Not reaching Absorb or Float stage -- all of a sudden

[Sunking]

Hi again,

1) If my batteries are dead/useless, why do I still have any power at all? Today and tomorrow are going to be rainy/snowy/cloudy. I can run the generator now and then and get enough power to run my basics. When the sun comes back out on Tuesday (or yesterday when it was mostly sunny), I seem to be able to manage throughout the day until the next day, albeit the day starts out at 48 - 49 volts.

I never said useless, I said toast meaning they have lost so much capacity makes them impractical. If your batteries are sized properly and good working order should last you 4 days. at 48 volts are near completely discharged. Assuming your battery reaches fully charged say by 2:00 in the afternoon, you should see 50 volts the next morning just before sun up.

2) From my last post, I did get a handle on our usage. At most it is 6,000 watts per day. Usually less than that, but hardly ever more. Most of that is during the day. We have one fridge, one well pump and not much else. We probably get 5 hours of sun in the winter (maybe only 4.5 on December 21) and 7 hours or more during the summer. If my current set up can handle 17.76 Kwh a day, 6 Kwh a day is about 65% SOC each day. Is that correct?

That would be correct, but you really do not want to go that low in a day. It does not matter which part of the day you use the power. If you use 6 Kwh per day you want a 30 Kwh battery. That is what CYA to cover you for 3 cloudy days, and maximize your battery cycle life.

5) We are assuming that my current batteries will only last 1 ½ to 2 years. I’ve admitted that I didn’t care for them like I should have. None of the cells are or ever were dry, but it is true that I didn’t EQ them like I should have and probably there are other things I should have done. However, I am assuming that 1 ½ - 2 years is atypical and that even these batteries should have lasted longer with proper maintenance and charging. However, how likely is it that my DOD, which was likely in the 35-40% range for most of the time would wear out any battery too quickly, even if I had maintained them properly? Are these batteries that much worse than many others?

DOD has significant impact on cycle life among other factors. Keep in mind manufactures greatly exaggerate cycle life claims. They test in a labe performing many cycles a day to gather data for their charts. But batteries also have a calendar rather they are cycled or not. The battery warranty gives you a very good idea how long they will last. Example a battery listed at 2000 cycles to 20% DOD daily (80% SOC) would make one think you have a 6 year battery. However it carries a 18 month full replacement and 36 month prorated warranty is a 2 to 3 year battery at best or roughly 600 to 900 cycles.

Anyway here is a chart from a good manufacture. It has a 60/90 warranty. Very expensive battery.

[Willy T]

If my batteries are dead/useless, why do I still have any power at all?

Any time your charging a set of batteries that can't carry your design load for the specified time, they are useless. That is usually when their capacity reaches 75-80% in the real world, but most RE folks keep on trying to 50% or so like you are.

Have you never had a battery in a car that causes the starter solenoid click , but the starter does turn the engine over ?? Is that Battery dead ?? It has voltage, but no capacity the same as yours.

Most people that take care would get more time out of the batteries you have, but your's weren't taken care of.

EQ them, get them up to 62 V and see what you can recover from them. Use your hydrometer.

[dalyxxdj]

Hi again,

1) If my batteries are dead/useless, why do I still have any power at all? Today and tomorrow are going to be rainy/snowy/cloudy. I can run the generator now and then and get enough power to run my basics. When the sun comes back out on Tuesday (or yesterday when it was mostly sunny), I seem to be able to manage throughout the day until the next day, albeit the day starts out at 48 - 49 volts.

2) From my last post, I did get a handle on our usage. At most it is 6,000 watts per day. Usually less than that, but hardly ever more. Most of that is during the day. We have one fridge, one well pump and not much else. We probably get 5 hours of sun in the winter (maybe only 4.5 on December 21) and 7 hours or more during the summer. If my current set up can handle 17.76 Kwh a day, 6 Kwh a day is about 65% SOC each day. Is that correct?

3) I understand that going off-grid wasn't going to be cheap or easy. Money isn't the issue per se -- understanding the basics is what is important. If my understanding from above is correct, my current setup, given my usage of 6,000 watts a day is 5% less than ideal if I want to maintain no less than a 70% SOC. Correct? It also doesn't leave me much/any room for cloudy days.

4) If I went with the batteries Sunking recommended, my watt hour capacity would be 22,272 watts, or 22.27 Kwh (464AH X 48 volts). Correct? Assuming my usage stays at 6,000 watts a day, or 6 Kw a day, my SOC on any given day only gets me to 73-74% SOC? Correct?

