep     Oct     Nov     Dec Annual Average
    SSE HRZ    3.18    3.87    4.95    6.31    7.27    7.54    6.44    5.72    5.69    5.07    3.89    2.99    5.24
    K          0.59    0.57    0.58    0.62    0.65    0.65    0.57    0.54    0.63    0.69    0.68    0.60    0.61
    Diffuse    0.85    1.16    1.51    1.73    1.87    1.97    2.24    2.07    1.48    0.89    0.69    0.75    1.44
    Direct     5.56    5.50    5.99    7.16    8.06    8.23    6.23    5.57    6.99    8.03    7.30    5.64    6.69
    Tilt  0    3.13    3.79    4.89    6.22    7.24    7.49    6.40    5.69    5.60    5.03    3.81    2.96    5.19
    Tilt 18    4.19    4.63    5.50    6.50    7.13    7.21    6.24    5.77    6.15    6.19    5.13    4.10    5.73
    Tilt 33    4.81    5.06    5.70    6.36    6.63    6.56    5.77    5.52    6.25    6.76    5.91    4.79    5.85
    Tilt 48    5.16    5.21    5.58    5.88    5.80    5.59    5.02    5.00    6.00    6.94    6.33    5.21    5.64
    Tilt 90    4.53    4.13    3.79    3.18    2.57    2.30    2.31    2.63    3.75    5.34    5.49    4.71    3.73
    OP         5.22    5.21    5.70    6.50    7.26    7.49    6.41    5.79    6.26    6.94    6.40    5.32    6.21
    OPT ANG    58.0    48.0    35.0    19.0    6.00    0.00    3.00    12.0    30.0    47.0    57.0    61.0    31.2
    [/FONT]
    
    These are my readings for solar panels and battery bank sizing.

    Regarding the charge controller I really wanted to know how one calculates the requirement for charging batteries. As in how do you determine what would be the best output amperes for a specific battery bank. This is a website where I found such information and wanted to confirm if the writer is sizing charge controller properly http://www.homepower.com/array-mppt-charge-controller-sizing-example

    Running on solar power for maximum number of hours is the plan for this since we want to utilize as much of it as possible to breakeven in a short period of time.

    Though based on the items listed what would you suggest as the best possible wire size from the solar panels to charge controller and so on till the inverter and if there would be fuses required in this system design.

    Once again thank you for the valuable input though it is always appreciable as I am trying to learn about solar designing as much as i can.
  • fm.109
    fm.109 Registered Users Posts: 33 ✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    And this is from where I gathered my Solar Data.

    https://eosweb.larc.nasa.gov/sse/
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    There is not a fixed current rate for any given battery type/size, there is a range. Almost all will require a minimum peak current of 5% of the "20 hour" Amp hour capacity. But that is very minimal and is net, meaning some allowance must be made for concurrent loads.

    10% works as a good rule-of-thumb when utilized with 25% DOD. If you intend to go deeper in discharge you need more panel. The idea here is to be able to charge the batteries fully on a good sunny day: the more capacity used the faster you have to put it back in order to have enough daylight to finish the job. However, there is also an upper limit. We used to say 13% was the upper limit for practical reasons, but due to lowering panel prices that isn't so anymore. You could easily arrange for enough panel to meet the particular battery's maximum charge rate (AGM's will take higher current than FLA's). This will be a battery-specific number, but most will take 20% peak current without any trouble.

    If your area is particularly short on sun you can severely "over-panel" the controller and program it to have a maximum limit so that the charge rate is not exceeded on those rare sunny days.

    I don't agree with the linked info for sizing. For one thing, 46 Volts is too low for a 48 Volt system. It has been my experience that it is better to go no lower than the nominal Voltage rating (under load) to be sure the battery is always a bit above 50% SOC. Nominal Voltage at rest indicates approximately 50% SOC so with the load removed the battery will 'rebound' above that level.

    So I use a three part calculation. The first is to calculate battery capacity for the loads needed:

    8520 Watt hours / 0.90 (inverter efficiency) = 9466 Watt hours (round up to 9500) / 48 Volts (minimum operating Voltage) = 198 Amp hours * 2 (for 50% DOD, * 4 for 25% DOD) = 396 Amp hours.

    Now due to the built-in fudge factors that number could be rounded down to 390 Amp hours which is an available L16 battery capacity. At least some of the daily power will be provided by the panels. But it is usually best to round up again in most cases. No one ever regretted having a bit extra capacity.

