I have owned a catamaran for a few years now that have all Victron equipment - 4 360W solar panels, 2 MPPT 150/70 controllers, a Phoenix inverter and 4 230ah Super Cycle AGM batteries. The batteries were installed in 2022.
I left the boat “on the hard” in Aruba in Feb 2024 with no issues. Left the solar on, all loads off, and batteries performing well. We never hook up to shore powe . Fast forward to now, and the batteries are no longer holding a charge. During the day, battery voltage runs up to 14.4, controllers flip to float, but when the sun goes, so does the battery voltage. In preparing to leave the boat, I read several threads that indicated leaving solar on was a good idea.
I’m hoping that there is something I can do to bring these back or there is a setting off somewhere. I’m going to dump screenshots from my BMV-712 with the hopes something stands out. We used this system for 18+ months no issues with these settings. Any insights are greatly appreciated!!
Hi Paul.
They’re not accepting charge either. For 920 Ah of battery they should be ready to drop from Abs to Float when they won’t accept ~30A. They’ve probably vented dry from overcharge. Failed. If the casings are bulged, that’s it for sure.
You seem to have an Absorb period of some 5 hrs happening there. Those are low resistance batteries and that time is too long.
Also you have 4x in parallel, so one battery can be taking most of the charge, getting hot too. They may all have suffered this, and failed one-by-one.
And I suspect you don’t have working Temp Compensation either, even if you chose the correct battery for the sensor.
Paralleled Pb batteries require an amended, much more cautious approach to charging.
To add further to the above, if you had left these with no loads on then all the solar had to do was too up self discharge and cover minor stuff like monitoring equipment. The solar should have flipped from absorb to float within a few minutes. You should consider setting a tail current exit from absorb. For long term storage on my boat I reduce absorb and float voltages to 13.8V and 13.2V to give a storage voltage level.
Thank you John and pwfarnell. So it looks like I’ll have to replace these. To summarize your replies, 1) removing the load didn’t provide enough outlet for the solar, and voltages should have been reduced while the boat was on the hard? Here are the settings in use. Definitely higher than suggested here.
Before I replace them I’d like to make sure I know what to do differently.
I have Victron telecom AGMs with temperature compensation. I normally run at 14.4V absorption and 13.5V float with end of absorption at about 1.5% of Ah capacity.However if the batteries are warm or lower internal resistance you may need a higher tail current. When away from the boat I set absorption to 14.0V and float 13.2V. Only loads left on are the Cerbo, router, heating thermostat, GPS, battery monitors, level gauges, trickle charger for engine and bow thruster taking 15W. At daybreak I may see absorption for 10-15min max and then float at nominally 13.2V = storage mode. Just finishing my 4th season, batteries are not as sprightly as when new, but no need to change them yet.
You also need to enable expert mode and let us see what is in there as it has a bearing on this.
Do you have a temperature sensor connected to your batteries or are you relying on the built in temperature sensor in the MPPT. The latter choice is not ideal if the batteries see large temperature swings from daybreak to peak daytime temperature as it uses daybreak temperature. Your temperature compensation seems a bit low, and looking into this number or my Victron AGMs 15mV/degF seemed to be the number, is 9 the default.
AGMs have the lowest cycle life and the highest cost per cycle of all lead acid batteries (and LiFePO4.) Part of the reason is the delicate nature of the cell design. Should the cells become overcharged, or overheated, the internal pressure can cause them to vent electrolyte, resulting in permanent capacity loss. AGMs are also called “starved electrolyte” batteries, due to the liquid being absorbed in membranes, so there isn’t a lot of liquid to vent before the battery fails.
They are temperature sensitive, so temperature compensated charging is a must. Also, charging above 30°C ambient temperature should be avoided.
Typically, Absorb cycles for AGM are much shorter than Flooded Lead Acid - on the order of 90 minutes or so. Its best to terminate Absorb by monitoring when the net charge current reaches the Tail Current (typically 2-3% of the battery capacity.)
AGMs have fairly low self-discharge, and a fully charged battery with no load can go about 3 - 6 months before needing to be “topped off”.
If long term storage is in the cards, and the battery is left “in circuit”, a float-only maintenance charge is generally sufficient.
IME, AGMs work great - until they don’t - then tend to fail catastrophically. As soon as one cell fails, it sets off a “domino effect” of cell failure.
Keeping parallel battery blocks in balance is another factor. The general operational rule of thumb is to restrict the battery to no more than 3 parallel branches.
When replacing the battery, look seriously at lithium ferro phosphate. Higher usable capacity, simpler charging, better high temperature tolerance, lighter weight. and very long storage at idle.
Thanks for your insights. Here in Aruba, it is often hotter and inside the boat, while on the hard, even more so (130+ on some days). I think this definitely contributed to the demise of the batteries. It doesn’t appear I have battery temp monitoring, as the BMV-712 has a dash where the temp would be, and the MPPT controllers show temps north of 130, which I assume is ambient temp from a sensor within the unit.
I think I will look away from AGM as a replacement per responses on the thread. Thanks to all for weighing in.
It doesnt seem like I have an external temperature sensor, and the MPPt controllers have an internal one. Please see attached showing batteries at 185. The problem is, they are cold to touch, controllers are also cold to touch. Where is this temp coming from?. I am also including the setting shown in expert mode.
185degF = 85degC which is my normal unit of measure is insane or an error. Normally, the MPPT takes its temperature at daybreak for battery compensation. No idea where the 185degF is coming from, You say the BMV-712 does not have temperature sensor, do you have the aux port connected to anything else and set correctly, if it is not used at all make sure aux is set to none or nothing. I also suggest that you go into your GX device settings and look at DVCC and see if STS (share temperature sense) is enabled and if so what the source of the temperature is. Do you have a Smart Network (Bluetooth) running as well as VE Direct cables, that can cause some odd effects.
Your expert settings for absorption are why you killed your batteries, your tail current exit is set to 2.0Amps, which will NEVER EVER be reached with 920Ah of batteries. Because the charge current could never fall to 2.0Amps, it maintained absorption for 6 hours every day on full batteries and without functioning temperature compensation did this to hot batteries at full voltage. To be honest, I am surprised that your batteries are not bulging or split after this. The tail current setting is often quoted as 2.0% (percent not Amps) of your installed capacity, so 2/100 * 920 = 18.4A. If you look at your daily chart the tail current peaked at about 11.0 Amps, which is below the 2.0% threshold so absorption would have stopped immediately the voltage started to increase, going straight to float had it been set correctly. The 6.0 max absorption should also be set lower to stop this thing happening, perhaps 2 hours max. Whatever you choose to buy next, make sure the tail current is set to around 2.0% for AGM, probably higher for lithium. And find the cause of the extreme temperatures.
This makes sense. I will check into this in the am and see what I can find regarding temp sensors. The batteries have no deformities at all, measuring various locations. Thanks!.
I just wanted to follow up on this topic and the crazy voltage temps seen on the MPPT units. It turns out the Aux input was set to temp when actually it was starter battery voltage being monitored. I hadn’t configured this change and it turns out the boatyard did when they were “troubleshooting” the alarm before I got in the boat. I’m doing the math on what the temps would record with the input being the battery voltage, the temps ranging from 130 to near 190 checked out.
