Victron 712 and Battery SOC ...some basic questions ...help!

RichardofYork

I have some very basic questions about batteries, which I find very confusing.  

I have a second-hand 2018 TAB 400, which I do not think was well treated in terms of battery management.  It has a 200 amp AGM battery.  So to help me manage the battery, I thought I would get the highly-spoken-of Victron 712 added when I added 200 watts of Gopower rooftop solar and a 100 watt Gopower solar suitcase.  The problem was I could not get into a Nucamp dealer as they were so busy they would only do work on units they had sold.  So I went to another dealer ...that mostly sells units that are made of "plywood, glue and staples".   When they installed the 712 they did it such that it did not "count" the solar coming in ....just the drain.  For that and some other issues, I do not have that much confidence in them, but I am somewhat stuck with them.  They did correct their installation, acknowledging that they had got it wrong, but my battery experience on our first trip this year still leaves me with concerns that either...(1) they have not done the 712 app set-up properly... (2) the AGM is nearly dead and should be replaced ... or (3) I understand battery things even less than I thought and I am irredeemable.  The evidence is currently heavily weighted on (3).

After towing for 4 hours the battery arrived at the campsite with ~13.7 volts ..... we would get back to this sort of level during a sunny day, even boosting the solar input (which the Gopower solar controller allows) one afternoon so that the voltage went to 14.2.  However the voltage seemed to very easily and very quickly plummet to 11.6 and sometimes overnight to 10.7.  See the 3 pictures. We were not drawing much at all.  Just the 2-way fridge, which eventually stopped working because the voltage dropped below their cutoff, and a few occasional lights.   According to the table and pictures below 11.6 voltage should be at 20% SOC  ....meaning 80% used up and, if repeated at this level, damaging the battery long term.  But the SOC per the Victron 712 shows 96%.  Even when I got down to voltage of ~ 10.? ...the SOC only went down to 93%.   What am I not understanding?  I thought the victron 712 SOC was going to be the easy way for me to tell where I was in terms of power, but I am also told that I should not go below 50% (per table below) ....although i have also read that going down to 20/30 % does not "materially" impact an AGM battery life and limiting to 50% discharge is leaving a lot of power on the table.  Also .... will I really get another 10 days (see below) if the draw continues at 0.33 amps???

I did manage to check that the Victron was now capturing both the rooftop solar and the suitcase solar ...so that is working.

So is the victron app properly set up?   Is it appropriate that the SOC can be 96% when the voltage is only 11.56?  What is the SOC supposed to tell me?  Do we think my battery is just gone....deceased?  Should I just book into the Hilton next time?

pthomas745

There is one more piece to the battery reading puzzle: the picture in your post shows the battery voltage when the battery switch is on, and current is being drawn from the trailer. It is pretty small, and might even be just the parasitic drains.  Try taking another reading with the battery switch off and see if there is a big change. 

Yes, if you are just seeing the parasitic drains like in your picture, that is only about 1/3rd of an amp per hour. Each day, about 8 amp hours.  80 amp hours for 10 days.  117 amp hours to use...yes, 10 days seems proper.  I think the time remaining number only goes to 10, I've never seen mine higher.

You need to sort out why the voltage number is that low...even the "rested battery" issue really should not bring it down that low with just parasitic drain.  I'd let the solar charge the battery ( or attach to shore power) charge the battery for a day, and take another battery voltage reading after letting the battery rest a bit.  If it isn't holding a charge, then something is wrong.

Sharon_is_SAM

“Battery starts synchronized” - I believe that it is better if that is turned off.  Otherwise, you may be synching a discharged battery to 100%.  That probably accounts for the voltage SOC mismatch.  

Victron factors in multiple variables to come up with the SOC.  Rate of discharge, temp., etc.  If you have set up the 712 correctly, Victron says to rely on the SOC.  

The original, single large Harris AGM batteries in the 400s had early failures.  Not unusual for a battery to charge, but discharge rapidly when they are failing.

https://tab-rv.vanillacommunity.com/discussion/13362/bmv-712-proper-settings-with-solar-panels


https://tab-rv.vanillacommunity.com/discussion/comment/165995#Comment_165995

Denny16

What Sharon said, the Harris battery in our TaB400 failed around 18 months after it was installed.  A new Interstate 200AH AGM was installed to replace it.
Next time, I will swap it out for 2/100AH or a single 224AH Lithium battery.  Meanwhile the AGM stays until it fails again.  So far 2.5 +/- years on this battery, with it getting a very low discharge one time, it is working quite well, not showing any signs of slowing down either.
 Cheers 

DenisP

My 2018 400’s 224AH batteries (2-6v) just failed during a long trip. They would take a full charge and discharge rapidly overnight. The 2 way refrigerator did not like the lower voltage and kept running but not fully cycling the compressor. I was able to have BattleBorn batteries shipped to me on the trip and replaced the AGMs with a single 100AH lithium to complete our trip. I made the full conversion once home, upgrading the converter and adding the second 100 AH battery. As a footnote, once the failed AGMs were switched to the single lithium, the refrigerator rebooted and returned to normal operation. 

