BMV-712 Proper settings with Solar Panels

Dutch061Dutch061 Member Posts: 377
The BMV-712 by it's default configuration will "falsely synchronize to 100% SOC" when combined with solar panels unless you actually read the manual and set things up accordingly.

This also contributes to the previously incorrect data I once provided on "how quickly the solar can recharge after running a 12 volt compressor refrigerator overnight". 

The settings that need to be carefully inspected and set up are in bold as follows, the rest are the settings that I used that do not affect the interaction with Solar Panels.   

Battery Capacity - I know, everyone had to set that up initially

Charged Voltage - this is automatically set based on the detected voltage IE 12 Volt is set to 13.2 Volts - this is NOT correct for use with a solar charging input. It needs to be set to 14.2 Volts

Discharge Floor - not that important because you can base the remaining energy on the display of the BMV-712 - ** appears to be used for Relay control more than anything else

Tail Current - I believe the default is set at 2% but based on the manual for the BMV-712 it should be set to 4%

Charged Detection Time - Default of 3 Minutes is fine

Peukert exponent - set to 1.10 based on Victron's app and the Harris Battery Info, mine was set to 1.25

Charge Efficiency Factor - was set to 95% but from what I was able to find on the info highway, AGM are about 80% ** Harris Battery confirmed that 80% is the correct value to use for their batteries

Current threshold - default of .10 Amps is fine

Time to go averaging period - default of 3 minutes is fine

Battery starts synchronized - default it is on, I turned mine off. It is my understanding that if your master switch turns the power off to the shunt, it will reset to 100% on power up regardless of the actual state of charge.

So, here is where I got into my "situation". Recently on 3 nights of boondocking, I woke up on day 1 having used roughly 55 amps of my available with a SoC of 81%. I turned on the invertor and made my coffee as usual, taking about 6 amps over the course of the 5 minutes to brew. Went hiking, came back a few hours later to find SoC at 100%, all is great!

Day 2, I wake up and once again I had used roughly 55 amps and had a SoC of around 80% remaining. Went to make coffee and it was a no go, there wasn't sufficient voltage available to operate the invertor under the high demand (draws about  55 amps) while brewing. So, I connected my generator and made my coffee.

In roughly an hour, I had "fully charged the batteries (BTW I am using a PD9260C installed within 12" of the battery junction block) but as I watched I could see that even though the BMV-712 showed 100%, that I was still pushing 40 amps into the batteries. This was obviously letting me know that "100% wasn't really 100%" based on the rate of charge still going on.

One would think that if you had something monitoring the amps used that once those amps were replaced that this would initiate the synchronization to 100%. However, that is not how the BMV-712 actually works.

Synchronization occurs as follows:

Example: by default if the Voltage is greater than 13.2 and the amperage flowing is less than 4.48 amps for 3 minutes, the BMV-712 automatically sets the SoC to 100%.

In order to overcome this, you need to set the Charged voltage to .2 volts less than the Absorption voltage (14.2 with the OEM installed Harris AGM's). This alone should correct the issue, but I also set the Tail current to 4% based on the BMV-712 manual. There was no need that I could think of to change the time period that these 2 conditions needed to be met. 

So now in order for SoC to be synchronized to 100%, I need to see greater than 14.2 volts with less than 8.96 amps flowing for 3 minutes. 

Disclaimer... I am still working on a couple of these settings and the Tail current being set at 4% of the amp capacity of the batteries may be too high (even though that is what Victron recommends). This is a work in progress and I will update things as needed. 

Brad

Edited adding information noted with asterisk
2020 400 BDL
2021 F-250 Tremor with PSD
Concord, NC 

Comments

  • Denny16Denny16 Member Posts: 3,292
    Nice info, thanks for sharing.
    cheers
    2018 TaB400 Custom BoonDock, Jeep Gladiator truck, Northern California Coast.
  • dlbdlb Member Posts: 87
    Thanks for this information.  I will check my settings since I had the 100% SoC show up and thought it could be fiction.
    2021 Tab 400 Boondock
    2020 Audi SQ5
  • Sharon_is_SAMSharon_is_SAM Moderator Posts: 7,570
    “ It is my understanding that if your master switch turns the power off to the shunt, it will reset to 100% on power up regardless of the actual state of charge.”

