Why No Inverters for Deep Cycle Batteries?

Every inverter I have been able to find shuts off at 10 or 10.5 volts. My deep cycle house batteries will produce usable current down to 5 volts. Have inverter manufacturers just not heard of the existence of RV's and deep cycle batteries? What is the problem here?

Does anyone know of an inverter that WON'T shut down at 10 volts?
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Comments

  • BB.BB. Posts: 25,138Super Moderators admin
    Re: Why No Inverters for Deep Cycle Batteries?

    What deep cycle batteries are you talking about? (link?).

    From my point of view, there are several reason you will not find inverters that will cutoff at 5volts.

    First, battery damage. Storage battery cells are not usually matched before connecting in strings (RC model folks will test discharge battery cells and match those in series strings with equal capacity). Standard storage batteries can have cell to cell capacity differences of up to 20% (roughly) between two series cells.

    What will happen is when you collapse the voltage in the "weak" or low capacity cells, the other series cells can actually "reverse charge" the weak cell(s)--For most battery chemistry's--that will destroy those cells.

    Second, is AC inverters are typically constant power devices... Remembering Power=Volts*Amps -- we see that an inverter that operates at ~15 volts (battery bank under charge) vs one operating at ~5 volts will draw 3x as much current to support the loads.

    Generally, when batteries are below ~10.5 volts (for lead acid storage cells), there is little chemical energy to support any substantial currents.

    Another reason -- Power is also equal Amps2 * R -- To design an inverter that can operate over a 3:1 voltage range (at constant power) will require 3x^2 or 9x as much copper, magnetics, capacitors, switching transistors, heat sinking, etc. to prevent overheating when operating at ~5 volts.

    Most batteries are, more or less, constant voltage sources (solar cell/spanels are actually, more or less, constant current sources)--So for standard chemistry lead acid batteries, I would wonder how much useful energy for a 12 volt battery is available at ~5 volts.

    My guesses--anyways...

    -Bill

    PS: I should clarify--the "matched series cells" for RC planes/cars/etc. is to prevent cell damage from reverse charging without having to add the electronics/costs to protect cells against "reverse charging".

    I don't believe it is to gain more usable energy from the battery pack.

    -BB
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    i'll give you the simple answer. they are considered dead at 10.5v.

    i suspect you believe just because they are deep cycle rechargables that they can be abused by running them into the ground. not so and in fact they shouldn't be run below 50% dod or their useful lifespan is more compromised.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    No such thing as a 12 Volt deep cycle battery that can be drawn down below 10.5 Volts and then be fully recharged.

    In fact, the "RV" type aren't even true deep cycles and won't take even normal off-grid use for very long.

    If you do draw a battery down below its "dead" point you can run in to the very interesting (and unrecoverable) state of reversed polarity.

    The current increase would be mind-boggling. 1200 Watts @ 12 Volts is 100 Amps. @ 5 Volts it would be 240 Amps.
  • bryanlbryanl Posts: 175Solar Expert ✭✭✭✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    re: "In fact, the "RV" type aren't even true deep cycles and won't take even normal off-grid use for very long." -- bull. (see the FAQ here, for example).

    If you can find some objective and available spec or measure I can use to tell an "RV" type from another type or even define "deep cycle" objectively, I'd truly like to know. I have been looking for years and haven't found one. -- keep in mind my context is the typical battery the average consumer can easily find intended for RV and auto service that weighs from about 40 to 200 pounds and is usually 6 or 12 volts.

    All lead acid batteries (and many other types as well) suffer severe life degradation with increasing cycle depth.

    Lab tests for this class of battery indicate the range is from about 200 up to about 800 cycles down to 80% discharged before capacity loss exceeds 20%. Variances of up to 20% result from many factors and that can complicate things out of the lab.

    All of these factors go into the cost analysis that indicates a 50% DoD is a good target for nominal use of these batteries (see smartgauge for a good rundown).

    Besides the battery use and cost effectiveness factors in answering the OP, another factor is one alluded to above. Once the batteries get below about 11.0v under load, the voltage will drop quite rapidly. You just don't get much more out of a battery run down that far and you do significantly increase risk of failure.
  • john pjohn p Posts: 814Solar Expert ✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    Does anyone know of an inverter that WON'T shut down at 10 volts? YES Its called a malfunctioning one

    You cant possibly serious to believe a 12v battery can give usable power output at 5v.THATS LESS THAN HALF A VOLT A CELL?????
    THIS HAS TO BE A JOKE POST
  • hillbillyhillbilly Posts: 334Solar Expert ✭✭✭✭✭✭
    Re: Why No Inverters for Deep Cycle Batteries?
    bryanl wrote: »
    re: "In fact, the "RV" type aren't even true deep cycles and won't take even normal off-grid use for very long." -- bull. (see the FAQ here, for example).

