Dual PV functionality

[Dave Festing]

Hi Dacian,

Say, both the big array and the small array are on during full cloud.

The sun breaks through and the SBMS0 switches from L3 to L2.  If there is
still too much PV input the SBMS0 will then switch from L2 to L1.  Will
that 2nd switch happen within the 1 second logging period?  What is the
response time for these switching events to take place?

Is the PV current reported through the UART only take place when the
SBMS0 has finished switching, ie the PV current is less than limit

set in the Dual-PV functionality plus 20%?

Thank you,

Dave

[Dacian Todea (electrodacus)]

Dave,

The switch from one level to the next can take up to two seconds. Unless you cover the panels and then uncover them instantly the clouds will not be able to move this fast so it will typically take longer than a two seconds to get from L3 to L1

 But there is no problem as the battery can easily handle even 1C especially for a few seconds and so are the fuses or circuit breakers that require much longer time to heat up and react.

The UART data is sent every second but there could be variation in the exact time the data is sent and so it is possible to have same time stamp on two consecutive UART data. The software on the SBMS runs based on the internal high speed clock while time stamp is based on the slow real time clock oscillator.

Current is measured multiple times per second but for the PV level switching it only uses the final one second average. So depending on when during that second the current starts to increase the average for that second can still be below the threshold.

If this switching will have been more critical I could switch much faster than at 1 second intervals as it was done for the DMPPT450 but that is not the case for the dual PV array on the SBMS0 where both the battery and fuse/breakers can handle peaks up to 1C the max will will normally have a dual PV array setup.

This slower switching also protects the switching devices in case of incorrect installation or setup of the dual PV array.

[Dave Festing]

Dacian,

Thank you for your response.  For some reason I wasn't notified via Gmail and have only just read it.

From your description it could take a maximum of 3 seconds to switch down to L1 from L3.  I was using a 2 second delay on my added array to give precedence to the SBMS0 dual-PV switching.  I think that gives a one second period when current could be above the threshold.  I will make my 3rd array respond every second to see if that helps.

The current spikes are not a significant concern, I just wanted to understand why they were happening.

Cheers,
Dave