Regulate battery voltage to inverter / load

Hello all,

My off-grid system batteries require an absorption voltage of 15.5v for 2 hours per the manufacturers specs. (15.5v for 2 hours at 80 degrees fahrenheit)

The battery bank is 12v 840ah and I have 1.7kw of panels. My loads are light and after 2 or 3 days with no sun the batteries are still 80'ish percent.

The problem is my battery room is only heated by a solar air heater and in the winter the batteries can see temps as low as 0 degrees celsius if it gets really cold. Typically the room is 10'ish celsius in the winter.

Using temperature compensated Morningstar Tristar 60 amp PWM and MPPT controllers the voltages when around 0 celsius can get as high as 16.25v.

My inverters are a Morningstar Suresine 300, max input voltage of 15.5v and a Xantrex 1800 watt Pure Sine, max input voltage of 16v (starts beeping around 15.7v).

How do I go about limiting or regulating the voltage from the batteries to keep it below 15.5v when feeding the inverters from the battery bank, other than the obvious of keeping the battery room warmer so the temperature compensated voltage isn't so high, or lowering the absorption voltage which I won't do as I want to stick to the manufacturers specifications. Is there some electrical device I can purchase? I've searched around but can't find anything that's capable of the wattage of the inverters.

As it stands now I have to watch the system voltage and switch between the Suresine and Xantrex when the voltage starts to rise, trying to find a way around having to do this.

Glen
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Regulate battery voltage to inverter / load

    Yea, that is a problem with float voltage requirements and that most 12 volt devices treat >15 volts as a fault and possibly damaging.

    Turning off the DC power to your loads, or even using a large diode to two in series with the inverter can drop the voltage--but probably not worth it.

    A manual option would be to use a pair of Battery A/B switches.

    Connect these to your solar charger and inverters and split your battery bank in 1/2... Run the equalize on 1/2 of the bank and run the power to your DC loads from the other 1/2 of the bank. Then switch and repeat.

    Finally, turn each switch to "BOTH" for normal operation.

    Not automatic--but at least you will have inverter/DC power for your home during this time.

    purplebox.giftrans_1x1.gifBlue Sea Battery Switch 1-2-OFF 350 Amp $28.05
    wind-sun_2185_970775 Blue Sea 9001e 350 Amp Battery Switch Make-before-break contact design allows switching between battery banks without power interruption Ignition protected - Safe for ... mounting Meets American Boat and Yacht Council (ABYC) requirements for battery switches 3/8"-16 tin-plated copper studs for maximum ...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Regulate battery voltage to inverter / load

    you could add insulation around the batteries, but you must give them a bit of room to breath so rigid insulation is good for that. i doubt this would give you peace of mind and i don't blame you as it could still rise too high in voltage.

    a goofy idea may be to have an electronic thermostat switch in a resistive load via a relay when the temp goes low enough to cause you problems. this helps bleed off a bit of power and raise the temp some. each wh will give a btu of heat and in an insulated small enclosure it will bump the battery temp slowly. much care should be made in implementing something like this due to the dangers of igniting gasses in the enclosure should something go wrong. do this at your own risk. the relay should be external as sparking from it is a large risk.

    too bad that morningstar does not have adjustability on the temp comp rate as that would've solved the problem. i don't think pulling the rts will solve this either.
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: Regulate battery voltage to inverter / load

    BB I dont think your idea of using 1/2 the battery bank at the time is such a good idea ,while recharging the other 1/2. You are going to have many problems trying to balance them when both charging together.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Regulate battery voltage to inverter / load

    [sorry, I confused with another thread with 1/2 AGM and 1/2 old flooded cell. -Bill B.]

    My suggestion was to use them, either separately, or in parallel.

    And if operated in parallel, only during equalization would I suggest charging equalizing the flooded cell by themselves. AGM really do not need equalization (at least no high voltage equalization)--But flooded cell do.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Regulate battery voltage to inverter / load
    BB. wrote: »
    My suggestion was to use them, either separately, or in parallel.