    If you can find some objective and available spec or measure I can use to tell an "RV" type from another type or even define "deep cycle" objectively, I'd truly like to know. I have been looking for years and haven't found one. -- keep in mind my context is the typical battery the average consumer can easily find intended for RV and auto service that weighs from about 40 to 200 pounds and is usually 6 or 12 volts.

    from the FAQ here at NAWS:

    "Starting (sometimes called SLI, for starting, lighting, ignition) batteries are commonly used to start and run engines. Engine starters need a very large starting current for a very short time. Starting batteries have a large number of thin plates for maximum surface area. The plates are composed of a Lead "sponge", similar in appearance to a very fine foam sponge. This gives a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. Automotive batteries will generally fail after 30-150 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).
    Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. This gives less surface area, thus less "instant" power like starting batteries need. Although these an be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge.
    Unfortunately, it is often impossible to tell what you are really buying in some of the discount stores or places that specialize in automotive batteries. The golf car battery is quite popular for small systems and RV's. The problem is that "golf car" refers to a size of battery (commonly called GC-2, or T-105), not the type or construction - so the quality and construction of a golf car battery can vary considerably - ranging from the cheap off brand with thin plates up the true deep cycle brands, such as Crown, Deka, Trojan, etc. In general, you get what you pay for.
    Marine batteries are usually a "hybrid", and fall between the starting and deep-cycle batteries, though a few (Rolls-Surrette and Concorde, for example) are true deep cycle. In the hybrid, the plates may be composed of Lead sponge, but it is coarser and heavier than that used in starting batteries. It is often hard to tell what you are getting in a "marine" battery, but most are a hybrid. Starting batteries are usually rated at "CCA", or cold cranking amps, or "MCA", Marine cranking amps - the same as "CA". Any battery with the capacity shown in CA or MCA may or may not be a true deep-cycle battery. It is sometimes hard to tell, as the term deep cycle is often overused. CA and MCA ratings are at 32 degrees F, while CCA is at zero degree F. Unfortunately, the only positive way to tell with some batteries is to buy one and cut it open - not much of an option."

    Not sure if that's what you meant? I'll agree with the overall sentiment that Coot was trying to put across here: that deep discharges down to ultra low voltage settings ARE damaging even to the best of batteries, let alone a cheaper RV type battery. I also think it's appropriate to point out that not all "deep cycle batteries" are built to withstand the same level of use and abuse...
  • john pjohn p Posts: 814Solar Expert ✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    Jack Kessler here is your simple answer. I just tested a 225 ahr deepcycle battery that is in good working order..
    I put a load on it 30a for 4 hrs it dropped its voltage to 11.2
    I then let it cool down for 2 hrs

    then put the load back on again in 1hr 42 mins it dropped to 10.3v
    35 mins under 30a load 9.1v (273w)
    10 mins later max output current 11.6a 8.5v (98.6w)
    5 mins later max output current 5.2 amps 7.9v (41w)
    3 mins later 7.6v and 2.3a (17.5w)

    This shows after it gets below 10.3 v you only have 35 mins of anything useful available from the battery.

    battery is now dead and most likely will not fully recover

    Now you know why inverters have 10.5v cutoff. the manufacturers are not quite as stupid as you thought they were..
  • hillbillyhillbilly Posts: 334Solar Expert ✭✭✭✭✭✭
    Re: Why No Inverters for Deep Cycle Batteries?
    john p wrote: »
    Jack Kessler here is your simple answer. I just tested a 225 ahr deepcycle battery that is in good working order..
    I put a load on it 30a for 4 hrs it dropped its voltage to 11.2
    I then let it cool down for 2 hrs

    then put the load back on again in 1hr 42 mins it dropped to 10.3v
    35 mins under 30a load 9.1v (273w)
    10 mins later max output current 11.6a 8.5v (98.6w)
    5 mins later max output current 5.2 amps 7.9v (41w)
    3 mins later 7.6v and 2.3a (17.5w)

    This shows after it gets below 10.3 v you only have 35 mins of anything useful available from the battery.

    battery is now dead and most likely will not fully recover

    Now you know why inverters have 10.5v cutoff. the manufacturers are not quite as stupid as you thought they were..

