batteries dead? or not?

terrorr · January 2014

Every time I think i have a handle on my system, something new comes up. Spent time on the forums and various websites but I still not sure so I was hoping someone could help clarify.

Are my batteries done? Have they reached the end of their life cycle?

I have a battery bank: 8 batteries Kirkland marine 12 volt wired in parallel 95 amphours each. They have worked flawlessly for 3 years. Now they don't last longer than 4 or 5 hours during the nite. I am using a trimetric 2020 to monitor the batteries.

Here are some specifics :

Fully charged at 13.3 volts at end of day.
Amp hours before full = 0
They used to last up to 200 amp hours which gave me a 30% discharge and a reading of around 12 volts in the morning. This was about the maximum they ever got discharged.
NOW - they only last about 50 amp hours before the voltage drops to 10.5 - 10.9 and the inverter shuts down.

I did a test and completely charged the batteries. Then with no load and no charge, waited 8 hours. The volt reading was then 12. 9 volts.

So they recharge, but don't last very long before they are completely discharged.

Any help or comments would be appreciated. Gracias!

Blackcherry04 · January 2014

Re: batteries dead? or not?

3 years they they could be done. Kirkland ( costco ?? ) it's hard to tell. I assume they are not sealed you can check the SG level with a hydrometer and equalize them and see if they will rise any. You need a charging source to take them up to 15.5 volts for as long as it takes to get to 1.265 SG level or so. Check the temperatures and keep them below 115 deg F while you equalize, if your making any headway you can stop and start again when they cool off.

Advice, get a set of GC-2 golf cart deep cycle batteries.

Cariboocoot · January 2014

Re: batteries dead? or not?

Welcome to the forum.

You have a couple of system design problems which are contributing to the failure. For one thing, Marine/RV batteries are not truly deep cycle and do not stand up to repeated cycling no matter what the salesman says. For another, you have eight batteries in parallel? There is almost no chance that they will be sharing current evenly on discharge/charge no matter how well done the wiring.

If you want to test a battery's condition accurately you need to measure the specific gravity with a hydrometer; each and every cell of every battery. Voltage alone is not reliable, even when done "at rest" as you did. You can in fact get a "correct" Voltage reading from a battery that is heavily sulphated; it has the Voltage, but its Amp hour capacity has drop drastically so the charge does not last long. This would seem to be what you are experiencing.

With eight 95 Amp hour batteries in parallel your bank is theoretically 760 Amp hours @ 12 Volts. That would require a very large array and charge controller to properly recharge; about 1200 Watts and an 80 Amp MPPT controller. This is probably not what you have, and that means you would have been running on deficit charging until the bank is no longer capable of being replenished sufficiently to provide the needed power.

I suggest you go back to the basics. Re-evaluate your load requirements and determine what size battery bank you actually need with a 25% depth of discharge limit. If it comes out as large as you have now, consider going to a higher Voltage system as the power is more efficiently utilized at higher Voltage. Then check the array and controller to see if it can support the battery bank.

Blackcherry04 · January 2014

Re: batteries dead? or not?

While I do agree with all that Coot has said, 3 Years is not 3 Months. A system that has operated that long it's doubtful that it's been deficit charging for 3 years. You could have a issue with the Information you are receiving from the Trimetric Monitor and checking to SG level and making sure they back each other should always be your first line of defense.

Having 8 battery in parallel is a issue, there just to many things that can cause a problem, thats a area I would think about.

Cariboocoot · January 2014

Re: batteries dead? or not?

Blackcherry04 wrote: »

While I do agree with all that Coot has said, 3 Years is not 3 Months. A system that has operated that long it's doubtful that it's been deficit charging for 3 years. You could have a issue with the Information you are receiving from the Trimetric Monitor and checking to SG level and making sure they back each other should always be your first line of defense.

It would depend on several factors, including actual load demand and recharging ability. Since we don't know either I felt the possibility should be mentioned as I have seen systems that were 'just short' of what they needed to be and as such had too many days of not fully charging which ends up slicing years off battery life.

It is also possible there has been a catastrophic failure somewhere in the system which caused a sudden drop in charging ability. To paraphrase a WW II axiom: "Loose wires sink systems".

vtmaps · January 2014

Re: batteries dead? or not?

Cariboocoot pointed out that 8 parallel batteries is a problem (among the other problems).
If you would like to learn more about that, here is a short discussion:
http://forum.solar-electric.com/showthread.php?14674

It's quite possible that you have only one or two bad batteries, but since they're all in parallel, when you are done charging the good batteries are discharging into the bad batteries. By the way, that can be dangerous and parallel batteries should have a fuse on each battery.

If you buy a DC current clamp meter, you can see how uneven the charging/discharging is.

One thing you can do now is charge and test them, one battery at a time. You may be able to figure out which batteries are dragging the whole bank down, and eliminate them.

--vtMaps

Blackcherry04 · January 2014

Re: batteries dead? or not?

