Hello! I'm replacing lead acid batteries in a older system, using four SOK 12V 206Ah LiFePO4 batteries (in parallel). I have a Outback FlexMax controller and am wondering how to change the settings and what they should be. I inherited the system with the property and the lead acid batteries are at their end.
Replacing old lead acid with lithium - flexmax mppt settings?
- Thread starter Jaya
- Start date
sunshine_eggo
Happy Breffast!
Neighbor has 2X FM80, so I'm somewhat familiar.
Disconnect your temperature sensor to disable temperature compensation. LiFePO4 (LFP) doesn't need it, and it can be bad for it.
Absorption to 14.4V
Absorption time to 1 hour
float to 13.6V
Disconnect your temperature sensor to disable temperature compensation. LiFePO4 (LFP) doesn't need it, and it can be bad for it.
Absorption to 14.4V
Absorption time to 1 hour
float to 13.6V
Thank you. Outback was zero help.
I'm guessing the temperature sensor is already disabled since there's nothing plugged in? (2nd telephone plug from the left)
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sunshine_eggo
Happy Breffast!
Correct. I'd take the opportunity to blow some cobwebs out with compressed air...
Hi;
Just signed up although I have watched the videos for awhile on Youtube. I have had a 1kW system for quite a few years and finally made the jump to the recommended SOK batteries.
I have a Flexmax controller as well that I bought in 2019 and I have the same issue as the OP. Question that I have though is as I understand it the Flexmax wasn't designed for lithium and it seems like the bulk charging voltage is simply to low to fully charge these batteries. The SOK is happiest with a bulk charge of 14.4v to 14.6 volts.
I just put in the SOK bank this morning (12v and parallel) and the outback is showing an input voltage of 15.2 volts currently and only 100 watts output as it's cloudy. But the output voltage is only 13.3 volts. Looking at the charger menu you can put in your current limit in amperage as well as set the absorb and float voltages. Borrowing the settings from #2 I set the absorb to 14.4 volts, time to an hour and float to 13.6 volts.
Problem is of course there doesn't seem to be a way to modify the MPPT settings to output a higher bulk charge voltage. Going into the advanced menu there doesn't appear to be a setting to increase the bulk charge MPPT settings. I'm just not sure that only using the solar that the batteries will ever get to a 100% state of charge.
Opinions or would it be better to s$it can the Outback and get one of Will's recommended chargers for lithium? Thought I would just add on to this thread instead of starting a new one.
TIA!!
Just signed up although I have watched the videos for awhile on Youtube. I have had a 1kW system for quite a few years and finally made the jump to the recommended SOK batteries.
I have a Flexmax controller as well that I bought in 2019 and I have the same issue as the OP. Question that I have though is as I understand it the Flexmax wasn't designed for lithium and it seems like the bulk charging voltage is simply to low to fully charge these batteries. The SOK is happiest with a bulk charge of 14.4v to 14.6 volts.
I just put in the SOK bank this morning (12v and parallel) and the outback is showing an input voltage of 15.2 volts currently and only 100 watts output as it's cloudy. But the output voltage is only 13.3 volts. Looking at the charger menu you can put in your current limit in amperage as well as set the absorb and float voltages. Borrowing the settings from #2 I set the absorb to 14.4 volts, time to an hour and float to 13.6 volts.
Problem is of course there doesn't seem to be a way to modify the MPPT settings to output a higher bulk charge voltage. Going into the advanced menu there doesn't appear to be a setting to increase the bulk charge MPPT settings. I'm just not sure that only using the solar that the batteries will ever get to a 100% state of charge.
Opinions or would it be better to s$it can the Outback and get one of Will's recommended chargers for lithium? Thought I would just add on to this thread instead of starting a new one.
TIA!!
