battery charge level discrepancy between Victron Charge Controller and SmartShunt on one setup, the other works fine

[mrfrozenpotatohead]

Lots of interesting stuff you guys are talking about! Stuff for me to review in the future. This morning have plugged fridge (approx 60w) into cigarette lighter plug and a iPhone into 5v 2.1a usb outlet. Sun isn't on that side of the house yet so MPPT has voltage fluctuating from 8-10v. The shunt started at 12.85v and is now at 12.58v and falling after a few minutes. The relevant devices circled in red:

 

[sunshine_eggo]

1. What do you measure with a meter?
2. Does the MPPT report the same 8.75V when you open it in the app?

I have observed a handful of Victron MPPT that read voltage significantly higher than actual, which can cause serious under-charging.

I'm also noting a significant discrepancy in the other pair. Does that concern you? Given the higher voltage, I would attribute it to OVP as initially suspected on your initial concern.

 

[mrfrozenpotatohead]

The screen on the fridge was showing fluctuating voltage from 12.1 to 12.3v after startup currently down to 11.7/11.8V after about 5 minutes now. The onboard voltmeter on the battery box is showing 12.6.v which does match the shunt at 12.57v.

 

[mrfrozenpotatohead]

The discrepancy between both pairs is just due to not much sun on this side of the house, in an hour or 3, it'll stabilize as more sun hits this side of the house. Actually looking outside, high cloud and only diffuse sun but supposed to be clear skies for the rest of the day.

 

[sunshine_eggo]

The screen on the fridge was showing fluctuating voltage from 12.1 to 12.3v after startup currently down to 11.7/11.8V after about 5 minutes now. The onboard voltmeter on the battery box is showing 12.6.v which does match the shunt at 12.57v.

Okay. Terminate discharge.

Get the shunt and MPPT into a VE.Smart network. If the MPPT measurement is in error, using the shunt voltage will enable full charge.

The discrepancy between both pairs is just due to not much sun on this side of the house, in an hour or 3, it'll stabilize as more sun hits this side of the house. Actually looking outside, high cloud and only diffuse sun but supposed to be clear skies for the rest of the day.

The position of the sun is not relevant. In almost all cases, MPPT and shunt readings - even when not in a VE.Smart network - should be very close.

There should be no discrepancy beyond measurement error - maybe 0.2V max. The MPPT is in absorption outputting 14.2V, but the shunt is only recording 13.5V. Either there is a HUGE voltage measurement error, or you have a horrible connection somewhere, OR the battery is in over voltage protection mode.

Note your original snapshot:



That's a "normal" voltage deviation. I would conclude the system corresponding to the above circled devices is in OVP due to 13.5V on the shunt and 14.2V on the MPPT.

NOTE that voltage deviation > 1% is grounds for warranty replacement of a Victron MPPT.

 

[HRTKD]

The SmartSolar 75/15's reading of 8.75v should be a huge red flag. At stated above, the solar charge controller's battery voltage reading (what it thinks the battery's voltage is) should be very close to what the shunt reports. There's either a bad connection or a bad solar charge controller.

Break out the voltmeter and start checking the voltages for yourself.

 

[mrfrozenpotatohead]

Def. voltmeter time, battery box offline and shunt also offline, but SCC still online. You'll notice the other 2 are in sync and steady green on the SCC.

 

[mrfrozenpotatohead]

I'll swap the SCC, since nothing is currently charging, battery and battery bank still offline however the MPPT is showing 13.5V. I have a second 75/15. Might also redo the Anderson connectors and the ferrules on the cables for the MPPT

 

[mrfrozenpotatohead]

With battery still in box and shunt still wired in but all external connections removed, voltmeter across terminals is showing 3.8V.... ick. Recommended next steps?

 

[sunshine_eggo]

With battery still in box and shunt still wired in but all external connections removed, voltmeter across terminals is showing 3.8V.... ick. Recommended next steps?