I did a test and completely charged the batteries. Then with no load and no charge, waited 8 hours. The volt reading was then 12. 9 volts.

So they recharge, but don't last very long before they are completely discharged.

My posts were made taking this information into account. If you had a bad battery or a dead cell you would have never had the standing voltage you have after 8 Hours. I read you post.

Parallel battery banks do have issues that have to address. I like to take mine apart once a year and clean all cables and shuffle the location of the batteries in the bank. The first one or two batteries on the positive end will always carry more of the load and use more water and age the fastest. Parallel Banks are a fact of life and used everywhere, 8 batteries is getting way out on the limb of viability though. The most I ever do is 5-6 sets of GC-2's.

terrorr · January 2014

Re: batteries dead? or not?

Thanks everyone for your replies, lots of good info.

Just to back up abit, this is unfortunately not my " dream" system but what was designed and put together based on budget but more importantly, availability. I have a small casa in Mexico and it is more or less powered by my solar PV system. The marine batteries were the only thing I could find. It is very hard to obtain the most basic things

Everything was kind of cobbled together as best as I could but it has run very well for 3 years.

Regarding 8 batts in parallel I did not know and never read anything about that being a problem so thank you for pointing that out and I will look more into it. Battery bank sizing was based on this:

1800 watts or 152 amp hours used per day
this would drain the batt bank about 20% per day
which would mean a batt bank of about 760 amp hours.

would there be another way to string the batteries together to get this? it is a 12v system with a 12 volt Samlex 600watt pure sine inverter. Would it have been better to only have 4 95 ah batts and drain them deeper everyday?

Another question re: recharging. I have 4 120w panels. Factoring in inefficiencies etc and depending on the DOD they seem to be able recharge the batt bank full everyday. I know I could use more panels but if the batt bank is down 150 ah (for example) and the panels recharge it 150 ah during the day and the trimetric sez it now has 0 ah to full charge, is it still not fully charged?

terrorr · January 2014

Re: batteries dead? or not?

vtmaps wrote: »

Cariboocoot pointed out that 8 parallel batteries is a problem (among the other problems).

If you buy a DC current clamp meter, you can see how uneven the charging/discharging is.

One thing you can do now is charge and test them, one battery at a time. You may be able to figure out which batteries are dragging the whole bank down, and eliminate them.

--vtMaps

will look into that!

terrorr · January 2014

Re: batteries dead? or not?

Cariboocoot wrote: »

Welcome to the forum.

You can in fact get a "correct" Voltage reading from a battery that is heavily sulphated; it has the Voltage, but its Amp hour capacity has drop drastically so the charge does not last long. This would seem to be what you are experiencing.

.

that is indeed what I am experiencing so if the batteries are heavily sulphated can they be saved?

BB. · January 2014

Re: batteries dead? or not?

Here is a quick explination of how to wire a parallel battery bank "Better":

http://www.smartgauge.co.uk/batt_con.html

If you are happy with the ~3 year life? That is probably not a bad life for a Marine Battery based bank.

Can you get some sort of "golf cart" battery there (typically around 6 volts and ~220 AH)? Those would be (usually) a better bet. But getting 3-5 years would be doing go for them.

You could go with a slightly smaller AH bank, but a "good nominal" design is ~25% of battery bank capacity usage per day--You are already pretty close to that.

You don't want to go with a smaller AH battery bank with the Marine Batteries--They will not last very long at all... But If you get 1/2 the number of batteries and they last ~1.5 years--The result is about the same.

That is the "problem" with battery banks... Pay 2x as much and they (may) last ~2x longer.

Many folks "kill" their first bank or two--Either through mistakes (not checking water levels, over/under charging, something failing and not catching it soon enough, too large or too small battery bank, etc.). You sound like, that you are not doing bad--Not even taking into account what you are up against.

A DC Current Clamp DMM (Sears has a pretty cheap one that is "Good Enough" for our needs) would be a good investment. And a good glass hydrometer too.

-Bill

terrorr · January 2014

Re: batteries dead? or not?

Cariboocoot wrote: »

Welcome to the forum.

With eight 95 Amp hour batteries in parallel your bank is theoretically 760 Amp hours @ 12 Volts. That would require a very large array and charge controller to properly recharge; about 1200 Watts and an 80 Amp MPPT controller.

Doesn't that depend on the load or discharge everyday? If it discharges only 20% everyday and 6 + hours of sun?

BB. · January 2014

Re: batteries dead? or not?

A Lead Acid battery bank charging at 5% to 13% rate of charge is recommended. You should not go below 5% (of battery 20 hour rating) and, for solar, going above 13% rate of charge is not usually cost effective (batteries are "full" pretty early in the day).

A 760 AH battery bank should be 5% or 38 amps minimum... 10% is better if you are deeply cycling every day (some industrial/larger batteries have a 10% rated minimum charge). If you go below 5% rate of charge, the batteries tend to be undercharged and take a few days to recharge. And if you have loads during the day, then the 5% rate of charge becomes even less.

