New LiFePO4 installation charge parameters

[Muskoka]

Need some assistance, guidance. I've been using lead acid for many years with my Midnite Classic Lite, with MNGP, Whizbang Jr. I have 1540watts of panel.

My lead acid batts were done, end of life. So I've switched to LiFePO4. The battery I purchased is a REDODO 24V 200ah, with a 200a bms.

https://www.redodopower.com/products/redodo-24v-200ah-lifepo4-battery-5-12kwh-5-12kw

I've had the battery since Monday, today was the first day of sun to give it a full solar charge cycle. I had been charging it with a charger and generator for a few days. The charge cycle today was fine, put 130ah back in the battery in about 4 hours, went from Bulk to Absorb, then Float after 15 mins.

Here's the charge parameters I used. From everything I've read the recommended rates from battery sellers are too high. The fellow that posted these also uses a Midnite controller. I did change the end amps though, the manual recommended 4a.



First issue, the controller went to Absorb at 28.2v and within maybe 7-8 mins the charge amps had dropped to zero. Why didn't the controller go to Float when end amps had been met. It kept going for the programmed 15 mins of Absorb.

Second issue. The voltage and controller mode are jumping around. There's no meaningful load on the system, my internet router,  but the controler is going from Float, to Bulk MPPT, to Absorb, rinse and repeat. Voltage is going from Float 27.9 drops to 27.1, controller switches to Bulk, then slowly climbs for a few minutes, then jumps to 28.2 in Absorb again, then Float at 27.9, then within a minute or two the voltage drops to 27.1 and the cycle continues. It's currently in Bulk, it's end of day so the sun is gone, so no more data to share.

Here's the recommended charge parameters from the booklet that came with the battery.



Open to any and all advice, no experience with Lithium Iron, other than the hours of reading online to prepare for the installation. I thought I'd ask for some advice here before I contact the battery seller, hoping it's not a BMS issue.

[boB]

So, it actually goes to Float ?   I was wondering because you mentioned it and I think you are saying that the CLassic is going back to Bulk/Absorb again, SOON ?  What amount of time is there between Float and back to Bulk/Absorb again ?

When you see zero amps, is the battery voltage AT the Absorb voltage ?  I think you are seeing 28.8V and 29.2V  as the range ?

During ending amps change to Float from Absorb,  the battery voltage must be in that Absorb range, the mode in Absorb for 60 or 90 seconds.   Is the Classic going from that zero amps at Absorb voltage and then jumping back to Bulk ?   If so, then when it gets to Absorb again,  the battery current has to be below 4 amps for that 60 to 90 seconds (I can't remember which time it is)

You are using the Whizbang Junior for Ending Amps, right ?   In the CHARGE--- Advanced menu, it will allow you to pick Shunt or CLASC   (WB Jr or Classic's internal shunt)...

How are you viewing the stages and voltages, etc ?   As I remember, the Lite does not come with a MNGP remote but, that other one with LEDs and switches.

OR, are you using the Local-App  control software on a PC ?

boB

[Muskoka]

Yes, it goes to Float, just not when it should. End amps were set to 4a. Absorb is set to 15 mins. About 7-8 mins into Absorb, charge current was down to 0, end amps had been met, but it stayed in Absorb for close to the full 15 mins of the Absorb cycle. It was at the set 28.2v for Absorb. While the current was basically zero it kept trying to push the voltage up, I saw 28.3, 28.4, no higher. That went on for about 7 mins. It then went to Float right around the 15 min mark.

The cycling I have no clue. It was in Float, had been for close to 2 hrs maybe so it was end of day and the sun was going down. Next I see the Voltage on the Trimetric is showing 27.1, Float was set for 27.9 and it was there for a few hours. I look at the Classic Monitor on my phone and I see it's in Bulk MPPT, but why did it go from Float 27.9 to 27.1, with no real load. Anyways, it stayed in Bulk MPPT for a few minutes, climbed quickly to 28.2, went to Absorb, and then pretty quickly into Float, and not too many minutes later repeated that cycle again. By then the sun was gone and it was switching into Rest.

[boB]

Are you using a Whizbang Junior shunt on the battery ?

As far as going back to Bulk, it could be that the Re-Float voltage setting is too high.

Check that setting.

boB

[Muskoka]

Yes, I have a shunt on the battery. Was never a issue with the lead acid batteries, if current dropped below the end amps setting while in Absorb it would go to Float pretty much straight away, slight delay. But that was always after hours of Absorb, not 15 mins like now.

