Off Grid Wiring Question

RogueValleyHomestead
RogueValleyHomestead Registered Users Posts: 11
So I finally bought all of my solar components for a small off grid DC solar setup (panel, controller, batteries), and I'm getting ready to wire it all up and connect my loads, but I have one nagging question (due to basic electricity theory ignorance):
When I connect my charge controller (MPPT) to my battery bank (12 volt), and then connect my loads (pump, AA charger, etc.) to the battery terminals- aren't I just creating a circuit to the charge controller since those wires are meeting at the battery terminals? And wouldn't that then be providing too much voltage (bad!) to my loads?
Again, my ignorance of electric theory is deep, so I may be coming up with a ridiculous idea here, but I don't want any of my electronics to give up their magic smoke too soon!

Also, in case my components are relevant to the answer, they are:
1 x Kyocera 235 watt panel (8 amps)
1 x Morningstar MPPT 45 controller
2 x Trojan T105 6 volt batteries

I hope this question is clear enough, but if not, I could try and complicate it further with another explanation.

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Off Grid Wiring Question

    The answer is: perhaps.

    In fact we do see this problem on strictly DC systems, because the charge Voltage is generally 14.4 (14.8 for your Trojan batteries) Volts and even worse the equalization Voltage is usually 15 or more. Some DC devices do not like these higher Voltages and could be damaged by them. You have to get the actual Voltage range for each device.

    There are ways around it, depending on what it is you've got to power. Mostly it involves either "re-regulating" the Voltage or adding some method of taking out a Volt or so to the sensitive device.
  • RogueValleyHomestead
    RogueValleyHomestead Registered Users Posts: 11
    Re: Off Grid Wiring Question

    So it looks like my theory is correct?

    I have no idea how to remove a volt or two, so I suppose I could buy another 'cheap' charge controller and just use it's 'load' side only, but I do hate spending money unnecessarily (I'm probably not alone in that).

    As for finding a voltage range on a device, I only have the manufacturer's suggested voltage on each unit (9 volt, 12 volt, etc). Is there another way of finding out a devices voltage range? The fact that a device is AC/DC probably doesn't make any difference here I assume.
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Off Grid Wiring Question

    Most car chargers can take up to 20 vdc. Automobile alternator regulators run a similar voltage range (14.5 v absorb, 13.4 v float) as PV charge controller except the autos do not do equalize cycle (15.5 vdc).

    If you are concerned about any of your 12 vdc gear just disconnect them whenever you do an equalize cycle on the batteries. (equalize is manually initiated and you should only do it every several months to avoid too much stress on batteries)
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Off Grid Wiring Question

    The "Load" terminals of a charge controller are not necessarily regulated to exactly 12 VDC at all times either. Probably a waste of money to try that.

    Manufacturers specifications are about all you can go by, as far as Voltage range is concerned. Sometimes they will list an operating range, other times they just say "12 VDC". Otherwise you try it and see if you fry it. Not the best method to determine suitability.

    The type of device can be a clue. For instance things meant to be run in a car will usually take 13.8 VDC, but often not more. Any transformer (wall wart) powered things will have a mA rating on the power supply, and there may be some difference between it and any built-in battery capacity. Sorry to be so vague, but there's lots of variables here.

    The most sure-fire way to get the right Voltage is with a Voltage regulator circuit. It has to be able to take the current requirements. It would probably also have to be homemade. There are other folks on this forum who work with that sort of thing more so than do I, and they'd have a better idea.

    Otherwise you can fall back on the plan of in-line resistor (good with resistance loads, maybe a bit finicky with other types) or using a diode or two to knock off a Volt, remembering that it reduces Voltage at the low operating range too; your 14 Volts may go down to 13, but when the battery goes down to 12 the output would be 11 - some things may shut down before you want them to.

    There are plenty of 24 Volt to 12 Volt converters available, but you probably don't want to up the system Voltage just to ease the operating margin.

    Any minute now someone else is going to chime in and ask: "What are you wanting to run?"
  • RogueValleyHomestead
    RogueValleyHomestead Registered Users Posts: 11
    Re: Off Grid Wiring Question

    Thanks for the responses so far folks, it's much appreciated!

    I thought keeping my system DC only would be an advantage, but it's looking a bit more difficult than I hoped for.

