Not sure what is going on here, have you guys seen this in your setups?
I have 7 classic charging a single 48 volt battery bank.
5 x 150s (Soon to be 6)
2 x 250s
They seem to be changing modes together(Follow me), but a couple seem to drop in to Absorb charging 0-3W even thou the voltage has dropped below float and the PV panels are 75+ volts?
Really frustrating, I have a battery voltage of 47.8, and 5 classics are in bulk charging over 2K each trying to get back to ~48.5, but 2 CCs are at ~0-3W charge in Absorb no codes showing etc?
The current voltage is below EQ and Bulk, so why do two of them drop out?
(http://randalboydllc.com/Pix/Absorb1.png)
Just for grins I tried hit EQ on one of the low controllers and it took off charging 2400+ watts for a minute or two then it drops back to Absorb 0-4 watts?
Every once in a while it will start charging then drop back down.
** I have previously adjusted the voltage offset get the displayed voltage with in +- 0.1 while resting.
All 7 wired for follow me and set to:
Solar = ON
Absorb 48.7 (2hr) I have tried changing this to 4 hrs no change.
EQ = 49.2
Re-Bulk = 48.4 (Used to be lower but raised it trying to jump start the lagging controllers)
Days between = 0
Float 48.6
insomnia = off
LoMax on/Reset Night AH on/
Follow Me = on
Follow Master Battery on (except the on with a sensor)
It would be nice to see a graph of all those together to see if the two that dropped out got to absorb voltage earlier.
I don't remember if they did that in Follow Me if they should have gone to Float or if they wait for the master controller to do that.
There are two ways to set up Follow Me and one method you don't bring the final wire back to the master. It is explained in Midnite Knowledge base.
I would also check to make sure Ending Amps didn't get turned on those two somehow ?
Look at the Master / Slave topic and any others on Follow Me
https://www.midniteftp.com/support/kb/faq.php?cid=1
Larry
1. What graph(s) are you referring to? (Built in or custom?)
* I do limited data collection already via Modbus data I pull for may web info and store it to a CSV file.
CC Name / current Time/ Battery Voltage/ Fet Temp / etc.
** Don't recall mode being on of the items but I can probably add that if I don't have it...
2. I have not heard of leaving the Follow me loop open, not sure the advantage etc?
3. As far as getting to voltage 1st, they are all wired to the same bus bars, so not sure that is possible?
** If I have the mode data in my files I will try to put together a graph.
Today I saw the 1st one switch at 47.7 well short of Absorb or even float voltage.
It switched to Absorb 4watts while every other was still in bulk 2K plus...
See Images.
Yeah I was meaning making custom graphs.
Do you use Home Assistant ? It can grab the modbus data directly now.
I have only used Grafana to make graphs using mqtt data - mainly for my batteries but would probably work for morn than one Classic.
Are you using Lithium batteries ? Doesn't seem like it with those voltages .
I know that the Classic will sometimes go to Absorb too early when on lithium batteries.
Larry
Gotcha I will try to whip up a graphing tool later this week. (Time permitting)
And actually it is a LI battery bank, made up of Tesla Model S 24 Volts modules.
I am targeting 3.55 to 4.05 per cell in my S12 configuration.
S12 * 4.05 = 48.6
On the low side my transfer switch, transfers to shore power at ~ 42.5
side note I had one controller drop to Absorb early again, so I turned off follow me on that controller and it started charging... kinda scetchy...
There are some other discussions in the forums here about how the Classic will sometimes go to absorb early when charging lithium. I have had it happen with mine. I think what I did was tweak the settings to make it work like I wanted it to.
boB had started working on a firmware update to address that and made the regulation tighter. It worked pretty good but there was some bug in the firmware that caused the SOC to quit working right and only show 0% SOC. He never did find out exactly why and sadly boB isn't with us any more. I used the new firmware for a long time and never had the 0% Soc - for a long time until if suddenly happened. I think it may have been tied to the time somehow.
But I wonder if you have all those Classics in Follow Me and they follow the master - if that would matter ?
Anyway do a search on the forums if you want more info. For some reason when doing searches on forums you need to be on the forum home page or search doesn't work right.
Larry
Also if you haven't seen it here are some good Classic monitoring options that Graham developed. https://github.com/ClassicDIY
Crazy - Thanks for the info.
BTW. I wrote my own monitoring software with VB .net and open Modbus a few years back.
I read about 43 values from all the controllers and and parse it for display and logging.
Oh I forgot to mention! I turned off the "Follow me" feature off on the offending controllers and most of them behave much better now. (Charge a lot more often etc.)
** Not the way I want it setup but it works for the moment...
Now I am getting an RFR 38
** High external battery voltage relative to float value (I think anyway) on one controller.
Always the same classic 150, and about the same time of day.
Once I get the error, there is no more charging off that controller till sunset or the next day.
Really weird only one controller of 8 does it.
I tried raising the float value etc but still same issue.
F.Y.I.
I track the battery voltage reported from each controller every 2 min across the day and none of the values exceeded the float value in question. Actually the battery bank peaked out ~.3 volts below my float target...
** I track the PV and Battery voltages so I can display low and high battery & PV voltages on my display.
As previously mentioned I should probably add "Current Mode" in the data I collect and display on the web.
Maybe as a text color etc...
Electrical noise?
Or an bug in that classic??
The way I understand the RFR 38 code is when something else has the voltage up higher than the settings on that Classic.
So if ( and I do ) have different controllers on the same batteries. If the other controllers are higher voltage , the the Classic would go to the 38 code and quit charging .
