Odd Occurrence with L-16s

pvoffgrid · February 2013

Hi, I am new here and hope you can help with an issue I am having.

I have been living off-grid for 12 years now. I am experiencing an odd occurrence with my batteries and I am looking for thoughts. I am having L-16’s go bad in the middle of my strings. I am going to replace the batteries this week to the tune of $5k - $6k but I need to make sure there is no other issue in my system before doing so.

1st, I will admit I am not the greatest at maintaining my batteries and when this current set of L-16s was 42 months old I went about 2 months without checking the water level. UGH, and other non-printable words. What an idiot as I discovered a few of the batteries had the plates exposed. But, it is what it is and I wanted to give some background as to the history of the batteries. When the batteries were 46 months old I did end up replacing 2 of the L-16s. The batteries are currently about 54 months old.

The original PV system was a 1.92kW PV, 48v system, 24 L-16 batteries wired in 3 series –parallel strings, 2 SW5548 inverters with 1 Outback MX60 charge controller with a Kohler 11RMY generator. When the system was about 4 yrs old the PV was increased to 2.08 kW when the PV modules were replaced under warranty. This was the size system in place when I failed at my maintenance.

When the batteries were 46 months old, which is when I replaced those 2 L-16’s, I increased the size of the PV system to 4.6kW, adding a new Outback charge controller and redesigning the previous inefficient battery layout: the 3rd string at end of 2 side by side strings which had unequal length cables coming off the inverter feeding the 3 strings. I now have 3 side by side strings with the cables coming off the inverters to a buss plate with other equal length cables going from the buss plates to the strings.

The generator normally ran about every 2 days or so in the winter time. In the summer time the generator ran about every 4 – 5 weeks. The generator ran for the 1st time about 10 weeks after increasing the PV output the middle of last summer and this winter the generator did not run but once a week until the mid-part of January when it started to run about every 3 – 4 days and this past week it has run daily. I also am once again started religiously checking battery water level every 4 – 5 weeks and only add a little bit of distilled water each time. However, I am now checking the water level weekly but again adding very little water.

Below are the odd occurrences since last October:
October: Checked battery water level at 4 weeks since checking last time and found all batteries in the middle string had plates exposed. What!*? I do not remember if I checked the battery water level before or after the generator ran for that 1st time 10 weeks after not running, which was the time prior to making this discovery. All I know is I checked the water level every 4 weeks since I discovered the exposed plates at 42 months old. So, filled them all up and went on my merry way.

February: 3 weeks ago I discovered 4 bad batteries…well, 1 is kind of bad..in all 3 strings. So, I dropped from 3 strings down to 2 strings, leaving 4 batteries connected to each other but not connected to the PV system. There was 1 bad battery @ 1.x v in 1 string, and 2 @ 4.xv in another string. That is 3 bad batteries and the 1 kind of bad battery? It is not in the system now and still reads 6.2v without having been charged in over 3 weeks But, it was in the 3rd string & I pulled it out because I discovered the cable had gotten so hot the outer sheath had pulled back over the inner sheath and the cable actually pulled itself thru the lead terminal, leaving me with 1 string completely disconnected in the middle.

February: this past 4 days I have replaced 2 L-16’s using the disconnected 6.2v batteries. I now have one of those 2 L-16s reading 4.9v after it read 6.2v when I put it in the string. And, it is in the middle of the string. Also odd was one of the end batteries did not read 6.x v..it read 11.x volts whereas the other batteries all read 6.xv (after I changed the 4.x battery out). The next day it read 2.x v so it got changed out.

It does appear the cables...guessing about 12" long in an s-shape do have corrosion inside as I can hear crunching noises on some of the ones I have removed when I try to straighten them.

It appears the middle batteries in 1 string are going bad.

Any thoughts as to why the middle batteries are going bad?

Any thoughts as to what would cause that middle battery cable to get so hot it pulled thru the terminal
Can I still use that melted terminal battery if I clean up (file the terminal flat again) the terminal and sandwich the cable to the terminal somehow, using larger diameter washers, etc?

Anyone ever use metal bars to connect the batteries instead of cables? If so, where can I buy them? I would think that would be better for corrosion purposes, but worse given the safety aspect of more exposed metal connecting the batteries vs. just the terminals.

Inverter settings can be provided if needed. Inverter is set to come on automatically once voltage drops to about 47.6v over 2 hours, if I remember correctly. Voltage usually ranges from about 49.2v – 50.2v during the evening when we are home using things and the fridge is running, tv is on, freezer runs, well pump comes on, etc, and is about 1/2 - 3/4 volt less in the morning when we wake up, usually about 48.8 – 49.4v.

