Solar / lithium question
- Thread starter xavpil
- Start date
200 watts is about 16 amps, and overnight you’re running it for about 12 hours or more before the solar can do anything again. To a reasonable approximation that’s about 200 amp hours, or half of your capacity. If you’re starting the night at 85% you should still have something left by morning.
How are you measuring your State of Charge and loads? Is it possible that something is out of calibration there and either you’re starting at a lower SOC than 85%, or you’ve got some other loads that aren’t counted in the 200W?
How are you measuring your State of Charge and loads? Is it possible that something is out of calibration there and either you’re starting at a lower SOC than 85%, or you’ve got some other loads that aren’t counted in the 200W?
Simple math - you’re drawing an average of 16 amps @12v or 15.4A@13v. You should be able to run them to zero in about 24 hours in theory. Maybe you’re drawing more, have less than rated capacity, or not accounting for some other losses.
IMHO your house bank should be rated for more of a safety factor, and you should install a low voltage disconnect (LVD) so you don’t run them to flat zero (food is cheaper to replace than lithium batteries).
IMHO your house bank should be rated for more of a safety factor, and you should install a low voltage disconnect (LVD) so you don’t run them to flat zero (food is cheaper to replace than lithium batteries).
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I am looking at the Victron screen that shows the data
I guess I need a bigger battery bank then
I went through my system today and can’t see or think of anything that isn’t accounted for….
Victron must offer that feature.
great idea
That's a lot of power draw overnight. What exactly are you running? Remember running AC loads off the inverter is very inefficient, with about a 10% loss in the conversion from DC to AC. Time to look for inefficiencies in the system and shut down any unnecessary electrical devices.
lets find out what the loads are first.
Turn off all DC loads then check your Victron meter to see if any loads are showing up. then turn on 1 item at a time and see what the load is , turn it off then due the next. now you will have some idea what your total loads are. I did this and found that with 200 ah I could last 2 days without solar (have 600 watts) so I added another 200 ah of batteries so I can be on the hook for a week before I need to worry.
Turn off all DC loads then check your Victron meter to see if any loads are showing up. then turn on 1 item at a time and see what the load is , turn it off then due the next. now you will have some idea what your total loads are. I did this and found that with 200 ah I could last 2 days without solar (have 600 watts) so I added another 200 ah of batteries so I can be on the hook for a week before I need to worry.
Are you sure the Victron devices are set to the right bank size (400 AH)? If you’re going down to 0 overnight and getting back to 85% with solar that suggests you’re putting 4000 watt hours back into the bank over the day. That amount of recharging should only be possible with about 1000 watts of solar panels, which is a solar array usually only seen on multihulls. So either you’ve got more solar than I expect or your Victron equipment is underestimating your bank size, thereby judging that you’ve exhausted all your capacity before you really have, and put it much of it back in before you really did.
All battery monitors do is to offer an educated guess as to state of charge. The programming of battery capacity, Puekert exponent, and charge efficiency variables all affect the accuracy of the guess.
What Victron screen? Do you have a shunt based monitor (BMV-712 or SmartShunt)? What solar controller? 99% of the time I see someone report a disparity between actual SOC and Victron reported SOC it is due to an improper “Charged voltage“ setting in the BMV/SmartShunt. The default setting doesn’t work with most solar charged systems. You should have the “Charged voltage“ set at 0.2V below the absorption voltage in the solar controller. Also if it is a Victron SmartSolar MPPT be sure to set up the ve.smart network and connect to the BMV/SmartShunt, if that’s what you have. This will ensure the MPPT compensates for voltage drop and doesn’t float early.
Setting up a battery monitor correctly requires some effort and homework. Maine Sail has covered this, of course at Marine How To - DIY for Boaters - Marine How To
On my Link 2000, I rarely bother with the SOC display, but rather deal with AH, both in & out.
This is correct. Also, you should not “float” lithium. Your charge controller should be set to stop charging after only about 5 minutes of reaching max charge.
This video explains it
Yep. My on the hook Solar float voltage is 13.4V which allows a small discharge… but I try to rarely get there. You can almost always take advantage of excess solar to do something. On shore power I usually set around 13.2V. As far as absorption time, there‘s a lot of competing advice there. I think Kilovault was 6 minutes. Lithionics is 30 minutes for balancing with a full charge recommended every 2 weeks. Victron says 2 hours per month, and Nordkyn design recommends tail current based on absorption voltage. When I use tail current the absorption time varies from 5-15 minutes.
There might be a mismatch between your actual state of charge and what is showing on the Victron screen. When we installed our batteries, we used the batteries' internal regulator via Bluetooth to make sure we charged to 100%. Then we synchronized with the Victron unit. Now, the information on our Victron screen is pretty close to what comes up on the batteries' internal regulator. if you have Bluetooth, you can easily check your actual state of charge. If not, it might be difficult.
Victron monitors have a setting called 'discharge floor'. If its set to 50% (which is default i think) then the monitor would read zero if you discharged to 50% of the batteries capacity. I set mine to 0% so i always know exactly how much energy is still in my batteries but many people set it to 20% for lithium as that is the recommended depth of discharge for most lithium. I'm wondering if your settings are correct.
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The SOC calculation isn’t affected by the “Discharge floor”, so that shouldn‘t be his issue.
“7.2.3. Discharge floor
The “Discharge floor” parameter is used in the "time remaining" calculation. The battery monitor calculates the time it takes until the set “discharge floor” has been reached. It is also used to set the state of charge alarm defaults.
For lead-acid batteries set this to 50% and for lithium set it lower.
Note that this setting only appears when accessing the battery monitor via the VictronConnect app. In case the battery monitor is accessed via the head unit, see the Low State of Charge (SoC) relay setting instead.”