Ah capacity is reduced while battery voltage and SG good

elesaver

I have received helpful information pertaining to the absorb voltage time and settings to bring my forklift batteries back to proper level.  During the last couple of days, we have had a lot of wonderful sun and plenty of absorb time, etc.  My SG in all cells (24V system) is 1.285+.  The battery voltage is higher than what I think it should be...31.2+...which is really what the EQ voltage should be. 

My concern is that the amp hour capacity has not returned to full.  It should be 938 aH.  This morning, with no load, it was at 804 aH. but the voltage was high as mentioned above.  I decided to put some load onto the system so at least harvest what is available now.  But, my question remains.  How do I get the aH capacity up?  I would hate to draw down too far and not be able to bring it back up.  With this amount of sun, I would think it would increase rather quickly.

The aH capacity has increased from 804 to 848 with Bulk MPPT and 4 hours of absorb.  Westbranch mentioned that I need to increase the absorb voltage which I have just done and will let it absorb for the remaining 2 hours or so of good sun.

Is this just a matter of "tinkering" with the absorb and EA to get it right? If so, which values will increase aH the most?   I'm concerned that the high battery voltage will damage the batteries.  Overcharging cannot be good but if the aH are not full, is it overcharged?

Mountain Don

How are you determining that the amp-hour capacity is reduced?  Some sort of a meter system?  Does it have a temperature sensor and is the temperature colder than previous?  Cold reduces AH capacity.

Also with a meter system the indicated AH capacity is only as good as the information input. 

elesaver

The WhizBangJr gives the aH reading.  I have just attached a temp sensor to the top of one of the cells.  There isn't room in the battery compartment to attach it to the side of one of the cells.  Yes, it is colder, so perhaps that is the issue.  Is there a way to calculate the drop of aH with outside temperature reductions?  Thanks for your ideas.

Vic

elesaver has noted in another Thread,  that he is using the MidNite WBjr current sensing module,  and that is working.

So elesaver,  what does the Classic show for battery temperature,  in the ' Temps '  menu?

Also,  in the WBjr setup,  there is a setting for the percentage compensation you want for changes in battery temperature,  you might want to check this.

ID the batteries are cold,  then this AH Remaining Capacity could well be correct,  as Mt Don mentioned.

Your batteries should be compensating for temperature variation at --5mV per degree C of change from 77 or 80F,  times the number of cells  --  this results in a compensation of --60 mV per degree C for your 24 V battery bank.   AND  if the batts are cold,  this could well be the reason for increased Vbs and reduced C as shown.

Vic

elesaver

I knew there was compensation per degree of temperature but not for the percentage of compensation.  So, on the actual number for temp compensation, I should have a -60mV per degree entered?  I thought that screen to say PER CELL.  Maybe I need better glasses? :-)

Vic

Hi elesaver,   You are correct about the amount of compensation entered to the Classic,  as it scales this number,  based upon the nominal battery voltage for the system.

BUT,  regarding the total amount of compensation for your 24 V bank,  --60mV/C is correct,  and this,  plus the battery temperature reading from the Temps menu will tell you if the Vabs seems fairly accurate for your battery conditions  --  know that recently,  the Temp sensor had not really been attached to the battery.

What IS the noted battery temp?
What is the percentage compensation of Capacity that has been entered in the WBjr setup?

More Later,  Thanks,   Vic

elesaver

At the T-comp screen, using the soft button under more, there is a voltage set point at which the temp comp is activated.  At least, I gather that's what it's saying.  The voltage set point matches the absorb set point which, at this time, I have set at the absV @60V based on westbranch's experience with forklift batteries.

Temp screen
FETS  26.4
PCB 35.6
Remote  22.3
Battery 8.4

vtmaps

The whizBangJr is a shunt based battery monitor that counts amphours into and out of the battery.  Like any other shunt based monitor, it needs to be calibrated to the battery it is monitoring.  The way to do that is get the battery 100% charged.  Do NOT trust the whizBangJr & Classic to tell you when the battery is charged, unless you KNOW by other means that the battery is fully charged.  That means use an hydrometer!   If the hydrometer says the batteries are not at full charge (when the Classic goes to float) then the whizbangJr is not set up correctly. 

As mentioned, temperature might be a factor... in two ways.  First, if the batteries are cold and the absorb voltage is not increased by the Classic's temp sensor, then you are going to be deficit charging.  Second, the whizbangJr also uses temperature data to adjust downward the ah capacity of the battery.   Even if temperature is the real issue, you won't know that for sure unless you put an hydrometer to those batteries.

--vtMaps

Vic

OK,  thanks for the data ...   so the 8.4 C battery temp will yield,   essentially a 1.0 volt increase in the battery Absorb,   EQ,  AND Float voltages,  as long as these conditions remain.

