AGM vs Flooded Bulk Times

Since I can get a Deka 31 for $190 I am placing the order in Jan. for the toad. With a 94 amp starter draw fron the center tunnel to the starter can use 4AWG. Right through the firewall to a 1/0 lug on the starter motor with twin cables. A 140 amp breaker will reside astride the battery. I can sell that 2 year old calcium calcium 34 nightmare for $50 and afterwards I can overnight with BiPAP and even an inverter for gas station snoozes. The original battery tray can hold food warmer items - hot sandwich soup and coffee. Call it Escape Pod Environmental. Film at Eleven.

Hi,

After ten days of idle, solar is keeping the batteries at 13.2. After dusk that drops to 12.9. I plugged the Magnum into shore power. It started at 27 amps @ 14.6 volts and within five minutes was at 20. After 15 minutes it was at 12 @ 14.4 volts.

I expect that by tomorrow the demand will be much lower.

For nearly 18 months, I have had only the one 90Ah Northstar AGM battery for both house loads and engine starting. The location underhood where engine battery is supposed to reside, is empty.
This battery has no issues cranking my engine at 65Ah from full. I am not sure of my plan in the future. I was thinking about a small 16 or 18AH Odyssey AGM battery just for emergency jump starting and a possible portable 12v battery, but I thought that a year ago and never bothered.
The Odyssey can handle huge charging amps too.

I would like the t-1275 for PSOC cycling on solar only, if I were to be less mobile, or did not have access to grid power for plugging in MeanWell. In my experience, the NS AGM is not happy without high amp recharges every so many deep cycles.

After figuring out the screwy 31's charging sweet spots, the Northstar AGM is easy. Just hold absorption voltage until amps taper to 0.XX amps, to determine full, and when possible high amp recharge it from its most depleted state. That is key to its performance, in my observations.

The screwy 31's amp taper at absorption voltage had very widely swinging Specific gravities. I found it much harder to finesse the screwy 31 to 'full' but honestly 'full' only happened after 45 minutes at 16v and then SG each cycle thereafter dropped a little more with the 14.9vABS and 15.3v finishing charge regimen.

The NS Agm is likely in the 450 deep cycle range (under 60% SOC) with several hundred shallow cycles and several thousand engine starts.

Perhaps when it is due for replacement, the firefly carbon foam AGMS will have been more battle tested, or I will get 100Ah of Lifepo4 prisimatic cells. Honestly another Northstar would be great too, as this battery has impressed me since cycle 1.

Good info coming in on charging AGMs; must be of interest to those who have them with solar and get to high SOCs.

I suppose monitor inaccuracy doing that is from the CEF going crazy above 80% SOC same as with Wets.

LY has his AGM hidden away where he could not get at a Wet there to do hydrometer checks. So once you have the AGM, now you want to know how it works and what changes might be applicable to your charging routine from when you had Wets. Interesting topic!

Sounds like LY should get a second AGM for just the engine, and forget the T-1275 or whatever. He can run his rig on just the one hidden away house AGM. The new one would be something of a spare until it takes over someday to do both jobs when the first AGM wears out.

I think the explanation by LandYacht abut every 5 days is very close to my observations. For what ever reason every 5 to 7 days of consecutive 95 to 98% state of charge is not enough on an AGM. I say this because being on a 2 week trip, and doing only one as close to 100% full recharge after 7 days ( I was a little lazy on this) then another 7 days of camping caused me to pull the battery when I got home (like I always do) and recharge in the man cave with the MegaWatt with 14.4v and watch the RC charge indicator for voltage and take rate. What I thought would be done and down to 0.75 amp hours by just before lunch time was closer to being finished by the end of a football game at 4pm.

I can only speculate, but from my limited backround, lack of full 100% SOC recharges perhaps somehow increases the internal resistance inside the battery to get to full charge. It's like the sulfur grows adhesive powers if left on the plates too long, and gets more and more hardened and stubborn to remove and get back in to ionic liquid state. Or maybe it's a battery acid circulation problem inside the plates and the solution in the mats surrounding the plates that prevents anything but time to force the sulfur back into solution.

I don't know the why, I just know what I observe. It's no big deal to me at home if it takes 3 hours or 8 hours to get that .75 amp recharge rate. It is a big deal to me when boondocking.

"What If" scenarios not based in obective terms (usability) tend to frustrate folks who look for the parameters of the concept. As our professor in our EE class snared: "You just made a statement. Defend it".

Using a throttled I limit both power supplies li
Ited to X optimum voltage PLUS A X FACTOR TIME LIMIT there can be argument as to Is An Amp an Amp?

But extend the X time parameter BEYOND the Vab decline point in the flooded battery and suddenly the VRB is all over the flooded. Both decline indeed but the ENERGY UNDER CURVE for the VRB is appreciably greater. It is not a linear decline so how does one express it and in real-world terms, a throttled charge curve may be confusing to many.

"Not worth the effort" response on my part would have been a cop-out. The real answer was and is to take advantage of strong points. It was sort of like querying what is the per pencentage chances of a flat between a 100 mph tire compared to a 130 mph tire when both are used at 60 mph?

Charge receptivity can be expressed as a curve. But multiple charts are needed for de-rates according to cell temperature. Impressing 30 amperes needs interpretation as to total amp hour capacity in question. Is there a rational way to explain this in a fashion that could be employable by members of this forum?

For me it distilled into a "Damned if you do, Damned if you don't choice". I elected for the least ambiguous answer. Want to get there faster increase your speed. Of course holding a smaller map the disstances are shorter (Just Kidding!)

"I imagine if one were relying on generator only, no solar, that 50 to 80%, even if 80 is not really 80% anymore, takes longer and longer to achieve, the more partial state of charge cycles that have accumulated."

