90AH capacity AGM, 18AH from full, How long to full?

[SternWake]

At 10:42 my battery monitor indicated 18AH from full.  I want some hot water in the morning for a post surf rinse/ crevice wash, so I plug into the grid so my 50 watt heating pad heat my 5 gallon shower bag.  Might as well top off the battery too.

I plugged in my 40 amp power supply, set to ~ 15 volts to ensure it maxes out power supply.  

In about 3 seconds of 40 amps, voltage had already risen to 14.5v, and amps started tapering, I back off the voltage dial to keep it below 14.6v.

  Without increasing voltage further, there is NO WAY to recharge this battery any faster at this point.  Northstar recommends 14.46v absorption voltage at 77F.  I'll guess my battery is around 64F.

 If the battery was more depleted, it would have taken much longer for voltage to rise to 14.5v.
If the battery were newer( It  ~2.5 years old), and did not have ~240 deep cycles( 50 to 60%) on it and another 100+ shallow cycles to 80% SOC, voltage would have risen slower.

@ 10:52  14.5v accepting 19.2 amps and Ah counter reads 13 from full
@ 11:05 14.5v accepting 13.1 amps , 9AH from full
@11:17  14.5v 9.2 amps 7Ah from full.


When amps taper to 0.4 at 14.5v, this AGM battery can be considered 100% fully charged, a lead acid battery getting its happy ending.

Any Guesses as to how much longer it will take to reach this point? 

 

It's only 7Ah away from full, can't take long right??

@ 11:23 14.5v 8.1 amps,  6Ah from full.

@ 11:28 14.5v 7.2 amps, 5Ah from full

I'll see if when the AH counter returns to zero from full, if Amps also taper to 0.4a at that point, when held at 14.5v.

I've never really monitored such a generally shallow discharge to full.

@72 amp hours of 90 Total, the battery should have been at 80% State of charge, if it actually still has 90AH capacity, which is unlikely at 2.5 years and 250+ deep cycles.

So some room for error here.
@ 11:40 14.5v 5.6 amps 4Ah from full

Only "4" AH to go, how much longer will it take until amps taper to 0.4?

Will My Blue Sky IPN pro remote battery monitor be correct, will AH read 0 from full the same time amps taper to 0.4a at 14.5v?

Stay tuned......

yawn

or not.


I'm suspecting the AH counter will read 0ah from full, well before amps taper to 0.4.

I usually ignore the % remaining screen usually, but it says 96% at 11:46

 

[SternWake]

@12:42, 2 hours into test...

14.5v, accepting 1.7 amps and 1Ah from full.

The 1Ah from full is incorrect, it is going to flip to 0AH from full and 100% any second now, but the battery is not full until amps taper to 0.4. LIAR!

I will be rezeroing the battery monitor after this test. the next time the solar controller reverts to float voltage it will reset the 'full' marker, and then it will slowly drift away from that accuracy again.

I'll guess another hour before amps taper to [email protected]

 

[SternWake]

@12:52 battery monitor reads 100%, 0Ah from full

Battery is not full, still accepting 1.4 amps at 14.5v.

 

[SternWake]

@1:21 14.5v accepting 0.8amps

Only 0.4a more tapering to go until full.

 

[SternWake]

@2:12am 14.5v accepting 0.4 amps.

Double check IPN pro remote battery monitor with clamp on meter.......... 0.41 amps.

Reduce voltage to 13.6v, reset battery monitor.

So 3 hours 30 minutes to get from 80% charged to 100% charged, returning ~18AH.
This is as fast as this battery can possible be recharged in this range.

This is with a charging source capable of sustaining 40 amps and holding the proper absorption voltage required. Since 40 amps on initial application, only took 3 seconds to bring battery voltage to 14.5v, A more powerful charging source could NOT charge it any faster, unless voltage was allowed to go higher, beyond the manufacturer recommendations of maximum voltage.

I think the battery was closer to 19Ah from full when started as the battery monitor was obviously off. It took 1.5 more hours at 14.5v after the monitor indicated 100% and 0Ah from full for the battery to actually be full. Perhaps a trimetric or Victron or other AH counting battery monitor would be more accurate, IDK.

This particular Northstar AGM battery also needs the High amp recharge from a lower state of charge every so often, to perform well. This battery got a 40 amp recharge from 60% 2 nights ago, so that 3.5 hour figure is still accurate enough for this test.

This time of year, if Sunny, my 198 watts of solar has enough time to hold 14.5v until 0.4amps, but 4 or 5 cycles of solar only, lower and slower recharge, then battery performance tanks. Voltage held for the same Ah removed is noticeably lower and gets worse each cycle, until it gets that high amp recharge.

This AGM is NOT a good solar only recharge battery for this reason, but especially when discharged to the 50% range
regularly. Even if the solar can hold ABSV for long enough for amps to taper to 0.4v at 14.5, it is not enough to maintain peak performance. It simply needs the high amp recharge every so often to remain near its potential,.
Each low and slow solar only recharge, the time it takes for amps to taper to 0.4a at 14.5v increases.

