SmartSolar dropping to float before shunt hits 100% - am I missing something?

DIY
, ,
1

Hoping someone can help me figure this out.

I have a Multiplus-II 12/3000, SmartSolar 150/100, SmartShunt running as the network master, and 2 SOK 206ah in parallel. Both chargers set to 14.4 absorption and 13.6 float. VE.Smart Network is up and the MPPT is getting voltage and current from the shunt.

Here is My Problem: when charge current is high, the MPPT shows 13.6 at its terminals while the shunt shows 13.1-13.2 at the battery. So the MPPT thinks were done and drops to float. SoC stalls around 96%.

I thought VE.Smart was supposed to handle this so the MPPT uses the shunt voltage instead of its own. Is that not how it works? Or do I actually need to run VSense wires to the battery? Any ideas on how to fix this?

Thank you for anyones willingness to try and help out.

2

Maybe try without the BT smart network to see if the mppt is going to do its full job.

If it is not reaching rhe programmed absorption voltage after that, then we can look further into the why.
Do you have decent solar panel voltage?

3

Thanks for replying. Ill give that a shot.

To answer the panel voltage question - 6x 200W panels wired 3S2P, im seeing around 61V at the MPPT input on a decent day. So I feel like Im good there.

When you say leave the network off, do you want me to actually leave the SmartSolar out of the network entirely, or just disable the voltage sense option specifically? Want to make sure I test it the way you mean.

4

Definitely good not even close to battery voltage which is a common mistake

Remove the mppt from the network entirely. Let it use its own internal readings etc.

5

Here is an update on the Float diagnostic. I removed the MPPT from the VE.Smart Network as you suggested (SmartShunt and VE.Bus dongle still innetwork). Two data points worth your review:

5:12 PM - Generator charging, no solar:

MultiPlus: Absorption, 14.58V, 6.8A

SmartSolar: Float, 14.48V, 0.0A

SmartShunt: 100% SoC, 14.44V, +17.43A

5:30 PM — No Generator, Solar producing 315W (22.40A):

SmartShunt: 13.32V, 97% SoC, +11.66A

SmartSolar: 13.79V, State: Float

Delta: 0.47V between SmartShunt and SmartSolar voltage

A few other things I noticed while in the configs:

- SmartSolar Absorption time: 15 minutes

- MultiPlus Absorption time: 1 hour (fixed)

- SmartSolar voltages: 14.60V Abs / 13.80V Float

- MultiPlus voltages: 14.40V Abs / 13.60V Float

What’s your read on the 0.47V discrepancy and the MPPT being in Float in both snapshots?

Thanks

6

What you do need to check with a meter is if the mpot is reading its terminal voltage correctly. So the meter and the mppt must agree (to at least within 0.1v) at the mppt voltage

It is also possible to set using the expert mode on the mppt a much longer absorption voltage.

It is not necessary for both to be in the same state just as an FYI. what does matter is the battery is being charged correctly and not being overcharged or undercharged.

There is not much difference at this point. 0.04v is nothing.

For the solar to supply a load it does need to raise its potential up a bit to make it flow so that is expected.

7

Here is a great example of my concern. We used the batteries last night and this morning at 9:35am the shunt shows as being at 61% of battery yet the cobfroller is putting into float whoch then results in approx 15 second intervals of charge, no charge. This cant be how it should work correct?

Screenshot20260523093434
Screenshot202605230934341440×3120 202 KB

Screenshot20260523093427
Screenshot202605230934271440×3120 190 KB

Screenshot20260523093420
Screenshot202605230934201440×3120 202 KB

8

What size cable is installed between the charge controller and bus bar/battery.
Do you have DC loads?

That is quite the jump in voltage in such a short time.
The float state not changing is certainly interesting.

It points to a physical issue. Have you verified it with a meter?

9

Multimeter check done as you requested.

Snapshot during shore-off, MPPT in Float, 330W solar producing:

Multimeter at MPPT terminals: 13.77V
SmartSolar app: 13.78V

Multimeter at battery (shunt): 13.28V
SmartShunt app: 13.39V

Voltage difference between MPPT terminals and battery: The cable the installer used from the MPPT to the battery is a little thinner than my pinky finger.

20260523141540
202605231415401920×1440 641 KB

10

The voltage drop is happening at that black box that looks like a disconect then?

The cable is a small one, but i am going to assume you don’t have 5000watts of solar installed, so the installer has assumed you don’t need it bigger than that.

The mppt and meter agree so there is no issue with the charge controller it is in the wiring and connectors between. For the voltage drop issue.

11

Thanks for the clear diagnosis. The cabling from the MPPT and the black box are leftover from the original 200W solar setup the trailer came with — the installer reused them when upgrading us to 1200W of solar.

Should the box and cabling both be replaced given the upgrade?

One more thing while I have you — we have 1200W of solar installed (6x 200W panels, wired 3S2P), but we’ve never seen anywhere close to that output. The highest we’ve ever observed is around 650W, even on the clearest sunny days in Southern California.

Any ideas why we might be capped at roughly half our nameplate?

Appreciate all the help.

12

The box is definitely a suspect. Very high resistance causes voltage drop and rise like you are measuring

The cable gauge may be ok for the solar you have installed. I usually use 25mm² to 35mm² on that sized controller but also have 5kW of solar installed on it so it will push its 100amps.

Your pv cabling is also not great for the parallel set up. Should be at least 6mm² there. If not 10mm²

There can be many reasons, ranging from damaged panels to bad connections to heat and irradiance and panel type.

13

This is a photo of the guts of that black box, what do i even search for in replacing this?

The fifth wheel is a 2024 so it not particularly old. The solar panels are brand new.

Screenshot20260502154829Gallery
Screenshot20260502154829Gallery1440×3120 560 KB

14

Oh dear, its a bit more complex than a simple switch out as your dc stuff is there.

15

I would hire an rv mechanic to do it, i just have no clue what to buy to replace it.

16

Myabe it just needs to have the mppt moved to a different connection point. Although i can see some logic in connecting it directly to dc loads

17

Is it possible some of the configuration setting in the VictronConnect app or VE Config 3 software is causing some of the issues around premature float, etc? If so, what aettings would you suggest that i need to check?

18

The battery is reaching the 14.4v.

You can use VC to set a longer absorption time in settings it will keep the higher voltage for longer.

And then re bulk offset can be changed

19

Thank you again for your time with this.

Two questions:

  1. What specific values would you recommend? Currently I have Absorption at 14.4V, 15 mins fixed duration, re-bulk offset 0.40V. Would you suggest a longer absorption time (and how long), and what re-bulk offset should I target?

  2. Would installing the VSense physical wires on the MultiPlus-II help resolve this? They weren’t connected during the original install. My thinking is that if the MultiPlus sees actual battery voltage instead of terminal voltage, it could compensate for the voltage drop in the cabling. Would that address the premature float issue, or is that primarily for the MultiPlus and not the MPPT?

Thanks again for your time.

20

This is dependent on the battery.

Usually they are an hour long it depends on the cell balancing internally.

Some people use it to keep the battery ‘fuller’ for longer.

Can be 0.1v

Will work for the inverter.

But the BT ve bus dongle if it is connected to the battery terminals will do tha same thing.