battery charging voltage

DConlyGuy

During the constant voltage phase, the charger voltage limit is regulated to the gassing point of 2.42 volts per cell. that what my battery specs says to do. so is constant voltage the same as absorption on a charge controller?

BB.

Absorb (and float) stage(s) are constant voltage charging.

So, the answer is yes.

-Bill

DConlyGuy

so by what the specs says my float should be 14.52 for 12 volts?

vtmaps

DConlyGuy said:

so by what the specs says my float should be 14.52 for 12 volts?

I doubt it.  14.52 sounds like absorb.   --vtMaps

Vic

DConlyGuy said:

so by what the specs says my float should be 14.52 for 12 volts?

That Float voltage seems astonishingly HIGH to me.   Assume that these are Flooded batteries,  but,  still  very,  very high for FLAs,  if that is what you are using.

Normally,  the Vflt is well below Gassing voltage.  Vflt is the voltage that will just,  barely keep a fully-charged battery,  fully-charged.

We DO always say to follow the recommendations of the manufacturer of your specific battery.

2.42 VPC  is probably a good place to start for the Absorb voltage.   Would expect that this is well above Gassing voltage.

What is the target SG reading for your batteries,  assuming again,  that they are Floodeds?   What is the manufacturer and model number for your batteries?

Opinions,   Vic

DConlyGuy

Following discharge, constant current charge the CR-235 battery at 25 to 30 amperes until the battery voltage measures

2.42 volts per cell (7.26 volts open circuit voltage).

The constant voltage charge phase begins after the gassing point (2.42 VPC) is achieved. During the constant voltage

phase, the charger voltage limit is regulated to the gassing point of 2.42 volts per cell, while the input current is allowed to

gradually fall off. When the input current drops to the finish rate setting of 9 amperes, the charging phase will change

from constant voltage to a sustained 9 ampere constant current mode. The charging cycle will be terminated 3.5 to 5

hours from the gassing point, with factors such as ambient temperature, battery condition and depth of discharge

affecting the charge completion time. this is what it says to charge the battery it is confusing to me since it dotn say float and absorb stuff. 

vtmaps

The constant current charge is Bulk.

The 2.42 vpc constant voltage is absorb.

--vtMaps

wooffi

Hi guys,

Time for me to chime in, after 25+ years off the grid, I am finally paying attention to proper battery charging, scanning every possible site about the correct absorb voltage/time. The reason after pretty much killing my rolls bank (after 10 years maybe not so bad), I gut a brand new 1576 AH forklift bank from GB Industrial Batteries. I want to treat these babies with satin gloves.

Looking at the Rolls Surrette instructions the absorption time for my bank can be about 12.5 hours and I can do that only every once in a while, my 1800 watt of solar cannot ever bring them up without the generator support, no grid available. 

I have had the bank running now for about 3 weeks and kept the SG around 1240-1245 consistent. After a dying and gassing rolls bank this is a real pleasure. 

My Kubota diesel is very generous and when I do a long absorption charge will support the house juice and do the trickle absorption charge via the old xantrex 4024W, it only uses about 1/2 gallon of diesel an hour, possibly less.

My question, can I do an absorption run lets say every 10 or so days? The batteries get charges up to 28.8 (24 volt system) pretty much every other day. But according to experts that is only an 80% charge. Will I build up too much sulfating that way?

Thanks
Wolfgang

Vic

Dconly ..,

Some QUESTIONS:7

OK,  so perhaps,  maybe your batteries are Crowns ??  ??  ?   Is that guess correct??

Guess that your batteries are Flooded batteries??  Is this correct ??

What is the target SG that you are looking for,  IF they are Flooded batteries ??

What is the nature of your system.  Is this system Off-Grid??f   Assume that this is the case, as you mentioned that you run everything off DC ...

What is the target SG that you are looking for,  if your batteries ARE Flooded Lead Acid batteries ?? ?

The charge parameters that you have mentioned are really for Grid charging,  and are generally not achievable with off-grid systems,  particularly with PV charging and Solar Charge Controllers.

Could you please answer these questions,  please ?? ?

Thank You!!   Vic

DConlyGuy

Vic yes they are crown battery's , yes they are flooded 6volt battery's, yes the system runs  off dc only even my computer .the sg i got today was 1.275 its in the green on the hydrometer thing.  and the charging thing i posted is all i can find out from the crown spec, so that what i was going by

Vic

Hi DConly..,

Thanks for the answers.

