Schneider Electric Conext MPPT Config

Lookaflyingdonkey

Solar Enthusiast
Joined
Mar 16, 2021
Messages
29
I have installed a Conext MPPT 80 600 and the SW 4048 at an offgrid cabin and it has been working well after a couple tweaks, I recently setup monitoring as I was seeing the battery run down overnight when I wouldn't have expected it to.

From the graphs it looks like once the battery is charged (often by middle of the day), the MPPT shuts off and doesn't produce any more output, I was thinking that it would still produce enough to satisfy the current load on the SW4548.

So what appears to be happening is the system is charging the battery to 100%, HV cut off is being hit, solar is shutting down and not kicking back in until the battery is down enough to trigger it to recharge.

Any suggestions on how to optimize this? Looks like we are losing alot of daytime sun, I was hoping that the battery would just take up the slack as the sun goes down or clouds come in.

1636375106550.png
 
Last edited:

Lookaflyingdonkey

Solar Enthusiast
Joined
Mar 16, 2021
Messages
29
48v LiFePO4 (Lishen Cellls with overkill BMS)
Absorption voltage is set to 55.2v with an Absorption Time of 2 minutes
Charge Cycle is set to 2 stage (No Float)
By ReBulk do you mean Recharge voltage? I have 55.2v set for my Bulk and 51v set for recharge
 

sunshine_eggo

Happy Breffast!
Joined
Oct 26, 2021
Messages
1,918
Location
USA
The lack of a float voltage is why the system is behaving as it is. You need to specify a float voltage of 3.4V/cell.

That's what's misleading about LFP - no. You don't need to float them to keep them fully charged, but in a cyclic power system, you need to float them so the PV will provide your power. It's the FLOAT VOLTAGE THAT TELLS THE PV SYSTEM TO SUPPLY POWER RATHER THAN PULL FROM THE BATTERY.

At 3.45V and a 2 minute absorption, you are likely falling well short of full charge, but that depends on your current at termination. HOWEVER, once you specify a float voltage OF 3.4V/cell, you'll likely get well into the 90%'s during the float phase depending on your loads/solar.

Recharge = Rebulk, i.e., when to restart a bulk charge. I'd set re-bulk to 3.25V/cell.

Summary:

Bulk/Absorption: 3.45-3.55/cell
Float: 3.4V/cell
Re-bulk/Recharge: 3.25V/cell
 

Lookaflyingdonkey

Solar Enthusiast
Joined
Mar 16, 2021
Messages
29
That makes sense, it is effectively saying to stop charging short of 100% and then just "trickle charge" the remaining 5-10%, effectively keeping the PV turned on and supplying the majority of the power to the inverter.

Solar hits around 2kw peak and probably 1.5kw average while it is bulk charging, and loads are minimal (200w or so constant).

The current issue is that we hit 100% at around 11:30am then the battery just drains all the way through to the next day, so if the next day is cloudy we are already 30-40% drained, whereas if the PV is powering during the day, the battery will just cover night loads and only be 10% or so drained going into the next day.

I am about to add more battery capacity to try and stretch the number of days out of the system.

Will having rebulk so close to float/bulk cause the battery to short cycle, and only cycle between like 60-100%? Currently on sunny days we drop down to approx 40% and then back to 100%.
 

sunshine_eggo

Happy Breffast!
Joined
Oct 26, 2021
Messages
1,918
Location
USA
The current issue is that we hit 100% at around 11:30am then the battery just drains all the way through to the next day, so if the next day is cloudy we are already 30-40% drained, whereas if the PV is powering during the day, the battery will just cover night loads and only be 10% or so drained going into the next day.

Again, setting float as described will stop this. It will 1) ensure your PV supplies the loads and 2) keep the battery at 100% until loads exceed PV as the solar degrades in the afternoon/evening.

Think of it this way... fully charged at 11:30, but you have enough solar to power loads until 3:30. Before, your battery was powering your loads for 4 hours when it didn't have to. With a float, PV will power those loads AND keep the battery floated - you'll have 4 hours more capacity than you did before.

As a guestimate from your SoC plot, you'll be using 10-20% less battery capacity in a 24 hour period. Furthermore, as mentioned later in this message, you will likely get your battery much closer to true 100% SoC, so you may have another 10-15% more capacity available from proper charging/floating.


Will having rebulk so close to float/bulk cause the battery to short cycle, and only cycle between like 60-100%? Currently on sunny days we drop down to approx 40% and then back to 100%.

Only if you have intermittent sun and your loads drive your voltage down substantially. 3.25V/cell is actually pretty far from the float because it's in the flat portion of the discharge curve. It shouldn't drop that low except in poor solar conditions.