    @Cariboocoot: I definitely don't want to up the system voltage, and I'm not too keen on taking on a DIY project for a regulator circuit either. The in-line resistor idea looks good, although it's a bit of a mixed bag as you mentioned.

    @RCinFLA: That's very interesting info about car alternators absorb and float stages, and if it's true then there should be no worry whatsoever (as long as I disconnect loads for equalization, of course). My electronics aren't too precious anyway, so maybe I'll just 'plug and see' in hopes that they can take the slightly higher voltage.

    What I would like to know though, is if my original question is correct or not. It seems to be true, but whenever I try and corner people with this question definitively (I've asked a few unsuspecting electronics folks) I've never been able to get a solid 'yes' or 'no'. So, does anyone know the answer to my original question absolutely (i.e. Does a load connected to the battery terminal pick up the current from the controller because they are both connected at the same point)?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Off Grid Wiring Question
    What I would like to know though, is if my original question is correct or not. It seems to be true, but whenever I try and corner people with this question definitively (I've asked a few unsuspecting electronics folks) I've never been able to get a solid 'yes' or 'no'. So, does anyone know the answer to my original question absolutely (i.e. Does a load connected to the battery terminal pick up the current from the controller because they are both connected at the same point)?

    Sort of. :p
    The current from the charge controller goes to the battery. Loads draw off the battery. The amount of the load reduces the effective charge rate of the battery by the amount of the load. So in essence if your controller is providing 15 Amps to the battery and the load is drawing 5 Amps from the battery the battery receives 10 Amps of charge. If the load is greater than the 15 Amps from the charge controller then the charge rate is zero, or more correctly a negative number as the deficit is made up from the battery reserves. This is not really the same as saying the loads are running off the charge controller, because the battery is an integral part of both circuits; the charge circuit and the load circuit.

    Clear as mud, eh? :p
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Off Grid Wiring Question

    If you have a device that comes with an AC power pack that provides a regulated 12 vdc output for the device (like a printer or netbook computer), I would not run that directly off the two T105 batteries and charge controller.

    If it is designed to run from a cigarette lighter in a car then it is okay. (minus perhaps an equalize cycle).

    Something like a 12v portable fluorescent lantern is probably okay, definately if they sell a cigarette lighter adaptor plug for it that is just a cord adaptor. The plug-in 12vdc jack on the side will disconnect the internal batteries when run from external supply. A 12vdc Igloo cooler is okay, (although very inefficient for refrigeration. They use Peltier heat transfer modules)

    Never run eight alkaline batteries in parallel with the two T105's / charge controller.

    For something that needs regulated 5 vdc supply most off the shelf USB cigarette lighter chargers will work. They all put out a minimum of 500 mA but can buy ones that put out up to 2 amps. They use switching buck power converter so they are pretty efficient.
  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    Re: Off Grid Wiring Question
    Clear as mud, eh?
    You can think of the battery as a very low resistance stabilizing voltage source to a point. IF you are using a PWM charge controller, the voltage will gradually rise as the battery gets more charged until it reaches its bulk voltage, then drop to the float voltage as set by the charge controller, usually around 13.2 volts or so. I have found most all DC devices that I have tried work OK past the 14 volts, but would not want to put 15+ volts on them unless they are rated for it. Some devices are rated to 16 volts or better. What are you trying to power? My DSL modem works fine to 16 volts DC, actually it is designed to run on a 15volt AC transformer, but will work just as well on DC. My Weather station works on 5 Volts, so I just use an off the shelf Regulator to deliver 5 volt to power the weather station. Many cordless phones will work on 9 volts, so also could be powered by a off the shelf regulator.
  • RogueValleyHomestead
    RogueValleyHomestead Registered Users Posts: 11
    Re: Off Grid Wiring Question

    @Cariboocoot: Thanks for the explanation, but I think I should refine my question a bit better though;

    The charge controller is connected to the battery terminal via a crimp terminal like this one:
    http://www.alliedelec.com/search/productdetail.aspx?SKU=5343525
    And the load connection (a female cigarette lighter adapter, for example) is also connected at the terminal with another crimp terminal like the one above.
    When both are connected at the terminal, their connectors are resting one on top of the other with their metal contacts touching, and that's where my confusion begins. Because they are touching each other (at the terminal), doesn't that just make a new circuit between them (controller and load)?