I've seen it take 10 hours for amps to taper from 2 amps to 0.4 amps after 2 weeks of Solar only and incomplete charging.

SO, if you have an AGM, and do not have an Ammeter, you do not know when the battery is indeed fully charged, and it will suffer a shorter lifespan, more noticeable with deeper discharges.

If you have a flooded battery, the amps will not taper as much. When only 2 to 3 amps are required to hold the100AH capacity flooded deep cycle battery at manufacturer recommended absorption voltage, adjusted for battery temperature, then the battery is in the 99 to 100% charged range.

but, With a flooded battery, one can dip a hydrometer, compensate for electrolyte temperature and get a true reading as to state of charge.

The blinking green light on your solar controller or 'smart' charger, indicating full charge, is lying to you, unless you can verify it is not. If you cannot, then it mocks you, and your battery will not live as long as it could.

How much longer? Impossible to guess. Can you set the time at absorption voltage, or the amp threshold at which float voltage is triggered? If so, then do so, and use an Ammeter or a hydrometer to see how long this requires.

My point in this thread is to demonstrate just how long it takes to get from 80% to 100%, with a high quality and hard working, but well cared for AGM battery.

Flooded batteries will likely require longer times in to go from 80% to 100% than the northstar AGM battery used in this demonstration.

And all sulfated/aged/abused/chronically undercharged batteries, depending on the level of sulfation, will take significantly longer than this to reach 100% charged. They need more time held at absorption voltage.

And attaining a TRUE 100% charge regularly, often, is the key to maximizing Lead acid,( Flooded/AGM or GEL), battery longevity.
98% charged is not good enough to achieve ideal maximum potential lifespan, but 98% could yield an 'acceptable' lifespan.

'Acceptable' is subjective and different for everybody.
Ideal is pretty absolute.

Find your happy medium, armed with the knowledge of what ideal is.
Don't assume your charging sources know when the battery is full. They are guessing, and likely mocking you.

But they are only batteries, and only rented.

 

[BradKW]

Hey Sternwake, I was just wondering if you give your batteries names?

I mean, it's totally cool if you do, and I think you should feel comfortable sharing that here. I'm sure that they each have individual personalities that become very apparent after hours of conversations...

 

[TMG51]

Hey Sternwake, I was just wondering if you give your batteries names?  

I mean, it's totally cool if you do, and I think you should feel comfortable sharing that here. I'm sure that they each have individual personalities that become very apparent after hours of conversations...

This makes me think of the line from Count of Monte Cristo, and the exchange between Edmond Dantes and Abbe Faria when they first meet. Edmond: "There are 72,519 stones in my walls. I've counted them many times."

Abbe Faria: "But have you named them yet?"

I think Stern is gettin' there. But we benefit from his descent into madness.

 

[highdesertranger]

nice write up. I hope people pay attention to how long it actually takes to fully recharge a battery. highdesertranger

 

[jimindenver]

See, this is what happens when you do not have quality entertainment. lol

Stern

Both of my controllers tell me what is being accepted by my bank. When it's idle it does take a while to get down to the mark I need for "full" but it gets there. In use there are constant draws on the system and while the solar can out pace the loads and get it full, it's impossible to know that it is.

 

[SternWake]

Good point about a solar controller amp display, It does not know the loads on the battery at the time as the shunt or hall effect sensor is in the controller, Not between battery and loads/sources

YOu could put a clamp on meter over a battery cable near the battery and see how much the battery is taking of that solar output, and see how much the loads are consuming. The clamp on ammeter is a wonderful enlightening tool.

What is nice about my Blue Sky IPN pro remote is it works with my BS sb2512i solar controller, so when there is only 0.4amps going into the battery, monitored with a shunt between battery and loads/sources, does it decide to end absorption voltage and let float begin.  The system might be making 10+ amps and 9.5 of those will be going to power loads.

I do have the absorption timer set at 3.5 hours too.

My battery monitor is at my right hand when I sit in my third chair, laptop in place and my TV on, feet up on my bed, so actually monitoring the progress of this 80 to 100% charge was hardly something that took any effort. Press button, notice time, return to screens.
 The meanwell power supply was doing all the work.  The only effort I put into this test was busting out my clamp on Ammeter and hooking it over the ground cables to my as yet nameless battery to verify, as it reads to the hundredth of a amp and my monitor is only the tenth of an amp.

It took about 30 minutes for amps to taper to 0.4 from 0.5.

So from 99+% to 100% took a half hour, and 99.5% does not cut it either, in the ideal battery longevity department.

So no, no naming the battery, even though they do have distinctive personalities if one has the tools and desire to notice. That would be as crazy as believing a blinking green light saying all is well, or thinking a drive to the store and back is enough to fully charge a depleted battery, because a voltmeter displayed 13+ volts on engine shutdown.

