my 12v offgrid system

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

  1. Scott Mac

    Scott Mac Well-Known Member Premium Member

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    The regulator should not allow the voltage to get that high in charging your 12V batteries. 15V for equalization, 14.2V for bulk, 13.8 for absorption and 12.8-13.2 for float. if your reg say each 12V, 200W panel is charging 10-11 amps, this is the most accurate way to work out max current for the 4x200W panel array. Still allow for greater current unless as you say the reg will prevent the extra current the reg's not designed to produce. Sunny day with cooler wind on panels may produce more current/power.

    It's been a while since I needed to know exact charging voltages, so a google would be advised
     
  2. Mark

    Mark Founder Staff Member

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    Moved this excellent thread to our Energy section - seems more appropriate there :cheers:
     
  3. Scott Mac

    Scott Mac Well-Known Member Premium Member

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    Also, 12V has a problem with voltage drop over quite short runs of cable. larger cables have a benefit in carrying the voltage further. Google the voltage drop calc and this will help choose cables. http://www.kilowatts.com.au/calculator-voltage-drop.php

    eg.
    Allowable Voltage Drop5 %
    Run Length10 m
    Current Demand30 A
    System Voltage12 V
    Voltage Drop2.00 mV/A.m
    Recommended Cable Size25 mm2
     
  4. stevo

    stevo Backyard Farmer Premium Member

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    I plugged in the new panels this weekend.

    As the sun rose the amps started coming in to the regulator, the regulator heat sink started to get really hot, I put a temperature gauge on the heatsink and it got to 60 degrees C when there was 25amps entering the regulator. I didn't really like the heat so unplugged one panel and was getting 20 amps in and the temperature sat around 45 - 50 degrees C on the heat sink. I didn't like that either.

    Other observations:
    With all four 200watt panels plugged in the 10mm cable temp raised a couple of degrees by feel, around the same temp at both ends of the 10m cable. Not hot but just warmer than normal.
    Over the 10m cable length, the 200watt/4 x 10amp panels only reach 27amps.
    On short cable they do output 10amps each.

    So I may need to upgrade the cable to 25mm as suggested to get the best result, though I don't think that will affect the high temps from the regulator.

    Regulator is a Fangpusun PR3030, I looked inside and the connection from the cable terminal to the board is a fairly thin strip of tin, so I think that could be weak link. Even if I put 25mm cable in that little bit of tin is going to let it all down I think. I'll have to connect the 30amp regulator up using a short cable to see if it makes a difference.
     
  5. stevo

    stevo Backyard Farmer Premium Member

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    I emailed the re-seller of the Fangpusun regulator and they said the high temps are normal, and I could add air flow to help cooling. I find it a bit suspect that something runs that hot, 60 degrees at 25amps, so what if I put in 30amps like it's rated for, does it go to 65 or 70 degrees? I think that'd be a risk of failure? I'll have to try on the weekend. I can only do testing during the day in full sun, and unfortunately I'm at work!

    I also emailed Fangpusun, but no reply from them.
     
  6. Scott Mac

    Scott Mac Well-Known Member Premium Member

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    high temp at heat sink can be ok, as that's where the heats meant to be dispersed. does sound hot though. cable does raise temp with the flow of current. My 60A reg has a built in fan. Does your regulator offer charging 12V from a 24V array? wire 2 panels in series and then two banks in parallel back to regulator. cable size stays 10mm, current drops, higher voltage and heaps less voltage drop from cable. I have a 48V array charging a 24V bank. Or double up on the 10mm effectively giving you 20mm. 10M is not far, though with a low voltage, it can drag the efficiency down. the voltage drop from the regulators thin tin strip is unlikely an issue due to mm of run for the current. length of run in meters does makes a difference. On an acreage where I have to run mains under ground from a pole for a few hundred metres to the house meter box, i'll raise the cable size to maybe 35mm or greater and then drop back to 16mm inside the meter box.

    if you've tested a panel with the reg and got 10 amps, I'd be surprised. what was the state of charge off the batteries? If their 75% charged, the current will be lower than if they were at 50%. what is the size of the battery bank? with 800w of panels at 30Amps, your bank size will also determine the ability of current flow. I'd have a minimum of 400AH, though prefer 800AH bank for that amount of current.

    My bank is 1600AH @ 24V and I charge it at 60Amps with my 24V inverter/charger and generator and around 45-50 amps via regulator via a 1400W array. max current from panels if you don't include losses is 58.3A.

    If the panels have a cool breeze on them on a sunny day, you'll get higher current.

    Lots of factors there.
     
  7. stevo

    stevo Backyard Farmer Premium Member

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    Interesting, some good ideas there. I checked and looks like my regulator does 12 / 24 volt.

    I only have 2 x 12v 120ah batteries, 240ah total for the main system. I'd like to increase the battery capacity but at the moment that's all I've got.

    I could experiment and wire two panels in series to get the benefits you suggested. I'll have to wait til the weekend to make any changes so i'm at home to put any fires out. (just joking)

    1600AH ? gees there must be some money in batteries! I've just got the pov pack hobby set up.
     
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  8. Scott Mac

    Scott Mac Well-Known Member Premium Member

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    Charging a small bank with large current isn't a good idea. 25amps is max recommended. How many watts do you use a day? If 1000, a bank should re charge in 5 hrs easy with a couple of panels.
     