    @RCinFLA: I do have a cigarette lighter power cord that was made specifically for my laptop by the manufacturer, are you saying that type of device would not be a good thing to plug in because it's voltage restrictions are more strict? I know that my AA battery charger and water pump were designed for auto use, so no trouble with those.
  • Slappy
    Slappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    Re: Off Grid Wiring Question

    the battery acts like a big capacitor, the charge controller connects to battery, you load is also connected. in theory yes you do draw from the controller, but the battery smooths every thing out, if the equipment that you are using is made for automotive applications it should be safe on a 12 volt solar set up.....you will be amazed, at what you can run. But dont let me steer you wrong, I am just saying if it is for automotive, or 12volt DC it will be fine. But for your controller, turn the automatic EQ off or set it to manual. if you ever have to EQ your battery, it is best to disconnect your loads.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Off Grid Wiring Question
    @Cariboocoot: Thanks for the explanation, but I think I should refine my question a bit better though;

    The charge controller is connected to the battery terminal via a crimp terminal like this one:
    http://www.alliedelec.com/search/productdetail.aspx?SKU=5343525
    And the load connection (a female cigarette lighter adapter, for example) is also connected at the terminal with another crimp terminal like the one above.
    When both are connected at the terminal, their connectors are resting one on top of the other with their metal contacts touching, and that's where my confusion begins. Because they are touching each other (at the terminal), doesn't that just make a new circuit between them (controller and load)?

    The mechanical connection in this case doesn't really matter, as both are directly on the battery posts.
    The thing to remember here is the term circuit, which means loop. It's not just electrons going from the charge controller to the battery, but also going back to the controller. The same is true of the battery to load circuit: out one wire, back in the other. Two loops of flowing electrons that happen to cross paths within the battery.

    It might be easier to think of it as the charge controller is "filling" the battery while at the same time the load is "emptying" it.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Off Grid Wiring Question

    can i ask just what it is that you are worried about connecting? can i also ask if it has an ac adaptor to plug into the wall and if so then tell us what the dc output voltage and current is listed at from the adapter? some adapters can supply 18v and when the item is turned on it drops the voltage lower to acceptable voltages and these often list 12v. if it can take that initial high voltage it certainly can run from the voltages seen by your battery from the charge controller. in fact, most things can run up to 16v which is about the limit for electrolytic caps put into many 12v electronic items, but there are exceptions and it is difficult to know if any of your loads are an exception or not at this point. i would never advise running say 15.8v or 15.9v to electrolytic caps as i believe in giving some leeway on stamped limitations of parts.
  • RogueValleyHomestead
    RogueValleyHomestead Registered Users Posts: 11
    Re: Off Grid Wiring Question

    @mikeo: Thanks for the response. I've got a MPPT controller (Morningstar TriStar 45 amp model), and only a few specific items to run:
    An old laptop with a DC plug made by the manufacturer (say's 16 volts on the AC supply, so it's probably a safe bet for charging),
    A Shurflo Classic series pump at 12v (which the manufacturer claims will accept a somewhat variable voltage for direct connecting),
    And a small LaCrosse AA/AAA battery charger (BC500 Alpha) which came with a car adapter, and claims to be 12v in it's literature and markings.
    And by 'off the shelf regulator', do you mean something like this:
    http://www.radioshack.com/product/index.jsp?productId=2062599
    Or is there some other solution that doesn't require soldering?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Off Grid Wiring Question

    i think with those loads you should be fine.
  • RogueValleyHomestead
    RogueValleyHomestead Registered Users Posts: 11
    Re: Off Grid Wiring Question

    @niel: I just posted the definitive list of my loads, and it's looking like they are well within range.

    @Cariboocoot: Thanks for that explanation, it's finally starting to register in this little brain of mine:D

    @Slappy: It seems generally that if I have a 12v DC device, with a proper DC power adapter for it (for the rated output to the device), I should be pretty safe connecting directly to the battery (via a female cigarette lighter adapter), as long as I'm not running an equalize charge. Sounds easy enough for me!
  • RogueValleyHomestead
    RogueValleyHomestead Registered Users Posts: 11
    Re: Off Grid Wiring Question

    Once again, thanks to all who responded. I'm feeling far more confident now about putting all of my pieces together and powering up for the first time!
    Next on the list: that nifty Tri-metric 2020.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Off Grid Wiring Question

    Technically, equalization should be done with all loads off anyway. :D