New User - Having a little trouble understanding the Classic 150...

[SunTim]

Hi all,

I'm new to Solar as well as the Midnite Solar Classic 150.

I've had this system running for a few weeks now, very happy except I haven't got the charging working as well I think it should. The robustness of this device is superb! I just cant figure out how to make it work.

I'll state my situation, then provide a lot of system information further below as well as some attachments.

Here's what I THINK, maybe, that I know...
1) Classic 150 evolved as a Lead Acid charger which is now also commonly used for LiFePo4 applications.
2) The settings for controlling LiFePo4 charging basically include:
  >> Absorb Voltage (55.4V @ 3 minute max). This effectively triggers transition from Bulk MPPT to Float.
  >> Float Voltage (53.4V)
  >> Rebulk Voltage (51V) triggers return to Bulk MPPT if battery voltage falls too low.

Here's the concern I'm having...
Under varying sunlight conditions, I've been unable to consistently charge.
  >> In strong sunlight, Bulk MPPT really goes to town, up to 80 amps, but creates a higher voltage in doing so. This voltage reaches Absorb Volts and ends Bulk MPPT prematurely, then, once in Float, the battery may only be at 75% SoC. Float (delivering about 1 to 3 amps) is way too slow at getting the job completed.
  >> In cloudy weather, Bulk MPPT produces a smaller charging current (and resulting voltage) allowing Bulk to go longer that it should. Once it finally switches to Float, it takes an hour or two to bleed current to get reduce 'over' charge.

In other words, the process appears to be only related to voltage and does not pay attention to charging current.

I'm sure I am misunderstanding some of this and hope someone can help me to understand.

Also, If there exists a detailed description of the strategy that the Classic uses, I haven't found it yet.

Thanks, Tim, Jackson, TN USA

BTW, my charge profile graph is generated from data collected by an Arduino datalogger which saves A, V, and SoC once per minute. This chart shows what happened today, cloudy / rainy, premature end of Bulk at about 76% SoC.

My background:
Retired, EET degree from 70s, proficient with electronics and power systems.

System Components:
Panels:    14 ea Trina 415W Mono Panels, 7 strings of 2
Charge Cont:    Midnite Solar Classic 150
Batteries:    4 ea KiloVault LiFePo4 2.4kWh 200Ah 12V HLX+
Inverter:    Magna-Sine MS4448PAE
NOTE: Detailed schematic and equipment list is attached

System Goals:
Off Grid to reduce Grid load while providing backup.
   Currently supplying to Water Heating, Refrigerator, Freezer, and Water Heater
   No connection to grid in any way
Charge daily to about 90-95 % SoC

Classic 150 Charge Controller Setup

VOLTS         
Equalize Voltage           56.4      Used only for Lead Acid batteries
Absorb Voltage      55.4   
Float Voltage      53.4   

CHG TIME         
Absorb Time      3 minutes   
Equalize Time      0 minutes   Used only for Lead Acid batteries

T-COMP         
Enable / Disable   Disabled   Used only for Lead Acid batteries
EQ         
Start / Stop      Stopped      Used only for Lead Acid batteries

ADVANCED         
Ending Amps      2.0 Amps          Used only for Lead Acid batteries
ReBulk Volts      <51.0 V   
Skip Days              0 Days      Used only for Lead Acid batteries

LIMITS         
Output Amps      88 A   
Input Amps      99 A   
Skip                               Used only for Lead Acid batteries
T-Comp (min)      52.8V      Used only for Lead Acid batteries
T-Comp (max)      58.4A      Used only for Lead Acid batteries
Hi Batt Temp      170 deg C           Used only for Lead Acid batteries

NOTE: Setup Sheet pdf is attached      

[Vic]

Hi Tim, welcome to the Forum,

You mentioned,

"Here's the concern I'm having...
Under varying sunlight conditions, I've been unable to consistently charge.
  >> In strong sunlight, Bulk MPPT really goes to town, up to 80 amps, but creates a higher voltage in doing so. This voltage reaches Absorb Volts and ends Bulk MPPT prematurely, then, once in Float, the battery may only be at 75% SoC. Float (delivering about 1 to 3 amps) is way too slow at getting the job completed.
  >> In cloudy weather, Bulk MPPT produces a smaller charging current (and resulting voltage) allowing Bulk to go longer that it should. Once it finally switches to Float, it takes an hour or two to bleed current to get reduce 'over' charge".

