Off Grid Power

Discussion in 'Off Grid Living' started by er1c, Nov 2, 2014.

  1. er1c

    er1c Monkey

    Hello, I am new to the forum but I thought I would join as I am very interested in off the grid living. I live in the UK in a very rural area.

    I thought I would post some pics to explain the project a bit more but also bring a human element instead of my saying why doesn't it work :)


    So the task at hand it a Hut.... I will cover other bits later but my problem at the moment is the power.

    2 250w Solar panels provide power at present. I must add power demand is minimal, for a water pump 1kw which rarely runs and a 240v circuit should it ever be needed.


    These go into a not great charge controller but I accepted a little inefficiency when purchasing. I believe this is 33 percent less efficient that a modern one.. But still as you can see 18amps is going into the controller.


    As you can see above the battery percentage is 72 percent (this is worth remembering later). I haven't hooked the LOAD up to this charge controller as I don't think it is adequate for the potential pull from the inverter. So the load comes straight off the batteries.

    This charges 2 250AH deep cycle batteries via the controller. These are 12V batteries in Series with the inverter connection coming from the positive on the left battery and the negative from the right battery.


    All of this goes to a 3KW inverter (pure sine wave). Note I have increased cable size to that of the large black one below and not the small red one I had originally. I have also added the earthing cables since the picture was taken.

    Note the switching box allows for mains (if I ran an extension cable up to the hut and plugged it in) or "2" which is batteries below.

    So everything works as it should... I was concerned about the gauge of the cable going from the batteries to the inverter, so despite it working I went for the biggest cable I could which is for welding and meets the spec of 400 amps which the inverter could pull (but never will in my scenario).

    I also reduced the length of the cables, I think the longest is about 2 metres which should be well in the safety range. I did have some issues with the connectors for the cables, I wasnt sure if they were up to the potential amps going from 12v to 240 but the fuse below gives me a safety element. They are the biggest the electrical place had, I had to hammer crimp them on then drove a nail into the middle to pinch it.

    To be extra cautious I added a 100 AMP fuse on the circuit between batteries and inverter.

    The Problem

    So the charge controller tells me the batteries are at 99 percent (which is max) in this state no power will be sent from the panels to the battery. As soon as I turn the inverter on (even with the master hut power set to OFF) the battery drops to 72%.

    I left this on for a couple of days and it was at 68%.

    Is this a problem? Is this due to the cables (I cant see how it could be) or is it down to the fact the load for the inverter doesn't go through the charge controller ?

    Should I be worried about this ? The inverter when it is on does produce some heat which I accept (the cables are cool even under load) and the draw should be minimal. the 250 AH batteries 2 will have 500 AH in them and are brand new so I don't understand the 28 percent drop ?
    Dunerunner likes this.
  2. KAS

    KAS Monkey+++

    BT !!!!!!!!!!!!!!!!!!!!!!!!!!
    AmericanRedoubt1776 and kellory like this.
  3. kellory

    kellory An unemployed Jester, is nobody's fool. Banned

    AmericanRedoubt1776 likes this.
  4. er1c

    er1c Monkey

    I assume you mean he is the chap to ask :) I shall await his viewing of this thread :)
  5. Yard Dart

    Yard Dart Vigilant Monkey Moderator

    Welcome to the Monkey @er1c !! There are many here with extensive solar knowledge!!
    Maybe @Cruisin Sloth may have some input as well. :)
  6. Dunerunner

    Dunerunner Brewery Monkey Moderator

    Hi @er1c , welcome to the Monkey!!

    My first question would have to be.... How old are the batteries? Secondly, have you checked the connections at the battery and inverter for tightness? I ask because the load you are applying to the batteries is the inverter itself. Is there a fan that operates on the inverter or is it convection cooled? Whether or not there is any output from the inverter, it does represent some amount of load for the batteries. A faulty connection anywhere between the batteries and the inverter will act as additional resistive load when the circuit to the inverter is completed.

    I would check those things first. Are these measurements with or without the charge controller providing power from the solar array?
  7. Mindgrinder

    Mindgrinder Karma Pirate Ninja|RIP 12-25-2017

    Wait for a reply from the experts here....

    At a glance...this is how i'd prolly troubleshoot it...
    (never done solar b4 so again I say..wait for the expert reply)

    Test bank charge with a different device when inverter is on and off. Same results?
    Perhaps your charge controller thinks 72% is actually 99% and only displays accurately when being pulled on?
    Try it with 1 battery.
    Physically unplug everything past the investor and retest. (not just shut off)
    This should give u an idea if the loss is between battery and invert.
    Smaller fuse? Retest.

