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

[ClassicCrazy]

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

How are you calculating SOC ?
I don't understand - according to your graph you only got a bit over 55 v . If that is what you have the absorb set for that is too low.
MyMidnite is capable of graphing all the data also - though without a Whizbang it won't show the system amps ( what is actually going into the batteries) .
But it will show the classic charging state.
With the MyMidnite graph you can choose which data you want to show on the graph , and then drag your mouse across it to show the data at any particular time.
Maybe you can do that with yours.
But I don't understand how the voltage on your batteries would jump up so high if their SOC is so low.
I will have to look at your schematic again.
Larry

[ClassicCrazy]

Where on your wiring is the current sensor located ?
With a whizbang - the shunt would be located on the negative wire between the battery and all the other  negatives.
There would only be one connection from battery to one side of the shunt. Every other negative in the system would be on the other side of the shunt .
That way it can tell exactly what is going into and out of the battery .
It counts the SOC down as the power is drawn out , and counts it back up as the power goes in. None of the power going to a load directly from the charge controller will be going through the shunt.
Does your bms data show the amount of current charging or discharging  in each battery ?
Larry

[ClassicCrazy]

good luck figuring out the best charging practices for lifepo4 batteries.
The forum topic linked below seems to have been 2 years of numerous people debating how to interpret everything with voltage and current
https://diysolarforum.com/threads/lifepo4-voltage-chart.3156/
The Australian garage guy video I watched he said he couldn't tell by voltage and had to watch the current to truly tell for each cell.
I will try to find that video.
Seems to be too much info and a lot of depends on bms or amount of charge or discharge going on or if cells are at a rest for awhile.
Larry

[boB]

Hi Tim.

So, as far as the Classic not outputting any current to the battery for a while after Absorb, that is OK since the battery voltage is above the Float set point.

There is no place for the power to go at that time.  Not until the battery voltage drops below the float voltage.  If your system had a larger load on it, then that voltage should drop faster.  No need for that though.

If, in Bulk, you think there is not enough power going out, please take note on the PV input voltage at that time and also the Voc of the array.  The open circuit voltage.  With no partial shading on the PV array, that MPPT voltage  (Vmp) will be somewhere around 80% of Voc.

For Absorb and Float, it could be almost anywhere above the Vmp all the way up to the Voc.

If you have the Absorb time set to 3 minutes and it does NOT do any Absorb, try either changing the ending amps to zero (disabled)  or raising the 3 minute time to, say, 10 minutes and see if it Absorbs.    Last I checked, Absorb should work fine at 3 minutes.

Lettuce know what you find 

boB

[dapdan]

**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.

I really think the main reason why you are at 75% is that you are under charging your batteries (due to the 55.4V absorp setting). You mentioned  that the voltage shoot pass the float voltage, which is 2V less than what you set the absorb voltage at. Did it shoot pass the absorp voltage of 55.4 that you have set.

In my view it is either you trust the midnite CC to curtail charging at or around 55.4V or you dont. Even if you dont trust the CC the BMS in the battery should open the circuit and automatically stop receiving charge from the CC. Either way my advice would be to set the Absorp voltage as the white paper suggest, 56.4V, and trust that the CC and the BMS will protect the battery from over charge.

When you set the voltage so low in Lithium it has a benefit of extending the life cycle of the batteries tho so the system will still work. It is whether or not you are storing enough capacity for loads you wish to maintain. you can stay at 55.4V/75%, but may have to increase capacity by installing more batteries if your loads are not being maintained.

I must also add that you have a lot of charging and a relatively small bank. As a comparison I currently have 5.8kW of panels charging a 25.5kwh Lithium bank. I have it programme to only charge up to 85-90% of capacity to extend the life of the bank. I had to offset the reduction of capacity, as a result of under charging, by increasing the battery bank size because I have prioritized cycle life.

Hope this helps.

Damani

PS

I should also add that the kilovaults seems to be on the very low side of trypical LifePO recommended absorp voltages. If you research and read enough on this topic you will discover that most absorp voltage for this chemistry sits around 3.60-3.65V, so even going with the lowest at 16cells that would be 57.6V vs 56.4V for the kilovaults. this suggest that they have been very conservative in their design and probably did this so that they could reach the desired 7yr warranty without any issues(sorta like what the auto manufacturers are doing with their warranties on electric vehicle battery banks, where they warranty for 10yr and dont let the bank be charged at more than 80% hence ensuring that they meet the desired 10yr lifecycle). The result is that decommissioned e-vehicle batteries still have alot of life left in them even after service life, as evidenced by the very robust, popular and in high demand 2nd life EV lithium batteries that have flooded the market in the past 5 to 7yrs.

