Battery-Inverter Dilemma

[Eric Hardee]

Hi, I am new to this forum but not new to off the grid energy. I recently changed inverters and battery configuration and am puzzled by what seems to be low performance with the new setup. I was running a 12volt 2800W Heart Interface inverter
for more than 10 years powered by 10-L16 Trojan batteries in series/parallel. That arrangement had a battery capacity of about 1600 AH. When the bank was new we typically cycled down to minus 300AH or more but typically tried to stay well above 50% of charge (by voltage). All of our charging was originally by generator but we have integrated in a small PV array more recently, although that should be unrelated to the problem that I am experiencing. I am now running an Outback VFX 3524 inverter with a battery bank of 8-L16 (L16H-AC) 2-strings of 24 volt. The AH capacity of this configuration should be about 840 AH. I use an E-meter (brand) monitor for system info (like I did before) and am typically getting less than a 100amp hour discharge before my bank voltage drops below 50%. These batteries were new within the last 4 months. This seems really weak to me, I was expecting to cycle down to at least 25% of the rated AH capacity say 200AH consumed before I would see the bank voltage down to 50% of charge. Could someone please give me some ideas/observations about what may be going on with this system. Please please please.

[Sunking]

Hi, I am new to this forum but not new to off the grid energy. I recently changed inverters and battery configuration and am puzzled by what seems to be low performance with the new setup. I was running a 12volt 2800W Heart Interface inverter
for more than 10 years powered by 10-L16 Trojan batteries in series/parallel. That arrangement had a battery capacity of about 1600 AH. When the bank was new we typically cycled down to minus 300AH or more but typically tried to stay well above 50% of charge (by voltage). All of our charging was originally by generator but we have integrated in a small PV array more recently, although that should be unrelated to the problem that I am experiencing. I am now running an Outback VFX 3524 inverter with a battery bank of 8-L16 (L16H-AC) 2-strings of 24 volt. The AH capacity of this configuration should be about 840 AH. I use an E-meter (brand) monitor for system info (like I did before) and am typically getting less than a 100amp hour discharge before my bank voltage drops below 50%. These batteries were new within the last 4 months. This seems really weak to me, I was expecting to cycle down to at least 25% of the rated AH capacity say 200AH consumed before I would see the bank voltage down to 50% of charge. Could someone please give me some ideas/observations about what may be going on with this system. Please please please.

L16 is non descriptive and only indicates the battery case size. So what did you use before and what voltage?

The biggest clue you have given and most relevant is you are now using solar rather than a generator. Assuming you are using a mppt controller minimum panel requirement for a 24 volt 840 AH battery string is 2000 watts with an 80 amp MPPT controller. However that no way means that is enough panel wattage to replace what is being used. So I can only guess something is not sized correctly. You need to determine your daily watt hour usage first before you or anyon eelse can pin point the problem. Most likely something is way off you never noticed with a generator before. For now get the generator back on to get the batteries back up.

Only thing I can calculate right now based on battery size they are capable of giving you up to 4 Kwh per day, but only if you can generate 6 Kwh per day. That will take depending on where you live 2000 to 4000 watt panel system. Based on your location solar may not be capable in the shorter fall, winter and early spring months. WA i snot good unless you live in the eastern half of the state.

[Eric Hardee]

Clarification, we are still using the generator as our primary charging component.

L16 is non descriptive and only indicates the battery case size. So what did you use before and what voltage?


The biggest clue you have given and most relevant is you are now using solar rather than a generator. Assuming you are using a mppt controller minimum panel requirement for a 24 volt 840 AH battery string is 2000 watts with an 80 amp MPPT controller. However that no way means that is enough panel wattage to replace what is being used. So I can only guess something is not sized correctly. You need to determine your daily watt hour usage first before you or anyon eelse can pin point the problem. Most likely something is way off you never noticed with a generator before. For now get the generator back on to get the batteries back up.

