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mikeymike avatar image
mikeymike asked

Smart MPPT 100/50 Re-Bulk/Absorption changed?

Hi,

yesterday i upgraded my MPPT+BMV to the latest Software-Version (don´t now the last Version from last year). Did something changed in Bulk/Absorption handling?

Situation:

Today we used 1000W load. The MPPT is limited to 36A and the rest comes from battery. The battery soc reduced to 94% and because of the rebulk offset the state changed correctly to bulk while the voltage drops because of the heavy load.

After stopping the load the bulk phase is changed directly to float again with no absorption phase anymore. I ever used adaptive absorption. Last year the behavior in this situation was that the mppt loads in Bulk and after a time x goes into Absorption before then go to float, so that the battery can charge again the reduced load. Now my battery only "charge" a little in float mode so that possibly the battery won´t charge again to 100 percent today before the sun goes down. Starting and stopping the MPPT results in the same behavior: Only short Bulk and then float. Maybe the "minimum" absorption time changed to 0 or something like this?

Shouldn´t it be at least Multiplicator 1/6 * maximum absorption time?

Help would be nice because this situation will be very often the same again in summer.

MPPT Controllers
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3 Answers
JohnC avatar image
JohnC answered ·

Hi @MikeyMike

It's quite a while back now, but there was a change to Tail functionality. If you've added networking to the BMV in the meantime this might also have introduced what you see..

1646489311057.png

Given you haven't mentioned Tail, you may be unawares. Actually a great feature, but you may need to lower the Amp setting to prevent it dropping from Absorb prematurely.


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mikeymike avatar image
mikeymike answered ·

Hello JohnC,

yes i know this feauture but i used all the time adaptive time without problems. At first i changed to fixed time with a low tail current to get my battery full today.

Do you think its the better solution to work via tail current?

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JohnC avatar image JohnC ♦ commented ·
@MikeyMike

There may be differing views on this, bui I think the battery Tail is a great feature, and I much prefer it personally.

Doesn't mean that Adaptive is abandoned though, and it can remain in place as backup.

As an example, imagine a doubtful solar day when there hasn't been quite enough sun to reach Absorb V, and Adaptive has predetermined say 90 min as it's target Abs time. Yet by 4pm SOC is >99%, and the sun comes out. At >99% I'm happy to see no Abs at all, certainly not 90 min. Tail to the rescue. With some sun Abs is hit quickly, the batts can't handle much charge, and the drop to Float only delayed by the detection time.

Extreme example maybe, but we all see this in practice to differing degrees. Adaptive is good, but it can't predict your solar day. Tail rules for me, and I love it.

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mikeymike answered ·

Thank you for explanation.

After reading i also think it´s the best solution. Maybe you´re also a battery expert. I have one more question.

I use 6 gel cells from an electrical pallet truck (Hawker Evolution 160Ah). I know that my "end" current is about 0,3A. With adaptive loading most time i reached this current and my BMV is also at 100% at this time. So now i also set the tail current to 0,5A at first. Most people say the tail current should be 1% of the bettery capacity. But i think my battery is not fully charged at 1,6A. Do i overload? I think not. What should happen? There is a temperature regulated Voltage to be below the gasing voltage and the battery resistance is doing the rest. What am I misunderstanding?

If you like you can take a look at my actual Setup. Choose one of the last days of this week in the drop down to see my loading behaveior on other days.

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JohnC avatar image JohnC ♦ commented ·

A lot of this stuff is personal preference, and I have reactive floodeds, not gels. So it's hard to compare, but I drop to Float at ~3% of batt capacity. At Abs V, 1% would be way too long an Abs for me, and actually may never reach that level.

For me that's ~99.0% SOC, or a touch more with warm batts. The rest I finish off in Float. And I can add water if I bubble some away, but I might even be more careful if I had sealed batts. Your 0.4A is ~equivalent to where I sync the shunt, but that's at the lower Float 13.5V (@12V).

So you push the Abs time way further than I do. But I won't say you're wrong doing that, they're your batts and for you to decide.

Edit/: Great graphs, I must learn to master those, but the language there too foreign for this beginner.

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