Help with absorption time, ( lifep04 16s)

[Wycowboy]

Hi all I would love some quick help
I final built my diy 16s battery with
Catl 302 cells
Have a charge profile I’m good with but does any one have a good recommendation for the absorption time?
Thanks a bunch!


Charge controller. Midnite classic 200

 

[Ampster]

does any one have a good recommendation for the absorption time?

It is not a critical issue with Lithium batteries. If you are off grid or in a self consumption mode while on grid you may want it longer so when the sun goes down you are at the highest SOC at the end of the day. If your pack needs some balancing, then a longer absorption time to give your balancer time to work duriing the lower current stage of Constant Voltage (absorption).

 

[Wycowboy]

We are off grid. So longer may make sense.
So is that like 2hrs?

 

[sunshine_eggo]

56.8-57.6V for 30-60 minute absorption and/or .05C tail current (15A)
55.2V for 2-4 hour absorption and/or .01-.02C tail current (3-6A)

Both of the above should get you to 98%+ SoC.

54V float

If charging on generator, 56.8-57.6V is preferred to minimize genny run time.

 

[alcook62]

56.8-57.6V for 30-60 minute absorption and/or .05C tail current (15A)
55.2V for 2-4 hour absorption and/or .01-.02C tail current (3-6A)

Both of the above should get you to 98%+ SoC.

54V float

If charging on generator, 56.8-57.6V is preferred to minimize genny run time.

That's pretty much what I settled on for my system. I've programmed my Midnite 200 to absorb until I get to 25A tail current (510ah system) and/or 75 minutes and float at 27V (24V system).

 

[Wycowboy]

Thank you so much! This was exactly the help I needed


Could you explain to me about the tail
current settings? I’m not sure I’ve seen that on my midnight controller or overkill BMS app?

 

[AKvalleyguy]

That's pretty much what I settled on for my system. I've programmed my Midnite 200 to absorb until I get to 25A tail current (510ah system) and/or 75 minutes and float at 27V (24V system).

Do you have a WizBang Jr that makes the settings possible? I'm running several Classic 150's and the tail current setting doesn't seem to make any difference.

 

[alcook62]

Do you have a WizBang Jr that makes the settings possible? I'm running several Classic 150's and the tail current setting doesn't seem to make any difference.

Yes, I do have the wizbang Jr. I do believe that is necessary to use tail current for ending absorption.

 

[Wycowboy]

I have a wizzbang,, just installed it today. So learning my way around,
I see an “end amp” setting is that the same as tail amps? If so should I set it around 15?

There also seems to be an “re bulk volt” setting. Do I mess with that?

Truly appreciate this help!

 

[sunshine_eggo]

I have a wizzbang,, just installed it today. So learning my way around,
I see an “end amp” setting is that the same as tail amps? If so should I set it around 15?

There also seems to be an “re bulk volt” setting. Do I mess with that?

Truly appreciate this help!

END AMP is the same as tail current.

 

[AKvalleyguy]

Yes, I do have the wizbang Jr. I do believe that is necessary to use tail current for ending absorption.

Right on! I've got one sitting on the bench that I never got around to installing, yet.

 

[Tomthumb62]

56.8-57.6V for 30-60 minute absorption and/or .05C tail current (15A)
55.2V for 2-4 hour absorption and/or .01-.02C tail current (3-6A)

Both of the above should get you to 98%+ SoC.

54V float

If charging on generator, 56.8-57.6V is preferred to minimize genny run time.

Trying to wrap my head around absorb time here. If I understand your comment here, you're basically saying that the higher the absorb voltage, the shorter the absorb time is needed. So converting for a 12V 200Ah system, does this make sense:

14.2-14.4V for 30-60 minute absorption and/or .05C tail current (10A)
13.8V for 2-4 hour absorption and/or .01-.02C tail current (2-4A)

By the way, my battery manufacturer (Powerurus/Roypow) recommends 14.4-14.6 and an absorb time of 2 hours and a float of 13.5.

So I assume that the first case (higher voltage, shorter absorb time) gives you a few more Ah's into the battery. Are we talking like 3 or 4 Ah or more? And I assume the second case (lower voltage, longer absorb) gives a bit less capacity but you will likely extend the number of cycles of the battery. I'm thinking in our use case (RV), since it won't see daily cycling, we might be better off just charging based upon the first example of 14.2 for a 60 minute absorb time.

 

[Tomthumb62]

14.2-14.4V for 30-60 minute absorption and/or .05C tail current (10A)

Ok, another issue here. The Victron IP22 12/30 charger I have won't let me set a tail current any higher than 7.5A. Should I set it to that or just disable it altogether?

 

[lightbulb]

Trying to wrap my head around absorb time here. If I understand your comment here, you're basically saying that the higher the absorb voltage, the shorter the absorb time is needed. So converting for a 12V 200Ah system, does this make sense:

14.2-14.4V for 30-60 minute absorption and/or .05C tail current (10A)
13.8V for 2-4 hour absorption and/or .01-.02C tail current (2-4A)

By the way, my battery manufacturer (Powerurus/Roypow) recommends 14.4-14.6 and an absorb time of 2 hours and a float of 13.5.

