Victron smart shunt state of charge

[Willbiker]

Hi all. Thanks to help from people on this forum, my Vicron smart shunt is set up and working well except the state of charge doesn't seem correct. I have 3x 130ah (C20) lead acid leisure batteries and here are my battery settings which other forum users reccomended.

The only issue is the state of charge seems to be inaccurate. It shows 65% when the rested voltage is 12.16v. I thought 12.1 was 50% discharge for lead acid?


Its also shown 58% soc at 11.96 volts ( i took my eye off the ball and woke up to this :S)

How can I make the SOC be more accurate?

Thanks

 

[newbostonconst]

Your charged voltage seems high to me though I don't do acid.....

Guessing 13.5 might be a better number.

 

[chrisski]

The charged voltage is fine. It just needs to be less than your absorption voltage. The spec sheet for my class was 14.7, so I’d set it to no higher than 14.6.

The Victron may be correct. Seems like you may be draining the batteries too much for FLA. I’d fully charge and watch the monitor when the batteries are in float with no load and when the charging amperage gets no lower, I would manually reset the SOC to 100% if it does not read 100%. I do find 0 amps charge/discharge odd. I always see something with FLA. perhaps less than 1 amp in float. When there’s no charge and no load there’s always a slight parasitic draw on the system from things like the 12 volt CO2 detectors and the natural lead acid draw.

what do you think is wrong? When i look at your voltages, the SOC you mention may be about 10% high compared to a voltage chart, but either what you’re seeing at 65% and 12.16 v or 58% at 11.96 volts is uncomfortably low for me. On a voltage chart 12.16 v is 55% And 11.96 v is 40%. To measure SOC by voltages the battery needs to be resting for a while with no load. The deeper the discharge, the more the battery will dip with current.

 

[rmaddy]

The "Charged voltage" setting of your SmartShunt should be set to 0.1V lower than whatever charge voltage you are using to actually charge the batteries.

Also make sure you fully charge the batteries to 100% at least every two weeks. The SOC should auto reset to 100% when you do this. If you don't do this the SOC reading will not be accurate. This is in the manual for the SmartShunt.

 

[l00semarble]

How old are the batteries? What has been their history since new? Any idea of how many cycles? Freezing temps? deep discharges? What brand, make and model of batteries? are you maintaining them (keeping electrolyte topped up?) Have you ever let the electrolyte get low?

Are you sure you started at 100% with a good synchronization when the charger was definitely in float? If you are sure you are starting a discharge cycle with a fully charged battery AND a synchronized battery monitor than the issue is simply that your batteries are not actually making their rated capacity.

But it seems that your setting are not going to trigger automatic synchronizations. The charged voltage does look to be way too high. There are some suggestions above but we have to be much more specific. What is the battery charger (brand/make/model) and what are the exact settings of the battery charger? Specifically what are the bulk, absorbtion, and float voltages of the charger assuming it is an intelligent 3-stage charger? Also what are the battery manufacturer's requirements for bulk, absorbtion, and float voltages?

The Smartshunt will only resynch with a full battery (reset to 100%) if two conditions are simultaneously met. The battery voltage must be above the "charged voltage" number programmed and simultaneously the charging current is below the tail current setting. Your charger probably should have a lead acid float voltage setting of about 13.4v (depends on what the battery manufacture specifies it wants for float voltage). You probably need to set "charged voltage" to something like 13.2v but without the full information on your system we can't be sure.

Do you have solar or any other charging source acting the batteries at the same time? If you have solar working on it there can be anomalies with a SmartShunt where due to sun conditions etc a system can reach "charged voltage" with minimal current below "tail current" but not because batteries are full but because solar is doing all it can given the conditions. This can be especially problematic for undersized solar implementations for the battery bank.

The tail current is pretty low at 2% of 390 a-hr which is just 7.8a or 2.6a per battery. The current needs to fall below this level for the BMV to initiate an automatic synchronization. Even after you fix the charged voltage maybe the batteries are just taking enough at float to prevent this? Maybe try 3-4% if necessary.

 

[chrisski]

The tail current is pretty low at 2% of 390 a-hr which is just 7.8a or 2.6a per battery. The current needs to fall below this level for the BMV to initiate an automatic synchronization. Even after you fix the charged voltage maybe the batteries are just taking enough at float to prevent this? Maybe try 3-4% if necessary.

I use 2%. That way, the SOC will jump from 98% or 99% to 100% when that 25 (7.8 amps chargign) is reached. I had it all the way up to 8%, or about 28 amps and SOC would jump from 86% to 100% as the battery entered absorption and the current started to drop off.

 

[Willbiker]

Thanks for the replies. I have 3x Hankook 130ah batteries as seen here - https://www.batterymegastore.co.uk/product/hankook-xl31-leisure-battery/

They are about 1 year old and have never experienced super cold temperatures, they have only once been discharged as low as 11.96v as previously mentioned and they have experience roughly 3-5 cycles so far down to approx. 12.1V

I am using a Epever Trace Solar charge controller which has a 400w solar array connected to it...see below.



