Correct settings for Outback Flexmax 80 charge controller

[Roger Dale]

Hi everybody I have 2 questions concerning charge controller settings for LFP batteries that seem to be simple and straight forward but in the course of my research I have gotten answers that are all over the map. First I'll describe my system. It is 4000w 48v and off grid. Panels consist of 12 Hanwha QCell 325 watt (37.5 Vmpp and 8.67Impp) in 4 strings of 3 = input of 112.5v and 34.68a to an Outback Flexmax 80 charge controller. I am changing out my SLA batteries for 8 LiTime 12v 200Ah LFP batteries in a 4s2p setup = 48v 400Ah. My questions : What is the correct current limit setting for this FM 80 controller? I've read that the default setting of 80 amps is too high for LFP batteries. Second question : What is the correct absorption time? I've read it should be 40 minutes (20 minutes per 48v battery string) Is this right? My other settings are : absorption/boost/bulk 55.2v, float (full charge) 53.6v, rebulk 52.6 vdc and end amps/return amps/tail current = 8 amps (2% of total Ah capacity of battery bank). Can any of you fellow travelers in the world of solar power help me out with this? Much appreciated Roger Dale

 

[sunshine_eggo]

Hi everybody I have 2 questions concerning charge controller settings for LFP batteries that seem to be simple and straight forward but in the course of my research I have gotten answers that are all over the map. First I'll describe my system. It is 4000w 48v and off grid. Panels consist of 12 Hanwha QCell 325 watt (37.5 Vmpp and 8.67Impp) in 4 strings of 3 = input of 112.5v and 34.68a to an Outback Flexmax 80 charge controller. I am changing out my SLA batteries for 8 LiTime 12v 200Ah LFP batteries in a 4s2p setup = 48v 400Ah. My questions : What is the correct current limit setting for this FM 80 controller? I've read that the default setting of 80 amps is too high for LFP batteries. Second question : What is the correct absorption time? I've read it should be 40 minutes (20 minutes per 48v battery string) Is this right? My other settings are : absorption/boost/bulk 55.2v, float (full charge) 53.6v, rebulk 52.6 vdc and end amps/return amps/tail current = 8 amps (2% of total Ah capacity of battery bank). Can any of you fellow travelers in the world of solar power help me out with this? Much appreciated Roger Dale

FM-80 doesn't have lithium settings, but it works fine on them. It can't provide any low temperature charge protection. You batteries must have that built in.

You MUST disconnect the temp sensor.

Most lead acid is rated for around 0.1-0.2C where most LFP batteries are rated for 0.5C charges. That's a claimed benefit of LFP - faster charging. Your 400Ah bank should be rated to accept 200Ah. The battery specs will tell you.

55.2V absorption is good (3.45V/cell).
2 hours absorption.
no tail current.
54V float (3.375V/cell)

Rebulk 52.6V is good.

Make sure you individually charge each 12V to full before placing them in series. This is critical.

 

[sunshine_eggo]

What is the Voc of your panels? 37.5Vmp suggests they may be dangerously high to the 150Voc limit on the FM-80 in cold temps.

 

[Roger Dale]

FM-80 doesn't have lithium settings, but it works fine on them. It can't provide any low temperature charge protection. You batteries must have that built in.

You MUST disconnect the temp sensor.

Most lead acid is rated for around 0.1-0.2C where most LFP batteries are rated for 0.5C charges. That's a claimed benefit of LFP - faster charging. Your 400Ah bank should be rated to accept 200Ah. The battery specs will tell you.

55.2V absorption is good (3.45V/cell).
2 hours absorption.
no tail current.
54V float (3.375V/cell)

Rebulk 52.6V is good.

Make sure you individually charge each 12V to full before placing them in series. This is critical.

 

[Roger Dale]

FM-80 doesn't have lithium settings, but it works fine on them. It can't provide any low temperature charge protection. You batteries must have that built in.

You MUST disconnect the temp sensor.

Most lead acid is rated for around 0.1-0.2C where most LFP batteries are rated for 0.5C charges. That's a claimed benefit of LFP - faster charging. Your 400Ah bank should be rated to accept 200Ah. The battery specs will tell you.

55.2V absorption is good (3.45V/cell).
2 hours absorption.
no tail current.
54V float (3.375V/cell)

Rebulk 52.6V is good.

Make sure you individually charge each 12V to full before placing them in series. This is critical.

FM-80 doesn't have lithium settings, but it works fine on them. It can't provide any low temperature charge protection. You batteries must have that built in.

You MUST disconnect the temp sensor.

Most lead acid is rated for around 0.1-0.2C where most LFP batteries are rated for 0.5C charges. That's a claimed benefit of LFP - faster charging. Your 400Ah bank should be rated to accept 200Ah. The battery specs will tell you.

55.2V absorption is good (3.45V/cell).
2 hours absorption.
no tail current.
54V float (3.375V/cell)

Rebulk 52.6V is good.

Make sure you individually charge each 12V to full before placing them in series. This is critical.

Thanks for the info. In addition do you have a suggestion for the Flexmax 80 current limit setting? I forget to mention that these batteries have a 200a BMS. I have already charged each battery individually and now I'm going to wire them in parallel and leave them set for 24 hours for balancing as the battery mfg. suggests. I don't have a temp sensor so no problem. I also made a mistake. The actual Vmp of the panels is 33.65v and the VOC is 40.4v. so 3 panels in series is 121.2 v which should be OK with the charge controller in cold weather. Thanks again Roger Dale

 

[sunshine_eggo]

Thanks for the info. In addition do you have a suggestion for the Flexmax 80 current limit setting?

No limit:

Most lead acid is rated for around 0.1-0.2C where most LFP batteries are rated for 0.5C charges. That's a claimed benefit of LFP - faster charging. Your 400Ah bank should be rated to accept 200A. The battery specs will tell you.

I forget to mention that these batteries have a 200a BMS. I have already charged each battery individually and now I'm going to wire them in parallel and leave them set for 24 hours for balancing as the battery mfg. suggests.

Perfect, but I would leave them on the charger once in parallel.

I don't have a temp sensor so no problem.

Good.

I also made a mistake. The actual Vmp of the panels is 33.65v and the VOC is 40.4v. so 3 panels in series is 121.2 v which should be OK with the charge controller in cold weather. Thanks again Roger Dale

Good. 121Voc is great on a 150V controller.

 

[Roger Dale]

No limit:





Perfect, but I would leave them on the charger once in parallel.



Good.



Good. 121Voc is great on a 150V controller.

By no limit for the charge controller setting do you mean leaving it at the default setting of 80amps?

 

[sunshine_eggo]

By no limit for the charge controller setting do you mean leaving it at the default setting of 80amps?

yes.

Your thinking is backwards. You likely should have set a limit with your SLA unless you had around 800Ah.

Again, your LFP bank can handle 200A. Your FM-80 can only output 80A.