FNDC "Float Mode"

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provo
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FNDC "Float Mode"

Post by provo » Thu Dec 19, 2019 1:16 pm

From the Outback Application Note titled “FLEXnet DC Programming & Guidelines”.

“[Float Mode] is triggered whenever the net ampere-hour value returned to the battery is greater than zero, the net charging current is positive, and the battery voltage is less than the Charged Parameters Met Voltage by 0.4V (this is independent of system voltage). Once triggered, the MATE3 will report a state of charge of 100%.”

Does the FNDC really do this? I have a Trimetric now and I’m considering switching to an FNDC, but this “float mode” seems like a bad idea. Doesn’t it basically negate the whole concept of a “charge met” condition, with voltage above a setpoint plus current below a setpoint?

Seems like it could create a lot of unexpected resets to 100% SOC when the true SOC was less than 100%.

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Re: FNDC "Float Mode"

Post by raysun » Thu Dec 19, 2019 1:48 pm

Recently, Ive seen several instances of "Float Mode" apparently being enabled on my system. Typically the SOC is around 96%+. The Float cycle stays engaged, during the next hour or two, the SOC increases to 100%, then is drawn down to 99% after which Charge Parameters Met is indicated.

I don't always notice this. Usually, Absorb is maintained to 100%, then float engaged.

Either way, the Amp Hours in and out add up for me on the daily cycles.

I'm guessing "Float Mode" is used as a "kinder, gentler" profile for topping off the battery.

provo
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Re: FNDC "Float Mode"

Post by provo » Thu Dec 19, 2019 2:11 pm

Somehow I imagine once I’m in float, I’d see the Ah go negative for a while when a cloud comes in, then positive when the cloud leaves, etc. With float mode, every time the Ah goes positive, it resets again. I guess you could say it reached a “fully charged” condition, but definitely not as good a charge as it reaches after a full absorb.

I would just hope to see the true Ah situation, negative or positive, until the next “good” charge with a full absorb, even if those +8.0Ah readings were still reported as 100% SOC (and not 101%).

Later Edit: Maybe that's the problem -- if it won't report SOC as 101%, it doesn't "want" to keep track of Ah being +8. But I think the Trimetric does both.

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Re: FNDC "Float Mode"

Post by JRHill » Thu Dec 19, 2019 2:53 pm

provo wrote:
Thu Dec 19, 2019 2:11 pm
Somehow I imagine once I’m in float, I’d see the Ah go negative for a while when a cloud comes in, then positive when the cloud leaves, etc. With float mode, every time the Ah goes positive, it resets again. I guess you could say it reached a “fully charged” condition, but definitely not as good a charge as it reaches after a full absorb.

I would just hope to see the true Ah situation, negative or positive, until the next “good” charge with a full absorb, even if those +8.0Ah readings were still reported as 100% SOC (and not 101%).

Later Edit: Maybe that's the problem -- if it won't report SOC as 101%, it doesn't "want" to keep track of Ah being +8. But I think the Trimetric does both.
But then there is the re-bulk setting. Hit this and the charge cycle starts all over again. All your settings are repeated You can easily control this and it works well. But if you didn't finish the absorb it will start over. All in all the charge will complete if you have the power in.

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Re: FNDC "Float Mode"

Post by JRHill » Thu Dec 19, 2019 2:58 pm

JRHill wrote:
Thu Dec 19, 2019 2:53 pm
provo wrote:
Thu Dec 19, 2019 2:11 pm
but definitely not as good a charge as it reaches after a full absorb.
How do you get to float if you didn't finish the absorb?

raysun
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Re: FNDC "Float Mode"

Post by raysun » Thu Dec 19, 2019 3:04 pm

provo wrote:
Thu Dec 19, 2019 2:11 pm
Somehow I imagine once I’m in float, I’d see the Ah go negative for a while when a cloud comes in, then positive when the cloud leaves, etc. With float mode, every time the Ah goes positive, it resets again. I guess you could say it reached a “fully charged” condition, but definitely not as good a charge as it reaches after a full absorb.

I would just hope to see the true Ah situation, negative or positive, until the next “good” charge with a full absorb, even if those +8.0Ah readings were still reported as 100% SOC (and not 101%).

Later Edit: Maybe that's the problem -- if it won't report SOC as 101%, it doesn't "want" to keep track of Ah being +8. But I think the Trimetric does both.
Hmmm... guess in my case, Float is easy to maintain, as the system pretty much stays there until the sun goes down.

When you mention "reset", what exactly is being reset?

provo
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Re: FNDC "Float Mode"

Post by provo » Thu Dec 19, 2019 3:47 pm

I don't have an FNDC, but the app note just says "Once triggered, the MATE3 will report a state of charge of 100%." I assume the Ah is also set to zero. Yeah, its probably just my OCD here -- at a float voltage of 27.4V (today's value) and float amps of 0.4A, it would take a LONG time to get to +8Ah, so the fact I can't watch that happen on the FNDC is not the end of the world.

