Author Topic: Absorb times...  (Read 108 times)

alyaz

  • Full Member
  • ***
  • Posts: 202
  • Retirement rocks!
Absorb times...
« on: April 10, 2019, 08:31:19 PM »
Thought I kinda understood ‘absorb times’ but started questioning myself when explaining it to a friend today.  So is my reasoning faulty here?  This is how I explained it to him...

He completed the ‘Rolls FLA absorb equation’ and came up with 7 hours.  He only has a 1500 watt array and I don’t recall how many a/hrs his battery bank is.

Anyway, I told him that 7 hours is basically what his battery bank requires about every 7-10 days after he has been cycling it and it has not received a full charge.

So that got me to thinking, most people set their charge controllers up with that ‘magic’ number.  In his case he doesn’t use ‘end amps’ so his controller would be set up to run 7 hours of absorb every day - depending of course on how much solar he is pulling in.    During the summer it is feasible he could get 7 hours of absorb time on his battery bank every day for a period of time.  So that can’t be good can it? 

In my case, before I set up end amps with the Whizbang Jr, my controllers were set the same way (with the old battery bank).  Generally, my absorb times (using end amps) are about 2 - 3 hours now before I get to float.

So am I missing something here, or are absorb times using a ‘timer’ (without end amps) generally going to be excessive during the summer months and just overcharging and boiling off the batteries?

Just trying to understand this so I can actually speak intelligently about it, if that is possible.  Thanks.
3.3 kW solar. (1.5 kW Helios - MN Classic 150 CC; .8 kW CSun - MN Classic 150 CC; 1 kW Sharp - MN  Classic 250 CC); Magnum PAE-4024 Inverter, AGS, ARC, BMK. Whizbang Jr., Midnite Solar battery monitor, 5 Midnite SPD’s. 24V Rolls 4KS21P - 1105 a/hr FLA.  10 kW Perkins Diesel.

ClassicCrazy

  • Hero Member
  • *****
  • Posts: 2094
Re: Absorb times...
« Reply #1 on: April 10, 2019, 10:17:51 PM »
yeah 7 hours would most likely be way too long and bubbling  the batteries way too much -- might be harming them.
2 hours for absorb time  would be a better number to start with and see how it goes. 

If your friend has such a big battery pack and not enough PV to sufficiently charge it that isn't a good thing. Even if that was the case it would probably be in bulk a lot longer and then when it got to absorb it would start its count down then.

Whizbangs and ending amps take better care of the batteries when set up correctly because it will compensate for different charging conditions .

Larry
« Last Edit: April 10, 2019, 10:21:39 PM by ClassicCrazy »
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

mike90045

  • Hero Member
  • *****
  • Posts: 690
    • The Ranch (via facebook re-direct)
Re: Absorb times...
« Reply #2 on: April 10, 2019, 11:00:40 PM »
The best Absorb system I've come across, is measure the time required to BULK the batteries, and use that time for Absorb.

That sort of covers your array size, nightly depth of discharge and costs nothing.
http://tinyurl.com/LMR-Solar

Classic 200| 2Kw PV, 160Voc | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph )| Listeroid 6/1, st5 gen head | XW6048 inverter/chgr | midnight ePanel & 4 SPDs | 48V, 800A NiFe battery bank | MS-TS-MPPT60 w/3Kw PV

Vic

  • Hero Member
  • *****
  • Posts: 2092
Re: Absorb times...
« Reply #3 on: April 11, 2019, 11:53:41 PM »
The best Absorb system I've come across, is measure the time required to BULK the batteries, and use that time for Absorb.

That sort of covers your array size, nightly depth of discharge and costs nothing.

In decades gone-by,   the venerable OB MX-60 MPPT CC would use this Bulk time = Absorb time,  if no EA,  and no Absorb time was set  --  at least with early FW versions.

The early MN Classics also had this option.   I was one those who was begging boB to remove this option,  as it  often would result in considerably longer Abs times than necessary.   This approach is quite variable,   depending upon WX patterns,  elevation/azimuth of PV array,   view of horizon,  etc.

