question

Hi @Dave

Given you haven't mentioned the 'Tail' setting in the mppt, this is possibly your issue. Not the same as Tail in the BMV, the mppt's will drop Absorb target to Float when Abs V is reached and Current drops below Tail for x minutes. And with DVCC it will be using Current from the BMV rather than the mppt's own.

You can remove it if you don't want it to override your Adaptive or Fixed settings. I think it's a great feature though, use it myself.

Just be careful that passing cloud and the sluggishness of pb's reaction of V to changing I doesn't cause a false trigger.

Thanks for the reply. I have tail percentage in the bmv set to %2 per the rolls battery experts advice. In the two mppts I have tail current set to the highest setting of 10 amps because that the highest it will take despite my battery bank of 1518 AH needing a tail current of 30 amps. At least now I know that when dvcc is used the bmv takes over with its tail current value. I had spent hours trying to find online! I have it set to wait 5 minutes. Today there were zero clouds. And the mppts would go from bulk straight to float in a matter of hundreds of milliseconds, the orange absorb led would just blink. And again when testing my gravities the batteries were NOT fully charged… they were in the 1.230 to 1.240 range, mostly hovering in the 1.23x’s. I never have a hard time getting them up into the 1.26x range when a full absorb is allowed to happen. Ran my generator they the Quattro for several hours and it knew to absorb. This is an all of a sudden problem. Any suggestions ?

So doesn’t an MPPT need to know at what amperage it should stop charging? Or does it use the time I have set? I don’t think I’ve ever seen absorb charging at less than 17 amps actually. I will try setting it to 5 amps and see what happens tomorrow. The mppts are running 3.07. The bmv 712 is running 4.08

What exactly is the %2 tail current setting in the bmv doing?

I will report back what happens tomorrow after bulk.

thanks again, Dave

dark black clouds and rain today... only generating 1500 watts at most.. will have to wait a few days for the storm to pass to even reach absorb.... does the time length of absorb charging change depending on DOD from previous cycle?

Ok, so i had a complete charge yestserday. Absorb completed after 4.5 hours without flipping over to float. Interesting thing is the amps were down around low teens and maybe even 10 amps, yet i have my Tail Current at %2 in the BMV-712. %2 at 1518 amp hour battery (C20) is 30.36 amps... Absorb cycle spent a LOT of time way lower than 30 amps. Is this killing my $14k battery bank?

TODAY, bulk charge brought things up to around %92 (weird, i thought bulk usually brought batteries up to around %80?) then absorb worked for about 1.5 hours, then it flipped to Float. Ugh. my BMV-712 said it was at %94 when it entered float. i synced the BMV yesterday after i got a full absorb charge... did a specific gravity test on all cells and they were reading in the %100 zone.

At a loss here, really don't want to destroy my Rolls batteries. Difference between yesterdays charge cycle and todays it that this morning the batteries started out down around %61 SOC and i ran a 3000 watt hot tub heating element starting at 2:30 pm.

concerning screen shots: can i share my login so you can go in and get any screen shot you need ? otherwise i don't know where to start grabbing screens and that seems very cumbersome.

Dave

Sorry John, that was a pretty disordered response, i was flitting back and forth between days.

Yesterday (Monday): bulk charge brought things up to around %92 (weird, i thought bulk usually brought batteries up to around %80?) then absorb worked for about 1.5 hours, then it flipped to Float. Ugh. my BMV-712 said it was at %94 when it entered float. I had pulled the batts down to around %60 i think the night before.

I am not using adaptive charge per the Rolls technician advice.

any ideas what might cause the Abs to quit so soon?

I am doing a fixed 4.5 abs cycle

Will be interesting to see what happens today. took them down to %64 overnight. if abs quits early today i will test the cells again to get some numbers

concerning screen shots: can i share my login so you can go in and get any screen shot you need ? otherwise i don't know where to start grabbing screens and that seems very cumbersome.

John, here is another update. i would appreciate a reply from you as this problem isn't yet resolved. I just went two days without any interrupted absorb stage, that was wed, thurs. Today is friday and my batteries got themselves up to %97 percent charge after spending about 2 hours in absorb . Not anywhere close to 5 hours in absorb phase. checked specific gravities and they are averaging 1.240. Nowhere near the 1.265 to 1.270 i should be seeing and have been seeing when reaching full charge. After checking to be sure they weren't actually at %100 via specific gravities i turned the charge controllers off and then back on again. As with the original problem in my very first post; The charge controllers start out in bulk, perhaps for 2 minutes THEN briefly (as in 500 ms) flash absorb and then settle down in float charging. I really need to be able to charge my battery array fully. Please advise. A side note to the problem is that despite the BMS-712 having a tail current setting of %2 as noted above and suggested by Rolls battery technician. The charge controllers do NOT turn off at 30 amps. Despite me having turned the tail current settings in the MPPT to zero. i will be awaiting some suggestions

@Dave

I've given this a lot of thought actually. I can't recall such being reported on this forum. And nobody else has chimed in either, so it's uncommon.