    @Dutch061 - Do you mean the battery switch when you say master switch?  Our BMV has a cable to the positive battery terminal, so even if the battery switch is off and the TaB is isolated from the battery, our BMV display remains operational.  Since the display is wired to the shunt and the shunt is off the negative terminal of the battery, you should not lose power to the shunt with your battery switch off the positive battery lead.  
    Sharon / 2017 [email protected] CSS / 2015 Toyota Sienna Minivan / Westlake, Ohio
  • Denny16Denny16 Member Posts: 3,292
    Yes, this is how our shunt is installed.
    cheers.
    2018 TaB400 Custom BoonDock, Jeep Gladiator truck, Northern California Coast.
  • TomCanadaTomCanada Member Posts: 225
    @Dutch061 I read your post with interest as I've been researching these settings myself.  Everything you wrote makes sense - though I would suggest definitely backing off the tail current.  I have mine set to 1.5% and although I have not yet done extensive testing, it would make sense that the lower setting would keep the BMV from synchronizing too soon (9A is still a lot of tail current at the 4% setting).  Let us know how your experiments go!

    ps. the "discharge floor" is used as the basis for the SOC calculation.  So if you set your discharge floor to 50%, and you've used 10%(22.4Ah) from your 224Ah battery, your SOC will be reported as 80% (not 90%).

    pps. The efficiency factor is a hack of a number - in bulk phase, the charging is 99% or so efficient, and this gradually decays as the battery goes into absorption and higher SOC.  The last 1% of capacity can take hours at extremely low efficiencies.  But the battery monitors aren't smart enough to know what phase of charging you're in, so they just use a constant 'efficiency' number.  So nobody really knows if 80%, 90%, or 95% is best - it depends on your battery's SOC while you're charging.
  • Dutch061Dutch061 Member Posts: 377
    edited April 16
    “ It is my understanding that if your master switch turns the power off to the shunt, it will reset to 100% on power up regardless of the actual state of charge.”

    @Dutch061 - Do you mean the battery switch when you say master switch?  Our BMV has a cable to the positive battery terminal, so even if the battery switch is off and the TaB is isolated from the battery, our BMV display remains operational.  Since the display is wired to the shunt and the shunt is off the negative terminal of the battery, you should not lose power to the shunt with your battery switch off the positive battery lead.  
    Yes, Master Switch. If the power for the BMV-712 is connected directly to the battery and not "switched off" with the master, it will not synchronize when turned on. I installed mine (hence the reason I have discovered the issues caused by not reading the instructions) and connected mine directly to the battery positive also. I only mention this because someone could certainly install it so that it is switched, which could be better for someone who stores their camper in a building over the course of a very long winter. 

    Brad
    2020 400 BDL
    2021 F-250 Tremor with PSD
    Concord, NC 
  • Dutch061Dutch061 Member Posts: 377
    edited April 16
    TomCanada said:

    ps. the "discharge floor" is used as the basis for the SOC calculation.  So if you set your discharge floor to 50%, and you've used 10%(22.4Ah) from your 224Ah battery, your SOC will be reported as 80% (not 90%).
    Although it is used "for scaling", my experience was that I used 55 Ah and had a SoC of 80%. This is a little off of the actual 76% it should have shown (55/224 = 24.5% used) but could have been caused by a "false SoC of 100%" on Day 1. Using this as a sole basis for calculations, the SoC would have shown 51% (55/112 = 49.1% used)

    It appears that this is used more for calculating "time to go" at the present load and can also be used to control of the relay (which I am not using and doubt anyone else is either) based on the information in the manual. It makes sense though, you could set a minimum battery level and use the relay to shut down the load to prevent further discharge IE having a dead battery in the morning.

    On the Tail current, I agree with your logic but for the voltage to make it to 14.2 on solar alone, the Tail current will have to be very low. I set it to 4% based on the manual and it may be one of those I go back to later and set back to 2% where it was originally. 

    I have also requested a Charge efficiency factor from Harris Battery and will modify the original post when I have it. 