I think I explained that correctly. For example if there is a generator on charging the batteries via an inverter charger and it is pushing in more power and raising the voltage , then the Classic won't charge and go to resting with the 38 code.
Larry
Just a quick thought, as I don't own a classic and not very familiar with them. Is it possible that the misbehaving classics need to have their voltage offset. Thinking of either a corroded connection or somehow it lost calibration. I can't point you through the menu, but I believe the voltage can be tweaked.
Good luck,
Ed
@UpNorthMan
I thought similar. (Voltage offset)
But I have adjusted them a few nights ago, and and re-verified them last night.
I do it at night so the voltages are more stable, and the charger controller output is not contributing to the reading...
@Crazy I think you have that correct about error 38.
But I only have the classics, no generator etc.
And my Inverters have charging disabled not to mention I track the voltage
based on the feed back from the charge controllers.
My data does not paste in here real easy but I here is an example on what I see when it switches to Absorb.
(Prior to 38 code...)
This is the minute charger 5 changed to Absorb still charging.
Then a few minutes later no charging. It will do this a while then rest with RFR 38...
FYI my Absorb is 49 ATM and float is 48.7 so we are not even charged yet and it changed to Absorb...
** Note the high battery value 45.x I track peak battery voltages etc..
MC5 Time = 603 (Min of the day )
Voltage_5 = 45.5
AmpsIn_5 = 23.6 (From PV)
AmpsOut_5 = 31 (To Battery Rail)
Watts_5 = 1410 (Current charging @ ) ** The other 6 are over 2000 watts ATM and this one is dropping)
Fet_Temp_5 = 50
PV_Voltage_5 = 61.6
High_Bat = 45.4
Classic_5_Charge_State -> 4 (The other six are a 3)
Battery_5_Charge_State-> 4
Side note Here is all 7 controllers Charge status at that time:
Classic_1_Charge_State 3
Classic_2_Charge_State 3
Classic_3_Charge_State 3
Classic_4_Charge_State 3
Classic_5_Charge_State 4
Classic_6_Charge_State 3
Classic_7_Charge_State 3
---------
Then a few min later: it dropped to 500 watts with the other controllers @ 2500-3800 watts each..
ugggg
Just for grins I forced EQ at 49 and it took off charging 2300+ watts. so there is pv power to get...
I will follow up once I get an RFR 38...
Quote from: Randaltb on June 19, 2025, 05:41:46 PM@UpNorthMan
I thought similar. (Voltage offset)
But I have adjusted them a few nights ago, and and re-verified them last night.
I do it at night so the voltages are more stable, and the charger controller output is not contributing to the reading...
Actually you want to adjust the offset when they have the largest current on them because that is when the cable would have the most voltage drop. With no current there won't be much voltage drop at all. Use a multimeter on the battery terminals or look at bms voltage , and then compare to the voltage on the terminals in the Classic . Or on the MNGP it should show the voltage in the offset section of what the Classic is reading.
Larry
@UpNorthMan Thanks for the info.
I previously tried that (configuring off sets while under load/heavy charging)
But due to the weird issues I went to doing it an night / no load as an alternate/more stable way to do it. (Basically a sanity check)
** Also not much voltage drop due to large gauge fine strand welding cables. :)
Both ways of setting the offset seem to have similar behavior overall.
A. Two of the CC drop out to absorb early (Same ones each time 1 and 5)
B. #1 will drop to float and shut down charging error 38 (High external voltage)
Just #1...
** I track the voltages and never see it get out of range...
So it either does not get out of range or is is a short spike I miss while tracking?
And since all 7 are connected top the same bus bars on the same batter bank, why one one?
LOL
I just checked my system and #1 has dropped to Absorb early no charging again..
Fet temps are fine, and absorb voltage is 48.6ish (Never got there)
Bank 1 Voltage : 47.8
CS: 3 BS: 3 -> Watts-1 : 0
CS: 4 BS: 3 -> Watts-2 : 2933
CS: 4 BS: 3 -> Watts-3 : 2947
CS: 4 BS: 3 -> Watts-4 : 2682
CS: 4 BS: 3 -> Watts-5 : 1486
CS: 4 BS: 3 -> Watts-6 : 2415
CS: 4 BS: 3 -> Watts-7 : 3785
** And if I force EQ it will jump back up to 2000+...
Yep I selected EQ and it went to 2500 for a minute or two then back to Absorb no charging then float no charging...
I have an observation.
Battery Temp is shutting me down. :o
I unplugged the temp sensor and the 150 classic in question started charging again.
When I plugged it back in the classic stopped charging.
* sensor shows ~34C ~(93F)
** Batteries are not really that hot but the room gets warm along the wall..
Even if they did get that warm, these are Tesla modules and that temp is not a big deal.
I have relocated the temp sensor away from the hot exterior wall in the room and it is now charging again.
I understand the CC will/can throttle down due to high battery temp, but full stop with no warning or error seems wrong?
An hour later...
Moving the temp sensor seems to have helped Classic #1, but I still had to turn "Follow Me" off on two controllers so it is not solely temp related...
Also very odd it did not shut down the other 6 charge controllers?
They are all wired and configured with "Follow Me" Following the Master Battery sensor and kept on charging...
Can I adjust the temperature related shutdown?
I don't want it to shut down every time the sun hits the wall or the steel building.
I am in AZ it gets a bit warm here...
Next Day update.
Yesterday after moving the temp sensor it charged until ~sunset.
But this morning the #1 CC was in CS: Bulk BS: MPPT but not charging again with the other 6 charge controllers over 2500W ea.
I turned off insomnia on CC #1 and it started charging again...
* Is there a know issue with insomnia mode?
what do you have the temperature compensation set for ?
Larry