So I assume that the first case (higher voltage, shorter absorb time) gives you a few more Ah's into the battery. Are we talking like 3 or 4 Ah or more? And I assume the second case (lower voltage, longer absorb) gives a bit less capacity but you will likely extend the number of cycles of the battery. I'm thinking in our use case (RV), since it won't see daily cycling, we might be better off just charging based upon the first example of 14.2 for a 60 minute absorb time.

Think of the battery like any other sealed container you fill up. Air bed, balloon, car tire, water tank, etc. Higher voltage = higher pressure. As the battery fills you need more pressure to keep packing more energy into it. It can only take so much. The higher the pressure, the faster it fills. Once it is full, it is full. In an ideal world you would need no absorb time. You would stop when it is full. In the non-ideal world, you may need some absorb because the cells in the battery(s) do not fill at exactly the same rate and for non voltage sensing controllers, the voltage / pressure at the charger is greater than at the battery, due to resistance.

You can not pack more energy into the battery once it is the same voltage as your charge controller. However, to keep it from wearing out, you want to minimize the time you keep the battery at high voltages. That is why you want to reduce the voltage after it is full (when the current is close to zero or 5 or 10amps whatever you are happy with). 7.5A too...

BTW this is for lifepo4. Other chemistries may need time, at high voltages, for chemical reactions.

 

[sunshine_eggo]

Trying to wrap my head around absorb time here. If I understand your comment here, you're basically saying that the higher the absorb voltage, the shorter the absorb time is needed. So converting for a 12V 200Ah system, does this make sense:

14.2-14.4V for 30-60 minute absorption and/or .05C tail current (10A)
13.8V for 2-4 hour absorption and/or .01-.02C tail current (2-4A)

By the way, my battery manufacturer (Powerurus/Roypow) recommends 14.4-14.6 and an absorb time of 2 hours and a float of 13.5.

So I assume that the first case (higher voltage, shorter absorb time) gives you a few more Ah's into the battery. Are we talking like 3 or 4 Ah or more? And I assume the second case (lower voltage, longer absorb) gives a bit less capacity but you will likely extend the number of cycles of the battery. I'm thinking in our use case (RV), since it won't see daily cycling, we might be better off just charging based upon the first example of 14.2 for a 60 minute absorb time.

Battery manufacturers may recommend longer times to ensure that cells are kept at peak voltage long enough 1) to fully charge and 2) for balancing time.

My recommendations are to ensure peak charge.

Ok, another issue here. The Victron IP22 12/30 charger I have won't let me set a tail current any higher than 7.5A. Should I set it to that or just disable it altogether?

It If you can specifiy a fixed absorption period, the tail current may simply serve as a means to end the charge early. If the goal is to get fully charged, the tail current is fine. If the goal is to get fully charged and allow for a little balance time, disabling tail current is probably required.

 

[Tomthumb62]

It If you can specifiy a fixed absorption period, the tail current may simply serve as a means to end the charge early. If the goal is to get fully charged, the tail current is fine. If the goal is to get fully charged and allow for a little balance time, disabling tail current is probably required.

Thanks a bunch. This makes much more sense because you give goal options. I think I’ll just keep the tail current setting turned off.

 

[Steve_S]

48V/300AH Battery: EndAmps/TailCurrent is 300AH X 0.05 = 15A
Set EndAmps in the Classic Software / Config / Tech submenu to 15A and Check the use WizBangJr for EndAmps.
Absorb is recommended @ 10 Minutes per 100AH capacity, therefore your Minimum Time should be 30 Minutes for absorb. You may find that it never actually lasts for 30 Minutes and will transition to FLOAT before that... You can take that to 1 Hour if you wish, but it will transition when EndAmps is reached regardless.

Midnite Classic Charge Controller Settings
All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT)
Absorb: 54.8 for 60 minutes (3.425vpc) (some call this boost)
Equalize: OFF
Float 54.7V (3.418vpc)
MIn Volts: 42.4 (2.650vpc)
Max Volts: 57.2 (3.575vpc)
Rebulk Voltage: 51.2 (3.200vpc)
End Amps: 15A (*1) (** Using WizbangJr Smartshunt to control) (*** Allows for full Saturation at set Float Voltage)
(*1): End Amps is calculated from the LOWEST AH Battery Pack in a Bank. IE: (100AH X 0.05 = 5A 280AH X 0.05 = 14A.
NB: Victron Forum discussion says EndAmps = TailCurrent
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.
This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are at 3.41Vpc.
I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off. (which is minimal)
* Do Not forget to adjust for Voltage Offsets between Actual Voltage @ Battery Terminal & at Solar Controller.

Hope it helps Good Luck.
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