WBJR Net AH Reading

[smanners]

Hi Guys,

I recentky doubled my charging capacity by adding a second solar array and Classic 150. Both classics are connected and set with "Follow Me" which seems to be working great. My quoestion is simply around the Net AH reading registered by the WBJr. As expected my battery bank charges up its bulk phase very quickly and then goes to absorb as it should. Once absorb is done it goes to float and at that point the Net AH is reset to 100%.

However during the day the Net AH keeps increasing slowly but steadily sometimes up to like +50 Ah or more depending on how sunny it is. Is this normal or am I not staying in Aborb long enough. I suppose the problem is really only I use the SOC% low to turn off a relay at 80%  So if my AH is 10% over the actual cut off might more like 70%. Maybe this isn't quite how it works it out, I'm only speaking from observation.

Cheers

[Resthome]

Hi Guys,

I recentky doubled my charging capacity by adding a second solar array and Classic 150. Both classics are connected and set with "Follow Me" which seems to be working great. My quoestion is simply around the Net AH reading registered by the WBJr. As expected my battery bank charges up its bulk phase very quickly and then goes to absorb as it should. Once absorb is done it goes to float and at that point the Net AH is reset to 100%.

However during the day the Net AH keeps increasing slowly but steadily sometimes up to like +50 Ah or more depending on how sunny it is. Is this normal or am I not staying in Aborb long enough. I suppose the problem is really only I use the SOC% low to turn off a relay at 80%  So if my AH is 10% over the actual cut off might more like 70%. Maybe this isn't quite how it works it out, I'm only speaking from observation.

Cheers

How long are you staying in Absorb and what kind of batteries and what is their size? Net AH will continue to increase but SOC will not increase over 100%. If you are using End Amps what value do you have it set to?

[smanners]

Hi,

Absorb is the default 2 hours.

My batteries are 4  x 280ah made by Giant Power connected in parallel for 12v bank for a total of 1120ah. I would use the wbjr for end amps but was unsure as to correct config for this battery type.

Specs are:

(DC-12V-280AH)

Giant Power 12V 280AH AGM Deep Cycle Battery
Nominal Voltage   12V
Nominal Capacity (20HR)   280.0 AH
Rated Capacity   280.0 AH/14.0A (20hr,1.80V/cell,25 C)
Max. Discharge Current   2500A (5s)
Internal Resistance   Approx 2.5m?
Operating Temp.Range   Discharge : -15 ~ 50oC (5 ~ 122oF)
Charge : 0 ~ 40oC (32 ~ 104oF )
Storage : -15 ~ 40oC (5 ~ 104oF)
Nominal Operating Temp. Range   25 3 C (77 5 F )
Cycle Use   Initial Charging Current less than 75A.
Voltage 14.4V~15.0V at 25oC (77o F)
Temp. Coefficient -30mV/oC
Standby Use   No limit on Initial Charging Current
Voltage 13.5V~13.8V at 25oC (77o F)
Temp. Coefficient -20mV/oC
Capacity affected by Temperature   40oC (104oF) 103%
25oC ( 77oF ) 100%
0oC ( 32oF ) 86%


Many thanks for your help!

[Vic]

Hi smanners,

I had wondered if the increase in Net Ah might be due to an increase in battery temperature ...   but the battery mass is fairly large.

How did you place the Battery Temperature Sensor (BTS)?  If the BTS is placed on the top of the battery,  this fairly large change in Net Ah,  but if the BTS is on the top of one battery,  it might still be due to an increase in battery temperature,  as heat does rise.

As these are AGM batteries,  you might want to ask Giant for EA setting guidance.  Some AGMs like a very long Absorb,  to a vanishingly small current.   Some AGM manufacturers  rate the correct way to end Absorption is based on the Rate Of Change of current,  which is not supported by almost any Renewable Energy charging source.

It is very nice more detailed specs for these batteries,  including a different Temp Comp value for cyclic use verses Float.

FWIW,   Thanks,   Vic

[smanners]

Hi Vic,

Thanks for your response. The battery sensor is about half way down the side on the inside second battery making it as close to the centre of the battery cluster as I can make it. The batteries have about an inch clearance between them for heat dissipation but they rarely even get moderately warm. Temperature fluctuations is definitely a possibility. They are well ventilated and temperature probably fluctuates between around 15-26 degrees depending on the day.