    Do you mean to say that you just killed a perfectly good battery in order to provide a thorough answer to this post??? In that case I've been asking the wrong folks here for answers to all my questions :-) That's going the extra mile to answer his question!
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    john p has about the greatest job in the world and we're all envious! :D

    He also has on more than one occasion delved into some real-world testing relevant to this forum and come up with some great data, for which I'm sure we're all grateful. :D
  • john pjohn p Posts: 814Solar Expert ✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    Dont worry hillbilly the cost of that battery didnt come from my pocket im at work. im in the process of testing air pumped into 5 brand new lead acid batteries that will have no use after testing.. be just scrap( the test is in regard to anoth post on this site..)
  • hillbillyhillbilly Posts: 334Solar Expert ✭✭✭✭✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    Ha! Ok then, I was wondering... my head spinning actually, trying to figure out what a gentleman you must be to go to such lengths to answer such a question.
  • BB.BB. Posts: 25,138Super Moderators admin
    Re: Why No Inverters for Deep Cycle Batteries?

    I suggest to leave the thread go quiet for a bit... Jack has not been back since his first post--So 24 hours and 10+ posts later (including a test to destruction--very cool :cool:) may be getting ahead of him a bit.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • john pjohn p Posts: 814Solar Expert ✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    sorry for mabe making this too much for him to absorb, but did it mostly to show anyone that is interested what realy happens when you do go below the 10.5. :cool:

    dont worry about the battery it over 6 months old and for here thats ancient. but it was in perfect condition before testing ,, in last hour it wont accept charge it just gets very hot....
  • BB.BB. Posts: 25,138Super Moderators admin
    Re: Why No Inverters for Deep Cycle Batteries?

    John, don't worry---I was just trying to slow down the thread until the original poster returned and had a chance to reply/ask more questions.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bryanlbryanl Posts: 175Solar Expert ✭✭✭✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    re: "Not sure if that's what you meant?" -- The FAQ has its problems and needs careful and critical reading. What I suggest is to first look at the data and measure and give those precedence over the 'descriptive' stuff. Take note of the variances in battery life by type given. Take note of the description of the major influences on battery life. Take note of how terms are defined.

    The question I posed is worth (I think) considering: how is a 'deep cycle' battery defined in a manner I can see in a relevant, pertinent, and objective specification I can find for batteries I'd use for a typical small system and that are readily available at retail?

    The facts are that you don't 'deep cycle' any lead acid battery if you want cost effective performance. The nominal lifespan is typically defined by factors other than cycling which makes that gauge irrelevant as well. There is much more along that line but such thinking seems to be deeply offensive to some so it's best to let it drop.
  • WindsunWindsun Posts: 1,164Solar Expert admin
    Re: Why No Inverters for Deep Cycle Batteries?

    One of the answers as to "why" is related to the internal chemistry - at 10.5 volts, the majority of the acid is "used up", and simply cannot do much more. At full charge - 1.265 specific gravity - , the acid is around 35% to 38% vs water. At 10.5 volts it is around 10% or less. At around .835 volts per cell (5 volts), the specific gravity of the battery acid is very close to 1.zero - what you have left in the battery is basically just water.

    There is some more specific info here http://giantbatteryco.com/GLOSSARY/Specific.Gravity-Industrial.Batteries.html

    That pretty much falls in line with the actual tests done by john p.

    And yes, the OP has not been back, but the test he did is useful info for anyone that uses a battery based system.
  • stephendvstephendv Posts: 1,571Solar Expert
    Re: Why No Inverters for Deep Cycle Batteries?
    bryanl wrote: »
    The question I posed is worth (I think) considering: how is a 'deep cycle' battery defined in a manner I can see in a relevant, pertinent, and objective specification

    Some batteries have this expressed as a cycle life at a specific DoD and temperature, e.g. 1500 cycles at 80% DoD at 25C is a typical rating for OPzS stationary batteries and forklift batts.
  • bryanlbryanl Posts: 175Solar Expert ✭✭✭✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    re: "stationary batteries and forklift batts." -- this is why I have been very careful to qualify the batteries I am talking about, which are not 'industrial' or 'traction' batteries.

    But even these do not have a clear demarcation that defines 'deep cycle' from whatever other types marketing hype may create.

    So, let's keep the conversation honest (and productive) and respect the conditions, caveats, relevance, and context of the information provided, what say?
  • john pjohn p Posts: 814Solar Expert ✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    Im not sure how relavent this all is to the original.. ""Why No inverters for Deep Cycle Batteries"

    To the person looking for a "perfect " definition of a deep cycle battery using a lead acid battery as the base.