I had sent an inquiry to Outback about the settings for Lithium batteries and what could be done to up the voltage enough to properly charge the batteries. The following is what was sent to me. FWIW the clouds have cleared out a bit and seeing some more sun and the outback is outputting 14.2 volts. Also running the AIM charger to bring the battery bank up full so I can reset the monitor to 100%.
/snip
Hello *******,
Thank you for contacting OutBack Power Post Sales Technical Support Team.
There won't be a bulk charging stage to set in the Outback charge controllers. This bulk charging is the first stage in the three-stage charge cycle of the batteries. It is a constant-current stage which drives the battery voltage up towards the Absorb voltage settings configured and suggested by your battery manufacturer. This stage is not timed. It will charge as long as necessary to complete the stage, regardless of any timer set points. If little PV energy is available, it may take a long time for this stage to complete. If the Flexmax is in a different stage and little PV energy is available, it may return to Bulk. This stage is temperature-compensated.
Make sure that you have the battery charging parameters (voltages and timers) listed in the setup menu as recommended by your battery manufacturer.
Regards,
Ravi
OutBack Power Tech Support.
/snip
/snip
Hello *******,
Thank you for contacting OutBack Power Post Sales Technical Support Team.
There won't be a bulk charging stage to set in the Outback charge controllers. This bulk charging is the first stage in the three-stage charge cycle of the batteries. It is a constant-current stage which drives the battery voltage up towards the Absorb voltage settings configured and suggested by your battery manufacturer. This stage is not timed. It will charge as long as necessary to complete the stage, regardless of any timer set points. If little PV energy is available, it may take a long time for this stage to complete. If the Flexmax is in a different stage and little PV energy is available, it may return to Bulk. This stage is temperature-compensated.
Make sure that you have the battery charging parameters (voltages and timers) listed in the setup menu as recommended by your battery manufacturer.
Regards,
Ravi
OutBack Power Tech Support.
/snip
sunshine_eggo
Happy Breffast!
A 12V 100Ah battery is fully charged at 14.6V when the current drops to 5A or 0.05C.
LFP batteries can EASILY be charged to 100% and beyond at lower voltages with longer charge times.
If you are charging your batteries to 14.4V and absorbing for an hour, you are absolutely, positively getting your batteries fully charged.
Thank you for your comment. Not that I'm doubting you but how can it be that if using photovoltaic alone and so far with the current settings of the Outback I'm seeing a maximum output of 14.2 volts how is it possible to get to a state of charge of 14.6 volts? Once the battery bank gets to the 14.2 volts that the Outback is putting out wouldn't the bank cease to charge? How can you get a greater battery voltage than the input voltage?
sunshine_eggo
Happy Breffast!
PV voltage must always be higher than battery voltage. It must also be sufficiently high to enable MPPT operation.
Furthermore, there must be sufficient energy hitting the panels to provide the needed charge current.
Output voltage is always just slightly above battery voltage because they are connected. It can't be any higher than that dictated by the current and resistance. Battery voltage will only increase if there is sufficient input voltage AND current.
If your PV is only 15.2V the FM is likely not receiving sufficient input, or the array is malfunctioning or improperly configured.
Furthermore, there must be sufficient energy hitting the panels to provide the needed charge current.
Output voltage is always just slightly above battery voltage because they are connected. It can't be any higher than that dictated by the current and resistance. Battery voltage will only increase if there is sufficient input voltage AND current.
If your PV is only 15.2V the FM is likely not receiving sufficient input, or the array is malfunctioning or improperly configured.
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I think it’s wired correctly. The panels are all 12v nominal wired in parallel. High overcast today and at this moment 200 watts output with 15.8 volts input. In full sun it’s closer to 16.5 volts input or so. Perhaps it isn’t an issue as of course as the input voltage goes up in MPPT so does the output voltage. It’s just that I’ve never seen 14.6 volts output out of the Outback. I’ll have to wait until the Outback indicates fully charged and goes into float and see if that is enough to get the BMS to cut out and see what the resting voltage is. The lithium batteries are new to me so there will be a learning curve here.
