Smart Shunt SOC in linear fall despite charge cycles

[CueBall]

I have installed a multitude of Victron kit into our motorhome including Smart Shunt, MPPT, B2B, IP22 Mains charger & a 12/1200 inverter (Multiplus wouldn’t quite fit in the space available, so went for separate charger and inverter).

The battery is a 280aH LifePo4 from EcoWorthy.

All settings are correct for the battery across all chargers and the shunt.

I used Victron Smart Connect via the app, to link everything together and all worked well.

Then I went one step further with a Raspberry Pi 4, running the latest version of Venus and a small touchscreen, which works well.

I have a circa 1.5A draw on the DC side from the mobile 4/5G router the Pi, plus other bits in standby.

At first I noticed that the Blue Smart IP22 allowed the battery to discharge quite heavily before re-bulk (despite the settings) and was holding the MPPT back from doing anything at all unless in bulk mode. So I took it off the Smart Connect network and now the MPPT does what it is supposed to. VRM/Venus can’t see the IP22, as it doesn’t have VE Direct.

With the access to VRM that the Pi has given me, I have now noticed something odd…

The SOC won’t climb or re-set to 100%, despite the shunt seeing a positive charge from the MPPT, then a float charge and the battery voltage holding steady at 13.6V throughout the day.

The charged voltage is set to 14.1V in the shut, and the shunt reports a voltage of 14.2V during the absorption phase of the MPPT each morning, before it drops down to the float voltage of 13.6V and holds it there.

This is my first post here so be kind haha.

[pwfarnell]

Two comments.

1. Have you wired everything you can to the rPi and left the VE Smart network running over Bluetooth. This can give erratic results, best to only have one comms network if possible. It works OK for some but not others.
2. It sounds like your shunt is not wired correctly and you have a charger negative connected directly to the battery negative so the shunt is not counting the charge current coming in to increase the SOC.

Read my FAQs in the DIY section.

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[CueBall]

Thank you for your reply.

I actually read your FAQ’s in the DIY section a few weeks ago when this started happening.

Before installing the Pi/Venus - When I was on mains power, I could look at the Victron Connect App and the SOC would sit around 99% with an infinity symbol sitting in the “time to go” line. The MPPT wouldn’t do anything, as if the IP22 (via Smart Network) was keeping it turned off.

If I went off grid, I could see the SOC falling when the sun went down, then when I got a chance to check it in the morning (after sun rise), the SOC was back up to 99-100%.

When I installed the Pi/Venus, the first thing I plugged in via VE Direct / USB was the smart shunt, before leaving it to see if it was happy (and that my touch screen was displaying data and working etc).

That was when my trouble started. I couldn’t get the SOC to stop falling in a perfect linear line, despite me being able to physically see the chargers working, plus the voltage and current rising/falling or holding stable (as you can see in the graphs above).

Firstly, and foremost, I cannot understand why the SOC will not rise, nor re-set to 100% when all the conditions in the “fully charged” state settings are met, conditions which are met and reported by the shunt itself…

It’s a really odd one.

Everything is wired correctly, there is one negative cable on the battery to the shunt, then a bus bar after the load side of the shunt, where everything is routed back to.

There are only x2 connections on the positive side of the leisure battery, the main cable and the smaller 12v+ monitor cable for the shunt.

There has to be something going on, but for the life of me I cannot work out what it is.

[pwfarnell]

Turn off VE Smart Networking, but I have no reason to believe that this can affect the SOC calculation.

Then disconnect the SmartShunt from the rPi and see if it works again.

Is the shunt definitely showing positive current when it is charging.

An odd one for sure.

[CueBall]

I will turn off smart networking, but as you say, that shouldn’t affect the SOC calculation, especially not the simple SOC reset, which is essentially “if X, Y Z conditions are met, re-set to 100%” - But it never does.

The shunt is definitely showing positive current when any charger is active, you can see it in my first post, where the shunt widget shows a positive current, in line with the current on the MPPT graph.

Shunt reports the same if I force a charge on the IP22, which I have to do manually by either unplugging it and plugging it back in, or switching mode from custom mode to Lithium and back again (otherwise it just sits in float/storage until however many days I have set re-bulk to, currently 3 days from memory), as the battery is basically fully charged.

50A B2B is the same, if I start the engine, it jumps to 48-49A for a few seconds then goes into absorb, then float (as the battery is fully charged).

I might just go back to basics, turn off the rPi, revert to Victron connect with everything on smart network again, in the hope that everything does what it did before (as in it all worked). Then go from there…

[pwfarnell]

I have had another look at your data for the 24hour period.