When MPPT CCs are in Absorb, and Float (and for LA batts, EQ),  it is the battery Charge Acceptance that determines the battery charge current.

If you feel that Bulk ends too early,  you can increase the Absorb voltage (if this is OK with your batts), and the same, for the current in Float.

Forgot to look,  are you using the WbJr battery current monitoring accessory?  This allows monitoring the current going into the batts.

I know, essentially nothing of Lithium batteries.

Many others here know much more than I.   BTW,  you might want to keep the EQ voltage set to the same value, as Abosrb,  and some folks with LiPO batts,  DO seem to use EA, on occasion ...

EDIT, to add:  Here is a Link to a reseller  for the WhizBang Jr monitoring device, (which you may have already):
https://www.solar-electric.com/midnite-solar-whiz-bang-jr-current-sense-module.html

Later,  Vic

[SunTim]

Hi Vic,

Thanks for your quick response!

I've worked with adjusting both Absorb volts and Float volts, trying to get the Bulk MPPT to coast into float at the right point. Unfortunately, the optimal adjustments for today, based on sunlight supply, user load, and starting SoC, will not be right if any of the conditions change.

I'm hoping that there's a lever I haven't discovered yet to make the system a little more adaptive to conditions.

Regarding battery current, I'm using an eddy current sensor which measures battery current, however, I only use it for Arduino datalogging and SoC calculation. No connection to MNS CC.

You have to be careful when a retired geek starts playing with Arduinos, no limit to what can be done with these things 

I wonder if having the WB Jr installed changes the way the CC works?

Thanks Again!  Tim

[Vic]

Hi Vic,

Thanks for your quick response!

I've worked with adjusting both Absorb volts and Float volts, trying to get the Bulk MPPT to coast into floatat the right point. Unfortunately, the optimal adjustments for today, based on sunlight supply, user load, and starting SoC, will not be right if any of the conditions change  ...

   ...   I wonder if having the WB Jr installed changes the way the CC works?

Thanks Again!  Tim

The WbJr will need to mount onto a 50 mV, 500 A Shunt, that is in the negative battery lead.  This shunt probably exists in the Magnum DC panel.

The Classic CC can be told to use the Wb battery current to end Absorb (it is an OR function twix the Absorb timer, and the Wb reaching a setting [EA] that you choose),  SO,  YES, the Wb charge current measurement can change the end  of Absorb, based on time, OR the EA setting.

Wb Manual"
https://www.midnitesolar.com/pdfs/10-264-1_REV_F.pdf

Later,   Vic

[SunTim]

Hey Vic,

Thanks for the eye opener!

I was aware of the WB Jr, but had no idea it was a needed add-on for reliable LiFePo4 charging. I already had plans for battery current and SoC tracking so I did not consider the WB Jr.

I bought all of the major equipment from altE last year and was provided a 'whitepaper' describing how the Classic would work with the KiloVault LiFePo4 battery set. I may be missing something but I never understood that this additional device would be needed for charging.

whitepaper attached

I'll need to do some studying to figure out what to do next. Ideally, I'd like to use my controller to tell Classic when to go to float, have no idea whether or not that's feasible.

Thanks Vic, you've helped me a lot already!