Believe that the Target SG that you are looking for is about 1.275-ish  --  this should be nominally fully-charged,  with the battery at about 77 - 80 degrees F.

Would bet that an appropriate Float voltage would be about 2.21 VPC  --  about 13.25 V on a 12 V system.   Try this,  and try to see if the battery maintains full charge after a few hours in Float,  as long as the Charge Controller (CC)  is able to maintain this Float voltage.

Try to get a good Hydrometer,  or two  --  glass outer tube,  glass float,  and numbers marked on the float.

Perhaps you could contact Crown battery and ask for charge parameters for Renewable Energy (RE,  as in Solar charging).

Your proposed Absorb voltage seems like a good start.  The correct Absorb time for your batteries depends upon the Depth Of Discharge (DOD)  that they experienced in the previous discharge cycle.

Measuring your SGs  will give you a fairly good idea about how well your Vabs and Absorb time are doing in generally getting the batteries fully charged on most days.

Later,   Thanks,   Vic

Vic

wooffi said:

Hi guys,

Time for me to chime in, after 25+ years off the grid, I am finally paying attention to proper battery charging, scanning every possible site about the correct absorb voltage/time. The reason after pretty much killing my rolls bank (after 10 years maybe not so bad), I gut a brand new 1576 AH forklift bank from GB Industrial Batteries. I want to treat these babies with satin gloves.

Looking at the Rolls Surrette instructions the absorption time for my bank can be about 12.5 hours and I can do that only every once in a while, my 1800 watt of solar cannot ever bring them up without the generator support, no grid available. 

I have had the bank running now for about 3 weeks and kept the SG around 1240-1245 consistent. After a dying and gassing rolls bank this is a real pleasure. 

My Kubota diesel is very generous and when I do a long absorption charge will support the house juice and do the trickle absorption charge via the old xantrex 4024W, it only uses about 1/2 gallon of diesel an hour, possibly less.

My question, can I do an absorption run lets say every 10 or so days? The batteries get charges up to 28.8 (24 volt system) pretty much every other day. But according to experts that is only an 80% charge. Will I build up too much sulfating that way?

Thanks
Wolfgang

Hi Wolfgang,

Generally would recommend that Flooded batteries get fully-charged several times per week.

For Forklift batteries,  believe that SGs that are "kept around 1.240 -1.245 consistent"  is not high enough.  A fully charged Lift battery should have SG readings around 1.280,  compensated for temperature,  if the batteries are very far from about 25 degrees C.

Forklift batteries need fairly frequent EQing,  often at least once per month,  some say that this should be done weekly.

Here,  we charge our Surrette Flooded batteries every fourth day.

More later,   FWIW,   VIc

DConlyGuy

Hello,

 

I am contacting you on behalf of Crown Battery Manufacturing Company. To answer your question the charge control settings for your 12 volt system please refer to page 3 of the attached deep cycle support brochure. The suggested settings for your 12 volt system are also listed below:

 

Daily Charge (Absorption):           14.5

Equalize:                                              15.5

Float:                                                     13.5

 

The bulk setting should be set at the same or a little higher than the absorption phase (14.5 to 15). This is the phase where 80 to 85% of the current is returned to the battery. The absorption phase will follow the bulk phase and is where the battery is "topped off" to insure that the battery receives full charge.

 

These settings are assumptions based on the depth of discharge being limited to between 30% and 50% of the batteries rated capacity. Also that the panel array / turbine capacity output (RE power source that is being used) is properly matched to the battery bank's capacity, which should be approximately 8 to 10 amps of current charge input for every 100 amp hours (at a 20 hour rating) of the battery's rated capacity. It is recommended that at a minimum that you equalize your batteries every 30 days. If you are discharging your batteries below 50% of their rated capacity you should equalize more frequently.

 

To maximize performance and life of your deep cycle batteries they should be fully recharged after each discharge period. To verify full recharge of your batteries it is important to monitor individual battery voltage and specific gravity after every charging period (battery testing instructions are located on page 6 of the attached brochure). If the battery bank is not at least 2.12 volts per cell (VPC) and have a specific gravity (SG) rating of 1.265 per cell after absorption has completed, the absorption voltage settings need to be increased or the time needs to be extended.  The suggested initial time setting should be 2.5 to 3 hours for the absorption phase and 1.5 to 2 hours for the equalization phase. However if the batteries are reaching the 2.12 VPC and the 1.265 SG and are gassing excessively the absorption voltage settings need to be decreased or the time needs to be reduced.

