Battery life lessons

[Woutah]

We bought a fully off-grid property with lead acid batteries about a year and a half ago, which were already not in the best state ever. At that point, we hadn't even heard about charge controllers, lead acid batteries, ...
https://www.solarpaneltalk.com/forum...your-batteries... already makes a lot more sense to me, compared to a year ago when I had absolutely no knowledge whatsoever. I now feel confident-ish to start asking some questions...

In winter time, here in Portugal where I live, we only get 4 hours of proper sunlight due to hills in the east/ west (days are about 8 hours). We use about 1.5 kW every day (on non- hoovering days) and with float set to 14.8 we generate about 1.5 kW/ day. When we set EQ (15.4) on in the morning, we'd generate about 2.5 kW/ day
I'd like to get to a better understanding of some (basic concepts) to adjust the settings to make sure we get most out of our new batteries in the future and to see how far we can stretch the life of our current battery.

The specific gravity has not been at its peak compared to measurements in September/ October (where we'd get more than the double of direct sun)
1. If Absorb and Float are both set to 14.8, what's the difference between the two stages? I want to find out what I should do with the time for the absorb phase.
2. If Float and EQ are both set to 15.4 and currently the battery is on 15.0V, would float and EQ at that point behave the same?
3. Currently absorb/ float is set to 15; if I let's say up this to 15.2 then this basically becomes the same as my EQ V was in summer time. In the sticky thread, I read that you shouldn't EQ too often so I don't know what to make/ do with this info. I understand this is to avoid corrosion, but should I worry about this having 6-year-old batteries which went unmanaged through many of these winters.
Can I go too high with float voltage (as long as I don't go over my batteries max Voltage)?
W

[Mike90250]

Read some stickies (link below) - you have some incorrect info you typed out

https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/general-batteries

EQ'a should be done in limited amounts every other month is good.

if your SG is low. you must run your generator, preferably in AM, so the solar can finish the absorb & bulk parts of the cycle. When the SG is low for more than 24 hours, the sulfate crystals start to harden and become difficult to return to solution. This is called Sufated Battery and generally, cannot be easily reversed, the longer it sits low (below 80% of full) the deeper the damage

[Mike90250]

Absorb & BULK are generally the same voltage, Float is a slightly lower voltage to gently finish charging and not stress the battery too much. Float will seldom happen wintertime, off grid

If you can't extend your Absorb time longer, increase the Bulk/absorb voltage slightly ( just 0.2 v at a time) till you see some current (amps) reduction part way through absorb. A week of long absorbs may be needed to get the battery charged enough to be able to EQ it. Only a fully charged battery can be EQ'd

If your batteries are 6 years old, they may have reached their End of Life. What was the warranty on them ?

[Woutah]

Read some stickies (link below) - you have some incorrect info you typed out

https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/general-batteries

EQ'a should be done in limited amounts every other month is good.

if your SG is low. you must run your generator, preferably in AM, so the solar can finish the absorb & bulk parts of the cycle. When the SG is low for more than 24 hours, the sulfate crystals start to harden and become difficult to return to solution. This is called Sufated Battery and generally, cannot be easily reversed, the longer it sits low (below 80% of full) the deeper the damage

Thanks Mike - I understand that if you can't get enough power from the sun, you need to use the generator. However, I'm trying to configure my voltage points in the best way. (I appreciate that for my current out of warranty batteries all hope is lost, but we take this as a good time to learn as much as we can )
I read the sticky threads and based on that I've set Absorb = float which triggered the questions I asked.
I more or less understand the different phases if we'd have 20 hours of sun every day, but want to make sure I get as much charge to my batteries now in winter time as I understand it's silly to have my batteries float at 13.7 if there are only 4, 5 hours of proper sun to be used.

ps: This is from the sticky thread
"

[Sunking]

1. If Absorb and Float are both set to 14.8, what's the difference between the two stages? I want to find out what I should do with the time for the absorb phase.

Only difference is voltage set point. Absorb, Float and Equalize are Constant Voltage modes. Absorb is not a timed event. Thus why solar charge controllers fail to completely charge batteries. Absorb is a Current Event. Full charge is achieved when charge current tapers to 3% of C. That can take 6 to 10 hours. Equalization can take up to 24 hours.

