Equalizing batteries and thinking they are getting to hot!

[Fe-Wood]

I decided to equalize my batteries today and the ambient temp is about 88 Deg. F. The batteries very about .002 points of SG between cells at this point. I'm wondering if I should stop because the batteries are approaching 98 deg.

[BB.]

They sound "close enough" (usually difficult to measure closer than 0.005). And you are below the 0.015 to 0.030 range for equalization.

Normally, the recommendation is if all the cells' specific gravity stop rising after 30-60 minutes of charging, then the battery bank is fully charged/equalized.

You certainly don't want to go much above the 100-120^oF range.

-Bill

[Vic]

Hi Fe..,

I agree with BB Bill. STOP! Dunno hot is "hot", but heat it not good for your fairly new battery bank.

Looked through your past posts, and found this, "I have a 4024PAE with 8 batteries @6VDC with a combined 790Amp Hrs"

So you have two strings of batts on a 24 V system. Just to make certain, do you have BTS/RTS (temp sensor) on all charge sources?

How are you measuring the SGs? Glass Hydrometer, Refractomerer, or ... ?
What is the SG that you measured when you were seeing that 2 point variation? AND, just to be clear you are seeing a variation of, 1.265 on one cell, and 1.267 on an other? ... just as an example.

In another thread you mentioned using a generator for charging, do you have some PVs? And, what brand/model are the batts? Just curious.
At some point if you could create a signature this would help some. Thanks. Vic

[Fe-Wood]

Thanks for the replies!!! I waited a bit hoping someone would jump in with a quick recommendation.... Not seeing that, I did stop.

I'm using a Hydrometer with the thermometer built in. Purchased through our host. I'm wondering about its accuracy and my ability to read/understand it. Sadly I did not have it until long into the batteries service life. Today, when I took my first reading I was getting 1.75 plus 2 of the intermediate lines. In my mind this should equal 1.185. Then add the .004 temp adjustment for 89 deg. and I get 1.189. On the battery monitor, I was showing Float Charge @ 100% Charge. The above mentioned was a low cell. The high cell was 1.204. So the difference was 0.015 between cells. After Equalizing for about 1.5 hrs the difference is about 0.005 between cells or 1.223 and 1.228. My battery monitor said I was at 97% of charge. The Volt read on the batteries is 6.191 to 6.205 at 96% of charge. Its looking like I am vastly undercharging! I should read about 7.056 Am I right? I had the charger set at 100% recharge rate. I just changed it to 85%.... This is SOOO confusing! I think I need some BIG help here...

I have Crown Batteries, model CR395 6 Volt. The magnum 4024PAE with battery monitor and temp sensor. I am charging off the Generator with the Magnum. No Panels as of yet... On the list....

[BB.]

Measuring voltage on a battery is a bit of guess work... If they are charging/resting/discharging, the numbers are all different. And other than resting voltage, have only a weak relationship to state of charge.

The Hydrometer (properly calibrated and used) is going to give you the most accurate numbers. Using this Crown Battery Manual (PDF):

Specific Gravity
State of Charge Level

100% 1.265 or Greater
75%  1.225 - 1.230
50%  1.185 - 1.190
25%  1.140 - 1.175
0%   1.125 or Less

And they also list battery voltages too (after a 15 second load test--to take of the "surface charge"?)...

Note that your batteries should read about 6.3 volts fully charged (room temperature, resting voltage).

And about 7.3 volts (~29.2 volts) voltage set point for absorb charging.

There are lots of theories about how best to charge your battery bank... Pick one that works for your charging setup and then monitor the bank... If the bank is "undercharged", then add time and/or voltage. If the bank is overcharged, drop time or voltage a bit...

Depending on how your charge controllers can be programmed... One method is to measure the time to Bulk Charge (from below ~29 volts to absorb point at ~29.2 volts) if that took 2 hours, then add two more hours for the absorb time (holding at ~29.2 volts). Then turn off or drop back to float (if you have a genset, you will pick turning off the generator).

Another method is to set Absorb to ~29.2 volts and set the Absorb Timer to 2-4 hours... 2 hours if the bank is lightly cycled and ~4 hours if the bank is deeply cycled.

Watch the specific gravity and water usage... If you have to add water about every 2 months to a cell--you are probably OK. If you have to add water more often that once per month, you may be charging a bit too much (excessive charging/"boiling"/equalizing is not good for a battery bank). If you are not adding water, you probably are undercharging.

A 4kW inverter/charger is pretty good sized... Your ~790 AH at 24 volt battery should be charged around ~5% to 13% rate of charge (at 20 Hour rating--these are typical numbers, always refer to mfg. instructions to confirm):

• 790 AH * 0.05 = 39.5 amps minimum
• 790 AH * 0.10 = 79 amps "nominal"
• 790 AH * 0.13 = 103 amps "healthy maximum"

Depending on the programming/capabilities of your inverter/charger, and the capacity of your genset--hopefully your numbers fall somewhere in the ~80-100 amp range for charging this batteries.

If you are having problems getting the batteries above ~1.260 specific gravity and you have a "big genset", you can try running longer with a smaller genset and battery charger to save fuel (a Honda eu2000i and ~30 amp, or a bit less, AC charger or if the inverter/charger can be programmed for lower charging current to finish the charging).

You do not know what the initial "fill" S.G. was... So you don't know if you can reach ~1.265 or not. And if absorb charging (and some deeper cycling--exercising) does not bring the S.G. back up--Then you may have started to sulfate the battery bank (unrecoverable early aging).

Battery Monitors usually have some sort of "reset to 100% full"--Like if they see 29.0 volts for >1-3 hours or something). If you do not reach those conditions, the Battery Monitors will "drift" from "true" 100%. Also, sulfation will reduce battery capacity--which the Battery Monitor cannot detect.

