Has worked great, untill my BMS disconnected the loads.
This because temperature setting on thermostat on which it would start to heat (5C), was set lower than allowed by setting in BMS (6C).
Disconnect was around 2AM, noticed it at 8AM, connected with BMS and lowered the allowed temp setting to 4C and restarted.
Worked as expected, Victron system came back online, but it looks like the voltage readout is lower since this event.
Not really visible in this graph, heating element (130Watts) was on for few minutes.
Please note, this is just a question âas expected? possible to reset/correct remotely?â It could even be that solar power is to low anyway (about 250Wp connected). It might even solve itself with a few good sunny days. But the graph looks so weird. âAs expectedâ could be due to decreasing solarpower, its my first âwinterâ with this setup. Eventually (below say 26V?) I will go onsite to measure things.
Why would mppt voltage be lower than than battery voltage and still charge?
It looks to me that only explanation should that the voltage reported by the battery is incorrect (to high). But still have to measure. Will do this tomorrow evening.
Thanks for your reply Yetlag!
Yes, the settings are still the same, at that point I was just able to connect to the battery (wifi over mobile hotspot with internal battery, love it),
And lowered the allowed temperature for loads to 4 degrees C instead of 6, which was an error on my part. Than reset the BMS to be sure, and all came back online. So in fact the battery did ââdisconnectâ (was switched off) for around 6 hours. I know there are Mpptâs which can damage the loads by voltage overshoot while disconnecting, but could it be damaged by just reconnecting to the battery? At almost zero sun? Plus, it still seems to work. But with strange voltage reading. The PID thermostat is set to 5 degrees, so heating was on for probably around 5-10mins (130watts). So I understand the battery voltage sagged a bit, it is in a quite low state anyway, due to the limited solar energy of december. So the battery is already in the region where the voltage drops faster per consumed Wh.
My current assumption: itâs just really low on solar power at this moment, and the short heating usage made the difference in voltage. Nothing wrong, will solve itself with a few days of good sun. I will go onsite Thursday evening to measure things. No panic, just another learning experience Thanks for your at least emotional support haha
Replying to myself again; this evening I will go onsite to measure things. I changed the graph a bit, it now shows the battery current, instead of PV charger current. That hides the current which is needed to keep the Victron stuff running. Mostly the XS1400 charging my starter battâs, but also Quattro 5000W -switched off-, GX, Mppt) Starter batts are brand new and charging them takes about just a peak of 200mA once a week / small peaks of mAâs to keep them on float voltage. I noticed the graph now showing the Lifepo4 batt voltage level declination is flattening. Which feels to be on par with a bit increased solar input.
Battery current is significantly lower than PV current. The difference of solar input is consumed directly by rest of system.
2 shutdowns, after first one the minimum needed temp (edit: on BMS) was lowered to just switch on the loads, after second shutdown the thermostat was set 1C higher.
I still donât quite understand the rather sudden drop of voltage the mppt is showing, compared to what the battery is showing; But I do I sort of assume itâs normal behaviour, just at the same moment battery did consume energy to warm up after the short shutdown and solar inpout dropping.
I also looks like my relative small solar panels (2x 130Wp, laying almost flat) are barely able to deliver enough power in december. and january probably
Me again. Measuring while dark, without solar power isnât as informative as hoped. Measured resistance of cabling, about zero. Voltage on battery and MPPT are the same, but without current thatâs as expected. Measured voltage of battery with fluke, is exact the same as BMS reports. I noticed in the graph that the difference in voltage between what mppt reports, and what bms reports, is always 0,6V. MPPT being the lower one. e.g. Just a diode/FET threshold?
But still, all is working perfectly fine. I still assume itâs just due to my quite limited amount of Wp solar. (2x 130W in series, laying flat).
Once it will be freezing the energy usage of the heating will be the killer, but Iâll manually charge the battery before that.
Question: is a lifepo4 battery in high SOC prone to lose more energy per day than a battery in a lower SOC?
The MPPT canât charge the battery if the MPPTâs charging voltage is lower then the battery voltage. So this visualisation canât be correct.
It does not depend on the solar power, because only 10W from the pv modules would charge the battery with the correct voltage, but only with low current.
You should definitly measure the MPPTâs voltage (at the terminals) when there is solar power, - even if it is a few watts only. I assume the voltage is correct (at least the same as the battery voltage or slightly higher). Otherwise there would be no positive charging current into the battery.
Another aspect could be, to reset the widget. Maybe you delete it, and create it again from scratch⌠donât know why, but it might be visualizing incorrect somehowâŚ
And no, a LiFePO4 battery is fine with a high SoC. If you want to store it for month or so, then it would be better to store it with about 30-50% SoC, but if you cyclically use it, then it is still fine. It depends more on the voltage, so if possible you can drop the battery to a float voltage (e.g. 3,35V/cell), that is lower then the absorbtion voltage (~3,45V ⌠3,5V/cell).
Yes totally agree, thatâs why Iâm a bit puzzeled by the situation. I do have a spare mppt too. Will be back there tomorrow to spend more time. Regarding the widget, canât remember 100%, but I thought I created it only afterwards. But in any way, this same voltage showed up in other graps showing mppt info.
BMS voltage info was consistent before and after the disonnect. Also BMSâs Highest and Lowest Cell voltage where consistent before and after.
Me again, special message for Jetlag. Was onsite yesterday, swapped the mppt for new one, problem solved. That unit is seen as new device (ID), widgets will need to be adapted (not an issue, I only have a few). But to prevent this and off course actually test the old one, I swapped the old one back in. (edit: and worked fine again)
I had the new one in for only a short moment, so the graph only shows the info of the old device. I changed the scale of the graph a bit to see the difference in voltage better. At the end the mppt is 1mV higher then wat BMS says.
Apparently the solarpanels still produced some voltage, but not enough to actually charge?
A well, it looks solved. Will keep an eye on it all day haha. I assume it will charge as much (/as little) as before in December.
Still weird event
So did I get you right, the hard reset of the MPPT solved the issue and the old MPPT is again working correct?
But interessting would be to know what voltage did it provide before you swapped it. I canât imagine, that the voltage of the MPPT was really lower then the battery voltage. In such a case the MPPT would consume energy from the battery. Did you measure this before disconnecting it?
Yes that is correct, solved after the reset.
Before the reset it did work (charged etc), but reported the battery voltage to be lower than reality (or what bms reported).
What Bms reported was the same as before the temporary shutdown of the battery. But after this shutdown, the MPPT showed .. say 0,6V lower voltage.
Yes, to be sure measured again briefly, was same as before. Measurements were ok, reported info in graph wasnât (Reported MPPT voltage was lower than wat BMS reported).
Thanks for your at least emotional support haha
