my 12v offgrid system

Discussion in 'Energy' started by stevo, Jul 6, 2013.

  1. stevo

    stevo Backyard Farmer Premium Member

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    Last edited: Jan 3, 2014
  2. stevo

    stevo Backyard Farmer Premium Member

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    update: i'm still thinking about the fridge idea. I may get an 12v - 240v inverter anyway, because I have a new laptop and it seems HP decided to use a DC power plug that no one has an adaptor for so my normal laptop car charger doesn't have a plug that fits.

    Not long ago someone gave me two 6v 110ah batteries, and I had a spare regulator and panel, so I just put this system together this afternoon to see how it would go.
    This system is made up of: 1x 85watt panel (at the moment). 1x 15amp regulator, 2x 6v 110ah batteries to make 12v, 1x 300watt inverter, and this is currently running the 240v pond pump. I'm not really sure how it will go but is coping so far. If it runs a bit low I can connect up my spare 200watt panel.

    [​IMG]
     
  3. stevo

    stevo Backyard Farmer Premium Member

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    update: Some geeky stuff...

    I have had this security camera system set up for a while but it has been running "on-grid" 240v through transformers to 12v. I have just converted it to run from the 12v system. It's a cheap ebay Sunluxy system with 4 cameras. I have put a 1TB hard drive in it so it records forever. It runs 24/7. It is connected to the TV so I can either watch previous recordings or while watching TV I can flick across and see what's happening. I used to have it set so it uploaded photos to my website every 30 minutes so I could look at it from work, but the software was too buggy and kept crashing so I didn't worry about it. The cameras are night vision aswell so you can see most movement at night, like rats.

    photo is of the TV screen. Top left - Chicken coop, Top right - Pond, bottom left - back door, Bottom right front patio

    [​IMG]
     
  4. Mark

    Mark Founder Staff Member

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    You sure have a fair few things running on your off-grid setup - nice.

    Chicken cam is pretty cool :) I could do with some extra eyes in my chook pen to see what's stealing my duck egg every morning lol...
     
  5. Scott Mac

    Scott Mac Well-Known Member Premium Member

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    4amps for fridge is not quite right. 1000watts divided by 12volts = 83 a/hours per day. Plus what ever the inverter uses to convert the voltage current etc. allow probably 100a/h/day. If you then trust the manufacturers calcs.
     
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  6. stevo

    stevo Backyard Farmer Premium Member

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    cheers Scott. I'm still trying to get my head around it. Do you have an idea of what amps the 240v fridge would draw while running? My guestimate was 4amps. Although if it only runs 50% of the time, then maybe it draws 8amps when running? I'm trying to work out what kind of system/panels/batteries i'd need to be able to run a 240v fridge. I know I can run a 12v fridge easily but the purchase price is double/triple compared to 240v.
     
  7. stevo

    stevo Backyard Farmer Premium Member

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    Today the delivery man brought me an inverter. Projecta IP600 PureSineWave (600watts).

    I couldn't resist, I found a 5ah battery, that's the little battery at the end of the red and black wires. I hooked it up and plugged the 240v fan in, works easy and reads 25watts, so 25 divided by 12v is 2amps? I think that's how it works?

    Now I'm keen to get home and try the inverter on my systems at home to see what I can run... stay tuned, possible explosions :goinghome:

    [​IMG]
     
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  8. stevo

    stevo Backyard Farmer Premium Member

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    Lastnight i hooked up the new 28okWh 240v fridge to the inverter and batteries.

    woooo my guestimate was right?, it draws 8amps when running.

    More dodgy calculations:
    Assuming it runs 50% of the time we'll call it 4amp draw? My 240ah batteries would run it for 60hours, but i think we'll just call it 48hours/2 days.

    Now to see if i can get enough power back in to the batteries during the day with the panels. It will probably depend on the amount of sun i get, and length of day, so winter might not work out so well, but it would run less in winter.

    Some of you might know all this stuff but I'm still learning so it's pretty interesting for me. I must have too much spare time.
     
