Battery Measuring Question

Discussion about the OutBack Energy Cell Batteries

Battery Measuring Question

Postby Wanbli on Fri Apr 13, 2018 8:51 am

I have an Enersys battery bank (same mfg as the Outback Batteries, see attached picture). The battery bank was mfg in 2006, so it's 12 years old. It has been used on my solar system, primarily as a back-up type system until last year when I began using it to supplement my home. The problem I'm experiencing is that it doesn't seem to last anywhere near as long as it used to (actually about 50% less). I have completely disconnected the battery bank from the system and tested each cell to see what the voltage reading are to see if that would lead me to a bad battery or not. All cells read 2.1vdc except for battery #11, which reads 2.0vdc. I had this happen last year, but that battery (01) didn't read any voltage 0, so I replaced it and the battery bank worked fine until now.
So, my question is; does a .1 volt drop indicate a bad battery? Any help would be deeply appreciated.
IMG_20180413_113518.jpg
Battery Bank 1100Ahr/24vdc
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Wanbli
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Posts: 13
Joined: Mon Oct 14, 2013 6:35 am
My RE system: System Name:OutBack Power Technologies
System Type:Backup
System Nominal Voltage:24 VDC
PV Array Wattage:2KW
Battery Ah Capacity:1020 Ah
Flexware 500
2-VFX3524
1-FM80
FNDC
Generator kW Rating:12.0 kW
Max Inverter Output kW:7.2 kW
Max Charger Output kW:2.8 kW

Re: Battery Measuring Question

Postby raysun on Fri Apr 13, 2018 10:49 am

Measuring battery capacity is at best a complex and tricky affair. Without some very sophisticated equipment, the best that can be done is a rough estimate.

Voltage measurement alone is not a good indicator, there are too many variables, internal and external, that affect cell voltage. Of the simple methods available, the most common is a load test in which a fully charged battery is subject to a moderate load and discharge is timed to a specific voltage end point. Amp Hour capacity can be derived from the discharge data, compensated for temperature. This type of test is OK for "ballpark" capacity estimating, but can in itself be somewhat inaccurate. It's better than nothing however.

The type of cells in your battery may be designed primarily for daily cycling use. If left on standby for appreciable lengths of time, most deep cycle batteries will degrade chemically. 12 years of service life is a good long run for sealed batteries.

Pure speculation on my part here, but the newer cell measuring a lower voltage at full charge than the other cells may well be due to imbalance during the charging cycle. As cells age, they accept less charge, and so are fully charged at a lower capacity than a new cell. It may be the other cells are indicating full (by the voltage rise) before the new cell reaches maximum charge - leaving that cell in an undercharged state.
raysun
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Posts: 192
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower One: FX3048T, MX80, MATE3s, FlexNetDC
Outback 200NC batteries (8 @ 48v)
Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 4Sx3P)

Re: Battery Measuring Question

Postby Wanbli on Fri Apr 13, 2018 11:08 am

Thanks for the quick response.

The New Battery is Battery #1 & it measures 2.1vdc like all the others. The battery measuring 2.0vdc is actually battery #11, an original battery. Just to be sure we're on the same page.

Today, at 12:17pm HBX dropped the grid (Battery voltage was >27.8) and switched to battery running a load that varied between .9 - 2kw. Then exactly an hour later at 1:17pm HBX re-engaged the grid because the battery voltage had dropped below the 22.7vdc threshold to 22.1vdc. All the while I was also producing via the Charge Controller between 650 - 800watts from my small solar array. This battery bank used to run for most of the day at this load level, so I definitely have an issue. I'm just trying to figure out what that issue might be and then I have to figure out if it's worth whatever cost is associated to get it back to where it was.

Again, any help would be appreciated.
User avatar
Wanbli
Forum Member
 
Posts: 13
Joined: Mon Oct 14, 2013 6:35 am
My RE system: System Name:OutBack Power Technologies
System Type:Backup
System Nominal Voltage:24 VDC
PV Array Wattage:2KW
Battery Ah Capacity:1020 Ah
Flexware 500
2-VFX3524
1-FM80
FNDC
Generator kW Rating:12.0 kW
Max Inverter Output kW:7.2 kW
Max Charger Output kW:2.8 kW

Re: Battery Measuring Question

Postby raysun on Fri Apr 13, 2018 11:39 am

Without other data, it's difficult to read too much into individual cell voltage that is near nominal for the battery chemistry. The open circuit voltage of a fully charged lead acid battery that is allowed to rest for at least 24 hours at 75°F should be 2.1. Measuring in any other conditions can lead to spurious results.

Also, terminal voltage is not necessarily a good indicator of battery health. A highly sulphated battery can reach a terminal voltage of 2.1, but won't hold it long during discharge.

If you want to confirm what you suspect, a load test will be the best route. You might want to contact the manufacturer regarding the setup for such a test.
raysun
Forum Guru
 
Posts: 192
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower One: FX3048T, MX80, MATE3s, FlexNetDC
Outback 200NC batteries (8 @ 48v)
Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 4Sx3P)

Re: Battery Measuring Question

Postby Wanbli on Fri Apr 13, 2018 12:47 pm

Thanks
User avatar
Wanbli
Forum Member
 
Posts: 13
Joined: Mon Oct 14, 2013 6:35 am
My RE system: System Name:OutBack Power Technologies
System Type:Backup
System Nominal Voltage:24 VDC
PV Array Wattage:2KW
Battery Ah Capacity:1020 Ah
Flexware 500
2-VFX3524
1-FM80
FNDC
Generator kW Rating:12.0 kW
Max Inverter Output kW:7.2 kW
Max Charger Output kW:2.8 kW


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