I did reset the state of charge to 100% when full however I was under the impression that I do not need to do this anymore as this will happen automatically when the voltage hits 14.3v for a period of time...which seems to take place correctly.

As shown in the table provided by Chriski, 50% should be represented by 12.1v however my voltage hit 11.96v and showed 58% SOC. This should be more like 40% SOC. I know the shunt calculates the SOC by measuring charge and load currents but does it not also use voltage to confirm this?

Shall I try another manual reset? When I know they are full, should I let them rest for a day or so before manually resetting?

Thanks

 

[l00semarble]

OK one step at a time:

Batteries - Those are sealed/MF Calcium batteries which require special charging often a specialized charger that most people don't have. I found some info on Hankook's website. They give two ways to charge the batteries:

1. Constant current - based on state of charge of batteries. They want you to measure open circuit voltage, then set a specialized charger to give a constant current based on state of charge. For example, if battery is OCV 12.0v you should give it (each battery) 6.5a for 18 hours. (I had to extrapolate their chart to get a 130ah battery.) Obviously this is impossible with your setup.
2. Constant voltage - They call for 16v for 24 hours. This is of course also impossible with your setup.

Battery Maintenance - ATLASBX Technical Information

Hankook AtlasBX Battery Maintenance information. How to handle battery, Installation and recharging, and Battery testing procedure.

www.hankook-atlasbx.com

So it would seem that we have established that you are not fully charging your batteries thus any manual sychronization that you have done is false. If you manually synchronized the smartshunt to 100% when the batteries were NOT full it would starting counting down amp-hours but the battery bank is not actually starting with 390 a-hr so it makes sense that after 165 a-hours the voltage is lower than you expect.

So the battery monitor will never work well if you never fully recharge your batteries so you have a broader system design issue, not just a smartshunt programming issue.

That said, you also will continue to have problems until you accept the facts about when auto synchronization occurs. you can't remain "under the impression that it will happen when voltage hits 14.3v for a period of time." Perhaps you should look at the book again. The important part of the smartshunt knowing when the batteries are full is that they stop accepting current (current falls below tail current even though voltage is above charged voltage.) Think about it - batteries are noted to be full when you are pushing voltage but current won't move as there is no space.

Based on the float voltage your have set (not sure where this came from?) in your MPPT controller the SmartShunt charged voltage should be 13.6v.

However with a small scale, and possibly undersized, solar setup the numbers jump around due to sun conditions and it can be difficult to make a smartshunt work smoothly unless you have another 120v charger you can use to fully charge the batteries periodically.

I'll paste a few things from the book for you:

10.3.4. Incorrect state of charge reading An incorrect state of charge can be caused by a variety of reasons. Incorrect battery settings The following parameter(s) will have an effect on the state of charge calculations if they have been set up incorrectly: • Battery capacity • Peukert exponent • Charge efficiency factor Incorrect state of charge due to a synchronisation issue: The state of charge is a calculated value and will need to be reset (synchronised) every now and then. The synchronisation process is automatic and is performed each time the battery is fully charged. The battery monitor determines that battery is fully charged when all 3 "charged" conditions have been met. The "charged" conditions are: • Charged voltage (Voltage) • Tail current (% of battery capacity) • Charge detection time (minutes) Practical example of the conditions that need to be met before a synchronisation will take place: • The battery voltage has to be above 13.8V • The charge current has to be less than 0.04 x battery capacity (Ah). For a 200Ah battery this is 0.04 x 200 = 8A • Both above conditions have to be stable for 3 minutes If the battery is not fully charged or if the automatic synchronisation does not happen, the state of charge value will start to drift and will eventually not represent the actual state of charge of the battery. The following parameter(s) will have an effect on automatic synchronisation if they have been set incorrectly: • Charged voltage • Tail current • Charged detection time • Not occasionally fully charging the battery

10.3.11. Synchronisation issues If the battery monitor does not synchronise automatically, one possibility could be that the battery never reaches a fully charged state. Fully charge the battery and see if the state of charge eventually indicates 100%. Another possibility is that the charged voltage setting should be lowered and/or the tail current setting should be increased. It is also possible that the battery monitor synchronises too early. This can happen in solar systems or in systems that have fluctuating charge currents. If this is the case change the following settings: • Increase the “charged” voltage to slightly below the absorption charge voltage. For example: 14.2V in case of 14.4V absorption voltage (for a 12V battery). • Increase the “charged detection time” and/or decrease the tail current to prevent an early reset due to passing clouds.

 

[Willbiker]

Thanks very much for taking the time to give such a detailed response. I was not aware that sealed lead acids must be charged a certain way to achieve a true 100% SOC. I am using the default charge controller settings, I will check these are in line with the battery requirements. Maybe my only option with my limited set up is to reduce the ah capacity value until (after resting) i can get the SOC to match the voltage....roughly. This may be as accurate as I can get with my set up.

Thanks again for the support