Question for the solar guys

[epretot]

Quick solar question.

I'm setting up my charge controllers for the solar and battery bank. My batteries have a recommended charge current of 40 amps. The maximum is 50 amps.

Here is my question. Because I have dual controllers, should I set the charge controllers to 20-25 amps? Or 40-50?

It makes sense to cut it in half. But then I considered the bank being series/paralell might allow for a greater charge current.

Any help is appreciated.

[freds]

Do you have enough solar panels that you can exceed this charge limit? Do both solar arrays output in sync or does one produce more more power in the morning and the other in the afternoon?

If you have Victron equipment you can have a GX control computer where you implement DVCC (distributed voltage charge control). Which would automatically balance between the two charge controllers to do maximum charging.

But it sounds like you already have your charge controllers, so yes set them both to 20 AMP's and maybe have less than full production.

[epretot]

Thanks for the quick reply. I do have two victron blue solar controllers.

I quickly realized I should have gotten smart controllers. Are the blue solar controllers able to interface with the GX?

The big disappointment in my setup is my controllers don't synchronize their charging.

To answer your question. I don't have enough data to definitively say if the output of the panels differ. I just turned them on yesterday. However, I'm getting 65-66 Volts from each array as it stands.

I also haven't really depleted my batteries much. I'm in testing so I'm going to leave shore power off for a while.

[epretot]

So you have all the info...

I have 2 arrays (3) 200 watt panels each.
24v battery bank (see charging specs above)
2 charge controllers 100/50 mppt

[freds]

Thanks for the quick reply. I do have two victron blue solar controllers.

I quickly realized I should have gotten smart controllers. Are the blue solar controllers able to interface with the GX?

The big disappointment in my setup is my controllers don't synchronize their charging.

To answer your question. I don't have enough data to definitively say if the output of the panels differ. I just turned them on yesterday. However, I'm getting 65-66 Volts from each array as it stands.

I also haven't really depleted my batteries much. I'm in testing so I'm going to leave shore power off for a while.

Yes they do interface with the Venus OS GX devices you need a USB adapter cable. Your options are:

1. Color Computer CCGX (old but works, going to sell mine soon).
2. CERBO GX which is the current device, but needs external screen. Lot's of interface options.
3. Raspberry Pi 4 with Venus OS image (which I am transitioning too).

The last two options allow you to run a large OS image which integrates Node-Red into the environment. With any of these options you get access to the Victron VRM cloud and use a phone app. Read through my 1980 Prevost build thread for more info.

What BMS are you using with your batteries?


Some more reading:

https://www.victronenergy.com/media/pg/CCGX/en/dvcc---distributed-voltage-and-current-control.html
https://community.victronenergy.com/questions/160294/clarifying-dvcc.html

[freds]

So you have all the info...

I have 2 arrays (3) 200 watt panels each.
24v battery bank (see charging specs above)
2 charge controllers 100/50 mppt

Ok 24v times 40 amps is 960 watts maximum charging rate and you have 1200 watts of panels. Your solar controllers can handle up to 2400 watts of solar panels.

I assume they are flat mounted so at the most you might get around 1000 watts and generally more like 800-900 watts.

So unless you are interested in automation and reporting just set each controller to 25 amps and there is little chance you will damage anything.

[freds]

A couple of YouTube channels you might like to watch are:

This channel deals mostly with the Cerberus GX:
https://www.youtube.com/@OffGridGarageAustralia

This channel deals mostly with Raspberry Pi 4 with Venus OS:
https://www.youtube.com/@tobisreallifeskillswithtobi

[epretot]

I really appreciate the help.

I'm learning a lot and it sorta makes sense. I just want to stay out of trouble for now. Learning to make the system more efficient is a future goal.

I'm using SOK batteries 206 amp hours. They have an internal BMS.

What are your thoughts on that?

[freds]

I really appreciate the help.

I'm learning a lot and it sorta makes sense. I just want to stay out of trouble for now. Learning to make the system more efficient is a future goal.

I'm using SOK batteries 206 amp hours. They have an internal BMS.

What are your thoughts on that?

I think you have to use the Victron Smart Shunt as the source of truth when using DVCC mode.

