Specific Gravity...

plongson

I'm a bit confused about my battery level. The system now has about 8 weeks on it, and all I can get is 1.225 SG on the batteries.

What is confusing me is:

1. The Midnite 250 going into float everyday, we've had great sun for weeks.
2. The max recorded voltage being 59.9v. The lowest was 48.2v
3. The battery monitor on the Magnum hits 100% SOC a couple of times a week

I didn't trust a Chinese cheepo hydrometer and bought a nice Brady with temp compensation from NAWS but they read the same. The batteries are new, and I've read they won't reach full potential for many cycles, but I'm kinda nervous.

What do you guys think???

jeffkruse

Re: Specific Gravity...

Get that SG up! What are your settings? I think all of my suggestions include increasing the absorb time!

Vic

Re: Specific Gravity...

Hi Paul,

YES, 1.225 is TOO LOW. Increase Asorb time, and perhaps Asorb voltage. Make certain that your CC Voltage is calibrated using a good DMM.

Does your bank use water -- some moderate water use is a good sign. AND, the improvement one sees with cycling battery banks is usually capacity. The charge parameters of Asorb voltage and time should be fairly stable over time, just the Asorb time may vary depending on variations in DOD.

Recall that your bank is in the garage, but make certain that your RTS/BTSes are mounted midway down a single battery in the center of the pack (IMHO), and perhaps covered with 1" (or so) thick styrofoam, to reduce the effects of room temp variation. But is is good that you are paying careful attention to your bank.

Good Luck, Vic

plongson

Re: Specific Gravity...

Hi Vic, Thanks for getting back with me.

Yesterday I checked voltages at the midnite and both array voltage and battery voltage were nearly spot on with the display voltage on the midnite graphic panel (MNGP). Right now the absorb is 120 min and absorb voltage is 57.6v.

The RTS is mounted midway up a center bank battery BUT is not insulated. The temp in the garage is steady now at about 45*f and the electrolyte was nearly the same on the hydrometer.

Dang, this has me as nervous as a cat in a tree right now. I sure don't want to FU and sulphate these batteries.

I'm gonn'a bump up the tme to 180 min and voltage to 59v.

Oh, and I'm not really using ANY water that I can see, and I've been checking about every two weeks.

Paul

westbranch

Re: Specific Gravity...

Paul, did you do a generator charge-up in the beginning? that too might be a help as well as a longer, higher absorb V.

BB.

Re: Specific Gravity...

If the specific gravity does not go up while equalizing--then that is the present maximum SG for that battery bank.

If you are adding some water (say every two months), then they probably are reaching their full charge point (no water or boiling cells so they need water every few weeks, then you have issues).

Here is a thread on Hydrometers and how best to use them.

I understand that some tropical locations will use a bit weaker electrolyte (batteries will have a longer service life?).

From this thread, the range of Electrolyte Specific Gravity seems to be:

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 General 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

Over charging / Over equalizing, if it does not raise the specific gravity (check every 30-60 minutes) is just going to "boil" off the water and cause damage to the plates/grids.

If the battery bank is otherwise operating correctly, and you have never seen higher S.G. before (when new and charged)--then this is the maximum SG you will see.

However, if the SG was higher and is lower now, then there is a good chance that the batteries are becoming sulfated.

-Bill

Vic

Re: Specific Gravity...

OK, Paul,

FLs are fairly tolerant of many things.

And kind of in the same vain as WB mentioned, believe that Surrette still recommends EQing a new bank as a part of commissioning it. So if you have not done this, it should not hurt.

It is good to get the SGs up to spec, and doing what is required to do this.

Great that you are paying attention to the bank. WIth larger banks, one can get into chasing one's tail -- making largish adjustments at one time, and making others the next day for example. It can take three, or so days to see the effects of changes made. Larger changes may take a bit longer. So you might want to watch these two changes you have made for days. It is possible that going from 57.6 to 59 is too large a step, especially along with the change from two, to three hours of Asorb time. However, why not leave it as it is, and watch it.

My Surrettes have been running at 58.3 Vasorb, which is a bit too hot. Asorb time has been about 1.25 hours. So have just started dialing back the Asorb V. Am using Return amps as the Asorb termination. But my banks are discharged to 90% SOC if that.

It is all a balance, and FLAs really are forgiving -- especially for those who pay attention to them.

Sounds like your BTS does not really need to be insulated, as you appear to have good circulation around the bank ... Whatta I know ? Good Luck, Vic

vtmaps

Re: Specific Gravity...

plongson wrote: »

Yesterday I checked voltages at the midnite and both array voltage and battery voltage were nearly spot on with the display voltage on the midnite graphic panel (MNGP). Right now the absorb is 120 min and absorb voltage is 57.6v.
The RTS is mounted midway up a center bank battery BUT is not insulated. The temp in the garage is steady now at about 45*f and the electrolyte was nearly the same on the hydrometer.

