Victron MPPT Solar Controller Failing to Enter Absorption Mode with LiFePO4 battery

DesertDweller · February 2021

Hello all. Please allow me to pick the brain of the solar power cognoscenti. Sorry for the long post, but I think full info would help in understanding my issue.

I have a 2019 T@B 320s (BD lite) with the factory installed solar. The panel is located just behind the covering for the vent fan. Creed once informed me that it is a 110 watt Sunpower panel.

I recently installed a Battle Born 100 Ah battery. I have the Victron 75/15 MPPT solar controller and the 500a/50mV Smart Shunt. Since my Li battery install, the controller never goes into absorption or float mode. (It worked fine with the SLA battery). Further, even in broad AZ sunlight, the controller will indicate intermittently that the charger is “off” due to “insufficient PV voltage.” At other times, it shows the charger in the “on” state and in bulk mode. As a result, the battery gets charged but only to about 13.18 volts or so which according to BB is about 70% or thereabouts.

I have confirmed with BB that my settings for the controller and shunt are correct for the battery. Unless I am missing something, that leaves me with a wiring or hardware problem. I have double checked all the connections I touched during the install and they appear to be correct and tight. I am wondering if, by coincidence, the OEM solar panel (or other hardware) began to fail at the same time I did my install. I generally do not believe in coincidences, however. I think it more likely that I did something wrong somewhere.

But, to rule a failing panel out, am I correct in assuming that the two 10 GA wires underneath the bench on the driver’s side and that connect to the PV terminals on the solar controller run directly from the panel through the double cable entry gland on the T@B roof? In other words, if I put a voltmeter directly on those wires while the panel is in full sun, would I be testing the PV panel output (as well as the wiring from the panel and entering through the roof)? If so, what output readings should I expect from the panel in terms of volts and amps?

Given the lack of entry into absorption or float mode, what other tests I should be doing? How do I check the wiring running from the cable entry gland through the T@B roof, down the inside of the wall, and emerging near the controller? Is it possible I loosened a connection when I was connecting the PV wires to the controller (it took quite a bit of effort to fit the 10 GA wires into the Victron terminals on the controller)?

Thanks for reading and any suggestions you may have.

Z

DougH · February 2021

I've got a Victron controller too, though aftermarket panels. I believe one sees around 20V of voltage per 100W panel, so you should see ~15V on your multimeter from those 10AWG leads in full sun from your 110W panel. You obviously won't be able to measure current with unplugged leads, but the voltage alone should let you know your wiring and panels are up to snuff. If you hook the leads back to the controller, and let the instantaneous voltage of the battery bank drop to 11.9V by putting a big enough load on the inverter for a while, do you see 2-10A either coming from the panels or heading to the batteries on the Victron app when in bulk charging mode?

DesertDweller · February 2021

@DougH Thanks for this info. I will probably have to wait until the weekend to try the testing you suggest. I cancelled a camping trip this three-day weekend so I can hopefully track the problem down. I posted today in the hopes of collecting suggestions (like yours) that I could try over the weekend. Thanks again.

MarkAl · February 2021

Doug H is correct most smaller wattage panels produce with normal sunlight about 20V. The voltage drops as more load (current) is added. The cool thing with the MPPT controllers is they monitor the PV (panel voltage and adjust the load to keep the panel from dropping too low. I don't know the software to do this but under most conditions this works very well. The controller requires a higher voltage to begin the control process but then works to within a few volts of the battery type voltage setting. In full sun you should see 19-20+ volts. I'm wondering if the controller is the problem or the Panel. If the panel and controller are good and in the sun, the controller will not pull the voltage down below what the charger wants to use for the battery/system loads.
You didn't list the shunt current while this is going on, knowing this may help troubleshoot. Also verify there are not excessive loads connected in the trailer. I think if you switch OFF the battery and monitor the shunt, the panel should still attempt to charge the battery only - not the trailer loads - the shunt will still display the battery current situation. Good luck.

Tabnero · February 2021

have you programed the Victron 75/15 MPPT solar controller for the specifications for the Battleborn battery? those specs are https://battlebornbatteries.com/programming-a-victron-smartsolar-charge-controller/

Dutch061 · February 2021

Tabnero said:

have you programed the Victron 75/15 MPPT solar controller for the specifications for the Battleborn battery? those specs are https://battlebornbatteries.com/programming-a-victron-smartsolar-charge-controller/

From the OP:

I have confirmed with BB that my settings for the controller and shunt are correct for the battery. Unless I am missing something, that leaves me with a wiring or hardware problem.