-Bill

Blackcherry04 · January 2014

Re: batteries dead? or not?

terrorr wrote: »

that is indeed what I am experiencing so if the batteries are heavily sulphated can they be saved?

Read post #2 that tell's you what to do, or it did before this went off somewhere else.

Cariboocoot · January 2014

Re: batteries dead? or not?

terrorr wrote: »

Doesn't that depend on the load or discharge everyday? If it discharges only 20% everyday and 6 + hours of sun?

Not necessarily.
You have to have a certain minimum amount of current to affect a charge in the batteries. Most manufacturers recommend 5% of the capacity for this: 38 Amps for that battery bank, before any load consumption. The current will of course taper as the battery charges, so that will not be constant current. As such targeting a peak current of 10% allows for some load draw, current taper, and array output power curve through the day enabling a bank discharged to around 25% to be fully recharged in one good, sunny day.

Therein lies another issue: hours of daylight does not equate to hours of direct sun on panels and thus full panel output. A fixed, South-oriented array will start out charging at a low current in the morning as the sun is at an angle and having to shine through more atmosphere. As the day progresses the array's output potential increases as the sun angle becomes more direct and the amount of air it has to go through decreases. At the same time the panels will heat up resulting in their output going down due to a lowering of Voltage. Meanwhile the batteries have been charging so their maximum current draw potential is on the decline. (Again we are ignoring load draw here.)

So it is never as simple as "the panels put out 'X' Amps and there's 'Y' hours of sun so they can charge 'Z' Amp hours of battery".

westbranch · January 2014

Re: batteries dead? or not?

To reinforce what has been said so far, you need more input Watts to get a good sharge rate on those batteries, actually any batteries with that much capacity.

I believe you might want to look into getting set up as a 24V system. This would remove some of the parallel battery issues you are having.

Also go to GC2's (6V) will cut the number of 12 v sets as they have ~2 x the Ahr rating (~220Ah) than your original Kirkland's did.

going to GC's and 24 volt would reduce the number of ( 12v) batteries to 1/4

hth

vtmaps · January 2014

Re: batteries dead? or not?

terrorr wrote: »

if the batt bank is down 150 ah (for example) and the panels recharge it 150 ah during the day and the trimetric sez it now has 0 ah to full charge, is it still not fully charged?

NO! , or at least not necessarily. Battery monitors are wonderful tools, but you must understand their limitations.

A battery monitor is often compared to the gas gauge in your car, but that is not a good analogy.

The gas gauge in your car actually measures the level of gas in your tank. A battery monitor doesn't measure the level of anything. It is more like the odometer in your car. The odometer counts miles and the battery monitor counts ampHours.

Suppose you have a car that gets about 25 mpg and has a 15 gallon gas tank. Suppose also that your gas gauge does not work. What do you do? You use your odometer. For example: After a fill up you drive 150 miles and you expect that you have used 6 gallons and have 9 gallons remaining in your tank.

But what if you do not completely fill your tank. For example, starting from a full tank you drive 150 miles and then you add 3 gallons to your tank and then drive 100 miles and then add 4 gallons to your tank and drive 150 miles and then add 5 gallons to your tank and drive 100 miles. At this point you estimate that you have 7 gallons remaining in your tank, but that estimate is not too accurate because your mileage is not ever exactly 25 mpg. The only time you know exactly how much gas is in your tank is when you have just filled it up (or when you run out of gas).

So it is with your battery monitor. It can be very accurate counting the amphours in and out of the battery, but it can only estimate the state of charge based on your assumptions of the battery capacity and of the battery efficiency. It can read 100% (by counting amps into the battery) before the battery is fully charged. The only time it is exactly accurate is when you fully charge your batteries and reset the battery monitor to read 100% full.

The trimetric can automatically reset to 100% based on criteria that you set. For example, you may have decided that your batteries are charged when the voltage is at least 14.4 volts and the current is below 20 amps for a minute. But is that really when your batteries are charged?

If you're going to train your monitor how to recognize a fully charged battery, then you yourself must know when the battery is fully charged. You may accomplish this by monitoring end amps during absorb charging and using an hydrometer or refractometer to know when your batteries are fully charged.

Bottom line: the longer its been since a complete charge, the less you can trust your battery monitor. And you can't trust it at all if its not set up correctly. That said, battery monitors are valuable tools in estimating your SOC, but you have to understand their limitations. You must have a hydrometer or refractometer, and and a way to monitor the current into the battery.

When you know the 'end amps' current and absorption voltage that represents fully charged, you can program the trimetric to be more accurate.

--vtMaps

terrorr · January 2014

Re: batteries dead? or not?

Thanks, everyone. I am working on the batteries right now.

BTW just noticed they are guaranteed for 30 months, I already got 3 years with no hassle out of them, so that's pretty good. But I'd like to squeeze some more mileage out of them

batteries dead? or not?

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