Xantrex Battery State of Charge…how accurate?

[jacwjames]

I had always questioned the state of charge on display of my Xantrex inverter.  After running the generator to charge the batteries it never really seemed to represent where the state of charge should be.  I became paranoid and would get up in the middle of the night and check

So last year I installed  Victron BVM 712.  It has bluetooth which is great to monitor both the house and chassis voltage.  I can bring it up under the covers and confirm the voltage. 

Yesterday I drove all day and as you'd expect the battery  was 100% when I stopped, which was pretty early but I'd driven ~450 mile and I was tired.  I did run the generator for a short time to cook some leftovers and when I went to bed the Victron said +90% but the Xantrex was ~85%.  I kept checking the victron through the night at at ~3AM I turned on the furnace as it was down to 35F outside and ~60F inside.  I did not start the generator and when the furnace kicked off the Victorn still said 82% battery. 

At some point ~5AM I checked the Xantrex display and the batteries were down to 70%. 

When I got up at 6AM I checked the Xantrex and display read 88% (I had to check twice) and the Victron was ~75%.   I started the generator to make coffee and did run a heater in the LR. 

So what's going on with the Xantrex display, how can I rely on it and how can it control AGS (which I have never relied on) if it is that far off. 

Just seems strange to me. 

 

[timaz996]

If you set up the BMV 712 when the batteries were truly at 100% it is measuring input and output amps and keeping track. That is the most accurate way to know what the state of charge is on your batteries. Your inverter  is measuring voltage and as your batteries rest with no load the voltage will come up but does not coincide With the actual state of charge. So believe the BMV 712 as it is accurate no matter what the load is on the batteries.

Edited October 8, 2023 by timaz996

[96 EVO]

9 minutes ago, jacwjames said:

 

At some point ~5AM I checked the Xantrex display and the batteries were down to 70%. 

When I got up at 6AM I checked the Xantrex and display read 88% (I had to check twice) and the Victron was ~75%.   I started the generator to make coffee and did run a heater in the LR. 

 

 

Furnace load on the batteries when you were checking it?

If your Victron was properly installed, I'd trust it!

22 minutes ago, jacwjames said:

 

So last year I installed  Victron BVM 712.  It has bluetooth which is great to monitor both the house and chassis voltage.  I can bring it up under the covers and confirm the voltage. 

 

 

That's too funny!

I better not install one !!

[waterskier_1]

I'd trust the Victron first. But I'd review all the settings on the Xantrex, including the battery capacity. 

  - Rick N 

[jacwjames]

6 hours ago, waterskier_1 said:

I'd trust the Victron first. But I'd review all the settings on the Xantrex, including the battery capacity. 

  - Rick N 

Good Point,  I'll check the settings on both. 

 

7 hours ago, 96 EVO said:

Furnace load on the batteries when you were checking it?

 

I checked before I started the furnace and checked after on the Victron, went from 82 to 80%.  Didn't get up and check the Xantrex until after the furnace ran.

What got me was the voltage went up after the furnace ran and when I got up ready to leave. 

 

I do have a residential refrigerator running, the batteries will usually drop about 20-30% overnight runner the fridge, depending on temps. 

[MyronTruex]

Grab a standalone voltmeter and check right at the batteries and then at the connections on the charger/inverter. 

Nice feature on the Lumos Harry Potter. Now Nox and go to sleep. 

[windsorbill06]

Jim,

I'd trust your Victron but they do need to be calibrated periodically.  Takes about 5 minutes.   I did mine the other day, first time in 5 years. 

 

https://www.google.com/search?q=how+often+do+you+calibrate+a+victron+bmv+712&rlz=1C1CHBF_enUS854US854&oq=&gs_lcrp=EgZjaHJvbWUqCQgAEEUYOxjCAzIJCAAQRRg7GMIDMgkIARBFGDsYwgMyCQgCEEUYOxjCAzIJCAMQRRg7GMIDMgkIBBBFGDsYwgMyCQgFEEUYOxjCAzIJCAYQRRg7GMIDMgkIBxBFGDsYwgPSAQkxOTE3ajBqMTWoAgiwAgE&sourceid=chrome&ie=UTF-8#kpvalbx=_cF8lZebbGP7LkPIP-eGK0Ao_51 

Edited October 10, 2023 by windsorbill06

[Ivan K]

My Xantrex SOC reading was always way off and I don't even look at it. Not sure if it is a firmware version issue since I had to replace the remote when we got it. This is why I have separate shunt meter, not a Victron but works well.

[Tom Cherry]

Per TROJAN & the other major battery vendors.  After the batteries are fully charged, theh throw a brief medium load….maybe a minute.  That knocks off the flash or surface charge.  Then  disconnect them via house switch.  Then pull the jumpers and let them recover for 10 or so minutes.  Then measure the voltage and if flooded, the specific gravity.  Use the charts.  That is the REAL SOC.  Then turn off ALL LOADS.  Hook back the jumpers.  Turn bank back on.  Then monitor.

Then read the SOC from your unit or if you have the Magnum BMK.  Interpolation

I have always wondered how accurate the shunt systems were and how they correlated to the “practical or laboratory” method.  

If you do that, please post.  Would like to see how accurate the systems are as the Trojan method for SOC is the gold standard….