Is my battery efficiency set too high

[dgd]

Ok so im interested, but.... In order to keep EA, the existing low side battery line shunt needs to stay. Thus one other shunt either in the charge or the discharge line, ought to do it. However to account for both shunts in the same time frame, i guess that takes us back to a matched pair of shunts and instrument amps, one for each of charge and discharge paths. That means 3 shunts, and 3 lots of 10x mV voltage drops. Joy.

Ok so use the WBJr shunt, with another amp. Thats down to two. Both in the low side, or one low and the other high? We kinda want to avoid negative bus potential differences, so maybe high side as you said.

Yes, I would forget about the Deltec shunt WBjr combo and leave it just for EA.
Two high side acs758, one load one charger but maybe bidirectional for both and at night the classic tare is measureable, the other on inverter/LV loads, although I would keep monitoring device loads with charger circuit as they tend to be permanent but small tare loads, Bi for inverter if it has battery charge capability.
If both are on the same Arduino then timing counts can be identical within millis.
Didn't all this get detailed in the Gregy discussion? (What happened to him?)

Dgd

Maybe moderator should move this 'new thread' to sensors in BB 

[dmkkeng]

Interesting topic - some good information, my scenario is as follows - I installed new Rolls flooded cell 6V batteries (660 AH), initially I used the Xantrex inverter charger to ensure the batteries were fully charged. Initial specific gravity readings averaged 1270 (1265-1280). I installed the Midnite Kid controller with the WBJR and (4) 100W panels in a series/ parallel configuration. After a month or so of using the solar system to charge the batteries, the specific gravity readings decreased to averaging 1240 (1230-1250), which appears to indicate the batteries are not being fully charged. Settings on the controller are per the manufactures recommendation, Battery Efficiency 94% and End Amps 13.2 Amps (2%). At this point I'm considering decreasing the Battery Efficiency setting and/ or increasing the End Amps setting. Any suggestions?

[Vic]

Hi dmk..,

Changing the Efficiency factor should not change the amount of charging the batteries receive.

Increasing the EA value would result in less battery charging,  as the Ibattery DECREASES,  as the battery becomes more fully-charged.

What is the Surrette model number for your battery?
What ARE your charge settings  --  Absorb,  Float and EQ?  What is the Absorb time setting?
What is your average total Solar power production per day?
What are the loads on the system.
What is the purpose of the system  --  Grid backup,  weekend cabin,  (etc) ?

Did you Commission the battery bank,  per Surrette's recommendations?

Assume that you are running a 12 V system (?).
Appears that even on a 12 V system,  you do not have nearly enough PV for that battery bank,  BUT,  not really knowing the battery model number,  it is difficult to determine.  If the system is just for backup with few and occasional loads  you can get by with less PV power,  generally.

Thanks for the answers.   Vic

[off-grid-geeks]

Agreed, the Battery Efficiency setting only changes the displayed SOC number rate of change. It has zero affect on actual charging. With a higher efficiency number, the displayed SOC will climb faster, and a lower efficiency number will slow down the rate of change of the displayed SOC. That's all it does.

[Vic]

Hello dmkkeng,

After doing a bit of sleuthing,  guess that this system is on a boat in the PNW.

Looks like you have three parallel strings of 2 6V batts in series.  Each batt has  about 220 Ah of Capacity.

Is this the battery that you are using (?):  http://rollsbattery.com/wp-content/uploads/specsheets/6FS220.pdf

Most Surrette batteries have a fill electrolyte SG of 1.265,  but they are normally rated as if the fill SG was 1.280,  this would only make a small difference in your EA  and AH Remaining.   What is the target SG that you are looking for as 100% SOC?

In the past,  you mentioned that your normal battery discharge was in the range of about 125 - 175 Ah (each day?),  is this still about the daily discharge of the battery bank?

One additional question;  How frequently do your EQ the battery,  and at what voltage?

Thanks,   Vic

[Westbranch]

dmk, from what has been posted so far it looks like you need to run your generator and do a BULK charge more often and let the solar do the absorb and float portiions of the charge cycle.

Also, how old are the batteries?
\if the have not had in the neigbourhood of ~50 charge / discharge cycles they may not have finished their commissioning period.....

hth

[dmkkeng]

Battery Model #6FS220 (Rolls)
Absorb set to 14.7V
Equalize set to 15.7V
Float set to 13.2V
I don't recall seeing a setting for Absorb time.
One thing I should have mentioned in my post is that the solar system has consistently charged the batteries back to 100% SOC each day - usually occurs well before the sun goes down and the solar cells stop producing.
I was expecting the specific gravity readings to be higher than 1265 at a SOC of 100%.
Originally I was anticipating daily usage of 125 - 175 AH per day however so far, on average, I'm using less than 100 AH per day.
Yes it is a 12V system and yes it is on a sailboat and yes it is a bank of six batteries and yes you have the battery model correct - good sleuthing Vic.
The batteries and solar system were installed May 2016 so they have only been in service for 3 months.
I have not equalized the batteries as I didn't think it was time to equalize.
I was down at the boat yesterday and plugged in my Xantrex charger to see if the specific gravity readings went back to where they were prior to using the solar system to charge the batteries.
The Midnite Kid is indicating is 100% SOC (660 AH) at an average specific gravity reading of 1.240. Per the Rolls manual 100% charge = specific gravity reading of 1.255 - 1.275, 75% charge = specific gravity reading of 1.215 to 1.235, an average specific gravity reading of 1.240 indicates the batteries are only being charged to approximately 80%.
Perhaps the Midnite Kid is not setup properly? With exception of the specific gravity readings everything else appears to be working as it should.