Once you specify a float voltage, you should see your battery stay at 100% or near 100% until the evening when loads exceed the availble solar.

Your definition of 100% is NOT 100%. If you're charging only to 3.45V/cell for 2 minutes, then you are short of true 100%. I can't say for certain, but I would expect it to be under 90%.

Assuming 16S 280Ah, 2kw is only pushing about 36A 3.45V or 0.13C.

I personally would not choose your 2 minute absorption, but I would choose two hours. At 3.45V/cell LFP can't accept a rapid charge rate, so you NEED a longer absorption period. Additionally, if you can specify a charge termination current of 14A (sometimes called tail current or end amps), that's probably a good setting. You should readily hit 95-98% SoC on good days.
 

Lookaflyingdonkey

Solar Enthusiast
Joined
Mar 16, 2021
Messages
29
thanks @sunshine_eggo I will give it a go when I head upstate next week, I would apply remotely but if it doesn't come back online for some reason its a LONG drive to head up to resolve it :ROFLMAO:

That SoC chart is actually coming out of the BMS, so should be "accurate", I will have to do a full cycle test and make sure its still accurate, last test it hit ~160Ah on a 150Ah pack.
 

sunshine_eggo

Happy Breffast!
Joined
Oct 26, 2021
Messages
1,918
Location
USA
thanks @sunshine_eggo I will give it a go when I head upstate next week, I would apply remotely but if it doesn't come back online for some reason its a LONG drive to head up to resolve it :ROFLMAO:

That SoC chart is actually coming out of the BMS, so should be "accurate", I will have to do a full cycle test and make sure its still accurate, last test it hit ~160Ah on a 150Ah pack.

I know you probably think I'm arguing with you, but it's probably not accurate. You're not meeting the 100% criteria of your cells with your short absorption time. BMS don't inherently know the state of charge of the battery. They count current and sometimes tare it based on voltage, but if the battery isn't truly hitting 100% SoC based on the charge termination criteria, the BMS can be fooled.

Charging at 3.45V and terminating at a current lower than 0.05C (it actually should be lower at 3.45V), your battery is not fully charged even if the BMS says so. Again, I'm thinking it's around 10-15% at most.
 

iamrich

Solar Addict
Joined
Dec 17, 2020
Messages
830
Location
Elgin, Texas
Kind of surprised the SCC doesn't have a setting to prioritize loads. I am running my packs at 26.7v and once they hit that voltage, the LV2424 throttles the PV input to just cover any load usage. If the PV is not putting out enough, the batteries will be used, but the second the sun comes back, the batteries are charged back up to 26.7v and then the controller throttles back.
 

sunshine_eggo

Happy Breffast!
Joined
Oct 26, 2021
Messages
1,918
Location
USA
Kind of surprised the SCC doesn't have a setting to prioritize loads. I am running my packs at 26.7v and once they hit that voltage, the LV2424 throttles the PV input to just cover any load usage. If the PV is not putting out enough, the batteries will be used, but the second the sun comes back, the batteries are charged back up to 26.7v and then the controller throttles back.

You've just described float voltage behavior, and we established that he did not have a float voltage. :)
 

iamrich

Solar Addict
Joined
Dec 17, 2020
Messages
830
Location
Elgin, Texas
You've just described float voltage behavior, and we established that he did not have a float voltage. :)
I think we are talking about two different things. My LV2424 when set to "Solar energy provides power to the loads as first priority" powers the loads first and if there is any left it goes to the battery. It will not use the battery if solar is available and it will not charge the battery if the load is equal or greater than PV in.

I understand what you have proposed is a work around, I am just surprised there isn't a setting in the software.
 

sunshine_eggo

Happy Breffast!
Joined
Oct 26, 2021
Messages
1,918
Location
USA
I think we are talking about two different things. My LV2424 when set to "Solar energy provides power to the loads as first priority" powers the loads first and if there is any left it goes to the battery. It will not use the battery if solar is available and it will not charge the battery if the load is equal or greater than PV in.

I understand what you have proposed is a work around, I am just surprised there isn't a setting in the software.

Because Voltronix/AiO does it back-asswards, and that's what you're used to. He does not have a AiO. He has an inverter and a separate MPPT.

It doesn't have that setting because it has no functional meaning outside the inverter. The inverter doesn't even see the MPPT, it just sees its DC power source that the MPPT happens to be connected to.

Normal behavior of MPPT:

Charge battery until float.
Hold float voltage. If float drops (loads), add current.
It continues that until it can no longer float the battery and then the battery powers the loads.

That is an SB priority. It's why even though manufacturers say "you don't need to float LFP batteries," you need a float voltage to tell the MPPT when to supply loads.
 
Top