5) We are assuming that my current batteries will only last 1 ½ to 2 years. I’ve admitted that I didn’t care for them like I should have. None of the cells are or ever were dry, but it is true that I didn’t EQ them like I should have and probably there are other things I should have done. However, I am assuming that 1 ½ - 2 years is atypical and that even these batteries should have lasted longer with proper maintenance and charging. However, how likely is it that my DOD, which was likely in the 35-40% range for most of the time would wear out any battery too quickly, even if I had maintained them properly? Are these batteries that much worse than many others?

As always, thanks again for all your help. Let’s hope the sun will come out tomorrow!

[Sunking]

Thanks again for the advice/suggestions. I've learned quite a bit in two days! I didn’t mind hearing any of the things you had to say at all, but my wallet groaned heavily when I priced the batteries Sunking had recommended!

Following Sunking’s calculations and patient explanations, I just wanted to break it down in a bit of a real world way now to see if I really get it, which will help me figure out how to proceed. Based on what you said, I went back and re-calculated what we actually use up here by testing everything we have plugged in and use regularly, i.e, measuring actual draws, and I was able to come up with a daily usage of about 6,000 watts, or 180 Kwh/mo.
So, in an ideal world, and if I had maintained my batteries properly from the start, the maximum amount of power we would want to use on any given day is 5.3Kwh, which is 30% of the 17.76 Kwh that my 6, 8V batteries can “store” at 100% SOC (6 batteries X 8 Volts per battery X 370AH per battery = 48 X 370 = 17,760 watts or 17.76 Kwh). Based on my usage, however, it seems that I’m using 6Kwh day, or 35% a day, on average. Correct?

You are on target Dan. But perhaps the wrong approach. A Off-Grid Battery system is designed based on how much energy you use in a day worse case. In practice two designs are done. One for Summer loads, and another for winter loads. Example if you use say 4 Kwh per day in winter and 6 Kwh per day in summer, the battery is sized to largest daily usage of 6 Kwh per day or a 30 Kwh battery.

Same with panels but things can reverse because of winters short days. If you only had say 2 Sun Hours in winter and 5 in summer the winter panel power is 3000 watts and summer is 1200 watts. You use worse case of 3000 watts.

As for batteries yes I know they are expensive, but which is cheaper? Buying the same battery you have now every 1-1/2 to 2 years, or the Trojans every 5 or 6 years? So what you need to get a handle on is how much you use each day. Once we know that we can zero in on batteries. As you are finding out be careful what you ask for. Solar battery is not cheap. That unfortunately is the choice you made going off-grid. You might not have realized that when you first went off-grid, but now you know and have to live with it. Hang in there, put a pencil to some paper, no rush, but figure out how much you use in a day in both winter and summer. You do no twant to have to go through this every 18 months and may not be as bad as you think. But you will not know until you have done your homework.

So once you figure out the daily wattage here is how you find your battery capacity (daily watt hours x 5) / battery voltage. Example 5 Kwh per day: ( 5000 wh x 5) / 48 volts = 520 amp hours. A good 5 to 7 year battery will cost you $200-Kwh so a 25 Kwh battery cost $5000. Or another way to calculate is $1000 x Kwh-day. Like I said be careful what you ask for, it gets expensive real fast.

With your panel wattage you have now of 2000 watts in winter can provide you up to 5.3 Kwh per day. 2000 watt panel can support a battery as small of 320 AH and as large as 480 AH @ 48 volts. You reall do not want to go outside that range with your panel wattage. Smaller batteries can be damaged by too much charge current, and larger will stratify.

[paulcheung]

Everyone,

paulcheung is partially correct. I don't have a faulty volt meter, I am a faulty volt-meter-reader I think. I have an analog meter and after his comment, I just now went and tried it again. I think I had read the wrong scale. I re-measured and they were all reading at about 6V and the total battery bank was at about 51V. My apologies to everyone, and yet again, I feel pretty stupid. I double checked the volt meter on my newish truck battery and it read 12V. So, I think the volt meter is OK. You all can tell me if you think that changes the theme that has emerged that the batteries are or may be bad. I won't have a hydrometer for another week, so I can't do any other kind of testing until then.

In the meantime, I was getting ready to post these thoughts about the discussion to date.