  9. stevo

    stevo Backyard Farmer Premium Member

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  10. Scott Mac

    Scott Mac Well-Known Member Premium Member

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    That's it. I find the best way to know is if your regulator shows a record of watts or A/H for each day, and if your bank hits float charge, that's the clearest way to know what your system uses per day. it shows all the losses that had to be made up for due to consumption of inverter etc. My inverter at 3kw uses roughly 24AH/day from memory.

    e.g.
    I get 220AH from the sun per day with a couple of hours of float charge time (Batteries full and trickle charge state). So 220AH x 24V= 5.28KW/day
    or 5280W/24V = 220AH So my bank of 1600AH will be fine for 2-3 days of rain, then charge so as not to allow the cycling of the batteries to get too low. cycling to 50% every now and again is ok, though not best every day, other wise short battery life.
     
  11. Lee-Mika

    Lee-Mika Active Member Premium Member

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    Hi Stevo
    I find this thread very interesting, have you found any distance issues yet. Do you know how long of a 12v run can be? I have planned out a system but it isn't very cost effective as of yet. hoping to get a hand planning this out.
     
  12. stevo

    stevo Backyard Farmer Premium Member

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    hrmm i haven't played around with my system for a couple of months as the budget ran out.

    I have a 10metre length of 10mm cable from panels to regulator, and it seems to lose some amps over that length but I didn't spend much time checking it at the time. I'd recommend shorter than 10metres for a 12v system, but you can't have everything I guess... it's all a bit of a compromise for each thing you do.
     
  13. Lee-Mika

    Lee-Mika Active Member Premium Member

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    I was looking at using a simple 12v simple so I could save on not having an inverter. But distance is were I came into a problem. I needed to run other lighting farther away. So I was forced in put a inverter in my solar project plan. which added another 1000,00+ dollars to the cost of my planned system.
     
  14. stevo

    stevo Backyard Farmer Premium Member

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    if you're just using 12v lighting at a long distance away from the batteries I don't think that'd be a problem as lighting wouldn't use much power and could afford to drop a little over distance. But you'll need an inverter to run your TV anyway? unless you get a 12v TV.
     
  15. Scott Mac

    Scott Mac Well-Known Member Premium Member

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    Hey all, just saw post. 12v systems end up costing more, special appliance, large cables etc. also very restrictive.

    To wire up 240v, don't even think about it unless your a licenced contractor, and find one who knows stand alone requirements. Many contractors don't understand stand alone needs, ie, never make an nem connection, earth and neutral not connected together. Hard to get shock due to the need to be touching both active and neutral, not earth. 120v present on neutral, etc etc. this is all electrical terminology, sorry, yet I feel you need to be aware that it's not something you can learn on the web and safely carry out 240v wiring. Fire is probably your greatest threat even only doing 12v wiring.

    I don't like putting a dampener on DIY projects. Legally I cannot teach you how to wire on the net as my electrical contractor's licence is under threat if I do. I've probably given too much instruction as it is.

    Have your house wired by a suitable contractor and have him install a 15amp inlet. Then carefully try the 12/24v solar with inverter and use a 15amp lead like a caravan set up.
     
    Last edited: May 28, 2014
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  16. Tim C

    Tim C Two heads are better than one Premium Member GOLD

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    200 watt panels are about $230 each. A solar charge regulator to suit $12. Don't bother with 12/24 volt dc appliances. My 3000/6000w inverter was $236 off ebay. A 240 volt fridge, and all appliances imaginable are 1/3 the cost and 100 times the life expectancy of 12/24 volts. Invest your money in a couple of good batteries instead. Put it through the inverter. The so-called experts will baffle you with bull**** to sell their products at 6-10x what it costs from China. They will insist on expensive and complicated control systems .They will charge you $60-120/hr to hook up a couple of wires and run tests But if you are not there to flick the switch, it makes no difference. Beeping controls only use more power. The trick is blocking diodes, so the power doesn't drain back to the panels at night, and thick 12/24v leads to avoid heat. Electricians are the last people you should seek advice from on dc-ac power. Old brown light switches were designed to handle 36v-dc, disconnecting fast and far to avoid dc burnout. new white switches don't.
     
  17. stevo

    stevo Backyard Farmer Premium Member

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    yeah Tim i'd agree with you there. This thread got a bit messy along the way. I should update my systems as they have changed along the way.

    Though, this thread was based around a small 12v offgrid system, and I still favour the 12v system for small offgrid situations. I understand that there's a point where it would be better to just go 48v / 240v appliances and i'm getting to that point now. It was a little project to learn and research offgrid systems because I don't really know much about the tech stuff. Panels are getting cheap, but batteries are still expensive. People are favouring more panels and less batteries because of the cost.

    My systems are still running, runs my 12v tv, computers, lights, pond pump, chargers etc , when I buy stuff I look for 240v/12v charge, my new dust buster charges on 12v! .....and I save money on the bills. I still like the challenge.

    As you stated, my new 240v fridge was 1/3 the cost of a 12v fridge of similar size, that's why I went that way. But, it needs more power than a 12v fridge, more batteries.

    anyways, I enjoy the journey, ... but... it would be wayyyy cheaper for me just to not do any of this and pay the normal electricity bills. Got to have a hobby but :blush:
     
  18. Tim C

    Tim C Two heads are better than one Premium Member GOLD

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    Too right, plus at least you have options should the power go out for any length of time. Reminds me of the beer ad with the dog on the treadmill, powering the TV.:cheers:. My keg cooler up north was a solar pond pump wetting towels wrapped around the keg in a cut off drum. As long as the keg was in the shade and the panel in the sun it cooled the beer to drinkable temp!! Any breeze and it was proper cold!
     
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