    And if operated in parallel, only during equalization would I suggest charging equalizing the flooded cell by themselves. AGM really do not need equalization (at least no high voltage equalization)--But flooded cell do.

    -Bill

    Bill;

    I think you got this thread confused with a similar one regarding two banks of different type batteries used in parallel.

    For this one, switching out 1/2 a bank for equalization as needed will avoid the over-Voltage problem just as you suggested. :D
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Regulate battery voltage to inverter / load

    Marc,

    Sorry, you are correct... This was to equalize and avoid over volting the inverters/loads.

    Equalization is intended to get all cells back to 100% in a string. The fact that the two 1/2 battery banks are equalized separately should not be a problem.

    They are otherwise identical banks and will charge to rated capacity (on average) with the same voltage and time.

    If one bank gets a little bit more time on equalize before switching over to float--I don't think it will be a big deal.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Muskoka
    Muskoka Solar Expert Posts: 103 ✭✭
    Re: Regulate battery voltage to inverter / load

    Thanks for the suggestions. Don't think I want to split the bank in two. I do use one of those switches to select the inverters though, works well.

    Might look for an inverter that has a higher input voltage, at least greater than 16 volts.

    Glen
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Regulate battery voltage to inverter / load

    don't discount my suggestion as batteries when that cold lose some of their capacity as well.
  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    Re: Regulate battery voltage to inverter / load

    Instead of a new inverter maybe a outback fm80 as I dont think the eq settings are temp compensated.You would then have a spare charger.
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Regulate battery voltage to inverter / load

    actually that represented the voltage as a function of the temp being at freezing for the batteries and applies to the normal charge stages going higher and not just the eq stage. we don't know the mv/degree c the battery manufacturer calls for for those batteries, but the controller is not adjustable anyway so it makes no difference.
  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    Re: Regulate battery voltage to inverter / load

    Just read your post again .I see it is not the eq voltage but normal bulk, absorb ,So my suggestion is of no use. Sorry .
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
  • Muskoka
    Muskoka Solar Expert Posts: 103 ✭✭
    Re: Regulate battery voltage to inverter / load

    Peter, no problem.....

    The 16.25'ish volts is probably the max voltage the batteries would ever see, as this would be the temperature compensated absorption voltage, if the temperature got to 0 celsius. This morning it was -10 celsius outside, +8 celsius at the battery. At these voltages I don't ever bother with equalizing, sg's are always very close and seldom below 1.24.

    The U.S. Battery specs are +/- .168 v for every 10deg F above or below 80deg F. I'm using the Morningstar default of .03v per 1 deg celsius on both charge controllers.

    The target voltage on "Live Data View" is showing 15.7v, that will decrease when my solar air heater starts up. I did lower the absorption voltage to 15.2v from 15.5v to give a bit of wiggle room 8), and I will keep an eye on the sg readings / check to make sure they still get bubbling. It's kind of frustrating when you have to adjust the adjustments to keep everything happy, small price to pay for being totally off grid I guess.

    Glen
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Regulate battery voltage to inverter / load

    those charge specs are much higher than the norm for most batteries and that does pose a problem for the max voltage on many electronic items, including inverters.

    i just had another idea in that diodes typically can drop voltage by .5v-.75v and if a high current diode was used inline from the batteries to the inverters it would keep the voltages at a safer level for the electronics without affecting the proper charge to the batteries. in the case of diode costs and availabilities it could also be a special arrangement of paralleled diodes with associated equalizing resistors on a large metal heat sink to accommodate the high currents needed by the large inverter. this could also have a switch across the diode to short out the diode when the drop isn't needed in warmer weather.
  • KJINTF
    KJINTF Registered Users Posts: 15
    Re: Regulate battery voltage to inverter / load