Battery is empty, BMS is in protection mode and reporting arbitrary low voltage. Recommend you get the MPPT on it ASAP. It should charge tomorrow as Victron MPPT will still output their absorption/float voltage even if a battery is not connected and can be used to "jump start" a battery in protection mode.

 

[mrfrozenpotatohead]

Wait a sec, the 75/15 MPPT and the 100W panel hooked up will take forever to charge. Are you suggesting

1) remove battery from box
2) attach MPPT to battery
3) attach 100w panel to MPPT
4) leave it for a couple days to charge and see what happens?

Or do I

Pull the battery and hook it up to my Noco Genius 10 charger in Lithium mode and let it run overnight.

Or, swap with the battery currently hooked up to home panel setup. Pic below



Or some other option or combination of options.

 

[mrfrozenpotatohead]

Listening to the YT video of guy in AU taking about VE Networking, I continued listening to his videos on autuplay while struck in traffic and the one about the OverKill BMS tool caught my attention. Seems both potentially useful/relevant to this issue but also potentially dangerous given my newbie knowledge level.

 

[sunshine_eggo]

When a battery is in protection mode, normal chargers may not be able to charge them because they are measuring a voltage too low to function. Some have modes that force a specific voltage/current output. I know the MPPT will wake up a battery in discharge protection mode. Once the battery is awake, charge by whatever means you prefer.

 

[mrfrozenpotatohead]

The Noco has a wakeup charge mode

NOCO Genius is able to detect and charge dead batteries as low as 1-volt. For extremely dead batteries lower than 1-volt, manually turn on Force Mode to detect and charge batteries all the way down to zero volts.
See also How do I use Force Mode on Genius?

However will try your suggestion of MPPT first.

 

[sunshine_eggo]

The Noco has a wakeup charge mode

NOCO Genius is able to detect and charge dead batteries as low as 1-volt. For extremely dead batteries lower than 1-volt, manually turn on Force Mode to detect and charge batteries all the way down to zero volts.
See also How do I use Force Mode on Genius?

However will try your suggestion of MPPT first.

The NOCO should work fine.

 

[740GLE]

Yet again having a battery with a BMS with Bluetooth coms to verify why it’s behaving why it’s behaving is key. What are the cells actually doing.

Its almost humorous and first the battery was over charged, now its under charged?

Seems like a monkey humping a football.

 

[740GLE]

With battery still in box and shunt still wired in but all external connections removed, voltmeter across terminals is showing 3.8V.... ick. Recommended next steps?

If you are measuring 3.8v, how in the world is the shunt reporting 12.4v

 

[mrfrozenpotatohead]

Noco attached, all other external supply (MPPT) or load removed and this is what I see



And state of charge is slowly rising.

 

[mrfrozenpotatohead]

If you are measuring 3.8v, how in the world is the shunt reporting 12.4v

That is certainly the question at hand, does not compute!

 

[mrfrozenpotatohead]

Looking at the Shunt settings and battery specs, does the former look reasonable?

 

[740GLE]

Why
Have
You
Not
Set
Up
A

VE.Smartnetwork?

That change voltage, 13.2? How did you come to think that was a good value? The SOC % is calculated off that voltage. This almost looks like default settings.

Here’s a good Andy video

Can you open up that battery box and show wiring of the shunt to the battery?

 

[mrfrozenpotatohead]

Lol just watched that video already this morning about an hour ago. But will wait until battery is (apparently) changed by the Noco before taking action.

He does says default settings should be "good enough".

Will take photo when charging is done, not safe to do now.

 

[740GLE]

Change the settings now, this won’t change how the Noco charges the battery.

 

[mrfrozenpotatohead]

Just to make sure, as per the battery label, it says CHARGING voltage is 14.6V but the Shunt says CHARGED voltage. Those seem to be very different things to me...

So I am changing Shunt CHARGED voltage to 14.6V to match the battery label of 14.6V CHARGING voltage?

 

[sunshine_eggo]

When charging with solar, charged voltage should be 0.2V below absorption. Set to 14.4V for now.

If you adjust your absorption voltage down in the future, and you should eventually, adjust the charged voltage down too.