DesertDweller · February 2021

As @MarkAl suggested, I was also wondering if the Victron 75/15 was a potential issue. So, just for giggles, when I got home last night, I swapped the Victron controller with the original NuCamp-supplied PWM controller. This morning on the way to work (T@B is stored a short distance from my home), I took the following three screen shots the Smart Shunt readings.

The first image is of the shunt readings with the PWM controller in full sun, (but not directly overhead) and with the battery disconnect switch activated (no juice going to T@B systems). The PWM controller indicated it was in "boost" mode which I think is the same as bulk.

Then, while I was there, the PWM controller switched to "night" mode meaning it thought there was not enough sunlight to generate a charge. I am equating this to the Victron's message that tells me the solar charger is "off" because of insufficient PV voltage. Here is a shot of the shunt readings during this condition.

Image: https://us.v-cdn.net/5021717/uploads/editor/ui/wptvbqzmtza9.png

Then, as @DougH suggested, I put the battery under load by deactivating the disconnect switch and putting my three-way Norcold in "battery" mode. The PWM controller was still in "night" mode during this situation and I took the following screen shot of the shunt reading.

While I was there the PWM controller never went back into "boost" mode. But, I did not stay long as I had to get to my desk. (Of course, I am there now typing this, so I guess I am working through lunch!

Any thoughts would be appreciated.

DougH · February 2021

Good experiment.

As MarkAI explained, without the load, and at a battery voltage of 13+V, any controller will report a 15-20V voltage, but hardly any current or wattage since there's simply no need to charge such a full battery.

Above and beyond just knowing the PWM boost versus night mode, which certainly points to the solar panel or wiring or any MC4 connectors, does that original PWM controller show you voltage and current from the panels to echo the "insufficient PV voltage" you got from the Victron MPPT? Even if it doesn't, it sure sounds like you've likely ruled out the controller. I keep a spare controller for the same reason.

If there are any MC4 connectors on the roof near the panels before the wires go inside the camper, you could check the voltage there in that same bright AZ sun (envious). Likewise if there are some connectors up there you can do a resistance / continuity check from the connectors to the wires at the point where they head into your controller to check the wiring.

Flexible panels can be easily damaged by hail and other environmental conditions, but only getting a year or two of life is very much on the shorter side of average life expectancy.

Not sure which is the least effort, replacing the wiring and re-Dicor-ing any entry point... or replacing the panel. But before doing either, I'd get the actual voltage number in full sun from the leads, or at the connectors on the roof if it has any... as well as the continuity check.

Marceline · February 2021

I'm not sure that this is related to your issue, but I've been looking at upgrading my solar arrangement and this came up in a conversation with a Victron dealer when I mentioned that I intended to use a Victron MPPT in conjunction with a 100w panel:

"The big issue you'll need to consider is voltage differential - the MPPT requires battery voltage + 5v from the solar array to turn on and start charging (ie, if your battery voltage is currently 13.2v, the controller needs to see 18.2v from the array to be able to start charging... which many panels will not themselves be putting out). With a Pb battery this isn't such a concern, but since LFP batteries have a much higher resting voltage, this can be an issue when trying to charge from a single panel: you'll want a panel with a VOC of at least 36v to ensure that you can start charging as early as possible and continue charging as late as possible!"

DesertDweller · February 2021

@Marceline Ouch! I did not appreciate this when I bought my BB battery. If this is the cause of my problem, then I either need to upgrade the panel on my T@B roof, add another panel, or sell my nearly new BB battery and go back to a Pb battery. If so, this was an expensive mistake on my part. Would going back to the PWM controller avoid the need for the 5V differential?

Denny16 · February 2021

You could always just get another 100 watt portable panel connected to the MPPT to being up the available voltage. You could also add a second solar panel to the TaB roof, but this is extra work, for a smaller gain, as may not have the roof panels in full sun. A portable panel can be put into the sun.

cheers

DougH · February 2021

@Denny16 In series for the higher voltage?

jkjenn · February 2021

Marceline said:

I'm not sure that this is related to your issue, but I've been looking at upgrading my solar arrangement and this came up in a conversation with a Victron dealer when I mentioned that I intended to use a Victron MPPT in conjunction with a 100w panel:

"The big issue you'll need to consider is voltage differential - the MPPT requires battery voltage + 5v from the solar array to turn on and start charging (ie, if your battery voltage is currently 13.2v, the controller needs to see 18.2v from the array to be able to start charging... which many panels will not themselves be putting out). With a Pb battery this isn't such a concern, but since LFP batteries have a much higher resting voltage, this can be an issue when trying to charge from a single panel: you'll want a panel with a VOC of at least 36v to ensure that you can start charging as early as possible and continue charging as late as possible!"

