US L16HCXC 420amp batteries in 24V bank

[TexSun]

Our 1st bank for off-the-grid solar contained Trojan J250's (20). These lasted from 2001 to summer '09 and then began to fail slowly one by one; some are still good. I thought 8yr life indicated we have learned proper care. But our 2nd bank, US L16HCXC 6v 420amp (16) purchased in summer'09 before US's new RE L16's for solar was announced, is failing rapidly. One cell of one battery in a series set fails, causing overcharging of another battery of same set, discovered quickly due inconsistency of readings on the TriMetric meter. System: Trace 4800 24v inverter, 3.1kW solar array, (2) 60amp charge controllers. We reacted in a panic by replacing 3 of the batteries with the same model and another one has failed.

Time for stop-loss on wrong battery for application? US Battery tech didn't seem to speak "solarese" and we need seasoned advice.

[BB.]

Sorry for the reasons of your first posting on the forum.

Hmmm... Sounds like you treated the first bank "right"--So, did you have any indications of things going wrong with the second bank (possibly even when the first bank was failing--I.e., did the first bank actually fail for cause)? What charge controllers do you currently have? Are you using remote battery temperature sensing?

Charging/discharging voltage? Water usage (higher/lower)? Any problems with over heated cable ends/battery terminals? What are your charging set points, what specific gravity do you measure, how deeply (voltage/specific gravity) do you discharge the battery bank? Does the battery bank get hot (during summer/heavy loading-charging)?

Are the banks wired with "equal" cable lengths for each string (see this web page for battery wiring)?

If you do not have one, I would suggest getting a DC Current Clamp type meter. Use the meter to check the charging and discharging current between all four (?) parallel strings and see that they are properly sharing current. This meter is fairly inexpensive and is "good enough" for debugging a DC battery system.

Anyway--That is where I would start. Hope you get the problem(s) under control. Batteries ain't cheap.

-Bill

[vtmaps]

Like Bill, I have more questions than answers at this point. Let me add one more to his reading list:
http://www.wind-sun.com/ForumVB/showthread.php?14674
--vtMaps

[niel]

the technician shouldn't actually care the charge source was solar as long as the charge source delivered the power properly and it sounds like you do have it right or the previous bank would not have lasted. go over your settings again informing us of the layout and settings you have and then recheck your wiring. if all is as it should be then try talking to them again and if they shrug their shoulders again then ask to talk to somebody higher up who does know the score. if they all claim ignorance then you bought the wrong battery make.

[mike95490]

Your 2nd bank, [ But our 2nd bank, US L16HCXC 6v 420amp ] is it a series bank, or are they series with parallel ??

[TexSun]

Sorry for the reasons of your first posting on the forum.

Hmmm... Sounds like you treated the first bank "right"--So, did you have any indications of things going wrong with the second bank (possibly even when the first bank was failing--I.e., did the first bank actually fail for cause)?

1st bank: Indication of gradual failure was on meter reading of indivual batteries and hydrometer readings plus uneven electrolyte levels (failing cell not "using"). Due to the 5 sets of 6V for the 24V system in the 1st bank, we occasionally moved batteries around within the bank. But these were 72 lb.; the L16s weigh more than I do.

What charge controllers do you currently have? Are you using remote battery temperature sensing?

Original 60amp controller was Trace (before 1st buyout); second, added with addition of more panels, was 60amp Xantrex (before 2nd buyout). Solar panel input to each controller is balanced within 0.2 amps. By sight, the circuit boards of these controllers are identical, but it's very hard to exactly match the settings of two devices with age differences (2001 & 2007).

Charging/discharging voltage? Water usage (higher/lower)? Any problems with over heated cable ends/battery terminals? What are your charging set points, what specific gravity do you measure, how deeply (voltage/specific gravity) do you discharge the battery bank? Does the battery bank get hot (during summer/heavy loading-charging)?

Bulk - 28.2, Float 27.6 US Battery tech said they sh/be 30 and 27. This area had 105 days of 100 or + degrees F. days, drought and blowing dust. Water was rationed and pressure here wasn't sufficient to wash off panels. Normal charge on sunny day is in 90amp range. Can't be specific about discharge as freezer & refrigerator cycle more often in hot weather, fans also used. Year-round is satellite internet, nighttime satellite TV, freezer & refrigerator which shows 9 to 11 amp dischage on TriMetric meter. Voltage falls from 29V to 25.2V under these loads when charge stops (both the J250s & L16s). If it falls to 24.3 before 2am, generator is run. When only load is battery room DC light, a 24.3V reading rises to 24.6V. (Disconnecting the system long enough to get readings at 72 degrees F. would result in food spoilage if it could be done - impossible from April to October.)

Yes, batteries do get hot - this is Texas.

Watering schedule during the first 2-1/4 years was 30 days ~1-1/4 gal. for the 16 6V L16s - schedule changed to 2 weeks after first cell failed. Failing cells overcharging others.

Are the banks wired with "equal" cable lengths for each string (see this web page for battery wiring)?

Cables are from 6-1/2" between those in the series set (short as possible on side-by-side negative-to-positive arrangement) and 27" between paralleled sets (end-to-end of sets). Cables from inverter enter the box from the front at mid-point and are each 7-ft. I do not understand the diagrams on this site unless the voltage application is the same as that of one battery or unless that box represents a series set. If you have access to a Trace 4800 watt inveter manual, our arrangement is that shown Techanical Information section. Our bank is not cross-wired; should I try to cross-wire without blocking access to the cells, cross-wiring cables would have to be long enough to fasten to the back of the battery box. If that would help to balance the charge-discharge, I will try. Please advise.