  9. Mark

    Mark Founder Staff Member

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    I think it's very interesting also - I don't know anything about independant solar setups personally but I can see a day when most people will be installing DIY solar to power small things around the home and then it'll slowly creep into home power once the technology becomes cheaper and easier for all to do and understand.

    It's probably happening already - people are looking for ways to save on grid power and solar energy panels/devices + improvements in battery storage/sizes/prices are become an attractive alternative.

    Just see how your own system as improved since the start of this thread...
     
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  10. stevo

    stevo Backyard Farmer Premium Member

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    I just keep throwing more money at it, solves the problem every time :ROFL:. I'm getting a bit offtrack from my 12v standard by trying to run a 240v fridge, but anyways :blush:

    The upright 12v fridges are atleast $1200 for a 100L size, and I think they were getting up to $2000 for a 200L size. These are meant for the RV/Caravan market. Sounds crazy to me when a 240v 200L fridge is around $500 and probably better quality. (but yeah you then need to spend a bit of money on more batteries and panels)


    I was talking to someone about my fridge, and they said they had one about the same size, it's an older one but still has a star rating.

    There's is rated 4.5 stars, but 660kWh !!
    Mine is 3 stars and 280kWh.

    So looks like they have improved efficiency over the years after all. Though I don't actually believe the kWh ratings, maybe they were tested in a cold country?
     
  11. Scott Mac

    Scott Mac Well-Known Member Premium Member

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    Hey Stevo,

    8amps sounds massive. A 240V fridge will have a info plate on it stating voltage, HZ and watts. Normally watts is around 360. Just looked at mine and it says 100watts which sounds too low. Start up current of a motor is always higher by around current x3, though should settle to specified current very quickly.

    the two important calcs to use is

    to work out how much running current an item uses
    360Watts/240V= 1.5Amps, if frigde runs @ 50percent of the time, cycle, 1.5amps or 360watts x 12 hours = 4320watts per day.

    remember this, voltage and current change, though power watts stays the same. 360/12V=30Amps. Cable must be able to carry 30Amps at 12 V so minimum of 4mm cable which can carry 32amps by regs. On the 240 side of the inverter 1.5Amps, so a 1mm flex cable can carry 10Amps. Power points must be run in a minimum of 2.5mm cable.

    say you have a 600W inverter, this may be able to run a fridge at 360W, with an allowance for a surge current of much higher.

    got to go, ill check for any questions latter
     
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  12. stevo

    stevo Backyard Farmer Premium Member

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    ay Scott

    The fridge says 280kWh on the rating.
    The inverter shows 100 watts when running the fridge. 100watts divided by 12v = 8.3amps ?

    It was a couple weeks ago so I forgot, but I think I plugged the inverter in through the regulator aswell and the regulator said 8amps draw.

    My old laptop draws 4amps at 12v. (according to my solar regulator)
    My 12v TV draws 4 - 5amps. (according to my solar regulator)
    The 240v fan drew 25watts so it's 2amps?

    so I thought 8amps sounded about right?

    100watts x 12hours a day = 1200watts. 1200watts x 365days = 438kWh actual fridge rating?
    The claimed fridge rating is 280kWh. 280 divided by 365days = 767. 767 divided by 12hours (50% cycle) = 64watts

    claimed rating of 64watts, actual rating is 100watts? assuming the 50% cycle rule?

    Now I'm getting confused :oops:

    Maybe it will run less than 12hours a day though, I'll have to plug it in to the regulator for a few days and measure what it uses.
     
  13. stevo

    stevo Backyard Farmer Premium Member

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    so..... if I connected two 12v batteries to make 24v, I would halve the amp draw? 100watts divided by 24v = 4.1amps?
     
  14. armysnail

    armysnail Active Member Premium Member

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    When you finish, could you translate your findings into English so I know what to do?
     
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  15. Scott Mac

    Scott Mac Well-Known Member Premium Member

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    ok, your calculations are pretty much right till you reverse the calculation estimating 64 watts. Watts are stable at 100 watts and the cycle is variable.
    - your fridge uses then 8.3A x 12 hrs = 100AH/day. now add up all the other appliances. i'll use lighting as an example

    - 60w total for 6 hrs per day = 360watts per day / 12V = 30AH/day (3x20W compact fluros on during darkness)

    Add the two AH's together and you use 130AH/day

    - 130ah/5 hrs of sun = 26ahrs/hr minimum preferred charge. W=VA so W = 12Vx26A=312Watts wo..rth of panels for your system will keep the batteries charged. I like to use 5 hrs for poor winter charge. Summer is great for charging.

