Battery charge differs between solar controller and BMS - Why?

themcgillcrew · August 3

Last year we replaced the stock 6V AGMs with two Aolithiuim 100Ah batteries in our 2022 Tab400 BD. I've recently noticed the solar controller is spending way too much time in float mode and being pretty ineffective in recharging our batteries. The solar controller sees the state of charge in the batteries as almost 100% so switching to float would make sense. However the Aolithium's app shows the batteries at 84%.

I do not have a background in trailer electrical (or any electrical for that matter) but can anyone suggest why the solar controller and BMS disagree on the battery voltage? Is there a way to sync them up?

Thanks in advance for any advice.

pthomas745 · August 3

Show us the settings page for your Victron solar controller. Find your battery manual, and lets make sure your settings in the Victron are correct for lithium battery charging.

This Battleborn page has a guide on how to use the "Expert" mode in the Victron to get the settings correct. Use your specific battery settings for the various voltages. (They won't differ by much).

https://battlebornbatteries.com/programming-a-victron-smartsolar-charge-controller/

It seems....with the lithium batteries now coming out with their own "apps" that there are many owners reporting this sort of "mismatch" between what Victron says and what the "battery app" says.

themcgillcrew · August 3

Attached are my Victron solar controller settings. I don't recall getting a manual for the Aolithium batteries and their website is down because the company seems to be out of that business now. I can try getting that information from other sources though if there are specific parameters in question.

Thanks!

Image: https://us.v-cdn.net/5021717/uploads/editor/fq/517b9934t4m3.png

Sharon_is_SAM · August 4

I believe I read that the built-in lithium BMS is specific to individual battery cells. So, The state of charge and voltage they will differ from the Victron BMS.

pthomas745 · August 4

@themcgillcrew I would, at the very least, go through the procedure for doing the "expert mode" settings from the Battleborn page. There are very few differences in lithium charging parameters. That "Smart Lithium" setting on the Victron setup page is designed for Victron's "Smart Lithium"...whatever that means.

themcgillcrew · August 5

Thanks for your suggestions.

I updated my Victron controller with the parameters from the Battleborn page but little changed unfortunately. It switched to bulk initially but soon returned to float. The solar controller is still seeing the batteries as fully charged (13.5V) while the BMS has them at 73% (13.11V). I'll continue my research but would appreciate any other thoughts.

pthomas745 · August 5

Find a multimeter. Learn how to measure your state of charge directly.

Bayliss · August 5

@themcgillcrew, maybe consider:

(a) disconnecting the power from the Victron system/battery monitor, waiting about a minute, and then reconnecting the power to see what happens. A system reset, like when restarting a computer, can often resolve issues like you are dealing with.

(b) disconnecting the batteries and using a separate charger to get the batteries to full charge before reconnecting to the Victron monitor and do a manual syncronization to 100% and see how things go from there.

(c) contact a Victron dealer and/or the battery manufacturer to see what advice they might be able to provide for your specific situation. It may just be a matter of tweaking specific settings for the Aolithium batteries, specifically to get the two apps to work together and provide consistent data.

themcgillcrew · August 7

Thanks again all.

I put a voltmeter on the batteries and both were at 13.18V (about 70%) so it would seem the BMS is correctly reporting the state of charge.

I went out in the bright sunshine again this morning and found the solar controller reporting the battery voltage as 13.86V (about 100%) and again stuck in absorption mode. I then disabled the solar controller for about 10 seconds then re-enabled it. Interestingly, the solar controller went to bulk mode.

Today I'll try @Bayliss's idea and depower the controller to try the old stop/start solution. I've also been in touch with the Victron supplier for nuCamp and started a thread with them. I'll report back here if anything comes of that as well.