 

It is important to allow the battery bank to float (rest) before the next discharge cycle begins. It is ideal to have the battery bank fully charged by late morning or early afternoon to give the battery bank rest time throughout the balance of the afternoon before the next discharge cycle.

 

Please remember that the information provided are suggestions and that RE systems are always changing (season changes, living arrangements, ect.). Please make the proper adjustments revisiting your charger settings periodically to ensure optimum system performance.

 

If I can be of further assistance or if you have any questions please feel free to contact me.

well my settings are close enough  it looks like. i am surprised at the sg for a full charge according  to crown though, 1.265 is only a fair reading on my hydro meter

BB.

To "know" what your "full" SG reading is--That is the final reading you get after completing equalization (equalization being ~5% rate of charge and ~15.5 volts) and measuring the SG every 30-60 minutes. When ALL CELLs SG readings stop rising between readings--Write those temperature corrected SG readings down (for each cell). That is now your 100% charged SG reading. Note: Watch cell temperature--If you get over your battery temperature (hot batteries = short life), stop equalization and resume after they cool down (or even next day).

Before equalization, all plates must be covered--Only fill to full after equalization (filling a cold battery to full then equalizing will probably "pump" electrolyte out of the top of the battery--Not a good thing, plus very messy--Operating a battery with exposed plates leads to a quick battery death).

For the most part, try to reach >90% SG reading once or twice per week (one vendor, Rolls, suggested once every 28 days for an otherwise cycling/daily use bank is possible). Do not try for 100% every charging cycle--That will shorten the life of your batteries.

A stored battery should be charged to >90% state of charge. Do not let a stored battery fall below ~75% state of charge (typically for a flooded cell battery that means a full charge ~once per month at ~75F--Or leave the solar panels+charge controller connected/operating when leaving the cabin for the winter).

-Bill

vtmaps

DConlyGuy said:

well my settings are close enough  it looks like. i am surprised at the sg for a full charge according  to crown though, 1.265 is only a fair reading on my hydro meter

Your hydrometer is probably meant for automotive batteries.

The SG of a battery is arbitrarily set by the manufacturer.  The higher the manufacturer sets the SG, the greater the capacity of the battery.  But higher SG also reduces the lifespan of the battery.  Heat also reduces battery lifespan.  In tropical or other hot environments, manufacturers often use lower SG.

--vtMaps

BB.

From this comment:

http://forum.solar-electric.com/discussion/comment/354210/#Comment_354210

I ran across this page on why different types of batteries have different starting s.g. fills... Is pretty interesting:

Specific Gravity vs Applications
1.285 Heavily cycled batteries such as for forklifts (traction).
1.260 Automotive (SLI)
1.250 UPS – Standby with high momentary discharge current requirement.
1.215 Geral applications such as power utility and telephone.

As mentioned earlier, the specific gravity (spgr.) of a fully charged industrial battery, or traction battery, is generally 1.285, depending on the manufacturer and type. Some manufacturers use specific gravities as high as 1.320 in an attempt to gain additional Ah capacity, but at the cost of a shorter cycle life.

...

Higher Gravity = vs Lower Gravity =
More capacity / Less capacity
Shorter life / Longer life
Higher momentary discharge rates / Lower momentary discharge rates
Less adaptable to "floating: operation / More adaptable to "floating" operation
More standing loss / Less standing loss

At 77F, the equation that relates S.G. to battery cell voltage is:

Specific gravity = single-cell open-circuit voltage - 0.845 (example: 2.13v – 0.845 = 1.285)
Or
Single-cell open circuit voltage = specific gravity + 0.845.

-Bill

DConlyGuy

hmm so maybe can help to read the hydrometer i got,  it said 1.275 and the little thermometer thing on it said to add 4 to the number. would that mean 1.279? 

BB.

Sounds right... But checking the SG of equalizing batteries is a bit difficult too... The water is "fizzy" with hydrogen and oxygen bubbles. You need to tap those off to get accurate readings (or the SG will read high with bubbles on float).

After you are done using the hydrometer, takes a couple of draws of distilled water to rinse the unit out (otherwise they can get sticky inside).

-Bill

Vic

Hi DConly..,

Glad that you were able to get RE charging parameters from Crown.