When you say your absorb voltage is 57.6, do you mean that is actual voltage or is that the voltage before temp compensation? At 45° F the actual voltage should be higher than 57.6.
--vtMaps

Volvo Farmer

Re: Specific Gravity...

Is it possible that the OP has some stratification of the electrolyte and that's why his readings are low?

waynefromnscanada

Re: Specific Gravity...

Are the batteries L-16 ?
Do the batteries ALL bubble freely before switching to float?

Vic

Re: Specific Gravity...

From memory, they look to be SUrrette S-Series, like S-530s perhaps ... forget the 20Hr capacity of the S-line. But from a pic, they looked like L-16s.

He should be using some water, so prob the Asorb was a bit too low. 59 V before temp comp shure should do it ... Done Guessing, Vic

offgrid me

Re: Specific Gravity...

Not to thread jack but I have a similar problem with my batteries. I have more than enough panel, low usage (15% dod) and bts hooked up. When sunny I go into float every day. My sg seem to be sitting at around 1.230 temp corrected. I dont think I can adjust the absorb time because the xantrex cc super seeds the timer when amps drop to 2% of battery bank. Both my absorb and bulk voltages are set at the battery manufacture recommended 59.2v. Should I up this to something higher. The sg's when new were all around 1.270

Ralph Day

Re: Specific Gravity...

It's easy to outthink your cc. If you need absorb for longer than it's max time amount then (if you're there and checking, monitoring everything) set your float voltage to the same as the absorb voltage. Sometimes you just have to out-think the engineers. Perhaps generator for a few hours then solar to finish....but finished isn't until you're happy with the SG value.

Ralph

Vic

Re: Specific Gravity...

And, ogm,

How are you measuring your SGs? Hope that it is a high quality glass-flost type Hydro. And too bad that the Xantrex CC does not allow you to set the Return Amps directly. BUT, you can lie about the size of the battery bank, to get that 2% to be the current that you want it to bel.

I had to give up on my Xantrex SCC ... it was too Stupid for the job, and too BUGGY.

Ralph is correct. You could set the Float voltage to be the Asorb V that you want, or do the same with the EQ voltage. And in setting the EQ to the desired Asorb V, you have the ability to terminate that extra charge cycle based on an "EQ" time that you can set.

offgrid me

Re: Specific Gravity...

Vic
Yes I have two good quality glass float hydros. They agree with each other. I like the idea about lying about the battery bank size. I think I will tell it I have a 200ah bank so the absorb cut will be at 4 amp. This should up the absorb time. Another flaw with the xantrex is that Eq time is factory set at 1 hr and can not be modified as far as I can tell. I also found a loose connection between the CC and battery bank last night that may have been part of the problem. High resistance = confused charge controller. We will see.
Ned

samuel

Re: Specific Gravity...

Another flaw with the xantrex is that Eq time is factory set at 1 hr and can not be modified as far as I can tell.

offgrid me, I'm having a similar problem. I'm using Xantrex chargers (PV and generator). The strange thing I'm noticing is that no matter what I do I can't quite get my batteries to a temp-corrected full charge (1.277-1.280 in summer). The Xantrex/generator charger kicks out after 1hr of EQ. An attempt to do a second EQ failed after 18 minutes, and after that point it would fail in about a minute after each attempt. My 6V golf cart batteries are only reaching 1.250 temp corrected SG (1.264/45°F).

offgrid me

Re: Specific Gravity...

Samual
What I do know is that the 6048 inverter charger needs to cycle through a complete charge cycle each time equalize is set. If you try and get it to go right back into equalize it will show a fault. You need to start it at bulk again. It should go through bulk and absorb very quickly and revert back to equalize. I was able to do 3 hrs of eq the other day by doing this.
Ned

Ralph Day

Re: Specific Gravity...

At the risk of repeating myself (I do that a lot anyway), if you're around and in control/monitoring things, set your absorb setpoint up to the eq setpoint...set the "new" absorb time limit and voila! Just remember to re-set the absorb to it's proper voltage and time after your eq charge is done. I have to do this all the time with my SW4048. It's "smart", just not smart enough to do what I want it to do, when I want it to do it:p

Ralph

offgrid me

Re: Specific Gravity...

This sounds like a great idea. Would I reset the absorb voltage just before the cc transitions to float so the batteries would be fully charged before starting the faux equalize charge. Im guessing the cc would never hit the end amp threshold at the higher voltage so would use the ab time threshold instead. Is this correct. Pretty clever Ralph thank you.
Ned

plongson

Re: Specific Gravity...

Here is just an update on the original post, remember the system was suffering from low SG.

I did a closely monitored EQ and got the bank up to about 1.240 before I started to loose sun. I did make changes to the Midnite CC and bumped the absorb to 58.7 and upped the time to 3 hrs from 2.

