Overcharge & undercharge issues

[RVrover]

Hi everyone,

Below is my electric setup in a Sunseeker 2018 3010DS Class C motorhome

1. 30A shore power
2. Onboard Onan 4k generator
3. Ford E450 heavy-duty alternator 220A
4. Progressive dynamics Mighty-mini PD4000L Series Lithium Power Centers
5. PD5110010Q 120 VAC 30-Amp Automatic Transfer Switch
6. Lithium Battery Isolation Manager
7. Two 12V 100A battleborn lithium batteries – 200A total in parallel
8. Two Richsolar 190 Watt 12V Solar Panels Monocrystalline – 380W total in parallel (Can be tilted)
9. 3000w Pure Sine Wave Inverter connected to 2 independent AC outlets and has remote toggle switch.
10. Victron SmartSolar MPPT 100/50 Charge Controller
11. Victron BMV-712 Battery Monitor
12. Blue Sea Systems Heavy Duty Battery Switch
13. Power Cut Master Switch Disconnect Isolator for solar disconnect

The two issues in my new installed solar setup:

Prior to installing my solar panels, everything tested and worked as expected. For testing purposes, the 200A battery bank produced up to 210A and lasted me almost 3 days on normal usage without any charge. Solid performance until the last Amp. I was able to charge it using shore power, generator, and alternator mentioned above without fail. It took 4.5 hours to fully charge a battery from 10V. to 14.55V – See chart for the voltage parameters of this battery. I carefully follow the voltage reading beside the SOC figures on my battery monitor, which I found to correlate to the number of Amps tracked by the battery monitor, not the voltage.

Issue #1 (overcharge):

After disconnecting ALL charge inputs (Shore, Generator, alternator, and solar) and even disconnecting the chassis starter batteries, there is an exact 1.4A current going into the battery! See attached.

Where is this current coming from?

Issue #2 (undercharge):

My 24 hours Amp consumption is around 75A, which 30 to 40A of them occur after sunset around 4pm to 8am. To start testing with fully charged batteries, using my generator, I charged the bank until a 100% state of charge in terms of Amps and voltage. During testing using my battery monitor, my solar setup produced enough to replenish my night usage, day-time usage, and have Amps surplus for the last few hours of sunlight going into the batteries (1 to 4pm).

Seeing this scenario, one would expect that the battery bank returns to 100% SOC in terms of Amps AND voltage. Not the case! Only, I can see the Amps SOC returns to 100%, but not the voltage. See attached from my MPPT app. Voltage keeps dropping over the course of 5 days so far. In the next day or two, I expect to run my generator to fully charge a completely empty bank! As of today, I am starting the day with 12.74V SOC.

Am I missing something? Why the solar panels' sufficient Amp production is not bringing the battery back to full charge?

Thank you in advance for your thoughts and solutions. - Sam

 

[babock]

You have 2 issues I can see right now. One is your peukert constant is incorrect but that would cause you SOC to be lower than it actually is. It should be 1.05.

If you have everything disconnected from the positive side of the battery, you need to calibrate the monitor so it is showing 0A.

Is your BMV-712 measuring battery voltage right at the battery? I assume it is since that is likely that coiled wire. Have you confirmed with a volt meter? And it has to be a good voltmeter...not a Harbor Freight freebie.

Does the battery voltage indicated by your solar controller match your BMV? Do you have the two of them networked together? Doesn't look like it since you don't have the icon showing on the BMV screen.


Not that it matters much since your settings are similar, why not use the lithium setting for you solar controller?

 

[babock]

BTW, these are the BattleBorn suggested setting for your BMV with one BattleBorn battery. You would double the capacity obviously.

01 Battery Capacity — 99AH *
02 Charged Voltage — 14.4v *
03 Tail Current — 4.0%
04 Charged Detection — 03
05 Puekert Exponent — 1.05 *
06 Charge Efficiency Factor — 99% *
07 Current Threshold — 0.10A
08 Time to Go Averaging Period — 03
09 Zero Current Calibration — ZERO
10 Synchronize — SYNC
11 Relay Mode – DFLT

 

[RVrover]

You have 2 issues I can see right now. One is your peukert constant is incorrect but that would cause you SOC to be lower than it actually is. It should be 1.05.

If you have everything disconnected from the positive side of the battery, you need to calibrate the monitor so it is showing 0A.

Is your BMV-712 measuring battery voltage right at the battery? I assume it is since that is likely that coiled wire. Have you confirmed with a volt meter? And it has to be a good voltmeter...not a Harbor Freight freebie.

Not that it matters much since your settings are similar, why not use the lithium setting for you solar controller?

Thx for the feedback. peukert constant setting was recommended by battleborn, but I think it shouldn't hurt to use 1.05.