You said,  "well my settings are close enough  it looks like. i am surprised at the sg for a full charge according  to crown though, 1.265 is only a fair reading on my hydro meter"

I disagree that your settings are close enough.  The stated Float voltage,  previously,  was 14.52 Volts.   This was,  and still will be FAR TOO HIGH A VOLTAGE.   From the above info from Crown stated that Float voltage should be 13.50 volts.   A difference of one volt in Float voltage is HUGE.   And,  the longer time that your system spends in  Float,  the worse that the very high Vfloat will be for your batteries.

Also,  it is essential,  that each of your charge sources use a Remote Temperature Sensor  (RTS,  or BTS).  This will help make sure that the batteries can get fully charged,  but not overcharged with varying battery temperature.   Your CC may be your only charge source,  but,  be certain that you get and install an RTS for the CC (at a minimum).   We do hope that your CC has provision for using an RTS,  and that it has settings for charge & EQ voltages,  as well as EQ and Absorb times  (not just several DIP switch charge profiles,  IMO).

YES please DO get several good,  glass Hydrometers,  hopefully,  ones without showing their opinions on how well your batteries have been charged  --  just numbers on the float is best,  as there are many different target SGs used by battery manufacturers.  You need to be the judge,  based on what YOUR batteries need.

Here is an article from Surrette Battery on measuring SG of Flooded batteries:
http://support.rollsbattery.com/support/solutions/articles/4347-measuring-specific-gravity

FWIW,   Vic

BB.

An alternative to glass--This one has been pretty well received (~$30+ shipping, temperature corrected display):

http://www.solar-electric.com/midnite-solar-battery-hydrometer.html

Note that once you have two or more hydrometers--You will never know what the true SG is.

Segal's law

Segal's law is an adage that states:

• "A man with a watch knows what time it is. A man with two watches is never sure."

-Bill

DConlyGuy

well my new mppt controller is a pain in my butt right now, seriously thinking of going back to my cheap pwm until i can get the screen that controls the victron controller, it only has one dial i can set absorb at.   all the floats are 13.8,  i have absorb set at 14.7 because the next dial setting is less than what crown wants me to set it at. 

Vic

Hi BB Bill,

Yes,  am familiar with the Hydrovolt Hydros,  did get a few of them   ...   one needs to be banged a bit on the top of the battery for it to register anything ...   it gets ;hung up.  Also,  they require diligent cleaning,  as there is a huge surface area,  wetted by electrolyte,  compared to a simple glass Hydrometer (IMO).

For the main battery banks here,  the sample tube is simply several inches too short to reach the electrolyte,  unless the battery happens to be over-filled ...  too bad that they do not have a too-long tube that could be snipped off if the length bothered the user.

Omitted from my previous remark on Hydros,  that good ones can be found in a real Auto Supply store,  like NAPA,  and that is often a benefit for off-gridders,  as these stores are often very accessible.

Personally,  my favorite Hydrometer is still the Freas (the one without the thermometer).  Just numbers on the float,  no colors or judgments on its feeling about the SOC.

Good CCs will read out the BTS-measured battery temp,  and comp is easy,  at about three points per 10 degree F change from the Reference temp,  IIRC.

The reference to having several  Hydros allows on to test them,  initially,  and see how well that they agree.  By experience,  the variations between good quality glass Hydros seem to be at or less than the Repeatability of the instrument ...   good enough for me.    Reserve one or two Hydros,  in case one is broken,  or needs a new bulb,  etc,  and one has another in reserve.

Personally try to always use the same Hydro,  as trends are usually more important than absolutes,  and,  if kept clean,  a single Hydro becomes a "known"  in the process ...   and so on.

The old reliable Freas has been in service for 12 years,  and remains an accurate tool.

And so on,   Vic

BB.

Be careful how you set the hydrometer down and store it.

More than a few glass hydrometers have rolled to the floor and broke.

-Bill

wooffi

Vic,

Thanks for your reply. That helps a lot, I can time that perfectly. Especially in the heat of the summer, running the ac, I can run the Kubota all night, it takes care of the 'Friedrich' ac I have and puts a nice 12 hour absorption charge into the bank.

This is just the discussion I was looking for.

BB, I just got that Hydro Volt, a little easier than messing with a refractometer. Great little gadget, made in Germany I guess.

Thanks guys I will join the forum a bit more often. So happy with my new bank. Don't ask how I got them situated, The total weight was 2500 pound, the cases alone 300 pound each.  

