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adrianp105 avatar image
adrianp105 asked

One Bus Bar set for Multiple Arrays and Controllers?

Hi all, I've designed my system to have three (3) PV arrays (one east facing, one west, and one south - all 18v max @ 100w) - the eccentricities of the area required this odd combination to achieve the desired output. I have three SmartSolar MPPT 75/15s that I intend to connect to a Cerbo GX with VE.Direct cables. It is my understanding that I need the Cerbo with arrays facing different orientations and drastically different performance throughout the day. All of my loads will be 12v DC, so I will not be using an inverter. I had initially planned on doing a separate busbar out of the load side of each controller, then connecting a group of loads to each of those busbars. But I have seen a few schematics where multiple arrays have one positive and one negative bus bar for the entire system. I want to take advantage of the controller load output to regulate the load for sensitive electronics. Is there anything wrong with doing separate busbars for the load out on each controller or am I missing an important feature/benefit to combining the busbars. Thanks in advance.

MPPT Controllerscerbo gxVE.Directbusbar
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Mike Dorsett avatar image
Mike Dorsett answered ·

Separate load outputs are fine, you can even set different voltage limits for each of the controllers load switches. I don't see the need for a Cerbo in such a simple system, unless you are also using managed lithium batteries. Careful setting of the MPPT voltages will be needed, as well as attention to volt drop on the battery cables to the MPPT's.

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adrianp105 avatar image adrianp105 commented ·

@Mike Dorsett Thanks! I've been careful to limit the voltage drop between the controllers and battery, and I feel confident that I can calculate/observe that drop. What voltage setting are you referring to that I should be careful about and how do I incorporate the voltage drop information?

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Mike Dorsett avatar image Mike Dorsett adrianp105 commented ·
The only way of incorporating the volt drop information is with software, either custom, or by a venus device. With small arrays, this should not be requuired, as long as the volt drop (rise) between the mppt and the battery busbar is <50mV. (This can be dificult to do on larger systems - at 70A, my mppt has a 200mV rise ).

The voltage settings for Absorption and Float need to be carefully set, as one MPPT reaching Absorption can put the others into float - particularly if their arrays are shaded at that time. This can cause a loss of energy harvest if one of the MPPT's in float mode later becomes unshaded, and the original mppt then becomes shaded. This can be overcome either by a software command to go back to bulk mode, or by keeping the Float voltage higher on he last mppt to be illuminated

This also depends on your battery type, and how much excess energy you have in your system..


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Leslieanne avatar image
Leslieanne answered ·

Hi,

If you were to add a BMV or a Smartshunt to your system (well worth it anyway so you know what your battery is doing), then voltage drop and coordination of controllers is no problem at all. Simply set up a ve network over Bluetooth (BMV or Smartshunt first, then add the mppts to that network), set the same charge parameters on each controller and that's it. It's very simple, no need for a GX device.

Cheers, Leslie

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adrianp105 avatar image adrianp105 commented ·

I did order a Smartshunt based on your comment and others as well. I've been searching Victron's prodigious catalog of manuals and data sheets to find something I read a while back, no luck finding it though. Basically it said that if you have arrays facing different orientations (such as one facing east and another facing west) the Cerbo (or other GX) is required as the VE.Direct between the controllers alone is not sufficient to optimize the charging algorithm. Does anyone know which manual that would have been in or if that makes any sense?

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Leslieanne avatar image Leslieanne adrianp105 commented ·
Hi Adrian,


Maybe you are worrying too much!

If you use the ve Bluetooth network (no ve direct cables needed) then the true battery voltage and current (from the smartshunt) is sent to the mppts, and they will all switch to absorption and then float, based on your battery voltage and tail current settings...as they should, regardless of orientation. If the battery voltage later drops as you use power, then the mppts will switch back to bulk according to your rebulk setting. Make that close to your float setting if you want to keep the charge level very high until sundown. I have had a similar system with 2 x 75/15 mppts and a 100/30 mppt with LiFePO4 batteries for years on a caravan. It works well, as it did even before Victron introduced the synchronised charging feature to the Bluetooth network. But, seeing all controllers switch states at the same time seems to keep some folks happier!

Cheers, Leslie


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adrianp105 avatar image adrianp105 Leslieanne commented ·
Thanks!
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kevgermany avatar image
kevgermany answered ·

An observation. You say max panel voltage is 18. You need to be higher than this for the MPPTs to start charging ( more than actual battery voltage+5). Hopefully your panels will be wired in a series/parallel setup.

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adrianp105 avatar image adrianp105 commented ·
Thank you, I did a test and my multimeter is reading 25v and the open circuit voltage is actually listed as 21v in the data sheet (the labeling on the back of the panel saying 18v max appears to be incorrect.)
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Leslieanne avatar image Leslieanne adrianp105 commented ·
That "18v max" is the voltage for "maximum power", and is typical for so-called "12v" panels, with OCV around 21 volts.
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