Thanks again for the advice/suggestions. I've learned quite a bit in two days! I didn’t mind hearing any of the things you had to say at all, but my wallet groaned heavily when I priced the batteries Sunking had recommended!

Following Sunking’s calculations and patient explanations, I just wanted to break it down in a bit of a real world way now to see if I really get it, which will help me figure out how to proceed. Based on what you said, I went back and re-calculated what we actually use up here by testing everything we have plugged in and use regularly, i.e, measuring actual draws, and I was able to come up with a daily usage of about 6,000 watts, or 180 Kwh/mo.
So, in an ideal world, and if I had maintained my batteries properly from the start, the maximum amount of power we would want to use on any given day is 5.3Kwh, which is 30% of the 17.76 Kwh that my 6, 8V batteries can “store” at 100% SOC (6 batteries X 8 Volts per battery X 370AH per battery = 48 X 370 = 17,760 watts or 17.76 Kwh). Based on my usage, however, it seems that I’m using 6Kwh day, or 35% a day, on average. Correct?

I see where a 370Ah rated battery isn’t quite big enough to allow for a 70% SOC, and certainly wouldn’t allow for any real storage for those cloudy days. In theory, if we reduced our usage to 3.5 – 5.3 Kwh, couldn’t we get away with the same size battery we currently have if we maintain it properly. Conversely, if we want to maintain our “extravagant” lifestyle of 6Kwh, then we would need at least a 420Ah rated battery, as suggested.

I just now saw that you posted hoping I’d get back to you soon, so here it is.

Dan

6000 WHs, if the load is spread out evenly, it is about 250 watts, which is less than 6 Amps at 48 volts., that is about 50 hours rate on a 370 AH FLA battery, it is equal to 394 AHs at that rate. remember, during sun hours the load is from the panels not the batteries, so you only draw about 16 to 18 hours from the battery, the Watt hours you draw from the battery is about 4000 to 4500 WHS. that is about 25% DOD for a 394 AHS from 48 volts system.

The battery Sunking suggest is one of the best battery which could easily last you over 10 years for your application if you take care of them, but you can also buy the Trojan L16RE-B 370 amp hours battery which can yield you 394 AHs when you only discharge them at 6 amperes.

My battery system is 750 amp hours at 48 volts, I consume 20 to 23 KWH each day. I do a lot of load during the day , my nightly consumption without sun is around 10 KWH. My battery bank voltage in the morning under 15amps load is around 48 volts before sun comes out. it gone 18 months already and I wonder how long my batteries will last.

[Mike90250]

Some other things to factor in

Daytime usage needs to be subtracted from the power available to recharge the batteries, with some clever timing, you can charge batteries, run the dishwasher and fill 3,000 gallons of water in the tank. Don't try any 1 of those things at night, on a cloudy day, or 2 at the same time. it's all about load management

Any loads you can shift to solar hours (10am -3 pm) are loads the battery does not have to carry. nighttime, it's only 2 fridges, 1 freezer, and about 100w of incidentals - lights, TV & bidet.

[Living Large]

Everyone,

You all can tell me if you think that changes the theme that has emerged that the batteries are or may be bad. I won't have a hydrometer for another week, so I can't do any other kind of testing until then.
Dan

The two tests that Sunking suggested were open circuit and with C/10 load. Open circuit is simply measuring the voltage with nothing connected - there should be a disconnect in your system. C/10 means a current through your 48V bank of your AH capacity divided by 10 - in your case 370/10 = 37 Amps, @ 48V, or a load of about 1800 Watts.

[dalyxxdj]

Everyone,

paulcheung is partially correct. I don't have a faulty volt meter, I am a faulty volt-meter-reader I think. I have an analog meter and after his comment, I just now went and tried it again. I think I had read the wrong scale. I re-measured and they were all reading at about 6V and the total battery bank was at about 51V. My apologies to everyone, and yet again, I feel pretty stupid. I double checked the volt meter on my newish truck battery and it read 12V. So, I think the volt meter is OK. You all can tell me if you think that changes the theme that has emerged that the batteries are or may be bad. I won't have a hydrometer for another week, so I can't do any other kind of testing until then.

In the meantime, I was getting ready to post these thoughts about the discussion to date.

Thanks again for the advice/suggestions. I've learned quite a bit in two days! I didn’t mind hearing any of the things you had to say at all, but my wallet groaned heavily when I priced the batteries Sunking had recommended!

