What value does End-Amps REALLY use for switch Absorb to Float?

[nlt999]

Hi!

Does anyone know FOR SURE(!) which type of value the KID uses with the WBJR option for End Amps: Rate of change in charging amperage, or actual ampere value of charging during Absorb stage?

Reason I ask is that the default value in the End Amps parameter in our KID as it came from MidNite is 0.1A.  This just happens to be the value that our battery mfgr gives for the End Condition of the Absorb stage of charging:   "Charge until change in current < 0.10A per Hr / Max time: 12 Hr" (Deka 8L-16 batteries). 

However, the KID manual states: "The End Amps function works by monitoring the current going into the batteries during the absorb stage.  As the batteries charge, the current needed to maintain the Absorb voltage set-point reduces and depending on the battery bank type and size there is a current flow level that indicates that the batteries are full.  End Amps are that level, if the current flow goes below the End amps setting for one minute then the Absorb cycle will be terminated and it will go to Float stage."  If I use this statement, it sounds like the KID is using the actual charging current to make the decision to go to Float mode, which results in a much different value for the End Amps parameter (7.4A according to the Deka tech...... 2% of C/20, or 2% of 370 Ahr in the case of our 8L-16 batteries)

I just want to be sure we are setting the End Amps parameter correctly!

Thanks for any clarification!  Nick

[Vic]

Hello nlt..,

As you may know,  the KID actually knows very little about your specific battery type,  Capacity,  or required charge parameters.

The KID relies on YOU to set meaningful parameters that it will use to fully charge your batteries.  And,  if these parameters are not quite correct,  the KID (or any other brand/model of CC)  expects that you will notice,  and make appropriate changes when necessary,  based on YOUR measurements and charge parameter changes.

Manufacturers of batteries that specify Rate-Of-Change in charge currents as the method of ending Absorb will find that there are essentially NO Solar Charge Controllers (CCs)  that can accommodate these Absorb-end parameters.  The quote from your battery  maker about how to end absorb,  is just that;   a Rate-Of-Change parameter   ...   ""Charge until change in current < 0.10A per Hr / Max time: 12 Hr" (Deka 8L-16 batteries)"    ...

There are many types of batteries,  and many differing specifications from different battery manufacturers on just what are the correct Absorption voltages,   and methods of ending Absorb.   Really,  it is up to the user of the system do decide what charge parameters are appropriate for the exact batteries that they are using,  given the conditions in which  their systems operate.   CCs will arrive at the user's location with Default settings,  and the inability to know from clairvoyance or any other  alchemy  anything about your battery,  other than,  perhaps the nominal battery voltage.

It will be up to you to inform the CC,  by your settings,  entered into it,  just how to charge YOUR batteries.

If you could possibly give information on the components of your system,   there may be others here,  that can give you input on their experience with similar systems,  and how they have set their CCs to  treat their batteries well ...

When you can,  please try to make a Signature which lists brand and model for the batteries,  system voltage and battery Capacity,  your PV array brand/model and total PV rated STC string voltage, and total wattage,  your inverter,  and other system components.   This will reduce the amount of guessing and asking of questions,  that other members of this Forum must do ...    which will speed meaningful replies to your questions or concerns.

I do not want to be too hard on you,  but really,  it is up to YOU to tell the components of your system what YOU expect them to do,  how to do it,  and when,   IMO ...

Thanks!!   Vic

[nlt999]

Thank you Vic!

I am new to this, so appreciate your input.  I took your advice and made up a signature that I hope will be helpful in the future.  From your comments, it sounds like the KID (and I guess other controllers) use actual Amperage for the End Amps parameter, even though the battery mfgrs sometimes give ending conditions in RATE of change instead, like Deka does for our batteries.

If I have that right, I will go ahead and change our End Amps parameter from 0.1 to 7.4 which is the figure the Deka tech gave me on the phone.

Really appreciate your help!  Nick

[ClassicCrazy]

Nick,
I have the same batteries that you do and I set my end amps to 2.2 amps. I use a Classic and Whizbang.
The way I came to this number was by using the MyMidnite monitoring website . I played around with settings and graphs - basically watched for the system amps ( what is going into the batteries)  to come down to a point where it began to level off. And at the same time I also would check the batteries with the hydrometer ( or refractometer in my case) to see that the specific gravity was at charged point at about the same time end amps said it was. I also was watching the SOC count backwards - so if it was -50 amps when it got close to filling up that 50 amps - along with the inefficiency of the charging lead acid batteries along with watching the system amps kind of level out along with the specific gravity - well then I was pretty confident I got it right .
But I think this ending amps number may change a bit depending on the battery temperature and other variables of the season. I should watch tomorrow and check the specific gravity again when it gets close to ending amps to confirm I have it correct !

It would be nice if the controllers had some logic to monitor and calculate the level off part of the system amps - but they don't so you have to do it yourself. At least with the online monitoring available for the Classic on Mymidnite it makes it a lot easier than watching the screen for a few hours.