Only thing I can calculate right now based on battery size they are capable of giving you up to 4 Kwh per day, but only if you can generate 6 Kwh per day. That will take depending on where you live 2000 to 4000 watt panel system. Based on your location solar may not be capable in the shorter fall, winter and early spring months. WA i snot good unless you live in the eastern half of the state.

Our small solar array is still only an adjunct for our sunny season(now expired). The solar array was also in use with our
previous inverter and battery configuration. Those were 10- 6volt L-16P-AC batteries. I upgraded our current batteries slightly with a slightly higher amp hour rated battery, L-16H-AC. I am still using 6volt batteries but now configured in 2 strings for 24 volt. I am still reworking numbers on what our actual daily use is but I can say that our typical load at 24volt is 15-20 DC amps, we typically consume about 160amp hours (at 24volt) over a 12 hour period

[Sunking]

we typically consume about 160amp hours (at 24volt) over a 12 hour period

OK your batteries are sized correctly, so they are not an issue. Based on what you have leaked out sounds like you solar panel wattage is grossly undersized coupled with a poor location.

You are using roughly 4 Kwh per day. That means you must generate 6 Kwh at the panels to replace that 4 Kwh used. With a off-grid solar system you must design for worse case, and for you that is November, December, and January. Mainly December. I said earlier your location is poor, I lied, it is horrible.

November Sun Hours = 1.41
December Sun Hours = 1.02
January Sun Hours = 1.26 Sun Hours

Anytime you go under 3 Sun Hours makes it almost impossible to use solar which I will get to in a minute. You do not get above 3 Sun Hours until mid March, and go under 3 late September. Here is why it is important. Panel Wattage = [Daily Watt Hours x 1.5] / Sun Hours. Plug your numbers in for worse case December. [4000 watt hours x 1.5] / 1.02 Sun Hours = 6000 watts. OK if you wee to run 6000 watts into a 24 volt battery generates 240 amps of charge current. That would require 3 very expensive MPP 80 amp charge controllers with 2000 watts of panels on each charge controller. If you were to pump 240 amps into a 840 AH battery would cook them.

Here is where 3 Sun Hour minimum comes to the picture. [4000 wh x 1.5] / 3 sh = 2000 watts with a single 80 amp MPPT controller. That will generate 80 amps of charge current which is perfect for a 840 AH battery. Only way you can make this work with solar is to use 2000 watts of panels which will work from Mid March to the last week of September. After that you have to go on the generator to make up for the shortages for the next 6
months.

Food for thought. If this system were in Tuscon AZ with a December low of 5 Sun Hours only requires 1250 watts and works year round. Location is critical to make it work.Sorry I know that is not what you want to hear, but the numbers do not lie.

[inetdog]

To take advantage of that 1 solar hour, I also think that it would be essential to use AGM batteries to be able to take the highest current possible at the peak output of the panels. Unless the battery bank is very much oversized in terms of the power actually used, that is.

[Sunking]

I think he already has the batteries? With that said he would be better off operating at 48 volt battery and turn those two parallel 24 volt strings into a single 48 volt battery. If he used a Midnight Solar Classic 150 he could go up to 5200 watts, but does not solve the high C charge rate. His location has him snookered behind the 8-Ball.

[SunEagle]

Ok so getting back to the OP's issue and forget about using his PV system to charge the batteries (which is an after thought and not the main charging source),

The OP started out with a; 12volt 1600Ah battery system (10 x 6v 320Ah battery in a 2 x 5 series/parallel connection) or about 19.2kWh system using a Heart Interface 2800watt 12volt inverter, used about 300Ah + a day and got good number of cycles and years out of the batteries.

He now has a 24volt 840Ah battery system (8 x 6v 420Ah battery in a 4 x 2 series/parallel connection) or about 20.1kWh system using an Outback VFX 3524 inverter rated 3500Watts, using about 160Ah a day and is seeing battery degradation.

Both sets of batteries where charged using the generator.