[SunTim]

Thanks for all the help so far.

I found two videos at Off-Grid Garage which were very helpful...

LiFePO4 charging and discharging curve explained. How far to go?
https://www.youtube.com/watch?v=uNFIkNtsd1c
Takeaways:
1) Absorption Setpoints: 3.45 >> 55.2
2) Float Range: 3.35-3.375 >>  53.6-54.0


Finding 20% and 80% SOC with LiFePO4. Why charging current and charging speed matters!
https://www.youtube.com/watch?v=qZg4Jxftw-c
Takeaways:
1) The achieved SoC at the reaching of Absorption varies greatly based on how much charge current is involved.
2) This problem can be reduced by using the optimal absorb voltage (somewhere around 3.45V)
3) Since CC does not actually regulate the charge current during the Bulk MPPT phase, this variation is not going away. It needs to be compensated by adjusting the Absorb time

So, here's where I am...
1) I ordered the WB Jr last night. I now understand that you can't know when to end absorption cycle unless you monitor Absorb Current.
2) Until I get this installed I'll return to Midnite Solar / KiloVault recommendations while holding the absorb time to the 3 minute minimum. While this doesn't give good charge consistency, it is conservative and battery friendly.


Thanks, Tim

[SunTim]

** Larry Said...

How are you calculating SOC ?

>>  I measure battery voltage and current using a non contact 200A Hall Effect Current Sensor (LEM HASS 200-S)
The sensor is located in the jumper between two of the batteries so it is insured to capture true battery current flow.
SoC is derived by measuring and totalizing Ah in and out.
I routinely check my SoC against that reported by the KiloVault app, they track pretty well.


** Larry Said...

I don't understand - according to your graph you only got a bit over 55 v . If that is what you have the absorb set for that is too low.
MyMidnite is capable of graphing all the data also - though without a Whizbang it won't show the system amps ( what is actually going into the batteries) .

>> Whizbang on order now, I considered triggering float using my current measurement and the AUX2 input but didn't want to deviate from standard CC operating modes.



** Larry Said...

Does your bms data show the amount of current charging or discharging  in each battery ?

>> The KiloVault app indicates battery current in real time, that data seems to be in agreement with what I measure in the battery circuit.




** boB Said...

So, as far as the Classic not outputting any current to the battery for a while after Absorb, that is OK since the battery voltage is above the Float set point.
There is no place for the power to go at that time.  Not until the battery voltage drops below the float voltage.  If your system had a larger load on it, then that voltage should drop faster.  No need for that though.

>> Hey Bob, thanks for joining in. This makes sense, but if the voltage is higher than it ought to be then I already did something wrong.


** boB Said...

If you have the Absorb time set to 3 minutes and it does NOT do any Absorb, try either changing the ending amps to zero (disabled)  or raising the 3 minute time to, say, 10 minutes and see if it Absorbs.    Last I checked, Absorb should work fine at 3 minutes.

>> That's interesting, implies that the battery should already be nearly fully charged before it enters Absorb. So I've got a dumb question...
Why Absorb at all, why not just jump to float as soon as the correct Absorb voltage is sensed?




** Damani Said...

I really think the main reason why you are at 75% is that you are under charging your batteries (due to the 55.4V absorp setting). You mentioned  that the voltage shoot pass the float voltage, which is 2V less than what you set the absorb voltage at. Did it shoot pass the absorp voltage of 55.4 that you have set.
In my view it is either you trust the midnite CC to curtail charging at or around 55.4V or you dont. Even if you dont trust the CC the BMS in the battery should open the circuit and automatically stop receiving charge from the CC. Either way my advice would be to set the Absorp voltage as the white paper suggest, 56.4V, and trust that the CC and the BMS will protect the battery from over charge.
When you set the voltage so low in Lithium it has a benefit of extending the life cycle of the batteries tho so the system will still work. It is whether or not you are storing enough capacity for loads you wish to maintain. you can stay at 55.4V/75%, but may have to increase capacity by installing more batteries if your loads are not being maintained.

I must also add that you have a lot of charging and a relatively small bank. As a comparison I currently have 5.8kW of panels charging a 25.5kwh Lithium bank. I have it programme to only charge up to 85-90% of capacity to extend the life of the bank. I had to offset the reduction of capacity, as a result of under charging, by increasing the battery bank size because I have prioritized cycle life.


>> Hi Dasani, thanks for responding. I think your right that I had set the Absorb voltage too low. I was trying to avoid what I thought was overshooting of voltage prior to going into float. I'm learning.