Wolfgang

wooffi

This is slightly of the battery discussion or maybe not. I am unable to find the temperature compensation settings in my Xantrex 4024W.
Xantrex upgraded the settings.

On my old inverter (the stone age one from 1990) there was a way to adjust the temperature compensation.

On this one, not sure which year this is, the menu setting have some changes for example no more maximum generator run time etc.

A few days ago I accidentally was able to get into the tech's setup menu, but I have no idea how I got there.

We are right now in the 90's and it does not show any compensation at all, I have the sensor in the middle oft the bank. 

Thanks
Wolfgang

Dave Angelini

What is a 4024W?  If you have the old SW 4024 or 4024+ then all you do is plug in a good sensor and you are done.
You have a basic settings and an advanced settings. You can select and this is probably what you did. You do have a manual right?

wooffi

Dave,

Thanks and sorry, yes I have a Xantrex SW 4024, used to have a Trace SW 4024, that a guy in your neck of the woods purchased and refurbished.

Here is my current problem, yes I do have a manual an yes, I just plugged it in. However, when I look at the readings 'Battery actual temperature and 'Battery temperature compensation' I get the same numbers, no variations, we are in the 90's right now, there should be  a fluctuation or?

Thanks

Wolfgang

Vic

Wolfgang,

Yes,  you should see some Compensation,  if the battery temperature (as measured by the Temp Sensor)  is above or below the Reference temperature of about 77 degrees F.

As you know,  large batteries have a large thermal mass,  so the temperature of the battery changes slowly verses ambient temperature changes.

Out of curiosity,  what is the color of the cable that is attached to the Temp Sensor (RTS/BTS)?

If you have a DMM that can measure resistance,  you could unplug the RTS,  and measure the resistance on the 100 K Ohm scale.  Place one test lead on the each of the outside contacts.   One would expect a resistance reading of about 10 K ohms at a sensor temperature of about 77 F.  At about 90 F you would expect a reading less than that,  in the range of about 7 - 8 K,  IIRC.

If you have a old,  not in usse telephone wall outlet,  that the RTS connecter will plug into,  this will make it easier to use the DMM test leads.  The easiest leads to use are the Red and Green,  IIRC.

FWIW,   Vic

Dave Angelini

Measure the voltage as Vic said or buy a new sensor!

wooffi

Vic and Dave,

Great advise again, I just purchased this new sensor on eBay, the color of the cable is yellow, telephone plug in. But I will measure the voltage as you guys suggested.

Vic, you are also right, this large bank has not heated up at all, it's not in a casing, well ventilated, the sensor is in the middle of the bank.

So for now thanks again, never had such a large bank and have it set to not discharge more than 50%.

Wolfgang

Vic

wooffi said:

Vic and Dave,

Great advise again, I just purchased this new sensor on eBay, the color of the cable is yellow, telephone plug in. But I will measure the voltage as you guys suggested.

Vic, you are also right, this large bank has not heated up at all, it's not in a casing, well ventilated, the sensor is in the middle of the bank.

So for now thanks again, never had such a large bank and have it set to not discharge more than 50%.

Wolfgang

Hi Wolfgang,

Good that you have a new BTS coming.   Yes,  the color of the cable should be yellow.   Sometimes,  when there are a number of BTSes  available from a number of different Solar devices,  and  the wrong one is chosen for a given inverter or Charge Controller.   So good that you have been using the correct one.

I was WRONG on the RESISTANCE of the Trace/Xantrex BTS.   Just measured one,  on a Xantrex SW Plus 5548 inverter.   It appears that the reference RESISTANCE at 25 degrees C is 100 K OHMS,   (NOT 10 K ohms as I had previously stated).

Also,  believe that Dave had mentioned measuring the voltage of the BTS.  As the BTS is a Thermistor (a temperature dependent variable RESISTOR),  there will be no voltage to be measured with the BTS disconnected.  So,  you would want to measure the resistance on the 200 K ohm scale on your DMM,  to see if the original BTS is good or not.

It is possible that the BTS that you had been using,  initially,  is good,  but perhaps your battery happened to be about 77F (25 C),  and no compensation was needed.

Also,  my Xantrex SW Plus inverters compensate temperature in about 1 degree C steps (perhaps this is in 2 degree F steps).  So  the temperature compensation is a bit coarse.

FWIW,   Vic