    I personally think its easier to define what is NOT a deep cycle battery
    IE if the maker gives its specs as 500 CCA or something like that then its intended use is as a "starting" battery.. and not a deep cycle battery
    Its not easy to give an exact defination of a deep cycle battery as many are hybrids with varying degrees of "deep cycle""

    Its like asking or saying if a man has $500 in his pocket then he is not a poor person, but does that mean a man with $499 in his pocket is??
  • hillbillyhillbilly Posts: 334Solar Expert ✭✭✭✭✭✭
    Re: Why No Inverters for Deep Cycle Batteries?
    bryanl wrote: »
    re: "stationary batteries and forklift batts." -- this is why I have been very careful to qualify the batteries I am talking about, which are not 'industrial' or 'traction' batteries.

    But even these do not have a clear demarcation that defines 'deep cycle' from whatever other types marketing hype may create.

    So, let's keep the conversation honest (and productive) and respect the conditions, caveats, relevance, and context of the information provided, what say?

    I think we did loose the original thread question here, but perhaps if there is a point to make here you can make it a separate thread. I'm moderately curious about what you're driving at, as I'm always happy to learn more about batteries and their inner workings...
  • dgsloandgsloan Posts: 22Registered Users
    Re: Why No Inverters for Deep Cycle Batteries?

    The Lead Acid thing appears to have been flogged to death. At the beginning of the thread the RV and inverters was mentioned. Even newer RVers who want to be "Cost Effective" do not use Lead Acid batteries as the weight and discharge factors cost a lot if they do not have "shore hookup" available. LifePO4 and LiPO are four times the cost but quickly pay for themselves in 95 percent discharge and weight over gas costs not to mention the 3k to 8k full charge cycles to reach 90 percent capacity. In these batteries you could use some form of MPPT tracking on each cell to reduce charge time to a minimum but this is probably the time for another thread. If anyone wants to start a thread on these cells I would be glad to join in.
  • BB.BB. Posts: 25,138Super Moderators admin
    Re: Why No Inverters for Deep Cycle Batteries?

    We already have this thread if you want to continue those LFP discussions:

    Lithium Iron Phosphate Batteries; LFP; LiFePO4 discussions

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • creakndalecreakndale Posts: 27Solar Expert
    Re: Why No Inverters for Deep Cycle Batteries?
    Windsun wrote: »
    At around .835 volts per cell (5 volts), the specific gravity of the battery acid is very close to zero - what you have left in the battery is basically just water.

    Wouldn't the specific gravity be closer to 1 instead of 0 in the above scenario?

    creakndale
  • BB.BB. Posts: 25,138Super Moderators admin
    Re: Why No Inverters for Deep Cycle Batteries?

    I think he means 1.000 (water) specific gravity with zero energy content (all sulfuric acid is gone).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Why No Inverters for Deep Cycle Batteries?

    The reason is because of the kind of answers already given in this forum. This is actually a matter of contention with me as well, because the information given is largely not real world or from practical experience, but from labs and colleges, and kiped from the net so the people giving the advice can sound intelligent or educated.

    I have been experimenting with 12 volt batteries for the last 10 years plus, and I can say without a doubt that you can indeed run a 12 volt SLA and AGM down to 5V in a usefull manner and not destroy it. I am still using batteries from 10 years ago. As a matter of fact, I had two batteries that ran until last summer when I used them to experiment with the advice given in forums like this and they were killed almost instantly. A third I had no problems with until I started discharging it to only 11.9 which was also touted as the only proper way to discharge a battery, now it is dying a very slow death.

    The reason the controllers won't allow it is because, in the "college scheme", the 10.5v (now 10.1v) standard was set upon arbitrarily and has stuck. Much of the mathmatics that they use is also wrong, and they have no means of proving that it is accurate, because they are working with a preconceived notion, and of course all of their work now must conform to those standards.

    I don't want to get into an arguement with the people here as to the right way to use a battery, and I know that this post will get some hackles up, I'm just speaking from my own long years of real world experience.

    I do want to say that, depending on the controller, modifications can be made to make them run lower, or you can do what I do which is to use the controller to charge, but plug into the batteries with plugs and sockets to use the charge. Run your batteries down to the point that they will no longer run your device or system then immediately recharge them. Leaving them discharged for more than a couple days will kill them. Let me repeat; I have not ever damaged a battery from running it down to 6V or even a little lower and then immediately recharging it. What have I run? Water pumps, Light Bulbs, Computers, DVD Players, and a ton of other things. I recharge them at 500ma to 1A on a solar charge controller even in the dead of Wyoming winter.

    btw; I consider 30Amp+ (with massive 225Ah batteries) systems archaic and wasteful in this day and age. My system is not an over bloated, massive, wasteful system of yesterday, but a sleak efficient system that, while I am still working on it, already allows me to live on about 6 amps per day total. This is important, because it allows me to go deeper into my batteries and still recharge them quickly and not abuse them.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    No, it is not mere academics. Many more thousands of batteries than you can imagine have been in "real world" situations and end up being useless if discharged below 10.5 Volts. some will survive, others fail even if properly maintained. Batteries are always something of a gamble, no matter what.