    Now lets say after the 5 hrs, the batteries need enough storage to run system till next days charge. 19 hrs, so 130AH/24hrs x 19hrs= 102AH.
    if you have a 200AH battery bank you'll cycle the batteries down to 50% every day. I like to cycle no more than 20% so the batteries last much longer. Ideally 10%.
    so a 500 or greater AH bank is my opinion the minimum for a standalone system with no grid power for years of reliable supply. Obviously a stand alone ises more than just a fridge and lights, so all other appliances need to be added.

    I have a 1600AH bank at 24V and 1.4KW of panels and struggle during the winter.

    yes, the higher the voltage the less the current and the smaller the cables needed on the low voltage side of the system, ie batteries to inverter to solar regulator etc.
     
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  16. stevo

    stevo Backyard Farmer Premium Member

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    Thanks Scott :cheers:

    I tried the fridge on the inverter yesterday. It starts up at 100watts, but I checked it through out the day and it seems a bit random, I guess it depends on what it wants to achieve. Sometimes it'd run at 60watts and sometimes at 30watts. It one of those new "digital inverter" types, what ever that means.

    The fridge door was opened a fair bit and new warm items were put in so I think it ran more than usual.

    I just plugged in another panel so i'll see how it copes today.
     
  17. Scott Mac

    Scott Mac Well-Known Member Premium Member

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    when I said 312watts worth of panels, I would obviously go higher. if you have 700watts worth, an estimated 2 days worth of storage power is possible in winter per day, which helps when you have a rainy day. also panels aren't fully efficient, so don't count on the full 315w out of 315w worth of panels. expect at least 10% less.

    Batteries charge fast when low and the charge slows up the fuller they get. So many variables I know.

    fridge current is showing the 12V side of current. 240V side will be 100W/240V =0.4Amps

    if you wire 12v wiring, voltage drop plays a big factor and expensive cables may be needed. 240V is by far better as large runs of cable and smaller cheaper cables are possilble
     
  18. stevo

    stevo Backyard Farmer Premium Member

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    update: Another two 200watt panels turned up the other day (not connected yet) .. giving me a total of 800watts (40amps maximum) of panels for the main system. I currently only have a 30amp regulator so at full sun the regulator should discard any extra amps. (From what I've read it should discard extra amps and not catch fire, if you don't hear from me for a while maybe it caught fire)

    The idea of having more panels will work well to input more amps when there's less sun. I'll have to upgrade my regulator at some stage.

    Also, I added a 12v pressure pump for the water tank to my smaller offgrid system, it's working awesome, now I can pump water from the tank to the garden instead of gravity feed.
     
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  19. Scott Mac

    Scott Mac Well-Known Member Premium Member

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    800 watts divided by 12V = 66.6Amps. with loses maybe expect 50 plus amps. cable size, max charge current for bank, regulator size is all needed to be considered for fire prevention.

    watts= current (amps) x volts
    current = watts/volts
    cable sizes as an example only,
    1mm - 10A
    1.5mm - 16A
    2.5mm - 20A
    4mm - 32A
    6mm - 40A
    16mm - 80A
    Hope this helps, are you upgrading to 24V system. 800w at 24v = 33.3A expect less than 30A
     
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  20. stevo

    stevo Backyard Farmer Premium Member

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    Thanks for the info Scott.

    As far as I can see, all panel specs I look at state the watts divided by the maximum voltage, for example 200watt panel divided by 18volts = 11amps, and that's about what the regulator says at full sun , about 10 - 11 amps. Maybe I could get more out of it if I position the panel better. This is the specs for my panels, and I did a search on different panels and it seems they all do the same.

    I didn't know that about cable size, but I checked today and all my cable is 10mm :cheers:

    I didn't get them hooked up today, i'm still working on how to mount them with brackets etc
     
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