[ClassicCrazy]

Tim,
Did you tweak the voltage your batteries are at with the voltage the Classic is seeing ?
You want to do this for the high charge point ( Absorb Voltage ) .
Do your Kilovault batteries have the built in bluetooth and do you use their app to monitor the voltage and also the SOC ( if it shows that ) ?
You have a couple of things to consider.
One is the batteries built in BMS . It may have been programmed to cut off charging at certain voltages. I have heard that some lithium companies keep their top voltage lower so they don't get into balance issues. Not sure if Kilovault is one of them . If the cells have not been balanced at the top , then there could be some that are higher than others.
My friends have Kilovault batteries and the app for them does not show each individual cell voltage so it is tough to know what is going on exactly . Each of your batteries could also be a different voltage which of course will all add up to the total when you have them in series.
You can raise the absorb time if you want them to charge longer , or raise the absorb voltage too, though it may not do much if the bms is cutting off input at above a certain voltage.
Assuming you are going by the Kilovault settings you may just have to recalibrate your SOC to say it is 100% when the batteries reach the 55.4v you have in there.
You probably want to raise the Float voltage . The idea is that you want the controller to supply power to the loads as soon as possible after Absorb , but lithium battery manufacturers don't want you to keep charging in float. If you observe what is going on with your system , you can find that point and it is probably a higher voltage than 53.4v  . I have lithiums and have mine set to 54.6v . It takes awhile for lithium voltage to drop so between the time you are waiting from Absorb to Float you may see a resting period ( maybe reason for resting on the Classic will show 38) . In that time you using some of your stored power from the lithiums.
I agree with Vic that you need a shunt and Whizbang on your system to know much more of what is going on. That is the only way to know how much current is going into loads vs how much is going into batteries for charging. The Classic SOC calculations are very accurate .
Larry

[ClassicCrazy]

Hey Vic,

Thanks for the eye opener!

I was aware of the WB Jr, but had no idea it was a needed add-on for reliable LiFePo4 charging. I already had plans for battery current and SoC tracking so I did not consider the WB Jr.

I bought all of the major equipment from altE last year and was provided a 'whitepaper' describing how the Classic would work with the KiloVault LiFePo4 battery set. I may be missing something but I never understood that this additional device would be needed for charging.

whitepaper attached

I'll need to do some studying to figure out what to do next. Ideally, I'd like to use my controller to tell Classic when to go to float, have no idea whether or not that's feasible.

Thanks Vic, you've helped me a lot already!

According to the white paper you posted - you don't have your absorb voltage high enough.
Your white paper says 56.4v and you say you have your absorb set for 55.4v 
That would be one reason your batteries are maybe not filling up all the way.
Larry

[Vic]

Hi Tim, Larry,

I was hoping that Larry would reply, as he is much farther along in the LiPO, than I.

As I read it,  sometimes ReBulk (which can start another Bulk charge, based on battery voltage) has been used by some LiPO users to help get the charge results they are looking for.

Also, there is the Open Source Topic area on this Fourm that you might peruse.  Arduinos seem to have been kind of supplanted by the Raspberry Pis,  it seems to me,  here is a start, if you have not yet seen this:
http://midniteftp.com/forum/index.php?board=33.0

Later,  have Fun discovering all of the great functions that the Classics,  has as built-ins.  The Wb is a very inexpensive addition,  especially considering the additional info,  and control of the end of Absorb.

Later,  back to work, here,   Vic

[ClassicCrazy]

Hi Tim, Larry,

I was hoping that Larry would reply, as he is much farther along in the LiPO, than I.

As I read it,  sometimes ReBulk (which can start another Bulk charge, based on battery voltage) has been used by some LiPO users to help get the charge results they are looking for.

Also, there is the Open Source Topic area on this Fourm that you might peruse.  Arduinos seem to have been kind of supplanted by the Raspberry Pis,  it seems to me,  here is a start, if you have not yet seen this:
http://midniteftp.com/forum/index.php?board=33.0

Later,  have Fun discovering all of the great functions that the Classics,  has as built-ins.  The Wb is a very inexpensive addition,  especially considering the additional info,  and control of the end of Absorb.

Later,  back to work, here,   Vic

Vic - actually most of these batteries are LiFePO4  lithium iron phosphate
I think the designator LiPO ( lithium polymer I think ) usually refers to a different lithium chemistry ( and those are the ones more prone to catch on fire whereas LiFe are safer) .
Larry

[Vic]

Hi Larry,

Thanks for the correction.

Was trying to use more abbreviations, and forgot the correct one for LiFePO4.

