Batteries not charging much in full sun

descott12 · August 31

Hello all,
I have a new 2025 Tab320S with 390 watt panels on the roof and the victron smart shunt and charge controller. I have two LiTime 100AH batteries in parallel. Yesterday, in full sun, with the batteries at 80%, the charge controller was only showing 36 watts when it should have been closer to the full 390. A little while later is was showing 93 watts but still far short of what it should be doing. I have attached a few screenshots of the Victron app main page. I have not measured the actual voltage coming from the panels in full sun but I plan to do that ASAP.
Any thoughts? Does the "Smart" in SmartSolar MPPT mean it is trying to do something fancy when all I want is a fully charged battery??
Thanks in advance. I will contact Victron directly if nobody here has any ideas.
Cheers

Image: https://us.v-cdn.net/5021717/uploads/editor/jw/1pfkhfrg4101.png

MuttonChops · August 31

descott12 said:
. . . 2025 Tab320S with 390 watt panels on the roof
. . . charge controller was only showing 36 watts when it should have been closer to the full 390.
. . . later is was showing 93 watts

Big Picture - - - you will never see/get the solar panel 'rated' output of 390 Watts.
Solar Industry output measurement standard testing is done under very controlled conditions that can never be achieved in the real world. Many folks use a 60% to 75% of rated output as the realistic maximum power and you will only see that maximum output for a specific sun angle & time.

I don't use Victron components on my aftermarket mini-solar setup so can't comment on Victron App data/usage.

donmontalvo · August 31

As @MuttonChops said, the numbers are under perfect lab conditions, so gotta come to terms with that.

Curved solar panels will only ever get a fraction of the rated output even on perfectly sunny days, however they're great on overcast days, where diffused light can hit the entire solar panel.

I have a 2024 320S BBC with 2x190 solar panels. I hang a flat 100W solar panel on the aluminum tubes at the back. I point the back of the camper South (with iPhone set to Use True North), so it can get maximum sun.

On sunny days the 100W panel rules...on overcast days the 2x190 curved panels rule.

I added a second 100ah LiFePO4, for 200ah total, so power lasts longer.

Image: https://us.v-cdn.net/5021717/uploads/editor/lz/j82uyylvtacd.jpeg

descott12 · August 31

Hey guys,
Thanks for the comments. Yes, I understand that I will not get close to 380 watts. But 36 in full sun? I know I have seen it producing close to 200 watts previously in full sun.
But functionally, it should be pumping as much energy into the batteries whenever it thinks they are less than 100%. Correct?

donmontalvo · August 31

Curious how your battery settings are set up?

Here is what my SmartShunt and MPPT (the one used for my 2x190 roof panels).

Image: https://us.v-cdn.net/5021717/uploads/editor/g7/tjbysyq8ondc.png

Sharon_is_SAM · August 31

Did you sync to 100%?

descott12 · August 31

donmontalvo said:

Curious how your battery settings are set up?

Here is what my SmartShunt and MPPT (the one used for my 2x190 roof panels).

Thanks for the reply.
For the MPPT, The differences are as follows:
Battery preset = LiFEPo4
Expert mode is off
Equalization voltage is disabled
I don't have the Bulk or Absorption sections - I am guessing due to the Expert mode off.
Equalization is disabled

For the shunt:
Charged voltage = 14.2V
Tail current 2%
Peukert 1.05
Charge efficiency factor 99%

Not sure what all these do but it looks like you have customized your settings quite a bit.

donmontalvo · September 1

I'm not an expert, but I slept at a Holiday Inn...erm...I mean, I posted my settings to the Victron Energy page on Facebook. Tons and tons of feedback, after a couple weeks my solar settings hit the sweet spot and I stopped having power issues.

descott12 · September 1

Sharon_is_SAM said:

Did you sync to 100%?

Yes but now that you mentioned it, it seems like it things the batteries are topped off and it isn't trying to charge them more. Does that sound like a good theory? Maybe I need to sync them again.

descott12 · September 1

donmontalvo said:

I'm not an expert, but I slept at a Holiday Inn...erm...I mean, I posted my settings to the Victron Energy page on Facebook. Tons and tons of feedback, after a couple weeks my solar settings hit the sweet spot and I stopped having power issues.

I wish I could get on the page. I have been banned from Facebook forever. I created an account a 15 years ago, never even made a post. But I tried to reactivate it and I get denied. Even with new, completely unrelated email addresses. Go figure. I will contact Victron directly.

donmontalvo · September 1

Create a burner email account, then use it to create a burner Facebook account.

descott12 · September 1

donmontalvo said:

Create a burner email account, then use it to create a burner Facebook account.

I did. Several times. Somehow it knows who I am. Not sure how.

ckjs · September 1

donmontalvo said:

… Here is what my SmartShunt and MPPT (settings are)…
> MPPT
> Absorption 14.20 V
> Equalization 16.4

The 14.2V of Victron’s LiFePO4 preset is perhaps a bit low for your batteries, or, in fact, quickest charging of many brands. It will probably just take a little more time, no biggie.

The specifications for our LiTime 100Ah’s say to charge at 14.4V.

How did the Equalization voltage get turned on? It should be disabled for LiFePO4 batteries.

The shunt settings don’t affect the charging rate of the batteries. It’s better to consider them as helping the shunt estimate how much charge is in the batteries.

AnOldUR · September 1

ckjs said:
The 14.2V of Victron’s LiFePO4 preset is perhaps a bit low for your batteries, or, in fact, quickest charging of many brands. It will probably just take a little more time, no biggie.

I had my LiFePO4's at 14.4 for absorption and 13.5 for float voltages, but recently watched a Will Prowse video that recommended 14.5V / 13.6V. The reasoning was for better cell balancing when in absorption mode. I was close enough that I'll probably not notice the change, but if you're coming from 14.2V it could make a difference.

donmontalvo · September 2

ckjs said:

...[snip]...
How did the Equalization voltage get turned on? It should be disabled for LiFePO4 batteries.
...[snip]...

If you look closer to the screenshots I posted, I actually have automatic equalization disabled.

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