Making sense of Phi Absorb

raysun
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Making sense of Phi Absorb

Post by raysun »

Screenshot_20211123-171212_Firefox.jpg
The Absorb charge phase uses the Phi-specified 56.4V @ 0.1H and the FNDC reports Charged Parameters Met every day the battery gets a full charge with rare exception.

Typically the Absorb phase terminates in 5 minutes. Periodically it terminates in under 5 minutes. On rare occasion Absorb times out at 6 minutes (and CPM is not met.)

Its been challenging to come up with scenarios that define the different Absorb termination times. The graph above is a good example:
Day 1, Absorb termination = 3 min.
Day 2, Absorb termination = 5 min.
Day 3, Absorb termination = 2 min.

What the graphs can't show is the amount of "oscillation" near the Charged Return Amps (9A in this case). When CRA is approached, the declining current may suddenly take a small leap upwards several times within the Absorb phase, eventually settling below 9A at charge termination. I've guessed this to be some 'last minute' cell balancing by the BMS, but its just speculation on my part.
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Re: Making sense of Phi Absorb

Post by provo »

raysun wrote: Tue Nov 23, 2021 7:25 pm
Typically the Absorb phase terminates in 5 minutes. Periodically it terminates in under 5 minutes. On rare occasion Absorb times out at 6 minutes (and CPM is not met.)

Its been challenging to come up with scenarios that define the different Absorb termination times.
If you ever get it figured out, I'll be very interested! My "time in absorb before CPM" has varied from 3m to 12m, with rare instances of no CPM within my absorb time setting of 12m. As discussed in an earlier thread, it appears directly correlated to the charging current when absorb starts.

On a sunny day when I enter absorb at 45A after 2h of bulk, it can take 11m to reach CPM.
On a cloudy day when I enter absorb at 25A after 4h of bulk, it can be as little as 3m.
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Re: Making sense of Phi Absorb

Post by raysun »

On a sunny day when I enter absorb at 45A after 2h of bulk, it can take 11m to reach CPM.
On a cloudy day when I enter absorb at 25A after 4h of bulk, it can be as little as 3m.
My sense of it is the lower charge rate allows more ions to migrate to the anode before the battery voltage rises to the 56.4V Absorb voltage. Finishing the Absorb phase would take a shorter period of time.

At the higher charge rate, the battery voltage can rise to the Absorb voltage with less ion migration, it seems. Absorb takes longer to complete.

Of course, looking at the graph data seems to suggest just the opposite. Ugh. I attribute that to my being terrible at reading graph data.

My charge current tends to fall fairly naturally around 60 - 75A, or 10 - 12A per block. A relatively low rate of charge. Absorb tends to stay within the 5 minute mark.
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Re: Making sense of Phi Absorb

Post by provo »

raysun wrote: Tue Nov 23, 2021 10:39 pm
My charge current tends to fall fairly naturally around 60 - 75A, or 10 - 12A per block. A relatively low rate of charge. Absorb tends to stay within the 5 minute mark.
My charge current on a sunny day is often >40A entering absorb (and >50A earlier in bulk.) That’s >20A per block entering absorb, and my time in absorb before CPM is often 11m.

The batteries are 24V (abs setting of 28.1V), but maybe it's mostly the current that is important.

If I had 4 batteries instead of 2, maybe I'd see 5m absorbs also. $$$$$ :eek:
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Re: Making sense of Phi Absorb

Post by raysun »

Screenshot_20211124-074511_Firefox.jpg
Screenshot_20211124-074638_Firefox.jpg
Here's an oddity. Absorb appears to have been reached and executed for 5 minutes. Yet, Charged Parameters were not met.

The last hour of charging was a gross current of 84AH, net 74AH. Peak charge current unknown.
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Re: Making sense of Phi Absorb

Post by JRHill »

provo wrote: Tue Nov 23, 2021 10:08 pm On a sunny day when I enter absorb at 45A after 2h of bulk, it can take 11m to reach CPM.
On a cloudy day when I enter absorb at 25A after 4h of bulk, it can be as little as 3m.
Yup, it is curious. During the summer and charging consistently via solar, CPM was consistent.

Precharging the batteries on the generator in the morning but not all the way and then finishing with solar, not so much.

Charging entirely by generator, it doesn't happen. Unless I initiate a new bulk charge and then maybe twice.

I've tried adjusting the CPM parameters slightly with no success. All in all, I really don't care. If I rebulk it is charging in a way that I don't like anyway.
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Re: Making sense of Phi Absorb

Post by raysun »

Ultimately, its much ado about nothing.

My main interest in CPM is syncing the FNDC. However, the monitor is reasonably precise enough to go several cycles without syncing, IME. If one leaves a decent operating margin (I have the system programmed to the 20% SoC lower limit, but use 30% as the operating limit) there can plenty of room for meter error.