    Maybe I am missing something......................
    Why not simply create a different config file for the MPPT 60
    It's simple to change the temp compensation
    Download a cold winter Cfg file and a warmer summer file
    I change the configuration settings on my Tristar MPPT 60 depending on time of year and location (RV install)
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Regulate battery voltage to inverter / load

    kjintf,
    i wasn't sure if that was adjustable on that cc or not, but if so i'd 2nd bringing the temp adjust settings down a bit as it is better to be slightly off in the voltage than to kill all of your electronics. if this is done the op should readjust back to the proper temp compensation during warmer months. of course the op could just let the settings be and not have any loads on it during the day in winter. nothing difficult is ever easy.;)
  • KJINTF
    KJINTF Registered Users Posts: 15
    Re: Regulate battery voltage to inverter / load

    Download the MsView application from Morningstar. It's free, open it up there are hundreds of configuration settings. The temp compensation is only one of hundreds. I see WAY too many installations not taking full advantage of the capabiltiies of these great controllers. Makes me wonder what folks are thinking sometimes. In the RV Solar business there are several good wire nut guys that stop at the dip switch settings and call it good, but hardly any designers / installers that finish off the installlation w/ the Rs232 / Ethernet interfaces and firmware upgardes, configuration files, etc. needed IMHO.
    Keeps me in business
  • Muskoka
    Muskoka Solar Expert Posts: 103 ✭✭
    Re: Regulate battery voltage to inverter / load

    As I stated in an earlier post I've basically done that by adjusting the absorption voltage so the temperature compensated voltage is lessened.

    Whether I adjust the temperature compensation value or the absorption voltage makes no difference as long as I decrease one of them.

    Perhaps you missed that in my earlier post?
    I did lower the absorption voltage to 15.2v from 15.5v to give a bit of wiggle room

    The real problem still exists though. The batteries need 15.5 volts for 2 hours. If left with the manufacture specs for temperature compensation the voltage could rise to 16.25 with the low temperature my room could see. This isn't really a problem for the batteries, as that temperature compensated value is the voltage they need to stay healthy.

    The problem is the lack of voltage regulation going to loads and the inverters. That is what truly needs regulating, not the battery voltage, it's fine and right on the manufacturers specs. I am actually under charging the batteries by decreasing the temperature compensation or the absorption voltage just to satisfy the voltage requirements of other electronic devices.

    If I could find an inverter that had an input voltage tolerance of say 17 volts, all my problems would be solved.


    Edit: Or purchase batteries that don't require such a high absorption voltage. Seeing as there not even a year old and cost me $1200, that's not about to happen.

    Glen
  • KJINTF
    KJINTF Registered Users Posts: 15
    Re: Regulate battery voltage to inverter / load

    I did see the earlier post
    Just wanted to add another possibility.... there are several ways to skin a cat
    How about this setting? See attached picture - I have used it on several occasions on both my systems and customers systems
    I do not let my system get above 15.25Vdc unless it is during a planned EQ stage. During EQ stage things get disconnected just in case they do not like the higher voltage,

    Hope you get it resolved
  • Muskoka
    Muskoka Solar Expert Posts: 103 ✭✭
    Re: Regulate battery voltage to inverter / load

    Thanks for all the suggestions.

    I've got my HVD set at 16.5v on both controllers, probably a little high but it's set that high to cover a range of temperatures that the battery room might be exposed to. I really have little control over that, other than Niels suggestion to keep the batteries warmer.

    I really don't want to lower the charge voltage, to me that makes no sense going against the manufacturers specifications. If they're saying the batteries need these high voltages to maintain health, then that's what their going to get.

    Again, the problem is not the batteries, it's the limitations of the inverters. Even with no temperature compensation the absorption voltage needs to be 15.5v and that pretty much rules out the Suresine inverter. The Xantrex gets to about 15.7v before it starts beeping.

    These are U.S. Battery L16HCXC 6 volt 420ah batteries. The absorption voltage of 15.5v seems to be common for a battery of this size.

    What absorption voltage are others using with L16 batteries?