Thanks!
Thanks!
sunshine_eggo
Happy Breffast!
How many amps are flowing to the battery?
LFP also charges differently than lead-acid. Lead acid reaches absorption voltage pretty quickly and stays there for hours before fully charged.
The vast majority of LFP charging occurs below 3.40-3.45V/cell. Depending on your connection quality, resistance and charge current, the voltage may read higher.
You might experience improved performance if you can wire the array in a 2S configuration such that your Voc is 40-44 and your Vmp is closer to 34-36V.
The FM60/80 can also have the Vmp value programmed as a reference.
The current setting is simply the maximum, i.e., if an FM80, this defaults to 80A. If you have some reason to reduced the output current, like if you're battery can only be charged at 50A, then you would lower the output to 50A. It still depends on available solar.
LFP also charges differently than lead-acid. Lead acid reaches absorption voltage pretty quickly and stays there for hours before fully charged.
The vast majority of LFP charging occurs below 3.40-3.45V/cell. Depending on your connection quality, resistance and charge current, the voltage may read higher.
You might experience improved performance if you can wire the array in a 2S configuration such that your Voc is 40-44 and your Vmp is closer to 34-36V.
The FM60/80 can also have the Vmp value programmed as a reference.
The current setting is simply the maximum, i.e., if an FM80, this defaults to 80A. If you have some reason to reduced the output current, like if you're battery can only be charged at 50A, then you would lower the output to 50A. It still depends on available solar.
The system is just for my radio room for emergency communications as all the radios run 12 volt along with led string lighting, etc. Also have a Honda 3kw generator if needed. I have only run the panels in parallel and into a combiner box and then into the charge controller. The charger is a FM60 and the 1kw of panels is overkill but I have never run down the batteries enough for full output from the panels so that isn’t an issue with exceeding the 60 amp rating. Had 400ah of 6volt trojans in series/parallel and the new batteries are 2 of the SOK 206ah batteries.
With the Aim charger today with the dip switches set to the lithium setting I was getting the full 75 amp output. On solar only with the lead acid batteries it was rare to get more than 40 amps out of the charger as I simply didn’t run the batteries down that much. If I was going to run the whole thing off grid I know enough that I probably want to run 36v or 48v with the proper inverter and then have a dc/dc converter to step down to 12v.
My trojans were only a few years old but with the economy and supply chain issues the lithium batteries probably won’t get any cheaper if you can get them at all and that is why I did the upgrade. Also a bonus that it effectively doubles the usable capacity of the bank so not limited by a 50% depth of discharge like with the flooded batteries. Would save on generator time in an extended winter outage at least.
Tempting to do a whole house upgrade and run everything off solar/lithium looking at grid prices going up. Brings the payoff down a lot but the limit is I’m in the U.P. of Michigan and the solar angles and clouds in winter require a lot of panels to be effective.
With the Aim charger today with the dip switches set to the lithium setting I was getting the full 75 amp output. On solar only with the lead acid batteries it was rare to get more than 40 amps out of the charger as I simply didn’t run the batteries down that much. If I was going to run the whole thing off grid I know enough that I probably want to run 36v or 48v with the proper inverter and then have a dc/dc converter to step down to 12v.
My trojans were only a few years old but with the economy and supply chain issues the lithium batteries probably won’t get any cheaper if you can get them at all and that is why I did the upgrade. Also a bonus that it effectively doubles the usable capacity of the bank so not limited by a 50% depth of discharge like with the flooded batteries. Would save on generator time in an extended winter outage at least.
Tempting to do a whole house upgrade and run everything off solar/lithium looking at grid prices going up. Brings the payoff down a lot but the limit is I’m in the U.P. of Michigan and the solar angles and clouds in winter require a lot of panels to be effective.
That is close to the response I got from Outback, but they were more helpful to you, thankfully.
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