    The second part is to calculate charge rate and array size for the recharging. Normally with 25% DOD a 10% rate will suffice (unless loads are expected to be heavy during charging times). With 50% DOD it probably will not be, so let's try 15% (using 390 Amp hour batteries):

    15% of 390 = 58.5 Amps * 48 Volts (lowest Voltage is usually where you see the need for maximum current) = 2808 Watts, less typical derating factor of 77% (average output in good sun of panel & controller) = 3646 Watt array (round up to nearest available size; again no one ever regretted having a bit extra capacity).

    Third part (you haven't fallen asleep yet, have you?): checking array size to make sure it meets the minimum 'harvest' for Watt hours.

    Array size * hours of equivalent good sun (not the same as daylight hours, even with tracking) * over-all system efficiency (0.52 typically; this can vary) = AC Watt hours harvested per day.

    If we use a 4 hour minimum here we get: 3646 Watts * 4 * 0.52 = 7583 Watt hours.

    As you can see that is too low for the 8.5 kW hour usage requirement. So then it becomes a matter of adjusting factors:

    Check hours of equivalent good sun, i.e. daily insolation. If it is 5 then the output rises to 9479 which will work. (It should always be a bit higher for preference).
    Adjust efficiency factor. Are there circumstances that can be used to improve it, such as East-West split array, utilizing more power during daylight, high elevation/cooler temps which will improve panel output (likewise the inverse is true).
    Increase array size to meet power needs.

    How's that work for you? Confusing enough? ;)
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    Regarding the array to charge controller sizing article... I think it is fine on temperature issues, however, I think their sizing of the controller (amps) is not really useful:
    4,920 W (array peak size) ÷ 46 V (min. battery voltage anticipated) = 107 A

    It assumes too much current from the array/controller combination into a battery near dead. For most people, they are not ever going to take a battery to near dead (at least very often) and solar arrays do not usually produce near their maximum output power (into MPPT) controller except in very cold weather.

    A more "cost effective" calculation would be:
    • 4,920 Watt array * 0.77 panel+controller derating * 1/59 volts battery charging = 64 amps

    Most people are going to have their system (when charging) spending most of its time >75% SOC, and that is going to be with the battery much more in the range of 52-59 volts (higher the battery State Of Charge and the higher the charging current, the higher the battery voltage and lower amount of current from an MPPT controller).

    Yes, there will be some times when the controller spends a bit more time "current limiting" in colder weather (usually sub freezing), but that will usually a hand fulls of days for not much time during the day, and not really cutting back that much on output power (few "lost watts" * factions of hours per day * few days per year).

    If you are looking at 80 amp or larger MPPT charge controllers, that is the difference between one or two charge controllers for that example array.

    Sizing the battery for the most efficient use of system... If you want to really try for that then running the battery from 80% State Of Charge to 50% SOC 6 days a week and one day a week get the battery recharged back over 90% SOC (to reduce sulfation) is a very interesting profile (you need to cut back on power use one day a week and/or use Grid/Generator one early morning per week to help get the battery over 90% SOC). Lead Acid batteries are much more efficient when operated in that SOC range. And there can be some interesting arguments that this may be good for battery life and lower distilled water usage (less gassing/higher voltage charging should both help extend battery life). The charging back to >90% SOC once or twice a week should help keep sulfation down (I have seen numbers to recharge >90% from every 5-5 to 10 days, to as much as every 30 days as long as you are actively cycling the battery relatively deeply--don't "store" the battery at less than near fully charged over days/weeks/months--Sulfation will occur). Again, this is somewhat dependent on battery type (flooded cell deep cycle has been recommended)--Do your own research as I do not have an off-grid battery system and never have tried this type of cycling.

    So, your usage is 8,520 Watt*Hours per day. 30% discharge per day would be:
    • 8,520 WH * 1/0.85 inverter efficiency * 1/48 volt battery bank * 1/0.30 battery cycling = 696 AH @ 48 volt battery bank

    Next, the minimum array needed to recharge your bank based on 5% to 13% rate of charge:
    • 696 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 2,666 Watt array minimum
    • 696 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 5,332 Watt array nominal
    • 696 AH * 59 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 6,933 Watt array "cost effective" maximum

    And, if you are running A/C, then usually you will be pulling power during the day--So the 710 Watts will reduce the available battery charging current:
    • 710 Watt * 1/0.77 panel+controller derating * 1/0.85 inverter eff = 1,085 Watt Array "added" to the above array battery charging numbers.