So his battery system is the relatively the same size and his daily Ah use is about the same (300 to 320Ah) but the 24volt system is not lasting.

Could there be an efficiency issue between the old Heart inverter and the newer Outback which is draining his batteries faster? Or maybe a wiring issue with the 24volt system which is not allowing his 8 batteries to get equal charge.

[Sunking]

Could there be an efficiency issue between the old Heart inverter and the newer Outback which is draining his batteries faster? Or maybe a wiring issue with the 24volt system which is not allowing his 8 batteries to get equal charge.

Perhaps I am missing something. My understanding he was using generator on the old batteries and has switched to solar on the new batteries?????.

[SunEagle]

Perhaps I am missing something. My understanding he was using generator on the old batteries and has switched to solar on the new batteries?????.

No. He is using the generator also on the new batteries. The small solar pv system is an add on during the summer to get a few more charging amps which was also used on the old batteries system.

He would have a problem using pv panels for all of his charging as you have explained but I don't believe that is his issue.

My understanding of his question is why his old 12v 1600Ah system lasted so long and his new 24V 840Ah system seems to be having an early death. If he is using the same generator to charge the batteries and is using roughly the same amount of Ah daily then I think he has either a wiring issue or inverter issue.

[Sunking]

My understanding of his question is why his old 12v 1600Ah system lasted so long and his new 24V 840Ah system seems to be having an early death. If he is using the same generator to charge the batteries and is using roughly the same amount of Ah daily then I think he has either a wiring issue or inverter issue.

If that is the case, then what kind of charger did he get for the 24 volt system? His 12 volt one would not work. I am still missing a relevant peice of info.

[SunEagle]

If that is the case, then what kind of charger did he get for the 24 volt system? His 12 volt one would not work. I am still missing a relevant peice of info.

I agree we are working with only part of the puzzle pieces.

[Eric Hardee]

Further

If that is the case, then what kind of charger did he get for the 24 volt system? His 12 volt one would not work. I am still missing a relevant peice of info.

Thanks for continuing the thread, I was offline yesterday. Sun Eagle got the question correct. There seems to be something different about the operation of the 24 volt inverter which is an Outback VFX 3524. The problem is that I am not getting the depth of discharge that I was expecting before the voltage drops below a 50% level. My amphour rating for the 2 strings of 6volt batteries is about 850AH, I am not even getting to 100AH discharge before I see an unacceptable drop in voltage. Our
useage is modest, typically a discharge rate of 15-25Amps at 24V DC. The charger in the outback typically ramps up to about 72DC amps at 24volt and the bulk charge rate is about 28.5 volts. The inverter/charger is running on factory defaults
and I just ordered a Mate so that I will be able to custom program the Inverter. That could be part of the problem but I don't think it is. For some reason that I don't understand the batteries are not delivering the reserve that they should have and they are less than 5 months old.

By the way, yes we are in a brutally difficult are for solar but my ace in the hole is a micro-hydro system that I intend to put in within the next 2 years.

Any further ideas about my battery problem would be very appreciated

[Sunking]

By chance are your batteries exposed to the elements most notable temperature? Colder temps means less capacity. Don't use voltage as SOC, it is meaningless. Only way you can truly measure SOC is with a thermometer and hydrometer.

[Eric Hardee]

Temperature

By chance are your batteries exposed to the elements most notable temperature? Colder temps means less capacity. Don't use voltage as SOC, it is meaningless. Only way you can truly measure SOC is with a thermometer and hydrometer.

Temperature is not a big factor since our battery bank is in our upper attic, heated from the house by convection from
an air intake from the house. This time of year temperature in the box is about 60 degrees.

[Sunking]

Get yourself a good temperature compensated battery hydrometer and see what is really going on. Volt meter is not really telling you much of anything when it comes to battery health other than voltage balance between cells. Only the specific gravity will tell you where the SOC is at. Best $15 investment you can make. Sounds to me like undercharged battery and you just don't know it yet. Find out before it is too late, you might be chasing a ghost.