question

Hi @Fra

In my view, the mppt Tail function (fed by shunt) is by far the best way to terminate Absorb with Pb batteries. It works on rebulks too.

It's in Amps of course, but 1.8% is a bit low for my floodeds. I use ~3%, and that gives me ~99.0% SOC. I Float in the last 1% SOC.

Absolutely recommended. A great feature.

Ah ok thank you. I put 1.8% of capacity because are AGM. And ROLLS (not mines)

recommends prolonging absorption 1 hour after the current drops to 2%. With his agm.

Do you think with 1.8% risk overcharged?

however I have seen that the end-of-charge current varies a little depending on the circumstances (temperature and above all previous discharge). After repeated light discharges the tail current tends to be lower, even reaching 2.6A.

After a deep discharge, at some point, around 3.3A, it stops dropping.

Curious phenomenon that I don't understand what it depends on.

And also the working voltage of the battery improves after deep discharge compared to repeated light discharge.

my AGMs are at 99/100% when the current is between 1.5 and 2%.

Do you think tail current with shunt is the best method for bluesmart ip22 too?

eliminating adaptive absorption based on bulk phase?

I'm not sure if tail current with shunt is able to lengthen the absorption time after deep discharges..

as victron recommends. (but rolls for example recommends a fixed absorption time regardless of the depth of discharge..

and always quite long).

In your opinion?

@Fra

You're delving deeply now. Ask 20 people the same things and you'll get 20 different opinions.. so gospel this isn't, based only on experience with my own GC2 pattern batts..

Temp has a big effect. Cold batts are sluggish, sag badly in V under load, and really need that realtime boost in charge V's. I use -100mv/C (48V), and at that the charge seems to need much the same Abs time seasonally. They may taper in Tail a little more slowly in the cold (which usually happens for me when discharge is a bit deeper too), but I haven't found a need to change the Tail setting.

I don't hold ultimate faith in batt makers settings. Lab conditions aren't always the same as in the 'wild'. Up to the user. They'd need to actually provide me with a feasible reason why I should add another hour to Abs. My Abs time is like 1-1.5hr to 3% Tail, but I'm 'sneaking up' on Abs with a solar day. I don't use 'shore' charge to go beyond Abs.

And on a couple of occasions on really long cloudy summer days I've actually reached 100% SOC without reaching Abs on the way. That's rare, but the shunt and V/Tail agreed.

The lab boffins don't test like that. There may of course be other reasons like stratification, but I'd need convincing..

I understand exactly what you mean.

I also get to 100% without ABS sometimes.

I believe that the higher the bulk charge current, the longer the ABS will be.

if you charge a 200ah bank at 2A, at beginning of the ABS voltage they will already be charged, without having to keep the ABS voltage for a long time.

Rolls said that their thick plate AGM will sulphate if the ABS times are not respected.

But I gave the same example of a 200ah bank loaded at 2A and they told me that in theory this way, at the start of the ABS it will actually already be charged.

You can check your flooded batteries carefully with the densimeter to know the real 100%.

I can't do that with AGMs.

Victron says a deeply discharged battery also needs 6 or 8 hours of ABS.

Maybe.

but it probably depends on the bulk current. The higher it is, the more inefficient it is.

Solar charges at low progressive current during bulk.

there are many mppt manufacturers that don't even allow abs longer than 3 hours. probably for security reasons.

In addition, solar charging if it doesn't complete one day, it will do it the next day or 2 days later...

Even as a schunt, I reach about 100% in 1.5-3 hours of ABS. and this corresponds to a tail current of about 1.5-2%.

What you say about your Flooded makes sense, as the agms have lower internal resistance I think.

One day I want to try starting from 60% soc, loading from bluesmart immediately at 20A bulk, how the behavior changes compared to solar.

I expect ABS to start at a much lower SOC and consequently longer ABS. Compared to the progressive current bulk of the mppt (I think more efficient).

a question:

If one day, after a relatively deep discharge, I see that the current stops dropping below 3.3A (2% of my batteries), can I try to insist on ABS for another 2 or 3 hours to see if it drop again?