    Brad
    2020 400 BDL
    2021 F-250 Tremor with PSD
    Concord, NC 
  • jkjennjkjenn Member Posts: 6,343
    edited April 16
    For posterity, I am adding a link to a PDF from Victron with the correct settings for a Lion Energy Safari Lithium  battery. 

    There is an interesting note with the charged voltage (13.9)

    "This is where things differ a bit from other Lithium 
    Ion battery manufacturer’s batteries. Due to the 
    nature of the (very good) battery management 
    system (BMS) in the Lion Safari UT batteries, the 
    state of charge (SOC) measured by the Victron
    BMV battery monitor can get out of sync with the 
    actual SOC of the battery causing the displayed
    battery percentage to drop slowly over time. To 
    avoid this the Charged voltage is set to 13.9 volts. 
    (This change will also be made later in the MPPT 
    charge controller as well)."

    https://community.victronenergy.com/storage/attachments/18212-lion-safari-config-for-victron-bmv-battery-monitor.pdf

    2021 [email protected] 320 Boondock "Mattie Ross" | 2021 [email protected] Nights: 115 | Total nights in a [email protected] 326 | 2018 Jeep Grand Cherokee Trailhawk | [email protected] owner since 2014

  • Dutch061Dutch061 Member Posts: 377
    @jkjenn, thank you for sharing; I had seen this on BB's website also. I will likely end up with Lithium in the end but would like to believe that I can use the AGM's for at least 2 years possibly 3 before I do. 

    BB is very good at providing all of the information and probably have the overall best Lithium Iron Phosphate Batteries on the market today for the price point. I base this on hours of reading, research, and dissection of batteries by Will Prowse on YouTube. 

    Brad
    2020 400 BDL
    2021 F-250 Tremor with PSD
    Concord, NC 
  • jkjennjkjenn Member Posts: 6,343
    Dutch061 said:
    @jkjenn, thank you for sharing; I had seen this on BB's website also. I will likely end up with Lithium in the end but would like to believe that I can use the AGM's for at least 2 years possibly 3 before I do. 

    BB is very good at providing all of the information and probably have the overall best Lithium Iron Phosphate Batteries on the market today for the price point. I base this on hours of reading, research, and dissection of batteries by Will Prowse on YouTube. 

    Brad
    I saw Will's video and personally, I thought his video had some issues. 

    He mentioned the strength of the plastic. Thickness does not equate to strength. Some YouTube have dropped Lion Batteries from ladders onto concrete and the batteries were fine, but the concrete was not.

    Also, regarding battery terminals, if mounted properly, you shouldn't need the terminals to be as strong as Fort Knox. What Wll fails to mention is that you can always choose another type since the Lion Batfery terminals are replaceable.

    After reading and watching a number of reviews, I went with Lion primarily because they use a cylderical cell, which allows the Lion Energy batteries to be smaller and several pounds lighter. I also was able to get them for about $150 less per battery. I have a video coming out tonight to show the installation.

    2021 [email protected] 320 Boondock "Mattie Ross" | 2021 [email protected] Nights: 115 | Total nights in a [email protected] 326 | 2018 Jeep Grand Cherokee Trailhawk | [email protected] owner since 2014

  • TomCanadaTomCanada Member Posts: 225
    Dutch061 said:
    TomCanada said:

    ps. the "discharge floor" is used as the basis for the SOC calculation.  So if you set your discharge floor to 50%, and you've used 10%(22.4Ah) from your 224Ah battery, your SOC will be reported as 80% (not 90%).
    Although it is used "for scaling", my experience was that I used 55 Ah and had a SoC of 80%. This is a little off of the actual 76% it should have shown (55/224 = 24.5% used) but could have been caused by a "false SoC of 100%" on Day 1. Using this as a sole basis for calculations, the SoC would have shown 51% (55/112 = 49.1% used)

    It appears that this is used more for calculating "time to go" at the present load and can also be used to control of the relay (which I am not using and doubt anyone else is either) based on the information in the manual. It makes sense though, you could set a minimum battery level and use the relay to shut down the load to prevent further discharge IE having a dead battery in the morning.

