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Math not adding up on solar/battery system


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#1 steve whiteside

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Posted 24 April 2021 - 02:54 PM

Gents,

So I am still getting calibrated on my Victron Battery system.  I have 2ea 1300watthr batteries.  Yesterday I was down to ~21% based on my BMV 712.  It was overcast day here in San Diego.  Around noon I pulled the truck out of the garage and went to the beach. Intermittently, I saw 70-130 watts input on the Victron.   I have 4 ea 100watts panels on the roof.  

 

At 7pm I went back out to the truck to see I was at 100% capacity and the watts in were at ~7-8watts indicating I was full of capacity.

 

It seems to me that I got to 100% way too fast.  There were hours in between checking the victron for "watts in" but the conditions didn't really change.  Im assuming not more than 150 watts into the system based on the overcast Sky.

 

For instance, say at 21% I had 600whr left in the batteries.  Then say I averaged 100watts generated from the panels for 7 hours. that would be 600+700= 1300 = 50%.  For me to have made it to 100% I would have needed to generate 385watts for all of those 7 hours- which wasn't in line with what I saw with my intermittent checking.

 

I checked that my setting capacity is correct at 210amp hours.  

 

Thoughts?

 

Steve


Edited by steve whiteside, 24 April 2021 - 02:57 PM.

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#2 rando

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Posted 24 April 2021 - 04:03 PM

My guess would be that your BMV712 is 'auto syncing' at too low a voltage which resets the unit to 100% sooner than it should.  In the app, under battery settings, what are the values for 'charged voltage', 'tail current' and 'charged detection time'.   Also what sort of batteries do you have?


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#3 ri-f

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Posted 24 April 2021 - 04:48 PM

So I am still getting calibrated on my Victron Battery system. It seems to me that I got to 100% way too fast.

That's happened to me in the past, too, on a couple occassions. I also noticed that regardless of the SOC reading 100% I was always a few amp/hrs in the negative on the BMV712 (with everything shut down - zero load). Recalibrating/syncing, at night, corrected this. If you find that all of your settings on the BMV712 are correct for your particular battery, then make sure that when you calibrate/sync next time, you do it when you are sure the batteries are 100% topped off and the resting voltage confirms that. Try doing your sync/calibration process at night when the sun can't interfere with the voltage fluctuations of your panels. Also, turn off all electrical loads that could draw from the battery, with the master on/offl switch set in the off position and see if that changes anything.
 


Edited by ri-f, 24 April 2021 - 06:31 PM.

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#4 steve whiteside

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Posted 24 April 2021 - 07:32 PM

Rando, My charged voltage is set at 13.2v.  tail current= 4%. charged detection time= 3 min.    My batteries are Lion Energy UT1300.  1300whr each.

 

Rich, You say make sure your batteries are fully charged. If the solar charging shuts off too soon how do I get them "fully" charged?  Use some other source of charging I guess?  Also I can do the re-sync inside my garage that is fully blocked from the sun.

 

steve


Edited by steve whiteside, 24 April 2021 - 07:41 PM.

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#5 steve whiteside

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Posted 24 April 2021 - 07:46 PM

Also each battery has a built in capacity gauge on the top of the batteries.  Each one is indicating 80% full.

 

steve


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#6 ri-f

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Posted 24 April 2021 - 07:56 PM

Steve, a Battleborn will typically have a charged voltage setting of 14.2 (13.2 seems low) about 0.2 loxer than absorbption voltage of 14.4).. Can you charge your batteries to 100% with a portable charger plugged in (like a Noco Genius 10 for example)? Your batteries should see a 14.2-14.4 charging stage for say 60 minutes or so every once in a while for a 200ah bank (about 30 min per 100AH x 2). Once your batteries are topped off, try calibrating/resyncing again in your garage or at night. Does Lion Energ suggest a 13.2 charging voltage or is that the suggested float volltage? Or you might be able to simply raise the charged voltage parameter on your BMV712  from 13.2 to 14.2, assuming you have an absorb voltage of 14.4, and charge up with solar omce again and see if that brings the batteries up to 100% SOC. Then recal/sync after that.

 

Rich


Edited by ri-f, 24 April 2021 - 09:03 PM.

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#7 rando

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Posted 24 April 2021 - 09:41 PM

Rando, My charged voltage is set at 13.2v.  tail current= 4%. charged detection time= 3 min.    My batteries are Lion Energy UT1300.  1300whr each.

 

Rich, You say make sure your batteries are fully charged. If the solar charging shuts off too soon how do I get them "fully" charged?  Use some other source of charging I guess?  Also I can do the re-sync inside my garage that is fully blocked from the sun.

 

steve

 

That is your problem right there, the charged voltage is too low causing the BMV to sync too early.

 

You don't (and shouldn't) need to manually sync the batteries, the BMV-712 will do this for you once they have reached full charge (charged voltage) and the they are no longer accepting current (tail current).   

 

If you mainly use solar to charge, then you should set the 'charged voltage' to about 0.05V below the absorption voltage on your solar charge controller.    A tail current of 4% is fine, and 3 minutes is also fine.   Change the settings, then park in the sun for a day to make sure the batteries get all the way full and the BMV will automatically resync.

 

For the solar charge controller, you can go with whatever Lion energy says for the settings or an absorption of ~14V and float at 13.4V would work well.   On occasion (like once or twice a year) you may want to take the battery up to 14.4V and hold it there to balance, but if you typically only charge to 14V it should stay in balance for a loooong time. 


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#8 BrianG

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Posted 24 April 2021 - 10:21 PM

I was recently told that my non-lithium IOTA converter (2015 Hawk) would only charge my Battleborn 100ah to 80%. This may not help, I just saw the 80% SOC reference and it rang a bell!


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#9 buckland

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Posted 24 April 2021 - 10:38 PM

You might need the IOTA  dongle that is cheap... for the LiFePo4 profile... if charging from shore power.


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#10 steve whiteside

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Posted 24 April 2021 - 11:22 PM

A couple hours ago I hooked the batteries to my Noco genius 7500 which will slowly bring my batteries up to full.  Based on your suggestion I looked at the Lion Energy FAQ and saw,

 

"We recommend setting all voltages to a max of 14.6 per UT in series or at least close to it. 

End amps or tail amps need to be set as low as possible and inverter low voltage needs to be set to 11.5V. 
Victron inverters charger and charge controllers should be set to 13.9 volts for a 12 volt inverter and 27.8 for 24 volt inverters."

 

 

​Based on the above Im guessing I should change the charge voltage from 13.2 to 13.9?  Or should I go higher?  

 

steve


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