My absorb voltage is too low compared to my set value with temp compensation off

[Taos]

I've recently upgraded my battery bank to lithium and lithium batteries don't need temp compensation voltage setting , so I disabled the compensation on the classic and it shows this in the setting  however I noticed my classic 150 controller goes to absorb from bulk  at a lower then programmed voltage setting .( aprox .5 volts )I didn't check if this is the same for float voltage ,  I've also have the Wiz bang junior shunt set to classic as I don't have info on what amperage batteries should go to float when there fully charged and temp for batteries set by default set to 25 c as I'm not sure on what temp these lithium batteries are supposed to be set . So just left it on default for regular fla batteries. I'm also running firmware 2245and mngp 2197, not sure if this is a software issue or if when wiz bang junior is set to classic it has some default temp .
Thanks in advance

[ClassicCrazy]

Yeah the Classic does that with lithium batteries.
You just have to try and do some trial and error with the different absorb voltages until you find one that works for what you want to achieve.
Also note that with lithiums the voltage compensation for the cables is important to calibrate. You need to do that at the highest charge voltage . It will be different at the float voltage so that again you need to do some trial and error and check everything with volt meter until you get the settings in the Classic doing what you want them to do in real life.
You should not need to use end amps with the lithium batteries and won't use any temperature compensation for charging.
What kind of batteries do you have and what Absorb, Absorb Time, and Float  are you using ?
Larry

[Taos]

Thanks Larry!
I have 16 12volt Aolithium 4s batteries ,4in series and 4 in parallel , with identical length 2/0 cables connected to buss bars , they all have Bluetooth modules so it's easy to see all the battery cells info , I've tried a few settings I'm getting closer to what I want in settings ,classic is set to absorbs 55.0 volts and time set to 1.5 hrs , float set to 53.8 volts , rebulk 53.7 volts shunt set to classic no temp compensation , I have my aux 2 setting for diversion load through a digital a.c. relay ( water heater lower element ) set to start at -.4volts below absorb and float voltages and to turn off at  -.6volts ,,I didn't like these setting originally as I was thinking I wanted my batteries full charged as this is what fla batteries should be ,but lithiums are very different and couldn't adjust the diversion load setting to shut off the diversion load quickly to prevent discharging the batteries ,as lithiums then to have very little voltage fluctuations in voltages to state of charge then started to think lithium batteries don't like to be full charged for a long time and not being used as I'm off grid during the day and on grid at 7 pm so it's better if I discharge the lithiums a bit before they sit all night , I've also adjusted ( calibrated ) my p.v. And voltage in the classic using a fluke 88 multimeter , you mentioned something about the cable's compensation ,is this what your talking about , but I should do it when I'm getting high output from the panels .
Thanks Don

[boB]

Yeah, with the regular Classic software, there is that 1/2 volt hysteresis where the Absorb voltage can be lower than your set-point.  It should at least start out at your set-point voltage and not move around that much.  Less than 0.5 volts.

BUT newer firmware/software is being tested and worked on that reduces this hysteresis to much closer to set-point voltage.

Larry (Classic Crazy) tried this as beta software and encountered some problem so it's back to working on it.

Larry, others at MidNite have been playing with that and things are OK but a couple of glitches to fix yet.  Getting Close !

Watch again here for new Classic firmware to help this problem, Taos !

boB

[Taos]

Thanks Bob !  I thought I had everything set properly and was wondering if I missed something ,,, today was a cold cloudy day here and I kept checking on the charge controller to see at what voltage it went to absorb ,caught it ! It was  . 5 volts lower than my setting.
Thanks again everyone I will be waiting on a firmware update 👍🏻

[ClassicCrazy]

Thanks Bob !  I thought I had everything set properly and was wondering if I missed something ,,, today was a cold cloudy day here and I kept checking on the charge controller to see at what voltage it went to absorb ,caught it ! It was  . 5 volts lower than my setting.

