Please Remind Me--AGMs to Full by Ammeter Action?

[BFL13]

Probably LY, maybe Mex, but there was something about the way an AGM will initially be seen to get to Full by getting to lowest amps at a voltage--say 14.8v (charging spec for my AGMs) then --this is where I can't remember the post(s) on this---amps can rise again?

I finally got an ammeter (Trimetric) on my two 100ah AGMs in parallel during a recharge and they worked their way up to 14.8 then after a while, amps tapered down to about 0.9 for the pair.

I turned the voltage down to 13.7 for the night and this morning (at 0.01 amp at 13.7 for the pair) turned it back to 14.8 to see if amps would drop to zero like Phil gets as his idea of Full. (Only he does that with 13.8) So amps were back up to 0.9 again at the higher voltage, but later I noticed 1.0 and then 1.1 so amps were rising slowly. Same voltage.

I remember something was posted about that and what it all means, or at least I think I remember something about that 🙂

Anybody know about this? Thanks.

[MEXICOWANDERER]

"So that is the point of the OP- to make sure I get them truly full on a recharge at home, and no errors......without breaking a sweat.

[BFL13]

Mex is right again!

You can way over-do fussing with the batteries, when it is so cheap to just replace them every few years.

The advantage of fussing with batteries and not having to replace them yet, is to be able to run a big inverter off a battery bank (that is still in good shape) to run the high amp drawing 120v appliances without too much voltage drop that would trigger the inverter alarm at 11v, and keep doing that down to 50% SOC on the inverter's batteries.

Anybody can go Rving for a long weekend on a pair of 27s as long as he doesn't have a big inverter. This is all about pushing the envelope using what you have, if you do rely on a big inverter to run the MW etc..

EG, I have learned on here that a pair of AGMs can do as well as four 6s for running the big inverter. I have tried it and it works out. So I am fussy about my AGMs since they are only 100AH each and cost a bundle.

I have the new to us Class C rigged up with the big inverter on just the two AGMs, while the rest of the rig 12v runs on a different bank of four older Wet batts. Each batt bank has its own converter and can be fast-charged from a portable gen, and each will have its own solar array--similar to how I did the 5er in 2013 in one of my set-ups back then.

I am not nearly so fussy about those four Wet batts, because I can make up for any abuse by Equalizing, adding water, kicking them, whatever--but I can't do all that with the AGMs. Gotta treat them right! So that is the point of the OP- to make sure I get them truly full on a recharge at home, and no errors.

[pnichols]

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[pnichols]

BF,

Batteries are also like peanuts - you can't have just one "jar". :B

[MEXICOWANDERER]

"Adequate years of service performance and lifespan is the ultimate BS detector"

Too bad this cannot be "adequately" translated universally. Perceptions vary.

$ invested per kWh transacted is the ultimate formula but how many folks would understand how to audit such as this - never mind do it.

On a giant system it costs X total gross $ to extract "X" kWh of energy from a battery bank. It includes costs of first generation purchase of storage batteries, cost of recharging mode, cost of installation, subjective "cost" of maintenance, and ambiguous determination of end-of-service life capacity.

Complicated by adjustments of amortization for subsequent replacement of batteries, repair of charging and electrical transmission circuits. AKA cables, terminals, all maintenance. Includes $ distilled water for flooded batteries.

A full system audit demands meticulous record keeping, including maintenance man hours, cost of procuring fuel, man hours to clean solar panels, cost projection for warranty claims, etc.

To say this exercises the keypad of a calculator may be an understatement.

It can only be rationalized on an extremely large system.

[BFL13]

Amps are like peanuts--you can't have just one.

It was about ten years ago that the evil time2roll (who used to be smk) who suggested I use two Vector chargers--a 20 amper that I was using and a 35 amper that I had just acquired-- to get 55 amps. It worked perfectly. It was all downhill from there as I became his creature adding more chargers. I had four Vectors doing a total of 130 amps. Then I got the PowerMax 100 amper and later a 55 amper, and solar.

Last combo I tried, it was 155 amps from the two PowerMax plus 15 amps of solar so I saw 170 amps on the Trimetric going into the battery bank.

It is all time2roll's fault. I don't know if he has an Igor that assists him.

[pnichols]

BFL13 wrote:
The thing is that Phil's routine is not to just use 13.8 all the time.

You may be right.