When I go the shop on Tuesday, I'll have everything disconnected from the positive side of the battery, and zero-current calibrate. That might fix the 1st issue of 1.4A current.


Any thoughts for my 2nd issue?

 

[babock]

Thx for the feedback. peukert constant setting was recommended by battleborn, but I think it shouldn't hurt to use 1.05.

Never seen their recommendation to be other than 1.05.

https://battlebornbatteries.com/configure-victron-bmv-700-bluetooth-dongle/

Do you have power draws greater than 5A often?

So the way Peukert constant works is that since the 100AH spec is how much current in 20Hr makes the battery completely discharged, Anything more than that will cause it to discharge much faster and you would have less capacity. Conversely, you could have more capacity if you discharge less. I kinda doubt you are getting 210AH. I have discharged mine once all the way and I saw eaxtly 200AH.

BTW, I would not get in a habit of completely discharging these. I know they say they can do it but I wouldn't. You risk getting the individual cells imbalanced in the battery.

 

[babock]

As far as your second issue, that is part of the Peukerts number problem and I asked some questions about voltage.

I also asked you about your solar controller setting and why you aren't using the lithium mode. You know how to set it right?

Also, you have the BMV and the controller networking turned on?

 

[RVrover]

Never seen their recommendation to be other than 1.05.

https://battlebornbatteries.com/configure-victron-bmv-700-bluetooth-dongle/

Do you have power draws greater than 5A often?

So the way Peukert constant works is that since the 100AH spec is how much current in 20Hr makes the battery completely discharged, Anything more than that will cause it to discharge much faster and you would have less capacity. Conversely, you could have more capacity if you discharge less. I kinda doubt you are getting 210AH. I have discharged mine once all the way and I saw eaxtly 200AH.

BTW, I would not get in a habit of completely discharging these. I know they say they can do it but I wouldn't. You risk getting the individual cells imbalanced in the battery.

Not often, maybe 1/3 of the time when couple appliances like TV and computer are on. Mostly under 5A and 2A while asleep or out. I got the entire settings from their rep., Roni Ventura, and I followed and confirmed it with this screenshot to him. I adjusted it to 1.05 as of now.



I followed your feedback and calibrated the current WITHOUT disconnecting anything from the positive side. It worked. When I disconnected all load, the reading now is zero. Not sure why it picked up this 1.4A to show?


FYI, I chose these setting because this is what battleborn also recommended
https://battlebornbatteries.com/programming-a-victron-smartsolar-charge-controller/

 

[RVrover]

Not often, maybe 1/3 of the time when couple appliances like TV and computer are on. Mostly under 5A and 2A while asleep or out. I got the entire settings from their rep., Roni Ventura, and I followed and confirmed it with this screenshot to him. I adjusted it to 1.05 as of now.



I followed your feedback and calibrated the current WITHOUT disconnecting anything from the positive side. It worked. When I disconnected all load, the reading now is zero. Not sure why it picked up this 1.4A to show?


FYI, I chose these setting because this is what battleborn also recommended
https://battlebornbatteries.com/programming-a-victron-smartsolar-charge-controller/

I also agree with you about avoiding the complete discharge. It was only for testing and I confirmed with Battle-born that it won't damage it.



https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries


BTW, The BMS actually shuts the battery before going ALL THE WAY to zero.

Actually, you can get more than 200A. I have a screenshot somewhere if you like to see it. Also, I found out that the actual capacity of these batteries is 108.8Ah making my bank almost 218Ah if the BMS allows it! https://youtu.be/G5E30u-66VI

 

[TitanMike]

I pay little attention to the "voltage chart", The difference between 100% (resting) and 40% is only .5 volt. I prefer to rely on the "Coulomb Counting" operation of the BMV itself.


I too notice the continuing current after reaching 100% SOC. At first I wrote it off to "cell balancing" but when it remained about .4 amp after a week of charging I called Battleborn. Their answer was that this was normal when charging at 14.4 volts and that was why they recommend turning off charging power when RV is in storage for any length of time.


babcock----

The Ah capacity of 99 has been restated by BB in their videos as a setting for an older battery.

Also, I am seeing greater than 100 ah capacity as measured by my BMV, especially if discharged over longer time than 20 Ah rate. My calculations show a combined capacity closer to 220-230 Ah but realize that may be due to the lower rate.

FWIW, even with my furnace, TV, refrigerator, and a few lights running I rarely see more than 15 amp discharge. That may go up as I just removed outside kitchen refrigerator and replaced with a freezer that fits the same space. It runs on an inverter and only draws around 5 amps when running. From noon today it's only drawn a total of 12 ah. Only thing running and I'm trying to see how much it will draw over 24 hours. So far so good

Once again, I quit referring to voltage charts when I got rid of my Lead Acid batteries.

