Is the "full-conditions-met" battery voltage temperature compensated?

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jnh
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Location: St. Augustine, FL, US

Is the "full-conditions-met" battery voltage temperature compensated?

Post by jnh »

On a 24V grid-tied system with 415Ah of AGMs, I've had my FNDC's full-conditions set as

Code: Select all

ADV/DC/CHARGE -
  return amps       8.0
  battery voltage  28.6V
  params met time   1 minutes
  charge factor    96%
While charge sources were targeting 29.2V Absorb. The FNDC manual recommends setting its target voltage at least 0.2V below charging voltage at 12V or 24V, and I was 0.6V below.

This worked well for a long time, but recently the FNDC has been refusing to declare Full Conditions Met, even while reporting 29.0V battery voltage, battery charge current well below 8.0A, and 100% or 99% SOC. I can't remember if I changed something that might have triggered the change, but don't believe so.

To avoid hours of lost PV production, I had to stop using the advanced grid-tie control feature, or else remember to manually set the FX from NoSell to GridTie each morning. Only following an extended grid outage two weeks ago, which allowed batteries to rise to Absorb for an hour or two, did it finally declare them Full.

I tried rebooting the FNDC by unplugging its Hub cable for 10 seconds, to no effect. Didn't try RESET or CLR on Mate page 3.

Today, just on a hunch I lowered ADV/DC/CHARGE->battery_voltage to 28.4V, and it went to Full Conditions Met in less than a minute!

So, is that voltage setting treated as an absolute value, or is it adjusted up and down based on the current BTS temperature? Or, can anyone think of another explanation for this strange behavior? Voltage readings from the various components (FX, CC's, FNDC) are always within 0.1V of one another, so it isn't a calibration issue.
fcwlp
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I install and maintain grid-tied and off-grid systems in my area and consult on solar system design/operation.
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Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by fcwlp »

Being in FL, I expect your temps are lower than they were this summer, so the compensated voltages should have be higher.

I don't recall any issues this past summer when I had several battery banks at customers running at ~95F. I know that the off-grid customers all hit 100% after a full charge cycle.

Your charge factor at 96% is on the high side.
Mike Curran
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My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters, normally direct grid tied, manual switch during winter or grid outage

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by Mike Curran »

So, is that voltage setting treated as an absolute value, or is it adjusted up and down based on the current BTS temperature? 
Good question. When I look at the battery voltage reported by the FNDC in Optics' Device Map, it displays the actual voltage, not the temperature compensated voltage. So I would tend to think that the charge parameters met voltage is the actual voltage, but that doesn't seem like the way it should be, since absorb voltage setpoints are looking for the T-C voltage.

When you say "worked well for a long time", does that include the full range of battery temps, summer and winter?

My battery boxes are kept at a constant temperature so I haven't seen the behavior you describe. Maybe someone else can offer better insight. In the meantime maybe your best interim solution is to keep the lower battery charged voltage setpoint. It's only 0.2 volts lower than your original setting so doesn't seem like it could hurt.
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
jnh
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My RE system: GVFX-3524, FM-80+FM-60, ~4.9kW PV in mixed panels on movable platforms, 415 Ah AGMs @ 24V, 80Ah @ 12V, Hub4, Mate, FNDC, Brultech GEM 32-ch AC datalogger, Midnite E-Panel, homebrew DC-DC crossfeed to 12V system, Honda EU-1000i, Iota DLS-27-25
Location: St. Augustine, FL, US

Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by jnh »

Mike Curran wrote: Wed Dec 09, 2020 7:13 am When you say "worked well for a long time", does that include the full range of battery temps, summer and winter?
Yes, it had been behaving itself for well over a year under the old settings. The only changes I'd made between last winter and now have involved the FNDC's AUX relay setpoints, which makes me wonder if there's some unintended interaction between those and the charged parameters, perhaps due to a software bug. Very odd to have this just start happening suddenly. I think it was September or October that I first noticed it never showing Full.
Mike Curran wrote: Wed Dec 09, 2020 7:13 am My battery boxes are kept at a constant temperature so I haven't seen the behavior you describe. Maybe someone else can offer better insight. In the meantime maybe your best interim solution is to keep the lower battery charged voltage setpoint. It's only 0.2 volts lower than your original setting so doesn't seem like it could hurt.
That's what I've settled on doing. This being a grid-tied system, the batteries are rarely cycled very much, and any small shortfall in Absorb time caused by the lower threshold should normally be made up within just a day or two.

My battery box is in an attached, uninsulated garage, but with a thin insulation layer affixed to the walls of the box itself (none on top or bottom). So, batteries are buffered against the outside temperature. With a 35F low this morning outside, it was only 52F in garage, with a 59F battery temp reported by BTS, which later dropped to 57F (one Celsius degree, maybe random jitter) before starting to rise again.
jnh
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Posts: 411
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My RE system: GVFX-3524, FM-80+FM-60, ~4.9kW PV in mixed panels on movable platforms, 415 Ah AGMs @ 24V, 80Ah @ 12V, Hub4, Mate, FNDC, Brultech GEM 32-ch AC datalogger, Midnite E-Panel, homebrew DC-DC crossfeed to 12V system, Honda EU-1000i, Iota DLS-27-25
Location: St. Augustine, FL, US

Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by jnh »

fcwlp wrote: Fri Dec 04, 2020 12:41 pm Your charge factor at 96% is on the high side.
These are relatively new AGMs, which have slightly higher Columbic efficiency than flooded, I think due to the higher plate surface area and lower internal resistance (pricey as they are, it's nice to see there's some small performance advantage). At the FNDC's factory default setting (94%?) I was showing some accumulated negative amp-hours even when batteries were showing full based on low absorb or float current. The numbers seem to balance out better at 96%.
jnh
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Posts: 411
Joined: Fri Jun 01, 2007 11:56 am
My RE system: GVFX-3524, FM-80+FM-60, ~4.9kW PV in mixed panels on movable platforms, 415 Ah AGMs @ 24V, 80Ah @ 12V, Hub4, Mate, FNDC, Brultech GEM 32-ch AC datalogger, Midnite E-Panel, homebrew DC-DC crossfeed to 12V system, Honda EU-1000i, Iota DLS-27-25
Location: St. Augustine, FL, US

Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by jnh »

This happened again today, resulting in loss of nearly a full day's production, since I didn't check on the system until late afternoon.