    Just thoughts...
  8. Airtime

    Airtime Monkey+++

    Your charge controller is making an estimate of the battery state of charge based only on voltage that it is seeing at it's terminals and the current it is supplying. Without other inputs such as the actual battery temperatures (as opposed to environmental) and a voltage measured at the terminals of the battery this is an estimate at best. So when the inverter is turned on, it does have some current draw even though there is nothing being powered by the inverter. This draw reduces the voltage seen by the charger just a bit and will cause the charger to supply some more current which partially supplies the inverter and that makes it think the batteries are now not fully charged.

    Is this a problem? Probably not. The invertors have a low voltage cut off so they don't drain the batteries down too far. Generally you don't want to discharge a lead acid battery less than 50% as deeper discharges significantly reduce their life. You have monster cabling between the batteries and inverter which is great as this helps keep the inverter from thinking the batteries are at a lower state of charge than they are.

    If the charge controller or inverter have provisions for battery temp sensors, install them! This will help prevent over charging, over discharging or shutting down the inverter when the batteries still have adequate charge to keep running. If they don't, see if you can co-locate the charge controller right next to the batteries in their area so the environmental temp it reads (and maybe it is assuming is close to the battery temps for assessing state of charge) is closer to the batteries' actual temps. This might (I wouldn't hold my breathe) improve the charge reading for the batteries.

    If you really want to know for sure what might be going on, get ahold of the actual voltage/temp/charge curves for your batteries. Using a decent volt meter and thermometer in contact with the battery (or even in the acid assuming non-metal probe) and determine for yourself the charge. A hydrometer to measure the specific gravity of the acid isn't too bad either. You can now get an assessment of just what the charge controller is indicating under different conditions and how off it is. Hope this helps.

  9. techsar

    techsar Monkey+++

    Dunerunner has some good areas to check for potential problems (no pun intended). Do you have an ammeter to insert inline to check for excessive current drain? Even a new inverter can be defective... BTW be sure to bypass an ammeter when initially applying current to the inverter. Very high current is normal for a very short time...enough to destroy many meters.

    But in the end, as Airtime noted, the "meter" on the charge controller is a guesstimate at best. If everything else turns out normal and within specs, don't lose sleep because of a poorly programmed Chinese microchip ;)

    ETA: Good call on going with the largest DC conductors you could and making the runs nice and short. Simple things that can make the difference between success and failure.
    AmericanRedoubt1776 likes this.
  10. er1c

    er1c Monkey

    Thanks folks, as stated they are new batteries so should be fine. They are deep cycle sealed units designed for this and everything is tight as I wanted to avoid sparks. It makes sense that a few .3 of a watt may make the controller think its low on the percentages. The controller has a temp sensor and the inverter has thermal and over under voltage shutdown. I will run a multimeter over all the connections at the weekend (next) to see what is produced.
  11. AmericanRedoubt1776

    AmericanRedoubt1776 American Redoubt: Idaho-Montana-Wyoming Site Supporter+

    Welcome to the Survival Monkey tree, my favorite preparedness forum on the Net -- broad depth of knowledge with kind civil members. Ol' Blighty has such beautiful rolling green hills out in the countryside. Thanks for your detailed (well-documented with pictures) interesting post. @BTPost will be most helpful.
  12. BTPost

    BTPost Stumpy Old Fart,Deadman Walking, Snow Monkey Moderator

    Hello Er1c, Your system is very similar to the one I just setup for a "Close" Neighbor (Close = 20 SqKm) here in Bush Alaska.... The Drop in Charge % that you are experiencing, is due to the Voltage Drop the Controller sees when the Inverter Load is connected to the Battery Bank. Since these are "New" batteries, there "should" be no question as to the "Stiffness" (Battery's ability to hold voltage while pulling a moderate amount of Current from them) of the Battery Bank. Things to check on are:
    1. Take a Volt Meter and measure the Voltage Drop across each of the Battery/Inverter Cables, while under load. (should be under .5 VDC)
    2. Measure the Battery Bank Voltage, at the Inverter Inputs, at No Load, when they are Fully Charged. (should be near 28.8 Vdc)
    3. Measure the Battery Bank Voltage, at the Inverter Inputs, at Idle Load, when they are Fully Charged.
    4. Measure the Battery Bank Voltage, at the Inverter Inputs, when the Inverter is loaded at 25%, when the Batteries are almost Fully Charged.
    5. Buy as 50 Mv Amp Shunt, and a Meter, for it that measures up to 200 Amps, and install it in the Inverter/Battery Positive Lead, to monitor
    the Inverter Loads.
    6. Calculate the Residual Loads on the Battery Bank from all other loads that are NOT the Inverter.
    The answers to the above questions, will let you characterize your System, and the efficiencies, of it, and point out any Issues, that might be present
    in the design, as it sits, NOW....
  13. er1c

    er1c Monkey

    Thanks for your reply BT..> Sorry for the delay I hauled myself up to the hut last week only to find my multimeter battery was flat :)

    Interesting findings. So with the Inverter on but no load on it, it has reduced to 23 percent over the last 3 weeks.