    I suggest everyone, especially new comers, take the post by zone4guy with a grain of salt. That is one man's experience versus the experiences of many, including professional testing labs that have been working on battery research for decades. (No, this is not a scheme to sell you tons of batteries and panels.)

    I will also say that for RE purposes the old system of Amp hour ratings is not the best, but it's what we're stuck with for practical purposes. A better system which would include rating for maximum depth of discharge and cycles combined with usable power under controlled conditions would be grand. But we haven't got it so it's back to the long, hard calculations - and having to explain to people why you can't use all 225 amp hours in a T105. :roll:
  • XRingerXRinger Posts: 493Solar Expert ✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    I'm sold on not discharging my four marine/RV batteries below 12.0 volts under load.
    But my 48v inverter cuts-off at 40v. That's only 10v each!

    I know the voltage will bounce back up after the load is gone, but I worry
    that a light load (50wattish) working very slowly will bring the batteries
    down to 10v each, thus causing the bounce-back, to be very small..
    It just seems like 10.08~ volts isn't going to be good for the bank.

    I think 44v would have been a better cut-off.
    Wish cut-off was adjustable.
  • john pjohn p Posts: 814Solar Expert ✭✭
    Re: Why No Inverters for Deep Cycle Batteries?

    Zone 4 guy ,Sorry but I honestly think your post is just a load of rubbish.. What you are saying just goes against all known FACTS including the tests in REAL WORLD in post #9.. Im not an academic I spend evey working day doing real world testing.. I have at my disposal for doing such tests hundreds of thousands of dollars worth of testing equipment and a good sized budget to purchase just about anything I want to test.
    I can assure you the results of the tests I did on that deep cycle battery are very consistant with many others doing similar tests.. there is simply NO USABLE POWER available from a 12v battery below 10v.. Anyone that says different I dont believe..
  • waynefromnscanadawaynefromnscanada Posts: 3,009Solar Expert ✭✭✭✭
    Re: Why No Inverters for Deep Cycle Batteries?
    No, it is not mere academics. Many more thousands of batteries than you can imagine have been in "real world" situations and end up being useless if discharged below 10.5 Volts. some will survive, others fail even if properly maintained. Batteries are always something of a gamble, no matter what.

    I suggest everyone, especially new comers, take the post by zone4guy with a grain of salt. That is one man's experience versus the experiences of many, including professional testing labs that have been working on battery research for decades. (No, this is not a scheme to sell you tons of batteries and panels.)

    TOTALLY agree. I've been in electronics professionally almost 40 years, and around this stuff long enough to know right from wrong. Thus I totally agree with Cariboocoot!
  • icarusicarus Posts: 5,070Solar Expert
    Re: Why No Inverters for Deep Cycle Batteries?

    Batteries are not electrical storage devises contrary to popular opinion. What they are are electrical generating chemical factories. What they do in simple terms is take electrical energy, and turn it into chemical energy, and then in turn, that chemical energy is then reconverted into electrical energy.

    The media to do this is the acid concentration reacting to the lead in the plates. When the battery begins to loose voltage, it is because the concentration of acid is reduced, to the point of a being that the SG of a completely dead battery is that of water. Another way one might look at AH capacity would be, how long would it take (or how much power could you draw) from a battery before the acid concentration drops low enough to be effectively useless?

    So the question becomes one that I am certainly not competent to answer, but one that centers around the chemistry of the battery rather than the voltage per se.

    Tony

    PS. I am going to stick with the recognized opinions of others before I am willing to commit my batteries to a new regimen. Zone4guy suggests that he only draws "6 amps per day total" Unless he omitted the time factor in error, I might suggest he doesn't really understand the factors in energy equations. On the other hand, if he uses 6 Amp/Hours that would translate to ~ 72 watt hours (12 vdc). Even the most sulphated battery of reasonable size might be able to deliver ~ 6 ah/day for a hell of a long time.

    If the OP is willing to risk his batteries, I would challenge him to do a real world side by side test. Take two batteries, daily run each down, one to 20% SoC and the other to 80% SoC using what ever loads one wishes. Then charge each battery fully each day. In 1 year, do a load test on both batteries and see which has the greater capacity. Then give a calc regarding efficiency of deep discharges.
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