Image: https://us.v-cdn.net/5021717/uploads/editor/y2/uqo1fcpjj2cm.png

SC stuck in absorption mode

Image: https://us.v-cdn.net/5021717/uploads/editor/5r/888czgkianf3.png

BMS sitting at 70%

Image: https://us.v-cdn.net/5021717/uploads/editor/sa/c2tzfe0kuhoa.png

SC in bulk mode after disable/reenable

Image: https://us.v-cdn.net/5021717/uploads/editor/eb/vjcp2iz8e7vs.png

BMS after disable/reenabling SC

Image: https://us.v-cdn.net/5021717/uploads/editor/fr/whnojylymy7j.png

SC charge history showing periods of bulk charging mode

I still don't know why the SC sees the batteries as full when the BMS says they're not. Also, I don't understand why disabling the SC then re-enabling it flips the SC to bulk mode for a while, yet not enough to fully charge the batteries.

I'll try depowering the SC today and see if that changes anything.

Glen

Bayliss · August 7

Thanks for the update, @themcgillcrew. One more suggestion, although you may have already done it...........be sure to test the battery itself for its SOC when the battery has been fully disconnected from the system (that is, not actively charging), and after it has "rested" (not charging) for about 1/2 hour.

I am only adding this comment, because I am not sure if the 13.18V reading is with the battery disconnected and after having "rested."

Good luck!!

ckjs · August 7

themcgillcrew said:

Attached are my Victron solar controller settings…
Absorption voltage: 14.20

I suspected that this isn’t enough, and prowled around for mentions of Aolithium. I found a video which happened to show a page of its printed manual:

It’s uncertain whether it is the same model as yours, so I suggest raising the charge setting to 14.4v, which is common for many LFP batteries.

It’s also possible that its internal BMS is flakey; I found a few discussions of dealing with warranty returns. (No surprise that they seem to be out of business)

themcgillcrew · August 7

I checked the voltage again after isolating the batteries for over an hour from the trailer and solar controller and got a reading of 13.24V. The AOL app agrees showing 13.22V (about 70% SOC). So it seems it's the solar controller that is off base.

ckjs · August 7

themcgillcrew said:

... So it seems it's the solar controller that is off base.

If you mean that the solar controller "isn't charging the battery well enough", I agree. One of the Victron's settings adjusts the Absorption Voltage. If you change that to 14.4v, it is likely that the battery will "fill up".

themcgillcrew · August 7

Thanks @ckjs. I've been playing around with the SC settings including an absorption voltage of 14.6V but it's still reading the battery voltage too high. See below.

Image: https://us.v-cdn.net/5021717/uploads/editor/0q/dq40lkp57bfp.png

Image: https://us.v-cdn.net/5021717/uploads/editor/yo/4mkbk245loj2.png

themcgillcrew · August 7

I finally got around to @Bayliss's idea and pulled the fuse for the SC to the battery located in storage locker on passenger side of trailer on our Tab400.

After waiting a few minutes, I replaced the fuse and low and behold the SC saw the 70% charged battery which agrees with the BMS. When I left the trailer this evening, the SC was in bulk mode and all seems good. My fingers are crossed that tomorrow's sunny day will be spent in bulk mode charging our batteries.

Thank you again all for your ideas and suggestions! I'll update this thread when I confirm the fix tomorrow.

Bayliss · August 8

Fantastic, @themcgillcrew!! I am looking forward to the hopefully (fingers crossed for you) final update.

themcgillcrew · August 8

I think I've made progress but not sure it's the solution.

After pulling the fuse for the battery connection to reset the SC, the voltage for both the SC and BMS were the same. As the day went on, the SC stayed in bulk mode but the SC battery charge showed almost full while the BMS was less.

Image: https://us.v-cdn.net/5021717/uploads/editor/t8/6me136yihml3.png

By the end of the day, once again, the battery voltages between BMS and SC were the same. I'm going to track voltages throughout the day tomorrow to see if I get the same behaviour.

Fun.

themcgillcrew · August 9

Same behaviour as yesterday.