Three stage charging does not work with Solar because the sun does not shine 24 hours. You have to use you hydrometer to set voltages. You want to force your controller to be a simple CC/CV charger and the way you do that is set Bulk = Absorb = Float. Start at 14.4 volts. As the sun sets check specific gravity. If it is low, raise the voltage. This time of year you will likely find there is no voltage high enough. There is simply not enough sun. This is why you must have a generator.

Take Mike's advice and read the stickies. Starting with this one.

[Mike90250]

What stickie says set "Absorb = float" ? That needs correction or further investigation. Bulk=Absorb, Float is for long term idle, and generally not useful in solar, or in winter

Setting BULK=ABSORB=FLOAT is valid, for short sun hours, but you can overcharge batteries in the summer with that setting.

[citabria]

Mike , you suffering from old timers disease like some of us? https://www.solarpaneltalk.com/forum...ge-controllers
This is how I found this forum.

[Sunking]

What stickie says set "Absorb = float" ?

This is 1 or 3 of them.

That needs correction or further investigation. Bulk=Absorb, Float is for long term idle, and generally not useful in solar, or in winter

Mike you can fully charge a Pb battery with a Float Charger. In fact it is the best way and maximizes battery life. It just takes up to 24 hours which is useless for solar and daily cycle applications. I really dislike names like Bulk, Absorb, Float etc because they are meaningless terms. Every charger made, with the exception of some nickel base chargers. are CC/CV. Only difference between Bulk/Absorb/Float is a voltage set point. Regardless of what voltage you use to any charger is CC/CV and all behave the exact same way. Float voltage ranges from 13.2 to 13.8 volts. Bulk/Absorb voltage ranges greatly from 14.8 to 16.2 volts

Setting BULK=ABSORB=FLOAT is valid, for short sun hours, but you can overcharge batteries in the summer with that setting.

I agree with a caveat. That assumes the system was properly sized to begin with. Rarely does that ever happen. Without a hydrometer, a user has no clue what is going on.

Bottom line is a user has two charge options.

1. Under charge
2. Over charge

Under charging yields shortest battery cycle life and lowest capacity. There is no such thing as perfect for solar. You want to error on the over charge side of the razor blade. The only way to balance on the Razor's edge is with a precise Float Charger using temp compensation and a hydrometer like a telephone or utility uses.

[Woutah]

What stickie says set "Absorb = float" ? That needs correction or further investigation. Bulk=Absorb, Float is for long term idle, and generally not useful in solar, or in winter

Setting BULK=ABSORB=FLOAT is valid, for short sun hours, but you can overcharge batteries in the summer with that setting.

my previous post got cut off - the questions came from the you're killing your batteries sticky thread.
The question does indeed related to the winter period, I understand that if there's more sun I should lower my voltage points.

[Woutah]

Only difference is voltage set point. Absorb, Float and Equalize are Constant Voltage modes. Absorb is not a timed event. Thus why solar charge controllers fail to completely charge batteries. Absorb is a Current Event. Full charge is achieved when charge current tapers to 3% of C. That can take 6 to 10 hours. Equalization can take up to 24 hours.

Three stage charging does not work with Solar because the sun does not shine 24 hours. You have to use you hydrometer to set voltages. You want to force your controller to be a simple CC/CV charger and the way you do that is set Bulk = Absorb = Float. Start at 14.4 volts. As the sun sets check specific gravity. If it is low, raise the voltage. This time of year you will likely find there is no voltage high enough. There is simply not enough sun. This is why you must have a generator.

Take Mike's advice and read the stickies. Starting with this one.

Thanks - believe me, I read the stickies multiple times. A year ago I understood absolutely nothing of them, now I understand the concept and am learning every time I re-read them. Believe me, they are hugely appreciated!
I understand I need to use my generator on a regular basis to fully charge my batteries - clear.
Back to my questions. I'm asking as I don't want to make false assumptions!
1. I set bulk = absorb = float. I understand absorb is not a timed event, but I have to set a time. So what do I put here?
2 & 3. "If it is low, raise the voltage" If at the end of the day the specific gravity is not at its maximum, I just up my Voltage levels? I can keep increasing till either I've reached the max level allowed by the battery manufacturer or till I'd reach the max spec. gravity (probably won't happen without genny, but in theory...)

I hope my questions are more clear now!

[Sunking]

Back to my questions. I'm asking as I don't want to make false assumptions!
1. I set bulk = absorb = float. I understand absorb is not a timed event, but I have to set a time. So what do I put here?