I did ask Giant Power about ending amps for charging but received no response. I might start a campaign of hassling them to see if I can get a response. Customer service sometimes isn't as good as it could be.

They are expensive batteries so I do baby them quite a bit given their service life is around 12 years (I want to keep them in top condition).

Any other ideas would be greatly appreciated.

Cheers

[smanners]

I actually had a very good conversation with one of the Giant Power technicians about Absorb times on the batteries. Basically he said that Absorb time is based on the bulk time x 10 with a minimum of ten minutes and a maximum of eight hours.

Because of the random nature of the bulk charging time the charge controller must be able to work this out and set the Absorb time accordingly. I am know digging through the Minute Classic 150 manual to look at this.

[Vic]

Hi smanners,

Good that you are getting good support from Giant.

Our Renewable Energy (RE) Charge Controllers,  and inverters,  etc,  simply cannot accommodate this type of an Absorb stage.   And,  they cannot accommodate the other desire of manufacturers of AGM batteries  --  watching the Rate Of Change of battery current in Absorb,  and end Absorb when  some incredibly small rate of change is seen over a set period of time.

You are correct,  that the deeper the battery has been discharged,  the longer the Bulk and Absorb stages will need to be   ...

You can carefully monitor the charge current into the battery (via WBjr/Shunt),  and get a fair idea of how long the Absorb stage needs to be,  for a given DOD of your battery.

FWIW,    Vic

[smanners]

Hi Vic,

What you have said is pretty much the conclusion I have come to. There are two formulas Giant Power gave me for calculating the Absorb duration:

1. (0.42 x Batt-Capacity) / Charge Current; this is all but useless as charging via solar cannot give you a known charge current. It goes up and down like a yo-yo some days and on perfect days you get a nice bell curve of input.

2. Bulk Time x 10; also fairly useless as again bulk charge duration fluctuates from day to day. Plus anything longer than 30 minutes of bulk would effectively mean that potentially you never get to float.

I suspect these formulas are the manufacturers best case for absolute maximum theoretical charge capacity. In real life its not really obtainable.

So as you have mentioned its now about observation. Watching how the input current tapers off during the absorb cycle and setting it accordingly whilst still allowing enough time to go into float. Its hard to sift fact from cr@p as some sites for AGM batteries say that for this chemistry type Bulk = Absorb = Float which is 14.4v, that is these three phases of charge are essentially the same voltage set points. I don't know about that...

Its not an exact science that's for sure!

Cheers

[boB]

D'day, smanners !  Welcome to the forum !

I think what you were seeing when the NET AH reset to 0 AH  when going from absorb to float stage is because the TWEAK is set
to ON that makes that happen.   If you go to the same TWEAKS menu that the Follow-Me is set in you will see the last option...

WBRST     "WB JR NET A-HRS RESETS AT FULL"

All it does is reset the NET AH when the Classic goes to float, which is assumed to be "full" at that time...  It isn't
necessarily full then unless the absorb time is about right or longer than necessary.  After it goes to float and you
see NET AH go to 0 AH, it will still count up or down.  I think that NET AH does NOT take into account AH efficiency.
"NET" in this case means that this number is signed and always goes up and down in value.  It is more useful for
seeing what has gone IN and OUT of the battery during charge and discharge but will only sort-of balance itself
to 0.0 amp-hours because it still counts up (positive) after getting back to 0...  So without it resetting to zero
once in a while, and absorb to float is a handy time to do this, it will almost always have a NET positive value
and go up higher and higher (more positive) until it does reset to zero.

NET AH isn't the most handy display, really.  Remaining AH is really more important.

As for absorb time, the Classic used to absorb for as long as it took to bulk....  This method may have an advantage
but only in rare cases, usually when the site is unattended and you don't want to boil the batteries by absorbing
for a long time every day.  The latest thinking is pretty much that a battery does not need to go through
an absorb cycle every day. In fact, it is detrimental to battery life.  Absorb is really used as a kind of equalization
charge to keep the plates fro sulfating. Of course, with AGM / VRLA batteries, this is a bit different than with normal
old flooded lead acid batteries.

Absorbing for 10 times the bulk time would usually be way overkill, although probably not bad every once in a while.
So, if it took 3 hours to go from first bulk to absorb, then you would absorb for 30 hours ?  It might be OK if bulk took
1 hour and you wanted to absorb for 10 hours but even that is ~usually~ longer than necessary, except rarely maybe.