This Laptop keyboard is flaking out, and the more that is typed, the more re-typing that is needed, as more, and more keys do not work reliably,  makes touch-typing difficult  ...

Thanks,  Glad that you chimed into this conversation.

73  Take care, Vic

[SunTim]

Hi Larry and Vic,

Tons of info thanks!!

**Larry Said...
Did you tweak the voltage your batteries are at with the voltage the Classic is seeing ?
You want to do this for the high charge point ( Absorb Voltage ) .

>> I have not done this yet. I have a 10V precision reference IC on order, should be here next week. Right now I see deviation between my DVM (12 year old Omega), The CC Voltage reading, and the Magnum Battery Voltage display. Typical deviations .1 to .2 volts. Once I get the reference I'll try to get everything trued up.


**Larry Said...
Do your KiloVault batteries have the built in Bluetooth and do you use their app to monitor the voltage and also the SOC ( if it shows that ) ?

>> Yes, they have a Bluetooth app which reports: SoC, terminal voltage, as well as the individual cell voltages. I used to check the individual cells but they were always within 10mV. Probably need to circle back on that one.


**Larry Said...
You have a couple of things to consider.
One is the batteries built in BMS . It may have been programmed to cut off charging at certain voltages. I have heard that some lithium companies keep their top voltage lower so they don't get into balance issues. Not sure if KiloVault is one of them . If the cells have not been balanced at the top , then there could be some that are higher than others.

>> I'll start keeping a closer eye on individual cells to verify there's not a problem there.
Also, I don't believe I've ever caught the KiloVaults interrupting charge current. I imagine this would be hard to miss and the CC would freak out.


**Larry Said...
You can raise the absorb time if you want them to charge longer , or raise the absorb voltage too, though it may not do much if the bms is cutting off input at above a certain voltage. Assuming you are going by the KiloVault settings you may just have to recalibrate your SOC to say it is 100% when the batteries reach the 55.4v you have in there.

>> I have tweaked the Absorb and Float Voltages in a .3 V range to try to get more consistent charging. As of now, I've put them back at recommended settings.


**Larry Said...
You probably want to raise the Float voltage . The idea is that you want the controller to supply power to the loads as soon as possible after Absorb , but lithium battery manufacturers don't want you to keep charging in float. If you observe what is going on with your system , you can find that point and it is probably a higher voltage than 53.4v  . I have lithiums and have mine set to 54.6v . It takes awhile for lithium voltage to drop so between the time you are waiting from Absorb to Float you may see a resting period ( maybe reason for resting on the Classic will show 38) . In that time you using some of your stored power from the lithiums.

>> Yes the float voltage has been interesting. altE Tech Support told me to set float at 53.4 rather than the 55.20 shown on the white paper. I believe he was concerned about not overcharging/damaging the KiloVaults. I have played around with float voltages, looks like 53.4-53.6 floats with no net amps through battery. More work needed here, though. My biggest challenge is that the settings which seem to work change day to day based on conditions.


**Larry Said...
I agree with Vic that you need a shunt and Whizbang on your system to know much more of what is going on. That is the only way to know how much current is going into loads vs how much is going into batteries for charging. The Classic SOC calculations are very accurate .

>> I'll look at the WB Jr but I have been quite happy with my homebrew SoC meter. The current measurement is surprisingly accurate and consistent. OTOH, If I have to add WB Jr to get proper charge management then I'll bite the bullet.

Also, I wonder if the Aux2 input which forces float would be of any use. Does it just switch the mode to float (good?) or does it hold it in float (bad?). I could easily trigger it with my device, but I don't want to jump the gun.


**Larry Said...
According to the white paper you posted - you don't have your absorb voltage high enough.
Your white paper says 56.4v and you say you have your absorb set for 55.4v That would be one reason your batteries are maybe not filling up all the way.