Just trying to remove some of the mystery of battery charging, hoping to prevent premature batterycide, and save people money and hassle.  "cheap" is in the forum title afterall, and batteries are not cheap.

  It has always been a pain in the ass when the battery's capacity is so diminished to  no longer be acceptable and replacement is necessary.  Dreading that day, I decide to make them recur as far apart as possible, and I can say that day is no where near my immediate future, with total confidence.

And I only have one the one battery, for house and engine starting duties. 

 8 years ago I had 345Ah of total capacity and was replacing 230Ah of that capacity every 2 years, because I did not understand that I was not fully charging them, even though that green light on my system said I was, and kept saying all was well, when it was anything but.


You  faithful green light followers could be bitch slapped at any time by reality too.

80 to 100% takes 3.5 hours on my healthy  hard working AGM. It can be achieved no faster, not by any magical charging source or faith in a higher power.
 It could take 5 hours on your chronically undercharged, capacity compromised marine battery, but that solar controller will happily throw that green light at you after 2 hours and whisper soothingly over and over, day after day that everything is 'just fine'.

  There is bliss in ignorance and ignorance in bliss, until the 'just fine' genie dives in for that 5 finger prostate exam of reality.

 

[666JTK666]

5 finger prostate exam of reality.

Love that discriptor , going to right that one down.

 

[regis101]

So standing nekkid out in the front yard sprinklers on one foot facing true north with the right hand index finger touching the nose while the left hand has a firm grasp on a glass of cheap red wine isn't helping just yet.  Maybe I should try mag north.
nah, just kidding.  Very good read, as usual.  Thank you a hundred times over.
I did copy/paste this from above.  
"SO, if you have an AGM, and do not have an Ammeter, you do not know when the battery is indeed fully charged,"
any brand name in mind?  I have a cheapy craftsman VOM with clamp style ammeter.  That could prolly work.  Won't know until I try I guess.  Might have to start doing my own testing this weekend now that the MB 37qt freezer if safely tied into place.

 

[user 37446]

Wow, after reading all that well recorded and described information, I'm glad that I will be budgeting for at least a 2:1 solar ratio and drive 30 plus minutes daily (that's the plan since I will still work) with the thick cabling from the alternator...  While that is decidedly unscientific, I just don't see myself going through all the SW info to keep the servant battery going another 100 cycles or another year.  

Kudos to those of you who can or who will do this monitoring, it's very accurate and will lead to much longer battery life and more efficient use of your resource(s), however I will continue to assist the economy and destroy the planet by buying a new AGM battery sooner than I should have.

 

[regis101]

...every coupla years. There. Added that in fer ya. Or maybe thats me. yeah. Thats it

 

[regis101]

I'm at the very very beginning of all this madness.  I absolutely love reading all this stuff.  Over and over and over.

My rig is at the bottom of the spectrum.  Our Vanagon Weekender is factory set up with an aux battery wiring charging system , piggy backing, off the starting battery via a relay so as not to drain the starting battery.  I just bought an sla1161 44aH duracell AGM since thats about all that will fit the battery box these days.  OE would be a group 41 or 42., same size as the starting battery.

So.  So far everything is wrong.  Or at least not better than it can be.  

Using the new to us portable freezer will allow me to monitor its power requirements and beat up on the battery.   It's going to get a shakedown run next weekend as a four dayer.  I will have shore power at the campsite. No solar since I'm still shopping and want to go through amazon to put coin in Bob's pocket, but agree with the 2:1.  Almost seems like a must have.  I still have an itoa from a previous project that I attached jumper cables onto and can charge up that way from the shore power pedestal.

...and the band played on

 

[user 37446]

I'm at the very very beginning of all this madness.  I absolutely love reading all this stuff.  Over and over and over.

My rig is at the bottom of the spectrum.  Our Vanagon Weekender is factory set up with an aux battery wiring charging system , piggy backing, off the starting battery via a relay so as not to drain the starting battery.  I just bought an sla1161 44aH duracell AGM since thats about all that will fit the battery box these days.  OE would be a group 41 or 42., same size as the starting battery.

So.  So far everything is wrong.  Or at least not better than it can be.  

Using the new to us portable freezer will allow me to monitor its power requirements and beat up on the battery.   It's going to get a shakedown run next weekend as a four dayer.  I will have shore power at the campsite. No solar since I'm still shopping and want to go through amazon to put coin in Bob's pocket, but agree with the 2:1.  Almost seems like a must have.  I still have an itoa from a previous project that I attached jumper cables onto and can charge up that way from the shore power pedestal.

...and the band played on

Thanks for adding that postscript, you're likely correct!!

Have you read Sternwakes thread where he busts on himself about the evolution of a dweller's electrical system?  I'm in good company!  

 

[regis101]

Fer schure. I've been rolling trolling using abusing this site for a while now.
Always trying to pick up what others are putting down. Hurts sometimes but I get over it.