question

What is the float voltage of your AC charger?

Whar are the voltage settings of your MPPT?

Float charge of my Zantrex Marine 30 charger appears to be 13.45V. It can't be adjusted. Two networked SmartSolar 100/50 are set to 14.6V Bulk and 13.7V Float. Each MPPT controller is connected to one 400W LG 72-cell panel. They charge 4 batteries connected in parallel, those are 170Ah Victron SuperCycle AGM so total of the bank is 680Ah. I just don't want to shorten the battery life by overcharging them when docked in the marina.

The simplest solution would likely be just to turn off the Xantrex charger when plugged in - you have enough solar to recharge batteries next day right?

My system is not in the same league as yours, but this is what I do. My charger is always turned off even when plugged in to AC power.

Well, even on a sunny day while on the West coast of Florida in the winter I still see 10 to 15 Ah hours shortage at the end of each day when using just solar for charging. So while your suggestion might work in the summer I need to figure something out for now. Would an AC relay, disconnecting MPPT output when on shore power do the trick?And why Victron can't make their SmartSolar controllers smarter and account for shore power chargers. All they have to do is prevent them from starting a new cycle when they see float voltage in the morning...

I have both shore power ProNautic 30 amp AC and Victron MPPT 100//30 charging my house bank and the shore power charger overrides the MPPT. The MPPT senses the charge coming in from shore power and ceases to charge from the PV. Plus, your Victrons should have BMS which would prevent overcharging. My Battle Borns have built in BMS, but I think Victron BMS is external.

"Would an AC relay, disconnecting MPPT output when on shore power do the trick?"

I have installed such a relay that automatically switches our RV TV plug from inverter to shore power when plugged in, but personally would not want to add extra things in the solar system circuits which could be potential problems.

If turning Xantrex off doesn't work for you, then toggling off charging in the app for your controller might be the next best easy thing. The downside to that is you have to always remember to turn it back on when under way.

Making a preset with lower voltages for your controller and switching to it while on shore power could work too, but really just easier to switch charging off, not really a solution.

But, maybe this is not really a problem at all - what does history show for time in absorption when on shore power?

If controller is set to adaptive absorption, the amount of time spent there should really be very short if solar starts for the day with batteries already at ~13.4V.

Tail current can also serve to keep absorption time short when solar starts for the day with fully charged batteries.

The history tab of the app shows that when the MPPT controllers wake up in the morning to float voltage maintained by the AC charger they go into the bulk mode for 2 hours on average and then into absorption for slightly over an hour...

I just checked my history from last year (I live in upstate NY so the boat’s in storage now). I was running 2 114AH FLA batteries off a Victron smart 100/30 MPPT and a Pronautic 30A charger. I see that each day the charger was on shore power the history showed a range of 30-140minutes on bulk then absorption then float for most of the day. You could set the bulk voltage lower on the MPPTs is that’s a concern. I’d not be as concerned about voltage if the amps were not high during the bulk phase. Does your AC charger show amps during its charging phases? Again, bulk phase without high amps shows the batteries are coming up to capacity, same with absorption and float phases. You could turn off shore power at sunset, run off your DC loads for the evening and then see what parameters the MPPT goes through the next day. Then do the same thing with the MPPTs, turning them off at night, running off DC loads and see what your AC charger does the next day. Finally, how old are your AGMs? Maybe time to sell your first born into slavery and get LFPs with internal or external BMS. I’m replacing my FLAs with Battle Borns this year when all this cold white stuff goes away.

My batteries are 2 weeks old, so I won't be replacing them any time soon and thus I want to ensure the longest life span possible. My concern is that while in winter the solar panels might not produce that much current if I leave the AC charger on and the MPPT controllers on in the summer they can overcharge the batteries every day. Now, the Victron manual says that disabling the output of the SmartSolar via VictronConnect should only be done for "maintenance". Does it mean I can't shut down the MPPT output for a long time when the boat is connected to the AC power? How about disconnecting the MPPT output from the battery via a manual switch or some sort of an AC relay? Will this ruin the controllers in the long run? I like Victron products but find that local dealers have little clue about intricate details and the tech support at the headquarter is practically unreachable...

Here’s what I did. The breaker switch leads from the panels to the MPPT so I can shut it off before the MPPT. I use a 30 amp model and it works just fine for my needs. You can use the Victron Connect to shut down the MPPT regardless of the warning. But I think the first option is better and more hands-on friendly.

And....I agree with you about Victron support. I’ve found really good support at Blue Sea and Battle Born, but sometimes the endless posts on Victron Connect leave me dizzy. The manuals and downloads are very good, but chock full of details that might appeal to EEs but are sometimes beyond the brain cells of we mortals.

