Why No Inverters for Deep Cycle Batteries?

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.

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.

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...

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!

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..)

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.

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?

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...

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..

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.