Is this correct?

[Spower]

This is my 12 volt system: 2 100ah battleborn lithium batteries (1 yr old), 40A renogy rover mppt controller, 3-190w solar panels. Batteries/panels are in parallel.

The controller goes into Boost mode every day (14.4v) is this ok?
Then when it gets dark my batteries (lcd battery monitor) read 13.24v - 13.26v. According to the chart below that is only like 70%! Shouldn't they be reading like 13.4v? If so, how do I fix this?

Thanks for your help!

 

[Tomthumb62]

You can’t know your SoC by voltage, especially with lithium, unless you disconnect the battery from the system and let it sit a couple hours. Even then, with lithium, voltage is tough to go by.

If you really want to know more accurately, you’ll need a shunt monitor like the Victron Smartshunt or the many cheaper variants like the Renogy or Ailli ones. Or if your batteries have Bluetooth and has its own built in shunt, there might be an app that can show you this info.

In other words, completely disregard that chart you posted, it’s essentially useless.

 

[Spower]

You can’t know your SoC by voltage, especially with lithium, unless you disconnect the battery from the system and let it sit a couple hours. Even then, with lithium, voltage is tough to go by.

If you really want to know more accurately, you’ll need a shunt monitor like the Victron Smartshunt or the many cheaper variants like the Renogy or Ailli ones.

In other words, completely disregard that chart you posted, it’s essentially useless.

I do have a shunt battery monitor, that is where I am reading the voltage from.
I guess every system is different but it seems my friends voltage at night is higher then mine.

 

[Rednecktek]

It also looks like your MPPT is undersized a bit. The 14.4v boost is fine, that's where most of your bulk charging is happening. Are you running LFP settings or something else?

Trying to get SOC via voltage isn't very useful. A shunt would be your friend. Keeping track of the SOC by amps in/amps out is more accurate. Many cheapie "shunt" units out there still base everything by voltage.

What shunt are you using?

 

[BentleyJ]

There are several factors involved.
1) LFP chemistry has a very flat line chart when plotting SoC vs. Voltage. What Tomthumb62 said above is essentially correct.
2) How well calibrated is the battery monitor? A couple tenths of a volt deviation is a 29% SoC variation according to your chart. 13.2V vs. 13.4V
3) How much stand-by load is on the batteries and how long after charging stops are you checking the voltage.

13.25V resting is 3.31V per cell, 3.35V per cell (on a 48V battery) is generally what I see a few hours later after a charge cycle stops. You may not have a problem at all. If its going to cause you to loose sleep then take the time to verify everything with a good handheld Volt meter.

 

[Tomthumb62]

The shunt should have a SoC reading, use that instead of voltage. What does it say?

 

[Spower]

It also looks like your MPPT is undersized a bit. The 14.4v boost is fine, that's where most of your bulk charging is happening. Are you running LFP settings or something else?

Trying to get SOC via voltage isn't very useful. A shunt would be your friend. Keeping track of the SOC by amps in/amps out is more accurate. Many cheapie "shunt" units out there still base everything by voltage.

What shunt are you using?

This one

 

[Rednecktek]

Huh, looks like it shows operating wattage but not tracking total in and out over time. Is there a constant draw on the battery? That will show a voltage drop while current is flowing.

Units like the Aili, Renogy, or Victrons work by basing the SOC by how much has gone through it over time. When you get the unit you fully charge your batteries without a load. When you connect up the unit you press some buttons to tell it "This is full" and "The battery is XXXAh". From that point it has the info to start keeping track of how much goes in and out. When those show you the SOC it's based on "××× watts have gone out, $n watts have gone in, so the battery has WXY watts left".

 

[Spower]

I do have a 2000w inverter wired to the batteries, at standby it draws about 1.5 amps

 

[Rednecktek]

I do have a 2000w inverter wired to the batteries, at standby it draws about 1.5 amps

That will cause a slight voltage drop, and as close as voltages are on LFP it's not suprising you look a little light. If you want a more accurate reading either get a better shunt or disconnect ALL your loads and see what it says.

It doesn't look that far off, I suspect it's a matter of a little here, a little there that's all adding up.

 

[Spower]

That will cause a slight voltage drop, and as close as voltages are on LFP it's not suprising you look a little light. If you want a more accurate reading either get a better shunt or disconnect ALL your loads and see what it says.

It doesn't look that far off, I suspect it's a matter of a little here, a little there that's all adding up.

Ok thanks! I am thinking of upgrading to a better shunt with better readings.

 

[Rednecktek]

I really like the Renogy shunt as it's a really nice display and tracks by watts in/out. Also MUCH cheaper than Victron.

 

[Spower]

I really like the Renogy shunt as it's a really nice display and tracks by watts in/out. Also MUCH cheaper than Victron.

Thats the one I was looking at! ?

 

[Spower]

Ordered the Renogy Shunt. Hopefully it shows I was (maybe) getting an inaccurate reading with my cheaper LCD monitor? I would like to see voltage read at least 13.4 when the sun goes down. If not, back to the drawing board I suppose..stay tuned!

 

[richard cabesa]

As others have said, make sure you turn ALL 12V load off to do your testing.

My system has a constant 7-8 watt draw from the refer brain and the CO detector. My Battleborn bank will show 13.28-.29 with those items after a 14.4V charge 13.6V float while the sun is still up and then a rest after dark.
If I shut off those loads, the batteries will show 13.40-.42 all night if I leave it that way.

I worried about your concerns at first (hence the monitoring) but don't even think about it any more.

I use Victron BMV712 to monitor.

 

[Tomthumb62]

Also remember you originally said that you’re comparing your end of day voltage to your friend’s and yours was always lower. There’s a ton of variables to consider here. The accuracy of your shunt is just one. But unless you and your friend’s system have the exact same components, bought and installed and started using at the exact same time, and you each verify with a good shunt that you’re charging the exact same amount and using the exact same amount of juice, etc, then it’s really very difficult to compare yours and your friend’s end of day voltage.

This thread has really only focused on one aspect, the measuring with a good shunt and it sounds like you have one on the way. Now if your friend also gets the Renogy shunt, then you’d be better able to compare. Not compare voltage, but compare how many Ah go into the battery (via charging) and how many go out (through loads) each day. Then you’ll be comparing much more closely of apples to apples.

 

[Spower]

Here is part of my concern....my controller (on the wall) shows battery at 14.1, same as app is showing, but monitor is showing 13.59 (see attached)

 

[Rednecktek]

So the controller is charging a little bit low, I would expect that to be more like 14.4v, and your "shunt" isn't showing anything going in or out. I'd say at this point wait until the Renogy shows up and see what that says. It may also be that only getting ~12a going in it's the "slow" part of the charging at the top of the curve.

 

[Spower]

Hi all,
Finally got the renogy monitor and installed it. Below is what my controller is doing and what the monitor says. I have no idea if this is good?

 

[Rednecktek]

Looks like you have about 11a worth of load running at the moment between what the SCC is pumping out and what the battery is taking in. Not sure why the voltages are so far out of whack though...