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Hi, i need to add more panels to my boats solar system , i i am already using a 75/50 controller with a colour control and 12v/3000 multiplus, the controller is near to its limit, can i add another controller to the system , will it cause any conficts ?
Many thanks
Gordon
Hi @Macca61,
Yes you can have 2 (or more) MPPTs on the same battery bank.
If it was not possible, you would never be able to have, more panels, than can be handled by 1 MPPT, in 1 system. And we know that is possible.
Any MPPT (or PWM) solar charger, has a limit to how much Wp it can handle, eg. the max Wp of a 100/150 or 100/250 SmartSolar is 5 800Wp.
It also does not have to be the same size MPPT's, or the same size panels.
But make sure that all the panels on a single MPPT, is the same size. You don't want to mix sizes in a single array, as they will all be derated to the smallest panel. Eg, 2 x 150Wp, mixed with 2 x 250Wp in same array, will all be derated to 150Wp. As if you had 4 x 150Wp.
Each MPPT will behave according to the battery voltage it reads. And will work independently from each other. They will almost never be exactly in sync with each other, due to different voltage drops in cable lengths between MPPTs and battery bank. The different cable lenghts, will result in slightly different voltage readings, which in turn will give the MPPT different "instructions" on what to do.
It is standard / normal practice to have more than 1 MPPT in a single system (battery bank).
Some examples of actual systems we have installed, to illustrate:
1) 42 x 250Wp panels (total of 10 500Wp) installed with 2 x 100/150 SmartSolar. Panels configured in strings of 3, thus total of 14 strings, resulting in 7 strings of 3 panels each, per MPPT.
That comes to 5 250Wp per MPPT, which is within it's limit of 5800Wp max.
I have attached a screen shot from VRM Portal, showing battery voltage readings and total daily production of these 2 MPPTs. The top one is about 30 cm further from the battery bank, and show but lower battery voltage and always show lower production. 1 panels was broken, so now that Mppt only has 6 strings. That is also contributing to the lower production of that MPPT. 
2) 44 x 325Wp panels) total of 14 300Wp), installed with 3 x 100/250 SmartSolar. Panels configured in string of 4, thus total of 11 strings. So 2 of the MPPTs will have 4 strings each (total of 4 x 4 x 325Wp = 5200Wp per MPPT), while the 3rd will only have 3 strings (4 x 3 x 325Wp = 3900Wp).
In both cases, it is within the max limits of 5800Wp of the MPPT.
Hope this give some clarification and understand g on using multiple solar chargers in 1 system.
Cheers,
Anita
@Macca61 A very good question. I can't understand why none of the solar gurus here have not responded. From my experience (we have 3 sets of panels feeding 3 controllers) you can run more than one controler on the same battery bank. That said, someone commented that MPPT controllers might conflict with each other, which has been a big question in my mind. In our case, I do not see any conflict in the output readings. Each set of panels appears to be contributing as it should. Hope that helps.
There can be some conflict in the transition stages, from bulk to absorption and absorption to float. If one controller switches earlier than the others, they will not all contribute to power the system (battery + loads), at least not ideally. The one with higher voltage will dominate. But will not harm anything. When all controllers are in same state, there are no issues.
It is public that there is work undergoing to synchronize smart MPPTs (with bluetooth interface) that addresses this scenario. Hopefully Victron will release new firmware soon.
Note: maybe this question should be placed in the general questions area...
Thanks all for answering my question