The SC and BMS agree on the rested battery SOC. There's plenty of solar coming to the SC and the charge state is bulk yet the SC says the batteries are fully charged which they are not.

The batteries seem to be accepting only a couple amps so I'm not making as much progress as I'd expected. I'm certain that just this spring the solar was topping off our batteries without problem so I don't know what has changed since.

I'm very confused but starting to think I should try changing out the solar controller.

Image: https://us.v-cdn.net/5021717/uploads/editor/ss/pisyahsgqxkq.png

Bayliss · August 9

@themcgillcrew, I went back and re-read your original post. What stuck out to me is that you "replaced the stock 6V AGMs with two Aolithiuim 100Ah batteries." (I am assuming those are 12V batteries.)

Are your batteries wired in "series" or "parallel." The reason I ask is because you most likely had the two 6V batteries wired in series, which allows the two 6V batteries to become 12V. Since you now have two 12V batteries, you want to wire them in parallel so that they remain at 12V/200Ah (rather than 24V/100 Ah.) You can read more about the differences via a Google search.

I'm just wondering if maybe that could the problem, because your solar controller and BMS are set for 12V, but your batteries might be wired to create 24V. Just a thought, because I am running out of ideas to share with you.

Also, I may have missed it in your comments, but did you charge each of the batteries to 100% with a separate lithium-capable charger? If not, do that before reconnecting them to the trailer solar/BMS. You can then do a manual reset to 100% synchronization to see how things go from there.

Finally, have you received any helpful input from nuCamp's Victron supplier? Just curious.

Below is a depiction of the difference between series and parallel wiring, BUT NOTE: Although the wiring is accurately depicted, there is a typographical error in the text below the "Wired in Parallel" heading. The text should read “2 batteries wired in parallel . . . .”

Marceline · August 9

Re: “yet the SC says the batteries are fully charged which they are not.”
Where are you getting this? Where does the SC say that the batteries are fully charged?

ckjs · August 9

themcgillcrew said:

The SC and BMS agree on the rested battery SOC. There's plenty of solar coming to the SC and the charge state is bulk yet the SC says the batteries are fully charged which they are not.

The batteries seem to be accepting only a couple amps so I'm not making as much progress as I'd expected. I'm certain that just this spring the solar was topping off our batteries without problem ….

The bolded text misinterprets the solar charger’s voltage during active charging. It’s only the resting voltage which can show you the S.O.C. While charging — pushing current into the battery— the SC must drive it at a higher voltage that the current state of the battery: otherwise the current won’t “go in”.

You’ll notice that the charging graph of last few days shows that the max voltage reached 14.6v on the occasions that it switched to “float”. That’s a strong indicator that a LiFePO4 battery is full.

Re: the battery “accepting only a couple amps”: that’s probably just the amount of power that the panel can provide at the time. Solar panels only generate their nameplate power when 1) flat rather than curved, and 2) pointed perpendicular to the sun on a clear day. The history graph shows a peak of 115w of generation a few days ago, so charging at 85w now is reasonable.

It’s still possible that something is broken, but I’m not seeing any evidence yet.

themcgillcrew · August 9

Thanks again @Bayliss. Yes, the two Aolithiums are 12v wired in parallel and I did charge both to 100% before installing them. The Victron supplier responded to me promptly at first but seemed to be talking about a shunt for some reason. Nothing since.

And @Marceline, I’m getting the SC battery charge level from the VictronConnect app under Battery (13.50V in the screenshot above). Let me know if I’m misinterpreting this.

Thanks both for the responses.

themcgillcrew · August 9

Thanks @ckjs.

Yes, when I measure the rested voltage of the batteries, that matches what the BMS sees (13.28V). So I still don’t understand why the SC doesn’t run more amps into the batteries in bulk mode.

Bayliss · August 9

Thanks for the responses, @themcgillcrew. At least that eliminates those possibilities.