    Finally, you need enough sun to recharge the energy used per day. I am not sure I understand your solar charge exactly, but lets say you average at least 5.0 hours of sun (5.0 kWH/m2/day) power on days where you need A/C:
    8,520 WH load per hot/sunny day * 1/0.52 typical end to end efficiency * 1/5.0 hours of sun per day = 3,277 Watt array "break even"

    So, it would appear that an array between (2,666+1,085=) 3,751 and (6,933+1,085=) 8,018 Watt array should work well. and the total amount of power for such an array would be:
    • 3,751 watt array * 0.52 system efficiency * 5.0 hours of sun per day = 9,753 Watt AC power available (minimum array)
    • 8,018 watt array * 0.52 system efficiency * 5.0 hours of sun per day = 20,847 Watt AC power available (maximum array)

    I have made some assumptions about your system (usually you will be running A/C a lot during most days, but there will be some cloudy days where you will want AC power usage too). The battery bank may be a bit oversized if most of your energy use is during the day (the above is based on worst case; charge during day and use power at night). A smaller battery bank can save costs--While the solar array supplies power to A/C directly during the day (smaller battery, not going through 80% battery efficiency during day and instead directly to inverter/AC power, you could use the closer to 3,751 watt array or a bit smaller).

    Anyway--That is one way to look at your system. If you have grid power available and want to make up for afternoon/daily power failures, you can build a system with battery bank+AC Inverter+AC battery charger first, then backup generator + solar array as funding permits.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    Besides which there is no single controller that can handle 107 Amps, so going by that guide someone would buy two controllers when (as Bill demonstrated) really one would do for the same system.
  • fm.109
    fm.109 Registered Users Posts: 33 ✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    Thank to you both (BB & Cariboocoot) I am now beginning to understand solar sizing better and no cariboocoot it is not gettign confusing it is actually helping me understand dynamics of sizing lol which is kind of fun.

    Though I would really want to know a few things regarding this sizing.

    How do you determine an end to end efficiency of 0.52 and how do you know or calculate a derating of 0.77 for panel + controller.

    Is there some sort of a specific formula to it? or does it depend on the components being used (I would appreciate a clear description of these factors or possibly a link to where I can read more about it to understand it better)

    And yes BB the consumption would be such that power would be utilized during the day as well. Though I would like to know about fuses and wire sizes as to how should they be sized or possibly if you can also provide a link on that matter where it explains hwo to do so. When I research online I keep finding different data with not so much consistency. The same case occurred with charge controller sizing where I found a particular site but then again now that you clarified it better I understand that he was trying to bring the battery down to almost 0 charge.

    I am really trying to understand the system better so that I can use this knowledge to design better when it comes to dynamic regions of work.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    One place that explains the overall possible losses is the PV Watts site:

    http://rredc.nrel.gov/solar/calculators/pvwatts/version1/derate.cgi

    Regarding the derating factors we use around here:
    • 0.81 derating for "normal" operating solar panels on a MPPT charge controller (hot panels, depressed Vmp)
    • 0.95 typical derating for MPPT Charge controller

    • 0.81*0.95=0.77 panel+controller derating (note this number works pretty well for PWM panels+controller -- but different derating calculation)

    • 0.85 typical inverter efficiency (inverters can be >0.90 at "optimum" loads, or less than 0.80 or even 0.50 at high power or very low power)
    • 0.80 typical flooded cell efficiency (really 0.8 to 0.9+, but can be worse too, depending on how bank is operated)
    • 0.90 typical flooded cell efficiency (again, really 0.9 to 0.98, again depending on how bank is operated)

    So:
    • 0.81 panel * 0.95 controller * 0.80 flooded cell * 0.85 AC inverter eff = 0.52 end to end efficiency

    Fusing and breakers... There is calculating the "loads" first. Note that some devices are voltage dependent (electric heater; higher voltage, more current draw, more power used). Some are constant power (AC inverter, Motors, etc--P=I*V)... If you have a 100 watt AC load:
    • 100 watts * 1/0.85 inverter eff * 1/14.5 volts battery charging = 8.1 amps @ 12 vdc bus
    • 100 watts * 1/0.85 * 1/10.5 low battery+wiring drop = 11.2 amps @ 12 volt bus
    • 11.2a / 8.1a = 1.38 or almost 40% more current at low battery voltage and/or lots of voltage drop

    Then there is heating of the wiring... Wires themselves have resistance and will overheat and fail. Add that the wiring insulation will prevent some cooling, plus different types of insulation can withstand different "maximum" temperatures. Wire inside conduit (or buried underground) cannot dissipate heat as well. High ambient temperatures (roof top, in attic, etc.) raise base temperatures plus "hot copper" has higher resistance.

