Bulk > Absorb > Float questions

[openplanet]

I understand that with a Classic controller, Whizbang Jr., and flooded lead-acid batteries:

1. As Bulk charging proceeds, battery voltage increases, until...
2. the battery voltage reaches the Absorb voltage setpoint, at which point...
3. the charging stage transitions from Bulk to Absorb, voltage is held at that setpoint, and...
4. charging current decreases until it falls below the End Amps setpoint, at which point...
5. the charging stage transitions from Absorb to Float.

I have three questions:

1. The rule of thumb for setting End Amps is 2% of the bank's c/20 rate.  In my case, with a 48 volt bank of 8, 6 volt, 370 ah batteries, this would be around 7.4 amps.  But the actual behavior of my system is that Absorb amps level off around 10.5 amps, at which point the battery temp starts to rise.  So I've set End Amps at 11.  What does this behavior tell me about the health (or sickness!) of my batteries?

2. How much time does the voltage need to be at or above the Absorb setpoint in order for the Bulk charge phase to transition to Absorb?

3.  How long does Absorb amps need to be below the End Amps setpoint in order for the charge phase to transition to Float?

Thank you.

[ClassicCrazy]

The thing you need to add to your first points are
Once the voltage gets to Absorb setpoint it changes to Absorb - never timed it but pretty quickly.
When in Absorb current decreases as it holds the Absorb setpoint.
The Absorb goes to float when it meets ending amps or the Absorb time - which ever comes first.

I don't think there is a set time for when it gets to Ending Amps  to change to Float -- it seems to let it go a bit over and under the Ending amps point to kind of average out the readings and make sure that the ending amps point is staying steady .

Yes it is best to figure out the exact ending amps for your battery pack and  you confirm the proper setting by taking readings of the battery electrolyte using a hydrometer or refractometer and make sure that this agrees with your battery manufacturer  specific gravity 100% point.

Did you read the info in the Midnite Knowledge base on how to determine ending amps ?
there is knowledge base link at top here http://www.midnitehelp.com/

Larry

[Vic]

Hello open..,   Regarding:

  1.  The recommendations for the EA value does vary a bit  between the various battery manufacturers.   It is usually stated as between 1 and 3% of 20-hour Capacity.  Young batteries,  which are broken-in by cycling then 20- 50 cycles often need a lower EA setting.  There appears to be some variation in optimum EA value,   verses the Depth Of Discharge of the battery in the previous discharge.  The EA setting will vary with the Absorb voltage setting (Vabs),  so, the EA setting would need to be changed,  if the Absorb voltage is changed.

It appears that If the Flooded batteries really need an EQ,   this can also change the necessary  EA setting.   As batteries age,  often the Vabs will need to be increased a bit to attain full charge,   this too,  require resetting EA.

If your WbJr current levels off at about 10.5 Amps on a 370 Ah battery bank,   it seems high to me.  What is your Vabs setting?  What is the range of Vabs recommended by the battery manufacturer?

On many systems (at least the ones here), there is a considerable amount of WB current Jitter  in Absorb,   when viewed on the MNGP.   This can make it quite difficult to really determine what is the average WBJr current,   and is it really still decreasing.

Voltage drops in the cable to the battery from the Classic,   and in the breaker in that circuit can also cause a significant change in WbJr current (for loads that cycle,  like A/C units) --  about one amp change for a load change of about 15 Amps in the current that the Classic is delivering to all loads during the Absorb stage (here).   This can add some uncertainty,   as well.

  2. Once the Temp Compensated battery voltage reaches the Absorb voltage setting,   the Classic immediately transitions to Absorb.

  3.  The time required for EA to trigger the transition to Float is about 30 (or is it 45?) seconds that the WbJr current is never above the EA setpoint.

FWIW,   IMO,   Vic

[openplanet]

Very helpful Vic.  Thanks!

[openplanet]

Here's another thing that prompted the question(s).  My End Amps setting is 8.4.  Absorb voltage is 59.5, float is 54.  Fairly often I get what's shown in the attached snip.  Yellow=bat. volts, Orange=WbJr. amps. System Absorbing along happily, WbJr. amps steadly decreasing, then BAM, Amps drop suddenly, and system goes to Float.  It's as though it's not reading the End Amps value correctly.  Could this have anything to do with Temp Comp?  Batteries get up to around 34 deg C.
Thanks.

[Vic]

Hi open..,

The end of Absorb is controlled by WbJr EA (if it is set to a non-zero value),  OR  Absorb time being met.

Is it possible that your set Absorb time had been met,  in your example?

Vic

[openplanet]

That's just it Vic...my WbJr. EA setting is 8.4, so that precipitous transition to Float when WbJr. amps is still up around 12.5 is what I'm having a hard time understanding.  It's as though the Classic is somehow misreading what I've set as EA...
And that's why I'm wondering is temp comp has anything to do with it, given that my batteries typically get to 32-35 deg c. after Bulk and Absorb.