Yes, I can play with all the settings, but nothing explains why it left Float of 27.9v, and dropped to 27.1v, with no load on the system. I have a feeling it's something in the BMS, but it's a closed, sealed battery, and I have no idea how it was programmed. I have contacted the seller, looking for exact charging parameters, and info on how the BMS was programmed. I found the literature quite lacking, what I posted above from the booklet doesn't help at all. It doesn't make sense that in less than a minute a battery can go from Float at 27.9v, to 27.1v with no load.

[Muskoka]

One thing I have adjusted, the Classics voltage reading was 2/10ths lower than the actual battery terminal voltage.

Not expecting sun for close to a week by the looks of it. Going to try with low end of recommended absorb, 28.8v, and set the Float and Rebulk a fair bit lower, next solar charge cycle. Genny and charger until then.

[Muskoka]

I received a response from the battery seller. They provided some parameters which look quite high to me, after everything I've been reading. Anyways here they are.

1. I want to clarify that lithium batteries, including the one you have, typically don't have a float charge phase as seen in traditional lead-acid batteries. Unlike lead-acid batteries, lithium batteries do not require a continuous low-level charge to maintain their state of charge.
For lithium batteries, once they reach their set voltage in the Absorb phase, the charging process often transitions directly to a period of rest or a low-current state, rather than a distinct float phase. This characteristic is one of the differences between lithium and lead-acid battery chemistries.
2. Here are some parameters for your reference:
High voltage cut-off: 31.2V
Charging limited voltage: 29.2V
Balance charging: 29V
Boost charging: 28.8V
Float charge: 27.6V
Boost charge return voltage: 25.6V
Overcharge return voltage: 23.6V
Low voltage warning: 23.6V
Over-discharge voltage: 22.4V
Discharge limited voltage: 21.6V
Over-discharge delay time: 10s
Balance charging time: /
Boost charging time: 240 mins
Balance charging interval: /

I'm still confused with the terminology used, and have no idea how I should setup the Midnite Classic Lite with these numbers provided, they look so high. He states that Float shouldn't be used, and then provides a value for Float, confusing.

Isn't Boost charge the same as Absorb, they're suggesting 4 hrs for Absorb? If Boost is Absorb, and they suggest balancing at 29v, how is that achieved with the Midnite Classic, and solar input only.

Only way to limit the Bulk voltage is "Charge "which is the Absorb voltage in the Classic, along with the current limit setting in the Classic. How do I allow the cells to get to 29v for balancing during Bulk, then back to 28.8v for Boost/Absorb, for their recommended 4 hours? There is the Equalize voltage setting, but I'm not going there until someone says it's a good idea, which I'm doubting.

Because I don't have access to the individual cells for balancing, 29v, I have to balance the whole battery using some voltage figure input into the charge controller.

I will be presenting these questions to the battery seller, but some input, thoughts, on how to properly input these values into the Classic would be appreciated.

Some more info if it's helpful. The battery currently sits at 26.4v, and it's down to 79%, after harvesting just over 4kw yesterday in solar charge. Battery capacity was at 30% first thing yesterday morning, was at 100%, and in Float around 12:30 pm.

[FNG]

Those are some odd settings for Lithium, The values are SO close together it is going t hit rebulk steady when in float. I see this making the Classic always bounce around in different stages. Do you have a make and model of this battery? Sorry if I missed it.

Usually I see float at least 1v lower than absorb on lithiums

[Muskoka]

Link to the battery is in the first post. The actually cells, I have no idea, sealed unit.

Were your comments about the original parameters used, or the ones provided by the battery seller I posted this morning?

[boB]

28.8V to 29.2V should not make any difference when the batteries are balancing so I would not worry much about those 2 voltage settings.  Not all charge controllers have a boost charge sage anyway.

I should have said Re-Bulk  and not  Re-Float, before.

boB

[Muskoka]

I went ahead and set Absorb to 29v to hit the recommended balance charge voltage, 4 hours Absorb per their recommendation, end amps 4a, recommended, which it hit within a few minutes after going to Absorb the first charge cycle, so it'll never see 4 hours of Absorb, Float to 27.6v as per their recommendation, and Rebulk to 25.6v, again as per recommended. See how it goes. Actualy getting a bit of sun today.

[Muskoka]

Ok, today was the first day of sun since last post. Classic is still acting weird.

Absorb is set to 28.8v, low side of the recommended 28.8v to 29.2v. End amps 4 amps, Absorb time 5 minutes.