    On the Tail current, I agree with your logic but for the voltage to make it to 14.2 on solar alone, the Tail current will have to be very low. I set it to 4% based on the manual and it may be one of those I go back to later and set back to 2% where it was originally. 

    I have also requested a Charge efficiency factor from Harris Battery and will modify the original post when I have it. 

    Brad
    Re: depth of discharge, the manual states "The battery  state of  charge  indicator  (see chapter  7  “Display”)  scales  between the configured  discharge floor  and 100%  state of  charge  and reflects  the effective  state  of  charge.". Are you saying you're not seeing this behaviour?  What's your discharge floor set to?

    Re: "for the voltage to make it to 14.2 on solar alone, the Tail current will have to be very low" I don't think this is the case. The BMV is monitoring the output voltage from the solar controller.  You should see 14.4V as soon as you hit absorption mode which can still have quite high current until the battery tops up towards the end and the controller drops to float. The intent of the high 'charged voltage" setting is to set a level where clouds that drop output current below the tail current threshold don't result in a false "battery full" condition (because the voltage will drop below the "charged voltage' threshold, eliminating one of the prerequisites for the "battery full" condition).  

    I wonder if perhaps you have a condition of moderate solar intensity where your solar output voltage is still above your "charged voltage" threshold for 3 minutes, but where your tail current has dropped behind your 4% tail current setting, so the BMV thinks it's full prematurely.  Lowering the tail current here would help if that's what's happening. Victron recommends 4-5% tail current in general but other RV and marine forums I see people running mostly 0.5-1.5%..

    Did you confirm your 55Ah recharge matches what the solar controller actually fed in (via checking the controller's history in the app)?  If solar delivered less (eg 20Ah) than what you used (55Ah) and the BMV is showing 100% SOC, this points to an early "battery full" aka synchronization event.

    Tom
  • Dutch061Dutch061 Member Posts: 377
    edited April 16
    @TomCanada, my Discharge Floor was set to 50% during my last boondocking trip. This is why I mention even though the manual states it scales between the Discharge Floor and SoC, this is certainly not what I experienced. since I was showing 80% SoC after using 55 Ah. 

    As mentioned previously, I agree with your logic on the Tail Current but set it to 4% based on the manual. I may have to go back and set this to 2% where it was originally.

    Looking at the history, the Peak voltage for Monday was 13.3 which exceed the Charged voltage setting of the default 13.2. Watts were only 400 Wh for the entire day, so if we use 13.3 as a constant (which it wasn't) then 400/13.3 = 30 Amp hours which is just over half of what was shown for a discharge. This confirms a synchronization event that wasn't accurate even though the Amp hours would be slightly higher due to a lower voltage to begin with it still wouldn't have replaced the 55 Ah that was consumed. Minimum voltage was 11.84, so if we use that as a constant (again it isn't) 400/11.84 = 33.78 Ah, which is still over 20 Ah off from what was used. 

    I will likely have to set the Tail current back to a lower value but wish to monitor things as is for at least 1 trip to evaluate the behavior of the current settings. 

    Brad
    2020 400 BDL
    2021 F-250 Tremor with PSD
    Concord, NC 
  • ColoradoSunColoradoSun Member Posts: 109
    I had assumed the batteries were at 100% SOC when the charge controller went into float mode. Not that simple.
    2021 [email protected] 400 BD, 2020 Toyota Tacoma Double Cab
    SW Colorado
  • TomCanadaTomCanada Member Posts: 225
    @ColoradoSun I think that's mostly accurate but the questions are - when does the controller decide to go to float (what criteria does it use) and secondly, assuming float does indeed reliably indicate 100% SOC, does the controller tell the BMV that (assuming they're networked/linked) and does the BMV use that information to sync to 100% SOC?  Might need to do some more digging..
  • Dutch061Dutch061 Member Posts: 377
    edited April 19
    The 'default settings" in the MPPT 75/15 (that I believe is the most common Solar Charge Controller installed by NuCamp in recent years) or at least what is set in our 2020 400 BDL is as follows:

    Absorption is 14.4 volts

    Float is 13.8 volts

    Equalization is 16.2 volts

    These settings can be edited by turning on the Expert mode, if I were to change any it would likely only be the Equalization voltage setting. However, since "automatic equalization" is turned off, there is no value to make that change. If memory serves me correctly, I read somewhere that equalizing AGM batteries wasn't necessary or at least didn't add any additional life to them. The Absorption and Float settings are similar to what is programmed into the PD9260C that I installed, which is the topic of an entre different post as to reasoning behind this. 

