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

[SunTim]

** Larry said...

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

>> Thanks Larry, I hadn't visited the KB yet. Looks like lots of useful info. I can imagine that the current limit should make the charge process much more repeatable.

A question, I have not been able to figure out which Firmware rev I am running. Since my Classic is less than a year old, Id assume that my firmware is correct for the WB Jr, but I'd like to verify.


** littleharbor2 said...

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.

>> Hi littleharbor2, thanks for the info, I'll be doing several trials once I get the WB Jr current controller installed. I know that for right now, as I run at 56.4 V Absorb, I'll see charging current hitting 80 amps, about .4C. I'd be a little nervous about going beyond that.

Thanks All!

[Vic]

Hi Tim,

Regarding finding the FW Revs that the Classic is using;
From  the MNGP display, from the Main Status screen, press the small round, grey button on the left about six times, and you should find the Cl FW, MNGP, and,  IIRC, the Net FW versions.

From the Local Status APP, that runs on Win machines,  it is probably also available, under the Info selection ...  do not have a Classic available here, am in town.

Larry, thanks for the info on the bat charge current limiting info being on the Knowledge Base,  was using the Forum Search (from the top, Index page,  and the KB info, was generally not there,  probably because the subject name was not my search term ...  thanks.

FWIW,  Vic

[ClassicCrazy]

** Larry said...

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

>> Thanks Larry, I hadn't visited the KB yet. Looks like lots of useful info. I can imagine that the current limit should make the charge process much more repeatable.

A question, I have not been able to figure out which Firmware rev I am running. Since my Classic is less than a year old, Id assume that my firmware is correct for the WB Jr, but I'd like to verify.


** littleharbor2 said...

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.

>> Hi littleharbor2, thanks for the info, I'll be doing several trials once I get the WB Jr current controller installed. I know that for right now, as I run at 56.4 V Absorb, I'll see charging current hitting 80 amps, about .4C. I'd be a little nervous about going beyond that.

Thanks All!

You can see the firmware version number on the MNGP - one of the screens shows it
Are you using Local Status app ? It is good tool to backup and change your settings . Anyway it says version number on a screen on there too.
Your 56.4 should be okay .
I am glad you asked about the current limiting of the Classic because I had never used it before - but I did today and it is pretty much what I need.
I have some cells out of balance but when they are charging full current from PV voltage raises too high too fast and balancing won't work right.
So today when the batteries were showing close to 100% full I experimented by turning down current. It let the voltage rise much slower and I could watch when balancing started and nothing overshot too much.
My batteries are a bit different than yours - I have three 48v and they communicate with each other to keep the voltages of each battery close . The BMS will turn on or off current as needed to do this. So everything works much better with lower current - I started with 15 amps for all three but then lowered it to around 3 amps. I think there is a minimum that it won't go below even though the setting goes lower - maybe it is 5 amps ? Anyway I will need to experiment to find out how this works out.
By the way - when you get into the current limit - if you hold the top left button you can scroll through numbers faster - not sure if that is in the instructions or not. I just figured it out.
Larry 

[SunTim]

Thanks for the Firmware locations, I'll check it out.

BTW, is there a way to update firmware without putting Classic on line? Can I just download it to me PC then connect to Classic later and install?
I don't have wireless in the barn, I suppose I could wire up a router out there but I'd like to avoid that.

I'm attaching chart pdf from today's charge cycle...
>> Absorb 56.4V   Float 53.6V
>> No clouds today, charge current was steady at about 40A
>> Charge went from 72% to 100% (56 Ah) took about 1.5 hours, so the numbers work out pretty well.
>> Voltage not exactly what I expect, I'll feel better when I get all the voltages calibrated. USPS has my Standard Reference IC about 60 miles from me, so that means I might have it another week 

Downside is that the charge got jerked right to 100% SoC, I want to control that better.
I'd like to see it coast into about 90% SoC without the day to day variation.
I'm starting to understand that just tweaking voltages won't get me there.

This is getting fun! Tim

[ClassicCrazy]

Yes you can download firmware update and just do it from that download.
That is how I do it.
Just make sure you do both the classic update and the mngp update since they work together.
I have been thinking of getting a nice power supply that is programmable for constant voltage, constant current and will switch over automatically.
That would make getting the cells in my battery balanced much easier. Yeah you would think they might come balanced but that isn't the way things work when you don't spend the $$ .
Larry

[ClassicCrazy]

You will have to figure out how to get the individual cell data graphed - that would tell a lot.
Larry

[FNG]

It is also important to understand when a controller transitions from Absorb to Float it can not pull the battery voltage down so it has to back of or even go to resting until the voltage sags down to the float voltage. This is not an over shoot it is just how batteries work:

So if absorb is 56.4 and Float is 55 when the classic times out and goes to float it will make 0 amps until the battery drops to 55, This is not considered absorb still in the battery world as we are now discharging not charging.

Can you elaborate on "Blew past Float voltage" as the classic is very fast at regulation so this seems odd?

Ryan

[SunTim]

Good morning Ryan, Thanks for chiming in.

Glad you mentioned that concern as I was getting ready to discuss a related observation.

IR Drop is a consideration which has been associated with DC Motors forever, it is a voltage drop that exist 'inside' the motor.  The IR Drop is considered to be in series with another voltage which is called Counter EMF. The CEMF is a function of motor speed and field strength. So in a fixed field situation, the CEMF will be exactly proportional to speed. So, when you want to control the speed of a motor, controlling the armature voltage works poorly because the varying IR drop will cause the CEMF will not be constant and the motor speed will also vary. OTOH, a "CEMF Regulator" calculates IR drop and makes appropriate adjustments to the motor voltage, resulting in fairly constant speed over a range of loads.