    Also, in the US (North America), the regulatory and safety agencies have decided on "deratings" for current. For example, if we have a 15 amp rated circuit and fuse/breaker, we can only use 0.80 (80% or 1/1.25) of the capability:
    • 15 amp circuit * 0.80 (or 1/1.25) NEC derating = 12 amps maximum continuous current

    If we use >12 amps for minutes to hours, the fuses/breakers will eventually trip (we have fast trip, slow trip devices. Breakers may be thermal trip or magnetic trip, etc.).

    For example, a 1,200 watt AC inverter running on a 12 volt battery bank:
    • 1,200 watts * 1/0.85 inverter eff * 1/12.5 volt nominal = 113 Amps @ 12 volt bus
    • 1,200 watts * 1/0.85 * 1 / 14.5 volts charging = 97 Amps charging battery bank
    • 1,200 watts * 1/0.85 * 1/10.5 battery cutoff = 134.5 amps with 11.5 volt battery and 1 volt wiring drop
    • 1,200 watts * 1/0.85 * 1/10.5 battery cut off * 1.25 NEC derating = 168 amps NEC Branch Circuit minimum (round up to next standard fuse/wiring)

    So, for our 1,200 watt "100 amp" inverter, we need a 168 amp minimum fuse and wiring. Looking up fuses and breaker, in the US we have:

    http://www.solar-electric.com/infubr.html

    So, we have 175 amp as the next standard breaker/fuse size.

    Then we proceed to some sort of table that lists "safe current" for various wiring conditions/materials. For example, here is an example of one of the NEC wiring tables (don't worry, probably will not make much sense in AWG wire sizes and various "classes" of insulation):

    http://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    Looking at the table, we see that we can range from OO to OOOO size cable (note insulation temperature rating is the difference here). Or in metric:

    http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=guide_awg_to_metric



    [TH]AWG Number[/TH]
    [TH]Ø [Inch][/TH]
    [TH]Ø [mm][/TH]
    [TH]Ø [mm²][/TH]


    6/0 = 000000
    0.580
    14.73
    170.30


    5/0 = 00000

    0.517
    13.12
    135.10


    4/0 = 0000

    0.460
    11.7
    107


    3/0 = 000

    0.410
    10.4
    85.0


    2/0 = 00

    0.365
    9.26
    67.4


    1/0 = 0

    0.325
    8.25
    53.5



    Or almost a 2:1 difference in copper wire cross section area (i.e., 2x more copper ~ 2x the cost of wire).

    You can also use other wiring charts, such as the ABYC (American Boating and Yacht Council):

    http://www.acbsphl.org/Tips_and_hints/ABYC_Wiring.htm

    Which would allow us to use as small as 2 AWG wire:



    2

    0.258

    6.54
    33.6



    Which is much smaller.

    But, we still need to check voltage drop. Say you want 134.5 amps with 0.5 volt drop (most "good" inverters will run 2x rated power for a few seconds, so you still need to meet the, for example 11.5 volt and 1.0 volt drop = 10.5 battery cutoff voltage). Using a generic voltage drop calculator... Say you want 3 meter (10 feet) one way run of cable from battery to inverter for DC wiring (note, wire length is 2x run length. Some calculators use run length, others use actual wire length). Using this generic voltage drop calculator:

    10 feet (one way run) with 134.5 amps and normal air temperature will give ~0.5 volt drop with 2 AWG wire.

    So do you use 2/OO/OOOO wiring--I can tell you that open 2 AWG wiring will appear to meet my above example requirements. If I was to install in conduit, then my NEC code would require 2/O to 4/O wiring (minimum).

    That is the short answer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    Pretty long "short" answer Bill. :D

    The 77% derating is "typical" of panels & controller, but not absolute.
    Likewise the 52% derating for a whole battery-based system is "typical".