Up til now my goal was to try and get the batteries above about 90% SoC by end of each day. My rationale is that if I fail to keep the batteries near full then I could be caught short if / when I need them for backup during outage.

When you refer to "programme to only charge up to 85-90% of capacity to extend the life of the bank" can you tell me how you accomplish that? That's what I'd like to be doing, I just haven't figured out how to get there.


** Damani Said...

I should also add that the kilovaults seems to be on the very low side of trypical LifePO recommended absorp voltages. If you research and read enough on this topic you will discover that most absorp voltage for this chemistry sits around 3.60-3.65V, so even going with the lowest at 16cells that would be 57.6V vs 56.4V for the kilovaults. this suggest that they have been very conservative in their design and probably did this so that they could reach the desired 7yr warranty without any issues(sorta like what the auto manufacturers are doing with their warranties on electric vehicle battery banks, where they warranty for 10yr and dont let the bank be charged at more than 80% hence ensuring that they meet the desired 10yr lifecycle). The result is that decommissioned e-vehicle batteries still have alot of life left in them even after service life, as evidenced by the very robust, popular and in high demand 2nd life EV lithium batteries that have flooded the market in the past 5 to 7yrs.

>> I completely agree that KiloVault would like me to baby the battery, that makes good sense. OTOH, I am being careful not to do anything reckless that could affect battery life.

Thanks for all the help!!
Tim

[SunTim]

Here's a little additional info...

Updated Schematic including Battery Monitor

A few photos

Have a great day! Tim

[dapdan]

Tim,

When you refer to "programme to only charge up to 85-90% of capacity to extend the life of the bank" can you tell me how you accomplish that? That's what I'd like to be doing, I just haven't figured out how to get there.

I am using 2nd life lithium ion (nmc) and using 4v per cell (translate to 32V for a 24V or 8cell system) and programmed the midnite CC accordingly (i.e. absorp set to 32V for 10mins and float set at 31.6V, so that the PV and CC are carrying the loads of the house up until resting). So the end effect is that the system voltage at the end of the charging day is as close to 32V as possible and discharges down to about 29V which is approximately opperating between 85/80% down to about 35% ideally to at least get a doubling of life cycle.

Review the below link at battery university. it is such a good resource to learn about all types of batteries. It is a highly recommended read.

https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

Damani

[ClassicCrazy]

Tim,
It is possible to program the Classic to limit just the charging current to the battery while leaving it also capable of providing full current to any loads.
That probably wouldn't benefit you though.
Larry

[SunTim]

Thanks Damani,
It appears that there is a pretty severe life-cycle penalty for hot-rodding these batteries, I had read that but hadn't looked at test data.
A question... The article refers to Li-Ion batteries rather than LiFePo4, I wonder how similar they are from the life cycle point of view?

Hey Larry,
To accomplish the limiting of battery current, does the WB Jr needs to be in place?
I had seen the limit parameters for input and output amps, but it didn't seem very useful if it doesn't differentiate between inverter and battery juice. It would certainly help protect the CC or PVs, but not much else.
I first balked at having to add the WB Jr, but I'm warming up to the idea. 

Thanks for the help, the knowledge found on this forum is a great asset!

Tim

[Vic]

Hi Tim,  I am not Larry,

But, because the MidNite Classic CCs are the by far most versatile on this planet,  there is a function that will Limit battery charge current, and still supply loads (up to the total available available from the input to the Classic.  Think that Larry alluded to this.

Had a bit of trouble finding the White Paper on it, but, this is, at least an early version of the paper,  attached.

The WbJr is the mechanism that allows the Classic to work this magic,  let's see if this works.

Later, Vic

[SunTim]

Thank You Vic,

Its now in my file folder waiting for the new toy to arrive.

Seems like the WB Jr will allow a lot of additional capability.

I had noticed, in my equipment search last year, that there were very few CC that incorporated a Battery Monitor. Perhaps that's due to the way that the LiFePo4 technology arrived and turned the tables.

I think I remember seeing a Chinese label, maybe HiWatt? that incorporates CC, Inverter, and Battery Monitor in one unit. However, I was scared of committing to equipment where user support might be a problem.

Thanks! Tim

[ClassicCrazy]

The current limiting info is also in the Knowledge Base along with a lot of other info you might be interested in
http://www.midniteftp.com/support/kb/faq.php?cid=1
Larry

[littleharbor2]

If it were me I'd raise the charging setpoints. Your absorb setpoint is netting you 3.462 Vpc.(volts per cell). I tried using conservative setpoints early in my LiFePo4 battery life. I found without getting a full charge I was ending up with a pretty low Soc. in the morning. Raised my setpoint closer to 3.65 Vpc = 58.4 and corrected that problem.