This is a pretty big deal and I would like to learn more about this. I am wondering if this could be a part of why the solar panel on my 2021 Boondock with dual 6v AGM batteries cannot keep up with the fridge draw. I was aware of the 5v minimum and it really showed up on cloudy days last summer. I picked up a 100w Renova panel and a second Victron controller but haven't had the chance to test it yet. Sounds like a second 100w panel might be in order.

Marceline · February 2021

@jkjenn
Here’s more of the conversation.

Me: “ If I understand correctly, the downside to a smaller [100w] panel is that it would mean that the Victron controller will only trigger charging once the battery has been depleted to 5v below what the solar panel is outputting. Once the controller does see that +5v threshold and starts charging, will it continue to charge until the battery is fully charged? Or does it stop charging again once it reaches that +5v threshold again?”

Victron dealer: “So no, once the controller is charging, it will continue charging as long as there is at least +1v differential between array voltage and battery voltage, so that's not bad - it's the initial trigger that requires that high differential.”

jkjenn · February 2021

Here is an example of it charging with less than. A 5v difference. This was probably due to partly cloudy weather.

Edited due to size of screenshot - see screenshot below. - Moderator

jkjenn · February 2021

Also, when I used 200w of solar back in 2016, I ran 2, 18v panels in series. 36v would have kept the panels going all of the time.

jkjenn · February 2021

I am now curious how it will work when you network 2 Victron controllers. Will it account for both of them?

MarkAl · February 2021

Be aware if you series 2 or more panels to get the best power output they should match as much as possible and be in a similar solar environment. If not the lesser output of the two will determine the current (not voltage, it will still add). But this is a difficult solution as the load (current) and solar input determines how much the voltage drops.
I suspect your problem (if in full sun) is not the voltage limit of the panel, it will be a factor with the BB battery, but only limit how rapidly they were charged. Once the voltage starts dropping significantly on a panel the issue will be lack of solar collection.
I have 2 controllers - one for the factory installed panel and one for the remote panel(s). I then series or parallel these based on the solar situation. Then each controller works the panels independently. I can charge in very low light situations but in the winter and w/ trees at best not more than a 10-30 watts (for 4-5 hrs) at times. Yes the hassle is rarely worth it. It does extend the time I can go without a generator or turning off the refrigerator...

jkjenn · February 2021

MarkAl said:

Be aware if you series 2 or more panels to get the best power output they should match as much as possible and be in a similar solar environment. If not the lesser output of the two will determine the current (not voltage, it will still add). But this is a difficult solution as the load (current) and solar input determines how much the voltage drops.
I suspect your problem (if in full sun) is not the voltage limit of the panel, it will be a factor with the BB battery, but only limit how rapidly they were charged. Once the voltage starts dropping significantly on a panel the issue will be lack of solar collection.
I have 2 controllers - one for the factory installed panel and one for the remote panel(s). I then series or parallel these based on the solar situation. Then each controller works the panels independently. I can charge in very low light situations but in the winter and w/ trees at best not more than a 10-30 watts (for 4-5 hrs) at times. Yes the hassle is rarely worth it. It does extend the time I can go without a generator or turning off the refrigerator...

How do you have it configured to switch between the two? Are you using Anderson connectors or some other quick disconnect?

TomCanada · February 2021

The open circuit (no load) voltage of the 110W panels is well over 20V, and this voltage does not get significantly impacted by load or irradiance (as long as you meet a minimum low level of light). This means meeting the +5V threshold to get started is easy. Then, once the controller sees this and turns the output 'on', you only need to maintain +1V over the batteries, which again is easy. So I don't think you should be having a problem here due to the +5V startup requirement.. the only time the controller will turn off is overnight.

BirdieJane · February 2021

I have 2 Victron Controllers connected to create a network. This seemed to work well.

https://www.victronenergy.com/upload/documents/Manual-VE.Smart-Networking-EN.pdf

DesertDweller · February 2021

So, thanks everyone for your comments. Today in mostly sunny skies I put the multimeter to the + and - wires which would normally be connected to the panel terminals on the solar controller. I got 0 V. Shouldn't I have been getting something out of those wires since they were disconnected from the controller and there was a fair amount of sun?