On the systems in use here,   Bulk begins before Sunrise.   In the Summer,   Bulk begins around 5:30 AM,   and Absorb is often not reached,  until about 10 - 11 AM.   This could easily dictate an Absorb time of five, or so hours.   This would be about double the typical required Absorb time.

If one has  morning clouds/fog,   the Bulk time could be further-extended,   causing even un-necessarily-longer Absorb times.

Wb EA  is about the best approach that I've found.   Even that  has  some variables that seem to make it not quite perfect.

Absorb time for the main bank here is usually between 2:15,   and 2:30 hours.   If Bulk time was used,  it would usually be more than twice that.

That Surrette Equation for Absorb time seems to yield  poor results,  for off-grid systems.   Believe that it is for Grid-Charged systems,   with Constant Current Bulk.   RE-charged (solar charged)  batteries  do not have the advantage of prescribed,   controlled Bulk charge current (IMO).

Just my opinions,   YMMV.    Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

boB

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2929
Re: Absorb times...
« Reply #4 on: April 12, 2019, 12:39:29 AM »

In decades gone-by,   the venerable OB MX-60 MPPT CC would use this Bulk time = Absorb time,  if no EA,  and no Absorb time was set  --  at least with early FW versions.

The early MN Classics also had this option.   I was one those who was begging boB to remove this option,  as it  often would result in considerably longer Abs times than necessary.   This approach is quite variable,   depending upon WX patterns,  elevation/azimuth of PV array,   view of horizon,  etc.


Absorb time = Bulk time   (minimum I think it was ?)

wasn't terrible but it was the wrong thing to do, in hindsight...

The charge current in bulk might be limited for whatever reason like, maybe it was cloudy for most of the morning and then the sun comes out ?

Just have it absorb long enough time to keep sulfation to a minimum.  Don't even absorb every single day maybe to keep water use down and possibly increasing the life of the batteries while being able to use more of the day's solar energy for other things like pumping water or selling back or whatever.

Similar thing with using ending amps to end absorb all the time.  If EA somehow keeps the battery from getting a nice long-ish absorb cycle once in a while, then maybe the batteries will sulfate sooner ?

Just when you think a product has the best way of doing something.....


K7IQ

Vic

  • Hero Member
  • *****
  • Posts: 2092
Re: Absorb times...
« Reply #5 on: April 12, 2019, 01:57:18 AM »

Absorb time = Bulk time   (minimum I think it was ?)

wasn't terrible but it was the wrong thing to do, in hindsight...

The charge current in bulk might be limited for whatever reason like, maybe it was cloudy for most of the morning and then the sun comes out ?

Just when you think a product has the best way of doing something.....

boB,

Was not trying to speak negatively about either the MX-60,  or the Classic.   Each of these CCs were and still are revolutionary.   SO many useful functions built into each of them.   No  other designers/manufacturers even try to come close to creating such useful products to so many users.

Think that the  Magnum PT-100 CC copied from this earlier work   ...

It seems that there is no real perfect solution for setting the needed Absorb time.   Just too many variables involved.

There are times when the EA value that was fine for the previous discharge/charge cycle  will simply not be reached in a reasonable amount of time,   etc.   It is for this reason that we Skip Days,   use Wb EA,   but EQ a bit more frequently,  than we might,   if we used  a fixed (and too long) Absorb times.

As you have noted,   it is much better to use Absorb times that are a bit too long,   verses ones that are generally too short   ...   thank goodness,   Flooded LA batteries are fairly forgiving.

Please DO keep up the great work,   boB.    We all are counting on you and the MidNite crew,   to continue the string of terrific new products.

Realize that all of the functions that are built into MN products take more development time,  debug time,   Support time,  etc.   And all of this makes your products  the absolute best available,   and may have somewhat smaller profit margins for MN,  than do products from others,  who are not "swinging for the stars",   as MidNite is doing.

Nothing is perfect,   but you guys sure are working hard at making your products far closer to perfection than any others on this planet  ...   IMO.

People like me,   were begging,   and begging you to ship the Classic.   We simply could not wait to get the Classic into our hands!   Had one of the very first Classics made  --  shipped in December 2010,   IIRC.

Thanks,   and was not trying to be snarky.     73   GL,     Vic
« Last Edit: April 12, 2019, 02:01:31 AM by Vic »
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!