For RE charging of Traction batteries,  agree that a Vabs of 60V nominal,  and then temp comped should be fine.   SG readings will dictate how this setting and that for Absorb time need to change.

In transit now,  so more later,  Thanks,   Vic

elesaver

"Even if temperature is the real issue, you won't know that for sure unless you put an hydrometer to those batteries."

Yes, Vtmaps.  I have measured the SG and the readings in all cells is at 1.285 or 1.290, so I know the SG is good.  The voltage matches between my voltmeter (per cell and per bank total)  and whizbangjr.   Because the aH capacity does not return to 938 (or thereabouts), I am questioning how to determine the status of the battery.  It appears that the cold may well be the main factor but I'm interested in knowing the ins and outs of this.

"First, if the batteries are cold and the absorb voltage is not increased by the Classic's temp sensor, then you are going to be deficit charging."
How do you increase the Vabs by the temp sensor? 


I'm going to leave a small load on the batteries overnight tonight to see how much things change and then see how well the charge completes tomorrow if we have some good sun.

As always, thanks for your help. 

BB.

And to carifly on "default" temperature compensation:

-5mV per Degree C per Cell
-0.005 volts / (C * per Cell)
-0.005 volts * 12 Cells (aka 24 volt battery) /C = -0.060 Volts / C

-Bill

Dave Angelini

You increase the absorb setting to increase the voltage and set the temp come as per Bill in the previous. How cold is the room?
Setting a small load overnight is not going to tell you much. You need to cycle the battery by load testing or taking it down 30 or 40 percent from full. The AH counter is really not helping you learn much in fact, it is probably hurting. I like using the charge controller to measure the AH or the KWH harvested on days that have float time. Much more accurate!  The hydrometer is your best bet.

elesaver

Thanks, Dave for the input.  I'll have to get a thermometer to measure room temp accurately.  I do watch the KWH harvested.  And, I've already listed the hydrometer readings.  I'll keep working at it.

westbranch

What can get confusing here as well is that you are adjusting 3 factors at the same time, Temp compensation in 2 places, Absorb V and Absorb Time,  just work on one at a time.
You do need to get the correct adjustments set  for temp compensation entered as Bill noted above. 
As you have seen an increase in SG to what is recommended, I suspect you are close on the Voltage.

It is easiest to work on Absorb time first. I believe you started at 2 hours, and you have increased it to 4 hrs now, correct?.  A longer time is in order but don't increase in large increments.

This will test the  validity of the present Absorb Voltage for reaching End Amps (~ 1% Capacity) within 4 hrs, as you will enter FLOAT after 4 hours.
 
If you don't get to EA in 4 hrs you can  increase the time parameter...or test a higher V. 

Time to be writing it all down   Batt temp, ambient temp, Batt V, Absorb Voltage, Absorb time and SG all ~ 3 hrs after charging has finished.

hth

vtmaps

elesaver said:

How do you increase the Vabs by the temp sensor? 

You don't do anything except set Vabs to what you would want it to be if the battery were at standard temperature.  The temp sensor will raise or lower the ACTUAL absorb voltage, depending on the temperature.  Thus, for example, your Vabs setting could be 60 volts but what you measure at the battery might be 61 volts if the battery is cold.

elesaver said:

I have measured the SG and the readings in all cells is at 1.285 or 1.290, so I know the SG is good.

You have gotten some advice to adjust (increase) your charge settings... I'm not sure why.  If you are getting your SG where it should be, that's as good as it gets and you cannot increase the battery capacity by charging further.   Well, actually you can increase the capacity by overcharging... overcharging heats up a battery and a warmer battery has greater capacity.  I do NOT recommend warming your batteries by overcharging. 

Actually, you should aim for a lower voltage or absorb time, as long as you can keep the SG where it belongs.

elesaver said:

I have just attached a temp sensor to the top of one of the cells.  There isn't room in the battery compartment to attach it to the side of one of the cells.  Yes, it is colder, so perhaps that is the issue.

That very well may be the problem... attaching a temp sensor to a battery above the electrolyte level is known to be inaccurate.  Some manufacturers (Magnum comes to mind) attach their sensors to a battery lug.

--vtMaps

westbranch

Elesaver, just to add some complexity, when the spring solstice comes you can look forward to backing the settings off, as you will have both more hours of sun and more amps produced.  Lots to learn

Dave Angelini

westbranch said:

Elesaver, just to add some complexity, when the spring solstice comes you can look forward to backing the settings off, as you will have both more hours of sun and more amps produced.  Lots to learn

You can do this but when you are dialed in to the correct time and using the manufactures absorb voltage one should not have to do much besides routine maintenance. EQ's,  watering, clean the tops, and check a few cells SG. A yearly SG check of the bank recorded.
I make this easy for my folks as many do not think this is fun as some here do....Other things on their plates!

elesaver

Westbranch..."lots to learn" is definitely an understatement.