Being sporadic suggests cabling/plug contacts might be involved. And you could try bringing the firmware of all your kit up to date to ensure there's no untested quirks between generations.

You've mentioned rebulking and immediate return to Float, suggesting the mppts could be remembering they've reached the set Abs time from even the day before. Can you think of anything that you or your system does that could be related? Cos I've run out of ideas..

The BMV is really an aside, and shouldn't be involved. It's 2% Tail will only sync the SOC to 100%, nothing to do with the mppts. But you could try unplugging it's VE.Direct cable to isolate it to be sure.

Perhaps the OP could share a screenshot of the mppt's history?

An entire thread without a mention of battery voltages? Or a mention of mppt settings, or bmv settings?

@Dave When was the last time you equalized your batteries? Just thinking re acid stratification.

John thanks, sorry to be bringing a new problem to the forum. and admittedly i am new to solar. All of my connections, bus bars, cables etc. are tightened down to specified torque settings per manufacture (mostly victron gear). i have all properly sized cables, properly crimped etc. happy to share any gauges or pictures.

We discussed firmware updates a week back or so.. i've just checked again and there is no update, i'm running 2.84.

you had suggested i turn off the mppt's tail current because it was a new feature and i had mentioned that it only goes up to 10A. My batteries at %2 tail current would be just over 30A. going by the gravities it seems right now that my batteries need about 5 hrs in absorb phase to reach full charge. I'm still at a lost to why the mppt's will just stop after an hour or two in absorb mode when they may still be pushing 45 amps and my gravities put me in the %70 charged range....... frustrating when there is still several hours of sun left. in this case twice i have resorted to turning on the generator and it is happy to stay in absorb and fully charge my batteries.

I "rebulk" by shutting down the mppt's, waiting a few seconds and turning back on. the units enter Bulk phase for a small amount of time, perhaps 1 minute, sometimes 20 or 30 minutes but then literally flash through absorption on their way to float. nothing i do can make them finish absorb and when i test the gravities (of all 24 cells) they are clearly NOT fully charged. I don't know how to answer your suggestion that the mppt's "remember they've reached the abs time from the day before" i'm hoping you know how they are programmed..? i would hope after they turn off at night they wouldn't charge with reference to the day before but to my usage and the voltage and amperage being pushed to the batteries.?? i need help here folks i did not design the units, just need them to work for me or know if they need to be returned and repaired?

I have equalized twice now since going online. Seem to have no more difference between cell gravities of .02 So, one cell could be as low as 1.2520 and the highest cell may sit at 1.2720. It's a new battery bank and per the manufacturer i am trying to allow it to break in and equalize itself through usage which could take a few months. i do obsessively check gravities, temps and individual batt voltages and it's very obvious when the Victron equipment is not charging my batteries all the way. Last equalize was a couple days ago

the battery temp sensor seems to adjust the voltage the mppt's use to charge just fine. Mppt's seems to reach 141f when in a long bulk phase. what else, no cables seem to get hot, i have an air conditioned room, heater and AC.

battery bank is 12 Rolls 4 KS 27P series

i've carefully watched the temperature of the actual batteries itself via the bmv temp sender and the mppts seem to lower and raise voltage properly when referencing my Rolls temp/voltage tables.

In the two mppt 250/100 TR VE can units running in dvcc mode

max current: 100 A

abs 60.00v fixed at 5 hrs

float 53.75v

eq 62.40

auto eq OFF

@Dave

I don't know what's causing this. It's likely you're using CAN connectors from both mppts to the Cerbo (daisy chained). You could try changing them out for VE.Direct cables (the same as the BMV uses to the Cerbo). CAN does have one advantage in that it can synchronize the charge states of the mppts, but it shouldn't matter if you're using a fixed Absorb time. It's this synching that may have gone awry. Just make sure you have two spare VE.Direct ports on the Cerbo, as these aren't daisy-chained.

In the meantime, rather than start the genset to finish off, you could change Float to (say) 59.0V as required, and do it with solar. The batts will still charge fine, that's even within Rolls suggestions, and the 1V diff will show in your records.