[Vic]

dmkkeng,  Thanks for the added detail on your system and settings.

There IS a time setting in the KID ...   down a couple of levels in the <battery> menu.   There is a new recommendation from Surrette for a 15 Volt Absorb voltage.   When EA is being used,  this time period will be the Maximum time that the KID will be in Absorb.  If the set EA is reached before this max time,  the EA value will end Absorb  --  it is an OR function,  either EA OR Time will end Absorb.

Also,  IMO,  2% is a bit on the high side for EA,  although if you do increase the Absorb voltage,  you might just leave EA at 2%.   Also IMO,  the actual Capacity of your three parallel strings of 220 A --  660Ah total  -- should be reduced by 5% to accommodate for the 1.265 SG electrolyte verses the 1.280 that is used as the basis for the Capacity spec.   Really fly-specs,  but that probably would be better at about 12.5 Amps EA.   The Surrette batteries,  here,   ran many years with an EA of about 1% of actual Capacity.   This was with a relatively lower Absorb voltage of 14.4 V per 12 V battery.

Battery Monitoring devices give an approximate indication of the actual SOC of a battery bank.   They can only be as accurate as is the data entered about the battery characteristics,   and there are many parameters about battery charging,  discharge,  efficiency,  etc that we cannot know or enter,  that affect the actual SOC and Remaining Capacity,  etc.

But you do have Flooded batteries,  so you can measure actual SG,  as you are doing.   These measurements are the Gold Standard for SOC.

The Surrette Battery Manual details Commissioning of a battery bank,  recommended Charge parameters and EQ Voltage and frequency.  Here is the Link to the Manual,  if you do not have a recent copy (as it has changed in about the past month:
http://www.surrette.com/uploads/pdfs/documents/user_manuals/Rolls_Battery_Manual.pdf

An  EQ should only be done when the battery is fully-charged,  or very close to it.

Are you using the Battery Temperature Sensor (BTS) with the KID?  This is very important,  as it allows the KID to change the charge voltage based on the actual battery temperature.

So,  why not increase the Absorb voltage to 15 V.  You might want to try doing some more charging from the Xantrex.  Just make certain that its Absorb voltage is set high enough.  Often one can run a generator,  or shorepower in the early morning to get through Bulk,  and into Absorb,  and then try to let the Solar finish the Charge.  It is often better to not make too many changes all at once,  when trying to get batteries fully charged fairly quickly,  especially,  if one will not be present every day,  to monitor any improvements that the changes might make.

You may not really have quite enough PV power to do an EQ,  so the generator or shorepower may be needed to do that,  but an EQ is important for battery health,  when needed.

Good Luck,  and please let us know how you are doing.    Vic

[dmkkeng]

Vic thanks for the info, I'll likely start experimenting with some of the settings, I sent an email to Midnite and their response was to decrease the battery efficiency setting from 94% to 88% and end amps from 2% to 1.5%. First I'll check the manual link to see if anything has changed with respect to manufacturers recommended settings.

Yes I am using temperature sensor with the Midnite Kid.

When I equalize I will likely do it using the Xantrex.

What should the absorb time period be set to?

Thanks,
Doug

[Vic]

Hi Doug,

The Absorb time setting when using  EA,  should be longer than you expect the Absorb stage would ever need to be.   And,  as you know,   the required length of the Absorb,  will need to be longer with deeper discharge depth of the battery.

The required Absorb time will also be affected by the Absorb voltage,  shorter for higher Vabs  and longer for a lower Vabs setting.   EA needed to fully charge the battery will also vary with Vabs  --  somewhat higher EA for higher Vabs,  lower for a lower Vabs .   Not to try to make things too complicated.

Personally,  would set Absorb time about 50% longer than you would ever expect the battery would need at normal Depth Of Discharge (DOD).  When using WBjr EA,  the Absorb time setting is really there to catch anything that might keep EA from successfully ending Absorb.

As noted,   EA,  Vabs and the maximum Absorb time are all interactive.  This is one of the good reasons to not make too many changes at same time.

Would also suggest to use Surrette's recommended Vabs (it is now a fixed value for a given battery V,  as opposed to the previous range of Vabs).  And leave EA the same,  as you have had it.   Your battery has been undercharged for some time.  You may well be a bit short on PV power,  in general.  In these cases,  it can be helpful to increase further the Vabs,  to use as much of the available solar power to charge the battery as much as possible in the solar day.

If the Xantrex inverter is being run off of shore power,  you can try charging with it,  in addition to the KID's solar contribution.   This inverter should have its own Battery Temp Sensor.  If it does not have the BTS,  you can manually compensate its charge voltage,  from the battery temperature.

More Later,   sorry,  this may all seem a bit ambiguous.   Vic

[dmkkeng]

Increased Float voltage from 13.2V to 13.5V and Absorb voltage from 14.7V to 15"0V per the updated manufacturers specifications. Also changed Battery Efficiency from 94% to 88% and End Amps from 13.2A (2%) to 9.9A (1.5%) per Midnite support recommendations. I will let the system run for a couple of weeks on these settings to see if the Specific Gravity readings change. I was  going to leave the Xantrex charger on however it doesn't appear to be charging ... not sure why so I turned it off till I get some time to trouble shoot the problem ... always something ...

[zoneblue]

Since setting our system to 99% efficiency weve had one three day trip down to 75% SOC, and one two day trip down to 65% SOC. Both times returned to 100% SOC on 0.05% EA perfectly.

So, for AGM, the default WBJr efficiency of 94% is far too low.