 

[RVrover]

Is your BMV-712 measuring battery voltage right at the battery? I assume it is since that is likely that coiled wire. Have you confirmed with a volt meter? And it has to be a good voltmeter...not a Harbor Freight freebie.

Does the battery voltage indicated by your solar controller match your BMV? Do you have the two of them networked together? Doesn't look like it since you don't have the icon showing on the BMV screen.

Sorry, seem to miss some of your questions until I refreshed the page.


1. I didn't confirm with voltmeter, but I can check with the shop. I asked them to label these wires for reference.


2. yes, the battery voltage indicated by my solar controller matches my BMV. Both are listed under my VictronConnect v.5.13 App

 

[TitanMike]

Thx for the feedback. peukert constant setting was recommended by battleborn, but I think it shouldn't hurt to use 1.05.



When I go the shop on Tuesday, I'll have everything disconnected from the positive side of the battery, and zero-current calibrate. That might fix the 1st issue of 1.4A current.


Any thoughts for my 2nd issue?

That's not the correct way. Victron recommends disconnecting the negative cable between Shunt and Chassis or other system "ghround".

If you disconnect all the power from the positive side you'll have no power to the BMV as it draws it's power from the shunt.

I just unscrew the ground cable from the shunt on the end opposite the connection to the battery negative. Then do a zero current calibrate.

 

[RVrover]

I pay little attention to the "voltage chart", The difference between 100% (resting) and 40% is only .5 volt. I prefer to rely on the "Coulomb Counting" operation of the BMV itself.

Unfortunately, in my case Coulomb Counting is misleading. While it indicates that I have 100% SOC and zero consumed Ah (around noon everyday), the voltage is dropping at end of day, which is what really matters than just numbers of Amps.



I am literally putting 1KW a day in the batteries, more than my total usage, from full SOC 13.4V at rest, still I am on the verge of having a dead battery in the next day or two.


I have these Amps going into the batteries from the panels as shown by my BMV and MPPT. Both agreed. So why I have a deficit every day that leads to the gradual voltage loss and eventual 100% DOD even when my Coulomb Counting is no where zero or even 80%?

 

[RVrover]

That's not the correct way. Victron recommends disconnecting the negative cable between Shunt and Chassis or other system "ghround".

If you disconnect all the power from the positive side you'll have no power to the BMV as it draws it's power from the shunt.

I just unscrew the ground cable from the shunt on the end opposite the connection to the battery negative. Then do a zero current calibrate.

This is what babock recommended. I calibrated it without removing anything, which possibly incorrect. Not sure which way should I go about it now.

 

[TitanMike]

Unfortunately, in my case Coulomb Counting is misleading. While it indicates that I have 100% SOC and zero consumed Ah (around noon everyday), the voltage is dropping at end of day, which is what really matters than just numbers of Amps.



I am literally putting 1KW a day in the batteries, more than my total usage, from full SOC 13.4V at rest, still I am on the verge of having a dead battery in the next day or two.


I have these Amps going into the batteries from the panels as shown by my BMV and MPPT. Both agreed. So why I have a deficit every day that leads to the gradual voltage loss and eventual 100% DOD even when my Coulomb Counting is no where zero or even 80%?

I would double check wiring of the shunt and BMV (kind of simple but still worth double checking against the diagram that came with it) and then perform a Zero Current Calibrate as well as a 100% SOC Sync. That may well give you a different look at how things are.

 

[babock]

Also, I am seeing greater than 100 ah capacity as measured by my BMV, especially if discharged over longer time than 20 Ah rate. My calculations show a combined capacity closer to 220-230 Ah but realize that may be due to the lower rate.

Of course that is very possible if you discharge at a rate lower than the 20Hr rate. If you use the Peukert constant in the formula for the rate that you actually discharge, it will show that.

 

[babock]

This is what babock recommended. I calibrated it without removing anything, which possibly incorrect. Not sure which way should I go about it now.

You just need to remove all the loads. You can do it from positive or negative side Of course if you had removed the power to the BMV you wouldn't have been able to zero it because you wouldn't have been able to get into the BMV itself would you? You did fine.

I can let TitanMike give you all the instructions from now on since he seems to know more than me LOL.

 

[TitanMike]

You just need to remove all the loads. You can do it from positive or negative side Of course if you had removed the power to the BMV you wouldn't have been able to zero it because you wouldn't have been able to get into the BMV itself would you? You did fine.

I can let TitanMike give you all the instructions from now on since he seems to know more than me LOL.

Perhaps this link can explain the problem and offer a solution.

https://www.victronenergy.com/blog/2017/04/13/instructional-video-how-to-optimise-the-bmv-700-series-sync-parameters/


As for the "knowing more", go back and read the OP's statement about removing everything from the positive terminal(s). That of course will disable the BMV. Simplest and most foolproof way to make sure there is zero current through the shunt is to merely disconnect the ground side of the shunt (not the negative terminal connection. But then again, if one wants to pull all the "load wires", knock yourself out.