[Vic]

open..,

BUT,   what is the Absorb Time setting ?
The Logic to end Absorb,  is:
WbJr EA setting met,  OR  the Absorb Time setting met.

What is your Absorb Time setting?
Is it possible that the Absorb Time has been met?

Thanks,   Vic

[openplanet]

Bingo!!!
I always thought (mistakenly!) that if EA is set to anything greater than 0, then Absorb Time is ignored! 
Thanks so much for setting me straight Vic.
(Slightly embarrassed that I clearly didn't RTFM carefully enough.)

[openplanet]

So one last question Vic....would you say that a FLA battery bank getting up around 36-37 deg C. before dropping to Float is...too high?  THx again.

[Vic]

OK,  open,   that is an easy fix,  on the Absorb time.   The Classic is a very comprehensive CC.   There is a lot to "absorb"  in the manual.

If there is anything that you can reasonable  do to reduce the battery temperature,   that would be a good thing.

Your battery temps are not horribly high,   but those temps that you mentioned  will have some negative impact on your battery life.   But,   we can only do what we can do.

One of the main banks here  spent its first five years sitting in an unconditioned Cargo Container,   with Summer temps similar to yours.   That bank is somewhat less-healthy than the other main bank  which had lower temperatures.

Just do not be concerned about running needed EQs,   due to the temp rise during EQ.   Do EQs when needed even though the battery temp will rise further.   Getting behind on EQing  can be difficult to remedy at a later  time,  and those tardy EQs will take longer,   and have even larger impacts on battery temps.   It can be virtually impossible to recover from neglected EQs that have been delayed for some months.

However,  young batteries generally require somewhat lower EQ voltages,   and  will require less EQ time than ageing batteries.

Would suggest taking SG readings (and recording them in your battery Logbook)  every month.

Be certain to RINSE,   RINSE,  and RINSE yet again,   your Hydrometer after each measuring session,  using Distilled Water.

All just my opinions,   FWIW,   Vic

[openplanet]

All good suggestions Vic.
I DO rinse rinse rinse my HydroVolt...so there's at lease one thing I'm doing right!
THx again.

[openplanet]

OK, more information, and a continuing puzzle.  Please refer to attached drawing.  The first MyMidnite2 snip shows the system behavior before I changed Absorb Time from 2 to 8 hours.  The second, two days later, shows the system behavior after that change.  I checked and double checked that the settting had changed to 8...yet, as can be seen, the transition from Absorb to Float still happened after 2 hours.   Hmmmmmm....

[boB]

"3.  How long does Absorb amps need to be below the End Amps setpoint in order for the charge phase to transition to Float?"

It's 60 seconds I think.  If the WB Jr. current rises above that setting, the count restarts at 0 again.

Question....   Have you changed the Ending Amps in that advanced menu to SHUNT  instead of CLASSIC  ?
SHUNT means that the Classic is using the WB Jr. instead of its own internal shunt for Ending Amps.

Just a note...   When someone uses Ending Amps  ONLY and the system never spends much time in Absorb, that means that the batteries may not be getting a good long Anti-Sulfation Stage  charge cycle.  (A**) 

A good Absorb cycle at the raised voltage for a couple/few hours should be done every week or so (at least ?) for Flooded batteries to keep them in good shape.
So, this could be a down-side to using Ending Amps.  A better algorithm might use Ending Amps along with state of charge reaching 100% WITH a counter/timer to make sure the system gets a good Absorb cycle once a week or so.

The closest thing that the Classic does to this is Bulk Skip Days where it gets to the Absorb voltage but does not spend hours in Absorb.  This tends to reduce unnecessary Absorb cycles every single day but does not use Ending amps.

My statement of the above charging theory is still up for discussion but does make good sense for long battery life at first thought having learned what I have about charging over the last 25+ years.

boB

[openplanet]

Thanks very much for the good information boB.
First off, yes, EndAmps set to Shunt.
But my bad...just checked, and one of my two Classics was still set to Charge TIme=2 hrs (even though I'm "sure" I changed it to 8...and hit OK to save ), so that must be the explanation for what I'm seeing.  Will confirm tomorrow and let you know.  Nonetheless, the info you've provided is (as always) very useful.

Question.  You said in your last reply

"The closest thing that the Classic does to this is Bulk Skip Days where it gets to the Absorb voltage but does not spend hours in Absorb.  This tends to reduce unnecessary Absorb cycles every single day but does not use Ending amps." 

So, for example, if you set Bulk Skip Days (which, if I understand correctly what it does, should perhaps be called "Absorb Skip Days")...if you set it to 1, that means that every other day, if and when it reaches the Bulk/Absorb transition voltage, rather than going to Absorb it goes straight to float. Now, are you saying that on THESE days it's not using Ending Amps (which makes total sense), or that when Bulk Skip is set to anything other than 0 the Classic will NEVER use End Amps, and only rely on Absorb Time???

Thanks.



Pax--Paul