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The manual of the MPPT states that the Vpv start voltage should be 5V above Vbat. That is not problem. After starting Vpv should stay 1V above Vbat to keep charging.
"● PV voltage must exceed Vbat + 5V for the controller to start. Thereafter minimum PV
voltage is Vbat + 1V."
What i see in the VE connect app is that the MPPT always keeps Vpv aprox. 5V above Vbat.
This causes the battery to not charge completely.
"This causes the battery to not charge completely."
How so? Battery voltage? Ah capacity? Load connected?
PV array specs? Panel #/Vmp/Imp?
A MPPT charge controller is designed to work best when the solar voltage is significantly above the battery voltage.
It's a different arrangement to an old PWM charge controller. If you cut this too fine (ie. use a solar array with a Voc/Vmp voltage that's not high enough) then you will have trouble, particularly on overcast days and during winter.
The +5v just refers to the 'wake up' PV voltage each morning. The +1v just refers to the 'shut down' PV voltage in the evening.
Normally during the day (when there is good sun) the the PV voltage should be somewhere around your solar array Vmp during charging and around Voc if the battery is fully charged. Ideally the system should be designed so that the PV voltage is at least 10v to 20v above the max battery voltage.
Thnx for the response.
I understand the principle of mppt.
But what is the use of a shutdown voltage of 1V Vdiff you stop charging at approx. 5V Vdiff anyway?
In my case it would be ideal to keep charging (with low power ofcourse due to pv specs) untill alprox. 2V Vdiff
Performance of my pv is at optimum at nominal bat voltage +10V. Ideal and max efficiency.
It is interesting that you believe charging stops if the Pv - Pbat is less than 5V. Is this from something you have read or something you have seen on your setup?
It should not be the case, and to illustrate this, here is a screenshot of my system today coming to the end of the 'charging day' where the voltage is starting to drop. I have panels in series so the usual voltage is much higher, but I found some time where I have a difference of under 2V.
The PV Panel is putting 14.94V and a current of 0.3A into the MPPT Controller (the VRM system only shows 1 decimal point for Amps); The controller is showing a Vbat of 12.95V but is still putting in a 0.3A charge into the battery.
The MPPT will keep charging all the way down to Vpv = Vbat +1V (although I wouldn't expect much out of it at this operating condition/point).
It's important to understand that when your operating at this limit, then the MPPT can control the PV voltage, depending on the load/current it draws from the PV.
It is constantly looking for the PV voltage vs current point that provides the most total power output.
It's also unwise for the MPPT to purposely operate exactly at the Vbatt +1v limit, as any sudden change in solar condition could then make it totally turn off (making it think that it's night time)
A good system design should have a significant buffer between battery and PV voltages to avoid ever operating in this region during the day.
My current setup has a PV array with a Voc of ~120v and a 24v battery bank - so even on highly overcast days the MPPT has plenty of PV voltage to 'play with' and conduct a regular MPPT scan/sweep.
It also helps the MPPT to 'wake up' early each morning and to keep charging well into dusk each evening.
I think the premise of the argument is too incorrect to really fully understand? maybe something lost in translation?
Vpv can be way above the Vbat in a properly working system. Right now, for example, in my system, the Vpv is 40.22V and Vbat is 13.57V.
The excess voltage gets converted into a higher current - so the "Ipv" is 0.8A and the "Ibat" is 2.3A
The Vpv being 1V higher than the Vbat is not a target for operational running, it is just a minimum difference that is required to keep the controller from shutting down.