I've decided charging LiFePo4 is like cooking BBQ - low and slow is the way to go.
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Re: Making sense of Phi Absorb

Post by provo »

raysun wrote: Wed Nov 24, 2021 10:21 am
I've decided charging LiFePo4 is like cooking BBQ - low and slow gives the best results.
On a few super sunny and cold days I've considered flipping off one or two of my PV strings for 1/2 hour before absorb would start. Haven't actually tried it yet, but maybe soon...
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Re: Making sense of Phi Absorb

Post by raysun »

provo wrote: Wed Nov 24, 2021 10:50 am
raysun wrote: Wed Nov 24, 2021 10:21 am
I've decided charging LiFePo4 is like cooking BBQ - low and slow gives the best results.
On a few super sunny and cold days I've considered flipping off one or two of my PV strings for 1/2 hour before absorb would start. Haven't actually tried it yet, but maybe soon...
I have an easier method, and probably greater "photonic opportunity". I'm going to limit total charge to around 60A.

Done. Its a sunny day. Let's see how that affects the charging curves and absorb time.
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Re: Making sense of Phi Absorb

Post by JRHill »

"I've considered flipping off one or two of my PV strings for 1/2 hour before absorb would start. Haven't actually tried it yet, but maybe soon... "

Believe me, I've flipped off a few solar things over the years. I didn't help but I sure felt better afterward.
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Re: Making sense of Phi Absorb

Post by raysun »

Screenshot_20211124-104039_Firefox.jpg
Funny I've never noticed this before. Global Charger Control current limit is net charging current to the battery, not gross current from the charging sources.

Here, its set for 60A.
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Re: Making sense of Phi Absorb

Post by provo »

raysun wrote: Wed Nov 24, 2021 10:57 am
I have an easier method, and probably greater "photonic opportunity". I'm going to limit total charge to around 60A.
In my case I'd like to limit the FM80 to maybe 30A output current. If the FM was getting enough from the panels to be capable of 60A output and I had the output current limited to 30A for the entire morning, could the FM do that without overheating?

Much like the overpanelling question -- how much throttling back can you do?
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Re: Making sense of Phi Absorb

Post by raysun »

provo wrote: Wed Nov 24, 2021 1:46 pm
raysun wrote: Wed Nov 24, 2021 10:57 am
I have an easier method, and probably greater "photonic opportunity". I'm going to limit total charge to around 60A.
In my case I'd like to limit the FM80 to maybe 30A output current. If the FM was getting enough from the panels to be capable of 60A output and I had the output current limited to 30A for the entire morning, could the FM do that without overheating?

Much like the overpanelling question -- how much throttling back can you do?
If the array is within the maximum power limits for the controller (24V x 80A) then the current can be "throttled" to a minimum of (IIRC) 5A.
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Re: Making sense of Phi Absorb

Post by provo »

raysun wrote: Wed Nov 24, 2021 1:55 pm
If the array is within the maximum power limits for the controller (24V x 80A) then the current can be "throttled" to a minimum of (IIRC) 5A.
Wonderful!

In 14 years I've never had it set lower than 70A...
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Re: Making sense of Phi Absorb

Post by raysun »

20211124_121647.jpg
Charging at 60A, equals 10A per battery block.
The FNDC read 100% before battery voltage reached 56.4V. Charging continued for another 6 minutes to reach Absorb voltage, adding 6AH or 1.5% of the battery capacity.
In the 3 hours @ 60A charge rate, the battery voltage was steady around 54.4V

20211124_121424.jpg
Absorb terminated in 5 minutes.
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Re: Making sense of Phi Absorb

Post by raysun »

A second day of the 60A (10A per battery block) charge profile. It was pretty much like the first day, however, Absorb charge termination took 4 minutes.
Screenshot_20211125-132908_Firefox.jpg
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Re: Making sense of Phi Absorb

Post by jainsw »

raysun wrote: Wed Nov 24, 2021 10:21 am Ultimately, its much ado about nothing.

My main interest in CPM is syncing the FNDC. However, the monitor is reasonably precise enough to go several cycles without syncing, IME. If one leaves a decent operating margin (I have the system programmed to the 20% SoC lower limit, but use 30% as the operating limit) there can plenty of room for meter error.

I've decided charging LiFePo4 is like cooking BBQ - low and slow is the way to go.
My setup gets to Absorb most days over the past two months, but the last time it set CPM was on November 13th. I have the original time to Absorb time set at 6 minutes. Wondering if I should push it to CPM tomorrow just to get things synced.
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Re: Making sense of Phi Absorb

Post by raysun »

jainsw wrote: Wed Dec 01, 2021 5:14 pm
raysun wrote: Wed Nov 24, 2021 10:21 am Ultimately, its much ado about nothing.