I've looked into the area on the forum for resouces but I don't see any books that would have information that would help refine things.  It would be "easier" if I had a way to learn other than continuously coming here to intrude into people's live to find answers to some of these things.  Would there be printed resources or is this knowledge that is gained from countless hours and personal experiences with solar devices?  Yes, I admit I started a square one (actually I was quite a distance behind square one) and with the help of this forum was able to advance.  The current system and its operation is due only to the help from here so I say a BIG thank you.  This situation will remedy itself, I'm sure as I continue to monitor and tweak.  I'd just like to be able to have a way to read, re-read, re-read, mull, re-read.  Hopefully, you know what I'm saying.

westbranch

This forum is one of your best sources.  I have not found any books that can match it , most being for beginners or pro installers, big gap no happy in between..  happy reading, keep posting

Vic

vtmaps said:

elesaver said:

How do you increase the Vabs by the temp sensor? 

You don't do anything except set Vabs to what you would want it to be if the battery were at standard temperature.  The temp sensor will raise or lower the ACTUAL absorb voltage, depending on the temperature.  Thus, for example, your Vabs setting could be 60 volts but what you measure at the battery might be 61 volts if the battery is cold.

elesaver said:

I have measured the SG and the readings in all cells is at 1.285 or 1.290, so I know the SG is good.

You have gotten some advice to adjust (increase) your charge settings... I'm not sure why.  If you are getting your SG where it should be, that's as good as it gets and you cannot increase the battery capacity by charging further.   Well, actually you can increase the capacity by overcharging... overcharging heats up a battery and a warmer battery has greater capacity.  I do NOT recommend warming your batteries by overcharging. 

Actually, you should aim for a lower voltage or absorb time, as long as you can keep the SG where it belongs.

elesaver said:

I have just attached a temp sensor to the top of one of the cells.  There isn't room in the battery compartment to attach it to the side of one of the cells.  Yes, it is colder, so perhaps that is the issue.

That very well may be the problem... attaching a temp sensor to a battery above the electrolyte level is known to be inaccurate.  Some manufacturers (Magnum comes to mind) attach their sensors to a battery lug.

--vtMaps

Hi vtMaps,

One of the ways that we have gotten to the place where elesaver INCREASED the Vabs,  and probably Absorb time is in the following Discussion:
http://forum.solar-electric.com/discussion/350281/cc-does-not-go-into-absorb-mode#latest

This system seems to really a Backup to the Grid,  and could probably benefit from some cycling.

It is also not clear that the RTSes are actually attached to the battery.

elesaver,  measuring the room temperature is not a very good indicator of battery temperature,   as large batteries have  a very large Thermal Mass,  which means that the rate-of-change in battery temperature is very slow,  compared to the air in the room.

Please attach the RTSes to a battery near the center of the battery bank.    Personally I would place these sensors mid-wan down the outside of one battery,  and place some Styrofoam over the sensors.   This Styro can be strapped in place,  or probably just taped in place with some 2" wide tape.

You DO NOT NEED TO ADJUST the Absorb voltage based upon the temperature of the battery,  the RTSes and the Classics or your Inverter/charger will automatically do this for you.

In the Classic,  in the Temperature Compensation menu under Charge,  just set --5mV.   Your inverter probably has a compensation value setting,  so also set this at --5mV there, as well.

Your Temp Comp Limits in the Classic look OK,  although,   25 V for the lower limit could probably be reduced somewhat  --  you really just do not want any limit on range of compensation voltage.

And so on,    Vic

vtmaps

Vic said:

Please attach the RTSes to a battery near the center of the battery bank.    Personally I would place these sensors mid-wan down the outside of one battery,  and place some Styrofoam over the sensors.   This Styro can be strapped in place,  or probably just taped in place

Vic, the OP has forklift battery and wrote:

elesaver said:

I have just attached a temp sensor to the top of one of the cells.  There isn't room in the battery compartment to attach it to the side of one of the cells. 

I suggested he try the Magnum approach... attach the sensor to the battery lug.  I'm not sure if there is a better way on a forklift battery.

--vtMaps

Vic

vt,  thanks for the reminder ..   and YES,  we have been discussing elesaver's Forklift battery for the past week or so.

Somehow hat the feeling that the sensors were not really attached to the battery.

It is very surprising that there is not that 1/4  - 2" of space to just tape the sensors to the side of the battery ...

