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Is it possible to link together 2 or more Smart Solar MPPT controllers using VE.Direct cables, without needing a GX or BMV device? Can they just be daisy chained with identical charge settings to work as one? I have a customer whose system requires 2 MPPT units but he can’t afford a GX or other extra equipment. Or will they possibly work together on their own Bluetooth network?
No, to all of those questions.
To get the mppts to sync with each other over bluetooth, you will need a bmv712 or a Smart Battery Sense. (get a blue one), to provide a master battery voltage/temperature. Smart networking.
Of course, you can use the mppts without requiring syncing.
Will they synchronise over VE.Direct when a Cerbo GX or similar is in the system?
You can use a GX device to exert a little more control of the Mppt's, but not to the point that multiple Mppt's will fully syncronise thier charge states. (transition between bulk/absorb/float)
By using a GX device, you can enable DVCC, SVS, STS, so that each Mppt is using the same master voltage and temperature reference (eg from a BMV 712). This eliminates any voltage differences a Mppt would see due to wiring losses, and ensure that all Mppt's register the same battery temperature.
When each controller wakes up in the morning, (they dont always start at the same time) slight voltage differences (from load switching/sun on other Mppt) will give each Mppt a different adaptive absorb time.
Even if you program in a fixed absorb time, the Mppt's wont switch to float at exactly the same time. This leaves any Mppt that is a little late exposed to increases to battery load or clouds dropping charge current/battery voltage.
