Fixed gel-battery charging profile for LFP battery?

carolinabigfoot

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I wonder whether I could use my Morningstar PS-30M Gen 2 to charge a LFP battery, using its gel-battery charging profile. The voltages in the profile differ slightly from the ones that the battery manufacturer recommends. Here are the numbers, first number is for the charging algorithm of the charge controller, the second one is the charging recommendation from the battery manufacturer:

absorption: 28.0V / 28.8-29.2V
float: 27.4V / 27.6V
low voltage disconnect: 22.8V / 21.6V
low voltage reconnect: 25.2V / 24.8V
high voltage disconnect: 30.4V / 30.0V

I am mostly concerned about the absorption number (will 28.0V be enough to sufficiently charge the battery?) and the high voltage disconnect (will battery damage occur if the solar input is cut off only at 30.4V instead of 30.0V?). Full disclosure: the battery in question is an Ampere Time 24V 100Ah.
 

Smokin

Solar Enthusiast
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Sep 8, 2021
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28 volts cutoff is fine for charging LifePO4. You would set GEL setting on the Morningstar.

"
The Battery Type rotary switch allows selection of 1 of 3 charging algorithms. These are broadly defined as the following battery types as noted on the lower label:

  1. Gel: Some gel and other battery types recommend lower regulation voltages and no equalization. This setting regulates to 14.0V (for a 12V battery).
  2. Sealed: AGM, "maintenance free" and some types of gel batteries. Regulates to 14.15V (12V battery) with 14.35V boost charging.
  3. Flooded: Vented cells that require water to be added. Regulates to 14.4V with 14.9V and 15.1V equalizations (12V battery)."
 

Short_Shot

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I think 27.4 float will be too high for the lifepo4 gathering from what I've read on this forum, 26.8 to 27.0 might be safer.
I agree ish. Depends highly on the usage frequency in my mind.

So here's my opinion, and please take it as just opinion.

27.4v is 3.425v per cell which just barely puts it into the steep part of the charge curve but a lot of bms units start balancing at 3.4v (ideally you can configure this in the bms of course).

If you're discharging it daily then the 27.4 will only be present for a limited amount of time and will be fine and give you a chance to let the bms work it's magic if needed.

If you're just using it on the weekend it's still probably not an issue.

For my very limited usage, I prefer 3.30v even which for 8 cells is 26.4v float.

The reason being that "float" typically only comes up when it's being stored anyways (for my uses) and I really don't want the thing sitting at or near a totally full charge long term. For this I use my crappy wfco converter. It actually results in a soc discharge until it reaches that ~3.3v mark through parasitic drains when holding it this low, which is better (but not ideal) for storage anyways.

When I plan to use it I stick a regular lithium charger on it a couple days before that will fully charge and float high enough to effectively maintain a virtually full charge at just over 3.4v per cell and allow balancing to enable, which most of the time doesn't occur as my balance doesn't get very far off anyways.

For 8 cells again this would be 27.3+ volts.
 

carolinabigfoot

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Thanks!
Now is in y'alls opinion the fact that the high voltage disconnect of the solar panels performed by this charge controller takes place at 30.4V instead of 30.0V (manufacturer recommendation) a reason to be concerned? Do you think that battery can take 0.4V more on the high end without getting damaged?
 

pollenface

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I would stick to the manufacturers recommendation.

Question though, doesn't "high voltage disconnect" usually refer to loads connected to the charge controller?
 

smoothJoey

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11,833
Thanks!
Now is in y'alls opinion the fact that the high voltage disconnect of the solar panels performed by this charge controller takes place at 30.4V instead of 30.0V (manufacturer recommendation) a reason to be concerned? Do you think that battery can take 0.4V more on the high end without getting damaged?
The battery bms should trip long before you hit that.
 

mikefitz

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May 28, 2020
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The gel setting is the only usable setting for lithium but its not ideal. 14 volts charge voltage will fully charge the battery and 13.7 float will keep it in a high state of charge.
Long term use of this PWM charge will not do your battery any favours and may reduce useful battery life.

The high voltage protection is associated with the load outputs and to limit the solar panel voltage input to the controller. In no way is this protection for the battery charge voltage.

I recommend, other than for a short term use, you replace the PWM controller with a MPPT solar charger with user setting for the charge parameters. Not only will you be able to set ideal charge conditions for efficient charging and long battery life, you will get up to 30% more solar yield from your existing panels.

Mike
 

carolinabigfoot

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I recommend, other than for a short term use, you replace the PWM controller with a MPPT solar charger with user setting for the charge parameters. Not only will you be able to set ideal charge conditions for efficient charging and long battery life, you will get up to 30% more solar yield from your existing panels.
That has crossed my mind already. But there is just a partial shading issue that I have to figure out before to determine whether I can go with a MPPT controller or whether I have to stick with a PWM controller. To do this I need to hitch the new battery to this controller to measure the amps from the individual panels which I was a little apprehensive of. But even if I have to stick with PWM I think I would get a programmable CC or one that supports LFP. Now just out of curiosity if my current CC was all that was at my disposal wouldn't charging profile #2 (sealed) do a better job than the gel profile? The equalization isn't really an equalization but a "boost charge" that is still below the recommended absorption charge from the battery manufacturer. Could you also explain to me why the high voltage disconnect solar is not a protection for the battery charge voltage. I still try to get a thorough understanding of what is actually going on in my system.
 

Substrate

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Apr 28, 2021
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SoCal
The big question is can you DISABLE temperature compensation with those built-in modes designed for lead-acid?

If you can't, you'll be all over the place voltage wise for LFP. Too high when it is cold, and too low when it is hot.
 
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