Anyway--My guesses from behind a keyboard.

Good Luck!
-Bill

[Fe-Wood]

Wow! Thanks BB!
I'm going have to re-read this again in the morning.... Lots of good info! Testing to be done. All the numbers you are talking about are good with what I've been doing. Looks like I'm going to have to dig deeper. I'm thinking I may have set up/initialized the monitoring part of the charger without a full charge. Thoughts on that?

[BB.]

I really do not have anything I can add... Be do'in the same thing as you reading the manuals for setting up / configuring the monitoring system.

In the end, figuring out the present state of your battery bank and how, if needed, you will need to get it back to full/proper state of change. Hopefully, getting the battery monitor sync'ed will fall out at the end.

Depending on size of of genset and such--If you have a large genset and this is your only charging source--you may end up really needing a smaller genset (and possible mating AC to DC battery charger) to finish the charging. Bulk usually ends at around 80-90% state of charge, and "absorb" (tapering towards zero charging current) takes place over the next 2-4 hours. Using a "large" genset that can drink 0.5-1+ gallon per hour vs a smaller genset that may take 1/4 to 1/9th gallon per hour for those last "4 hours" may save you a bunch of fuel costs over the long haul.

-Bill

[vtmaps]

Hydrometers can be very tricky to use properly. Most installers I know use cheap ($50) refractometers. They have no moving parts and temp compensation is built in. You can buy them online or at an auto parts store. Search this forum for 'refractometer'.

There have been at least a few threads like yours on this forum that were ultimately resolved by learning that the hydrometer was wrong (or used improperly).

One more thing... this affects both hydrometers and refractometers: stratification of electrolyte. When charging you are concentrating the dilute sulfuric acid. The heavy, concentrated sulfuric acid sinks to the bottom of the battery. What you may be measuring is the dilute acid at the top. Industrial batteries often have electrolyte circulation systems. The way most of us deal with stratification is by charging far enough into absorb stage that bubbling (gassing) occurs. The bubbling stirs up the electrolyte.

Do you routinely achieve gassing? If not, you certainly have been undercharging your batteries. In addition to sulfation being a problem, the concentrated acid in a stratified battery really corrodes the bottom parts of the battery.

--vtMaps

[Fe-Wood]

I put these batteries online back in November and I haven't had to add any water. Or maybe I did add some once. I'm not positive on that. I do get the water bubbling so the electrolyte should be well mixed.

Here is the recommended profile for my batteries. These settings don’t correspond to any of the setting on my controller.

I currently have the Charge Rate setting on my controller set at 100% This allows me to charge at 97 to 100 amps during bulk charge.
I am currently running the absorb cycle 3.5 hours after the bulk stage has finished. From my understanding the bulk phase is an un specified length of time and is done to bring the batteries to a Specific Gravity or Voltage. Then the Absorb phase starts.

What does charge factor mean?

Recommended Charge Profile:
Following discharge, constant current charge the CR-395 battery at 40 to 50 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) 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 15 amperes, the charging phase will change
from constant voltage to a sustained 15 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.
The CR-395 battery should receive a full recharge following the completion of each discharge, along with a weekly
equalization service charge. During the equalization charge cycle the finish rate charge time is extended by 3 hours (6.5
to 8 hours from the gassing point).
The charge factor of the standard recharge should be equal to or greater than 1.07 (107%). The charge factor of the
equalizing cycle should be equal to or greater than 1.15 (115%).

As always Thanks for all the replies and help!!!!

[Vic]

Fe,

Thanks for the added info on your system.

Regarding the Hot batteries during the EQ yesterday:

EQ should be started when the batteries are fully charged. If the batts are not fully charged, there can be additional heat generated in the batteries. This is especailly true when using a generator or Grid power as the power source, as the average power delivered to the batts is usually considerably higher than charging/EQing from PV.

Since you have a good Hydrometer, it should not be difficult to get reliable readings from it. I assume it is a Brady brand with red rubber bulb and snout.


The hydrometer will help you calibrate your Battery Monitor, but it may take a bit of time to do this.

Hydrometers have been used for over 150 years to measure the SOC of flooded batteries, they work well if one is careful. Just a quick note on using one:

1. Fill and expell two samples from a cell, and measure the SG on the third fill. Be fairly gentle in filling and expelling the electrolyte -- it is cleaner, and does not blast debris on top of the Moss Guard into the guts of the battery.

2. Keep the Hydro's fill tube in the vent well of the battery as you take the reading. A flashlight can help yor see the readings. Keep the Hydro level, and make certain that the flolt is floating, not hitting the top stopper of the Hydro, and not sticking to the sides of the outside tube.

3. Record the readings in your battery notebook for future reference.

EDIT: 4. RINSE the Hydrometer in Distilled twice after each use, AND on the Brady, rinse the entire tip. (forgot to note this important part).

As BB Bill mentioned, having a genset as the only charge power source can be a bit tedious and expensive if the genset is fairly large -- a long run-time at light loads for finish charging.

As you know, there are two important settings for the Asorb stage: Asorb voltage, and Asorb time -- the amount of time spent at this voltage. The deeper the discharge of the battery, the longer the required Asorb time. Until you get the batteries fully recharged, Asorb times of 2-6 hours might be required. Near the end of Asorb, you should notice vigorous bubbling of the electrolyte. Agree that about 29.2 V Asorb or a bit higher for now is a good set point.

Flooded batteries are very forgiving. They do not llike to be run low on water, sit in a discharged state, and heat will shorten their lives. But am sure that you will get on top of the charging process. PV is a big help, as you know.

Forgot to ask about your generators. What are you using? Good Luck, Vic