>> I had lowered it a couple days ago after the charge cycle overshot and blew past the float value and had to discharge for a while. I have been a little gun-shy on doing much with the Absorb settings. I've kept the time at the minumum as I was cautioned by altE tech support. He considered this essential to avoid damage to the batteries.
So I have not used absorb for any period above 3 minutes. I'm still trying to understand how this thing is supposed to work.
Let me try to state it in my words and please correct me as needed...
1) Sunrise, Bulk MPPT begins at a couple amps and builds to 70-80 amps if there is enough sun.
2) When voltage reaches Absorb voltage level, mode changes to Absorb but only for 3 minutes (I wonder if this short time has any appreciable effect on charge?)
3) When Absorb 'times out' we switch over to Float. It seems like the system does not often coast into float, its generelly too empty or too full at that point.
This seems like a very rough process which will only succeed when I'm lucky, hence constant tweaking Absorb & Float voltages. I'm chasing my tail.


**Vic Said...
Also, there is the Open Source Topic area on this Fourm that you might peruse.  Arduinos seem to have been kind of supplanted by the Raspberry Pis,  it seems to me,  here is a start, if you have not yet seen this:
http://midniteftp.com/forum/index.php?board=33.0

>> Vic, I'll definitely dig into this, thanks! Yup, the Raspberry is a more powerful device, but so far Arduinos have always given me the performance I needed.

Tim

[Vic]

Hi Tim,

Regarding Aux 2,  the WbJr needs to have Aux 2 comitted for its exclusive use, as Aux 2, can be used as an Analog input, whereas, Aux 1, is not able to do Analog.

FWIW,   Vic

[ClassicCrazy]

Hi Larry and Vic,

Tons of info thanks!!

**Larry Said...


>> I had lowered it a couple days ago after the charge cycle overshot and blew past the float value and had to discharge for a while. I have been a little gun-shy on doing much with the Absorb settings. I've kept the time at the minumum as I was cautioned by altE tech support. He considered this essential to avoid damage to the batteries.
So I have not used absorb for any period above 3 minutes. I'm still trying to understand how this thing is supposed to work.
Let me try to state it in my words and please correct me as needed...
1) Sunrise, Bulk MPPT begins at a couple amps and builds to 70-80 amps if there is enough sun.
2) When voltage reaches Absorb voltage level, mode changes to Absorb but only for 3 minutes (I wonder if this short time has any appreciable effect on charge?)
3) When Absorb 'times out' we switch over to Float. It seems like the system does not often coast into float, its generelly too empty or too full at that point.
This seems like a very rough process which will only succeed when I'm lucky, hence constant tweaking Absorb & Float voltages. I'm chasing my tail.

Tim

Tim, ]
Not sure I follow you.
Lithium stay at a pretty constant voltage while they are charging. It is only when they get in the 90% full range that the voltage on them starts to increase towards the Absorb setting.
Depending on bms the cells may also start balancing sometime in this range . I can see it in the software I have but doubt there is any balance indication in software you have.
So once the voltage gets to the 56.4 they call for , every cell will ( or should )  be 100% full.
So charging is done at that point ( unless a very low amount of current was being put in and balancing happening - the bms only has limited balancing current its resistors for each cell can handle.
On a lead acid battery the transition to float works right away . But on a lithium the top voltage may stay awhile ( depending on loads ) and during this time the Classic will show resting and won't go to float until the lithium battery voltage drops down to or below the Float voltage setting. 
So if you watch your meter and don't see any current going into the battery - you want to put the float voltage up higher than lower so that PV will supply the loads as soon as possible instead of batteries stored power.
The bms should protect your battery from any over voltages , over currents, under voltages.
This guy has a lot of videos with lots of info on all his testing using all kinds of bms .
There was one video he made where he explained what he learned watching the cells charge but I can't find that one now
Anyway take a look - he is always tinkering
https://www.youtube.com/c/OffGridGarageAustralia/videos

Larry

[SunTim]

Thanks for the response Larry.

I noticed that the charge profile I attached in first post seems to be chopped off, making it impossible see the voltage values.

I'm now attaching a pdf which will hopefully do better.

I will study your comments and the videos to see if I cant get a better handle on what's happening.

Thanks again for your help. Have a nice evening.

Tim

[SunTim]

I went out and measured some voltages...

To be continued...

Thanks, Tim