However, I've stated many times that my recharging method may work because of our camping style ... which is not to squat for days on end, but to be on the road between camping spots often. So far our Ford alternator system has been up to the task of nicely breaking up the approximate 50-90 cycles our converter is most likely doing to the batteries while we're camped.

Lately I've been enhancing the converter's battery charging rate by paralleling it with an ancient Sears 10/2/50 charger set to it's 50 amp position. The output impedances of these two sources in parallel along with the input impedance of the parallel AGM batteries seem to all play well enough together such that I get at least a 50% increase in charging current flow into the AGM batteries.

By the way, I first got the idea to parallel RV charging sources years ago from posts in these forums by either ............. pianotuna ............. or BFL13. Many thanks to whichever of these pioneers suggested it!!

[BFL13]

I don't want to do any testing if I don't have to. LY has already done it and made the above very thorough report. OTOH I don't think Phil is wrong that his routine doesn't give him many years of service--clearly it does.

The thing is that Phil's routine is not to just use 13.8 all the time.

[landyacht318]

Define performance after a full recharge.

For me it is voltage held under load for Ah removed, and Mex's coined term of 'trends and tendencies.'

I've compared the two, slow recharging at 13.6 to 13.8v, until amps taper to near zero, then boosting voltage to 14.7 and seeing how long it takes for amps to taper to near zero.

And then comparing the voltage held under load after the 50% depleted 90Ah battery is brought to 14.7v at 40+ initial amps and held at 14.7v until amps taper to near zero. Almost as fast as the battery can be fully charged, within say 20 minutes.

The latter sceanrio obviously heats the battery more, which would make it appear to have more capacity and perform better the next discharge the next night, but it does not explain the better performance the following night after battery has cooled, or subsequent nights after the high amp recharge to full was performed.

So we can say the AGM battery is full by how many amps it accepts at absorption voltage, or have observations of dozens of cycles recharging at and to different speeds and voltages.



My Thin plate pure lead Northstar AGM Loves the high amp recharge, performs way better after receiving such, it will soon be 4 years old and have approximately have 700 deep cycles on it, many of those well below 50%.

It still easily cranks my 65f degree engine when deplted 65 of its original 90AH, and my voltmeters show that in this state of depletion, voltage remains over 10. It still rebounds to over 12.2v after removing 45AH from it. when it has recently gotten the high amnp recharge to full, but will not rebound as high when it gets the lower and slower 13.6 to 13.8v for the usual 36 hours i give it when i do plug in and recharge slowly to full and can't be there to manually lower voltage from 14.7v

The high amp recharge increase in performance is also noticeble during engine starting, how fast it occurs and how low the voltmeters register during engine cranking. Their refresh rate throws some uncertainty into this, but I have two digital voltmeters on the same battery right next to each other, as I no longer have a house and an engine battery but the same 90Ah battery for both and the sense leads are right on the battery terminal on one and further away on the other.

Not going to paint all AGMS with the same brush, but the Northstar loves the high amp recharge, and no way will I deliberately slow down charging, unless I will not be there to lower my meanwells set absorpotion voltage when the amps taper to 0.5% of capacity.

When I do do the 13.6 or 13.7v charge to full over the 20+ hours required, is when I notice the voltage sagging more under the next discharge, and sagging more as it cranks the engine slower.

I've observed this dozens of times. It is repeatable, and overwhelmingly obvious when low and slow 13.7v did its thing compared to a 40+ amp blast until 14.7v was attained.

I will not intentionally slow charge My well depleted AGM battery, and consider the high amp blast to be restorative when the battery appears to become lazier from repeated low and slow to full.

My starter is rated at 1.4KW, and my dashboard ammeter which reads to 100 amps will always display FFF when cranking the cold engine indicating over a hundred amp draw

I view each and every engine start as a mini load test, each overnight discharge as a longer load test, and have many hundreds of nights of observing the behavior of this specific AGM battery with an Ah counter to see the voltage held for how depleted the battery is, and I often rezero it.

And no way in heck will I call recharging at a max of 13.8v, just fine. I point fingers at noone here in the following sentence, mostly users on some other forums. In my opinion 'just fine' proclamations are usually made by the overwhelmingly ignorant who cant and don't have the ability to understand, all they know is thier methodology has not yet caused failure, but not being able to measure capacity or performance decline or accrue any data at all, any 'works just fine' claims, will and should, in my opinion, be ignored, as 'works just fine' could and often does simply mean 'has not yet failed, but could, tomorrow.'

