Confirmed MPPT switches to Limited the moment we hit absorption and the voltage drops to under 58. I was playing around going to charge voltage with DVCC OFF and too my surprise when it hit absorption the Voltage stayed exactly where it was! Thought I had nailed it until I noticed for whatever reason I was feeding into the grid at max the mppt could produce. I think the lesson is if the MPPT stays in Active mode (not limited) then I dont get the Voltage drop when I hit absorption (like I want it).
I did give him a battery temp sensor, connected to the Cerbo, to put between the cells to check their temp over and above the BMS temp sensors.
Not sure if this was installed in the end or if it is maybe interfering?
More points to consider ā¦
- Note: If is a 17 cell bank, hence the āhighā volts.
- There where Pylontechs connected to this Cerbo until recently. Had to reboot it to get things working.
Very soon I will have the exact same BMS installed. Then me and Deepsquatter can compare apples for apples.
Not installed yet so we can rule that out.
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Iām starting to think the voltage drop when the MPPT operation switches to āLimitedā mode is because of a faulty unit. I cant think of any other setting to try. 
Can you ārebootā the MPPT - shot in the dark
Disconnect the panels first.
Disconnect the battery pos wire from the MPPT.
Let the caps discharge, give it a few minutes.
Reconnect the battery and panels. (you must hear that clap when you connect the pos wire again.
)
I actually just tried this and yes I got the clap when closing my Mersen fuse holder again. No joy 
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Thatās what you would expect. It switches from maximising the current, to instead limiting the current to hold the voltage where it should be.
If we had seen it remain in MPPT mode, while the voltage dropped down, then we knew it was latching on to a local maximum in the power curve.
That sounds as if the setting āFeed excess DC coupled PVā is enabled. On the ESS menu under grid Feed-in. When that is enabled, no current limits are applied, so that all energy can be fed into the grid. The MPPT is instructed to charge 0.4V higher, and the Multi is instructed to feed this āovervoltageā into the grid. So the fact that THAT works is good news.
I still donāt get why it would limit once it hits absorption. Makes no sense. Doesnāt sound like a broken unit either.
VRM id, if you donāt mind?
Thats the first thing I checked when I noticed the feed in. Was definitely OFF. Will PM my VRM id. Thanks again!
Is it the BMS Settings on the JK? That for me is the first place to look.
You have seen Andyās settings, right?
This caught my eye on Andyās website, check the volts and then the Smartshunt volts ā¦ as Plonk explained. Interesting.
I had a look at his site. His MPPT has a very large calibration discrepancy of almost 2.7V. While shared voltage sense compensates for some of that, it has safety margins built in: It will compensate for max 2V of calibration. That creates a dead spot at the top where the MPPT does not start charging again until the battery has dropped by at least 0.7V.
Replacing the MPPT is recommended.
Edit: Oh, and the reason it stops so abruptly on going to absorption, is because in systems without a CAN-bms (ie no battery comms), a 4V offset is added during the bulk phase (to overcome and voltage drops on the cable, make sure we get there, etc). This is removed the moment absorption is reached. With the 0.7V calibration not compensated for, removing the bulk offset instantly drops the MPPT into a situation where it sees the battery voltage as being higher than what it should be. So it stops charging, as it should.
Itās all down to calibration.
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Really appreciate you looking, fantastic help!
Installed the new solar charger today and itās working brilliantly. Thanks all for the help especially @plonkster 
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