AND,  yes,  the battery manufacturer suggested gluing the sensor/s onto a battery lug ...   have never liked this approach,  but,  a non-ideal location is better than no RTSes at all.

FWIW,   Vic

elesaver

Vic said:

vt,  thanks for the reminder ..   and YES,  we have been discussing elesaver's Forklift battery for the past week or so.

Somehow hat the feeling that the sensors were not really attached to the battery.

It is very surprising that there is not that 1/4  - 2" of space to just tape the sensors to the side of the battery ...

AND,  yes,  the battery manufacturer suggested gluing the sensor/s onto a battery lug ...   have never liked this approach,  but,  a non-ideal location is better than no RTSes at all.

FWIW,   Vic

The answers...yes and yes.  Previously, I had turned off the temperature sensor because there was no room in the battery case to attach it.  No, not even 1/4".  The case is made to fit the cells and fit it does...like a tight glove.  Since having the suggestion to try to use the sensor, I have turned on the mode in the CC and I have super-glued the sensor to the middle battery lug as the manufacturer suggested when I approached them with the problem of being able to attach this.  I don't know how else to attach the sensor.  When I feel each of the cell tops, they are not even warm to the touch.  Yes, the electrolyte is lower in the cell but there is no way to touch lower.

Vic

Hi elesaver,

Am familiar with Forklift batteries.   I was thinking about trying to mount the sensor midway down the case of the battery,  under foam  --   usually,  the cells are installed into a metal can,  or case.   And the foam could help remove the effects of ambient temperature on the case,  under the foam,  and therefore might be more accurate than using a lug.

The lug will conduct the core temperature of the battery to a certain extent.   There can be some heating of the lugs due to voltage drops in the cable crimps,  and to a certain extent,  in the lugs and interconnects,  themselves,  but this effect is greatest at high currents.

All that we can do,  is all that we can do.

Later Xantrex CCs and inverters,  ant eht Schneiders,  as well,  also use a tab on the sensor to bolt to the lug ...  it's all good.

Thanks,   Vic

elesaver

Thanks for the idea, Vic.  Yes, the battery case is metal and about 38" (or so) tall.  My concern with mounting it to the case, even under foam to nullify the ambient temps, the metal case is going to conduct the temp from the entire metal.  I'll check things out again today to see if there is ANY way to get that sensor into that case.  I have a cell removal block but the cells are over 100# each.  If I could find a way to lift one of the cells part of the way up and out of the case, maybe the sensor would be forced to "go along for the ride" back down into the case.  It, however, would then be in contact with the outer metal and I don't know if that would affect having accurate temps.

As you say, all that we can do, is all that we can do.  

Dave Angelini

Well maybe, but the accurate measurement of a battery is not negotiable offgrid. It is not hard but is non-negotiable!

elesaver

Dave Angelini said:

Well maybe, but the accurate measurement of a battery is not negotiable offgrid. It is not hard but is non-negotiable!

Would you have any ideas as to how to resolve the issue I'm having in getting the accurate measurement needed? 

Vic

elesaver,

If you have a glass thermometer with reasonable resolution in the 30 - 90 degree F range,  you could determine how accurate each of the several approaches to use your existing RTSes might be in reflecting electrolyte temperature,  with reasonable accuracy and response time.

If you were able to cover a fairly large area of the outer steel container with foam,  the effect of room temperature on this covered area should be much reduced,  and could allow a reasonable accurate reflection of actual electrolyte temperature,   IMO.

This large area of foam would result in a somewhat increased battery temperature when the room is cool,  and the battery is warm,  as well as a bit larger increase in the temperature differential across the battery bank ...   so it is all a tradeoff.

FWIW,   Vic

elesaver

These batteries are in a room in the garage...no heat.  When it's cold outside, it's cold there; when it's hot out, it's hot in.  I think I'm going to have to just use the battery lug as suggested by the manufacturer and hope that it will be able to sense when there is a lot of heat.

Vic

elesaver said:

These batteries are in a room in the garage...no heat.  When it's cold outside, it's cold there; when it's hot out, it's hot in.  I think I'm going to have to just use the battery lug as suggested by the manufacturer and hope that it will be able to sense when there is a lot of heat.

OK,  sounds fine ...   BUT,  just to be clear,   the RTS is always going to compensate the voltages from the CC and the Inverter/charger  --  hot,  warm,  cool or cold.

AND,  it might be even more important on many systems that a cool/cold battery be compensated,  because a lack of compensation of a cool/cold battery results in undercharging.  So,  in a long cold spell this can be harmful to the battery.

FWIW,   Thanks,    Vic

westbranch

Is it possible to use a Dremmel type tool to remove a section of the case so that you can have direct access to the mid section of a middle cell/s so you can properly mount the RTS?