Try the experiment BFL, deplete to 50% and charge at 13.8v max for however long it takes for a goosing of 14.7ish v to have amps taper to near zero, then observe overnight and morning voltages.

Then do the full recharge at high amps until 14.7v amps taper to near zero and try and replicate the same variables when discharging. I bet the high amps will hold higher voltage for longer with the same AH removed, even accounting for the high amp recharging's higher battery temperature.

Whether the higher amps leads to more overall cycles from the battery before failure, is unknown, but my many observations of My AGM, make me believe it does.

[pnichols]

BF,

Both of my previous Interstate AGMs (built by C&D Technologies) said on their labels to use 14.X volts for Cycle Service recharging and my current Fullriver AGMs recommend the same for Cycle Service recharging.

NOWHERE, have I found in writing - electro chemically - an explanation of how AGM batteries are ruined by using less than 14.X volts for recharging. They MUST be periodically fully recharged however - which I use a built-in ammeter and a lot of time at 13.8 volts and a little time at alternator voltages to do.

Liquid lead acid batteries are of course another story. Stirring of their liquid (bubbling during charging due to using high enough voltage) makes a lot of sense in order to periodically restore uniformity of their liquid's chemical makeup. Plus, probably other chemical reactions at their plate-liquid interfaces are needed to restore plate surfaces eroded by the battery liquid over time ... and periodic higher recharge voltage may drive these reactions.

[BFL13]

Phil, to be clear, did the first set of AGMs have the 14.x charging spec and the linked info from that same company didn't care if you used 13.8 instead--or is it just the new batts that have the 14.x spec and you are going by the advice of the other company for the first set of batts' specs?

Just making sure it is apples to apples. Your actual results might be distorted by that alternator charging they get besides what the converter does.

[pnichols]

This C&D Technologies easy-to-read-and-understand technical paper is my "bible" in how to charge VRLA (AGM) batteries. Notice that they mention/imply/show-on-graphs throughout the document that recharging of VRLA batteries using 13.8 volts as just another voltage choice one can make for recharging - based on various conditions, parameters, and available recharge times. I can't seem to find anywhere in the paper where it states the one "must use" 14.X volts for AGM recharging in order to keep your AGM batteries from being slowly ruined. The paper of course makes the point throughout that AGM batteries must often as possible be fully recharged to keep from harming them in the long run. (C&D Technologies manufactured my first set of twin 12V 100 AH AGM RV batteries.)

Here's the easy to read technical paper I'm referring to above: http://www.cdtechno.com/pdf/ref/41_2128_0212.pdf

Here's a list of links to a whole bunch of other excellent C&D Technologies publications dealing with VRLA (AGM) batteries: http://www.cdtechno.com/resource/support_doc.html

[BFL13]

Seems clear to me that "cycle service" means running them down some and then recharging again as their normal existence. Float service would be like a stand-by power supply or UPS set-up.

Phil has a good reason not to follow the specs exactly ( equipment) and is getting away with it. I think Phil must be right that the occasional alternator charging at 14.x must be what is saving him.

So his example is not any proof that you could do "cycle service" with his batteries using only 13.8v. That is an unknown, unless Mex knows.

[pnichols]

MEXICOWANDERER wrote:
Where did you read AGM batteries must be charged at >14 volts?

David .... I read that everywhere, all the time, in these forums.

Also, on the labels of my AGM batteries is says something like "Recharge at 14.4 volts for Cycle Service".

I have no idea what "Cycle Service" means - if there even is an industry standard definition for it. I'm guessing that it means something like: "To help eliminate uncertainty as to whether or not one has reached a full charge after a discharge one should apply 14.X volts for the recharging voltage."

However, I'm assuming that if one is using an ammeter to determine when full charge is reached, one can use less than 14.X volts for recharging - if one has the time. (... Or if one drives long enough and often enough between camping sites so as to get alternator voltage levels applied to one's RV batteries while also monitoring with an ammeter when driving and camping.)

Another thing that I keep scratching my head over is ... for decades "common and industry knowledge" was that for best lead acid battery life, trickle charging should be used over many hours. Aren't "trickle charge" battery charger voltages usually in the 13.X range?