Thanks again everyone I will be waiting on a firmware update 👍🏻

Yes I meant what you did - use the voltage offset for the battery cables when the batteries are at their highest voltage - absorb. Of course when you do this the voltage may be off for where you want it in Float so  you would have to just figure out what is the right Float voltage setting to compensate for this.
I think you should consider getting a Whizbang to know your SOC when you have that many lithium batteries. The batteries bms may show an SOC but I have found those can not be so accurate. The Classic Whizbang SOC has always been more trust worthy for my setup. My batteries bms shown SOC gets off if they don't charge all the way up and just get partial charge for a few days.

I will look forward to trying the new updated firmware for the Classic
Larry

[Taos]

Ok thanks Larry , I will calibrate the classic today while there's lots of power in absorb  ( makes sense voltage drop ),yesterday was a cloudy day , oh and I do have a wizbang junior to monitor soc ,I also try and charge to lower voltages per cell 3.45 with absorb to let balancer do its job , also looking forward to new firmware ! Thanks Larry and Bob 👍🏻

[boB]

I found that this newer firmware revision that Larry has already tried has this problem.

I found an error in the TWEAKS aspect of Vbatt Offset.

But the released versions for the Classic do not have this problem as I remember.

Taos, I think your problem relates to the older Lead Acid operation which is not as tight as the newer software is supposed to be when set to Lithium battery mode.

Newer SW/FW coming soon !

boB

[Taos]

The other thing I ran into is my waste not function for my diversion load ( water heater ) it worked great with my agm batteries but with lithium it's a whole different ball game ,as I'm learning lithium batteries voltage don't vary as much as lead acid due to state of charge , and for me I can get around the voltage limits in diversion settings , as I don't run my system 100% off grid only during the day ,so during last daylight hours normally you want your lead acid batteries fully charged , but lithiums normally you want them 90% or less  charged if sitting for a bit  , not good for them to be fully charged for any longer time ,( from what I know ) I could be wrong ,,, it would be nice for the waste not voltage settings to be more variable for different diversion loads to be tailored  to many individual different requirements , I'm no engineer but think voltage can't really be used for waste not function when using lithium batteries but maybe using amp hours and percentage of battery state of charge for lithiums setting would be better to turn on diversion load and off .  Not sure if that's possible .

[Taos]

A other thing I noticed is the classic will go from bulk to absorb before it hits my programmed voltage setting I setup, (not sure on float setting, I dint wait to watch it  ) ,I've even tried several times to make sure I hit enter , and watched for the classic to acknowledge my settings , I've even had my fluke 88 on while watching the classic go from bulk to absorb ,, maybe I will need to use my fluke 98 ossiloscope as I know some multimeters are slow to respond and maybe I missed it , and the fluke 98 can record the data to review just incase it went so fast from bulk to absorb and couldn't see it on the classics display or the fluke 88 multimeter , funny as it was at least .5 volt away from my absorb settings ,, always learning ! I find it interesting !

[boB]

Taos, correct on the 0.5 V below setting not being great for Lithium.   That was meant for lead acid of course which is OK to do.

Was trying to correct that on the latest firmware which should be available after some more testing and a bit more work.
It has a lithium setting choice that sets that hysteresis voltage to be less.   0.2 volts I think it is.

It will have to be able to run with a small voltage difference but not 1/2 volt.

Would be interested in your scope capture.  Real slow sweep (data logging basically) but with a fast (peak) to be able to catch it if it goes there for a very short time.

boB

[Taos]

I will see what I can do boB ,lately the weather has been poor haven't seen the charge controller leave bulk mode .
 Update still no sun going on 6 th day still in bulk mode batteries 51%state of charge .
Don

[australsolarier]

just wondering when that new firmware is available. i have the same problems. (minor problems that is)

[boB]

just wondering when that new firmware is available. i have the same problems. (minor problems that is)

It is LATE, I will say that !

Good to know it will also help you.

boB