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crispyc asked

New Solar and Wind Charge Priority Questions

I have two questions on the new charge priority feature for solar over battery charger options.

I have a boat with a Victron MPPT 150/45, Inv/Chrgr w a VE Bus smart dongle, a Smart BMV 712, and dual bank 255 Ahr x2 lead acid batteries.

Inv/Charger works beautifully, MPPT works same. I wanted this new charge priority feature so when I am at a dock with shore power I can prioritize solar charging (nothing new), so I bought the dongle for the Inv/Chrg. The BMV and the MPPT are linked via VE.Smart Networking.

Q1- Should the Inv/Charger be connected VE.Smart Networking as well? The literature Ive read doesn't specify. I want the source battery temp and voltage to be the BMV 712 and I dont see a way to force this when the inverter is on the network.

I set the Advanced/Priority Charge feature to ON via a Mk 3 device and set the sustain voltage to the recommended Float minus 0.2V, 13.1 Volts for my system.

On a normal overnight with normal systems running my SOC would be about 91% in the morning when the solar kicks in. Im usually at 100% SOC in the early afternoon. FIrst day with this new setting I left the boat with batteries at 100% SOC from solar charging I came to the boat in the morning and the batteries were at 100%? Which means the charger kicked in overnight to cover the idle energy consumption.

What I want the system to do is permit the SOC to go down to maybe 75%, or about 2 and a half days at idle consumption, (undecided at this point) for times when Im on shore power for an extended amount of time but we have a series of cloudy days. My "idle" energy usage is about 1.0 kWh per day, but I can produce about 2.5 kWh per day on a sunny day. So I should be able to recharge significantly with a day of sun thrown in every now and then, without needing shore power, which I am charged $$ for.

Q2- If I want to allow the SOC to go to 70-80% before the shore power charger goes to work should I then set the "Sustain Voltage" to a voltage that corresponds to that the desired SOC? I dont see how what I want would ever happen with such a high recommended sustain voltage as float minus 0.2V.

EDIT: Corrected idle consumption and Solar production. Wrong decimal place.

Thanks in advance.

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2 Answers
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cardy01 answered ·

Question: Are you sure about your "idle consumption" values?

Answer to your Question 2: I assume that you want to support your AC loads from your battery as well as your DC loads? If so the Sustain mode is not what you want to select. Sustain mode prioritizes DC charging and DC loads from Solar but leaves AC loads on shore power.

https://www.victronenergy.com/live/ve.bus:solar-and-wind-priority

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crispyc avatar image crispyc commented ·
You are correct about the idle consumption value. Wrong decimal place, thank you. Its been corrected.


And thanks for the explanation. Its not really what I understood the new feature to do, but I think you are correct. So the feature is always wanting to keep the batteries topped up. Just for solar, during the day it will let the MPPT put in as much energy as it can. At night or high DC demand the Inv/Charger will charge the battery to keep it at least just below float voltage, correct?

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pwfarnell answered ·

Q1. From reading the manual you only need the Dongle on the inverter for the manual "charge to 100%" function, the inverter will use its own voltage. However if you can smart network it to use the BMV then I would do that but I do not know how as I have a Cerbo.

Q2. For lead acid I would set the sustain voltage to 13.2V, the same as the storage voltage. However, that would still keep the battery full. Sustain setting was never intended for what you want to do, the purpose is to keep the batteries full when there is no sun. If you want to allow it to use some of the battery capacity when there is no sun then you will need to reduce the sustain voltage to something like 12.5V. You will need to experiment to see how your voltage varies with SOC or look at your data. Temperature will also have an effect on the voltage for a given SOC. This could leave your batteries partially discharged for up to 7days which could start sulphation damage and is not recommended for lead acid batteries so you would need to manually charge to 100% if there were many days without sun.

There is also the issue noted above, all your loads need to be on DC for this to work, AC loads will always be supplied from shore power even with full sun.

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crispyc avatar image crispyc commented ·
Great information. Thank you. Yes, I got the dongle because it was listed as a requirement. I'm pretty disappointed by its capabilities, but that's another topic.


I think you are right, to do what I thought this would do would require tricking the system with the sustain voltage. Ill have to think about that. Probably wont mess with it.

One problem I currently have is my boat is 1993 tech. It originally had an inverter (removed before I purchased the boat) and I updated it with a Victron. The breaker panel has physical lockouts to prevent having the inverter on with shore or gen power tied to any bus. I dont really mind this, but I loose out on a lot of the nice features of a modern inverter/charger. Maybe one day I will update the breaker panel.

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