It shouldn't do any harm right?

In any case, every 21 days I do 1 hour of equalization at 14.75v at the end of the absorption at 14.45v.

It's probably useless, but I don't think it could hurt.

On AGMs the actual equalization would be harmful (over 16v). But some schools of thought allow for a mild EQ from time to time.

I have floating at 13.6v and -24mv/C°. For safety. Yesterday with battery at 36 C° the floating was 13.4 v!!! And abs at 14.2! I charged with alternator for 1 hour at almost 0.3C current. 50A for 178ah! I make these only occasionally.

On your flooded batteries (are they OPZS or traction type??) do you equalize?

hahahha, I didn't know Gospel meant gospel at all. That is, the 4 books written by the alleged disciples of the alleged Jesus.

I thought GOSPEL was just the typical black singing of American churches.

That's why I didn't understand.. now it's clear what you meant.

Are you American or English? or are you not english speaking? I'm Italian and my English sucks. A good half is from Google translate.

Which battery lasted you 1 year?

How was the 12v system a balancing nightmare?

What is the victron compatibility list?

The lifepo4 cells are all Chinese and they are good quality too I guess.

But the cheaply assembled batteries don't convince me. I am very skeptical that a 600 euro for 200ah lifepo4 renogy will last longer than an 800 euro for 200ah AGM Trojan

And I'm afraid that taking cells and bms on alibaba, even if they are EVE or CATL etc, I would not get the same result as a lifepo4 battery made by victron or Exide or Trojan etc etc ..

but maybe I'm wrong.

While I know that an agm Trojan will last me at least 6 years of cyclic use and a flooded maybe even more than 10.

And I'm afraid that if I make a lifepo4 in the garage in 2 years it will be thrown away for some unknown reason.

But... I'll stop here otherwise we'll go off topic.

I'll leave you my e-mail if you want to leave me yours with a message. In the future I would like to ask you more about Lifepo4.. Thank you

francesco.colantonio@gmail.com

ah ok I understand what you are referring to.
Perhaps it is more evident when there are many units in parallel.

For now, monitoring my 2 agms in parallel (of very different capacity), I have not noticed these problems.
The current is always divided APPROXIMATELY based on capacity...sometimes with a little advantage for one and sometimes for the other.
In any case, I charge at 0.1C on average, or less.. only sometimes with the alternator charged at 0.2/0.3C but for a short time.

Ah..the chargers are cross-connected. Positive on one and negative on the other.
They are not connected "in a cascade".

The cross connection helps so that no other unbalanced resistances are added between the batteries.

I have made installations on other campers with 2 agm in parallel (even different capacity) and I have not seen big differences in current (in relation to the capacity I mean).
However, even in these cases the charging current is quite low.

My batteries when charging increase the temperature by 2 or 3 degrees net of the increase in ambient temperature. Only if I recharge beyond 0.2 C does the temperature increase more noticeably.

In the world of campers there are a couple of Italian companies that produce "parallel managers for 2 batteries".
In practice they only put them in parallel if the load is large. With small loads they use them separately.

These devices do not exist in the industrial sector. I find it wrong to use lead acid batteries separately. Stress increases in all circumstances. and the available energy is reduced.
These things also swap batteries under chargers during the charge cycle..Which is often based on time and voltage..so in my opinion this is wrong.

Last thing...using 12V in a domestic environment doesn't make sense for a whole series of reasons (huge currents, huge cable sections, low inverter conversion efficiency, expensive high current mppts...).
Unfortunately in the camper I am almost forced by the stupidity of the (European) automotive industry, which still insists on 12v despite the enormous increase in consumption and solar power.

You were right to switch to 48v.. For me, switching to 24v on the camper is too fiddly.

But if I were to camper a van myself, I would DEFINITELY use 24v.