Thanks for the thoughts as if there is an issue with this system I want to get it fixed before I drop money on new batteries.

EDIT" PS..the room with the batteries is unheated.

Cariboocoot · February 2013

Re: Odd Occurrence with L-16s

Welcome to the forum.

Let's see what you got there. Twenty-four L16's of what size? 320 Amp hours? 390? Anyway you've got three parallel strings so it's at least 900 Amp hours @ 48 Volts. Right?

You're charging this with 2080 Watts of PV? You must be running the generator a lot, as that's about 3kW short on array size. One MX60 couldn't even handle the job is there were enough array. Any remote temperature sensor on the controller?

Then you admit that some of the batteries have had their plates exposed. The batteries are how old now? The oldest, that is, as it will "draw down" the newer ones to its level.

Do you really wonder why they're going bad? I'm not surprised they are. In fact I'm rather amazed it works at all. The ones in the middle of the strings may be failing first due to differences in heat dissipation.

You know you're not going to get out of this without re-evaluating your loads, battery bank size, and charging power - and then buying new batteries.

Avoid using metal bars for interconnects. I've done it; it works. But it's a pain to install (lack of flexibility) and the exposed metal is subject to corrosion from battery gassing. It also presents a big 'target' for dropped tools hitting some incredibly high current potential.

Sounds like your wires are being subjected to corrosion too, which is somewhat to be expected. Especially if you allow batteries to boil dry. You'll need new wiring, with sealed terminal ends and a good coating of something to keep the mist off them (dielectric grease, No-Rust, Vaseline - anything to seal the moisture away from the metal).

pvoffgrid · February 2013

Re: Odd Occurrence with L-16s

yep, important info missing. 24 L-16's of 375 amh each.

No, it was 2,080 watts of PV with 1 MX-60 without any temperature sensor, that I remember anyway, and yes, in the winter time the generator ran a lot but not in the summer time. And, no, this is not a home designed not installed system but a professionaly designed and installed system in 2001 to the tune of about $32k. Again, this WAS the system. It is now a 4,600 watt system with the MX-60 and also a Outback Flexmax 60 charge controller. there is now 2 remote temperature sensors and yes, this is till a professionaly deisgned & wired system.

Yes, I admit some of the batteries have had their plates exposed and YES, I KNOW what an idiotic thing that was to do.... As I wrote below the batteries are now 54 months old. And, yes, I know the oldest batteries will draw down the newer ones to their level...I look at it as the lowest common denominator. And, yes, I knew adding 2 new batteries to an old string was not the smartest thing to do but after spending thousands to get the new professionals to update and correct the system designed by the original professionals I did not have the money at that time to spend another $5k - $6k on 24 new batteries and I knew the batteries were on their last legs and it wouldbe just a matter of time before they needed to be replaced, and that any extra time I got woddl be icing ont he cake. Things were going fine until we go this cold snap 5 - 6 weeks which we cannot seem to shake for more than 2 - 3 days in a row. It is very unusual for it to be this cold for this long.

No, I am not really wondering why they are going bad and I think this one statement is not helpful, given what I wrote about what I did wrong & understood so I will ignore it. BUT, your comment about why the ones in the middle are failing is HELPFUL. THANK YOU.

The battery bank size, the evaluation of the loads, charging power, etc were all done last summer when the PV system was redesigned and evaluated. And, 24 batteries with 4.6kw with our usage was deemed to be appropirate. When the system was redesigned I actually had the professionals pull all new wire from the original PV array of 2.08kw as they were on the fence as to whether the original professional had used the right size wire or not. I told them to make this system perfect, which is why I ran out of money and could not replace the batteries at that time. So, yes, I do think I can get out of this without a complete reevaluation.

Ok, good thoughts on the exposed metal bars. That is what I was kind of thinking would be the issues with them. A neighbor here had them and it looked interesting but kind of scary. I only really see them now on the systems using the expensive AGM sealed type 2-volt cells.

Ok, new cables are needed and I planned n replacing them when I changed the batteries.

Can there be more explanation on the heat dissipation issue? Do I need to have more air flow to help keep the middle batteries cooler?
I think the cold has really hurt and was hoping to get back to warmer weather but did not make it. Are there any thoughts as to the cold "helping" the batteries go bad faster?