    As per the manual for the BMV-712, the recommendation is to set the Charged voltage to .2 volts below the Absorption voltage. I set it to 14.2 as per this information, I unplugged my camper yesterday and I will be monitoring it for a few days. I am not going to be able to get out again this week, working on my "honey-do list". I did go back and lower the Tail current setting to 1.5% as @TomCanada had his set. The logic is sound and after all my goal is to have the BMV-712 display accurate information without being "falsely synchronized to 100% SoC", otherwise it is like a gas gauge that reads incorrectly all the time.

    Brad

    ***Harris Battery confirmed that Charge Efficiency Factor should be set to 80% for their batteries
    2020 400 BDL
    2021 F-250 Tremor with PSD
    Concord, NC 
  • Dutch061Dutch061 Member Posts: 377
    I can confirm after Day 1 in my back yard that the Tail current setting should not be set at 4%. Had I left it at 4%, I would have had a false synchronization today instead of ending the day at 96%. Partly cloudy today in NC at times completely overcast. I do have the refrigerator operating so that it can draw down overnight. I have the 12 volt compressor refrigerator.

    Even partly cloudy and/or overcast the Solar Panel was able to produce 14.41 volts peak, which I am a bit surprised at. Even though it wasn't able to fully charge the batteries, I feel at least what I am looking at is realistic information!

    Brad


    2020 400 BDL
    2021 F-250 Tremor with PSD
    Concord, NC 
  • TomCanadaTomCanada Member Posts: 225
    Good progress! Btw if you want to draw down even faster, turn on your inverter :) 
  • TomCanadaTomCanada Member Posts: 225
    edited April 19
    The float voltage just keeps the battery from discharging and it powers your devices - so it doesn't need to be any higher.  When you charge your battery at 14.4V fully, if you disconnect it and let it sit and then measure its output, it's only about 13.2V.  So we charge at a higher voltage than we actually get out if the battery - and that's mostly just to increase charging speed.  You could actually charge your battery to 100% using just float voltage of 13.8V - it would just take a lot longer.

    Hope that helps :) 
  • Dutch061Dutch061 Member Posts: 377
    Okay, after my 3rd day of observations and realizing that the orientation of the solar panel to the sun is far less than ideal due to tree coverage, I have come to the conclusion that the settings that I am using are not correct. Instead of false synchronization happening, I never synchronize which creates the opposite problem which is a SoC that never shows 100%. In a way this is better than a "gauge showing a full tank that isn't" but it is still something that should be able to be configured to make it function properly. 

    I have sent a detailed email to Victron requesting input to reduce the trial and error time frame. It appears it could be as simple as setting the Tail current back to 2% and the Charged voltage to 13.9 or 14 volts. I may try this in the interim of waiting for their reply. 

    However, I will provide an update once I have a response from Victron.


    Brad
    2020 400 BDL
    2021 F-250 Tremor with PSD
    Concord, NC 
  • Dutch061Dutch061 Member Posts: 377
    Unfortunately, the reply from Victron was less than what I expected but I also understand that this certainly isn't a "one size fits all answer" either. After watching this in my backyard for several days, even though I would rather have them as camping days I wasn't able to.

    This is what I have found that works best for me so far:

    Charged voltage is set to 13.6
    Tail current is set to .5% which equals 1.12 Amps
    Charged detection time is set to 15 minutes

    So the battery voltage has to be 13.6 (or greater) while the charge rate has to be 1.12 Amps (or less) for a period of 15 minutes in order to qualify. 

    With these settings based on what I have been watching, it appears that this will work fine at least in NC with the factory installed Harris 6 volt AGM Batteries. 

    Brad

    2020 400 BDL
    2021 F-250 Tremor with PSD
    Concord, NC 
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