2 MPPT Controllers 1Array

Hi there. Probably a question for the man himself. Forgive me if this is a repeated enquiry but I struggle to find the answers/reasoning.
I have a Makeskyblue 60 A V119 controller that works well.
I have 2KW solar feeding LIFEPO4 and would like to add another 1KW
I have watched Wills video showing SCCs do not compete
I have been told (MSB) that splitting the input from my array helps keep the MSB SCC safe with 2 terminals sharing the input amperage. I asked about uneven share of the strands causing uneven sharing of the amperage and was told it was no issue.
So my question is why is it taboo to put 2 identical controllers on one array? If the amperage is shared and the controllers do not compete then what can be the downside?
Thanks for your help
Peter

The two controllers sharing one input will fight for control.....when one sweeps the other will be thrown off its MPP causing it to sweep which will cause the other to sweep endlessly.....

Splitting the array in half with each half on its own controller will work much better but it will still be a compromise as the controllers will upset each other from the battery side with a few exceptions such as MidNite Solar’s “follow me“ connection where one controller takes the lead and “commands” the other controllers to “follow me”, There are other methods to accomplish this task but it does require a “communications path” from each controller to the rest of the controllers.

Splitting the array with each seperate part feeding its own controller is the best that you can do as less expensive controllers do not have communications directly from one controller to the other controller to accomplish “load sharing”

I do have multiple MidNite Solar Classic 150’s in follow me mode and it works very well once everything is calibrated and in “sync”, there is a setup time to get everything on the “same page”

But that is the opposite of whats posted in Wills video? MPPTs don't compete on a single battery bank?
Admittedly that was for separate inputs

Apple’s and Oranges are not the same thing either.....I do not beleive Will Power said that two controllers sharing the same array can charge the same battery bank. If you understood just how a MPPT controller finds the MPP you would understand just why what i said is true.

Reference Article can be found at:..........Wikipedia : Maximum Power Point Tracking Controllers

So if you have 2 MPPT connected to the same array, they will interfere as they search for the MPP and mess each other up. What is the result of that though? Will they just fail to perform properly until 1 is disconnected, or will they fail in a catastrophic way?

I have this setup now. Makeskyblue 60 amp combined with an Outback controller. They feed into my 36 V 18 KWH battery bank. I also have another Makeskyblue 60 amp combined with an outback feeding a 5 KWH battery. All seems to be working fine for me. Now I imagine yes they do step on one another's toes, but energy is going into my batteries and there has been no safety issues as they both shut off at max voltage, and I am under max charge rate of the batteries.

macheung said:

So if you have 2 MPPT connected to the same array, they will interfere as they search for the MPP and mess each other up. What is the result of that though? Will they just fail to perform properly until 1 is disconnected, or will they fail in a catastrophic way?

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That's exactly what would happen, one would likely find its optimal MPP adjust thus knock the other of its MPP, repeating over and over, the one that sweeps the fastest would probably be more productive, though less than it would be if it were alone. Kind of defeats the whole purpose of having MPPT in the first place.

It probably will not destroy either controller but neither controller will be operating at its best effeincy, but as it is not possible for two controllers to share a single array. One major american manufacturer had a “twin mode” which paired controllers but that did not turn out too good, project has been since abandoned. They did have a communications link between the controllers where the “master” would do all the sweeping and send the operating parameters to the “slave” controller. Specifically designed to do pairing but even that did not work out.

It sounds to me like OP is talking about putting two controllers on one array/set of panels.

This would be an issue.

While others are talking about putting two arrays with their own controller onto one battery.

This would not be an issue.

The distinction is very important. It seems like OP is trying to trivialize the input portion of the equation when in fact its the most important part.

Each controller must have its own input panels which are electrically separate the other.

Separate inputs/shared output = fine.

Shared input/shared output = not fine.
Shared input/separate outputs = not fine.

Short_Shot said:

It sounds to me like OP is talking about putting two controllers on one array/set of panels.

This would be an issue.

While others are talking about putting two arrays with their own controller onto one battery.

This would not be an issue.

The distinction is very important. It seems like OP is trying to trivialize the input portion of the equation when in fact its the most important part.

Each controller must have its own input panels which are electrically separate the other.

Separate inputs/shared output = fine.

Shared input/shared output = not fine.
Shared input/separate outputs = not fine.

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Correct. Is am aware that 2 MPPT on one panel is not fine as normal operating practice, but I have a unique situation which would cause that situation to happen for a limited period of time before I can disconnect one of the MPPT. So I am wondering whether it would cause damage (bad) or it just won’t work well (which is OK)

The situation is that I am setting up a solaredge grid tie inverter which requires the use of their optimizer. These optimizer shut down when the grid is out. So I am trying to use a Y splitter between the PV and optimizer to also connect the panels to another off grid charger/inverter. This off grid MPPT normally will not be connected, only to be connected when the grid is out. However, when the grid comes back on, there will be a time when the off grid MPPT and solaredge optimizer are both connected before I can disconnect the off grid MPPT.

I can use a bunch of relays but rather avoid that if possible.

Sounds like you should contact the company and ask them why their product can't function during a power outage.

If you're manually switching over then can't you just install a transfer switch to physically swap between the two controllers?

Is there no battery in this system such that a power loss would occur in this scenario?



At any rate it seems to me like it would be fine as long as it's temporary and you get to it quickly.

hi I am asking this issue, may I know how to separate the 2 arrays? pls see my setting photo, if want to separate two arrays of batteries with 2 mppt, then how to connect to the inverter to the batteries group, if there are twp groups of the batteries, i am not a technical man, so anyone pls teach me

Bwong said:

hi I am asking this issue, may I know how to separate the 2 arrays? pls see my setting photo, if want to separate two arrays of batteries with 2 mppt, then how to connect to the inverter to the batteries group, if there are twp groups of the batteries, i am not a technical man, so anyone pls teach me

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The arrays are already separated by the MPPT's, in your drawing. Don't separate the batteries. That would only give you half of the voltage.

I think the point being missed is that mppt controllers put a load on the array to get the output voltage to the best power (V x A). Once the first mppt controller has done that, the second one woun't be able to and so can't work as an mppt. If it works for someone, then the second one has defulted to a pwm controller, relying on the first one to 'get it right'.

A good rule of thumb is one array per mppt

macheung said:

Correct. Is am aware that 2 MPPT on one panel is not fine as normal operating practice, but I have a unique situation which would cause that situation to happen for a limited period of time before I can disconnect one of the MPPT. So I am wondering whether it would cause damage (bad) or it just won’t work well (which is OK)

The situation is that I am setting up a solaredge grid tie inverter which requires the use of their optimizer. These optimizer shut down when the grid is out. So I am trying to use a Y splitter between the PV and optimizer to also connect the panels to another off grid charger/inverter. This off grid MPPT normally will not be connected, only to be connected when the grid is out. However, when the grid comes back on, there will be a time when the off grid MPPT and solaredge optimizer are both connected before I can disconnect the off grid MPPT.

I can use a bunch of relays but rather avoid that if possible.

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If I'm understanding this correctly. The Y connectors will be permanently installed. Which means that the optimizers will be permanently bypassed. Without adding one or two (possibly four) diodes at each panel , I don't see it producing much power in either situation.