Getting confused there! Each successive 50-80 takes less time because the 30% worth of Full is a smaller amount of AH each time (Full getting smaller each time)

That was how I first noticed progressive capacity loss while camping. Before I had a Trimetric. It was the time it took to do 50-90s getting less,

Also the morning voltage was getting lower each day after doing a 50-90. My daily AH use was the same but the battery bank was getting smaller even though I was doing a whole 50-90 (the 90 was by mark of 5 amps per battery)

SOC is a percentage. If it is a % of a shrinking AH total, that same SOC will be at ever fewer AH too.

It makes sense that as the bulk time shrinks, the absorption time gets longer (see my ugly graph!) to reach the same SOC.

Also, I wonder if that extended absorption time LY sees is including some "recovery time" even though recovery mostly needs a higher amp recondition.

I know most of this conversation is about bulk charging, and keeping maximum amperage flowing for as long as possible to reduce generator run times, and whether AGMS are any better than flooded in this department.

While I have a battery monitor, I trust it less and less the more cycles that have accumulated either without the high amp recharge, and/or the incomplete recharge, say getting to 95% instead of 100%

Many successive 95% recharges then require a very long time for amps to taper to 0.4a at 14.7v. I've seen it take 3.5 hours to taper to 0.4 amps once 14.7v has been reached at 40 amps initial bulk current. After many PSOC cycles and low and slow solar only as the charging source, then plugging in the meanwell, I've seen it take 10 hours for amps to taper to 0.4a after it first reached 14.7v.

When many PSOC cycles have accumulated, at least on my NS AGM, the progressive capacity loss, or temporary sulfation, or whatever term one is comfortable with using, not only means that a true full 100% recharge/ recovery, not only takes longer, but amps begins tapering sooner as well. I've been quite surprised to see the battery still 35Ah from full and reaching 14.7 at only 27 amps. Usually this is more like 22 to 24AH from full when amps start tapering at 14.7v.

I imagine if one were relying on generator only, no solar, that 50 to 80%, even if 80 is not really 80% anymore, takes longer and longer to achieve, the more partial state of charge cycles that have accumulated.

I really try not to go that many cycles without either the 100%, and this usually requires alternator or meanwell contribution, which also means no less than 40 amps initially. My battery craves the high amp recharge. Ideally, in my observations, it would get 25 to 40 amps from its most depleted state, every recharge. It is not happy with low and slow solar only, and I determine this by voltage held under load for AH removed the next discharge cycle and the one after that. This behavior is predictable and repeatable.

As my battery monitor is usually at my right elbow, I check it often each recharge and discharge cycle, and likely have much more trends and tendencies data than most here. In the future, if/When I decide I require more capacity, I am torn between getting another AGM or t-1275, as I love the no amperage limitation on Northstar or Lifeline or Odyssey AGM's. I love the high CCA, the no watering, and seeing 12.7v on a 90AH battery when the screwy31 at 130Ah capacity would show 12.4v at the same level of depletion under the same loads, fills me with warm and fuzzies.

Only caveat is the AGM I will use, requires the high amp recharge after so many cycles, to remain healthy and full of grunt and would not be a good long term solar only recharge battery.

Whether the Amperage limited AGMS are more suited to solar recharges, is unknown to me, but It is incredibly obvious, how much better my AGM performs after a high amp recharge, and recent battery temperature data also makes it obvious the battery does not appear to perform better, just because it is hotter from thre high amp recharge, as the next night 24+ hours later, when the battery temperatures have returned closer to ambients, performance is still increased despite the likely low and slow to 98% having not completed the job the next day.

The time it takes amps to taper to the required level to consider an AGM 100% charged, increased with PSOC cycling and battery Age/overall cycles accumulated. In wintertime, My 200 watts of solar needs to achieve absorption voltage on my 90AH AGM by 10:30am, or there is no hope of 100% happening that day without pluggin in and letting the Meanwell finish the task.

It just means the battery has a lower capacity after you don't do full recharges, leaving some sulfation, so now 100% next cycle is with fewer AH than before. It gets worse with each successive incomplete recharge.

That means with the same initial amps, you are starting off with a higher charging rate. That means you will get to Vabs sooner at a lower SOC.

Of course it also means with fewer AH making for 100%, it will not take as long to restore them to "full." Full is not as much as it was.

You have to do a "recovery" to get rid of the sulfation so then your battery can hold more AH and get back to near rated AH when indicating Full.

It is all about the charging rate. You can increase the charging rate by using more initial amps on the same size battery like in my ugly graph or get the same shifts in SOC by using the same amps on ever smaller battery banks.

This happens with AGMs same as it does with Wets.

You could compare charging a sulfated 110AH AGM with a clean 110AH Wet with the same initial amps and get the same recharge time because that 110AH AGM is not 110 amymore. Of course you would want to run a fair test, so you wouldn't do that :)

In the OP test (first guy) he may have had higher R wiring OR his batts may have been sulfated somewhat (or both things) but he said they were newish.

Hi landy,

BFL13 would call this progressive capacity loss. I'd call it reversible sulphation.

I LIKE your aim.

Yes the partial recharges are the bane of AGM. That's why they may require BIG amp recharge and may not be well suited to the "low and slow" solar approach.

Surplus acid AGM don't require the huge amp recharge to "wake them up" and in fact may be damaged by it. Hence the c/5 limitation on recharging. I'm hoping they are better suited to low and slow.

landyacht318 wrote:
Lots of low and slow recharges until 92% and then if 40 amps are then applied( to a 90Ah battery) amps will start tapering much faster than if the day before had a high amp recharge until 100% was achieved.

I Aim for no less than 95% and 100% every 5 cycles.

So how much partial state of charge cycling has been going on, in my opinion, will have huge impacts on when amps begin to taper when held at absorption voltage

.