With ADV/DC/Charge set to 28.4V for 1 minute, return amps = 8.0, the FNDC never declared full-conditions-met despite batteries remaining at 29.0V for 30 minutes (I'd lowered charge controllers' Absorb time to a half-hour after the last incident, to reduce risk of overcharging - remember this is a gridtie system that rarely sees significant cycling). It was only during the last 3-4 minutes of Absorption that charging current fell below 8A, but that should have been enough time to meet the FNDC's 1-minute criterion. Instead, the controllers transitioned from Absorb to Float, and spent the rest of the day loafing along at a temperature-compensated 27.8V, pushing ~2A into batteries and another 2A to small DC loads. With FNDC Full-conditions somehow still unmet, the inverter never went into Sell mode.

The only possible trigger condition I can think of is that it was a particularly cold day for this corner of FL, following our first actual freeze of the season. With outside temps in the 30s to low 40s today, the partially-insulated battery box in our garage got down to 55F, where usually it never drops below 60. I still suspect temperature compensation is somehow playing a role.

Well, the batteries got as close to an EQ today as AGM's should ever need, so I'm going to just disable Advanced Grid-Tie Control again for the time being.
Mike Curran
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Posts: 2030
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters, normally direct grid tied, manual switch during winter or grid outage

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by Mike Curran »

Mine acted this way recently when I enabled auto charge termination control in the Mate3s's global charge menu. Make sure this is disabled - if things worked properly before, no reason to think this got changed, but worth a look.
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
jnh
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Posts: 411
Joined: Fri Jun 01, 2007 11:56 am
My RE system: GVFX-3524, FM-80+FM-60, ~4.9kW PV in mixed panels on movable platforms, 415 Ah AGMs @ 24V, 80Ah @ 12V, Hub4, Mate, FNDC, Brultech GEM 32-ch AC datalogger, Midnite E-Panel, homebrew DC-DC crossfeed to 12V system, Honda EU-1000i, Iota DLS-27-25
Location: St. Augustine, FL, US

Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by jnh »

Mike Curran wrote: Sat Dec 26, 2020 7:17 pm Mine acted this way recently when I enabled auto charge termination control in the Mate3s's global charge menu. Make sure this is disabled - if things worked properly before, no reason to think this got changed, but worth a look.
I saw your earlier thread, but thought it might be a Mate3-specific issue. My Mate is the original oval Klaatu one, which lacks a setting by this exact name but does have

- ADV/MATE/PG3/CC -> enable CC float coordination?
- ADV/MATE/PG3/FN-DC -> enable FN-DC charge termination?

The second of which sounds like it might be equivalent. I had both set to Yes, and don't remember changing either, but could have while troubleshooting another problem, then forgotten about it.

"Enable FN-DC charge termination" is now set to No. Worth a try! I'm leaving the Advanced Grid-Tie setting Off for a few days though, until I have a chance to babysit it through early morning.

It's curious that the App Note you pasted from specifically says "If the Enable Charge Termination Control is set to Y, then the inverters will stop the absorb step and will move on to the float step or silent step ..." - inverters only, not Flexmax charge controllers? Like probably most grid-tie users I hardly ever charge batteries using the inverter, so if the intended effect is limited to that source, there's no possible benefit to enabling this, and no reason not to turn it off to squash any possible FNDC bugs.

Thanks for the suggestion.
Mike Curran
Forum Emperor
Posts: 2030
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters, normally direct grid tied, manual switch during winter or grid outage

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by Mike Curran »

inverters only, not Flexmax charge controllers?
I think so. You want the CCs to stay in absorb (OB says it's float with the setpoint raised to the absorb setting) to insure selling.

Hope it works for you. Klaatu shaped :?:
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
sbrownian
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Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by sbrownian »

The robots' viewport/raygun head opening looks somewhat like the outline of the old mate...
Mike Curran
Forum Emperor
Posts: 2030
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters, normally direct grid tied, manual switch during winter or grid outage

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by Mike Curran »

D'oh!
Screenshot_20201227-131906.jpg
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
jnh
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Posts: 411
Joined: Fri Jun 01, 2007 11:56 am
My RE system: GVFX-3524, FM-80+FM-60, ~4.9kW PV in mixed panels on movable platforms, 415 Ah AGMs @ 24V, 80Ah @ 12V, Hub4, Mate, FNDC, Brultech GEM 32-ch AC datalogger, Midnite E-Panel, homebrew DC-DC crossfeed to 12V system, Honda EU-1000i, Iota DLS-27-25
Location: St. Augustine, FL, US

Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by jnh »

The original oval Mate comes with this embossed picture on the inside of its back cover (or do not all of them have it? Maybe only early production lots?):
Attachments
mate-inside-cover.jpg
Mike Curran
Forum Emperor
Posts: 2030
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters, normally direct grid tied, manual switch during winter or grid outage

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Is the "full-conditions-met" battery voltage temperature compensated?

Post by Mike Curran »

Looks like Klaatu's hip is attached to the stern of a sailboat. :grin:
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
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