Following Sunking’s calculations and patient explanations, I just wanted to break it down in a bit of a real world way now to see if I really get it, which will help me figure out how to proceed. Based on what you said, I went back and re-calculated what we actually use up here by testing everything we have plugged in and use regularly, i.e, measuring actual draws, and I was able to come up with a daily usage of about 6,000 watts, or 180 Kwh/mo.
So, in an ideal world, and if I had maintained my batteries properly from the start, the maximum amount of power we would want to use on any given day is 5.3Kwh, which is 30% of the 17.76 Kwh that my 6, 8V batteries can “store” at 100% SOC (6 batteries X 8 Volts per battery X 370AH per battery = 48 X 370 = 17,760 watts or 17.76 Kwh). Based on my usage, however, it seems that I’m using 6Kwh day, or 35% a day, on average. Correct?

I see where a 370Ah rated battery isn’t quite big enough to allow for a 70% SOC, and certainly wouldn’t allow for any real storage for those cloudy days. In theory, if we reduced our usage to 3.5 – 5.3 Kwh, couldn’t we get away with the same size battery we currently have if we maintain it properly. Conversely, if we want to maintain our “extravagant” lifestyle of 6Kwh, then we would need at least a 420Ah rated battery, as suggested.

I just now saw that you posted hoping I’d get back to you soon, so here it is.

Dan

[Sunking]

I think he has a faulty volt meter, it is no way that the battery bank at 36 to 40 volts on a 48 volts system still can operate, he need to get a different meter to check the battery's voltage.

Paul if you read he put the batteries on generator and got them up to 51 volts at rest, but quickly discharge with a load applied. Classic sulfated battery. That tells us the batteries are done, but can also indicate he has a faulty charging system which needs to be checked out before replacing the batteries.

Hoping he gets back soon as I have a few more questions.

[paulcheung]

I think he has a faulty volt meter, it is no way that the battery bank at 36 to 40 volts on a 48 volts system still can operate, he need to get a different meter to check the battery's voltage.

[Mike90250]

A 6v battery has 3, 2v cells internally (thats why the 3 caps for water) Either all the cells have some damage, or one 2v cell is dead. in a large battery bank of 48v, it's likely both things have started happening.

Do you monitor any of the logging functions of the Classic ? it's data logs (if you configured them) can tell you a lot about the charge and discharge characteristics of the batteries.

Regardless, you are looking at new batteries, get a hydrometer and practice with what's left of this bank, to learn to protect the new bank.

[Sunking]

2) Measured each battery this morning before anything was happening and they all measured equally at about 4 volts. Should I be concerned that it isn’t 6V, or would that be natural given that it is first thing in the morning and the total voltage was low? I suppose it’s a good thing that they were all the same, no?

OK Dan I have a pretty good idea what is going on. You are not going to like a lot of what I have to say, but at least you will have an idea os what and how it happened.

You have a 48 volt FLA battery system, and there are some voltages you need to know especially when they are setting there doing nothing or being discharged like at night. A fully 100% charged 48 volt battery with no or little load should measure 51 volts (50.91 to be exact). At 80% State of Charge (SOC) 50 volts. At 50% SOC the voltage you never want to go under is 48.4 volts. At 0% SOC is 46 volts. See where I am going with this Dan? If you have 8 batteries x 4 volts = 32 volts.

3) The batteries are not the golf cart series of batteries. From the spec sheet, my batteries are the 8L16 batteries. Here is the link to the spec sheet -- http://www.bornay.com/en/products/pr...-batteries.pdf. They list two AH’s – one is Ah C20 = 370, and the other is AH C5 = 295. It also says the time to discharge at 75 amps is 190 minutes.

Well technically they are the exact same battery series. Nothing wrong with that just a larger version. So now we at least know you had a 48 volt @ 370 AH battery. You need to know what this means and how to apply it. To find the battery Watt Hour Capacity is easy = Battery Voltage x Amp Hours at the 20 hour rate. So you have 48 volts x 370 AH = 17,760 watt hours of 17.76 Kwh. That is a moderately sized battery. But here is the catch, you cannot use that much in a day, not if you want the battery to last more than a year or two. To maximize battery life you want to limit your 24 hour day discharge to 20 to 30% of the capacity and under no circumstances let your battery go below 50%.