You were taking out about a steady 1.3A so the SOC was falling, You then did some charging, but nowhere near enough charging to replace the 1.3 x 24 = 31.2Ah taken from the battery. You can see that there was a slight rise in the SOC at the time the charger was at 14.2V so the Ah counter and SOC is working and you only put about 1Ah back into the battery.

It should have synced back to 100% but with such low currents it might not be registering that it has started to charge for the synchronisation to work. Try and set some really easy to meet synchronisation values, high tail current and short time period or consider letting the batteries drop down lower in SOC before charging again.

if you have taken 31Ah out of a 280Ah battery = 11% SOC, the SOC has fallen by this amount so the maths adds up. However, if you had taken 11% out then from 80% SOC you must have put that amount of energy back in, but it has taken no energy in, so I am of the opinion that something is keeping the battery charged at 100% and is supplying this 1.3A which is passing through the shunt.

Is the 1.3A current being measured by the shunt actually going through the shunt but not coming from the battery because of some new wiring change creating a separate negative current path direct to the battery (ground loop), are you sure you have not got a charger somehow connected direct to the battery. How is the rPi getting power, the rPi power source should come from the load side of the shunt, could any wiring mods with the addition of the rPi have caused a change. I know I am clutching at straws but something is odd here and the math in the shunt looks good, but the shunt is not matching reality,

[CueBall]

As you say, something doesn’t add up… The rPi is powered via a 12v DC to USB hub, similar to that which you might plug into a cars cigarette lighter socket, just with +/- cables rather than the cigarette lighter plug - That is connected to the bus bars (so after the shunt) and the rPi is powered by that.

A slight update this AM, I read somewhere else that the “charged voltage” can be set to 0.2v below the absorption voltage setting.

I did that last night, so charged voltage is now 14v, with absorption at 14.2v (previously charged voltage was 14.1v). Obviously that didn’t make an immediate difference as no chargers were active (no sun for MPPT, BlueSmart IP22 in storage mode & B2B off as engine not running).

This AM, when the MPPT woke up and started a charge cycle (exactly as per the widget data I posted yesterday), the SOC auto reset to 100% after about 45mins of the MPPT being active.

So that’s sorted that out (albeit it might be a slightly premature SOC auto reset).

The next odd thing I noticed this AM is that my DC power use line/curve roughly matches the MPPT’s output line/curve - See image below, the lines are almost identical (albeit the DC use line sits higher due to the base load). Why would a charger output have any impact on DC use, that doesn’t make sense…

[pwfarnell]

The DC power is just a calculation unless you have a SmartShunt or BMV712 set up as DC energy meter. Therefore, if your battery monitor is not reading correct then the DC power calc will be wrong, the linked FAQ covers this. You still need to check all wiring.

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[CueBall]

@pwfarnell

You still need to check all wiring.

That is on the to-do list for today. I’m also going to perform a zero current calibration, not that I can see that it needs one as 1.2 - 1.5A seems about right for a mobile router, rPi and the victron kits own draws (plus I have to have the habitation electrics turned on for the mobile router, so there is other stuff in standby like the 12V TV etc), but just to be on the safe side I’ll do it, as the option is there.

[CueBall]

I just performed a zero current calibration, by disconnecting the load side of the shut (also turned off the DC+ rotary isolator to be on the safe side). I also turned off the habitation electrics first. The shunt immediately showed zero current and infinity symbol in “remaining time” on the app, but I did the calibration anyway.

What I did find odd (briefly), is that all the Victron kit remained active & visible in Victron connect including the Venus/rPi & they could all still see the leisure battery voltage.

I quickly realised that is probably because the mains (12/20 IP22) charger was plugged into mains power & so active and the MPPT/Solar was in the sun - So there was power to the bus bars from those chargers. They could all still see the leisure battery voltage because the shunt was still active via its 12v+ meter cable and so reporting the voltage to everything via smart connect (actually Venus as I have removed the smart network).

Unfortunately it looks like the slow SOC downward trend and energy in/out still isn’t adding up, so will be checking all the cables and connections next.

[CueBall]

I have just been advised on another forum that my 12V - USB hub which powers the rPi might be the issue…

The rPi 4+ is quite power hungry, especially with a multitude of peripherals connected (VE - USB in this case), but that shouldn’t stop the chargers from covering the load.

The hub I am using supports up to 3A, although it was a Chinese special, so that might not be quite true.

Apparently, if the rPi is underpowered it can mess with the data through VE, which in turn can create spurious readings and calculations.

Worth a go, will change the USB power hub for something more powerful/reliable and see if that makes any difference.