low battery cutout voltage

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Megunticook
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Posts: 242
Joined: Fri Sep 29, 2017 4:08 am
My RE system: 6.4 kW solar array (21 QCell 305 panels in strings of 3)
GS8048A FLEXpower Radian (Radian 8048A, 2 FlexMax 80 cc's, Mate 3s, FlexNet DC, Hub)
8x6v Rolls-Surette 550 FLA batteries, 428AH
Location: Maine
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low battery cutout voltage

Post by Megunticook » Mon Dec 23, 2019 5:17 am

Last night I intentionally dropped my grid connection in order to "exercise" the batteries with a discharge/recharge cycle. At one point I monitored the system with Optics while the well pump was running and the inverter was pulling 60 amps out of the battery bank, which was 95% SoC. Then suddenly the system went back to pulling from the grid. Puzzled, I opened the breaker in my main service panel to prevent this from happening. This morning, again while the well pump was running, the inverter shut down. I didn't see any unusual events in Optics, but when I checked the Mate3s I saw that a low-voltage event had been triggered. The battery bank is at 87% SoC this morning.

Does the initial surge from the well pump cause the battery bank voltage to drop below my low-voltage cutout setting, thereby shutting down the inverter?

I have this set to 46.8v with the delay at 6 seconds. Should I increase the delay? Lower the voltage? Haven't run into this before.

A few more details:
  • batteries are currently at -2°C
    batteries are 2 years old and in good condition
    all connections in GSLC recently checked for tightness
    battery terminals and cables all clean and tight
https://sunnypower.org

raysun
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My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
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Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: low battery cutout voltage

Post by raysun » Mon Dec 23, 2019 6:50 am

LBCO of 46.8 would seem reasonable as it correlates to 50% SOC when the battery is at rest. With the battery under load, voltage and SOC take on a more complex relationship. The 60A draw is not out of line for the battery, but it will cause a significant voltage drop. I'd think ambient temperature would also factor in.

OpticsRE is a great tool, but its "not-really-real-time" nature misses a lot of transient events. When trying to meter battery voltage vis-a-vis load, I like using the web server built into the mate. The updates are much more "real-time". Watching the battery voltage during pump startup may give some clues as to the drop under load.

IMO, the LBCO is too high, especially with high demand loads like a well pump. I don't recall seeing LBCO delay setting, I thought it was fixed at 5 minutes, but then again, my inverter is an older FX model.

I think I'd set LBCO to 44.5 with a setup like yours that would unlikely see the battery in a depleted state. The extended headroom for voltage drop under load should help avoid spontaneous shutdowns.

User avatar
Megunticook
Forum Guru
Posts: 242
Joined: Fri Sep 29, 2017 4:08 am
My RE system: 6.4 kW solar array (21 QCell 305 panels in strings of 3)
GS8048A FLEXpower Radian (Radian 8048A, 2 FlexMax 80 cc's, Mate 3s, FlexNet DC, Hub)
8x6v Rolls-Surette 550 FLA batteries, 428AH
Location: Maine
Contact:

Re: low battery cutout voltage

Post by Megunticook » Mon Dec 23, 2019 6:57 am

Thanks for the reply. Dropping the LVCO would probably solve this. But I wonder if that "delay" setting would also solve it and still retain the LVCO protection if the SoC happened to drop to 50% or lower.

Good point on the real-time data--I should've been observing the Mate datafeed directly in my browser instead of getting the "every 30 seconds" snapshots from Optics.

Maybe I'll try raising the delay setting and watching again when the well pump kicks on.
https://sunnypower.org

raysun
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Posts: 2275
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
Outback 200NC batteries (8 @ 48v)
Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: low battery cutout voltage

Post by raysun » Mon Dec 23, 2019 7:03 am

Where is the LBCO delay set?

User avatar
Megunticook
Forum Guru
Posts: 242
Joined: Fri Sep 29, 2017 4:08 am
My RE system: 6.4 kW solar array (21 QCell 305 panels in strings of 3)
GS8048A FLEXpower Radian (Radian 8048A, 2 FlexMax 80 cc's, Mate 3s, FlexNet DC, Hub)
8x6v Rolls-Surette 550 FLA batteries, 428AH
Location: Maine
Contact:

Re: low battery cutout voltage

Post by Megunticook » Mon Dec 23, 2019 7:18 am

It's in the Mate3s.
https://sunnypower.org

raysun
Forum Emperor
Posts: 2275
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
Outback 200NC batteries (8 @ 48v)
Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: low battery cutout voltage

Post by raysun » Mon Dec 23, 2019 7:23 am

Hmmm.... Under battery protection I see LB Cut-out Voltage and LB Cut-in voltage, but no LBCO delay. Perhaps because my inverter has a built-in 5 minute delay.

