Multiple charge controllers question.

[123easy]

I have often heard that if you want more panel capacity you can add a second charge controller. My initial feeling about that was concern that the charge controllers were designed to tailor their outputs by monitoring battery conditions and a second CC might adversely effect their algorithm. Is this simply false? If you really can add more charge controllers are there limits? Can you add two more panel CC sets? Three more panel CC sets? Would all that capacity dump current into the batteries too fast?

The ability of the system to use energy directly off the panels when the batteries are full is a function of a MPPT charge controller yes? Can you oversize the panel CC collection end and run multiple inverters without more batteries when the sun is shining to take advantage of this?

In my rookie mind the standard off grid system panel/battery ratio is about 3KW of panels and 8 L16s. Can you double, triple or quadruple the energy input to and output from those 8 L16s when the sun is shining? Limits?

[Mike90250]

I have 2 charge controllers, each with their own PV array. Everyone is happy, but the batteries keep asking me for a 3rd array and controller - which would not be a problem either.

Both controllers are different brands, both arrays are aligned differently. Took me about a week to tweak the settings so they tracked and shared the charging equally.

[chrisski]

I have two charge controllers for my 1 KW of panels. One for 600 watts of roof mounted panels, and the other for 400 watts of portable panels. Both at Victron and have a software that creates a shared network for the devices to work together automatically, almost as if magic. Saved the week of tweaking that Mike talked about.

The tilted 400 watt portable panels produce more power than the flat 600 watt panels, but the portable panels have blown over in a windstorm, but not the roof panels.

I want to get at least 400 more watts of power, probably more for my swap to 24 volts, and I will add at least one more charge controller for that,

My Victron does pull energy off the panels from the charge controller and panels when fully charged, but it does “lag” by a few seconds. Today my batteries were floating at about 6 amps, and I made myself a cup of coffee, which takes 70 amps of power for about 3 minutes. Within a few seconds, my charge controllers were providing 50 - 55 amps of power and the batteries were providing the other 15-20 amps. This did not happen instantaneously, but as I was watching the Bluetooth display, I could see where the energy came from.

The manual makes it seem like it takes 3 minutes to enter an absorption phase where more energy will be pulled form the panels and not the batteries, but with that high amperage load, it happened quicker.

I can only speak for the Victron 100/50, 100/30, and BMV-712 networking together like I mentioned. I’m unfamiliar with all the other multitude of combinations.

[123easy]

Thank you for the replies! Is there a spec listed in regard to charge controllers how fast they react when they see a big load come on and off?

[chrisski]

No spec for Victron about how quick it reacts to large loads that I’ve seen.

I'm finding the more charged my batteries are, the quicker the charge controller reacts.

Right now the sky is cloudless. My SCC is in the last few minutes of the absorption phase where the volts are a steady 14.7 and he current has tapered down from 25 to 7 amps into the batteries. At the same time the SCCs are sending 400 watts into the RV to power things, most of which is the electric fridge.

I think it’s neat that the SCCs is both charging and running that load steadily.

[Mike90250]

There is no spec for charge controller response, but I think it would be in the 10 second or less, ballpark

[MichaelK!]

Thank you for the replies! Is there a spec listed in regard to charge controllers how fast they react when they see a big load come on and off?

What is actually happening is that the controller is reacting to a drop in voltage at the battery. Under a low-load condition, your battery bank is fully charged, and at a certain voltage. As soon as you apply a heavy load, power is being pulled from the battery, which causes the voltage to drop. As soon as the controller senses a drop in voltage, it immediately starts sending more panel current into the battery to bring the charge level back up. All of these events take several seconds to take place. What you see is dependent on how big the load is and what your state of charge is. Another thing you can observe is that when the load is flipped off, the controller will continue to feed power into the battery, and will finally respond to the battery reaching full charge again by cutting back on the current. So, it not only a matter if your controller spec, but also your battery spec.