 

[RVrover]

Thank you, BOTH, for your very valuable comments and links that added much value to my thinking in general and to my specific issue. I am confident we are on the right track to resolve this very soon. Kindly, continue to share your knowledge and experience with me and the community. - Sam

 

[RVrover]

To sum up our effort so far, both of you are trying to communicate the same point. OP, to make a zero current calibration disconnect the loads and charger from the BMV so no current is able to flow through the BMV's shunt but leave the battery connected to the shunt.

I have a solar disconnect switch AND battery switch that I mentioned above. I turned BOTH off removing the load and charger from the equation, but still leaving the battery connected to the shunt through leaving Pos supply cable (see fig. 3 attached).

Then, I went on and did my calibration mentioned yesterday. I can't see the 1.4A current anymore. Does this accomplish what both of you are trying to do?

PS. Although the BMV have little draw on the battery, it is recommended to disconnect it during storage. The easiest way I found is to remove the inline fuse in the pos. supply cable.

Page 37 in the manual - "A residual discharge current is especially dangerous if the system has been discharged completely and a low cell voltage shut down has occurred. After shutdown due to low cell voltage, a capacity reserve of approximately 1Ah per 100Ahbattery capacity is left in a Li-ion battery. The battery will be damaged if the remaining capacity reserve is drawn from the battery. A residual current of 4mA for example may damage a 100Ah battery if the system is left in discharged state during more than 10 days (4mA x 24h x 10 days = 0,96Ah).A BMV 700 or 702 draws 4mA from a 12V battery (which increases to 15mA if the alarm relay is energized). The positive supply must therefore be interrupted if a system with Li-ion batteries is left unattended during a period long enough for the current draw by the BMV to completely discharge the battery."

 

[TitanMike]

To sum up our effort so far, both of you are trying to communicate the same point. OP, to make a zero current calibration disconnect the loads and charger from the BMV so no current is able to flow through the BMV's shunt but leave the battery connected to the shunt.

I have a solar disconnect switch AND battery switch that I mentioned above. I turned BOTH off removing the load and charger from the equation, but still leaving the battery connected to the shunt through leaving Pos supply cable (see fig. 3 attached).

Then, I went on and did my calibration mentioned yesterday. I can't see the 1.4A current anymore. Does this accomplish what both of you are trying to do?

PS. Although the BMV have little draw on the battery, it is recommended to disconnect it during storage. The easiest way I found is to remove the inline fuse in the pos. supply cable.

Page 37 in the manual - "A residual discharge current is especially dangerous if the system has been discharged completely and a low cell voltage shut down has occurred. After shutdown due to low cell voltage, a capacity reserve of approximately 1Ah per 100Ahbattery capacity is left in a Li-ion battery. The battery will be damaged if the remaining capacity reserve is drawn from the battery. A residual current of 4mA for example may damage a 100Ah battery if the system is left in discharged state during more than 10 days (4mA x 24h x 10 days = 0,96Ah).A BMV 700 or 702 draws 4mA from a 12V battery (which increases to 15mA if the alarm relay is energized). The positive supply must therefore be interrupted if a system with Li-ion batteries is left unattended during a period long enough for the current draw by the BMV to completely discharge the battery."

Sounds like you got it. At least the continual current issue.

As for the accuracy of SOC, that may take some time to determine. A charge/discharge cycle or two perhaps.

One tip that I learned by accident. Make sure the circuit board mounted on the shunt has good electrical contact. I took mine off when I re-did my wiring after installing the Battleborns and found that the circuit board contact surface as well as mating surface(s) on shunt were little "fuzzy". A cleanup with brass brush and reconnect, tightening the screws snug. Was it a problem? Don't know. Could it have been in the future? Good chance as bad connections can alter readings easily.

As for checking to see if you are reading draw from the battery (or charging for that matter) I'd connect a known load and run it for a couple hours. A 12 Volt 9006 Sylvania headlight bulb is rated for 55 wats. Hook one up (being careful to keep it away from combustibles as they get HOT) and then compare draw on the BMV watts readout with the rated draw of the bulb. An example, 4 hours of running that bulb should show 440 watts consumed on the BMV if you started with a full charge and 0 watts indicated. Otherwise just subtract starting reading from new total. Maybe even compare current draw with a multimeter's amperage function and compare your calc's with the BMV.

Let the light run for several hours and see how things compare.

FWIW, by correcting the current reading you've made a 33 amp hour difference in 24 hour readings.

As for disconnecting the BMV during storage, I don't store long enough to worry. I use my TT all year long and will be leaving as soon as Jan 2 for a month or more. I don't even use antifreeze to winterize anymore. Drain FW tank, blow out lines, and then just fill up the day before I leave. I can get away with this as I don't live in Minnesota