Outback Flexmax 80 MPPT 80 AMP Solar Charge Controller Question

I am new to the forum and this is my first post. I purchased (3) 300 watt panels and an Outback Flexmax 80 MPPT 80 AMP Solar Charge Controller. Unfortunately the controller did not come with an owners manual.... although I will be requesting one from the company.

The last system I had on a toyhauler had a Xantrex controller and I could set it to desufate the batteries on a regular basis. I can't find anything on line about this Outback controller having a desulfation mode. Does anyone have one and does it have this mode availible?



  • manzanitamanzanita Registered Users Posts: 37 ✭✭✭
    Why not wander over to [URL="http://{http://outbackpower.com/}"]outbackpower.com[/URL] and download a copy of the manual?
    Here is one link, perhaps not the right one.
  • petertearaipetertearai Solar Expert Posts: 437 ✭✭✭✭
    On the out back it is called Equalize. And yes all there manuals are on their site . I keep one at my holiday home and one at city home .
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
  • BB.BB. Super Moderators, Administrators Posts: 30,488 admin
    Also--Be careful about a "desulfate" mode... There is a lot of discussion about "desulfators" and what is desulfating.

    Most of the standard solar controllers have a function called Equalization. That is very different from desulfating.

    With lead acid batteries, we have 6 cells (12 volt) to 24 cells (48 volt) in series... And the cells can drift over time. One cell may self discharge a little faster than its mate. To where when the battery is fully charged--You may have 5 cells at 100% state of charge and 1 cell at 80% state of charge. The "capacity" of that battery is now 80% because of the "weak link/cell" in the series connection.

    Equalization is controlled over charging of the battery bank. The controller charges at 15 to 15.5 volts or so (vs 14.5 to 14.8 volts) so that we "force" extra current through the 100% full cells to recharge the one weak 80% cell and bring it up to 100% too.

    Lead Acid batteries sulfate (quicker) when they get (roughly) below 75% state of charge. You can see if if your 80% cell is now down to 60% SOC while the rest of the cells are at 80% SOC--that the one low charge cell will begin to sulfate while the others are still high enough charge that they will not. So--In that way, you can talk about a "desulfate" mode--But that is really what we call an Equalization mode--A preventative method to stop (excessive) sulfation from happening in the first place.

    What damages a battery is when the lead sulfate in a fluffy gray form over time (days/weeks/months) turns into a hard/black crystal. That is what we call "sulfating" for a lead acid battery. The fluffy sulfate is what charging/discharging our batteries use to produce current (with the sulfur in the electrolyte).

    The hard/black crystal lead sulfate is a stable form and does not participate in the charging/discharging cycle. It permanently reduces battery capacity and makes for "high resistance" on the surface surface of the lead plates. To a degree, "equalization" (gassing of the battery) can cause some sulfate crystals to shed from the plates--But it does not really "recover" the battery.

    A "desulfator" (or desulfator mode for a battery charger) is suppose to dissolve the crystalline lead sulfate and recover the battery capacity/lower resistance. Let us say there is a lot of heated discussions about desulfators and whether they work or not. Some say they work great, others say they don't work at all. And some say, why not use one--Won't hurt anything.

    There has been a few cases where desulfators (which create electrical pulses) have confused a solar charge controller and reduced its ability to quickly recharge a battery bank. So--There can be a down side to desulfators.

    I am not a fan of desulfators--But it is your time and money. Perhaps they will work for you (or doesn't hurt to try one).

    -Bill "sorry for my poor chemistry explanation" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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