My main interest in CPM is syncing the FNDC. However, the monitor is reasonably precise enough to go several cycles without syncing, IME. If one leaves a decent operating margin (I have the system programmed to the 20% SoC lower limit, but use 30% as the operating limit) there can plenty of room for meter error.

I've decided charging LiFePo4 is like cooking BBQ - low and slow is the way to go.
My setup gets to Absorb most days over the past two months, but the last time it set CPM was on November 13th. I have the original time to Absorb time set at 6 minutes. Wondering if I should push it to CPM tomorrow just to get things synced.
Look at the Event Log for the end if charge cycle entries, and post them.
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Re: Making sense of Phi Absorb

Post by provo »

raysun wrote: Wed Nov 24, 2021 12:44 pm
Funny I've never noticed this before. Global Charger Control current limit is net charging current to the battery, not gross current from the charging sources.

Here, its set for 60A.
That could be helpful, but the Mate3s manual says, "The FLEXmax charge controllers must be set to Grid-Tie Mode in order to establish priority for this function. (See page 21.)"

On page 21 it says, "When enabled, this setting automatically raises the charge controller’s Float voltage to equal its Absorption voltage."

That doesn't sound like something I'd want. Are you using Global Charger Control now?
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Re: Making sense of Phi Absorb

Post by raysun »

provo wrote: Wed Dec 01, 2021 5:42 pm
raysun wrote: Wed Nov 24, 2021 12:44 pm
Funny I've never noticed this before. Global Charger Control current limit is net charging current to the battery, not gross current from the charging sources.

Here, its set for 60A.
That could be helpful, but the Mate3s manual says, "The FLEXmax charge controllers must be set to Grid-Tie Mode in order to establish priority for this function. (See page 21.)"

On page 21 it says, "When enabled, this setting automatically raises the charge controller’s Float voltage to equal its Absorption voltage."

That doesn't sound like something I'd want. Are you using Global Charger Control now?
The FMs must have Grid Tie enabled to use the code that allows the Mate to modulate their output.

The reference about raising the Float Voltage to the Absorb Voltage must be a function of actually being grid tied.

My FMs are set to Grid Tie mode, but definitely use the Float Voltage programmed into their Battery Charge parameters.
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Re: Making sense of Phi Absorb

Post by jainsw »

raysun wrote: Wed Dec 01, 2021 5:17 pm
jainsw wrote: Wed Dec 01, 2021 5:14 pm
raysun wrote: Wed Nov 24, 2021 10:21 am Ultimately, its much ado about nothing.

My main interest in CPM is syncing the FNDC. However, the monitor is reasonably precise enough to go several cycles without syncing, IME. If one leaves a decent operating margin (I have the system programmed to the 20% SoC lower limit, but use 30% as the operating limit) there can plenty of room for meter error.

I've decided charging LiFePo4 is like cooking BBQ - low and slow is the way to go.
My setup gets to Absorb most days over the past two months, but the last time it set CPM was on November 13th. I have the original time to Absorb time set at 6 minutes. Wondering if I should push it to CPM tomorrow just to get things synced.
Look at the Event Log for the end if charge cycle entries, and post them.
Here is one from today.
Screen Shot 2021-12-01 at 6.57.34 PM.png
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Re: Making sense of Phi Absorb

Post by provo »

raysun wrote: Wed Dec 01, 2021 5:51 pm
My FMs are set to Grid Tie mode, but definitely use the Float Voltage programmed into their Battery Charge parameters.
Thanks for the tip, I'll try it :grin: ....

My target is a bulk charging current of around 22A. With that I get to absorb in 4h, and CPM happens 7m into absorb. Not 6m, but better than 11m!
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Re: Making sense of Phi Absorb

Post by jainsw »

here the summary from the FNDC today.
Screen Shot 2021-12-01 at 7.12.57 PM.png
Screen Shot 2021-12-01 at 7.14.33 PM.png
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Re: Making sense of Phi Absorb

Post by jainsw »

my summary for November, my first complete month after install on October 6th. Never had to run the generator. :grin:
Screen Shot 2021-12-01 at 7.19.10 PM.png
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Re: Making sense of Phi Absorb

Post by JRHill »

I have no idea about grid connected systems. But my off grid is dialed in for CPM via the charge controller. It worked EVERY day. Now on generator, I'm still trying to get it dialed in. The genset is only .4vdc lower on the inverter charger but all together different for CPM.

As discussed before, CPM isn't critical. But is nice once in a while to keep some kind of standard for SOC. At this point in time I can get CPM on generator if I rebulk. That's good enough for my purposes until I find the magic bullet.
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