Regarding the "shunt," I can see why Victron is asking you about that. If you had one connected in your monitoring system, that would be better for more precise monitoring. Also, one thing that makes it a bit complicated in trying to figure out what is going on is that you are using two different monitoring systems (Victron SmartSolar Controller and the Aolithium app.) Most of us are using the Victron BMV-712, which includes a shunt.

Rather than try to explain it, here is a quick "AI" blurb:

"A shunt in a battery monitoring system serves as a precise current measurement device. It allows the monitor to accurately track the flow of energy into and out of the battery, providing a more accurate state of charge calculation than voltage readings alone. This real-time monitoring is crucial for understanding battery capacity and preventing over-discharge, especially in systems with LiFePO4 batteries."

ckjs · August 9

themcgillcrew said:

.. So I still don’t understand why the SC doesn’t run more amps into the batteries in bulk mode.

It is likely that the solar panel isn’t providing more than 85w or so of power, due to curvature and non-optimal sunniness.

The most recent Victron graph shows that the batteries went to float 2 days ago. Do you remember what the aolithium app showed at the time? Would you leave it on the charger for a day or two, until the batteries go to “float” again (probably resulting in a Victron max voltage of 14.6), then check the BMS’s app again?
.

themcgillcrew · August 9

Thanks again @ckjs. Will do. I’ll leave everything alone for now with the SC charging the batteries.

This whole thing started when the SC shifted to absorption or float but the batteries weren’t nearly fully charged (70-80%). Pulling the fuse to reset the SC just meant it now gets stuck in bulk mode rather than float or absorption. Something has changed since this spring when the SC had no trouble topping up the batteries to 100%.

Thanks to all once again for the advice.

Marceline · August 9

themcgillcrew said:

Thanks @ckjs.

Yes, when I measure the rested voltage of the batteries, that matches what the BMS sees (13.28V). So I still don’t understand why the SC doesn’t run more amps into the batteries in bulk mode.

The controller is only going to send as power as is being produced by the panel to the battery. If you had a solar panel producing 180w of course the current (amps) to the battery would be higher.

In your screenshot, the panel is producing 85w at 21.36v and the controller converts the voltage to 13.5v for the battery input, which results in 6.1A (82.35w). There just isn't any more power for the controller to send to the battery.

Marceline · August 9

themcgillcrew said:

Thanks again @ckjs. Will do. I’ll leave everything alone for now with the SC charging the batteries.

This whole thing started when the SC shifted to absorption or float but the batteries weren’t nearly fully charged (70-80%). Pulling the fuse to reset the SC just meant it now gets stuck in bulk mode rather than float or absorption. Something has changed since this spring when the SC had no trouble topping up the batteries to 100%.

Thanks to all once again for the advice.

The controller should stay in "bulk" mode until the battery is nearly completely charged. I think the Victron manual discusses the parameters that must be met for the controller to shift from Bulk to Absorption and then Float.

The monitor that's built into your battery shows that the battery is down about 32.28aH (100aH - 67.72aH) so at ~6A it would take about 5hrs to recharge the battery (and I think you have two of them).

I'd suggest that you consider adding a Victron SmartShunt to your set up so you can get a better read on the SOC of your batteries as a pair. Also consider taking some time to read the Victron Solar Controller manual.

elbolillo · August 10

themcgillcrew said:

Thanks @ckjs. I've been playing around with the SC settings including an absorption voltage of 14.6V but it's still reading the battery voltage too high. See below.

Try changing your absorption duration to fixed. 1hr.

themcgillcrew · August 12

Thank you to all who responded to my thread. I've learned a lot about DC electrical systems for our trailer.

To summarize, after removing the fuse to the solar controller battery side found in the passenger side storage locker, the SC is now spending almost all of its time in bulk mode rather than absorption. As a result, I'm slowly approaching full charge as reported by the Aolithium BMS.

Once again, thanks for the assistance.

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Battery charge differs between solar controller and BMS - Why?

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