User avatar
Megunticook
Forum Guru
Posts: 242
Joined: Fri Sep 29, 2017 4:08 am
My RE system: 6.4 kW solar array (21 QCell 305 panels in strings of 3)
GS8048A FLEXpower Radian (Radian 8048A, 2 FlexMax 80 cc's, Mate 3s, FlexNet DC, Hub)
8x6v Rolls-Surette 550 FLA batteries, 428AH
Location: Maine
Contact:

Re: low battery cutout voltage

Post by Megunticook » Mon Dec 23, 2019 6:26 pm

It's actually the inverter settings where I have "Low Battery Cutout Voltage" and "Low Battery Cutout Delay"--I'm seeing that when accessing the GS8048A settings in Optics, but I could swear when I checked directly on the mate it just had the voltage setting, no delay. And my MATE manual shows just the voltage setting also, plus indicates the delay is permanently set at 5 minutes.

A little confused a this point. Another odd thing is when I checked the events in Optics I didn't see anything about a low-voltage cutout but when I checked the events directly in MATE3s I saw the LBCV events. Each entry showed two voltage numbers, the upper was 54 and the lower was 48.6. Not sure how to interpret this...intuitively I'd guess that lower figure must indicate how low the voltage got, but that figure isn't low enough to trip the event.

Probably need to actually run the well pump on the inverter and watch in real-time to see how low the voltage gets.
https://sunnypower.org

User avatar
Megunticook
Forum Guru
Posts: 242
Joined: Fri Sep 29, 2017 4:08 am
My RE system: 6.4 kW solar array (21 QCell 305 panels in strings of 3)
GS8048A FLEXpower Radian (Radian 8048A, 2 FlexMax 80 cc's, Mate 3s, FlexNet DC, Hub)
8x6v Rolls-Surette 550 FLA batteries, 428AH
Location: Maine
Contact:

Re: low battery cutout voltage

Post by Megunticook » Tue Dec 24, 2019 7:28 am

After looking carefully at the Radian manual, I can confirm has a non-adjustable 5-minute delay on the low battery cutout voltage setting.

Also says that if the DC voltage drops below a certain point, the quality of the AC output can be poor. Anybody know what that point would be? sounds like I need to lower the cutoff voltage but not so far as to compromise the quality of the AC output.

Also--I noticed the inverter output was 2.8kW when the well pump was running--well below 50% of the inverter's capacity. The battery bank, while modestly sized at 428 amp-hours, is relatively new and in good health. Why would the DC voltage be dropping that much? Is a 60 amp draw from a 428 amp-hour bank just going to do that even with healthy batteries?
https://sunnypower.org

raysun
Forum Emperor
Posts: 2275
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
Outback 200NC batteries (8 @ 48v)
Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: low battery cutout voltage

Post by raysun » Tue Dec 24, 2019 9:49 am

I've seen 42V published as the point the inverters start losing waveform quality.

According to Rolls 60A discharge is the C/5 rate for the S-550 and represents 300AH capacity. 428AH being the C/20 discharge rate.

There is a slightly hard-to-interpret graph in the publication below that shows voltage vs DOD for various discharge rates. By my estimation, the voltage drop difference between C/20 and C/5 could be as much as 3V.
Screenshot_20191224-075025_Adobe Acrobat.jpg
I'd think 46V would be a good LBCO point to start. I took mine to 45.6 to avoid nuisance cutoff around 45% DOD under typical load peaks.

User avatar
Megunticook
Forum Guru
Posts: 242
Joined: Fri Sep 29, 2017 4:08 am
My RE system: 6.4 kW solar array (21 QCell 305 panels in strings of 3)
GS8048A FLEXpower Radian (Radian 8048A, 2 FlexMax 80 cc's, Mate 3s, FlexNet DC, Hub)
8x6v Rolls-Surette 550 FLA batteries, 428AH
Location: Maine
Contact:

Re: low battery cutout voltage

Post by Megunticook » Tue Dec 24, 2019 10:30 am

Thanks--I'll have a closer look at that chart.

I reviewed the Rolls manual since my last post and found this:
To prolong battery cycle life, Rolls recommends setting the Low Voltage
Disconnect (LVD) between 1.85 volts per cell (VPC) to 1.95 volts per cell (VPC).
This may be adjusted up or down, depending how often you wish to run the
charging source (generator or alternative power) when the voltage of the
battery bank reaches the programmed set point.
I'm going to drop mine from 46.8 to 45.6, which is the midpoint of that range, and see if that solves it.
https://sunnypower.org

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