I then removed the 12 V TV and the plastic housing for it to see if I could trace those wires. I found them and they went into the A/C cabinet. I removed the A/C as much as possible as one person can do, and saw where the red and white wires were connected to the two wires that were coming in from the roof, presumably from the double entry gland where the panel wires enter the roof. The connections looked good as best I could tell given that I was holding the A/C on my knee with one hand. So, unless something is wrong with the wires from the panel entering into the roof, I think my panel may be shot. I am not really sure how to test the panel itself.

TomCanada · February 2021

Were the wires from the solar panels that you measured connected to anything else? If not, your panels might be dead :(. There should be a spot where you can measure directly on the panel but not sure if that's accessible on your unit - if you can measure up there, if you see a voltage up there then your wiring or connection to the panel might be bad.

DesertDweller · February 2021

@TomCanada. Nope. The wires were just connected to the multimeter via baby alligator clips. So, need to test the panel itself and then go from there it seems.

TomCanada · February 2021

Yup - I assume the multimeter is ok and you tested it on another source? Depending on the range you might need to go up to the hundreds (if your MM tops out at 20V in the tens (like mine), and the panel is outputting more than that (which it should if it's in the sun and not connected to any loads). In that scenario, it won't give you a valid reading until you notch it up to the hundreds range.

DesertDweller · February 2021

@TomCanada. Thanks, I did test the mm against the battery terminals on the controller and it gave a reading consistent with what the controller was giving for the battery volts as well as the SmartShunt. The meter has an auto range, I don't think I can adjust DC volts the same way I can adjust DC amps (don't have it in front of me). But, next time I am working on it, I will check that possibility. I may just throw in the towel at this stage and call a rv/solar tech to check the panel itself and replace with a similar one if need be. I would like to use the same holes that NuCamp used rather than put additional holes into the roof. So, I need the same size panel with the grommets in the same places.

Denny16 · February 2021

Two matched portable 100-watt panels in series should give you the trigger charge voltage needed, and both panels could be placed in the same sun conditions next to each other. This was my solution to supplement the roof so,are on our TaB. The portable panels are wired to their own MPPT Victron Bue Controller., which is connected to,the battery via a SAE plug on the TaB 400.
cheers

DesertDweller · February 2021

I think there is less real estate on the roof of the T@B 320s than the 400. Plus I am inclined to use the same holes that NuCamp made in the roof rather than making new ones. With a 100 Ah LiFePO4 battery and my usual frugal electric consumption, I think I can use a PWM controller and keep the battery charged or nearly so while boondocking with the OEM-style panel and a portable folding panel for the days that the T@B will need to be parked in the shade while camping. Dunno. Will have to see what is what.

By the way, does anyone know if NuCamp used adhesive on the T@B 320s solar panel (installed behind the fan vent) in addition to the four corner grommets and screws in between the grommets?

MarkAl · February 2021

@jkjenn Just saw your question on the series / parallel change over. I built up a small waterproof switch box with both panels coming in and 1 set out to the controller. I can supply the schematic but it was tight in the box. I used a double pole double throw, center off switch with 10 AWG wire. One way is series and one is parallel it satisfied all my engineering anal retentiveness.

Image: https://us.v-cdn.net/5021717/uploads/editor/gu/g138n4ndjjnr.jpg

jkjenn · February 2021

MarkAl said:

@jkjenn Just saw your question on the series / parallel change over. I built up a small waterproof switch box with both panels coming in and 1 set out to the controller. I can supply the schematic but it was tight in the box. I used a double pole double throw, center off switch with 10 AWG wire. One way is series and one is parallel it satisfied all my engineering anal retentiveness.

Thank you! I guess I am trying to figure out if the switch comes before the solar controllers and if you are using a bigger controller than the 75/10 controller for your portable panel? I have a portable 100w panel and thinking about the switch idea. A schematic would be awesome if not too much trouble.

MarkAl · February 2021

I won't bore people with my normal lecture but here's my series / parallel switch box but I found unless you have the two (similar output) panels in dissimilar solar conditions I'd just series them and connect into a MTTP controller. Switch is good when you can't guarantee similar solar input and want every watt possible.

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Victron MPPT Solar Controller Failing to Enter Absorption Mode with LiFePO4 battery

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