Nearing the end of the Bulk cycle (lasted roughly 3.5 hrs, harvested close to 4 kw) the voltage started climbing quickly to the Absorb set point of 28.8v. Once it hit 28.8v it started the cycling again between Bulk, Absorb, Float, it was changing within a second, bouncing all over the place. It was also spiking the voltage, I saw it jump as high as 34.4v for a second, of course it tripped my 2000w 24v inverter that has a high voltage shutdown of 30.5v.

I was standing right there in front of the controller so I quickly set the Absorb to 28.6v, and what looks to be the least amount of Absorb time, 3 mins? It's finally settled out, and is sitting in Float, 27.6v. It's been holding there for 15 mins maybe, voltage not budging from 27.6v, so that's promising. I have Rebulk set to 26.8v.

Any ideas why it's cycling rapidly once it reaches the Absorb set point of 28.8v?

And why would the voltage spike?

At this point I'm not too worried about what the voltage settings should be, I'm well below the recommended setpoints from the supplier of the battery. What I'd like though, is to get through a charge cycle without the controller going beserk at the end of the Bulk cycle, and trying to ruin my day by damaging something. Just to add, I've been using this controller for roughly 15'ish years maybe with lead acid batteries, and it never exhibited this behaviour.

It's now happened with Absorb set to 28.2v, and 28.8v, and Float set to 27.9v and 27.6v.  Both times the voltage has jumped high enough beyond those Absorb values to trip my inverter at 30.5v, something isn't right.

I do have a Morningstar Tristar Mppt 60 here, I'm tempted to swap it out with the Classic as a test to see if it's controller related, or maybe the BMS.

[boB]

If, when that 3.5 to 4 hour time going between Bulk/Absorb  was fairly low current, then the spikes to 34V may be the BMS opening up.  About how long did you see the Classic sit above 30 volts ?

Also, could it be that you had some large-ish inverter loads on when the inverter disconnected due to high Vbattery ?

Not a bad idea to try the Morningstar.  But loads and/or battery abruptly turning off can cause one end of that Tug-Of-War rope to quickly go down on one end.  That's an analogy I use for when one unit is trying to pull the voltage up on the DC side and another unit is  trying to pull that voltage down.
If one gives up (opens up) then it's all of a sudden un-even for a moment.

30.5 volts is slightly low for an inverter to turn off but could be worse as I have seen before.

boB

[Muskoka]

No loads of any significance, I'm totally offgrid, no fridge in the winter, no tv, woodstove for heat. The only devices on during the day are the inverter, and my internet router, typically the load is around 50w. A little more at night with a few lights on.

Bulk cycle started around 9am this morning. Voltage climbed to 27'ish volts and very slowly rose from there. Current topped out at 47 amps, steady. Right around 12:30, I noticed on the Classic App on my phone that the batt was getting close to full, so I went to monitor the last minutes of the Bulk Cycle.

Voltage was more rapidly moving upto the setpoint of 28.8v, but the current wasn't tapering off as fast as I would have liked. I'm new to this battery, so I don't know exactly how it responds, reacts. The current would have a steady dropoff with my lead acid batts, a nice gradual decline, this is much different now.

Anyways, it was getting pretty close to the 28.8v Absorb setpoint and the current was coming down, quite rapidly, then the controller starts cycling, jumps to Float, then back to Bulk, to Asborb, to Float, and so on, out of nowhere. I was more concerned with trying to keep an eye on the voltage, as it was jumping all over the place, down in the 27's up to 29's, at one point spiked over 34, then down in the 28 range. This all happened in maybe 10-20 seconds. After trying to see/comprehend what was going on, it was happening so quick, I quickly went into the controller and set the Absorb lower, and the Absorb time to the lowest it would go 3 mins. Took a second to get that cause it kept going back high as I got close to zero. I know now that 3 mins is the lowest I believe. That seemed to settle things down, it then went to Float, and stayed there, at the Float setpoint of 27.6v.

This is exactly what happened the first charge cycle, with the Absorb setpoint a fair bit lower than today. The first time it happened it also tripped my inverter shutoff.

The controller was acting like it didn't know what it should be doing, even with a full volt separating Absorb and Float. Battery manufacturer suggests end amps of 4 amps, I see others setting that value higher, like 10 amps, wonder if that would help?

This is now 2 failed attempts at a charge cycle, it's making me nervous, especially after going for years without a issue with lead acid, beyond the initial growing pains with a new system.

Here's the graph from MyMidnite if it helps in anyway.



That graph doesn't show any spikes in the voltage, but it was jumping all over on the MNGP, once the funny business started.

[Wizbandit]

Unplug the BTS aka Battery Temp Sensor...