    Glen
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Regulate battery voltage to inverter / load

    muskota,
    that would be a tough thing to do is to find electronics that are rated above 16vdc and even if you do it would be an expense as would getting new batteries that wouldn't require that high of voltage be.

    my diode idea would work as diodes do have a forward v drop around .5v-.75v (and some even more so read that spec when you shop as you don't need much more than 1/2v dropped for it to work) as i stated and would be your cheapest option as i'm sure you could find these power diodes for less than $10. some require a specific mounting thread and some can just bolt to the heat sink, but the heat sink is required for power diodes and can be any sizable piece of metal to dissipate the heat that builds up.

    http://images.search.yahoo.com/search/images?_adv_prop=image&fr=yfp-t-701&va=power+diode

    in that link the first row first pic as well as 2nd row 2nd pic are examples of it just bolting to metal with a hole drilled through it. the first row 2nd pic is a stud mount and needs a particular thread bored into the metal.
  • Muskoka
    Muskoka Solar Expert Posts: 103 ✭✭
    Re: Regulate battery voltage to inverter / load

    Thanks niel,

    I don't have any experience in wiring diodes, but do get the idea. Will look into this further, sure I can figure it out.

    I think this is going to be the "voltage regulator" that I was initially looking for, I just didn't know what I was looking for, or how to properly describe what I was looking for.

    Glen
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Regulate battery voltage to inverter / load

    regulator might be the wrong terminology for that, but i can see where you would classify it somewhat into that arena. being it would not be going to the batteries, but rather from them to the loads, the batteries will be able to stay fully charged. if you needed even more of a v drop then it is possible to put 2 in series. just be sure of the current rating (diodes do have high surge ratings so you need not worry too much about that) and the forward voltage drop. some may list peak inverse volts (piv) too and this i'd recommend to be at least as much as the highest voltage on your batteries and that shouldn't be much of a problem. if you say 17v tops then it could be 20v, 25, 50, 400v, or anything from that 17v on up and is not a factor unless lower than the 17v that i sighted as the example.

    i realize you aren't familiar with diodes, but be aware they are polarized. one way it'll work and the other way nothing. if you get nothing both ways then suspect the diode to possibly be bad or something else isn't quite right. again it would be in series with the + lead and do not ever go from the battery + to the battery - with the diode as it could cause a short on the battery.

    b+
    >
    load +

    b+ = battery +
    > = diode
    load + = positive lead to your load like your inverter, but a fuse is also good to have in this path.

    also, when you mount the diode's heat sink, be aware that the metal will be energized and should not come into contact with any other part of the system.
  • Muskoka
    Muskoka Solar Expert Posts: 103 ✭✭
    Re: Regulate battery voltage to inverter / load

    niel, thank you very much

    Yes, voltage limiter might be a better term to use in this case. I can see that this is going to work very well. I can properly set the charge points on the controllers and not have to worry about the increased voltage that the batteries require to stay healthy.

    I've added a crude drawing of my current set-up. The wire going from the bussBar to the breaker, then to the Selector Switch and inverters is 2awg wire.

    [IMG][/img]diodeinstall2.png Uploaded with ImageShack.us

    How would I install a diode into that circuit? Before or after the breaker, does it matter (I'm going to assume after the breaker), and how do I physically connect it. You mention needing a heatsink. Most of the diodes I've looked at so far look pretty small, can they handle upwards of 150 amps dc current? The Sursine (300watt) can't get that high, but the Xantrex (1800watt) is close. My system never sees that kind of current though, for high amp loads I use my generator. Max current used by the inverters is probably 80'ish dc amps, and not continuous.

    Can you point me in the direction of some examples or drawings with how they are physically installed. I've searched google and haven't come up with anything to get me started, even a simple pic would help. I don't understand how to connect the diode to the 2awg I'm using.

