Midnite Classic 150 - Turn Float Off ?

tr0y · May 2019

Hi All -

I am using a lithium based battery and the information available leans towards the battery not liking / it's unnecessary a float charge. I was wondering if any of the Midnite experts would chime in and give me some thoughts.

Is there a way to or work around to turn float off ? I assume that at a specified SOC or voltage I would enter rebulk ?

Thanks

mike95490 · May 2019

You simply set your float voltage to below something the BMS is happy with.

To be real clever, don't go so low that the battery discharges when start the blender at noon, leaving you with half a charge at sunset

And be sure to set ABSORB to only a couple minutes, generally that's all Li cells need.

mcgivor · May 2019

The information available on LFP charging varies dramatically depending on application, much of which is related to EV applications and doesn't relate to solar off grid use. With EV the battery is charged to capacity then terminated, discharge only occurs when the vehicle is used, however in off grid there are likely loads which deplete the battery as soon as a nominal state is achieved usually capped at around 95%, to avoid the stresses of upper voltage charging.

Without a float setting it would be possible that the battery reaches it's nominal fully charged state early in the day, if loads are present they would begin to discharge to a point of recharge voltage, this could be late in the day when there is insufficient sun to recharge. Having a float setting allows the battery to remain in a state of neither being charged nor discharged, but allows the PV to support loads until no longer capable, then it blends the two together until the PV terminates and the battery assumes all the load.

My personal settings are a mirror of the recommendations of SimpliPhi' for maximum cycle life with Schneider equipment , despite being a DIY bank, they are as follows,
Bulk 28V
Absorption 28V for 6 minutes
Float 27V
Recharge 25V
Equalization disabled
Temperature compensation 0
Programed capacity 0.5 of actual

Granted the controller is not Midnight but the settings could be programmed with such a sophisticated unit.
Can you describe the battery in question, is it a DIY, a drop in replacement type and what chemistry because the battery may need specific requirements, there is no one size fits all, as with all battery types.

tr0y · May 2019

Thanks Guys ! I'll do some setting changes.

mcgivor · May 2019

What batteries do you have?

MrM1 · May 2019

mcgivor, does this lead to what some on YouTube had called "Micro Cycling" of Li batteries. I responded to a negative YouTube video recently where the poster claimed Midnite and others lied about their diversion mode (seemed like strong language to me). How it wasn't really a diversion and how in diversion mode (after fully charged), the diversion would lead to Micro Cycling of the Li battery resulting in what would be (in the posters opinion) many extra complete cycles over the lifetime of the battery bank, thus shortening cycle life of the Li battery over time. I wrote that while this might be true of Li chemistries, this is not necessarily true FLA batteries as when diverting in float, there is around 0.5 amps going to the battery all the time while the array is producing excess power to support the load if the right solar conditions are available.

mcgivor · May 2019

That is an interesting point which I can't definitively answer, but from observations with my system, there is little current sent to the battery as long as the array can support the loads, much the same as LA. Having said that there may be something to do with the BMS used, most have a single charge/ discharge port which doesn't allow bi directional current flow, this may, in some way result in micro cycles, if in fact this is an issue.

This phenomenon brings up the question of EV dynamic braking, sending short bursts of energy into the battery, dose that constitute a micro cycle, and if so why would it be implemented as a benefit?

There are many unanswered questions, lithium technology depends largely on on electronics to safely control the parameters, I wonder if the chosen BMS is the pivotal factor, most applications are not geared towards off grid but rather to EV, which is very different in its dynamics.

Perhaps some are attempting to translate EV applications to off grid, thus achieving results which are unexpected, thereby blaming the equipment as incompatible for the supposed eronious outcome.

Just a collection of thoughts

MrM1 · May 2019

I know in the case of that one YouTube Channel, he has a BMS ... BUT has chosen NOT to install it yet. He is using used Telsa Batteries that have been in service for him for a year now. I watch the channel and enjoy it, but take most of his methods with a grain of salt as they are often less than code compliant. He does though have a separate detached battery building so if the batteries burst into flames he probably would not lose the house and would do no damage to other peoples property.

And I don't know if you looked at the video, but I do not feel like the manufactures of the Classic and Outback controllers have lied to us, but rather as you say, Li batteries in Off grid is fairly new and there are unanswered questions.

tr0y · June 2019

Thanks All !

Midnite Classic 150 - Turn Float Off ?

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