Just make sure you set  your absorb timer long while you monitor because if you time out absorb time the SOC is going to go to 100% even if it isn't truly there yet. ( there might be a setting that is a bit different in the Classic than the Kid for this )

Hope this helps ! Let me know what end amps you find is correct for your system.   

[Vic]

Hi Nick,

Thanks for that Signature ...  I had guessed that your batteries were AGMs,  so the Sig has already been a help.

Normally,  for Flooded batteries,  one would use between about 1% - 2% of 20 Hr Capacity for the WB Shunt EA setting.   The Surrettes here normally need 1-ish percent of C for WB Shunt C.

Am glad that ClassicCrazy (John,  I think)  chimed in with his experiences with the same batteries.

A Hydrometer will be a big help in allowing you to set the correct charge parameters in the KID.

Thanks!   Vic

[ClassicCrazy]

It is Larry   - Vic - ha ha .

One of these years  I will get lithium batteries and then can start all over again figuring out how to properly maintain batteries !

Larry

[nlt999]

I have one more problem that is driving me crazy:  The battery mfgr gives no value for me to enter in the "Rebulk" parameter.  My Absorb is set to 29.1V, and Float is set to 27.9V

Do I set the Rebulk a certain amount below one of those voltages, or is there another way to come up with a value to enter???

Anyone have some help for this please?

Thanks again!  Nick
And thanks for all the responses and help on the End-Amps question!!!!!!!

[Westbranch]

System is light-load, est. about 2.2 Kwhr per day avg. use.

that is a big load for 2 280W panels, for example I have a daily load of 1.5Kwh, and need 8 x 140W PV to replace the use, mainly a fridge and to power the fridge during the daytime hrs....

You have to derate by ~ 75% to estimate the actual output you can harvest and use
so my estimate is you would need 6.6hrs of GOOD sunlight to replace that 2.2Kwh of load...

If you don't want to murder your batteries you need to lower the use or put up more PV...

[nlt999]

Thanks for the tip!
Think I need to go back and recalculate our load more carefully.... probably lower than my first estimate of 2.2KWhr/day.

Nick

[Westbranch]

Also to give a 10% charge to those batteries you would want to have a bit more ( don't have the exact panel specs) than 4 panels.

[nlt999]

UPDATE:

I finally got a hold of another Deka solar battery tech on the phone and she said to use 10% of the C/20 battery capacity for the End-Amps setting.  For our batteries that works out to 10% of 370 Ahr @ C/20 which equals 3.7A

That seems in line with other's responses on the Forum so I will use that as at least a starting-point setting for our KID

She also said to use 28.2V as the REBULK VOLTAGE setting, which is just a tad below the low end of Deka's published Absorb Voltage setting for a 24V system using their 8L16 flooded batteries.

Thanks again to everyone for being so helpful on this Forum... great people!

Nick

[ClassicCrazy]

Get a hydrometer or refractometer and check the specific gravity just to be sure.
This is sort of like the cheapy refractometer I have
http://www.amazon.com/Grand-Index-Refractometer-P-RHA-200ATC-Compensation/dp/B00T93SQAU/ref=sr_1_10?ie=UTF8&qid=1440097314&sr=8-10&keywords=battery+refractometer

I may have turned my ending amps down since the batteries weren't filling up enough . But the sun is out again so I can double check if they fill up again today how well my ending amps relates to specific gravity that I have it set for.

[Vic]

UPDATE:

I finally got a hold of another Deka solar battery tech on the phone and she said to use 10% of the C/20 battery capacity for the End-Amps setting.  For our batteries that works out to 10% of 370 Ahr @ C/20 which equals 3.7A

That seems in line with other's responses on the Forum so I will use that as at least a starting-point setting for our KID

She also said to use 28.2V as the REBULK VOLTAGE setting, which is just a tad below the low end of Deka's published Absorb Voltage setting for a 24V system using their 8L16 flooded batteries.
Thanks again to everyone for being so helpful on this Forum... great people!
Nick

Hi Nick,

Thanks for the Update ...   There may be a typo in the above Quote ...  1% of 20 Hr. Capacity is what we run here.   And 1% of 370 Ah  is indeed 3.7 A for EA.  The set Absorption voltage will have an effect on the exact Shunt EA setting that works best for your batteries,  but 1% seems like a fine place to start.

Regarding ReBulk,  believe that the 28.2 V suggestion is FAR too high.  In the KID,  Classic,  and Outback CCs,  ReBulk  is a voltage setting that begins an additional complete charge cycle on any day where the battery voltage descends below this setpoint.

IMO,  you would normally need the ReBulk voltage set below the Float V setting.

The strategy of ReBulk is to try to enter evening with the most fully charged battery as possible.  This might be more important in Winter months,  or at times where three are more loads than at other times,  etc.

Using ReBulk may not be very common,  these days,  with PV modules being less expensive,  etc.
EDIT:   Here is a Thread where there is some discussion of ReBulk:
http://midnitesolar.com/Forum/index.php?topic=2295.0

And,  Larry !!  Sorry that I did not remember that you were Larry ...

More Later,   Vic