EDIT: And thanks for the welcome! Now, off to go measure the specific gravity & voltage of each battery now that the generator has stopped running after 2.5 hours and I am at 50v 30 minutes later with a 5 amp load. I am not sure what is drawing 5 amps as nothing else is on besides the house phantom loads, this PC & 24" LED monitor that is pulling 20w and 0.31 amps. The jet pump just kicked on & off & it pulls 20.8 amps when running at 240v but this is the last day or so of it as the well guy comes up tomorrow to remove it & put a submersible in the cistern. So, I am hopeful the new submersible is less than the current jet pump. This is not a good time: well work, car issues, now this...it all happens at once normally, doesn't it?

Cariboocoot · February 2013

Re: Odd Occurrence with L-16s

We can't blame the heat difference solely for the problems. It's just one factor which exacerbates the troubles caused by the lack of RTS (for some of the time), insufficient PV (for some of the time), multiple battery strings/connections, differing battery ages, poor maintenance, et cetera. When you have all that going on there's no chance the batteries would 'age' evenly, which is exactly what you got.

Your use of "professionals" for design and upgrading probably didn't help much, as it is practically impossible to upgrade a system anyway. But kudos for trying!

Now it's time to look to the future and try to avoid repeat trouble, right? The best step you can take for that is to try and eliminate the number of batteries used to make up the bank. Fewer batteries = fewer cells to check and fewer connections to go bad. Big advantage in both.

If you can't actually reduce the capacity (370 * 3 = 1110 Amp hours @ 48 Volts) by conservation I would suggest you use 2 Volt cells or forklift batteries (if possible to fit them in; they're bloody heavy). They cost more, but would work better. For example one string of 24 of these: http://www.solar-electric.com/repoba2vo10a.html gives 1000 Amp hours @ 48 Volts. Only 24 cells to check instead of 72, only 23 interconnections instead of 25, and only one string for current to flow through instead of three. Yes, the cost is a pretty big "ouch" at $18,000 or so.

Two 24 Volt 1000 Amp hour forklift batteries: http://www.solar-electric.com/crinba24vo102.html $10,000 or so. Yes: ouch again. Sometimes you can get these used yet still good for less money and of course locally.

You can see why I always suggest re-evaluating the loads. Also the reserve capacity: if you take the bank down 25% per day you've got 25% for the next day and can start the gen on the 3rd day if the sun still isn't shining. Forklift batteries can actually be discharged deeper (up to 80%) so you might get away with a smaller bank there.

Just throwing out some options to consider.

vtmaps · February 2013

Re: Odd Occurrence with L-16s

pvoffgrid wrote: »

Any thoughts as to why the middle batteries are going bad?

Any thoughts as to what would cause that middle battery cable to get so hot it pulled thru the terminal

Read about the perils of parallel batteries: http://forum.solar-electric.com/showthread.php?14674

Your middle batteries are the warmest which makes them draw more current which makes them warmer which makes them draw more current which makes them....

As the batteries get more and more divergent in their electrical characteristics, it finally gets so bad that after you're done charging them, one string will be discharging into another string.

Those hot cables can be dangerous... it sounds like your professional installer did not put a fuse in each of the three battery strings. A fuse would not really help the underlying problem of parallel batteries, but it would be a safer system.

Follow Cariboocoot's advice and get a single string of larger capacity batteries.

--vtMaps

inetdog · February 2013

Re: Odd Occurrence with L-16s

pvoffgrid wrote: »

Any thoughts as to why the middle batteries are going bad?

Any thoughts as to what would cause that middle battery cable to get so hot it pulled thru the terminal
Can I still use that melted terminal battery if I clean up (file the terminal flat again) the terminal and sandwich the cable to the terminal somehow, using larger diameter washers, etc?

Maybe two different problems?

1. A melted cable/battery post is almost always the result of a bad connection. A corroded or uneven surfaced battery post and connector, or a bad crimp from cable to cable end can cause a lot of local heating. You might not notice it at first with all strings working, but if you lose one or more of the other strings, the current would have to go up a lot. The heating, particularly heat cycling with load and charging could cause thermal expansion cycling which would make the problem worse, until something finally melts.

2. If the middle batteries within a single string are getting hotter than the ones on the end, you could be losing charging efficiency on them which would let their SOC drift down with respect to the other cells in that string. Unless you then do an EQ to bring them back up, the low SOC will allow sulfation, reducing their capacity and making the heating worse. Eventually those batteries would fail completely from sulfating, etc. before the rest of the string.
The best way to avoid that is to check SG regularly and do an EQ when necessary. If you can't to that, rotating the battery positions in the string would be an alternative, but that would not be nearly as easy as monitoring and EQing.

pvoffgrid · February 2013

Re: Odd Occurrence with L-16s

Interesting read about the parallel battery banks. And, no, there is no fuse going to each individual bank. I remember seeing one in-line small fuse going to the positive terminal buss but that is all I remember seeing.

