connect 2 mppt charge controllers to one pv array?

[somawheels]

Hi
If i connect 2 solar charge controllers to to the same pv array (via one shared cable) to charge battery, will they share the amperage from the solar panels equally? (50% each)

i.e could i connect a 40 amp pv array with two 20a mppt chargers charging the same battery bank - the charge controllers would share the same wire from the pv array.

[Raj]

A full system description and configuration would be helpful, however, the charge controllers need to be wired in parallel and for safety reasons I would split the array equally between them.

[somawheels]

Thanks
Splitting the array between them would use more wire/cable... so what exactly are the safety reasons? What could happen if i ran the 2 charge controllers from the whole array.

I don't have a full system description, because i don't have a system. Just planning at this moment. (which is why i asked this question).
The system would be a 12 volt 600-700ah batterry bank of about 6 12v batteries, connected to an inverter and charger .

[Raul]

Imagine you got a bottle of water in one hand and 2 empty cups on the other hand. Now can you fill the 2 cups at once from the same bottle to maintain a equal flow in each cup at any given time? I don't think so.
You got good advise already , split the array equally and run separate wires to each charger .

[inetdog]

With two PWM CCs you might get away with it, but the power distribution would not be perfectly equal.
But with two MPPT algorithms independently varying voltage and current and expecting to see only the results of their own changes, that scenario is not likely to work.
Neither CC would be able to see the Voc end of the panel output curve.
A quick and dirty MPPT that just looks at Voc and sets the operating point at 80% of that would cause a spiral to zero voltage and both CCs would lose.

[Raj]

Hi somawheels
I will assume you are designing a system based on your loads, which is the correct way to design one.
With 2 charge controllers on the same array and 1 fails, your going to feed 40 amps into your 20 amp controller. They are usually designed to handle more amps than they are rated for, but double the amperage just might smoke it. If your just designing a system and haven't purchased any equipment yet, then using a single CC that can handle the voltage and amperage of your array would be the way to go. Also 6, 12 volt batteries in parallel is not recommended because it will be unstable and become unbalanced. A single string of batteries is the most balanced method. Maybe 2 strings of 2, 6 volt batteries for 12 volts. If you can't get large amp hour batteries, you may want to go with a 24 volt system. That will allow you to use smaller batteries for more amp hours, i.e. 4, 6 volt batteries in 1 string or 8, 6 volt batteries 4 in each 2 parallel strings. If you want to design it yourself, then it would be a good idea to take your time and read the forums for awhile and get familiar with the various equipment and designs that are discussed here and on other sites. You not only do need this knowledge to build it, but also to maintain lt.

[grazza]

Apologies for opening this thread again, but I am trying to understand all the reason why two MPPT SC's. cant be used on one PV array, My understanding is as follows;

1. If one SC fails the full power of the PV array goes to only one SC and could damage the working SC? But if the SC's are speced individually to cope with the full PV output then that should not cause an issue??
2. The MPPT SC's would fight over the MPPT point.

The reason I ask is that my setup has grown as time has progressed and I wanted to add a new SC in parallel (and yes I should have designed it before I started on the project) and I do appreciate that it is not best practice. I have added a diagram rather than trying to explain the setup.Any advice appreciated? Solar_Setup_Wiring_Diagram.pdf

[solarix]

Won't work well to run charge controllers in parallel. They will fight each other for control of what voltage and current to run the array.

[grazza]

Thanks for the reply, its just a real drag as I have just the two cables running underground and will have to now split the PV array into two and run two additional cables, I guess its just the re assertion of the four P's principle. I presume running the output of the two SC's into one battery bank is ok to do once I have the two PV arrays?