The Trimetric can be set up to do a reset on float, but in the FNDC it appears built-in, so I was just wondering if anyone has had problems with unexpected SOC's jumping to 100%. No biggy.... :smile:

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Re: FNDC "Float Mode"

Post by sodamo » Thu Dec 19, 2019 11:05 pm

Haven’t touched a Trimetric is quite some time, are they measurement only still? If so I wonder if you could leave it hooked in as you adjust to the FNDC and see how both report?
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provo
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Posts: 172
Joined: Thu Jul 27, 2006 4:34 pm
My RE system: Sixteen Evergreen EC-120
(4 strings, total 1920W)
Eight Rolls S-550 (2 strings, total 800Ah @ 24V)
One FM80
One VFXR3524A
Mate3s
Trimetric
Location: Sierra foothills

Re: FNDC "Float Mode"

Post by provo » Fri Dec 20, 2019 6:38 am

sodamo wrote:
Thu Dec 19, 2019 11:05 pm
Haven’t touched a Trimetric is quite some time, are they measurement only still? If so I wonder if you could leave it hooked in as you adjust to the FNDC and see how both report?
Good question -- I could try two lugs under each sense screw on the shunt -- the currents in the leads should be miniscule, so I don't know why the Trimetric and FNDC couldn't run at the same time.

Yeah, the Trimetric isn't connected to the rest of the system at all, but I like the big bright display I can see from 6 feet away. Ancient eyeballs make that grainy little Mate3s display problematic when I'm near the system. I'd never switch to the FNDC if it weren't for Optics :smile:

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Re: FNDC "Float Mode"

Post by gtarolli » Mon Dec 23, 2019 10:42 am

This "float mode" confuses me too ... and I believe I have seen it trigger a few times - SOC jumps a few percent (e.g. 5%) to 100% but my chargers are still in Bulk mode. I wish there was some way to disable this, but it doesn't really seem to change the charging, just resets some numbers. Maybe someone from Outback can help explain this mode better, exactly how it works, what it does, and why, etc.

provo
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My RE system: Sixteen Evergreen EC-120
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Eight Rolls S-550 (2 strings, total 800Ah @ 24V)
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One VFXR3524A
Mate3s
Trimetric
Location: Sierra foothills

Re: FNDC "Float Mode"

Post by provo » Mon Dec 23, 2019 11:14 am

Here's the whole section from the App Note:

"Float Mode:

This is a safety mode for batteries that are not able to reach the expected voltages. If triggered, the Float Mode will cause the state of charge to jump to 100% to protect the battery. This mode is triggered whenever the net ampere-hour value returned to the battery is greater than zero, the net charging current is positive, and the battery voltage is less than the Charged Parameters Met Voltage by 0.4V (this is independent of system voltage). Once triggered, the MATE3 will report a state of charge of 100%.

The Float Mode is especially helpful when the system is programmed to make decisions based on state of charge. For example, if the batteries cannot reach the Charged Parameters Met voltage, but the generator has put enough ampere-hours into the batteries such that the total AH value is positive, the inverter will stop the generator via the AGS setting by using the state of charge value.

A second condition that will trigger the Float Mode is if the absorb timer is set too low and the net Ampere-hours become positive during the float stage. The extent of the state of charge “jump” will largely depend on the programmed Battery Charge Factor."


I've sort of concluded that it's not a bad thing -- after all, once you've returned enough Ah's to zero out the display, you actually HAVE achieved a full charge, just not with the extra overcharge that an absorb stage gives. I think it doesn't bother me, but I'd still make sure to go through my usual 3h absorb at least every few days.

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Re: FNDC "Float Mode"

Post by gtarolli » Mon Dec 23, 2019 11:30 am

OK, so as I understand it, it doesn't effect PV charging, just relays and other things that depend on SOC values. I guess that makes sense, else you might never shut the generator off.

provo
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Joined: Thu Jul 27, 2006 4:34 pm
My RE system: Sixteen Evergreen EC-120
(4 strings, total 1920W)
Eight Rolls S-550 (2 strings, total 800Ah @ 24V)
One FM80
One VFXR3524A
Mate3s
Trimetric
Location: Sierra foothills

Re: FNDC "Float Mode"

Post by provo » Mon Dec 23, 2019 12:16 pm

gtarolli wrote:
Mon Dec 23, 2019 11:30 am
OK, so as I understand it, it doesn't effect PV charging, just relays and other things that depend on SOC values. I guess that makes sense, else you might never shut the generator off.
That, but I imagine it resets your Optics-reported SOC value as well, which could "lull" you into thinking that the batteries were fully charged, day after day, even though they'd never gone through a full absorb. So a potentially useful feature, but caution is required....

gtarolli
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My RE system: Outback: off-grid
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- 2 FLEXmax 80
- 1 FLEXmax 60
- 30 (10x3) 300w panels (9000w total)
- 6 SimpliPhi 3.4 kWh LI batteries (400ah , 20kWh)
- 1 Honda 3000 generator + one spare
Location: Wainiha, Kauai, HI

Re: FNDC "Float Mode"

Post by gtarolli » Mon Dec 23, 2019 12:30 pm

agreed! .

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