I did the specific gravity and noticed I have 4 more batteries, 2 in each of the remaining 2 strings, that have a bad or at least suspect cell: 1.15 vs. 1.25 - 1.3 in the other cells. What is the downside of dropping to one string today for 1 - 2 weeks? Just the lower capacity?

How do you use the clamp-on meter? Put it around each of the negative cables to each string while the generator is charging or while the sun is shining? Around the positive cables? Or both?

All 18 of the houses here have 2 - 3 strings at either 24v or 48v using the L-16 375 ah batteries. I am going to look into the 2v cells and dropping the strings down. Thanks for the info. I will be back shortly to check onthe viability of dropping to one string. Now, off to change the generator oil & oil filter.

And, thank you for the help.

inetdog · February 2013

Re: Odd Occurrence with L-16s

pvoffgrid wrote: »

How do you use the clamp-on meter? Put it around each of the negative cables to each string while the generator is charging or while the sun is shining? Around the positive cables? Or both?

Assuming that you have DC capable clamp-on ammeter, you do two things:
1. Calibrate the zero setting of the meter while it is in roughly the same place and orientation as you will use to make the measurement.
2. Clamp it around any ONE of the cables in that series string. Positive, negative, end of string, middle of string does not matter. They all carry the same current.
Try to make the measurement on each string with the meter in a similar position and make absolutely sure that the clamp is all the way closed.
Check the zero again after making all of the measurements. If the change in the zero current reading is zero or at least small compared to the differences you measure between strings, your numbers should be good.

If you put the clamp around two cables at the same time, with the current flowing in the same direction through the hole, you will read the sum of the two current values.
If you want to measure small currents compared to the meter range, you can, for example, run ten turns of wire through the clamp and divide your readings by ten. (Only practical with small wires. :-) )

westbranch · February 2013

Re: Odd Occurrence with L-16s

pvoffgrid, charging them separately id a good thing , Know that you should have SG's of 1.26 or possibly higher... that is a fully charged battery. you may have to do an EQ cycle if the SG's do not come up....

Please add a descriptive list of your equipment by brand and model so we can know just what we need to reference. thanks.

ps dont forget to record the starting SG, by cell, for reference after charging!!

Cariboocoot · February 2013

Re: Odd Occurrence with L-16s

One string instead of 3 means 1/3 the (theoretical) Amp hour capacity. However, charging parameters have to be adjusted accordingly; you don't want to pump 3X as much current as the one string needs nor would you want the End Amps (if used) to be 3X as high as it ought to be.

DC (specifically; do not use an AC version) clamp-on Ammeter needs to be zeroed (frequently) and then it clamps on (or around) one wire. It will tell you how much current is flowing through that wire. It does not car if it's a positive or negative wire; in the same circuit the current is the same everywhere. Do not think of three parallel battery strings as the same circuit, as they are a divergence of the same circuit (hence the trouble with keeping current even).

One small in-line fuse is probably the output of the charge controller. With multiple battery strings it is best to have post fuses on each as vtMaps said. On top of which there should be a fairly hefty fuse or breaker on the line feeding the inverter from the (+) bus bar.

Any chance you could take some pictures of the set-up? It would be informative to see the layout as well as have specs on everything.

sawmill · February 2013

Re: Odd Occurrence with L-16s

I use L-16 batteries connected by solid copper bars. I changed to the solid copper after going through similar problems with crimpted 4/0 cables. Once the batteries are in place, use a caliper to measure the distance center to center, then drill your hole a little oversize. Copper is available that is already silvered which is good to help prevent corrosion.

I used heat shrink on the bars with a short section of notched rubber hose slipped over terminal ends so the rubber flap covered the terminals. With the crimpted fitting I still had exposed posts that was always a worry. Of course one could use the notched rubber hose on crimpted connection also. The more places that are covered around battery posts the better.

I never could determine a satisfactory way to inspect the crimpted cables before problems appeared.

gww1 · February 2013

Re: Odd Occurrence with L-16s

Sawmill
Where did you get your copper and how did you size; width and thickness?
gww

Blackcherry04 · February 2013

Re: Odd Occurrence with L-16s

I have a box full of Bars that I have removed over the years from Battery banks. They are way more trouble than they are worth. As batteries heat and contract they either work their way lose and pull on the posts until you have electrolyte leaking out. As a battery ages and you start to get positive post protrusion they can pull a post out of a battery and there is no give as the cases start to bulge. If you cube the batteries with them you cannot remove one and there is no air circulation between them to remove heat. I have had to beat way to many off with a hammer to ever fool with them.