    I managed to get some readings, FYI I turned the inverter off and it went to 24 percent, and these were taken a day later when it was backup to 29 percent.

    I haven't bothered with the load, as I don't have an issue with when its on.

    Battery 1 11.31 Battery 2 11.31
    Both 11.31 (just in case)
    At the inverter 11.31


    Battery 11.22/3
    At the inverter 11.24 ?

    I am a bit stumped, when I first recorded these I figured I had a .2 drop but reading my notes that's an increase which is not possible ?

    I will let it charge as I left it turned off and re-read...
  14. vonslob

    vonslob Monkey++

    That looks like a really nice place you have, man it is so green ( i live in the water starved west). Good luck to you bro, this is a neat forum, nice people.
  15. BTPost

    BTPost Stumpy Old Fart,Deadman Walking, Snow Monkey Moderator

    From the looks of the Readings, you need to get the MultiMeter Battery changed, before you redo the Readings..... You can't have a higher Reading at the Inverter, than at the Battery, unless the Inverter is charging the Battery....
  16. Cruisin Sloth

    Cruisin Sloth Special & Slow

    Nice inverter , drop the plug & wire it in hard . Your killing your battery's one day at a time , your massively under panelled. 500Ah(battery bank ) being charged from 9 amps max , plus your in Foggy UK . Real poor Charge controller .

    So Have I just Peed on your Marmite toast !
    Sorry M8 , but all true . Reason Dams have huge water & fall of it is the PUSH power , your two 250 watt panels at best will push 150-avg to 200w max times two so now were at 300 watts mostly to 400 and we have a drink!! while we watch the battery die . Those need a 75 amp min charge to bulk charge them if they are 500 Ah @ 20 hrs MINIMUM !!

    You need to Visit here : Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun
    And here : The MidNite Solar Forum - Index
    Plus here : MidNite Solar Inc. Renewable Energy System Electrical Components and E-Panels
    You need a Classic 150 & 2500 Watts of panel (just guessing because UK is Grey days) , & summer your over panelling will have power for table saws or bread makers & toasters . (im going off battery of 500Ah & nice large Inverter with pump)

    Sorry M8

  17. er1c

    er1c Monkey

    Will re-do multimeter readings, in regards the panels, VT the intention was 500w is more than enough as it was to rarely be used. However I hadn't counted on any slow constant drain feeding the inverter.
  18. Cruisin Sloth

    Cruisin Sloth Special & Slow

    All inverters use / parasitic draw , some its a wee bit , others don't "Sleep" or rest .
    Your main power is for the pump of 230 V AC & how many watts or Amps.

    Since you have a PLUG into your inverter , buy one of these brit plug types :
    P3 International P4460 Kill A Watt EZ Electricity Usage Monitor | eBay

    Plug 16A Watt Meter kWh Time Electricity Analyzer Power Monitor 110 220V Voltage | eBay

    And measure EVERY THING so you know .

    I use one of these for a sleeping inverter : SureSine » Morningstar Corporation

    Last edited by a moderator: Jan 26, 2015
  19. er1c

    er1c Monkey

    Cheers, I had a sleep option which was supposed to set sleep at something like 40w.. the problem was it never woke from sleep and it was never documented. I assumed over 40w would awaken it but it didn't. I have one of the electric usage meters handy.. The reason I was SURE it wasn't a problem south of the inverter is that plug goes into a connection box which had 3 options.. BATTERY/MAINS or OFF.. and its always been off.. so no power but I will check..

    I don't want to deviate too much as I have no issue with usage or even the draw, the concern is the drop from 100 percent to 76 percent when active. Which I was more thoroughly stumped by.
  20. Cruisin Sloth

    Cruisin Sloth Special & Slow

    M8 can you post the full specs on Inverter , panels , CC , Make model etc . Then if you have a kill-a-watt meter what is the pump draw & KW usage . Im down later this week into Arlington WA. USA. to meet up with Bob from Midnight Here :

    These are great tools to help configure the Classic and MNKID with your system.

    Classic String Sizing Tool

    MNKID String Sizing Tool

    Embed these String Sizing Tools into your website

    Im still saying that your badly under panelled for the extraction of power & the amount of time you can force it back in .
    My array is 14,640.00 watt size . won't ever harvest that amount , but will still charge on grey PNW / Great Britons foggy days .


    PM me also if you would like
    Last edited: Nov 18, 2014
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