What this means is want to limit your daily usage to 3.5 to 5.3 Kwh per day. It also means your panels must be able to deliver more power than you use in a day to over come system inefficiencies and make up for some cloudy spells. It has to be able to do this year round even in the short days of December and January.

4) The nearest big city is Colorado Springs or Pueblo. I go to Denver regularly as well, and if I have to get something up there, it’s no problem. We are at 38.38 N, 105.13 W and 7,100 feet if that helps.

5) Our solar array is 6, 327 watt, Sun Power panels for a total of about 2,000 watts. I didn’t see anything amiss with any of the wiring on the panels the other day when I looked. It is oriented due south (not magnetic) and tilted at about 33 degrees if that helps. Like I said, we generally get great sun and up until earlier this week, we were cycling normally.

6) Our charge controller is the Midnite Solar Classic 250.

7) Our inverter is Xantrex XW Hybrid Inverter/Charger, Model No. XW6048.

OK so you have 1920 watts of panels. How are they wired up? I assume 3 in series in parallel with 3 in series. Only other possible workable config is all 6 in series, depends on the Voc of the panels.

OK in winter for your area your best tilt angle is Lattitude plus 15 degrees gives you 4.1 Sun Hour which is excellent. That means your panels can generate at least 5.3 Kwh per day. It also means you batteries are just a bit small as 1920 watts @ 48 volts generates up to 40 amps. Idea battery size for you is 400 to 440 AH. 370 is OK but your panel wattage and sun hours can support larger batteries so you get a passing grade on equipment sizing.

8) I’ve always had a hard time figuring out our watt hours usage, so I’ll tell you what I know. At any given time, the meter reads about 175 watts during the day, a little less in the summer when we take off the heat tape that keeps our water from freezing.

OK this is where you are likely where you get into trouble. 175 watts x 24 hours = 4.2 Kwh in winter months. What is using 175 watts around the clock? Whatever it is is using 80% of your daily total only leaving you 1 Kwh a day to play with. You really need to nail this down as to how much energy you use in a day.

OK in closing your batteries are toast. Based on panel wattage and equipment you have A Trojan IND9-6V a 6 volt 460 AH battery with a 8 year warranty. Take care of them and do not let them go below 50% DOD and you got a solid 5 to 7 year battery. Next after you digest this we will talk about proper maintenace like EQ charging with your generator and how to use a hydrometer.

FWIW here is a SOC chart. This will let you know where you stand.

[Willy T]

Dead would be a term to describe them as useless. Almost total loss of capacity might better description for their condition. If they were 100% when new they may be at 10% capacity now. They are like this because there is so little plate material exposed to the electrolyte and the electrolyte is so weak because the plates are covered with sulfate that has crystallized that very little charging takes place.

Can these batteries be rejuvenated ?? Hardened Sulfate is almost impossible to remove. There ways with certain chemicals to do it. ( EDTA ) but it's not worth the effort and it's complicated to do.

You could try to do a Equalization Charge @ 62 V to see if you can break any loose. You have to keep the temperature below 115 ° F and use your hydrometer to look for a rise in the SG level. You may be able to get them to a higher level than they are now, it depends on how many $$$ you want to spend in gas trying. I have tried them for 24 hrs and got nothing in return and some will recover a little.

Bottom line, when you get new batteries, pay more attention to them.

[dalyxxdj]

Hi Mike,

"Thanks" for the info I kind of hope it is the batteries and not the panels or the controller. I had asked my installer separately what they thought could be the problem and they didn't mention anything about the batteries and assumed that it was a problem with the controller. I can't see how that is the case, but could it be?

I guess I have a basic battery question, though. If the batteries are dead, how is it that they will store some power during the day, enough to get us through the night at least? Also, I ran the generator yesterday for a bit and it was able to charge the battery bank up to the Absorb stage and to 57V. Once I turned it off, it went back down to 51V, but stayed there for awhile until ultimately ending up at 48.5 this morning. Now that the sun is out again today, it's back up to 51V. If it is the batteries, am I simply going to have to do this dance every day until I get new batteries?

Thanks for your help in advance!

Dan

[Mike90250]

2) Measured each battery this morning before anything was happening and they all measured equally at about 4 volts. Should I be concerned that it isn’t 6V, or would that be natural given that it is first thing in the morning and the total voltage was low? I suppose it’s a good thing that they were all the same, no?

measuring 4V on an unloaded 6v battery means that it is dead.