Jake_Elwood_and_us

DenisP, do you have any idea why your 224AH batteries failed? I assume they are not as old as the Tab or were they? I have the same in our 2021 400 and I'm trying to assess if we are having the same issue.

 BTW, the awning worked great on our last trip with rain and some wind!

Dutch061

In reviewing the settings, I used before installing Lithium in our 2020 400 BDL, I think there are a couple of changes I would make to the battery settings you have listed.

I would set the Charged voltage to 13.6 (mine was set to 14.2)
I would set the Tail current to 1%
I would set the Charged detection time to 5 minutes
I would set the Peukert exponent to 1.1 (Victron has an App that you can use to calculate this)
I would set the Charge efficiency factor to 80% (this is what Harris Battery told me with the 2 6-volt AGM I had)

As far as the "Battery Starts Synchronized" setting, if this is not on you will get no data displayed until the battery fully charges. So, in essence it is better to have it set to "On" rather than getting no Data (other than voltage VS Amp Draw). 

My suspicion (if the battery tests okay) is that you are getting a false reset to 100% SOC. This is exactly the problem I had with how the BMV-712 was set up in our camper.

How the SOC resets is based on the "Charged voltage" being met with less than "X" Tail amps for the period of time set in the "Charged detection time". So in your settings if 13.2 volts is reached with less than 8 Amps flowing in for 3 minutes, the SOC is reset. These are conditions that are too easily met and can be further complicated by mis-matched components. IE Solar Panel Capacity VS Ah Capacity of the batteries. 

Brad

richardspahn

Go to BattleBorn and look at their kits. I configured one of their kits for a Grand Design Trailer. I ordered a kit with a 2000W Victron charger-inverter to run roof air and a microwave. Battle Born customer Service configured it for me with a preset Victron and I gave it to an RV Tech I new and had faith in. He bet me it wouldn't work as the power was 110 coming from my F150 Hybrid with a built-in 7200W generator but it did.     I plan to order a new 2023 400 when I find out changes for 2023 and will call BattleBorn first. Here is the link to BB:        Towable LiFePO4 Battery Kits | Battle Born Batteries.   PS I'm an Engineer and learned long ago living on a sailboat with one solar panel and an aftermarket alternator amp control feeding a charger-inverter that lead-acid batteries were PFM.  I might add that you cant directly  FULLY charge a lithium battery driving down the road as 12v power from your towing vehicle has to be transformed to a higher voltage to top off the Lithium and capture its full capacity which you've paid dearly for. I also designed and installed a solar power system for a boat lift on Lake Travis for a cigarette boat. 

Denny16

Jake, Battery life depends on how much they are used and recharged, four years is about the average lifecycle for AGM golf cart type batteries.  Your trailer is fairly new, so you should have at least another two or three years (or more) left on your batteries.  

Cheers 

Jake_Elwood_and_us

Denny16, that's what I was thinking as well. The battery monitor I'll have installed by the trip after the next one should give me a clearer picture. On reading the post from Dutch061 and richardspahn it seems a bit complicated so I'll have a bit of a learning curve to entirely figure it out.

Denny16

Good, have a safe trip, relax and enjoy the ride…
cheers

DenisP

@Jake_Elwood_and_us my batteries were 4 years old and the Tab had traveled 28k+ miles when they showed failure. I guess they reach end of life. I am really happy the awning is working out for you. Take care. 

Dutch061

@richardspahn,

The solution to your statement "I might add that you can't directly  FULLY charge a lithium battery driving down the road as 12v power from your towing vehicle has to be transformed to a higher voltage to top off the Lithium and capture its full capacity which you've paid dearly for"  is to add a DC to DC Charge Controller. This allows the voltage to be boosted, limits the overall amperage draw from the TV, and allows charging with a "smart alternator". I installed a Victron 18 Amp Smart controller, it will provide 18 Amps while driving, and charges to 14.6 volts.

Others have used a higher amperage unit and added heavier wiring and an Anderson Connector. I chose the 18 Amp because I didn't want to run replacement wiring on my 2021 F-250. The OEM wiring on my TV is 10-gauge and can easily handle 18 Amps.

Brad

richardspahn

Brad, I concur it can be done but it needs a Victron controller properly wired in the right place in the right circuit by a skilled tech with wiring skills.