BTW,, I spent a lot of time wondering and worrying about two charging systems on at the same time and found that the answer was that one overrides the other. The MPPT senses the charge of the batteries and regulates that charge based on the state of charge (SOC) of the batteries. Same thing with the AC charger.

You can adjust the Bulk, Absorb and Float voltages on the MPPT using Victron Connect. It may go into Bulk in the beginning of the charge cycle, but the current (amps) will decrease as the battery starts to reach its capacity. Same with Absorbtion. By the time the batteries get into that phase they are being gradually built up to capacity, and Float will keep them that way.

Suggest you also contact your battery supplier or manufacturer via website or email about what they recommend and any other question you may have.

If you‘re not going to be at the boat for extended periods and think the panels will not produce enough power in the winter then think about turning off the MPPT and just using shore power to charge batteries. I use both here in the summer with no problems.

I‘m still of the opinion that the MPPT bulk phase that runs for two hours is simply “goosing“ your batteries up to capacity but will not cause damage to the batteries. Remember, you’re charging a 680ah battery bank, which is a pretty deep hole to fill. The Zantrek is doing the charging when it’s plugged in and the MPPT is PROGRAMMED to go into bulk phase before absorption and float stages. That’s it algorithm. I’ve been “playing“ with my 2 100AH Battle Born LFPs this past week wired in parallel and hooked up to the Victron IP67-25 AC charger on my work bench since the boat’s in storage till spring. I hooked up the IP 67 and plugged it in, and once I programmed the profile in Victron Connect for 14.4 bulk, 13.6 float and 13.2 storage voltages (per Battle Born specs) the IP67 went to bulk phase for almost 2 hours, starting at a full 25 amps. Then went to 13.6 at decreasing amps until it went to storage at 13.2. These phases were gradual, not instantaeous, and the batteries arrived at close to their storage voltages of 13.2. If you’re concerned about the AGMs then I’d use that breaker switch to turn off the MPPT at the input (pos) cable from the solar panels. The Battle Borns have a built in battery management system that will prohibit overcharging them. Hope I’m not being too redundant here..

I guess I am not quite sure about how the SmarSolar determines if the batteries are fully charged. Do they monitor the charging current and stop when it drops below the preset? If so, are they tricked by the fact that my boat constantly draws some current (like 5 to 7 Amps when refrigerators are running) thinking that the current goes into the batteries. Or are those 8 Amps supplied by the AC charger? Or are they divided as in 4 Amps supplied by the AC charger and 2 Amps by each controller? Should I increase the tail current setting of the MPPT's? There is got to be an intelligent solution to this problem and I am sure it affects many people who live on their boats or in their RV's for periods of time connected to the shore power...

Are those refrigerators only DC or are they AC/DC? If the former then you are drawing 5-7 amps DC every time they cycle on/off. If AC/DC then your shore power would handle the load (AC) and not have an impact on your Zantrek or MPPT chargers. If DC only, and they cycle 3 times an hour then those fridges are drawing 15-21 amps an hour, and if they do this over a 10 hour period (when there is little or no sun to power your panels) then that’s 150-210 amp coming out of your 600+ amp hour battery bank.. The MPPTs are battery chargers, just like the Zantrek, except they draw power from your solar panels not AC current from shore power. The MPPT is sensing the battery bank’s total capacity (in amps) and will replenish it over its programmed algorithm of bulk, absorption, and float. The Zantrek is doing the same. They don’t split the difference. If you’re happy with the Zantrek then install the breaker or breakers to disconnect your MPPT from the panels and use solar when you’re away from shore power. Either of your charging methods is designed to keep your batteries fully charged and should be programmed for the correct battery type. Be sure they are set for your AGMs and let them do their job. Read over the manuals for both chargers. Contact Zantrek and the AGM suppliers for their recommendations. Hope that helps.

As soon as I add solar to my setup, I'll be in a similar situation (although with a Multiplus as the shore charger). In my case, I have a Cerbo and Smartshunt, so my plan is to use DVCC for shared current sense and set the MPPTs to end absorption on tail current. They'll still run through the bulk / absorb cycle every day, but they should get up to absorb voltage and fall below the tail current setting pretty quickly when on shore power (as the batteries are already full), causing them to drop to float.

I don't expect the few minutes of higher voltage will be an issue in my case. With a planned 820 watts of panels and a 415ah AGM bank the voltage should come up pretty quickly.

It would be nice if DVCC could have the Multiplus control the MPPT charging phases without ESS, however. The Multi and Cerbo already know that AC power is available and the Multi is in float, so it should be able to command the MPPTs to go straight to float. If the Multi isn't charging or hasn't reached float yet, let them do their thing as normal.