I hear different thoughts on how often to absorb but every week or two is usually OK.  The battery will get "full" as long
as the amp-hours taken out is replaced with amp-hours + inefficiency so Absorb is not really necessary for it to be "FULL",
BUT, that is a very good point to tell the WBJR (or other state of charge meter) that it is full because it usually ~IS~ full
at that time as long as absorb time isn't set to some awfully low amount of time.

Something like this, anyway...

boB

[smanners]

G'Day boB,

Many thanks for your response and wise words!

My batteries pretty much always hit absorb each day and float most days unless its cloudy or raining. I have 2 x 1.2kW arrays going to 2 x Classic 150's. I started with one and thought it looked lonely so gave it a friend. At full speed they will pour in 60-70 amps each sometimes jumping higher with cloud edge effect.

I have been studying the behaviour of the battery charging to try and ensure I get the most out my battery and solar investment without stressing the batteries and ensuring long service life.

I utilise AUX2 that goes to a voltage sensing relay using SOC% High/Low. The relay opens up a 12V circuit to a Pure Sine Wave Inverter. The Pure Sine Wave Inverter is connected to an Automatic Transfer Switch (240V). It has the Pure Sine Wave inverter as master in with a mains connection as slave. So what I do is tweak the SOC% ON/OFF depending on time of year and an expectation of battery charge. I always aim to get battery say 95% charged as this will be in its Absorb cycle. As the absorb cycle progresses charge current is reduced hence to maximise energy savings the relay then kicks in and powers very specific GPO's in my house thus saving energy. The relay stays open generally to 80% SOC in winter and 70% SOC in summer. Doing this still means absorb will generally finish and hit float.

As you have correctly surmised I have indeed got the reset NET AHRS at float (full). This is what got me started on this whole palaver about Net AH and SOC%.

I did set the absorb cycle to three hours today and it was happy enough doing that and hit float no worries. Can't say it really made any difference than the default two hours but then again it was raining this morning with only afternoon sun so I think I will wait for a nice sunny day before touching it again. I would like to see Net AH be close to 0 before it hits float, but again there are a lot of factors involved including temperature variations between discharge and charge cycles (which pretty much always happens).

Interesting stuff this!

[smanners]

Hi,

Bit of a disaster last night. I have my classic set to turn off SOC% High at 80%. For some reason at 2300 hours (or as close as mymidnite2 tells me) the classic decided to reset SOC  to 100% and Net AH to 0! I was  sitting at about 86% SOC then the chart shoots up to 100% and my relay was still on this morning. Battery drained to about 60% so no harm done.

Actually I reckon it was midnight as mymidnite2 is out of whack with our locale and GMT (+10 Hobart) offset by an hour. That means the classic probably rebooted becuase I have set the auto restart feature. It must have lost its SOC% and Net AH values when it rebooted.

Does anyone know what would cause it to do that?

I might log a support ticket with Midnite Solar for that one!

Cheers

[russ_drinkwater]

Smanners,
When do the hydro electric plants in Tasmania run out of water?
And I also understand the underwater power cable from the mainland has been severed at some stage?
Just wondering if it stimulated you into a standalone power system.
Russ

[smanners]

Hi Russ,

It came close. The same dropped below 15% I believe after one of the dryest summers ever. However dam levels are rising again after some pretty good and consistent rains. The basslink cable has been waiting on the weather. Too rough for the ship but I believe it left port yesterday. Mid June they said it would be fixed. But the weather is rough this time of year.

I have had my growing little power empire for sometime. It's kind of a hobby for me. I live in rural dairy farming area so it pays to have a degree of self sufficiency.

Cheers

[boB]

Interesting...   The Classic saves the SOC % every hour and 1/2 or every two hours (can't remember) exactly)
and should recall this when rebooting.  At least I thought it did ?  This was so that if the Aux output was controlling
a generator using SOC% and an Auto-Restart (reboot) happened at 23:59 (midnight) it would not forget
where it was and come up in the wrong state.

Anyway, just some info for what it's worth.

boB

[smanners]

It had worked just fine until last night.

I have logged a support ticket for it but they seem to be having issues with that so tried emailing them directly for assistance. Might be indicative of some issue with my Classic or maybe a bug that raises its head every now and then. Either way its bad.

Cheers