Just my $.02

inetdog · February 2013

Re: Odd Occurrence with L-16s

sawmill wrote: »

I never could determine a satisfactory way to inspect the crimpted cables before problems appeared.

The best test is to use a voltmeter between the wire in the cable near the crimp connector and the battery post while either charging or discharging. A high resistance connection will show a much higher voltage than a good one.

gww1 · February 2013

Re: Odd Occurrence with L-16s

Blackcherry04
Thanks for you imput.
gww

Blackcherry04 · February 2013

Re: Odd Occurrence with L-16s

gww1 wrote: »

Blackcherry04
Thanks for you imput.
gww

Your welcome guy. They were in vogue for a few years on the Boats I work on and they are nothing but trouble. I guess everyone had the same problems I did and they stopped using them. Another issue is that if you change Battery Manufacturers they would never fit the same. If you make a set of cables and do a certified crimp on them and use heat shrink, they should last 20 years. One problem with older cables is that a lot of battery manufacturers have gone to 5/16 post bolts in the past few years instead of 3/8's and you have to make sure you use the right size flat washers and get as much contact on the lug as you can on both sides. You have enough problems with batteries without creating one, if you know what I mean.

gww1 · February 2013

Re: Odd Occurrence with L-16s

Blackcherry04
I don't know if I will try to make my own cables or will spend the money to buy them. If I make them what is your opinion of a hammer crimp like sold at naws? I will probly start with sams club six volt for my first set. 3/8" or 5/16" on sams clubs? Off subject, so answer or not, thanks for the previous advice.
gww

PS Before your previous answer I was toying with the ideal of using copper water pipe but didn't know how to rate it. I'm happy you answered.

Blackcherry04 · February 2013

Re: Odd Occurrence with L-16s

gww1 wrote: »

Blackcherry04
I don't know if I will try to make my own cables or will spend the money to buy them. If I make them what is your opinion of a hammer crimp like sold at naws? I will probly start with sams club six volt for my first set. 3/8" or 5/16" on sams clubs? Off subject, so answer or not, thanks for the previous advice.
gww

PS Before your previous answer I was toying with the ideal of using copper water pipe but didn't know how to rate it. I'm happy you answered.

A hammer crimper is fine. If you get them all cut and ready to crimp you could stop by a electrical contractor and smooze them a little and get it done, I have had the line crew from my Electric Company do mine before I owned my own crimpers. Sams Club GC-2's have 5/16" on the posts. I think you have OutBack Inverters they are 8 mm, so a 5/16" lug will work on them. Make sure you use heat shrink on them.

Here is a place that will do a custom sizes for you. Free Shipping.... @ $1.00 per crimp, but that adds up fast on a set.

http://shop.genuinedealz.com/?sck=86177166

gww1 · February 2013

Re: Odd Occurrence with L-16s

Blackcherry04
Thanks for the answers I will check the link and I guess I will quit highjacking this thread for now.
Thanks
gww

H2SO4_guy · February 2013

Re: Odd Occurrence with L-16s

What is the advantage of using shrink tubing instead of electrical tape? Is it that much better?

Cariboocoot · February 2013

Re: Odd Occurrence with L-16s

H2SO4_guy wrote: »

What is the advantage of using shrink tubing instead of electrical tape? Is it that much better?

Yes. It seals tighter and doesn't loosen over time and fall off. Especially if you use the type with glue inside.

Blackcherry04 · February 2013

Re: Odd Occurrence with L-16s

H2SO4_guy wrote: »

What is the advantage of using shrink tubing instead of electrical tape? Is it that much better?

This kind of Heat Shrink has adhesive that melts and makes a seal on the cable and lug that keeps out the fumes and acid out and keeps corrosion off the wire and lug. It'll just make your cables last longer keep a problem from happening. A good tape seal will work, but has a tendency to loosen up over time, there is heat in the cables when charging.

http://shop.genuinedealz.com/Marine%20Electrical%20Supply/Heat%20Shrink%20Tubing/?sck=86177166

waynefromnscanada · February 2013

Re: Odd Occurrence with L-16s

Blackcherry04 wrote: »

This kind of Heat Shrink has adhesive that melts and makes a seal on the cable and lug that keeps out the fumes and acid out and keeps corrosion off the wire and lug. It'll just make your cables last longer keep a problem from happening. A good tape seal will work, but has a tendency to loosen up over time, there is heat in the cables when charging.

Agree, tape is fine for the short term only, but if you want good, long term results, go with the suggestion by Blackcherry.

Odd Occurrence with L-16s

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