If you do not have one, I would suggest getting a DC Current Clamp type meter. Use the meter to check the charging and discharging current between all four (?) parallel strings and see that they are properly sharing current. This meter is fairly inexpensive and is "good enough" for debugging a DC battery system.

Link did not work but found others that did. I'd need a good gas mask to move the clamps around while charging and opening and closing the lid.

Anyway--That is where I would start. Hope you get the problem(s) under control. Batteries ain't cheap.

Thank you for your help and suggestions. Spoke to another experienced solar off-the-grider and no one has any long-term experience with the US RE batteries as only on the market about 3 yrs. In that time US has changed the wording on the L16HCXCs on their site which I feel speaks more to the scrubber, sweeper, forklift, etc. applications wherein equipment to used until discharged, then recharged offline.

[vtmaps]

TexSun, heat kills! You got 8 years from your first bank.... I think that's very good considering the heat down there.
Both your first bank (5 strings) and your second bank (4 strings) are what I call 'Massively Parallel'. When you changed from 5 strings to 4 strings you obviously changed your wiring, but you indicate (in your 2nd post) that you don't understand the wiring diagrams at smartguage.com. Getting the wiring right is critical in any parallel system. Can you submit a schematic or a photo of your wiring to this forum for us to evaluate? Read (or reread): http://www.wind-sun.com/ForumVB/showthread.php?14674

You did not answer BB.'s question about whether you have a battery temperature sensor. At high temperatures the charging voltages must be reduced or you will 'cook' your batteries. That is true even with one string of batteries. And even if you do have temperature compensation it is difficult to get all parallel strings charged properly because if one string is just a bit warmer than the others (inevitable) it will draw more current than the other strings which will make it warmer which will make it draw more current which will make it warmer which will make it draw more current, etc.

The current clamp meter will help you figure out whether you have equal current flowing in each string, whether because of wiring problems, different string temperatures, or battery failure. It is best to take the measurements while bulk charging.

Assuming you get the wiring and temp compensation under control, you might want to think of ways to keep the batteries cooler. I'm in Vermont and don't have to deal with that issue, but there have been several discussions on this forum... I recall reading about swamp coolers, battery sheds in earthen berms, a water cooling system (circulate water underground to cool it and then into the battery box, and then back underground).

Hope this helps, and let us know what you find diagnostically with your clamp ammeter.
--vtMaps

[SolaRevolution]

Here is a link to the US Battery charging instructions PDF:
http://www.usbattery.com/usb_images/...ion_2011_2.pdf


Your new battery bank is very different from your old one.

Things to consider:

With 4 parallel, 24v strings of 420ah batteries you have a 20hr rated capacity of 1680ah.
Your old ones were 250ah x 5 strings for a 20hr rated capacity of 1250ah.

Your 3.1kw solar array operating at 80% efficiency of STC would produce <100amps (< 6% C20 rate) of charging current for your new battaries.
This would have been 8% of C20 for your old batteries.

Having 4 parallel strings is a bit of a "performance limiting design factor" so your batteries are probably not getting the full advantage of the charging capacity that you have.

Let me go out on a limb here. My opinion, for what it's worth and from my experience as a service tech for many old systems, is that Trojans are "easier", that is, they seem to be more forgiving of less-than-ideal charging sources than some other "high quality" batteries. I was just at a job which had some 9 year old Trojan T-105 "golf cart" batteries which had never been equalized and had been working "satisfactorily" (client's claim) until the recent rains. Usually if you get more than 5 years out of "golf cart" batteries you are doing quite well.

Alex

[niel]

furthering vtmaps mentioning of how heat kills that this is a high possibility of what is going on here as it seems to fit. initially you were charging at what most perceived to be too low of a bulk charge voltage. this may have saved the first batteries if you weren't using a bts as the lower voltage prevented damage to the strings. i do agree the charge voltage should normally be higher, but that is generally at a battery temp of 77 degrees f and when ambient temps are higher the batteries can't dissipate heat any lower than that of ambient making the battery temps most likely far higher than ambient. i probably overlooked it in your answer, but if there i'll bet you had a much higher need of watering as i believe they may have been cooked due to no temp compensation or improper compensation when you upped the voltage. also exposing the plates to the air will lead the batteries downhill too so proper watering is essential.

i'm not saying this is a certainty or only cause for failure as we aren't right there to be sure you didn't overlook something else, but i'm leaning the batteries did cook because the low voltage you were feeding them prior did not cause battery failure due to undercharging as evidenced by them lasting this long.

[BB.]

Everyone else has pretty much replied what I would have said... Your battery voltage charging set point seems to be a bit on the low side but you are using a significant amount of water which would indicate higher voltages.

The float voltage is a bit high, could lead to higher water usage--But if you are cycling the batteries daily, it should not be a big issue.

Have you measured the actual charging/float voltages with an accurate volt meter--Especially when the bank is hot?

How often/how many minutes/hours do you equalize the bank?

I would not "cross wire" a battery bank. If everything is working correctly, cross wiring will not help anything. If there is a problem (open/shorted cell, failing cell), cross wiring makes it more difficult to find and diagnose a bad cell/battery.

Do you have good ventilation for your battery bank? Hydrogen gas and electrolyte "spray" can cause problems. Are the cells kept "too full"? Is electrolyte spilling out on the top of the battery bank?

It would be nice to have more solar panels for your larger bank.

The fact that your first bank lasted pretty well, it sounds like your basic system is OK.

-Bill