MPPT Algorithm and stopping charging to detect voltage

DIY
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1

Hopefully @lxonline or similar expert will have this in their brain with no need to look it up; I read a discussion online recently where someone suggested that the MPPT, in the absence of something like DVCC or a voltage sense wire, will periodically stop charging so that the charging current drops to zero, it then detects the voltage, and then carries on charging. The idea being that while no charging is occurring, there can be no voltage drop over the cables (between MPPT and battery) and therefore you see the true voltage of the battery, not the battery voltage plus cable voltage drop.

This initially sounds plausible, but how do you account for the fact that other components might be charging or discharging the battery rapidly at the same time, which the MPPT won’t be aware of? Also, if the MPPT feeds busbars, then you are only negating the voltage drop from MPPT to busbars, there could be massive drop from busbars to battery caused by another MPPT controller.

Anyway, the real question is; Do Victron SmartSolar and BlueSolar controllers do this? i.e. Is it part of their algorithm?

I’ve never seen this in graphs, but i have seen the dip on the PV side every 10-minutes when the full V/I sweep is done, so i know that the sweep is part of the algorithm (and we’ve already had the “can’t be turned off” conversation here).

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The first is possibly a theoretical thought on the 10 minute sweep behavior.

In commissioning (and indeed troubleshooting) a system, things like volt drop need to be checked with a good digital meter physically by the installer. It does several things one of which is checking if the mppt is actually reading voltage correctly (within margin of error i.e. 0.1v)

When there is no dvcc each component does its own thing with the information it has from itself.

What I would do with a battery that is not entirely compatible is use a shunt and then set that as the monitor in DVCC, then everything is using one voltage reading as its base for working.

It would more likely be a rise (and this can happen with any charge source if it is charging hard) and if your dc cabling is not right.