Solar Controllers - A Small 'Gotcha'

Discussion in 'Solar Power' started by Peter A Forbes, Mar 6, 2015.

  1. Peter A Forbes

    Peter A Forbes Funster

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    I've posted this elsewhere, it is something that needs to be thought about by those who take their 12V loads straight from the battery with no low voltage cutoff or disconnect.

    The solar controller electronics are fed from the battery the controller is connected to, not the panels. This means that if the situation arises where a continuous load pulls a battery down too far, the controller will cease working.

    If the load continues, the controller cannot start and the battery will be destroyed.

    It doesn't take much either, a three hundred milliamps over a week is 50AH, half what most folks have in the way of a battery, two weeks and you're looking at a severely flat battery.

    Loads that are connected to the battery through the controller LOAD terminals will be cut off by the controller's own internal circuitry, protecting the battery and keeping the solar controller alive.

    A single signal LED takes about 20mA, a small fan about 100mA and so on.

    A relay can be connected across the LOAD terminals to carry higher loads if needed. Very heavy loads like inverters are usually only run for short periods on load, but some have a quiescent load (standby load) when turned on but not loaded, that can be half an amp or so.

    Peter
     
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  2. hilldweller

    hilldweller Funster Life Member

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    So you are saying "use the solar controller LOAD output to protect your battery".

    A seriously good idea. With the heavy cables involved not trivial but still a good idea.

    We are more or less saved from doing this because the Electroblock controll box drops out when it's low battery setting is reached.
     
  3. pappajohn

    pappajohn Funster Life Member

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    My last mppt controllers load output was rated at 2 amps.

    My current £600 controller (already fitted by others) is rated at 2amps

    Not much use as a power supply.
     
  4. f6c

    f6c Funster

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    Well over my Head:whistle:
     
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  5. DiggerJon

    DiggerJon Funster

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    When you mention amps/volts/millipedes or whatever, my brain shuts off! I never did understand electrics and I really don't intend to try now!
     
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  6. andy63

    andy63 Funster

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    hi peter, im always keen to grasp these things lol, even if im a bit slow on the uptake..
    have I got it right that you are saying that a relay connected across the solar regulator load output terminal can be used to feed circuts that could then be switched off when battery voltage drops to low level.. that's my take on your post and sounds a good idea where it might be necessary to protect the battery..
    ta andy
     
  7. pappajohn

    pappajohn Funster Life Member

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    Got it in one....but unless you put a switch between the controller and relay you have no control when the controller is active, in other words you cant turn it off at random UNLESS your controller has a built in switch, not all have..
     
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  8. Peter A Forbes

    Peter A Forbes Funster

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    Most controllers, including ours and Andy's (Techno100) have 20A, 25A or 30A capability, and that goes for the load terminal outputs as well as the battery charging side.

    There's no real need to fit a switch to the relay unless you really need it, if you are straight on the battery at present you have no control either. Don't see that as a big issue, and 25A of output current gives you more than enough for most habitation electrics.

    This scheme is really for those who don't already have low volt cutoff on their existing electrics. If you have it via an Electroblock then no point in fitting anything extra.

    Peter
     
  9. Peter A Forbes

    Peter A Forbes Funster

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    It isn't rocket science, and getting to know your basic electrics and how they work could save you a lot of money in the event of a breakdown.

    Peter
     
  10. Peter A Forbes

    Peter A Forbes Funster

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    Basically, yes.

    That function is built in to almost every controller on the market.

    We had a Ring 2-socket cigar lighter and battery monitor plugged in to our batteries on the trailer, plus a small extraction fan for the kitchen area.

    These two things did exactly what we are trying to protect against, they pulled the battery down in bad/cloudy weather and eventually killed the battery. I had wired everything else through the load terminals except these two items.

    I had assumed that the panels would have kept that little load supported, but they didn't. The other circuit on the second pair of panels was fine, so I may fit some steering diodes between the two circuits so that they cross-feed to the other circuit.

    Peter
     
  11. DiggerJon

    DiggerJon Funster

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    Believe me, I've tried to understand this black art but fail miserably every time.
     
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  12. Wildman

    Wildman Read Only Funster

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    I have always advocated using the load terminals on the controller, that's probably why my batteries have lasted 8 years and still going strong.
     
  13. CWH

    CWH Funster Life Member

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    Yes it rotten well is!
     
  14. Wildman

    Wildman Read Only Funster

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    I did run a couple of 12v seminars at rallies to help enlighten those with no understanding maybe it is time for another, who knows but anyone who wants tuition is at liberty to ask anytime they are at my site for a rally or just camping am glad to be of help.
     
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