You are asking good questions. Enter max time like 4 or 6 hours. Essentially you will not have any Absorb phase. By setting Bulk = Absorb = Float converts your charge controller from a 3-Stage Charging Algorithm to a simple CC/CV charger. There is NO Absorb mode so it is a moot point other than you must set it to something.

2 & 3. "If it is low, raise the voltage" If at the end of the day the specific gravity is not at its maximum, I just up my Voltage levels?

Correct. However you may very well exceed the manufactures maximum range for Bulk/Absorb. Keep in mind in summer months you might very well be able to switch back to 3-Stage charging where you can set Bulk/Absorb to say 14.8 volts and Float to 13.5 volts. But in winter months despite going to maximum allowable voltage of your controller, it is possible you never reach full charge and have to use the genny once a week.

In winter months despite say setting the voltage to 15 volts, you may not ever see the battery get close to 15 volts. Example 14 volts may be the highest you see by sunset. If that is the case, you never reached gassing voltage (14.4ish). Next day the voltage may struggle to see 13.9 volts. That is called deficit charging with each passing day your battery is getting weaker and weaker and sulphation is growing robbing you of cycle life and capacity.

What you are doing is forcing your controller is to stay in Constant Current Mode (aka Bulk) which means it is harvesting using every watt the panels can produce from sunrise to sunset. The Controller never reaches the Constant Voltage Stage aka Absorb/Float/Equalize. Ideally what you are shooting for is at some point in the afternoon the batteries reach the set point voltage of say 15 volts and charge current starts to taper off before sunset, and specific gravity indicates full charge. When you see that happen, lower the voltage a bit and see what happens the next day.

You want to error on the over charge side if possible. Most likely you will see undercharging in winter which is telling you your panel wattage is too low. If you have a genny, chronic undercharging is not a big deal because it can be corrected with the genny. Just do not get in the habit of running the genny every day as that results in chronic Over Charging which needs to be avoided. If the panel wattage is correct, you should only have one month out of the year you need to run the genny once a week to top the batteries off. If you find yourself needing to run the genny every few days in winter is screaming telling you do not have enough panel wattage.

[Matrix]

I understand your dilemma. I have been there ( I usual AM there - Constant state of consfussion.) I have set my Absorb times to max on both my solar CC and my gen powered / AC powered inverter-charger. And if I set my voltage to the manufacture voltage of 29.6v (for a 24v system) I NEVER get a fully charged battery according to SG ... and I have 2 different hydrometers. The CCs never time out, they just reach a point and turn off charging, but the batteries are never fully charged. So have gone to upping the voltages until charged. Presently I am at 30.8v for absorb and my end amp setting (one of the 2 CCs has an end amp setting) is set to 5.7 amps on a 435 AH battery (which I know is low ... but it allows the CC to stay in absorb longer) on the system and at this point I seem to reach fully charged according to SG. But I have never had a time issue concerning the absorb timer. The system stops charging way before i hit absorb time ... based on amps.

SunKing, I see what your saying about float and Solar chargers ... but I run into the problem of not getting fully charged according to SG with my inverter-charger too ... UNLESS I set the volts higher than manufacture. I have no realistic absorb time cut off, the system just stops charging too soon unless I have the volts set to 30.8v

[littleharbor]

I see wide variations in voltage meter accuracy. Have you taken a voltage reading AT the batteries with a known accurate DVM? Could be different than your CC or inverter/charger is reading.

[Matrix]

I see wide variations in voltage meter accuracy. Have you taken a voltage reading AT the batteries with a known accurate DVM? Could be different than your CC or inverter/charger is reading.

Yes. While Charging, in Float and Resting ... They all match. I have a fairly accurate DVM

[Matrix]

I just went outside and did a full SG on all 12 cells. (4 batteries) Yes I have temp compensation set in my solar CC.

Conditions:
- 12:30pm / 45* F / Cloudy
- My 2.5kw array can produce at best 350 watts today
- Batteries started the day at 97%
- CC says batteries are at 100% by 12pm

SG readings
- Highest single cell 1.291 (all 3 cells in that one battery were over charged)
- Lowest single Cell 1.273
- On average, 3 batteries are at 100% or better
- 1 battery is over charged at an average SG of 1.289
- all batteries are at 100% or higher when SG is averaged per battery (not for the whole bank)

Do I lower my Absorb from 30.8v to 30.6v to not over charge the 1 over charged battery ... or keep it at 30.8v to insure all 4 batteries are at 100% even though one battery is getting over charged?