It needs a ve.Direct USB adapter https://www.amazon.com/Victron-Energy-VE-Direct-USB-Cable/dp/B01LZ6WTLW/ref=sr_1_2?crid=J4YMPDHOOLFU&keywords=victron+ve.direct+to+usb&qid=1691962832&sprefix=victron+ve.%2Caps%2C155&sr=8-2 just as the smart solar controllers need.

In my case I use a USB hub to connect these cables to and then a single USB cable into my CCGX device.

[epretot]

So...I had a little glitch in the system the other day. I looked at trends stored by the BMV and discovered this (see photo).

The battery voltage must have reached the max voltage shutdown of the battery bank causing us to have a loss of power. I'm still learning so I'm not sure where to go from here.

The graph shows the same spike every day. About the time the sun starts hitting the panels in the driveway. I turned the panel breakers off and lo and behold, no voltage jump. There is an exception. I got a similar jump one late afternoon.

Is this a problem? And should the controllers be managing this? The charge voltage is set to 25 amps.

[windtrader]

I did not chime in before as I'm more in line with epretot with respect to configuring Victron equipment. I swapped in a 24/3000 multiplus inverter/charger, a SmartSolar charge controller, and a Cerbo GX.
I have noticed a similar spike but have not studied to understand where it comes from. It could be the charge controller switching off for a moment but that would drive the open circuit voltage that would not pass through the system. This can be eliminated by watching for the spike once battery is full and in the evening. The other place is the inverter/charger might perform some operation but it couldn't generate voltage higher than the battery.

If the solar controller is switched off due to full charge, again, it can't pass higher voltage down the line. However, in cases where it is connected to th GX via the VE.Direct cable, it could and does send status so it could send open voltage.
I think I need one more Victron component but still assessing the need. The Multiplus is connected to the GX via VE.Direct and the SOC as those parameters are set in the inverter for calculations.
I was thinking is SOC may not be accurate as there is a dc-dc buck converter that does not flow energy through the inverter, thinking the SOC would miss this discharge from the dc-dc device, and be inaccurate. Then I thought the inverter could calculate SOC using voltage but that is faulty thinking. At present, I have not pressed the buy button for a SmartShunt placed right on the battery terminal line to ensure all drain from anywhere is captured and reported to the system, thus ensuring an accurate SOC value.

[thomasinnv]

The voltage spike and subsequent DC disconnect is due to the BMS high voltage cutoff. If you are charging to 29.2 that is most likely the high voltage protection limit of the BMS. With LifePo4 charging to 3.65v per cell is not necessary, and actually advised against. For a 24 volt system I would set the absorption voltage to 28.4 -28.6, float at 27.4 -27.6. Shunt settings should be charged voltage .1 to .2 volts below the absorption setting with a tail current 2% - 3%, peukert 1.01, charge efficiency 99% and charge detection time of 3 min.

If you are using 2 12v batteries in series, you need a balancer between the 2 series batteries. Contrary to what many people believe, lifepo4 batteries WILL get out of balance in series strings, especially if they reach high voltage cutoff.

[windtrader]

I see the same thing and have no Victron BMS. I do have a Victron charge controller that might cause this too. I will report back after studying it bit more.
I need to adjust 28.0 on charge cutoff (3.5* , maybe even less. It does settle down once it cuts the solar to about 26.5-27 and stays there for the duration (3.3*
Do you have a GX device? I've not had the time to dig into the logging and reporting. I'd bet the answer is found there as to what was going on during those spikes.

[epretot]

I see the same thing and have no Victron BMS. I do have a Victron charge controller that might cause this too. I will report back after studying it bit more.
I need to adjust 28.0 on charge cutoff (3.5* , maybe even less. It does settle down once it cuts the solar to about 26.5-27 and stays there for the duration (3.3*
Do you have a GX device? I've not had the time to dig into the logging and reporting. I'd bet the answer is found there as to what was going on during those spikes.

I do not have a GX...

[epretot]

The voltage spike and subsequent DC disconnect is due to the BMS high voltage cutoff. If you are charging to 29.2 that is most likely the high voltage protection limit of the BMS.

This was in fact the case. I changed multiple settings after reading through your reply and some additional research.

With that said. I set the Absorption to 28.8. The minimum recommended Absorption by SOK suggests 14.4 (x2).

However, I am still getting a glitch every morning. No complete power failure but glitches.