What is the optimal SOC range for cycling lead acid batteries?

Re: What is the optimal SOC range for cycling lead acid batteries?

I removed the sacrificial anode from my sdhw tank (to change the thermosiphoning characteristics...it got better). Are these anodes not present in most water heaters anymore? My understanding is the anode sacrifices (gives off ions or corrodes away to nothing eventually) to save the heating elements.

Ralph

Re: What is the optimal SOC range for cycling lead acid batteries?

vtmaps wrote: »

That's not good. From the wind-sun battery FAQ: Over at batteryfaq.org they say much the same, except they recommend cycles be at least 10%.

Welll my point was "shouldnt my charge controller know best". Apparently not.

I'm not sure how applicable this advice is to AGM batteries... my understanding (which is limited) is that they tolerate floating better than flooded cells.

Quite, they are a mystery to me as well.

but I am starting to notice more voltage sag with even moderate loads. I take this to mean that I am developing increased internal resistance because of positive plate corrosion.

Around here they say (for FLA anyway) to increase the voltages by 0.1V each year of the batterys age. At year 10 that would make absorb and float 1.0V higher. Its a way to overcome the growing internal resistance.

Stephendv has written about how the sunny island will not do a daily absorb unless the batteries are discharged far enough. I don't think I can easily mimic that with my controller,

This and your other comments below make your average charge controller look postively dumb. In a web connected world tomorows forecast is a simple http api request away.

but I am hopeful that lower absorb voltage with longer absorb time will have much the same beneficial effect.

What do you think of using EQ?

BoB: "I still believe it is better to overcharge and watch the electrolyte level than to undercharge.... That is, to err on the side of overcharging... If you have only those 2 choices."

Isnt that at odds with the premise of this thread? Because of positive plate grid erosion, that lead acid is better operated primarily in the mid zone, with regular but less frequent absorbs?

Re: What is the optimal SOC range for cycling lead acid batteries?

vtmaps wrote: »

Do you mean using EQ as a method of doing the periodic full charge? I suppose that might work. I've never used automatic EQ, and I seem to remember some discussion here about how some controllers, when they do automatic EQ, do not do a complete absorb first. Some controllers do not go into float after EQ. I plan to stick with manual EQ.

Some/most batteries need an equalizing charge, of flooded lead acid batteries, only Trojan batteries do not recommend a regular Equalizing charge(that I am aware of). Large forklift batteries should be equalized at least monthly as maintenance. There is also corrective equalizing which done to correct battery imbalances, and should be monitored. I've been quite happy to let my charge controller do maintenance equalizing every 30 days.

Re: What is the optimal SOC range for cycling lead acid batteries?

What i was suggesting, as a way to prevent the bank reaching 100% each day, is to reduce the absorb voltage to the float voltage, then set the eq voltage to the absoorb voltage, and set it to run every 7 days. As a way to prevent daily absorbs on banks with high SOC. The long pm floats will probably still bring the SOC up to 100% in many cases, but lowering the float voltage would combat that.

This is of interest:
"Disadvantages of the traditional 3-step charge curve:
• During the bulk phase the current is kept at a constant and often high level, even after the gassing voltage (14,34 V
for a 12 V battery) has been exceeded. This can lead to excessive gas pressure in the battery. Some gas will escape
trough the safety valves, reducing service life.

• Thereafter the absorption voltage is applied during a fixed period of time, irrespective of how deep the battery has
been discharged previously. A full absorption period after a shallow discharge will overcharge the battery, again
reducing service life. (a. o. due to accelerated corrosion of the positive plates)

• Research has shown that battery life can be increased by decreasing float voltage to an even lower level when the
battery is not in use.

http://www.victronenergy.com/upload/documents/Datasheet%20-%20GEL%20and%20AGM%20Batteries%20-%20rev%2007%20-%20EN.pdf

Re: What is the optimal SOC range for cycling lead acid batteries?

ChrisOlson wrote: »

My XW-MPPT60's don't do that. If our batteries go thru a normal absorb and get to float - then my wife turns on something big and makes the voltage drop to the Recharge Volts, the MPPT60's will take the battery back up to absorb after the load is off. But they will absorb for only a very short time before returning to float.
--
Chris

Since (temperature compensation aside) the Absorb stage will always use the same voltage, the timing of that Absorb stage will either be calculated by the CC in advance based on a fixed time, a time dependent on the length of the Bulk stage, or some combination of the two.
For the Absorb to be cut short based on the SOC of the battery, it is necessary to have a CC which terminates Absorb when the battery current drops below a set value. In some CCs with this feature, the End Amps setting is derived from the battery bank size (in AH) that you entered, in others it is a separate setting. In either case, if the CC supports it, it usually needs to be specifically enabled before it will be used.

Re: What is the optimal SOC range for cycling lead acid batteries?

THANK YOU THANK YOU



to everyone for your thoughts. Let me give you a bit of background and then ask another question.


The reason that I set the absorb for about 4 hours, and 14.7 was for several reasons.

We have had many friends of ours using Surrette's here and after a few years they are not holding a charge very we'll. After speaking to steve at Rolls his thoughts and mine where that the batteries were not receiving an adequate charge and in turn getting heavy sulfating on the plates.

After several weeks of adjust settings and such on our system, at the end of the day the SG's were only 1.260. I thought well maybe I have stumbled on the problem; the charge controller that we use here OB are not properly charging the batteries and the Rolls want more charge.

Steve at rolls had suggested that I should really try to get this number up to 1.275. I had a very difficult time getting the Outback to get the proper charge to get the SG's up. Yet when I called back to Rolls and spoke to someone else they suggested that as our ambient temp is 80F then 1.260 is a full charge. Does anyone know how to calculate the proper SG's based on ambient temps?

I was able to reach this 1.260 by adjusting the absorb time. I really don't want to have these batteries around for some time.

After reading much of what everyone suggested, I was left with a couple of questions:

"It seems like absorbing for 4 hours every day is a little excessive for batteries that only get discharged to 80% SOC every day. I hate timer-based chargers because they tend to do that. Is there any way that you can calculate your load amps, add in 2% of the amp-hour capacity, and use that for the ending amps so the charger exits absorb when the net current to the battery drops to 14 amps?


if 4 hours is excessive, then by your math I would calculate the end amps like so

Load amps are that which I am using,

freezer run 5a with about 7-8 hours a day of run time
If the water pumps comes on, maybe every two days it does that that changes this number to 11, what to do with that?

percentage of battery AH capacity would be .02*350=7

This would mean that 12 would be the number

Because there are a few items that get added each day maybe 14 would be correct. So your suggestion is to keep the 14.7 absorb, add an end amps time of 14 amps. Let it run for a few weeks and check SG's see how things are looking. If things look good then bump up the voltage to 15? Float voltage would be set to 13.1 and that would be correct?

This would reduce the overcharging and extend the life of the batteries. I can use more current, but at this point we have more than we need and have at times just turned on all the lights in the house, but at 2 amps for the whole house it is not a large load!


The other thought I had was what if I kept everything set as it, 14.7 for 4 hours for absorb and 13.1, every other day I just shut of the PV array and just charge batteries every other day?


Thanks and Thoughts

Ben