Yesterday I had GREAT sun all day long, not a cloud and about 45*f. When the system went to FLOAT I had a pretty solid 1.240 across the board. Still not high enough but getting better. I'm gonna give it a few days at this setting to see if they come up even more.

If the SG is still low should I add more absorb time and leave the voltage alone?

I also disconnected the SENSE module from the MAGNUM BMK and let it reset, reconnecting it and thus resetting the reference SOC point. It's gotta be better than it was, and in FLOAT should be somewhere in the 90% range.

westbranch

Re: Specific Gravity...

Paul can you refresh our collective memories, what was the original Absorb V set to?
Reason I ask FWIW is that I found a few tenths of a V change made a noticeable difference with my aging batteries performance when I got started.. as well as a time change, as Ralph has stated.

plongson

Re: Specific Gravity...

It was 57.6v and 2 hours. Now it's 58.7v and 3 hours.

mike95490

Re: Specific Gravity...

What's the water usage / bubbling like at the new voltage ?

plongson

Re: Specific Gravity...

Too soon to tell on water usage, up till now I haven't used any. But bubbling was just moderate when charging. What do you guys consider "normal" water usage??? Topping off how often??

waynefromnscanada

Re: Specific Gravity...

Don't know about others, and it will depend on how the batteries are being used, as well as their age, but I water my 10 year old L 16 batteries about every 3 months.

Grandpaclark61

Re: Specific Gravity...

Hope you can get that figured out! Keep trying stuff, you'll figure it out! I know there are personal tax benefits for having a solar powered home, but are there also business tax incentives for using solar power? I would love to have the same type of system as what's in my home be in my business. Seems like a viable option to me!

jtdiesel65

Re: Specific Gravity...

I used 29.6 for my old surrette t12-250 1000ah bank. Worked fine. Water use could be ~1/2 gal/month.

You might want to look at the history on the classic and see how production corresponds to your expected usage.

I'm curious what your resting voltage is when your SG is at peak?

I would think if resting v is high compared to SG, then electrolyte is stratified which would mean you need to apply high absorb or an EQ voltage.

My new battery is a different manufacturer but 28.8 doesn't move the electrolyte around much. I don't recall that it did much with my old surrettes either. They were chronically undercharged when I got them and the previous owners were using 28.8.

What I would do is bump it to 29.6 and after it's absorb phase, do a mini EQ upwards of 30.5. At 30.5 my battery boils like a pot of water on a stove on a low boil.

plongson

Re: Specific Gravity...

Bumping up the absorb voltage and time to 3 hours brought up the SG to 1.235/40 but still not enough. I'm gonna do an EQ using the genset today and it is a canned 4 hour process with the Magnum PAE. I bulked up this morning before sunup and I'll let the panels bring it to float, then sometime this afternoon, I'll EQ. Probably late in the day so we can use the extra power for something...

I'm almost thinking the daily absorb setting on the Midnite also need a bump like you said. They just aren't getting up where I think they need to be. Man, I'd faint if I I could see 1.260.

jtdiesel65

Re: Specific Gravity...

It could be that size of the battery may require a longer absorb. There is more plate material and electrolyte. Perhaps somebody who knows more about batteries could answer. It sounds like electrolyte is stratified and absorb in ineffective at those lesser voltages. You were probably cycling your battery in the 50-75% range or therebouts. I think you are getting to float because of a timer and have sufficient amps to keep the float voltage, but the battery really isn't charged at that point. So unless you look at SG everything looks ok. This winter I had a long stretch of no sun like a month long. I finally had to run the generator manually. There just wasn't enough sun for proper charge so the battery was hovering in the 75-80% range. I think this is the same scenario that you are seeing. So what I did was run the generator through it's cycle and then forced the generator to do an eq by changing the absorb set point to 30.5. My battery is 1560AH at 24v so it's roughly an 800ah 48v equivalent. It is a forklift battery so setpoints are generally higher than your battery's setpoints. My absorb is 3 hrs at 29.6. This is actually the same as what i used with my old surrettes. I think you will probably have some trial and error until you get the correct voltage and length of absorb that keeps your batteries charged without too much water usage.

BB.

Re: Specific Gravity...

And when "equalizing", check the SG of "all cells" once every 60 minutes. When the specific gravity of "all cells" stops rising between readings. Stop the equalization and save your generator fuel plus wear & tear on the batteries. That is about the best you can do.

-Bill

plongson

Re: Specific Gravity...

Jt, that's what I'm starting to think. All my indicators say it is in a state of full charge, but the SG says NO...I too think I've been running in a low state of charge. If I get a good EQ going should I see 1.260? If I plow in enough amps and enough time on the genset, it shouldn't have any chance but to go up?

BB, When I get going in a bit, I'll be sure to monitor all cell hourly.Thats good advise.

I'm also going to bump the absorb time to 4 hours on the midnite CC, and leave the voltage alone for a few days. I'm thinking if I can get the SG up and hold it there I might be good too go.

I'll let you guys know how it goes later.

Paul