OK, sorry for that side road, and apologies if I'm covering material that everyone already knows.

When I search for info about LiFePo4 IR drop concerns I find very little. Battery Internal Resistance is covered pretty frequently, which appears to be about 0.1 ohms. So, in my mind, battery IR drop must be considered for LiFePo4 batteries just as with DC motors.

Here's the reasoning...
Example:
56.4V Absorb for a battery with 0.1 Ohm Internal Resistance.
50 Amp charge current just before Absorb Voltage is reached.
At that time we are reading 56.4V

However, the actual voltage is 56.4 - IR Drop, or 56.4 - (50A x 0.1 ohm), or 56.4V - 5V, or 51.4 V.

So once the charge amps are stopped at end of Absorb, in this case, the voltage would immediately drop to 51.4 V.
If Float is set to say 53.6, then the battery voltage is shy and will be 'slowly' brought up by the float voltage.

I believe that a 'Correct" Absorb will have the battery voltage very close to the desired float voltage as soon as its done.

Practical Implications...
If you have a particular Absorb voltage set:
On a sunny (High charge amp) day, high current IR drop will cause the final voltage to be lower than expected.
On a cloudy (Low charge amp) day, low IR drop will cause the final voltage to be higher than expected.

Based on the above, there is no solid relationship between absorb voltage and SoC. For this reason, I believe folks opt for higher Absorb Voltage to be sure it can cover the range of IR Drop.

So I conclude that charging LiFePo4 batteries with no control of the charging current is a significant compromise.

When I get the WB Jr installed, I'll probably try to do a daily charge rate of 15 or 20 amps.

Interested in others thoughts on this. I'm a newby on these batteries so may be misunderstanding things. Also, I know nothing about Lead Acid batteries, so I have no comments on them.

Thanks, Tim

[ClassicCrazy]

Tim
The Classic was designed primarily for lead acid batteries.
When charging lead acid there is no lag between absorb and float. The absorb time for lead acid is hours , and once done the voltage on the battery will drop fast enough to go right to float.
So you kind of have to look at the Classic as being repurposed to use for Lithium.
Once you get to know your battery and what you want to do , you can certainly tweak all the settings to make it work pretty decently.
Of course there would be other features that would be nice to have for lithium and even if possible , those would have to be designed and tested with firmware revisions.
Where lead acid are very rugged and can take some abuse, lithium can not be abused . So they have a bms but every variation of bms  act a bit differently .
Anyway the Classic will do the job once tweaked for specifics.
Larry

[SunTim]

Hi Larry,

I hope my post didn't seem like a slam of the Classic 150, that was not my intention at all. I like the Classic, robust design and a lot of flexibility.

As you stated, one has to learn how to use that flexibility.  I think, once the WB Jr is in place, the Classic should do a fine job.

With all that said...
My reseller who helped me select the system did not have much to say about what types of challenges the charging would present.
I think it would be great if MN let their resellers know that the WB Jr is a very valuable and "recommended" add on for LiFePo4 clients.

Have a great day! Tim

[ClassicCrazy]

No I didn't think you were slamming the Classic.
They work pretty good and I haven't ever had a failure with mine in 10 years.
Larry

[boB]

SunTim said:
Downside is that the charge got jerked right to 100% SoC, I want to control that better.
I'd like to see it coast into about 90% SoC without the day to day variation.

The Classic with WB Jr. monitoring the actual battery current and SOC% calculation has a sanity check, "reset" to 100% SOC when it goes from Absorb to Float.   This is because the SOC% can be calculated without doing Absorb cycles, BUT it is assumed that when an Absorb cycle finishes, that the battery has been as fully charged as it can ever be.

That is why it goes to 100% at that time.  IF the Classic always seems to be going to 90% (ish) SOC% and then goes to 100% when going from Absorb to Float, then it is possible that the amp-hour efficiency in the Classic's WB-Jr. settings are set too low.   This is normally especially possible with lithium batteries.

boB

[ClassicCrazy]

I got the monitoring of one of my batteries working - thanks to Graham who has done all the ClassicDIY monitoring stuff.
I have esp32 plugged into battery which gets the individual cell data. I graphed that on Grafana and also added some data from the Classic so we know what is happening with that.
I had full current going into battery but then it clouded up - and I also went out and set current limiting on the Classic ( to charging ) to 30 which is 3 amps. I am not sure the Classic can reliably limit current this low but it is okay what I have observed . It keeps the current low enough so that the the battery bms can do its job.
I had figured out that the battery bms was set to balance at 3.5v  and I think 30mv differential between cells. I talked to Jakiper and they remote connected to my computer and then changed the balance threshold to 3.3v and 20 mv differential.  The bms will only start to balance cells when both those conditions are met. And the bms will only balance as voltage is rising - soon as it see zero current or a negative current the bms stops balancing. Anyway the imbalance I was seeing happened as the voltage neared 55.2v when battery was about 100% SOC.
The new monitoring lets me watch this now historically instead of having to sit in front of the computer watching it real time .
Here is the latest graph where you can see the cell voltages start to diverge as voltage comes up toward absorb setpoint.
Larry

[ClassicCrazy]

Here is the transition this morning to absorb voltage where you can see the cell voltages diverge. There was a 30 minute absorb time but the cells do not balance the whole time since the bms cuts off the current and balancing stops. Towards the end I raised the absorb voltage to 56v and you can see that rise on the graph. At the end it times out absorb and goes to float voltage of 54 but charge controller goes to resting( provides no current) until battery voltage drops to 54v . That is why it is showing negative current from battery to supply loads.

[boB]

Larry, so you have gotten an  ESP32 to work ?   

I have some of these but I hear from everybody that they do NOT work ?

I always wondered how they could sell so many of these if they did not work ?

boB