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Justin Tierney avatar image
Justin Tierney asked

Solar still trying to charge even though all devices configured to communicate

Let me start by listing some of the devices in my RV.

Mppt 100/30 solar controller

Multiplus ii 2x120

VE bus smart dongle

Gerbo Gx

2x LifePO4 batteries

I’ve got all the devices on a VE network and connected to the Gerbo. The Multiplus currently has the batteries at float because we don’t have much draw. The Solar controller is still in bulk (its a sunny day) and is trying to charge the batteries. It’s raised my float voltage from 13.8 to almost absorption level. It doesn’t appear to be putting in many if any amps but I thought the communication between all the devices would prevent something like this from happening? Is something configured wrong? I guess I could just turn off the solar controller from charging but seems to be against the whole design of these systems. Let me know thoughts, thanks!

Multiplus-IIMPPT Controllers
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Justin Tierney avatar image Justin Tierney commented ·
BMV 712 I also forgot to add.
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Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

Hi @Justin Tierney,

devices in a VE.Smart Network do not communicate with the Cerbo GX. If you want the Cerbo GX to control your MPPTs (provided DVCC is toggled on and your BMS/Battery talks to the Cerbo GX), they must connect via VE.Direct.

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Justin Tierney avatar image Justin Tierney commented ·
Correct, that’s the “and connected to the cerbo” I mentioned up top but I wasn’t very clear. All devices are also wired to the cerbo. I have generic internal bms batteries so dvcc I don’t believe is an option for me.
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JohnC avatar image
JohnC answered ·

Hi @Justin Tierney

Regardless of communications, the mppt will follow it's own charge algorithm, and won't be influenced by what the Multi is doing/has done. Unless of course it's under External Control, possibly with a system-controlling bms or even ESS. But you haven't mentioned such.

So look to your settings, the Multi first. If you were using a genset you'd probably want value from it, so you'd set it to a flat Abs V and switch the genset off maybe at >95% SOC. If a constant shore supply you could choose a flat Float V and let the solar do it's once-per-day Abs cycle. I don't want both to complete that cycle.

The standard mppt algorithm is pretty good on it's own, but there's little niceties like Rebulk V which add to how you really want it to work. The Tail Amps is really useful, as you get to choose from the battery's capability to accept charge at Abs V, how long to stay there. It can use it's own Amps, but best to use batt A from the BMV using DVCC (and I'm not sure why you want to dodge DVCC).

Actually the example you give in your question is what I want to see, not avoid. If there was plenty of sun and the batts were near fully charged, Abs V would be reached very quickly and drop to Float quickly too.

I guess my mindset is different to yours, but happy to discuss it further..

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Justin Tierney avatar image Justin Tierney commented ·
Thanks for the info. Honestly, I haven’t formed a mindset to either side. I don’t have enough knowledge or info yet to do so, but that’s why I enjoy this community. I’ve had my system setup for a while now and this is really the first time I’ve noticed this behavior. I was just wondering if it would cause issues with my batteries. To your point, there was enough sun to provide some good power but there were waves of clouds also. I think this is what made me notice this in the first place. It would start to get close to abs V then the clouds moved in and the voltage would hang for a bit until the sun retuned. I don’t have a genset, use ESS or such. My current configuration is set so only the solar does run it’s daily cycle and Multiplus is setup to cycle every 7 days, unless there is some large DC load but the Multiplus really handles that well. Glad to feel like my system is setup and working as it should. The only thing I’m confused about with your response is DVCC. Are you saying I should be using it or no? I only have generic LifePO4 batteries with built in bms’. Thanks again for the response.
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JohnC avatar image JohnC ♦ Justin Tierney commented ·
@Justin Tierney

Yeh, I shouldn't have used that 'mindset' word, we're all still learning. And I too will change my ways if I see/learn something better.

I'm saying a big YES to DVCC. I use it for all of it's 3 main functions, V, T and I. The I solely used for the mppt to terminate Absorb. And that tidied it all up, as I now never see excessive Abs, it ends when I want and never fails. Your Li's will have differing needs to my pb's, but you can adjust to suit.

The rebulking with intermittent cloud you can adjust too, but I don't think it would do harm in moderation.

Your system sounds fine to me, especially with a careful owner.. :)

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Justin Tierney avatar image Justin Tierney JohnC ♦ commented ·
Thanks for the info and direction! Much appreciated.
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