    Perhaps it's time for an electrican. ;)

    Glen
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Regulate battery voltage to inverter / load

    sorry to say an electrician wouldn't have a clue about diodes. the place to put it would be between the breaker and the switch and i won't get into that even though electrically it would do the same on either side of the breaker. it would be difficult to advise on mounting the heat sink and diode assembly as to what would be best for you. the heat sink, as i said, is active and you will be drilling a hole to mount a screw and nut to allow for wire lug connection. the other end of the diode can optionally have a wire and lug connection as you saw in the pics. i don't have that type of diode on hand here or i'd take a pic of it mounted. it really is simple, but descriptions to somebody who is unfamiliar with them can be difficult. if the breaker and switch are mounted on say a piece of plywood, then the diode and heatsink can also be mounted on that piece of plywood.

    i wish i could've found something on this around the net to show you, but searches seem to sidetrack to stuff you don't want.

    if you know you won't go over drawing say 100a you could use a 100a diode and the breaker should also have the same rating.

    you may have gathered that the metal is not paper thin and should spread out a bit to allow for good contact with the surrounding air. i'm guessing the metal to be no more than 8 inches across and should suffice for most applications. if you notice it getting hot then you could cut into the metal an inch or less and curve this a bit to make fins into the air. be sure to leave room to mount the diode and the other screw area for connecting your lug to from your wire. you could also add another slightly smaller sheet of the metal pressed against the first one (or several if you like if you don't have a thicker piece of metal) and fins can be put on it as well. commercial heatsinks can be bought, but i don't think the cost is justifiable.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Regulate battery voltage to inverter / load

    15.5V is very high for an absorb charge on an FLA bat, are you sure it's right? The trojan L16s need an absorb of 14.8 and EQ at 15.5.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Regulate battery voltage to inverter / load
    stephendv wrote: »
    15.5V is very high for an absorb charge on an FLA bat, are you sure it's right? The trojan L16s need an absorb of 14.8 and EQ at 15.5.

    Possibly they are Interstate batteries; they have very high recommended Voltages.
  • Muskoka
    Muskoka Solar Expert Posts: 103 ✭✭
    Re: Regulate battery voltage to inverter / load

    Thanks niel,

    Here's the batteries:

    [IMG][/img]usbbatusl16hcxcsmall.jpg Uploaded with ImageShack.us

    These are the specs they e-mailed me:

    [IMG][/img]chargeratessmall.png Uploaded with ImageShack.us

    Glen
  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    Re: Regulate battery voltage to inverter / load

    Muskoka,

    I've just purchased 1800 W of solar panels, and have been trying to figure out the optimum battery bank. Are you able to adequately charge 840Ah of battery? Thank you.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Regulate battery voltage to inverter / load

    Mmmmmmm those voltages look a bit strange, there should either be a bulk voltage or absorb, but not both. Some manufacturers call it bulk others absorb, but it's the same point: the voltage where bulk stops and absorb begins. 14.8 makes a lot more sense as the absorb voltage evause that's identical to the L16 setting (which btw is already higher than what most other fla's require.
  • Muskoka
    Muskoka Solar Expert Posts: 103 ✭✭
    Re: Regulate battery voltage to inverter / load

    I have no problem at all keeping my batteries happy. I re-arranged my system a little, and now have 1.38kw of panel, more than enough to keep things happy with the loads I have. The batteries seldom get low enough to see the full potential of the panels, but when they do I see charge amperage in the mid 70's - 80's. This gets them bubbling nicely.

    As stephen has stated the charge voltage seems a bit aggressive compared to "other" battery manufactures, but the batteries don't seem to mind. I did drop the absorption to 15.2v as stated in another post to accomodate other electronics during cooler weather due to temperature compensation. I will monitor the batteries closely, and adjust as necessary. Typically I have to top up the water once a month, and the sg of all the cells is within .1 - .15v, and the system is seldom below 12.4v, even after a few days of gray weather, and that was at the recommended absorption of 15.5 for 2 hours. Will see how it goes.

    For those still doubting U.S. Batteries numbers ;), this is straight from their faq, not Trojan or Surette, and happen to be the same numbers that were e-mailed to me for my batteries. Hopefully that will ease some doubt, besides they work.

    ratesh.png


    Glen