    Either one is affected by the actual installation, so things like expected insolation provided by PV Watts figure into what a particular system will do. But you've got to have some sort of derating figures to start the calculations. People who assume 100% efficiency are the ones that end up with dead batteries sooner rather than later.
  • fm.109
    fm.109 Registered Users Posts: 33 ✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    That was a pretty 'short' answer I would agree with cariboocoot lol.

    BUT I have to say that was enlightening. Now I am aware of how deratings are calculated. So basically deratings can vary from a one scenario to another based on climatic and system components.

    BB once again thanks, like always I appreciate your awesome help and cariboocoot thank you as well for pointing out a lot of ways in calculations.

    I am supposed to enroll sometime soon for solar tech training for both battery based and off-grid systems so hopefully soon I can help here too in giving some sort of answers, however in the mean while i am a very very very basic student lol so would be kind of annoying at times since I would be asking questions that would sound childish at times but for me the answers to those would be like revelations.

    Though I will bug you guys again as soon as i get stuck somewhere lol and once again thanks I would definitely have a look at fuse and wiring sizes.

    Thanks again BB and carboocoot.
  • fm.109
    fm.109 Registered Users Posts: 33 ✭✭
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    Though one small question, can you guys refer me to some good inverters and charge controllers.

    Since our AC power here is at 50hz and 220 Volts.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    We all started with zero knowledge, and with the help of others, we move ahead.

    And you are doing it in a "foreign" language--I barely get by in English (my only language).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Charge controller & fuse sizing.....Also need help in sizing inverter for refrigerat

    Our host has several good lines. Even if they are not available (or cost effective for you), reading about their capabilities will give some good ideas of what to look for in locally produced products.

    Also, in some of NAWS's website, they have some short papers that explain critical issues about the various options:

    Under Solar Charge controllers:

    http://www.solar-electric.com/chco.html

    All About Charge Controllers
    Read this page about power tracking controllers

    Midnite Solar has probably the most technically advanced MPPT solar charge controller today--and they are actively expanding capabilities. Outback and MorningStar make some good MPPT controllers (and MornngStar has a wide range of PWM--lower cost controllers). The Xantrex units are nice for use with the XW AC inverters.

    For off grid AC inverters, these really depend on your power needs. Some companies are very strong in smaller AC inverters (Morningstar makes a killer 300 Watt True Sine Wave 12 volt inverter with remote on/off and "seach mode" (power savings). There is nothing else in that range.

    Larger inverters--Outback, Xantrex, and Magnum have some nice inverters with lots of functions (off grid/grid tied, networking, remote on/off, search modes, split phase 120/240 VAC, 3 phase, and many of these inverters do have 230 VAC 50 Hz versions). And there are other less costly or more rugged inverter mfg. too.

    I tend to "push" TSW (true sine wave) inverters over MSW (Modified Square Wave). In truth, about 80% of AC appliances will work OK on MSW inverters. And about 10% will fail and/or have early life failures. TSW prices are still relatively high, but if you need off grid/reliable power (rather than emergency power), TSW are something to really save up for and purchase (if you can).

    http://www.solar-electric.com/inverters.html

    All About Inverters
    Choosing an Inverter - Home Power Magazine

    Another tool I really like to suggest are Battery Monitors (Victron is also a good brand). They put a precision power resistor (also known as a "shunt") in the negative lead of the battery bank so that all current into/out of the battery bank can be monitored/measured (amps*hours in/out) so that the battery state of charge can be estimated. Not perfect, but really helpful to understand what is going on in the battery without having to measure the specific gravity with a hydrometer every time. Also very useful with family members/guests to read a XX% state of charge meter (and hopefully, save you killing a battery bank).

    Note that Vicron is an European brand and makes some vary nice charge controllers and AC inverters too (and other equipment)--if European brands are easier for you to get (as well as SMA out of Germany for many models of AC inverters).

    There are many companies out there that I don't know about or have not mentioned that all make good equipment and (hopefully) have good customer support. But--I suggest 1) conservation of energy with efficient appliances/reduction of use and 2) sizing the system first, then start looking at hardware. After you have done a couple of paper designs, then you can start buying (there may be two or more ways of doing the same thing--And you should paper design both ways to see which is better for you).

    And I will suggest this Working FAQ--Lots of links to other websites/sources of information:

    http://forum.solar-electric.com/showthread.php?5556-Working-Thread-for-Solar-Beginner-Post-FAQ

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset