Battery Voltage low during Charge

[cpttom]

Howdy all, I am having a Strange thing happening with my Classic 150 at my cabin:  Within the last couple of weeks the voltage during charging is below what I have expected.  I have a 24 volt battery array (Specifics below), and I have the Charge voltage set as follows: EQ: 30.1v Absorb 28.6v Float: 27.2v.  The Classic will report the battery voltage at 25.1-25.5 while saying it is "Bulk MPPT."   At the end of all this the batteries charge to 75-80 percent.  Really very puzzling, any advice would be appreciated.

Thank you in Advance!

--CPT Tom

Firmware is 2054 for MNGP and 2079 for Classic.

House: 1344 Watt PV Array (2 in series x 3 parallel Sharp 224 Watt PV panels) Midnite Classic 150, Schneider Electric Conext SW 2524 Inverter, 2 x 4 6v 230AH Duracell Golf Cart EGC2 Batteries.(total 460AH) A 7.5 KW generator

[Westbranch]

Have you installed a Battery Temp Sensor on the charger?

Have you tried a manual charge with the SW 2524?

[Vic]

Hello Tom,

Bulk MPPT is not a voltage regulated charge stage.  The Charge Controller (CC)  is charging with the maximum available power from the PVs.  So,  as the batteries become more charged,  the voltage will rise.

The Absorb stage IS a voltage regulated stage,  and,  depending on the type of battery,  it will not begin until the battery is 80 - 85 % charged.

In NY,  the angle of the sun is lower in the sky,  than in Summer (as you know).   This equates to fewer hours of good sun,  and usually less power available at peak sun from the PVs,  etc.

Also,  PVs like a fairly high elevation angle in the Winter,  especially up North.   Also,  snow and ice will take  a  huge toll in solar production,  as you also know.

If your batteries are Flooded types,   you could probably use somewhat higher Vabs,  and probably Veq as well.   But,  you will need to get the batteries more fully-charged than they have been getting,  from all appearances.

If your batteries are Flooded,   use your Hydrometer to determine the actual SOC of the battery.

You do not want to get behind in charging those batteries.   So,  YES,  use some AC into the SW inverter/charger,  and try getting the batteries as fully-charged as possible.   Starting early in the morning with SW (from Grid,  or genset),   and on a sunny day,  the PVs might be able to finish the Absorb stage.

Will try to look up the specs on your batteries ... 
Vic

[cpttom]

Hi Vic,

Hmmm.  I've been through four winters a this site, this is the second with this configuration.  It did not do this last year.  As expected The watts are lower already (in the 200-500 range) noon down from almost a 1000 in the summer at noon. The voltage is usually constant for the PVs (around 60v) and last year at this time the amount of power produced would charge the batteries to 100 percent and the battery voltage close to the Charge voltage during the winter shutdown period.  We haven't had snow during the past few weeks until last night and that hasn't stuck around.  So the battery voltage during charge still looks lower to me than previously.

I don't understand how increasing the Vab and Veq will matter if there isn't enough power generated to get to the current settings for Vab and Veq?  Does the Charge controller put out that much, but the battery voltage is reported at the lower number?

Will up the Vab and Veq, though I am not sure I fully understand. How much more do you suggest?

Finally, I have been been charging the batteries every few days as close to 100 percent as time allows  with the SE SW 2524 Inverter / Charger using the 7.5KW generator.  There is no grid power at the cabin.    I am painfully aware of keeping ahead of this, but I don't live there as much during the winter, so I have to get things setup for things to survive on it's own for a period of time.

Thanks for your help as always.  --CPT Tom

Hello Tom,

Bulk MPPT is not a voltage regulated charge stage.  The Charge Controller (CC)  is charging with the maximum available power from the PVs.  So,  as the batteries become more charged,  the voltage will rise.

The Absorb stage IS a voltage regulated stage,  and,  depending on the type of battery,  it will not begin until the battery is 80 - 85 % charged.

In NY,  the angle of the sun is lower in the sky,  than in Summer (as you know).   This equates to fewer hours of good sun,  and usually less power available at peak sun from the PVs,  etc.

Also,  PVs like a fairly high elevation angle in the Winter,  especially up North.   Also,  snow and ice will take  a  huge toll in solar production,  as you also know.

If your batteries are Flooded types,   you could probably use somewhat higher Vabs,  and probably Veq as well.   But,  you will need to get the batteries more fully-charged than they have been getting,  from all appearances.

If your batteries are Flooded,   use your Hydrometer to determine the actual SOC of the battery.

You do not want to get behind in charging those batteries.   So,  YES,  use some AC into the SW inverter/charger,  and try getting the batteries as fully-charged as possible.   Starting early in the morning with SW (from Grid,  or genset),   and on a sunny day,  the PVs might be able to finish the Absorb stage.

Will try to look up the specs on your batteries ... 
Vic

[cpttom]

Yes and Yes.  A Manual Charge with the SW 2524 works just fine.  Thank you!  --CPT Tom

Have you installed a Battery Temp Sensor on the charger?

Have you tried a manual charge with the SW 2524?

[Vic]

DANG   !!! !   Just lost a Post ...

Tom,  was unable to find specs on "Duracell EGC2"  batteries.

Here is a Link to some specs from East Penn,  the apparent manufacturer of Duracell GC2s:
http://forum.solar-electric.com/discussion/339311/duracell-branded-6v-info

Note the relatively high Vabs.

And,  you are correct,  that regarding the CC Vabs and Veq settings will make NO difference,  until you get the batteries more fully-charged,  and get out of Bulk.  BUT,  some of what you may now be seeing is the possibility that the batteries have not been getting fully-charged,  for some time.

The low-ish Vabs would make a difference when charging from the SW inverter,  however,  depending upon how long that genset is run.   And,  when running from the Generator,  a higher Vabs should allow more charging in a bit shorter time.

From the searches for your type battery,  assume that these batts are Flooded,  is this correct?

When you measure the SG of each cell of each battery,  what is that SG reading,  on average.  What is your target SG?

How often do you EQ the batteries?
On average,  how much water is consumed,  and how often do you need to add that amount of water (assuming Flooded batts).

What Temperature Compensation coefficient is set in the Classic,  if you recall.

Thanks for some more answers.   Vic

[ClassicCrazy]

If you raise the Absorb voltage setpoint that means it will be Bulk for longer giving it all available amps . Once it gets to Absorb it cuts back the current to keep the voltage steady .

Probably just a lead acid battery thing - they are no where near perfect and as soon as they are made start to age and decrease in their efficiency .  What kind of batteries do you have and how old are they ?

If they are flooded you can check to find out what the specific gravity is for each cell during different parts of your SOC readings and see if when you get 100% they are actually at proper specific gravity .  As the batteries age their AH rating decreases ( higher self discharge ) .  AGM batteries are harder to tell what is going on and voltage is often no indication of their health.

Larry

[ClassicCrazy]

Vic and I posted about the same time and share some of the same thoughts  on the batteries.
All depends too how often and how deep they have been cycled as to their longevity .
Larry

[Vic]

Tom,

AND,  you have two parallel strings of batteries.   Often things start great with new batteries,  and can slowly degrade in time.  It is not uncommon for multiple strings of batteries in parallel have divergent charge acceptance  --  one string can hog much of the charging current,  and the other/s lag behind.   When the charging is complete for the day,  the lagging string can "charge itself"  by discharging the best string,  and so on.

If your batteries are Flooded,  careful,  and fairly frequent monitoring of the SG of each cell of the battery bank (and recording these in your battery Logbook)   will help you see signs of divergence twix the two strings,  etc.

Later,  Vic

[Westbranch]

I am having a Strange thing happening with my Classic 150 at my cabin:

Within the last couple of weeks the voltage during charging is below what I have expected.

I have a 24 volt battery array (Specifics below), and I have the Charge voltage set as follows:

EQ: 30.1v Absorb 28.6v Float: 27.2v. 

The Classic will report the battery voltage at 25.1-25.5 while saying it is "Bulk MPPT."   
--CPT Tom
/quote]
/quote]

OK, so from what you have stated the issue is not just with the Classic's charge but also the SW's charge,  I assume that the SW is set to the numbers you have quoted for the Classic.

You need to tell us what the bank was getting to last year, if it is higher than the  numbers in post #1 you need to raise the settings, also check the temp compensation value and report please. with the current winter temps you should be seeing as much , or more than 2 *C above those numbers...

good luck

[cpttom]

Vic, Doh! I just did the same thing...posted last night and it went poof!  Okeedoke here we go again:

DANG   !!! !   Just lost a Post ...

Tom,  was unable to find specs on "Duracell EGC2"  batteries.

Here is a Link to some specs from East Penn,  the apparent manufacturer of Duracell GC2s:
http://forum.solar-electric.com/discussion/339311/duracell-branded-6v-info

Thank you, thank you!  This is something I was looking for and haven't found.  This is most helpful, considering this is what I can afford for batteries right now.

Note the relatively high Vabs.
And,  you are correct,  that regarding the CC Vabs and Veq settings will make NO difference,  until you get the batteries more fully-charged,  and get out of Bulk.  BUT,  some of what you may now be seeing is the possibility that the batteries have not been getting fully-charged,  for some time.

The low-ish Vabs would make a difference when charging from the SW inverter,  however,  depending upon how long that genset is run.   And,  when running from the Generator,  a higher Vabs should allow more charging in a bit shorter time.

Okeedoke, well that all makes sense.    I am at the cabin today since 9am and I have adjusted the Vab and Veq according to the numbers in the link you provided. BTW the SW Inverter does not charge above 27v from what I can see in the settings, maybe I'm missing something. I have to look at all my data, but, looking at mymidnite2.com, it's been at least a couple of weeks or more of this kind of activity.

Answers to your questions.   

From the searches for your type battery,  assume that these batts are Flooded,  is this correct?
Yes Batteries are flooded.
When you measure the SG of each cell of each battery,  what is that SG reading,  on average.  What is your target SG?
last SGs taken a month ago and they were on average 1.25-1.275 at 93% SOC with some cells higher and lower.  However, looking at the data now (see attached) last battery on right bottom string ...had one cell sitting 1.21...I guess that isn't good, yes?

How often do you EQ the batteries?
set to EQ every 7 days

On average,  how much water is consumed,  and how often do you need to add that amount of water (assuming Flooded batts).
half a gallon of water for the set and filled about every two months.

What Temperature Compensation coefficient is set in the Classic,  if you recall.
-0.5mv
Thanks for some more answers.   Vic
[/quote]

Right now I am charging the batteries at the Cabin with generator through SW Inverter and the Classic is generating about 300 watts at 11am.  SOC is showing 89 percent and 28.8 volts on the battery.  Once fully charged, I'll shut everything down and  I am going to take SG readings of the cells. Hopefully that's the right way to do this.

[Vic]

Hi Tom,  thanks for the detailed answers.

Regarding the SW's charge voltage,  do you have the Schneider SCP and/of the Combox?  Either of these should allow you to set many parameters for YOUR needs.   If you have neither of these optional accessories,  then you will be stuck with the Defaults,  which are quite low,  but generally not appropriate for Flooded batteries.  (I am not an expert on the Schneider Inverter/Chargers,  though).

27 Volts for what Schneider may call a "Bulk" (most folks would call this setting Absorb) voltage is quite low.

Many of us would set Vabs a bit above the recommended Vabs,  to try to make best use of genset fuel.  Trying to charge the batts from the SW at 27 V,  will not do much charging,  and the charge current will taper to a low value,  long before the batteries are charged much at all.   A 30 volt setting for Absorb,  or Bulk,  or a bit higher should be OK.

Does the SW have the ability to Temperature Compensate its Charge voltages?  This compensation should help charging,  if the batteries are cool right now.

Your spread in SGs is fairly wide,  and would normally dictate that an EQ is in order.

That Link to the Wind-Sun Forum notes an EQ voltage that seems quite low,  to me,   but frequent EQs may mean that the EQ voltage need not be as high as would be needed,  if EQs were done monthly,  or less often.

I could not find the specs on the apparent model number of your batteries.   You might want to use the contact info from that Link,  to ask the manufacturer for recommendations on Absorb,  Float and EQ voltages,  EQ frequency,  or guidelines on when to know that an EQ is needed,  PLUS  the correct Temperature Compensation value,  and the SG reading for a fully charged battery.   Believe that the correct temp compensation value for Duracell GC batteries is  --3 mV per cell,  per degree C -  but that may have changed recently.

It is good that your batts are consuming some water   ...   this consumption does not seem excessive,  and is probably a bit on the low side of things.

Always use Distilled Water for battery water.

What type of Hydrometer are you using  --  plastic,  glass (??),   what manufacturer and model,  if known.

Here is a Link to another battery manufacturer's article on measuring SGs ...  you may well know this,  but just a good summary.   The SG verses SOC values are adjusted for 1.265 SG electrolyte for a fully-charged cell:
http://support.rollsbattery.com/support/solutions/articles/4347-measuring-specific-gravity

Back to a project,  more later,   Vic

[ClassicCrazy]

Here are East Penn Deka solar charging specs
http://www.eastpennmanufacturing.com/wp-content/uploads/Renewable-Energy-Charging-Parameters-1913.pdf

Larry

[Vic]

Hi Larry,  Thanks for the Link to the East Penn Duracell charging specs.

Had been searching for the,  "Duracell Golf Cart EGC2 Batteries"  that Tom mentioned were his exact batteries,  but could not find them.

The Temp Comp noted,  is -- 3mV/Cell/C,  but see no mention of the target SG for a fully-charged cell.

Thanks,   Vic

[cpttom]

First off, thank you Vic and ClassicCrazy, for your advice and information.  I am good with computers, but this DC stuff makes my head hurt a bit and I still am not comfortable troubleshooting that yet.

Regarding the SW's charge voltage,  do you have the Schneider SCP and/of the Combox?  Either of these should allow you to set many parameters for YOUR needs.   If you have neither of these optional accessories,  then you will be stuck with the Defaults,  which are quite low,  but generally not appropriate for Flooded batteries.  (I am not an expert on the Schneider Inverter/Chargers,  though).

I have the SCP (don't have the combox yet, I just ordered one after this.) and a few observations.  First, the Equalize volts can't be changed (that I can see), it seems to be tied to the type of battery, I did enable Equalize, and observed the battery voltage go during the equalize charge to be at 30.2, so that I believe is much better.   Also, during the "bulk" as 28.2. during float 27ish.  I suspect that some of this is set in the advanced settings mode that I need to explore more. There is obviously something I am missing in how Schneider handles charge.

27 Volts for what Schneider may call a "Bulk" (most folks would call this setting Absorb) voltage is quite low.

Many of us would set Vabs a bit above the recommended Vabs,  to try to make best use of genset fuel.  Trying to charge the batts from the SW at 27 V,  will not do much charging,  and the charge current will taper to a low value,  long before the batteries are charged much at all.   A 30 volt setting for Absorb,  or Bulk,  or a bit higher should be OK.

Does the SW have the ability to Temperature Compensate its Charge voltages?  This compensation should help charging,  if the batteries are cool right now.

There is temperature compensation, and I do have it set...have to see if it is adjustable.

Your spread in SGs is fairly wide,  and would normally dictate that an EQ is in order.

That Link to the Wind-Sun Forum notes an EQ voltage that seems quite low,  to me,   but frequent EQs may mean that the EQ voltage need not be as high as would be needed,  if EQs were done monthly,  or less often.

I could not find the specs on the apparent model number of your batteries.   You might want to use the contact info from that Link,  to ask the manufacturer for recommendations on Absorb,  Float and EQ voltages,  EQ frequency,  or guidelines on when to know that an EQ is needed,  PLUS  the correct Temperature Compensation value,  and the SG reading for a fully charged battery.   Believe that the correct temp compensation value for Duracell GC batteries is  --3 mV per cell,  per degree C -  but that may have changed recently.

It is good that your batts are consuming some water   ...   this consumption does not seem excessive,  and is probably a bit on the low side of things.

Since the batteries are in the basement, where it stays relatively cool even in summer, they are almost always below 25 C, I wonder if that effects water consumption?

Always use Distilled Water for battery water. Absolutely. 

What type of Hydrometer are you using  --  plastic,  glass (??),   what manufacturer and model,  if known.

Whatever NAPA had in the Store  .  It's plastic, It works, but it is not graduated finely. Do you have a recommendation for a better one?

Here are East Penn Deka solar charging specs
http://www.eastpennmanufacturing.com/wp-content/uploads/Renewable-Energy-Charging-Parameters-1913.pdf

Larry

Larry Thank you!  Gold! I appreciate it, now to plug in the numbers...and figure those out.  Thanks! --Tom